C-Audio Power Amp Head ...

[Arfa Daily]

Does anyone have a set of schematics for the C-Audio RA3001 that they could
let me have fairly urgently please ?

The links to the service manual on the supposed C-Audio 'website', just seem
to take you round in ever decreasing circles via other third party vendors
of everthing you can imagine.

TIA

Arfa

 

[Eeyore]

Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they could
let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable. First
job is to replace all the PSU caps that have been cooked by the hot exhaust air.
Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website', just seem
to take you round in ever decreasing circles via other third party vendors
of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too ! Ask there.
Except it's not Harman any more it seems but google that for starters. They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a
corner (I could tell another story) so they might be willing to get rid of some
unwanted and unloved bits. Unless they already put them in a skip (dumpster for
USAans)

Graham

 

[Arfa Daily]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:492B33FE.943628B6@hotmail.com...

Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could
let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable.
First
job is to replace all the PSU caps that have been cooked by the hot
exhaust air.
Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.


The links to the service manual on the supposed C-Audio 'website', just
seem
to take you round in ever decreasing circles via other third party
vendors
of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too ! Ask
there.
Except it's not Harman any more it seems but google that for starters.
They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled
into a
corner (I could tell another story) so they might be willing to get rid of
some
unwanted and unloved bits. Unless they already put them in a skip
(dumpster for
USAans)

Graham

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the same
thing with speakers built in like an AC30 or Fender Twin. I just follow his
lead, and call them the same. What do you describe as a "head"?

Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output. On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be a
good place to start looking.

Arfa

 

[Eeyore]

Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable.
First job is to replace all the PSU caps that have been cooked by the hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website', just
seem to take you round in ever decreasing circles via other third party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too ! Ask
there. Except it's not Harman any more it seems but google that for
starters.
They've moved to Letchworth. I think most of the C-Audio parts ended up
shuffled
into a corner (I could tell another story) so they might be willing to get
rid of
some unwanted and unloved bits. Unless they already put them in a skip
(dumpster for USAans)

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the same
thing with speakers built in like an AC30 or Fender Twin. I just follow his
lead, and call them the same. What do you describe as a "head"?

A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type amp is
a 'slave amp'.

Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.

Typical C-Audio !

On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be a
good place to start looking.

Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test. You
will find a fair few are totally open. Replace these and you're good to go but
DO replace the reservoir caps too. They will have been roasted by the searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction temp
was. Your trouble will be getting genuine Hitachi replacements as they stopped
making them and the Semelab/Magnatec and Exicon replacements aren't exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham

 

[Arfa Daily]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:492B9462.B4AA32F5@hotmail.com...

Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously unreliable.
First job is to replace all the PSU caps that have been cooked by the
hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website',
just
seem to take you round in ever decreasing circles via other third
party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too !
Ask
there. Except it's not Harman any more it seems but google that for
starters.
They've moved to Letchworth. I think most of the C-Audio parts ended up
shuffled
into a corner (I could tell another story) so they might be willing to
get
rid of
some unwanted and unloved bits. Unless they already put them in a skip
(dumpster for USAans)

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?

A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs
for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type
amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.

Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when
the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works
perfectly,
so I guess I can start comparing between the two. Just would have been a
lot
easier with a set of schematics to see where exactly the signal goes.
It's
got that nasty 'feel' about it, that says it's going to be something like
an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may
be a
good place to start looking.

Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test.
You
will find a fair few are totally open. Replace these and you're good to go
but
DO replace the reservoir caps too. They will have been roasted by the
searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp
was. Your trouble will be getting genuine Hitachi replacements as they
stopped
making them and the Semelab/Magnatec and Exicon replacements aren't
exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham

Well, if that's the case, it ain't gonna get done, as he only sold it a
couple of weeks ago as a cheapy second hand job. As a matter of interest,
does the circuit employ feedback to the front end then ? I wasn't expecting
this to be an output issue, as the waveform seems to distort quite early in
the chain, but now you suggest this, I guess it makes some sense of the way
that the amplitude of the waveform 'bounces' a couple of times before
settling, when the level is adjusted, externally or front panel.

Arfa

 

[Meat Plow]

On Tue, 25 Nov 2008 06:00:02 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com>wrote:

Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable.
First job is to replace all the PSU caps that have been cooked by the hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website', just
seem to take you round in ever decreasing circles via other third party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too ! Ask
there. Except it's not Harman any more it seems but google that for
starters.
They've moved to Letchworth. I think most of the C-Audio parts ended up
shuffled
into a corner (I could tell another story) so they might be willing to get
rid of
some unwanted and unloved bits. Unless they already put them in a skip
(dumpster for USAans)

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the same
thing with speakers built in like an AC30 or Fender Twin. I just follow his
lead, and call them the same. What do you describe as a "head"?

A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.

Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be a
good place to start looking.

Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test. You
will find a fair few are totally open. Replace these and you're good to go but
DO replace the reservoir caps too. They will have been roasted by the searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction temp
was. Your trouble will be getting genuine Hitachi replacements as they stopped
making them and the Semelab/Magnatec and Exicon replacements aren't exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham

Ran into the Hitachi mosfet issue years ago after acquiring a Sound
Code Systems (SCS) rack mount power amp. Had the 2SJ49/2SK134 pairs
inside if I recall correctly. I replaced them with J50/K135 devices
which at the time were still available. Now adays there are
replacements but with a little modification since they are not in a
TO3 package. I've had that amp now for 15 years after repair and
used it for 5 years as a bass guitar amp strapped mono. Now adays it
is the PA amp for my home studio. I've only seen one SCS amp and this
is it.

 

[Arfa Daily]

"hr(bob) hofmann@att.net" <hrhofmann@att.net> wrote in message
news:a0562a38-f323-4efc-956e-ebdbc2db2e5e@g38g2000yqn.googlegroups.com...
On Nov 24, 7:25 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

"Eeyore" <rabbitsfriendsandrelati...@hotmail.com> wrote in message

news:492B33FE.943628B6@hotmail.com...







Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could
let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously unreliable.
First
job is to replace all the PSU caps that have been cooked by the hot
exhaust air.
Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website', just
seem
to take you round in ever decreasing circles via other third party
vendors
of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too ! Ask
there.
Except it's not Harman any more it seems but google that for starters.
They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled
into a
corner (I could tell another story) so they might be willing to get rid
of
some
unwanted and unloved bits. Unless they already put them in a skip
(dumpster for
USAans)

Graham

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?

Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output. On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when
the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a
lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like
an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be
a
good place to start looking.

Arfa- Hide quoted text -

- Show quoted text -

On the western side of the big pond, "head" can mean what you folks on
the eastern side, I believe, call the "Loo". Think it comes from
nautical background when the in-ship toilet was at the front/head of
the ship/boat.

Bob H

That is exactly correct, Bob. The toilets on board a British naval vessel
are also known as "The Head" or sometimes "Heads", and when a cadet, I was
taught that it was because of them being at the front of the ship, which in
the days of wooden sailing vessels, was as far from the captain's quarters
at the stern, as they possibly could be. Don't know if the same terminology
is used on merchant vessels.

Arfa

 

[hr(bob) hofmann@att.net]

On Nov 24, 7:25 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

"Eeyore" <rabbitsfriendsandrelati...@hotmail.com> wrote in message

news:492B33FE.943628B6@hotmail.com...







Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could
let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable.
First
job is to replace all the PSU caps that have been cooked by the hot
exhaust air.
Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think  it was that model.

The links to the service manual on the supposed C-Audio 'website', just
seem
to take you round in ever decreasing circles via other third party
vendors
of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too ! Ask
there.
Except it's not Harman any more it seems but google that for starters.
They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled
into a
corner (I could tell another story) so they might be willing to get rid of
some
unwanted and unloved bits. Unless they already put them in a skip
(dumpster for
USAans)

Graham

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the same
thing with speakers built in like an AC30 or Fender Twin. I just follow his
lead, and call them the same. What do you describe as a "head"?

Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output. On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be a
good place to start looking.

Arfa- Hide quoted text -

- Show quoted text -

On the western side of the big pond, "head" can mean what you folks on
the eastern side, I believe, call the "Loo". Think it comes from
nautical background when the in-ship toilet was at the front/head of
the ship/boat.

Bob H

 

[Eeyore]

Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message

<snip>

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp was. Your trouble will be getting genuine Hitachi replacements as they
stopped making them and the Semelab/Magnatec and Exicon replacements aren't
exactly identical.. I may have a few but you WILL pay megabucks for them.

http://cgi.ebay.co.uk/2SK175-Transistor-2SK175_W0QQitemZ380026165076QQihZ025QQcategoryZ4663QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

http://cgi.ebay.co.uk/2SJ56-Transistor-2SJ56_W0QQitemZ380026165991QQihZ025QQcategoryZ4663QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

Probably cheaper to remove all the Hitachis (and sell them ?) and replace all
with Exicon or Semelab.

http://www.profusionplc.com/pro/gex/prodGen.html?prdtyp=lateral%20mosfet#

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=LKCDCHFQF3EAYCQLCIPZK0Q?N=317516+317520&Ntk=gensearch_001&Ntt=semelab+mosfet&Ntx=&_requestid=473126

You need the 'BUZ' parts.

Well, if that's the case, it ain't gonna get done, as he only sold it a
couple of weeks ago as a cheapy second hand job. As a matter of interest,
does the circuit employ feedback to the front end then ?

Oh yeah.

I wasn't expecting
this to be an output issue, as the waveform seems to distort quite early in
the chain, but now you suggest this, I guess it makes some sense of the way
that the amplitude of the waveform 'bounces' a couple of times before
settling, when the level is adjusted, externally or front panel.

It 'might' be something else. You'll only tell by removing the output devices
(thankfully easy enough) and testing them but C-Audio have a reputation for
eating them. And will do so again if driven hard into 4 ohms.

Graham

 

[Gareth Magennis]

"Meat Plow" <meat@petitmorte.net> wrote in message
news:2ce0vc.6i7.19.8@news.alt.net...

On Tue, 25 Nov 2008 06:00:02 +0000, Eeyore
rabbitsfriendsandrelations@hotmail.com>wrote:



Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously
unreliable.
First job is to replace all the PSU caps that have been cooked by the
hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website',
just
seem to take you round in ever decreasing circles via other third
party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too !
Ask
there. Except it's not Harman any more it seems but google that for
starters.
They've moved to Letchworth. I think most of the C-Audio parts ended
up
shuffled
into a corner (I could tell another story) so they might be willing to
get
rid of
some unwanted and unloved bits. Unless they already put them in a skip
(dumpster for USAans)

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's
rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?

A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs
for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type
amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.

Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when
the
input level, or front panel level, is varied. The problem is right up
the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works
perfectly,
so I guess I can start comparing between the two. Just would have been a
lot
easier with a set of schematics to see where exactly the signal goes.
It's
got that nasty 'feel' about it, that says it's going to be something
like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may
be a
good place to start looking.

Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test.
You
will find a fair few are totally open. Replace these and you're good to go
but
DO replace the reservoir caps too. They will have been roasted by the
searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp
was. Your trouble will be getting genuine Hitachi replacements as they
stopped
making them and the Semelab/Magnatec and Exicon replacements aren't
exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham

Ran into the Hitachi mosfet issue years ago after acquiring a Sound
Code Systems (SCS) rack mount power amp. Had the 2SJ49/2SK134 pairs
inside if I recall correctly. I replaced them with J50/K135 devices
which at the time were still available. Now adays there are
replacements but with a little modification since they are not in a
TO3 package. I've had that amp now for 15 years after repair and
used it for 5 years as a bass guitar amp strapped mono. Now adays it
is the PA amp for my home studio. I've only seen one SCS amp and this
is it.

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420



Gareth.

 

[Meat Plow]

On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis"
<gareth.magennis@ntlworld.com>wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420



Gareth.

Good to know when the old J50's and K135's decide to check out.

 

[Gareth Magennis]

"Meat Plow" <meat@petitmorte.net> wrote in message
news:2ce9pp.lbj.19.1@news.alt.net...

On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis"
gareth.magennis@ntlworld.com>wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420



Gareth.




Good to know when the old J50's and K135's decide to check out.

Well, I didn't say the BUZ were replacements for those, but C-audio did use
a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground bonding
or layout design, depending on who you talked to and what opinion they had,
or how much bullshit they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any, reservoir
capacitors though.




Gareth.

 

[Gareth Magennis]

"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote in message
newsCZWk.4$AS.3@newsfe25.ams2...

"Meat Plow" <meat@petitmorte.net> wrote in message
news:2ce9pp.lbj.19.1@news.alt.net...
On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis"
gareth.magennis@ntlworld.com>wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420



Gareth.




Good to know when the old J50's and K135's decide to check out.


Well, I didn't say the BUZ were replacements for those, but C-audio did
use a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground
bonding or layout design, depending on who you talked to and what opinion
they had, or how much bullshit they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any,
reservoir capacitors though.




Gareth.

Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in
club installs) being deposited on the PCB behind the fan intake. This would
eventually corrode lots of fine tracks running along the board, the most
common victim being part of the Protect/Speaker Relay circuit, so the amp
would stay in Protect forever.

Annoyingly, the corrosive substance would creep under the Speaker relays and
eat the tracks under them as well, so repairing these amps properly was
either very time consuming and expensive, or just plain uneconomical.

And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need
replacing.


These had their fair share of design problems, that's for sure.




Gareth.

 

[Eeyore]

Gareth Magennis wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets,

Not originally.

both T03 and T0247, which are still easily available.

But best not to mix them I imagine.

Graham

 

[Eeyore]

Gareth Magennis wrote:

"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote
"Meat Plow" <meat@petitmorte.net> wrote in message
"Gareth Magennis" <gareth.magennis@ntlworld.com>wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247, which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420

Good to know when the old J50's and K135's decide to check out.


Well, I didn't say the BUZ were replacements for those, but C-audio did
use a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground
bonding or layout design, depending on who you talked to and what opinion
they had, or how much bullshit they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any,
reservoir capacitors though.

Surprised at that. C-Audio's stance was they were a 'service item'. Like the mosfets presumably !

Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in
club installs) being deposited on the PCB behind the fan intake. This would
eventually corrode lots of fine tracks running along the board, the most
common victim being part of the Protect/Speaker Relay circuit, so the amp
would stay in Protect forever.

Annoyingly, the corrosive substance would creep under the Speaker relays and
eat the tracks under them as well, so repairing these amps properly was
either very time consuming and expensive, or just plain uneconomical.

And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need
replacing.

These had their fair share of design problems, that's for sure.

Which is why I didn't approve them to be sold under the Studiomaster badge and went on to design the much loved D Series.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=320314073435&ssPageName=STRK:MEWA:IT&ih=011

Siemens ODM'd the RA3001 though IIRC.

Graham

 

[Arfa Daily]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:492C39F9.69B567F8@hotmail.com...

Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message

snip

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp was. Your trouble will be getting genuine Hitachi replacements as
they
stopped making them and the Semelab/Magnatec and Exicon replacements
aren't
exactly identical.. I may have a few but you WILL pay megabucks for
them.

http://cgi.ebay.co.uk/2SK175-Transistor-2SK175_W0QQitemZ380026165076QQihZ025QQcategoryZ4663QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

http://cgi.ebay.co.uk/2SJ56-Transistor-2SJ56_W0QQitemZ380026165991QQihZ025QQcategoryZ4663QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

Probably cheaper to remove all the Hitachis (and sell them ?) and replace
all
with Exicon or Semelab.

http://www.profusionplc.com/pro/gex/prodGen.html?prdtyp=lateral%20mosfet#

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=LKCDCHFQF3EAYCQLCIPZK0Q?N=317516+317520&Ntk=gensearch_001&Ntt=semelab+mosfet&Ntx=&_requestid=473126

You need the 'BUZ' parts.


Well, if that's the case, it ain't gonna get done, as he only sold it a
couple of weeks ago as a cheapy second hand job. As a matter of interest,
does the circuit employ feedback to the front end then ?

Oh yeah.


I wasn't expecting
this to be an output issue, as the waveform seems to distort quite early
in
the chain, but now you suggest this, I guess it makes some sense of the
way
that the amplitude of the waveform 'bounces' a couple of times before
settling, when the level is adjusted, externally or front panel.

It 'might' be something else. You'll only tell by removing the output
devices
(thankfully easy enough) and testing them but C-Audio have a reputation
for
eating them. And will do so again if driven hard into 4 ohms.

Graham

You are right. One whole bank of FETs is o/c - hence the very asymmetric
output. There has been a further development. I rang the shop to tell him
the bad news that a set of twelve devices was going to set him back 100
quid, with the possibility of there being some o/c on the other channel (a
couple of them seem very cool under drive conditions, compared to their
neighbours, so a good indication that they may well be open as well) and
then the possibility of some smoothers as well. Turns out that when he sold
the guy this one as a s/h unit, he picked up the wrong one. This example was
sitting waiting to come to me for checking, so he has now given the customer
the right one, and is writing this one off, for the time being at least.
Thanks for the useful pointer to the FETs, anyway.

Arfa

 

[Arfa Daily]

"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote in message
news:9RXWk.18791$ZL2.7695@newsfe28.ams2...

"Meat Plow" <meat@petitmorte.net> wrote in message
news:2ce0vc.6i7.19.8@news.alt.net...
On Tue, 25 Nov 2008 06:00:02 +0000, Eeyore
rabbitsfriendsandrelations@hotmail.com>wrote:



Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that
they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously
unreliable.
First job is to replace all the PSU caps that have been cooked by the
hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product
for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website',
just
seem to take you round in ever decreasing circles via other third
party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too !
Ask
there. Except it's not Harman any more it seems but google that for
starters.
They've moved to Letchworth. I think most of the C-Audio parts ended
up
shuffled
into a corner (I could tell another story) so they might be willing
to get
rid of
some unwanted and unloved bits. Unless they already put them in a
skip
(dumpster for USAans)

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's
rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?

A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs
for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type
amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.

Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude
when the
input level, or front panel level, is varied. The problem is right up
the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works
perfectly,
so I guess I can start comparing between the two. Just would have been
a lot
easier with a set of schematics to see where exactly the signal goes.
It's
got that nasty 'feel' about it, that says it's going to be something
like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may
be a
good place to start looking.

Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test.
You
will find a fair few are totally open. Replace these and you're good to
go but
DO replace the reservoir caps too. They will have been roasted by the
searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp
was. Your trouble will be getting genuine Hitachi replacements as they
stopped
making them and the Semelab/Magnatec and Exicon replacements aren't
exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham

Ran into the Hitachi mosfet issue years ago after acquiring a Sound
Code Systems (SCS) rack mount power amp. Had the 2SJ49/2SK134 pairs
inside if I recall correctly. I replaced them with J50/K135 devices
which at the time were still available. Now adays there are
replacements but with a little modification since they are not in a
TO3 package. I've had that amp now for 15 years after repair and
used it for 5 years as a bass guitar amp strapped mono. Now adays it
is the PA amp for my home studio. I've only seen one SCS amp and this
is it.



IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420



Gareth.

Yes, they are BUZ's and yes, they are in the Farnell book, allbeit with a
different suffix letter to what is actually fitted now, but with six N's and
six P's in the equation, at 8 quid + VAT a pop, that's 100+ quidsworth trade
in devices for one channel, before we even start looking at the other
channel to see if any are open there as well.

Shop owner has deemed it uneconomic for the moment, so it will go back up
the corner to await its ultimate fate ... :-(

Talking of Farnell, do you order much from them ? Have you noticed how much
they seem now to be rationalising 'on the shelf' stock ? It used to be
*very* rare to ever catch them out of stock on any catalogue item. Now,
there seems to be something on every order. Also, have you noticed how you
get one order in two shipments ? One parcel comes from Leeds, and the other,
often something like a single transistor, comes in a box the size of your
head, by UPS, from Belgium. Surely, this can't make economic sense, let
alone (God forgive me for using the "e" word) ecological sense ?

Arfa

 

[Arfa Daily]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:492C7167.CAFF05EE@hotmail.com...

Gareth Magennis wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets,

Not originally.


both T03 and T0247, which are still easily available.

But best not to mix them I imagine.

Graham

This one that I had on the bench used BUZ's, and the soldering on them looks
original

Arfa

 

[Meat Plow]

On Tue, 25 Nov 2008 20:54:48 -0000, "Gareth Magennis"
<gareth.magennis@ntlworld.com>wrote:

"Meat Plow" <meat@petitmorte.net> wrote in message
news:2ce9pp.lbj.19.1@news.alt.net...
On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis"
gareth.magennis@ntlworld.com>wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420



Gareth.




Good to know when the old J50's and K135's decide to check out.


Well, I didn't say the BUZ were replacements for those, but C-audio did use
a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground bonding
or layout design, depending on who you talked to and what opinion they had,
or how much bullshit they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any, reservoir
capacitors though.




Gareth.

I looked through the BUZ lists at Farnell and the specs for the BUZ
pairs compliment or exceed the original specs.

 

[Meat Plow]

On Tue, 25 Nov 2008 21:49:23 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com>wrote:

Gareth Magennis wrote:

"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote
"Meat Plow" <meat@petitmorte.net> wrote in message
"Gareth Magennis" <gareth.magennis@ntlworld.com>wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247, which are still easily available.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=IO3Y2W2KBUIGECQLCIQJKBQ?N=0&Ntk=gensearch_001&Ntt=buz900&Ntx=&_requestid=486420

Good to know when the old J50's and K135's decide to check out.


Well, I didn't say the BUZ were replacements for those, but C-audio did
use a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground
bonding or layout design, depending on who you talked to and what opinion
they had, or how much bullshit they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any,
reservoir capacitors though.

Surprised at that. C-Audio's stance was they were a 'service item'. Like the mosfets presumably !


Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in
club installs) being deposited on the PCB behind the fan intake. This would
eventually corrode lots of fine tracks running along the board, the most
common victim being part of the Protect/Speaker Relay circuit, so the amp
would stay in Protect forever.

Annoyingly, the corrosive substance would creep under the Speaker relays and
eat the tracks under them as well, so repairing these amps properly was
either very time consuming and expensive, or just plain uneconomical.

And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need
replacing.

These had their fair share of design problems, that's for sure.

Which is why I didn't approve them to be sold under the Studiomaster badge and went on to design the much loved D Series.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=320314073435&ssPageName=STRK:MEWA:IT&ih=011

Siemens ODM'd the RA3001 though IIRC.

Graham

I own a Studiomaster 700D and would like to replace the quad set of
mains filters. These are low profile, I know there is a specific name
for them. The tops of these all seem to bubble upwards but when I
picked that part off it was just a cover of sorts for the real
container both overshod with heat shrink. I don't think they are bad,
haven't removed them but the amp works however I'm worried about it
being in service as my bass guitar amp. I'm also looking for a new
speaker binder set as one is broken off. Currently I'm using Spec-on
connectors. I bought this amp used at a thieves price.

Is there a place here in the US for factory parts or do i have to get
them from GB?