C-Audio Power Amp Head ...

[Eeyore]

Arfa Daily wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote

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.

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)

That's what happens. The weakest or hottest fail first (open) and the relatively large ON resistance for these devices causes assymmetry in the delevered peak
voltage to the load.

Graham

 

[Eeyore]

Meat Plow wrote:

Eeyorewrote:
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.

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.

NEVER seen that myself but those amps are getting old now. Original spec parts were Samwha (forget which series but the plastic film was dark
green) 3300uF/63V (yes they're overvolted off load @ 67V but we checked that for reliability with Samwha and they sent us detailed info to say
it's basically OK, the leakage current just increases very marginally at ~ 5% overvoltage and no load).

The alternative part was IIRC, Panasonic (again forget which series). Dumpy little black cans. Looked absurdly small. I expect that's what
you've got.

I specced the ripple current per cap at ~ 2.7-3A IIRC. You'll find something in Farnell that'll do fine. Use 105C caps if you want to continue
using it forever.

I assume you're driving a 4 ohm load btw ?

Want some more Oomph ? Fit 4700s. It'll reduce the dynamic headroom though.

What do you think of the amp btw ?

Graham

 

[Eeyore]

Meat Plow wrote:

I'm also looking for a new speaker binder set as one is broken off.

You must have a US model. Those weren't sourced in the UK. That means you have an Indian built one. Can't tell you what they used sadly.

Currently I'm using Spec-on connectors. I bought this amp used at a thieves price.

They go on ebay for 'reasonable' prices. I just bought one on behalf on my local music pub client for Ł72. 10 years old and looked almost new
inside. Just had some 'rack rash'.

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

Not at all. I gave data in my other post. Don't scrimp on the ripple current btw. Use good brand caps. I found Samwha to be excellent btw at a
reasonable price. My second preference is Panasonic.

Graham

 

[Eeyore]

Meat Plow wrote:

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

I'm fairly certain the original spec is the Samwha HC series 3300uF 63V.

Yes, this pdf includes the data sheet. The ripple current is in fact > 3A.
http://www.rapidonline.com/netalogue/specs/11-3100e.pdf

Now ask me how I remember that after over 15 years ago.

You'll easily find replacements.

Graham

 

[Gareth Magennis]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:fr1Xk.19688$ZL2.12902@newsfe28.ams2...

"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

Often C Audio would put little pink or green dots on the transistors,
presumably after testing them prior to production. Not the kind of thing a
repairshop would do, so this may indicate if they are the originals or not.

I often used to find only one or two devices not working or clamping at high
voltages, you may not have to replace the lot at all.




Gareth.

 

[Gareth Magennis]

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

I order just about all my stuff from Farnell. They don't tend to have much
in the way of unusual or older transistors, these I can usually find at
Cricklewood Electronics.
http://www.cricklewoodelectronics.com/Cricklewood/home.php

I get my stuff next day without fail from both Farnell and Cricklewood,
nothing is usually out of stock or comes from Belgium.

I'm in Leeds, so is Farnell, so maybe that might have something to do with
it, but shouldn't really. What kind of stuff is coming from Belgium?
Chocolate screwdrivers?



Cheers,



Gareth.

 

[Eeyore]

Gareth Magennis wrote:

I'm in Leeds, so is Farnell, so maybe that might have something to do with
it, but shouldn't really. What kind of stuff is coming from Belgium?
Chocolate screwdrivers?

I've seem multiple deliveries from them. Simple explanation. They don't hold all stock in a single place.

Graham

 

[Arfa Daily]

"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote in message
news:OS7Xk.2$Lg2.0@newsfe10.ams2...

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



I order just about all my stuff from Farnell. They don't tend to have
much in the way of unusual or older transistors, these I can usually find
at Cricklewood Electronics.
http://www.cricklewoodelectronics.com/Cricklewood/home.php

I get my stuff next day without fail from both Farnell and Cricklewood,
nothing is usually out of stock or comes from Belgium.

I'm in Leeds, so is Farnell, so maybe that might have something to do with
it, but shouldn't really. What kind of stuff is coming from Belgium?
Chocolate screwdrivers?



Cheers,



Gareth.

Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and ship
from Belgium, just one item out of an order of perhaps 10 items ? They also
seem to employ no rhyme or reason with determining how exactly the orders
are shipped by default. One day, they will deliver a transformer weighing a
couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of
transistors will arrive in a box a foot square, conveyed by UPS, who don't
usually get to me until late afternoon. One thing about UPS *really*
irritates me (must be my age). After having got it to the right address, and
asked me to sign for it, and after the same bloke delivering the same sorts
of packets to me from the same company, for a long time, he still says every
time after I finish signing "What's the surname, please ?" Aaaaarrghhh !!!

I haven't used Cricklewood for a while. I also hadn't used Grandata for a
while until a few weeks ago. They have really gone down the toilet compared
to what they were. I needed an STK, and a couple of power transistors for an
amp, as well as a few other bits and pieces - fuses and so on. All items
showed as in stock on the website, so I went ahead and placed the order,
credit card payment and all that. The next day, I was extremely annoyed to
get an e-mail informing me that half the stuff was on 3 to 10 day back
order. It has actually taken a total of about 5 weeks to finally get
everything that was on the order, the last transistor arriving just
yesterday ...

Arfa

 

[Eeyore]

Arfa Daily wrote:

Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and ship
from Belgium, just one item out of an order of perhaps 10 items ? They also
seem to employ no rhyme or reason with determining how exactly the orders
are shipped by default. One day, they will deliver a transformer weighing a
couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of
transistors will arrive in a box a foot square, conveyed by UPS, who don't
usually get to me until late afternoon.

Why do you think they charge the price they do ?

The use of 'satellite warehouses' is well established. Someone must have done the sums. You can bet UPS don't get their standard fee for such
an operation.


Graham

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:GY8Xk.460$fg7.253@newsfe21.ams2...

"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote in message
news:OS7Xk.2$Lg2.0@newsfe10.ams2...


IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and

I haven't used Cricklewood for a while. I also hadn't used Grandata for a
while until a few weeks ago. They have really gone down the toilet
compared
to what they were. I needed an STK, and a couple of power transistors for
an
amp, as well as a few other bits and pieces - fuses and so on. All items
showed as in stock on the website, so I went ahead and placed the order,
credit card payment and all that. The next day, I was extremely annoyed to
get an e-mail informing me that half the stuff was on 3 to 10 day back
order. It has actually taken a total of about 5 weeks to finally get
everything that was on the order, the last transistor arriving just
yesterday ...

Arfa

Grandata must have dumped or auctioned-off their back catalog when moving
address from Wembley to Ruislip and trading name to Thumbs Up , actually
thumbs down, earlier this year

A few totals of
IC types in 2000 Grandata catalog, 2008 "Thumbs Up"
TDA... 760 136
TEA.... 120 14
L.... 370 55
M.... 234 10

Anyone ever get to the Pike auctions in Nottingham?
Or is there any other electronic component auctions around since that one in
Stroud Gloucester closed down ?


BTW yesterday I passed a Maplins store as a pallet load of returns was being
tail-lifted on a lorry, well wrapping tape had Returns Centre printed all
over it. Does that turn up at Pikes with all the other returns ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Arfa Daily]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:492D1F52.BB6C17C8@hotmail.com...

Arfa Daily wrote:

Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and
ship
from Belgium, just one item out of an order of perhaps 10 items ? They
also
seem to employ no rhyme or reason with determining how exactly the orders
are shipped by default. One day, they will deliver a transformer weighing
a
couple of pounds, in a Jiffy bag, by regular post. The next day, a packet
of
transistors will arrive in a box a foot square, conveyed by UPS, who
don't
usually get to me until late afternoon.

Why do you think they charge the price they do ?

The use of 'satellite warehouses' is well established. Someone must have
done the sums. You can bet UPS don't get their standard fee for such
an operation.


Graham

Farnell don't charge me shipping, and to be honest, I've never felt that
their prices are excessive, given the stockholding that they have, and the
normal efficiency of their service.

Arfa

 

[Gareth Magennis]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:vidXk.407$rT6.376@newsfe22.ams2...

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:492D1F52.BB6C17C8@hotmail.com...


Arfa Daily wrote:

Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and
ship
from Belgium, just one item out of an order of perhaps 10 items ? They
also
seem to employ no rhyme or reason with determining how exactly the
orders
are shipped by default. One day, they will deliver a transformer
weighing a
couple of pounds, in a Jiffy bag, by regular post. The next day, a
packet of
transistors will arrive in a box a foot square, conveyed by UPS, who
don't
usually get to me until late afternoon.

Why do you think they charge the price they do ?

The use of 'satellite warehouses' is well established. Someone must have
done the sums. You can bet UPS don't get their standard fee for such
an operation.


Graham


Farnell don't charge me shipping, and to be honest, I've never felt that
their prices are excessive, given the stockholding that they have, and the
normal efficiency of their service.

Arfa

Likewise. I can phone my order for 1 transistor at 6pm if I need to, and it
is here, free delivery, next day. That's what I need to be able to do.

Certain things, like cable and connectors, are cheaper elsewhere, but for
everyday components I order from them exclusively and pay monthly.
Parts are usually the smallest part of the bill anyway, and the customer
pays for them, so ultimately I am not bothered about trying to save them a
few pence if it takes more time and hassle (and possible labour charge) to
do so. Neither, I suspect, are they.




Gareth.

 

[Meat Plow]

On Wed, 26 Nov 2008 05:44:07 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com>wrote:

Meat Plow wrote:

Eeyorewrote:
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.

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.

NEVER seen that myself but those amps are getting old now. Original spec parts were Samwha (forget which series but the plastic film was dark
green) 3300uF/63V (yes they're overvolted off load @ 67V but we checked that for reliability with Samwha and they sent us detailed info to say
it's basically OK, the leakage current just increases very marginally at ~ 5% overvoltage and no load).

The alternative part was IIRC, Panasonic (again forget which series). Dumpy little black cans. Looked absurdly small. I expect that's what
you've got.

I specced the ripple current per cap at ~ 2.7-3A IIRC. You'll find something in Farnell that'll do fine. Use 105C caps if you want to continue
using it forever.

I assume you're driving a 4 ohm load btw ?

Want some more Oomph ? Fit 4700s. It'll reduce the dynamic headroom though.

What do you think of the amp btw ?

Graham

Ok I archived this. IIRC the caps are dark green This amp spent most
of its life as a sub amp for my home entertainment system. So it spent
a lot of time idling. That probably did more harm than good. And it
was on 24/7 365 days a year for maybe 3 years before I went to powered
subs. One feature I like is that the fan only runs on demand and from
what I remember has infinite control. So this amp is good where fan
noise is an issue. As far as how I rate it sonically, it always
performed well for me although I haven't run too much full range audio
through it.

 

[Meat Plow]

On Wed, 26 Nov 2008 06:00:06 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com>wrote:

Meat Plow wrote:

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

I'm fairly certain the original spec is the Samwha HC series 3300uF 63V.

Yes, this pdf includes the data sheet. The ripple current is in fact > 3A.
http://www.rapidonline.com/netalogue/specs/11-3100e.pdf

Now ask me how I remember that after over 15 years ago.

You'll easily find replacements.

Graham

Archived