Guitar tube effect box.

[Jim]

RS wrote:

On Sat, 25 Jul 2009 16:19:43 -0700, Jim <jim@askmebeforeyousend.com
wrote:

but you may want to go with triodes for this particular app.
12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.
OP: Also check: http://www.dogstar.dantimax.dk/tubestuf/mctube.htm I
haven't built one.

Cool project. B+ is much higher than the Butler-designed starved
plate circuits, so I'd expect much less sensitivity to the brand of
tube used. That would be a good thing.

I agree with that one! I went through *several* 12AX7 before I was
happy, with my original rackmount Chandler Tube Driver. I still have
the original silk screened Chandler tube -- a nice long plate Ei Yugo,
but just doesn't sound best in that unit. One tube really did sound
best. It looks like a Mullard, but is missing the top seam in the
envelope, and is marked CEI (not the more common IEC). But other tubes
with a brand (like several Mullards) would each sound a bit different,
so that CEI is no guarantee for the next guy.

I'll often prefer the tone of a 12AY7 or even 12AU7 when gain gets buzzy.

Might be good to roll off extreme highs after the last OD stage in
that circuit. Most Tubescreamer and Marshall (diode-based) overdrive
boxes have surprisingly low corner frequencies on their post-filters,
but it does allow boosting of treble on the amp without getting harsh
top from the overdrive.

I think proper EQ is the key with any distortion. I tend to prefer a
bit of low cut and fairly wide mids boost, pre-distortion. Then high
frequency cut and sometimes low frequency boost post distortion. I
don't like the pointy guitar speed metal tone, sounds like angry hornets
in a coffee can.

 

[RS]

On Sun, 26 Jul 2009 13:32:31 -0700, Jim <jim@askmebeforeyousend.com>
wrote:

RS wrote:
On Sat, 25 Jul 2009 16:19:43 -0700, Jim <jim@askmebeforeyousend.com
wrote:

but you may want to go with triodes for this particular app.
12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.
OP: Also check: http://www.dogstar.dantimax.dk/tubestuf/mctube.htm I
haven't built one.

Cool project. B+ is much higher than the Butler-designed starved
plate circuits, so I'd expect much less sensitivity to the brand of
tube used. That would be a good thing.

I agree with that one! I went through *several* 12AX7 before I was
happy, with my original rackmount Chandler Tube Driver. I still have
the original silk screened Chandler tube -- a nice long plate Ei Yugo,
but just doesn't sound best in that unit.

Yeah, I think they used selected EI's for the Tube Works stuff as
well. EI's work well at low plate voltages, but there were lots of
quality control problems, mostly with microphonics. That would have
been a great tube if their manufacturing and QC was better.

One tube really did sound
best. It looks like a Mullard, but is missing the top seam in the
envelope, and is marked CEI (not the more common IEC).

Like this?
http://tctubes.com/12AX7-ECC83-CEI-Germany-O-getter.aspx

But other tubes
with a brand (like several Mullards) would each sound a bit different,
so that CEI is no guarantee for the next guy.

I've tried some nice NOS tubes (diamond bottom Telefunkens, original
Tungsols, original Amperex, etc) in 'starved-plate' circuits, and
always thought that EI's worked best. Some others were OK. The
Telefunkens didn't do it for me.

I'll often prefer the tone of a 12AY7 or even 12AU7 when gain gets buzzy.

I believe that schematics for both the Real Tube circuits are around.
One was lower gain. If the higher gain circuit is close to your
Chandler, you might be able to change a couple resistor values to
those of the lower gain RT circuit. They both sound good.

Might be good to roll off extreme highs after the last OD stage in
that circuit. Most Tubescreamer and Marshall (diode-based) overdrive
boxes have surprisingly low corner frequencies on their post-filters,
but it does allow boosting of treble on the amp without getting harsh
top from the overdrive.

I think proper EQ is the key with any distortion. I tend to prefer a
bit of low cut and fairly wide mids boost, pre-distortion. Then high
frequency cut and sometimes low frequency boost post distortion. I
don't like the pointy guitar speed metal tone, sounds like angry hornets
in a coffee can.

Kind of like RIAA pre/post EQ that was used in vinyl recording days.
Dave Barber used that approach in at least one of his pedal circuits.
I've done that in guitar amp circuits.

Yeah, I don't get the over-the-top scooped metal sound either.
Convenient for shredders' pinch harmonics and hammers, but even if
there's some tone there, the sound tends to drop out of sight in a mix
or in the sonic jumble of a live band. The best way to jump out front
is to use less extreme distortion and richer, punchier mids.

 

[Jim]

RS wrote:

On Sun, 26 Jul 2009 13:32:31 -0700, Jim <jim@askmebeforeyousend.com
wrote:

RS wrote:
On Sat, 25 Jul 2009 16:19:43 -0700, Jim <jim@askmebeforeyousend.com
wrote:

but you may want to go with triodes for this particular app.
12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.
OP: Also check: http://www.dogstar.dantimax.dk/tubestuf/mctube.htm I
haven't built one.
Cool project. B+ is much higher than the Butler-designed starved
plate circuits, so I'd expect much less sensitivity to the brand of
tube used. That would be a good thing.
I agree with that one! I went through *several* 12AX7 before I was
happy, with my original rackmount Chandler Tube Driver. I still have
the original silk screened Chandler tube -- a nice long plate Ei Yugo,
but just doesn't sound best in that unit.

Yeah, I think they used selected EI's for the Tube Works stuff as
well. EI's work well at low plate voltages, but there were lots of
quality control problems, mostly with microphonics. That would have
been a great tube if their manufacturing and QC was better.

One tube really did sound
best. It looks like a Mullard, but is missing the top seam in the
envelope, and is marked CEI (not the more common IEC).

Like this?
http://tctubes.com/12AX7-ECC83-CEI-Germany-O-getter.aspx

No, it has a simpler block print and Great Britain. And I just noticed
what could be a Mullard code, but lengthwise, instead of around the
base. It's a bit smaller than Blackburn codes, and is mostly worn, but
I see possibly I, then 162. So maybe an ECC83 made outside of
Blackburn? I dunno.

But other tubes
with a brand (like several Mullards) would each sound a bit different,
so that CEI is no guarantee for the next guy.

I've tried some nice NOS tubes (diamond bottom Telefunkens, original
Tungsols, original Amperex, etc) in 'starved-plate' circuits, and
always thought that EI's worked best. Some others were OK. The
Telefunkens didn't do it for me.

I'm sure I tried a few Ei when I tested this one. This one gave the
best distortion.

I'll often prefer the tone of a 12AY7 or even 12AU7 when gain gets buzzy.

I believe that schematics for both the Real Tube circuits are around.
One was lower gain. If the higher gain circuit is close to your
Chandler, you might be able to change a couple resistor values to
those of the lower gain RT circuit. They both sound good.

Might be good to roll off extreme highs after the last OD stage in
that circuit. Most Tubescreamer and Marshall (diode-based) overdrive
boxes have surprisingly low corner frequencies on their post-filters,
but it does allow boosting of treble on the amp without getting harsh
top from the overdrive.
I think proper EQ is the key with any distortion. I tend to prefer a
bit of low cut and fairly wide mids boost, pre-distortion. Then high
frequency cut and sometimes low frequency boost post distortion. I
don't like the pointy guitar speed metal tone, sounds like angry hornets
in a coffee can.

Kind of like RIAA pre/post EQ that was used in vinyl recording days.
Dave Barber used that approach in at least one of his pedal circuits.
I've done that in guitar amp circuits.

Yeah, I don't get the over-the-top scooped metal sound either.
Convenient for shredders' pinch harmonics and hammers, but even if
there's some tone there, the sound tends to drop out of sight in a mix
or in the sonic jumble of a live band. The best way to jump out front
is to use less extreme distortion and richer, punchier mids.

 

[jh]

RS schrieb:

On Sun, 26 Jul 2009 13:32:31 -0700, Jim <jim@askmebeforeyousend.com
wrote:

RS wrote:
On Sat, 25 Jul 2009 16:19:43 -0700, Jim <jim@askmebeforeyousend.com
wrote:

but you may want to go with triodes for this particular app.
12ax7's are easy to deal with, and you'd have a vast bank of
schematics for ideas (Fender, Marshall, just about every major amp).

Check website: http://www.schematicheaven.com for some schematics.
OP: Also check: http://www.dogstar.dantimax.dk/tubestuf/mctube.htm I
haven't built one.
Cool project. B+ is much higher than the Butler-designed starved
plate circuits, so I'd expect much less sensitivity to the brand of
tube used. That would be a good thing.
I agree with that one! I went through *several* 12AX7 before I was
happy, with my original rackmount Chandler Tube Driver. I still have
the original silk screened Chandler tube -- a nice long plate Ei Yugo,
but just doesn't sound best in that unit.

Yeah, I think they used selected EI's for the Tube Works stuff as
well. EI's work well at low plate voltages, but there were lots of
quality control problems, mostly with microphonics. That would have
been a great tube if their manufacturing and QC was better.

One tube really did sound
best. It looks like a Mullard, but is missing the top seam in the
envelope, and is marked CEI (not the more common IEC).

Like this?
http://tctubes.com/12AX7-ECC83-CEI-Germany-O-getter.aspx

wow

Siemens München...

Jochen

But other tubes
with a brand (like several Mullards) would each sound a bit different,
so that CEI is no guarantee for the next guy.

I've tried some nice NOS tubes (diamond bottom Telefunkens, original
Tungsols, original Amperex, etc) in 'starved-plate' circuits, and
always thought that EI's worked best. Some others were OK. The
Telefunkens didn't do it for me.

I'll often prefer the tone of a 12AY7 or even 12AU7 when gain gets buzzy.

I believe that schematics for both the Real Tube circuits are around.
One was lower gain. If the higher gain circuit is close to your
Chandler, you might be able to change a couple resistor values to
those of the lower gain RT circuit. They both sound good.

Might be good to roll off extreme highs after the last OD stage in
that circuit. Most Tubescreamer and Marshall (diode-based) overdrive
boxes have surprisingly low corner frequencies on their post-filters,
but it does allow boosting of treble on the amp without getting harsh
top from the overdrive.
I think proper EQ is the key with any distortion. I tend to prefer a
bit of low cut and fairly wide mids boost, pre-distortion. Then high
frequency cut and sometimes low frequency boost post distortion. I
don't like the pointy guitar speed metal tone, sounds like angry hornets
in a coffee can.

Kind of like RIAA pre/post EQ that was used in vinyl recording days.
Dave Barber used that approach in at least one of his pedal circuits.
I've done that in guitar amp circuits.

Yeah, I don't get the over-the-top scooped metal sound either.
Convenient for shredders' pinch harmonics and hammers, but even if
there's some tone there, the sound tends to drop out of sight in a mix
or in the sonic jumble of a live band. The best way to jump out front
is to use less extreme distortion and richer, punchier mids.

 

[ian field]

"RS" <RS@nonspam.com> wrote in message
news:cdsm65d81hf8dhn94d2qlc1qh85n8dnf8g@4ax.com...

On Sat, 25 Jul 2009 21:22:29 +0100, "ian field"
gangprobing.alien@ntlworld.com> wrote:


"RS" <RS@nonspam.com> wrote in message
[re 6DJ8 / ECC88]
Of the tubes you have, that would probably be your best bet, but I
still advise going with 12ax7 family. They're not expensive, and you
can swap in other tubes in the 12a-7 family (12at7, 12au7), as they
all have the same pinout and filament voltage requirements. Not so
with the ECC88.

Apparently the ECC88 was designed for use as the cascode pair in the front
end of BandII FM radios, it might well have been used in TV tuners but I
suspect BandI only TVs were obsolete by the time this tube appeared and a
variety of frame grid triodes were specifically developed for BandIII and
UHF tuners.

But then the tetrodes I was thinking of using are VHF types.

The ECC88 was widely adopted for audio designs, just not for guitar
amps (at least any that I can recall). They work very well, or
companies like Avalon would not be using them.

Tetrodes: Not likely to work well there due to the kink in the curves.

Is the signal swing likely to reach the kink on a front end stage? Perhaps I
could just tie the screen grid to the anode and hope I get away with fooling
the circuit into thinking its a triode.

Having downloaded a few present day amp schematics, I notice some
manufacturers are putting at least one tube *somewhere* in the audio path in
their solid state amps - usually some way in from the input with several
stages, whether it be transistors, FETs or OP-AMPs, in front of them. That
seems to suggest to me that maybe I should put a solid state "clean boost"
up front in a stand alone tube box.

 

[jh]

ian field schrieb:

"RS" <RS@nonspam.com> wrote in message
news:cdsm65d81hf8dhn94d2qlc1qh85n8dnf8g@4ax.com...
On Sat, 25 Jul 2009 21:22:29 +0100, "ian field"
gangprobing.alien@ntlworld.com> wrote:

"RS" <RS@nonspam.com> wrote in message
[re 6DJ8 / ECC88]
Of the tubes you have, that would probably be your best bet, but I
still advise going with 12ax7 family. They're not expensive, and you
can swap in other tubes in the 12a-7 family (12at7, 12au7), as they
all have the same pinout and filament voltage requirements. Not so
with the ECC88.
Apparently the ECC88 was designed for use as the cascode pair in the front
end of BandII FM radios, it might well have been used in TV tuners but I
suspect BandI only TVs were obsolete by the time this tube appeared and a
variety of frame grid triodes were specifically developed for BandIII and
UHF tuners.

But then the tetrodes I was thinking of using are VHF types.
The ECC88 was widely adopted for audio designs, just not for guitar
amps (at least any that I can recall). They work very well, or
companies like Avalon would not be using them.

Tetrodes: Not likely to work well there due to the kink in the curves.

Is the signal swing likely to reach the kink on a front end stage? Perhaps I
could just tie the screen grid to the anode and hope I get away with fooling
the circuit into thinking its a triode.

Having downloaded a few present day amp schematics, I notice some
manufacturers are putting at least one tube *somewhere* in the audio path in
their solid state amps - usually some way in from the input with several
stages, whether it be transistors, FETs or OP-AMPs, in front of them. That
seems to suggest to me that maybe I should put a solid state "clean boost"
up front in a stand alone tube box.

Ian,

forget that. What you see is the typical ALIBI TUBE that serves mostly
as an "argument" to sell the unit as "tube".

Normally this tube is visually presented and backlit with LEDs so you
see it "shine".

Jochen

 

[RS]

On Wed, 29 Jul 2009 11:43:28 +0200, jh <jh@org.de> wrote:

ian field schrieb:

Having downloaded a few present day amp schematics, I notice some
manufacturers are putting at least one tube *somewhere* in the audio path in
their solid state amps - usually some way in from the input with several
stages, whether it be transistors, FETs or OP-AMPs, in front of them. That
seems to suggest to me that maybe I should put a solid state "clean boost"
up front in a stand alone tube box.

Ian,

forget that. What you see is the typical ALIBI TUBE that serves mostly
as an "argument" to sell the unit as "tube".

Normally this tube is visually presented and backlit with LEDs so you
see it "shine".

Jochen

I didn't answer that cause I didn't know whether he was joking or not.
The original post was about using a tube in front of a solid state
amp. That was now presumably getting front-ended by a solid state
amp.

Yeah, the lone LED-lit tube is often just a marketing gimmick. But I
have had occasion to put a solid state booster in front of a tube. In
one case, it was a tube-based distortion pedal that didn't have enough
juice to overdrive the tube much. The tube was running at high
voltage so two stages were just starting to bump the overdrive zone.
The pedal had one tube socket, and the existing transformer was rather
low power, so I didn't see much sense in adding another tube. Hooked
up an FET to pre-boost the signal. It worked well.

When you think about it, most guitarists have solid state overdrive
pedals in front of their amps, so there's nothing sacrilegious about
doing that. But in a new design, why not just go all-tube?

BTW, the only amp/FX modeller that uses one of those LED-lit tubes
(that I know of) is the Vox Tonelab. Possibly coincidence, but I like
it better than any of the others (V-Amp, Pod, etc), and I find the
overdrive sounds easier on the ears. Not sure how much of that can be
attributed to the tube, but I believe their market-stuff says that
they're using it to try to emulate characteristics of a push-pull
output stage. I'd like to see that circuit.

 

[jh]

RS schrieb:

On Wed, 29 Jul 2009 11:43:28 +0200, jh <jh@org.de> wrote:

ian field schrieb:

Having downloaded a few present day amp schematics, I notice some
manufacturers are putting at least one tube *somewhere* in the audio path in
their solid state amps - usually some way in from the input with several
stages, whether it be transistors, FETs or OP-AMPs, in front of them. That
seems to suggest to me that maybe I should put a solid state "clean boost"
up front in a stand alone tube box.

Ian,

forget that. What you see is the typical ALIBI TUBE that serves mostly
as an "argument" to sell the unit as "tube".

Normally this tube is visually presented and backlit with LEDs so you
see it "shine".

Jochen

I didn't answer that cause I didn't know whether he was joking or not.
The original post was about using a tube in front of a solid state
amp. That was now presumably getting front-ended by a solid state
amp.

Yeah, the lone LED-lit tube is often just a marketing gimmick. But I
have had occasion to put a solid state booster in front of a tube. In
one case, it was a tube-based distortion pedal that didn't have enough
juice to overdrive the tube much. The tube was running at high
voltage so two stages were just starting to bump the overdrive zone.
The pedal had one tube socket, and the existing transformer was rather
low power, so I didn't see much sense in adding another tube. Hooked
up an FET to pre-boost the signal. It worked well.

When you think about it, most guitarists have solid state overdrive
pedals in front of their amps, so there's nothing sacrilegious about
doing that. But in a new design, why not just go all-tube?

BTW, the only amp/FX modeller that uses one of those LED-lit tubes
(that I know of) is the Vox Tonelab. Possibly coincidence, but I like
it better than any of the others (V-Amp, Pod, etc), and I find the
overdrive sounds easier on the ears. Not sure how much of that can be
attributed to the tube, but I believe their market-stuff says that
they're using it to try to emulate characteristics of a push-pull
output stage. I'd like to see that circuit.

Hi RS,
i had the RocPro series in mind and the Behringer "pro rack series". One
uses the tube as a "hollow state distortion diode bridge ", the other
one is starved plate....


I personally have one LED-lit hybrid pedal. In the HK TubeFactor the SS
is buffer and a bit of input gain, the Tube Stage is HV, marshally and
really good. That's the only compromise i can take. If it were all tube,
I'd be happpier, but the pedal is the only external
"distortion/overdrive" i've found yet that really sounds good for me.
As always: it's a matter of "how well designed is the unit". SS is
neither evil nor saint. Tubes are capable of producing low hiss gain,
placed in an appropriate environment. No need to help them into the saddle.


Jochen

Jochen

 

[ian field]

"jh" <jh@org.de> wrote in message
news:h4rl26$ame$1@news.eternal-september.org...

RS schrieb:
On Wed, 29 Jul 2009 11:43:28 +0200, jh <jh@org.de> wrote:

ian field schrieb:

Having downloaded a few present day amp schematics, I notice some
manufacturers are putting at least one tube *somewhere* in the audio
path in their solid state amps - usually some way in from the input
with several stages, whether it be transistors, FETs or OP-AMPs, in
front of them. That seems to suggest to me that maybe I should put a
solid state "clean boost" up front in a stand alone tube box.

Ian,

forget that. What you see is the typical ALIBI TUBE that serves mostly
as an "argument" to sell the unit as "tube".

Normally this tube is visually presented and backlit with LEDs so you
see it "shine".

Jochen

I didn't answer that cause I didn't know whether he was joking or not.
The original post was about using a tube in front of a solid state
amp. That was now presumably getting front-ended by a solid state
amp.

Yeah, the lone LED-lit tube is often just a marketing gimmick. But I
have had occasion to put a solid state booster in front of a tube. In
one case, it was a tube-based distortion pedal that didn't have enough
juice to overdrive the tube much. The tube was running at high
voltage so two stages were just starting to bump the overdrive zone.
The pedal had one tube socket, and the existing transformer was rather
low power, so I didn't see much sense in adding another tube. Hooked
up an FET to pre-boost the signal. It worked well.

When you think about it, most guitarists have solid state overdrive
pedals in front of their amps, so there's nothing sacrilegious about
doing that. But in a new design, why not just go all-tube?

BTW, the only amp/FX modeller that uses one of those LED-lit tubes
(that I know of) is the Vox Tonelab. Possibly coincidence, but I like
it better than any of the others (V-Amp, Pod, etc), and I find the
overdrive sounds easier on the ears. Not sure how much of that can be
attributed to the tube, but I believe their market-stuff says that
they're using it to try to emulate characteristics of a push-pull
output stage. I'd like to see that circuit.

Hi RS,
i had the RocPro series in mind and the Behringer "pro rack series". One
uses the tube as a "hollow state distortion diode bridge ", the other one
is starved plate....

A search for "starved plate" produced a number of forums, the consensus of
opinion seems to be that the manufacturers are cheapskates getting away with
cheaper low voltage components. Several people have suggested that dynamic
range suffers and its not very useful as an effect.

Generally speaking I got the impression that the comments were from less
technically minded people than here, so I'd welcome comments here.

 

[Les Cargill]

ian field wrote:

"jh" <jh@org.de> wrote in message

Hi RS,
i had the RocPro series in mind and the Behringer "pro rack series". One
uses the tube as a "hollow state distortion diode bridge ", the other one
is starved plate....

(posting designed to disambiguate aga from s.e.b
listeners...)

There's nothing wring with the Fender starved plate RocPro amps. I have
a Performer 650, and it's worked very well when used with a good
speaker cab.

If you read the Harmony Central reviews of them, they're all from
people who wanted a Mesa Triple Recto, couldn't afford one,
bought the Fender, decided it wasn't a Triple Recto and then
bought a Triple Recto. The few who bought it for what it was
love it to death.

If you set the gain well on it, and use the F/X loop properly,
it's a very flexible amp. In a room with a drum set, you
can't tell anyway.

A search for "starved plate" produced a number of forums, the consensus of
opinion seems to be that the manufacturers are cheapskates getting away with
cheaper low voltage components.

That's not what it's about at all. For guitar amp designs, it
works well. It bandlimits the signal. For mic preamps, it
doesn't work well at all.

Several people have suggested that dynamic
range suffers and its not very useful as an effect.

Guitar players don't care about dynamic range. That's why they
buy $2000 tube guitar heads to compress the signal. Recording
type equipment is not guitar amps.

Generally speaking I got the impression that the comments were from less
technically minded people than here, so I'd welcome comments here.

Starved plate is just a technique. Depends on what you use it for.

--
Les Cargill

 

[jh]

Les Cargill schrieb:

ian field wrote:
"jh" <jh@org.de> wrote in message

Hi RS,
i had the RocPro series in mind and the Behringer "pro rack series".
One uses the tube as a "hollow state distortion diode bridge ", the
other one is starved plate....


(posting designed to disambiguate aga from s.e.b
listeners...)

There's nothing wring with the Fender starved plate RocPro amps. I have
a Performer 650, and it's worked very well when used with a good
speaker cab.

If you read the Harmony Central reviews of them, they're all from
people who wanted a Mesa Triple Recto, couldn't afford one,
bought the Fender, decided it wasn't a Triple Recto and then
bought a Triple Recto. The few who bought it for what it was
love it to death.

If you set the gain well on it, and use the F/X loop properly,
it's a very flexible amp. In a room with a drum set, you
can't tell anyway.

A search for "starved plate" produced a number of forums, the
consensus of opinion seems to be that the manufacturers are
cheapskates getting away with cheaper low voltage components.

That's not what it's about at all. For guitar amp designs, it
works well. It bandlimits the signal. For mic preamps, it
doesn't work well at all.

Several people have suggested that dynamic range suffers and its not
very useful as an effect.


Guitar players don't care about dynamic range. That's why they
buy $2000 tube guitar heads to compress the signal. Recording
type equipment is not guitar amps.

Generally speaking I got the impression that the comments were from
less technically minded people than here, so I'd welcome comments here.


Starved plate is just a technique. Depends on what you use it for.

--
Les Cargill

Les,

i did NOT diss the RocPro. For SS amps, they sound nice; they are a
nigthmare to service if something breaks, but when they work....
My point was that the amp would definately sound the same, if the 12AX7
would have been substituted by red LEDs as clipping diodes!!!

I was talking 'bout havin tubes in amps just as a marketing gag.


Jochen

 

[Les Cargill]

jh wrote:

Les Cargill schrieb:
ian field wrote:
"jh" <jh@org.de> wrote in message

Hi RS,
i had the RocPro series in mind and the Behringer "pro rack series".
One uses the tube as a "hollow state distortion diode bridge ", the
other one is starved plate....


(posting designed to disambiguate aga from s.e.b
listeners...)

There's nothing wring with the Fender starved plate RocPro amps. I have
a Performer 650, and it's worked very well when used with a good
speaker cab.

If you read the Harmony Central reviews of them, they're all from
people who wanted a Mesa Triple Recto, couldn't afford one,
bought the Fender, decided it wasn't a Triple Recto and then
bought a Triple Recto. The few who bought it for what it was
love it to death.

If you set the gain well on it, and use the F/X loop properly,
it's a very flexible amp. In a room with a drum set, you
can't tell anyway.

A search for "starved plate" produced a number of forums, the
consensus of opinion seems to be that the manufacturers are
cheapskates getting away with cheaper low voltage components.

That's not what it's about at all. For guitar amp designs, it
works well. It bandlimits the signal. For mic preamps, it
doesn't work well at all.

Several people have suggested that dynamic range suffers and its not
very useful as an effect.


Guitar players don't care about dynamic range. That's why they
buy $2000 tube guitar heads to compress the signal. Recording
type equipment is not guitar amps.

Generally speaking I got the impression that the comments were from
less technically minded people than here, so I'd welcome comments here.


Starved plate is just a technique. Depends on what you use it for.

--
Les Cargill



Les,

i did NOT diss the RocPro.

Sorry - I didn't mean to say you had.

For SS amps, they sound nice; they are a
nigthmare to service if something breaks,

You got that right! I killed mine trying
to replace the input jack, but I'm not
really much of an electronics tech. ( I
powered it up with the reverb drive shorted -
Doh!)

but when they work....
My point was that the amp would definately sound the same, if the 12AX7
would have been substituted by red LEDs as clipping diodes!!!

Huh. Really? I did not know that.

When I bought it, I was purely being a
consumer - no real consideration to technology
was given.

I was talking 'bout havin tubes in amps just as a marketing gag.

I am not so sure that is true for *guitar* amps. It
probably started out that way - but when I was looking
for an amp in the early '90s, the Performer was the
all-around best thing Fender had to offer at the time.

I thought the "its gots a t00b" thing was silly, but
it worked anyway. Sounded to me like the old Fender
London amps.

Jochen

--
Les Cargill

 

[ian field]

"jh" <jh@org.de> wrote in message
news:h4p5k9$o4l$1@news.eternal-september.org...

ian field schrieb:
"RS" <RS@nonspam.com> wrote in message
news:cdsm65d81hf8dhn94d2qlc1qh85n8dnf8g@4ax.com...
On Sat, 25 Jul 2009 21:22:29 +0100, "ian field"
gangprobing.alien@ntlworld.com> wrote:

"RS" <RS@nonspam.com> wrote in message
[re 6DJ8 / ECC88]
Of the tubes you have, that would probably be your best bet, but I
still advise going with 12ax7 family. They're not expensive, and you
can swap in other tubes in the 12a-7 family (12at7, 12au7), as they
all have the same pinout and filament voltage requirements. Not so
with the ECC88.
Apparently the ECC88 was designed for use as the cascode pair in the
front
end of BandII FM radios, it might well have been used in TV tuners but
I
suspect BandI only TVs were obsolete by the time this tube appeared and
a
variety of frame grid triodes were specifically developed for BandIII
and
UHF tuners.

But then the tetrodes I was thinking of using are VHF types.
The ECC88 was widely adopted for audio designs, just not for guitar
amps (at least any that I can recall). They work very well, or
companies like Avalon would not be using them.

Tetrodes: Not likely to work well there due to the kink in the curves.

Is the signal swing likely to reach the kink on a front end stage?
Perhaps I could just tie the screen grid to the anode and hope I get away
with fooling the circuit into thinking its a triode.

Having downloaded a few present day amp schematics, I notice some
manufacturers are putting at least one tube *somewhere* in the audio path
in their solid state amps - usually some way in from the input with
several stages, whether it be transistors, FETs or OP-AMPs, in front of
them. That seems to suggest to me that maybe I should put a solid state
"clean boost" up front in a stand alone tube box.


Ian,

forget that. What you see is the typical ALIBI TUBE that serves mostly as
an "argument" to sell the unit as "tube".

Normally this tube is visually presented and backlit with LEDs so you see
it "shine".

Jochen

Are you saying some makers put a dummy tube in amps and light it up with a
LED?

The schematics I referred to show the tube is actually part of the circuit,
i.e. - if you cut off the heater supply the audio path would be broken.

 

[ian field]

"RS" <RS@nonspam.com> wrote in message
news:mdr175h6cs46ujh376ge835ms6jpe1avk3@4ax.com...

On Wed, 29 Jul 2009 11:43:28 +0200, jh <jh@org.de> wrote:

ian field schrieb:

Having downloaded a few present day amp schematics, I notice some
manufacturers are putting at least one tube *somewhere* in the audio
path in
their solid state amps - usually some way in from the input with several
stages, whether it be transistors, FETs or OP-AMPs, in front of them.
That
seems to suggest to me that maybe I should put a solid state "clean
boost"
up front in a stand alone tube box.

Ian,

forget that. What you see is the typical ALIBI TUBE that serves mostly
as an "argument" to sell the unit as "tube".

Normally this tube is visually presented and backlit with LEDs so you
see it "shine".

Jochen

I didn't answer that cause I didn't know whether he was joking or not.
The original post was about using a tube in front of a solid state
amp. That was now presumably getting front-ended by a solid state
amp.

I'm trying to understand the nature of tube input stage distortion and would
welcome any insights on the subject.

Apparently its common practice to maximise the available range of the effect
by putting a solid state clean boost box in front of a tube amp. DOD
produced an excellent JFET booster (no model number!) the circuit is very
simple, so if I'm putting together a tube stage to imitate the front end of
a tube amp, why not build the booster into the same box while I'm at it.

 

[ian field]

"Les Cargill" <lcargill@cfl.rr.com> wrote in message
news:4a71c7c7$0$5664$9a6e19ea@unlimited.newshosting.com...

ian field wrote:
"jh" <jh@org.de> wrote in message

Hi RS,
i had the RocPro series in mind and the Behringer "pro rack series". One
uses the tube as a "hollow state distortion diode bridge ", the other
one is starved plate....


(posting designed to disambiguate aga from s.e.b
listeners...)

There's nothing wring with the Fender starved plate RocPro amps. I have
a Performer 650, and it's worked very well when used with a good
speaker cab.

If you read the Harmony Central reviews of them, they're all from
people who wanted a Mesa Triple Recto, couldn't afford one,
bought the Fender, decided it wasn't a Triple Recto and then
bought a Triple Recto. The few who bought it for what it was
love it to death.

If you set the gain well on it, and use the F/X loop properly,
it's a very flexible amp. In a room with a drum set, you
can't tell anyway.

A search for "starved plate" produced a number of forums, the consensus
of opinion seems to be that the manufacturers are cheapskates getting
away with cheaper low voltage components.

That's not what it's about at all. For guitar amp designs, it
works well. It bandlimits the signal. For mic preamps, it
doesn't work well at all.

Several people have suggested that dynamic range suffers and its not very
useful as an effect.


Guitar players don't care about dynamic range. That's why they
buy $2000 tube guitar heads to compress the signal. Recording
type equipment is not guitar amps.

It may be a different thing entirely, but my compressor project is one
that's actually making decent progress at the moment.

Its another topic I'd welcome any insights - as yet I have no idea how to
design circuitry that distinguishes between attack and decay in a
compressor's gain envelope.

 

[RS]

On Thu, 30 Jul 2009 21:17:40 +0100, "ian field"
<gangprobing.alien@ntlworld.com> wrote:

It may be a different thing entirely, but my compressor project is one
that's actually making decent progress at the moment.

Its another topic I'd welcome any insights - as yet I have no idea how to
design circuitry that distinguishes between attack and decay in a
compressor's gain envelope.

I presume that you're talking about detecting the slope of the
envelope: Up = attack, down = decay. That's easier to do in digital
domain, but in analog, you could try feeding the output of the
envelope detector into a differentiator (like a cap in series) which
will give you a positive pulse for attack, etc. Then feed the diff's
output to a schmitt trigger (opamp with some positive feedback would
do it). You'd get a 1 or 0 for attack vs decay. Problem would be in
tweaking time constants, especially for the differentiator, as the
envelope slope for attack will be sharper than the slope for decay.

Another possibility, though I've never tried this: Feed the envelope
into something that will delay it (like a low-pass filter, if you can
live with the inconsistent phase delay). Then run both the delayed
and non-delayed signals into a comparator. This would probably get
tricky.

Why are you trying to distinguish between attack and decay?

 

[RS]

On Thu, 30 Jul 2009 21:10:23 +0100, "ian field"
<gangprobing.alien@ntlworld.com> wrote:

I'm trying to understand the nature of tube input stage distortion and would
welcome any insights on the subject.

Apparently its common practice to maximise the available range of the effect
by putting a solid state clean boost box in front of a tube amp. DOD
produced an excellent JFET booster (no model number!) the circuit is very
simple, so if I'm putting together a tube stage to imitate the front end of
a tube amp, why not build the booster into the same box while I'm at it.

Covered in my previous post. That's basically what I was outlining re
the pedal design. Also mentioned: If you're starting a new design,
why not go with all tubes? There's nothing magical about having a
solid state stage in a stomp box before the tubes. It's just easier
to power them with a battery--something you wouldn't need to worry
about.

 

[ian field]

"RS" <RS@nonspam.com> wrote in message
news:fg3475tf8ao17vuq3g6vhlousemd4n9onk@4ax.com...

On Thu, 30 Jul 2009 21:17:40 +0100, "ian field"
gangprobing.alien@ntlworld.com> wrote:

It may be a different thing entirely, but my compressor project is one
that's actually making decent progress at the moment.

Its another topic I'd welcome any insights - as yet I have no idea how to
design circuitry that distinguishes between attack and decay in a
compressor's gain envelope.

I presume that you're talking about detecting the slope of the
envelope: Up = attack, down = decay. That's easier to do in digital
domain, but in analog, you could try feeding the output of the
envelope detector into a differentiator (like a cap in series) which
will give you a positive pulse for attack, etc. Then feed the diff's
output to a schmitt trigger (opamp with some positive feedback would
do it). You'd get a 1 or 0 for attack vs decay. Problem would be in
tweaking time constants, especially for the differentiator, as the
envelope slope for attack will be sharper than the slope for decay.

At the moment I'm having problems with the variable gain amplifier bursting
into oscillation, I've tried to keep the feedback control as simple as
possible and I'm not sure if its the diode pump amplifier that's oscillating
or the whole loop

Another possibility, though I've never tried this: Feed the envelope
into something that will delay it (like a low-pass filter, if you can
live with the inconsistent phase delay). Then run both the delayed
and non-delayed signals into a comparator. This would probably get
tricky.

Delayed AGC would cause the strike of the note to be un-attenuated followed
by the quieter flat portion, I anticipate this being a big enough problem
without doing things that make it worse.

Why are you trying to distinguish between attack and decay?

Some crazy notion I got doing an internet search for any info I could find
on guitar compressors.

 

[ian field]

"RS" <RS@nonspam.com> wrote in message
news:334475lrak0mjb89v34ptbebnfkhb5q4h7@4ax.com...

On Thu, 30 Jul 2009 21:10:23 +0100, "ian field"
gangprobing.alien@ntlworld.com> wrote:

I'm trying to understand the nature of tube input stage distortion and
would
welcome any insights on the subject.

Apparently its common practice to maximise the available range of the
effect
by putting a solid state clean boost box in front of a tube amp. DOD
produced an excellent JFET booster (no model number!) the circuit is very
simple, so if I'm putting together a tube stage to imitate the front end
of
a tube amp, why not build the booster into the same box while I'm at it.

Covered in my previous post. That's basically what I was outlining re
the pedal design. Also mentioned: If you're starting a new design,
why not go with all tubes? There's nothing magical about having a
solid state stage in a stomp box before the tubes. It's just easier
to power them with a battery--something you wouldn't need to worry
about.

Its a pity nuvistors aren't easy to find anymore, the type 8056 is designed
for anode voltage as low as 12V. With a buck regulator to convert down to
6.3V for the heater it would give a decent running time from a very small
12V SLA battery.

 

[Stephen Cowell]

"ian field" <gangprobing.alien@ntlworld.com> wrote

At the moment I'm having problems with the variable gain amplifier
bursting into oscillation, I've tried to keep the feedback control as
simple as possible and I'm not sure if its the diode pump amplifier that's
oscillating or the whole loop

Obviously it has to go down in gain much faster
than it goes up. I believe you're experiencing
the control chain oscillating, creating its own
signal, then acting on it. Make sure there's
plenty of damping on the gain-up circuit.

For a simple compressor, you don't need any
feedback... this means you'll have to adjust it
for it to work right. It also means that your
oscillation problems will go away.

For the feedback scheme to work right,
you'll need better than silicon diodes for
signal rectification... it has to be continuous,
with no free motoring bands like you get
from a SI diode forward drop. There's a
circuit using op-amps that gets around this...
I forget how, IIRC it's in Coughlin-Driscoll.

This is all guesses, btw. Good luck!
__
Steve
..