High Gain Modern amp schematics?

[drz400]

Anyone have Diezel, Bogner, OD100 stuff ?? I have seen some Bogner but very sketchy. Never seen a Diezel If you have something could you PM me?

[Darkbluemurder]

I had a VH-4 once and sold it. This is a real complex amp with all the midi-switching and stuff. I tried to draw the tone stacks of the four channels.

Channel 1: typical Fender tone stack
Channel 2: 470pf treble cap, 22nf mid and bass caps, 39k slope resistor, 1nf cap from mid pot wiper to ground
Channel 3 and 4: 680pf treble cap, everything else like channel 2.

The amp has a lot of plate resistor bypass caps to cut down on highs. To my ears it was a dull sounding amp in all of the overdrive channels. Huge bass response though. Great for HM/TM/BM/DM etc. You will definitely need a modern 4x12" cab to go with it.

[lastwinj]

The amp has a lot of plate resistor bypass caps to cut down on highs.

they are also there to help prevent oscillation in an unstable circuit. removal will cause huge problems. pretty much what is required for super high gain circuits.

jeremy

[drz400]

The amp has a lot of plate resistor bypass caps to cut down on highs.

they are also there to help prevent oscillation in an unstable circuit. removal will cause huge problems. pretty much what is required for super high gain circuits.

jeremy

yes nothing wrong with plate bypass caps, you just dont amplify those frequencies. I prefer it compared to running a cap to ground

[Darkbluemurder]

The amp has a lot of plate resistor bypass caps to cut down on highs.

they are also there to help prevent oscillation in an unstable circuit. removal will cause huge problems. pretty much what is required for super high gain circuits.

jeremy

yes nothing wrong with plate bypass caps, you just dont amplify those frequencies. I prefer it compared to running a cap to ground

Yes, bypassing the plate resistor is certainly better than a cap to ground. But imagine this: the VH-4 has the 1 meg input ground resistor bypassed with a 470pf cap. This is a noise reduction method for sure.

FWIW you can build high gain circuits without having to dump a lot of highs. But I can imagine this will be very difficult once you attempt to build more than two channels. The layout will be quite cramped and it will be almost impossible to separate the sensitive wires from the emitting wires. No wonder the multichannel amps are all constructed on PCB (no rap intended - I have tried a Fuchs, I know it's PCB and sounds wonderful. I also still like my Mesa Mk III for its clean tones - it's PCB as well).

[VacuumVoodoo]

yes nothing wrong with plate bypass caps, you just dont amplify those frequencies. I prefer it compared to running a cap to ground

It's exactly the same. Plate supply rail is at ground signal wise. It's just mechanically simpler to wire the cap parallel with plate resistor than connecting it from plate lug on tube socket to a ground.

[Darkbluemurder]

With "cap to ground" we referred to a cap bypassing the resistor to ground in a voltage divider, not going to ground from a plate lug. Sorry for the confusion.

[drz400]

yes nothing wrong with plate bypass caps, you just dont amplify those frequencies. I prefer it compared to running a cap to ground

It's exactly the same. Plate supply rail is at ground signal wise. It's just mechanically simpler to wire the cap parallel with plate resistor than connecting it from plate lug on tube socket to a ground.

Yes and no. I'm talking about a cap to ground after the coupling cap.
I realize that the plate supply is at ground potential.
However you are not amplifying those frequencies in that stage, as opposed to amplifying them and then rolling them off later. It also seems easier to control in the plate since the impedance stays the same. IF you have a volume pot before a cap to ground things change as you vary the pot and the impedance. At least to me the two metods sound very different as does a cathode cap value being smaller/larger coupling cap compared to a smaller coupling cap/larger cathgode cap. With a smaller coupling cap the notes sound small. It this particular situation I have run tests trying to match a smaller coupling cap and large cathode cap compared to a smaller cathode cap and larger coupling cap. You cant get them to have the exact same frequency response/slope.

[David Root]

drz400 wrote "with a smaller coupling cap the notes sound small".

Is that why the SLO-100 uses .02 interstage coupling caps and then chops out the bass later?

[drz400]

drz400 wrote "with a smaller coupling cap the notes sound small".

Is that why the SLO-100 uses .02 interstage coupling caps and then chops out the bass later?

Well he uses a .022 and then maybe a .0022 parrallel with a 1M so he is still letting some bass through, just limiting it. What makes the SLO so high endy I think is too many small (1uf) cathode caps boosting the end gain. He also limits some squeakness with grid resistors, another way to limit high end response they work with the miller capacitance in the tube.

Diezels sound small to me even though they have a lot of bass in the power section the preamp section uses small caps like .0022 (so does a Shiva) which to me makes single notes sound small.

[David Root]

Probably drifting a bit off-topic, but in a four stage hi-gain circuit, should the FX loop be located Preamp--FX Loop--Tonestack--PI, or Preamp, Tonestack--FX Loop---PI, with the cathode follower immediately preceeding the tonestack in each case? I've seen it done both ways, but it seems to me that you would want the tonestack last so you can make final adjustments to the FX before hitting the PI. Or does it not matter?

BTW, I have a Bogner Ecstasy OD preamp schematic if you don't have it. Low voltage compared with Soldano or M-B.

[Darkbluemurder]

drz400 wrote "with a smaller coupling cap the notes sound small".

Is that why the SLO-100 uses .02 interstage coupling caps and then chops out the bass later?

Well he uses a .022 and then maybe a .0022 parrallel with a 1M so he is still letting some bass through, just limiting it. What makes the SLO so high endy I think is too many small (1uf) cathode caps boosting the end gain. He also limits some squeakness with grid resistors, another way to limit high end response they work with the miller capacitance in the tube.

Diezels sound small to me even though they have a lot of bass in the power section the preamp section uses small caps like .0022 (so does a Shiva) which to me makes single notes sound small.

Funny, I never considered the SLO to have a pronounced high end. It is rather middy sounding to me. This is probably due to the 0.047uF PI coupling caps (strange value to me, it doesn't add bass only some bloaty low mids compared to 0.022uF in that space) and the fact that he uses 0.022uF coupling caps throughout.

In high gain amps I tend to make the coupling caps small in the earlier stages and larger towards the power amp. I would not use anything less than 0.1uF for the PI coupling caps and 0.022uF for the PI input cap. I would use a 0.0047uF coupling cap after the first gain stage (or after the second) and use nothing higher than 0.022uF for the rest. I never found the tone to be small in this application (IMHO of course).

I agree that small CC/large cathode bypass cap (CBC) sounds different than large CC/small CBC. To me a small CBC creates a high/mid boost whereas a small CC limits bass/low mids.

[drz400]

This is probably due to the 0.047uF PI coupling caps (strange value to me, it doesn't add bass only some bloaty low mids compared to 0.022uF in that space)

I would not use anything less than 0.1uF for the PI coupling caps and 0.022uF for the PI input cap.

Is that a Typo? first you said .047 is bloaty and compared to .022 then you said nothing less than .1 ?

Well it all depends on the player, and cabinet but when I look at all the amps that use small couplers like Diezel, Cornford, Bogner, single notes sound small to me and fizzy, I can feel it. Personally I much prefer the SLO100 response, I just dont care for the 47k divider in the tone stack, 33k brings back some warm mids and guts. Plus the effects loop is useless and the amp is too noisey, more to do with layout and grounding.

As far as PI Couplers it really depends on what they are feeding and the value of the bias dividers 220k and .022 is the same as 110Kdividers and .047 frequency wise, just some level difference.

[Darkbluemurder]

This is probably due to the 0.047uF PI coupling caps (strange value to me, it doesn't add bass only some bloaty low mids compared to 0.022uF in that space)

I would not use anything less than 0.1uF for the PI coupling caps and 0.022uF for the PI input cap.

Is that a Typo? first you said .047 is bloaty and compared to .022 then you said nothing less than .1 ?

Well it all depends on the player, and cabinet but when I look at all the amps that use small couplers like Diezel, Cornford, Bogner, single notes sound small to me and fizzy, I can feel it. Personally I much prefer the SLO100 response, I just dont care for the 47k divider in the tone stack, 33k brings back some warm mids and guts. Plus the effects loop is useless and the amp is too noisey, more to do with layout and grounding.

As far as PI Couplers it really depends on what they are feeding and the value of the bias dividers 220k and .022 is the same as 110Kdividers and .047 frequency wise, just some level difference.

No, it's not a typo. I tried this in my 100W Marshall, starting out with 0.022uF. Good overall sound. I increased them to 0.1uF and liked the fuller bass. I then changed to 0.047uF. Gone was the full bass of the 0.1uF. Instead I got added low mids compared to the 0.022uF which sounded really weird. The 0.1uF "equalized" that to some extent. So I would keep them at 0.1uF and reduce bass elsewhere in the amp if it is too boomy (my favorite candidate would be the 0.022uF after V1a or after V1b - change to a 0.0047uF).

Of course if I wanted the power amp to distort then 0.022uF PI couplers are the better choice than 0.1uF but you wouldn't necessarily overdrive the power amp in a high gain amp.

I would also change the 47k slope resistor in the SLO to a 39k or 33k. That takes away some of the nasal tone and makes it a bit darker and warmer. It's all a matter of taste of course.

[drz400]

OK... don’t know why you get the observation
The .047 is in-between the .022 and the .1 and should give you a bass response in-between. It is after all just a coupling cap and the low freq cutoff is determined by the load and output impedance of the stage.
Maybe you used a different sounding cap for the tests.

My father spent a lot of time in the audio world with double blind tests, recording and empirical proof. Many times we don’t hear what we think we hear or the result is due to a different reason that we think.

Hey this Audio stuff is like religion! OK... I wont go there