cold clipper

[sbirkenstock]

Hi everybody,

tried out some "cold clippers".
I found several on the last stage before the cathode follower (in front of the tone stack) in several famous amps.
So it is simply an unbypassed cathode resistor.

The Marshall JCM 800 has 10k, Cornford MK50HII 15k, Soldano SLO 100 and Meas Dual Rectifier both have 39K. (Who was first????)
Checked with my USB oscilloscope and it really works! Only clips on side of the signal.

Also no "grid clipping" (see my post: "Booster tube in front of V1" from yesterday).

For fun I also checked 2k7 (unbypassed), but this does not work and still creates grid clipping.

Anyway, 10K work perfectly even with a sine wave higher than 200v point to point at the grid (without grid clipping)....
The difference between 10k and 39k seems to be be only the output.
The output with 39k is reduced by 2/3rds compared to 10K.
Guess that is called "local negative feedback".

The cold clipper tames things a lot (especially with 3 gain stages before the cathode follower, which seems to be the standard...).
Talking about taming unwanted feedback, howling, noise level. It actually goes away completely in my amp.
But it also reduces distortion quite a bit. With 39k the cathode follower is not hit that hard any more.....
For me, the Soldano SLO does not have enough distortion (for a high gain amp), the Dual Rectifier for example has way more (despite the same 39K).

Does anybody know why they use 39k? Is there some calculation behind it?
Is the "high" value mainly to reduce challenges and be on the save side (in mass production)?

Thanks a lot,
Stephan

[WhopperPlate]

For the record : soldano came first .

[martin manning]

For the record : soldano came first .

Earlier than JCM800 MV 21/2203 and 21/2204 from 1981?

[pdf64]

The Marshall JMP 2203 was 1976 https://el34world.com/charts/Schematics ... _2203u.pdf

[Lynxtrap]

Does anybody know why they use 39k? Is there some calculation behind it?
Is the "high" value mainly to reduce challenges and be on the save side (in mass production)?

I think Mike Soldano has said it was by accident, he was going to try a different value resistor but happened to pick a 39K and it sounded good.
Mesa Boogie copied Soldano's circuit.

[WhopperPlate]

Does anybody know why they use 39k? Is there some calculation behind it?
Is the "high" value mainly to reduce challenges and be on the save side (in mass production)?

I think Mike Soldano has said it was by accident, he was going to try a different value resistor but happened to pick a 39K and it sounded good.
Mesa Boogie copied Soldano's circuit.

This is what I was referencing Martin : 39k, not the 10k. It’s pretty well known nowadays that the mesa dual rectifier is essentially a soldano circuit , although the sonic results are apparently different for various reasons.

[Lynxtrap]

The reason Marshall did it was probably that they could make a 2 channel amp using the same chassis and circuit board as the "plexi", with minimal changes to the circuit. The 10K made it possible to cascade the first two stages as a high gain channel.
I'm pretty certain it had been done before by techs and tinkerers.

[martin manning]

The Marshall JMP 2203 was 1976 https://el34world.com/charts/Schematics ... _2203u.pdf

...and the 2203 amp actually came out in 1975.

This is what I was referencing Martin : 39k, not the 10k.

Ok, so Soldano gets credit for the colder clipper ;^)

[Andy Le Blanc]

I appreciate the statement about local feed back, stability and a cold clipper. In some jcm 800 bass amps, a 10k biased stage is used very early in the pre for stability. De-generation is useful.

[Lynxtrap]

tried out some "cold clippers".
I found several on the last stage before the cathode follower (in front of the tone stack) in several famous amps.
So it is simply an unbypassed cathode resistor.

The Marshall JCM 800 has 10k, Cornford MK50HII 15k, Soldano SLO 100 and Meas Dual Rectifier both have 39K. (Who was first????)
Checked with my USB oscilloscope and it really works! Only clips on side of the signal.

Did you check the headroom of the 10K "clipper"? When does it actually start to clip?

[WhopperPlate]

The Marshall JMP 2203 was 1976 https://el34world.com/charts/Schematics ... _2203u.pdf

...and the 2203 amp actually came out in 1975.

This is what I was referencing Martin : 39k, not the 10k.

Ok, so Soldano gets credit for the colder clipper ;^)

Lol i guess I blacked out the first part of that question of “which came first?” … I thought it was asking which came first with 39k specifically …reading back obviously he meant them all…my bad

[JD0x0]

Does anybody know why they use 39k? Is there some calculation behind it?
Is the "high" value mainly to reduce challenges and be on the save side (in mass production)?

I think Mike Soldano has said it was by accident, he was going to try a different value resistor but happened to pick a 39K and it sounded good.
Mesa Boogie copied Soldano's circuit.

I can't remember if it was Mike Soldano or Dave Friedman who said this, but I heard that they were playing with values and kept going until the waveform was symmetrical and that's how they ended up with 39k.

[romberg]

I can't remember if it was Mike Soldano or Dave Friedman who said this, but I heard that they were playing with values and kept going until the waveform was symmetrical and that's how they ended up with 39k.

It was on Friedman's Tone Talk youtube channel. Dave asked specifically about the 39k and Mike said he intentionally picked that value in order to get symetric clipping. So, that was intentional.

I remember another interview where Mike talked about being tired and doing something unintentional to the curcuit and finding out later that the mistake sounded great. But he never said durring this interview exactly what that change was. Since he seemed pretty emphatic about the 38k durring the tone talk interview, I'm assuming the unintentional change was something different.

Mike

[Lynxtrap]

It was on Friedman's Tone Talk youtube channel. Dave asked specifically about the 39k and Mike said he intentionally picked that value in order to get symetric clipping. So, that was intentional.

I remember another interview where Mike talked about being tired and doing something unintentional to the curcuit and finding out later that the mistake sounded great. But he never said durring this interview exactly what that change was. Since he seemed pretty emphatic about the 38k durring the tone talk interview, I'm assuming the unintentional change was something different.

Mike

That's interesting! The myth about the 39K being an accident is widely spread, perhaps because it's the odd thing that sticks out in the circuit.

I'm glad you got through that episode "Tone Talk" would be really great if they could focus on amp stuff and cut an hour or so of small talk and other irrelevant chatting.