Drive Channels: why two gain knobs?

AntonHunter

I've also never seen this on an amp (mostly playing clean Fender types anyway) but the more I read this thread, the more useful it sounds! Having a gain pre and post tone stack sounds really useful. 

ecc83

AntonHunter said:

I've also never seen this on an amp (mostly playing clean Fender types anyway) but the more I read this thread, the more useful it sounds! Having a gain pre and post tone stack sounds really useful. 

You might like to read Merlin Blencowe's book on valve pre amps? There is SOME maths but you don't really need it and in any case it is mostly Ohm's Law which is really just Time Distance Speed.He shows many variations of circuits that give varieties of distortions, many of which have never been explored by the main amp makers AFAIK. They are a (small c) conservative lot!

Boost then EQ a bit gives a different result from EQ then boost. Take that through a number of stages and vary the EQ frequencies and you get a very versatile tonal palette..

Dave.

AntonHunter

Ah nice. Will investigate. I'm not afraid of a bit of maths...

Neilybob

My ole Peavey Classic has a Post and Pre knobs for the lead channel. I think the Pre works as an master volume sort of and the Post is all out gain.  Really hard to photograph a mirrored back plate. 

steamabacus

Back in the 80s, a mate of mine had the little Squier 15 practice amp which has this Volume-Gain-Master setup.

I'm not sure of how this functions in the solid state circuit. My vague memories of it (and neither of us was very experienced at the time) was that balancing the volume and gain vaguely affected the tonality of the bee-in-a-jamjar fizz (of which there was oodles!)

ICBM

Neilybob said:

My ole Peavey Classic has a Post and Pre knobs for the lead channel. I think the Pre works as an master volume sort of and the Post is all out gain.

Pre is simply Peavey's term for 'gain' and Post for 'volume' (channel), although some other makers call this Master, if there isn't an overall master, just to confuse things further.

Ddigger

exocet said:

Ddigger said:

exocet said:

There's a lot of signal gain available when you cascade 4 ECC83 triodes together.

TBH, I don't know much about amps.

When you say 4 triodes, does that mean two ECC,83 valves and you are using both sides of each valve?

Yes. A single ECC83 / 12AX7 contains two triodes (2 gain stages).

Thanks Exocet.

HerbieTheRadDorklift

My Boogie Mark IV had this.

See pages 5 & 6 in the manual https://mesa-boogie.imgix.net/media/User Manuals/Mark 4.pdf

PS, reading that manual reminded me why the Boogie Mark IV is the greatest amp ever.

p90fool

I used a Burman in the early 80s which I'm pretty sure had three gain knobs on one channel. 

It sounded like arse whatever i did with them, but that might have been user error given that I almost exclusively played 4-hole Marshalls at the time. 

ICBM

p90fool said:

I used a Burman in the early 80s which I'm pretty sure had three gain knobs on one channel. 

It sounded like arse whatever i did with them

It did. They did. I couldn't get anything usable out of the overdrive channel either. The clean channel was OK.

They weigh as much as a medium-sized galaxy as well...

hywelg

On a Dumble the OD stage consists of two gain stages. So there is a volume pot at the entry to the first gain stage, another pot after it and another pot after the second gain stage. One of those pots is usually inside the amp on the circuit board but some makers moved it out onto the panel. I moved it to the rear panel on my OTS. 

Some have another pot in the fx loop recovery stage (CarolAnn OD3) but that is global and not exclusively and OD gain control

Wazmeister

Jay, your Redplate excels in this area, and is unusual...

The Gain when set to zero, can bypass the gain staging that is occurring. 

Together, gain and drive, are VERY interactive on the Redplate - which is why they 'bloom' so much imho.

I'd love to own another one.

Kittyfrisk

ICBM said:

p90fool said:

I used a Burman in the early 80s which I'm pretty sure had three gain knobs on one channel. 

It sounded like arse whatever i did with them

It did. They did. I couldn't get anything usable out of the overdrive channel either. The clean channel was OK.

They weigh as much as a medium-sized galaxy as well...

Close to killing the joke...