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So I've been looking over the Tri-watt schematic and I have a quick question.

For clean, I count 3 gain stages plus a cathode follower, not to mention a pretty gainy LTP phase inverter. Why did the original design of the Hi-Watt use so many gain stages to get what's basically a clean amp? Marshall JCM800 series amps have one fewer gain stage, but deliver crushing overdrive. Of course it has different plate resistors, cathode resistors, coupling and bypass caps, etc - but it makes sense when your trying to drive the bejesus out of the output. Why one extra gain stage just to get a huge clean?

I understand how you can get clean with so many gain stages - I'm trying to understand why Dave Reeves set it up this way.

Thanks!

This schematic is really interesting . . . it appears that it actually has 3 gain stages and not 4.

What's up with the second half of V3? Is that some sort of constant current source to keep the PI clean?

Zaphod will no doubt have further comments. The OD kicks in another gain stage too. I think the presence control is very interesting too. I believe that is a constant current source.

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Stephen
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Sorry, I missed this question somewhere along the way. I have to say that I agree that the Hiwatt amp design is pretty weird IMO. What needs to be born in mind is that most of the gain stages have their gain limited by either having no cathode bypass cap, or just a real small one. One of the gain stages appears to be a recovery stage after the tone stack. It's then DC-coupled via the cathode follower to the PI. Later Hiwatts didn't have the CF and instead used the spare triode as a voltage regulator which biased the PI. There's many a time I've wished Dave Reeves were still alive so I could ask him how come he designed his amps like that....

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Great tones come in small glass jars!

Small bypass cap just means different frequencies are passed through the cap. What did you mean by a small cap?

47nF is unusually small for a cathode bypass cap and just lets through frequencies at the higher end of the spectrum. Effectively, it acts as a treble peaking circuit. You can find these 47nF caps at various different preamp stages in different Hiwatt models. I would hazard a guess that Dave Reeves used to put them in at different points to voice an amp's high frequency response in conjunction with the Presence control. I would just love to have been able to meet that guy and ask him a few questions.....

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Great tones come in small glass jars!