Paul's raffle amp design

[Wombaticus]

I'm working on a fun project at the moment. This is the amp that I'm building as a fundraiser raffle project to benefit the Leukemia and Lymphoma Society that I mentioned in a thread in the Lobby here. So as not to overly abuse my posting privileges here, I'll stick to just the technical details in this forum area.

The current schematic is here

It's turned into an interesting mash-up, with a good measure of "smart sand" thrown into the mix. Main features/description are:

6V6 PP power section (20W more-or-less)
3x12AX7 preamp (input stages, OD stages, and mixer/cathodyne PI)
Three-band tone stack (James style B & T, with separate Framus-style mid)
Spring reverb (LM386 driver, LND150 initial recovery, tube-based virtual earth / local feedback mixer for wet/dry mix and additional reverb gain)
Tremolo (solid state LFO, driving a vactrol)
Two channels (Clean and Dumblestyle overdrive)
Footswitching (Tremolo, reverb, and OD)
Regulated DC heaters for the preamp tubes
Chokeless capacitor multiplier based screen filter

In some ways, this is kind of a simplified version of my D-inspired "Grail" amp, mashed up with (if you really squint sideways) something like an old Gibson scout..

Check out my latest blog post for layout and some build-log stuff.

I'm particularly interested to see how this approach to the tremolo works. .. you can see from the schematic that the solid state LFO of the trem is actually used to control the series resistance in a vactrol, which in turn is used to control the dry gain in the virtual earth mixer. I don't think I've ever seen that before -- but I've done some preliminary breadboarding experiments, and I'm pretty optimistic....

Cheers,

Paul

[tubeswell]

Looks interesting. I'd be keen to hear some soundbytes when its done

[Wombaticus]

Looks interesting. I'd be keen to hear some soundbytes when its done

Yes, I'll be working on that!

In the meantime, work on the main boards is now completed. I posted some build-log stuff already for the power tube board, but I've also completed the bias board and the regulated DC board. Now I just need to fab the two small PCBs for the relay/reverb driver and for the tremolo, and I'll be ready to start assembly. I got word from Ben Sykora, the builder donating the cherry wood cabinet, that it is ready and will be heading my way soon!

Don't forget guys, this is a raffle for charity. Even if you are already up-to-your-ears in amps, *please* consider making a donation to the Leukemia and Lymphoma Society through my fundraising page! If you live in the US, it's tax-deductible. While I've raised over $2200 so far, I should point out that the chances of winning are still excellent, as some of the donations are by folks who (foolishly) don't know or care about amps, while others are from amp people that made a donation but whose spouse would kill them if they brought another amp into the house!

Cheers,

Paul

[Wombaticus]

Looks interesting. I'd be keen to hear some soundbytes when its done

Tubeswell, this amp is finished and is getting sent off to the winner of the Raffle this Saturday. I need to post up a final version of the schematic, but in the meantime here are a couple of clips, including one that specifically demonstrates the slightly unusual trem circuit implementation:

Wombat amps Quest tremolo demo

Quest amp clean demo

I tried getting a decent sounding clip of the overdrive sounds, but my camera mic just wasn't up to the job, and they all came out sounding pretty rough. Perhaps the raffle winner will be able to properly record some more diverse clips.

[tubeswell]

Nice sounding amp! That trem sounds very nice