Nate Dort wrote: Mon May 01, 2023 12:57 pm Dismissing all Class D amps because one sounded bad is just like dismissing all tube amps for the same reason. There are some dogshit tube amps out there, just like there are dogshit Class D amps.

A lot of our favorite old solid state designs are anything but flat, even in the power amp section. I think what a lot of these class D amp-in-a-pedal designs get wrong is that they're basing their power-stage voicing on Infineon or Texas Instruments application notes that are shooting for the lowest distortion and flattest bandwidth. Lots of negative feedback and low-distortion components, like a HiFi system. That's not necessarily what you want in a guitar amp.

I've played some class D bass amps that sound great. I'm more talking about the cheap pedal ones like Mooer and EHX.

Nate Dort wrote: Mon May 01, 2023 12:57 pm A lot of our favorite old solid state designs are anything but flat, even in the power amp section. I think what a lot of these class D amp-in-a-pedal designs get wrong is that they're basing their power-stage voicing on Infineon or Texas Instruments application notes that are shooting for the lowest distortion and flattest bandwidth. Lots of negative feedback and low-distortion components, like a HiFi system. That's not necessarily what you want in a guitar amp.

To circle back: what kind of qualities could get a Class D amp more in the ballpark of, let's just stick to a PRF favorite, a Traynor SS power amp?

Krev wrote: Mon May 01, 2023 1:07 pm

Nate Dort wrote: Mon May 01, 2023 12:57 pm Dismissing all Class D amps because one sounded bad is just like dismissing all tube amps for the same reason. There are some dogshit tube amps out there, just like there are dogshit Class D amps.

A lot of our favorite old solid state designs are anything but flat, even in the power amp section. I think what a lot of these class D amp-in-a-pedal designs get wrong is that they're basing their power-stage voicing on Infineon or Texas Instruments application notes that are shooting for the lowest distortion and flattest bandwidth. Lots of negative feedback and low-distortion components, like a HiFi system. That's not necessarily what you want in a guitar amp.

I've played some class D bass amps that sound great. I'm more talking about the cheap pedal ones like Mooer and EHX.

I mean you said "cheap." The cost savings have to come from somewhere. Don't get me wrong, there's some pretty decent Mooer and EHX stuff (at least out of the box) but still I wouldn't order a Yugo and expect to get a Cadillac.

penningtron wrote: Mon May 01, 2023 1:31 pm

Nate Dort wrote: Mon May 01, 2023 12:57 pm A lot of our favorite old solid state designs are anything but flat, even in the power amp section. I think what a lot of these class D amp-in-a-pedal designs get wrong is that they're basing their power-stage voicing on Infineon or Texas Instruments application notes that are shooting for the lowest distortion and flattest bandwidth. Lots of negative feedback and low-distortion components, like a HiFi system. That's not necessarily what you want in a guitar amp.

To circle back: what kind of qualities could get a Class D amp more in the ballpark of, let's just stick to a PRF favorite, a Traynor SS power amp?

You could mimic the frequency response pretty easily on the front-end. Maybe put a discrete BJT input section (LTP / current mirror) before it hits the Class D stage.
Build a discrete Class D stage rather than using an off-the-shelf IC and control the amount of negative feedback. Use a discrete error amplifier rather than an opamp.
Throw a bunch of ceramic caps and carbon resistors in there also. Modern film caps and metal film resistors are pretty sterile sounding.

I don't know, when I think standalone power amp, I don't necessarily think about guitar. I'm more thinking about bass applications. That's not to say that the power stage of a Traynor TS-series amp doesn't have "a sound," but like 80% of the sound of a TS-50 is the preamp section. People aren't clamoring for a really colored SS power amp to run their Rusty Box through, you can put it through a modern 300 W Crown with a frequency response of 10 Hz - 30 kHz +/- 0.5 dB and it'll sound great.

Nate Dort wrote: Mon May 01, 2023 7:48 pm

penningtron wrote: Mon May 01, 2023 1:31 pm To circle back: what kind of qualities could get a Class D amp more in the ballpark of, let's just stick to a PRF favorite, a Traynor SS power amp?

You could mimic the frequency response pretty easily on the front-end. Maybe put a discrete BJT input section (LTP / current mirror) before it hits the Class D stage.
Build a discrete Class D stage rather than using an off-the-shelf IC and control the amount of negative feedback. Use a discrete error amplifier rather than an opamp.
Throw a bunch of ceramic caps and carbon resistors in there also. Modern film caps and metal film resistors are pretty sterile sounding.

Awesome info, thanks! I'm sure this is super niche and not at all marketable, but it's cool to know it might be doable.

I don't know, when I think standalone power amp, I don't necessarily think about guitar. I'm more thinking about bass applications. That's not to say that the power stage of a Traynor TS-series amp doesn't have "a sound," but like 80% of the sound of a TS-50 is the preamp section. People aren't clamoring for a really colored SS power amp to run their Rusty Box through, you can put it through a modern 300 W Crown with a frequency response of 10 Hz - 30 kHz +/- 0.5 dB and it'll sound great.

True for the most. I do think headroom, reliability, rack mountability shape those bass rigs just as much as sound quality, and fair enough as those are all important for playing out. I really liked the Traynor power amps I played guitar through for a while (with a Boxidizer, and other guitar pedals) that, even compared to a GK power section, seemed less stiff and brittle? I only quit using them live because the red light was going off a lot and made me nervous.

Some of that "sterile" sound in modern power amps also comes from having very stiff power rails. Lots of bulk capacitance to ride through hard bass hits.

Old SS power amps, especially guitar amps, generally didn't have that much capacitance. Caps were bigger and more expensive back then. So you get more rail sag at high volumes, which causes more non-linear distortion.

I have an ancient Ampeg V6B that actually breaks up like a tube amp when cranked. It also weighs 50 lbs.

I'm back on my weird shit again. After the Kurt Ballou rig rundown (and my dual amp thread), I'm ready to try my own stash here. I need a loud, reliable, stereo power amp solution. Also, I don't want anything too deep, which is a shame because old SS rack power amps are essentially free, but always deep. Nothing that uses a line lump power supply either.

I love what Kurt is doing with two small Quilters, but that's also pretty annoying; two amps, two power cables, etc. If I do go this route, I'd just build it into an old ammo case or something. Annoyingly, I have access to two Quilter amps, but one is a regular size head and the other is a 1x8" combo.

I own a Peavey CS200x 1U power amp. It's great, for moderate volume. As soon as I try to get over a rock drummer it will go into thermal shutdown.

I own a 20 year old QSC power amp that I bought NEW for bass in Replicator. It would be great, but heavy, deep, overkill, and loud fan.

I thought I might be able to get away with a GK800RB, but it lacks separate inputs for the power amps.

I considered stripping ice power modules from gear in the E-Waste bin at work, but once I put in a power supply and two power amps into an enclosure It will be just as big as other stuff that I already own.

There are two bandits on LA CL right now for a grand total of less than $200. I'm so tempted.

Crazy power amp ideas. no deeper than the average guitar cabinet, please.

Rocktron Velocity 300

2 x 150 W @ 4 ohms stereo, 300 W @ 8 ohms bridged mono.
1U
9.5" deep
18 lbs

I had one for a minute that I bought broken and fixed, probably should have kept it. Sounded pretty good. Has some sort of switchable reactance circuit in there to mimic a tube amp + speaker cabinet response.

There's a guy on my local CL selling a few for $200 each + shipping, which is a steal. I should grab one from him.

Nate Dort wrote: Mon Jul 24, 2023 7:22 pm

Rocktron Velocity 300

2 x 150 W @ 4 ohms stereo, 300 W @ 8 ohms bridged mono.
1U
9.5" deep
18 lbs

I had one for a minute that I bought broken and fixed, probably should have kept it. Sounded pretty good. Has some sort of switchable reactance circuit in there to mimic a tube amp + speaker cabinet response.

There's a guy on my local CL selling a few for $200 each + shipping, which is a steal. I should grab one from him.

Well hello there...