Class-D 100W Poweramp with built-in tube emulation (Baja Reactor)

esist · Post by **esist** » 12 Mar 2022, 10:28

Hello,
since years I am using my own pre-amps which I box into either Eddystone 26908PSLA or Hammond 1590C enclosures. These I place on my pedal board, they run in the loops of my Line6 HX Effects. By that, all I need is a cable from my guitar to the pedal board, "4-wire method" around HW Effects on the board and finally one cable from my pedal board to the power amp. I had since years the idea to build a Class-D power amp to get rid of the heavy Fender Bassman I used for too long now as power amp.
When I read about the Bajaman Reactor I thought I would give it a try to combine that into a small enclosure with a generic Class-D amplifier. I used the PCB layout from http://effectslayouts.blogspot.com/2019 ... actor.html
Here it is. It can be fed with 9V-24V DC. At loud home levels the pedal takes less than 100mA @ 24V and up to 150mA @ 12V. Hard to say exactly as the current follows the playing dynamics.
Doesn't sound to bad, still there is some room for improvement when it comes to that tube power-amp sparkle-warmth-whatever... Maybe a more complex saturation circuit could help ,as I only placed a 1k Pot in series with the two 1N4148 diodes ??

This post is firstly meant to give impressions on my idea and work. I want to thank all these highly skilled people that share their work with the community. Here I want to thank Bajaman and http://effectslayouts.blogspot.com/.
If anyone has a workable suggestion (something less than 6 op amps...??) to improve the feel of the amp I'd be thankful.

Greetings,
esist

MikeHartigan · Post by **MikeHartigan** » 22 Mar 2022, 13:46

I've been playing around with this exact idea for a while now. In fact, I built Bajaman's Reactor for this purpose but I didn't get it to work quite right. It wound up finding a home in my collection of "almost working" circuits! After seeing your build I'm going to dig it out and try again. Thanks for the inspiration!!

esist · Post by **esist** » 22 Mar 2022, 17:14

What is your problem ? I had issues with my first build on vero with oscillations I think. My second try on PCB works very well. Still, if I lift too much the diodes at the end of the signal path, it gets noisy or even creates interruptions in tone.
I am playing around with different diodes and caps and pots in series with the diodes to tweak the saturation. I found russian germanium D310s with a few Ks of resistance in series best so far.

Btw., in the meantime I got used to it's tone and tweaking and I have to say it sounds very good. Not exactly like my tube power amps, but in it's own way very nice. Better string separation and fat at the same time. I am still searching for the last percents on highs without getting cutting tones.

Frank_NH · Post by **Frank_NH** » 22 Mar 2022, 23:23

About a year ago I did some experiments with the power amp input to my Roland BC-60 (60W, 1X12 speaker). I set it up as follows: Klon-style pedal as a preamp --> Baja LA2A Limiter --> Baja Reactor --> Roland BC-60 Power Amp. I was astonished how good the Baja Reactor improved the tone. Without it, the tone from the dry power amp was very blah. With the Reactor, the sound improved immensely, with the ~100 Hz "bump" warming up the low end and the increased trebles adding some sparkle. BTW, the LA2A Limiter was fantastic too - I could get a very controllable and rich sustain from the overdriven preamp. I still have both circuits on my breadboard and plan to work on the concept a bit more. Should note that the Klon makes a good preamp as it can produce a healthy line level output with some good, crunchy distortion.

MikeHartigan · Post by **MikeHartigan** » 29 Mar 2022, 13:06

esist wrote: ↑22 Mar 2022, 17:14 What is your problem ? I had issues with my first build on vero with oscillations I think. My second try on PCB works very well. Still, if I lift too much the diodes at the end of the signal path, it gets noisy or even creates interruptions in tone.
I am playing around with different diodes and caps and pots in series with the diodes to tweak the saturation. I found russian germanium D310s with a few Ks of resistance in series best so far.

Btw., in the meantime I got used to it's tone and tweaking and I have to say it sounds very good. Not exactly like my tube power amps, but in it's own way very nice. Better string separation and fat at the same time. I am still searching for the last percents on highs without getting cutting tones.

Well, until a couple years ago, I hadn't picked up a soldering iron or looked at a schematic for many, many (10+) years. So long in fact that I had to use google to refresh my memory on some basic electronics equations. (I even treated myself to a new Weller soldering station. I was definitely a little rusty with the soldering iron too! LOL).. The Reactor was one of the boards that I built during that time. I've recently gotten around to troubleshooting some of those early builds. It's a good feeling to pick one up and almost immediately notice some type of "rookie" mistake that I made!

That being said.... From what I recall, I had similar problems with the Reactor. (oscillations and even signal cut out at a certain point). I have the board sitting on my work station and will be checking it out when I get home later today. If it's anything like some of the other boards I had trouble with, I'm expecting to find a part in the wrong hole, or a cut that I missed, etc.

Another mistake I was making was assuming it was ok to save money on cheap components. It's amazing to do a side by side comparison between things like the super cheap transistors from amazon and the actual name brands from a supply house. (Mouser for example)..

So again, seeing your nice looking build has inspired me to get it up and running. I even have a couple old small practice amp chassis to put it in. I'll post some pics once I put it together.