In another forum we were debating a battery powered Princeton type of amp and I thought SS would be a little more practical, not that practicality kept me from doing oddball things. I ran with it because I had a few Class D modules (TPA3118) and I wanted to try them out. I also have not played with Mu-amps so I thought I might try the two together. I had the tone stack in between the two stages but I felt I needed to clip the signal peaks going to the amplifier. I don't have too much time to play with this project so I just moved the tone stack after the second stage and used the second stage to clip the signal. It turned out not too bad. I decreased the coupling capacitor and added one in with a switch to bring back some bass. I had 0.1 uF originally but it muddied things up too much. I am sure I can play around with values to make this better but that is not a top priority for me at the moment. I want to add reverb yet, tremolo would be cool also.
The amp does a good job of giving the 8" speaker its money's worth running on 12V. The supply is a laptop type brick rated for 2.5A With meter on it the voltage is rock solid. I'll throw the parts on a perf board and leave some room for modifications but I think it is usable. I found I really did not care for the level of interaction from the Fender tone stack. I could dial things in but I found it a little annoying whereas I haven't as much on other projects before this one. We'll see how I feel about it after a while. As you can see I just grabbed one bag of caps and resistors, seemed to work so there you go.
(https://i.imgur.com/1E0rRc4.png?1)
From 1999, the predecessor to the BSIAB:
(https://www.diystompboxes.com/pedals/booster25.JPG)
Higher voltage power supply, 18v to 30v, will reduce the tendency to heavily distort, as will increasing the source resistors mentioned on the schematic.
Best regards, Jack
Knew about the booster, just seemed like there is much more recognition of the circuit by the BISAB and maybe somebody else will think of trying it as just a basic preamp. I was planning on going 19V for the supply but I was running 12V into my test speaker, an old 8" in a Fender Champ 600 sized cabinet and I realized how nice the speaker sounded but I doubt it can take more power. The Champ cabinet is just big enough to put a short reverb tank in it. I was going to use another TPA3118 board to feed the tank since it is a high impedance input. Just juggling projects for now, just finished gluing up four neck blanks to check out a neck carving setup.
Fred,
I'm not sure about the input headroom of the TPA3118 board, but you should make sure that it is not getting too much drive since most class D amps do not make a smooth distortion sound. If the booster/preamp is putting out too much signal, insert a resistor in series between the tone and volume controls. A 100k would be a good place to start.
If the spring tank won't fit, try the FV-1 digital delay since the internal reverb is not too bad. The experimentalnoize.com site has some modules that will do the job. :)
Best regards, Jack
I have been limiting the voltage with the second volume control while testing. I do want to do something a little more user friendly. I searched for preamps to drive a Class D amp to see what others have done and I found relatively few projects which I found odd considering how potent these little modules are. That is the reason I jumped in, I need another project like a hole in my head. I do have a FV-1 chip and originally planed on mating it with a Class D amp but not this one. The tank fits nicely in the bottom of the cabinet, part of the reason I want to do it.
Great! I just had another idea. What if I use the cab to do a tube Champ with reverb tank, I haven't seen one built in this small a cabinet. I may have to make another cabinet, I do have two tanks.