Stripped Down BSIAB As A Preamp For Class D amp

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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.

[amz-fx]

From 1999, the predecessor to the BSIAB:



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

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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.

[amz-fx]

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

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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.