Convert Solid State Amp to Stompbox (Brian May Content)

[electricb]

Hi everyone,

I recently picked up a Vox VBM1 (Brian May recording amp) that had been damaged and went looking for the schematic to try and fix it. The PCB had really been mangled and had some lifted traces, so it has fallen to the backburner. However, after looking at the schem, I wonder if I can't convert it into a pedal by omitting the amplifier section at the end. I had a couple questions that I was hoping some stompbox gurus could help with.

The amp has 4 major sections. A standard Brian May treble booster using the common values from the well-known schematic, a "Deacy section" that is the similar to Brian's Deacy amp using PNP silicon transistors. The transformers are simulated using opamps. Finally, there is a tone control followed by an output section with a direct record out and a standard out that is fed to the fourth section, an amplifier stage driven by an LM1875. I am going to omit this last stage and just feed the volume pot to a standard output jack.

1. The amp has a transformer that feeds the treble booster section with +9V, feeds the "Deacy" section with -9V and the opamps are biased at +-15V. I thought I would simplify by changing the transistors in the Deacy section to their NPN equivalent (KTC3198) and use the +9V supply here. I would then bias the opamps with +-18V fed from an LT1054. If you turn around all the polarized components (e.g., C8, C12, D1, etc.) in the Deacy section, would this be suitable?

2. The schematic is difficult to follow because you can't really tell where the junctions are. This is not always a problem, but there are some sections where this is confusing. For example do R24 and R25 connect? I don't think they should, but I suppose it's possible. R27 looks like it should connect with R28 and C21, but NOT R32, however these are depicted in the same way. I'm not that knowledgable about circuit design so can anyone shed light on this?

3. Is there anything special that needs to be done other than the above to make this suitable for use in a stompbox? Assuming everything is biased properly, it should sound the same as amp and maybe even better if you're not using the crappy speaker that it comes with?

Thanks for your help. Once I nail this down, I will do a double sided layout for a 1590BB and post it once I verify it.