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The "S" is critical because it specifies the expanded voltage and oscillator frequency range. The "CPA" means 8-pin DIP with 0 to +70°C operating range.

Brian, I mentioned this in a tech help thread on the Quasar (RC Booster), but if you could find a way to insert the filter comprised of the 10k resistor and 0.1uF cap before the Bax stack, you could offer this board as either an RC or AC Booster. Here's a link to the site showing the schematic for the AC Booster:

http://revolutiondeux.blogspot.com/2008/06/xotic-rcac-booster-overdrive.html

Best regards,

Scott

Looks like you could get pretty close by changing R5 to 10k, the gain pot to 500k, and jumpering D3, D4, and D5. There's an additional filter on the AC booster that would be hard to finagle on Brian's board. You'd have to cut the trace off of pin 1 and wedge a 10k and 0.1uF before C6. Actually, Brian might want to add those two components to his layout, then it could be used for either the AC or RC booster.

Here's a site showing the schematic for the AC booster with instructions for converting it to an RC booster. It shouldn't be too hard to compare to Brian's Quasar.

http://revolutiondeux.blogspot.com/2008/06/xotic-rcac-booster-overdrive.html

This 1N4739A zener from smallbear is 9.1v

I've never used one before though so it' just a guess on my part.  Anyone else know?

That part should work fine.

You definitely should use a linear pot instead of a log pot to spread out the treble control adjustment range more evenly.

To increase the gain a bit, you could try lowering R3 to 820r or even 680r, but don't go any lower, and note that the frequency rolloff character will change slightly with the voice control maxed out.

Pin 3 of IC1 looks low. It should be closer to 4.73 like pins 1 & 2. Pin 7 on both IC1 and IC2 looks high. They also should both be closer to 4.73 like pins 5 & 6.

The BOR does have a lot of bass, but it should have plenty of sizzle on tap too. A 100kA versus 100kB tone pot won't change the frequency curve, but it will shove all the adjustment toward the top 10% of the travel. If you can't get enough treble even with the tone pot dimed, double-check the values of all the components from C5 through to the output volume pot. You can remove C8 or C9 or both to increase the treble response.

Those substitutions should be fine and shouldn't be causing the symptoms of the problem you describe. Sorry to say, I think the cause lies elsewhere. Check the usual suspects, cold solder joints, solder bridges, active devices orientation, diodes and electro caps orientation, correct component values, etc. Are you using the board mounted pots, or do you have flying leads to your pots?

Get rid of the jfet switching and some of the buffers, convert it to true bypass, and this would make a nice project.