Fender Super 60 - Distortion Channel Volume Linearity Mod

[swhiteh3]

I recently picked up a Fender Super 60 and noticed that the distortion channel is rather un-friendly at bedroom levels (much like my Boogie DC-5). It goes from barely on to rather loud with just a slight breeze on the knob. I'd like to make the volume increase more linear and controllable in the lower regions without affecting the overall output of the amp at the higher levels.

I'd like to replace or mod the volume pot (Dist Volume, R16 on the schematic below) with one that is a little less sensitive at the bottom end of the range, and was wondering if anyone could recommend a pot value and slope, and hopefully a high-quality source. R16 on the schematic suggests a 1Mohm, and I assume I need to keep the total value the same but with a different slope? (I have a mechanical engineering degree and I work on racecars for a living, and do lots of electrical work, so although I know NOTHING about amplifiers or amp schematics, I'm capable of doing electrical work, soldering, etc...)

Enzo suggested a linear pot (what would in there now?) and mentioned that I need to make sure to find a CW (clockwise) pot. Would this be more friendly than whatever is in it now? Can anyone recommend a specific pot manufacturer and source?

[Rather than attaching the same schematic that's already located on the server, it's located in this thread for your convenience.]

[Chuck H]

I know nothing about the circuit of that amp (apart from the schem you posted). That is, I don't know if it uses 16mm PC mount pots or the larger chassis mount solder lug pots. I'll guess 16mm PC mount.

Fortunately for you the schem notes the taper as "30A" this is a 30% adjustment value when the control is set to five (assuming Fender is following proper notation practice). OP3 acts as a parallel VR but since I don't know the resistance or nature of this device I can't comment on adjustments there. You could look for a 1M A10 pot (whatever size and mount that pot is) to replace the exsiting "dist vol" pot. The "A10" designation would mean the pot is at 10% of it's adjustment with the control set to five. That should fine up the lower level adjustments.

Unfortunately most MFG's only list their log tapers as "audio" without the "Axx" designation. so this may require some emails on your part to find the right part. I do know that Bournes is one of the few MFG's out there that still makes A10 pots (in the 3/4" larger size). So they might be a place to look.

Bottom line is that your looking for a slower taper on the master vol pot, which will mean a slower adjustment at the bottom end of it's range.

Chuck

[pdf64]

A 10% audio taper is much more common and is the modern default type.
However, finding something that fits nicely may be a problem.
As an interim solution, make up a short attenuating patch lead for the effect loop. Say 10k / 1 k potential divider, so that there's a 10k resistor in series with the signal from the pre-amp out, then a 1k resistor across the power amp in.
The resistors can be tiny 1/8 watt types, mounted in the jack plug. A short bit of basic screened cable and you're done.
Mark up which plug goes into which socket, as you'll get hardly any attenuation the wrong way around.

[JoeM]

That's a common complaint with Fender's Hot Rod Series too. Volume comes up very quickly. pdf64's solution will work well. I built a little box with a pot and 2 jacks that does something similar (I dont even have the amp I made it for!), that plugs in the pre-out and power amp in jack to give some more fine control. I havent looked in a while, but there used to be some like this on e-bay.

[added]

something like this (no affilation with this seller)

http://cgi.ebay.com/Volume-Box-Carls...item4aa2e61edb

[swhiteh3]

I like the idea of an attenuating patch lead. I might just make up two because my Boogie DC-5 has the same issue.

Being a mechanical engineer (and definitely NOT an electrical engineer) can anyone give me a diagram of how to wire this device. Building it is not a problem, but I'd certainly need help spec'ing the parts and wiring it up. Thanks!