SWR Aural Enhancer Bypass

[duff2]

Does anyone here know how to modify an SWR bass amp in order to achieve a flat frequency response (ie turn the black curve into the yellow one on the graph below)?



Specifically, I'm interested in replacing the original aural enhancer knob with a pull pot on my SM-500 so that I can have access to either the original or flat preamp voicings. I'd also like to preserve the signal gain through the second half of the 12AX7 in 'bypass' mode.

Is this possible? If it is, where should the switch be positioned in order to to bypass the fender tonestack circuit circled in red?



Thanks,
Duff2

[J M Fahey]

Simplest is joining the output of the IC above the "threshold" label directly to pin 7 of the tube.
Your volume will jump 8/10dB when you bypass that lossy network..

[duff2]

Well, according to feedback I received on some other forums, trying to install a push-pull switch to accomplish this will not be easy. However, I did find out how to achieve a flat frequency response with all knobs in their 'flat' position. Apparently swapping the 220 nF and 1 nF capacitors in the red-boxed circuit below will turn the black preamp response curve into the yelllow one. It will also leave the aural enhancer in operation as an added gain/harmonic character control.

Anyone anticipate any unforeseen issues with this modification before I take my amp to a tech?

Thanks,
Duff2

[J M Fahey]

Try the mod I suggested, you don't need a tech for that one, just a soldering iron and a 4" piece of wire ... and when you close that switch the control *will* be flat and the knob will have no effect at all.
If you don't want the volume to rise, you'll need a dpst switch and an additional resistor.

[duff2]

Well, according to feedback I received on some other forums, trying to install a push-pull switch to accomplish this will not be easy. However, I did find out how to achieve a flat frequency response with all knobs in their 'flat' position. Apparently swapping the 220 nF and 1 nF capacitors in the red-boxed circuit below will turn the black preamp response curve into the yelllow one. It will also leave the aural enhancer in operation as an added gain/harmonic character control.

Anyone anticipate any unforeseen issues with this modification before I take my amp to a tech?

Thanks,
Duff2

Please disregard any suggestions I made regarding switching the 220 and 1 nF capacitors to achieve a flattened frequency response. The correct way to do this can be found here: SWR Aural Enhancer Bypass - TalkBass Forums

Sorry for any confusion my previous post may have caused.

Cheers,
Duff2

[J M Fahey]

Hi.
Please just post the suggested mod here.
Your link above refers to a 5 page discussion.
I got tired/bored after the 2º page.
Thanks.