strange behavior adding tone to SHO

[ugly_guitar_guy]

Hey guys, I built a SHO clone ad decided it would be nice to have a tone circuit on it since it can be a little bright at times depending on the guitar I use it with. So I made this circuit from the tone schematic that I found over at Beavis Audio:



My quirky problem that I ran into is that only the last 20% of the SHO pot has any boost above the normal guitar level. I've built this exact same circuit before and had plenty of boost passed the 50% point of the pot so this seems strange to me. I tried putting the tone in front and back of the SHO and the tone sounds better in front but the boost just isn't there. Does this sound like it could be because of an interaction of the two circuits, or is it possible that my BS170 is being quirky?

Thanks!

**edit**

Ok, I did the obvious and wired up the new SHO circuit without the tone circuit, and BAM, full boost like the others I've made, so I'm guessing this tone circuit is just too constricting for the SHO, but if the tone is BEFORE the SHO circuit, then why would it make the boost so much quieter??

[phector2004]

What if you squeeze an SHO with a trimpot in front of the tonestack then feed that "not-as-boosted" signal into your original SHO?
Maybe even add a DPDT to switch out the first section altogether...

[ugly_guitar_guy]

Well, I'm trying to keep this squeezed in a 1590A and adding another SHO circuit doesn't help that plan much, but it's certainly an option I suppose.

[Suicufnoc]

A BMP style tonestack like that loses a lot of volume, so the volume loss is to be expected.  I'd add a trim pot or fixed resistor to adjust the minimum gain of the SHO.  Or use a less lossy tone control.  Have a look at the Stupidly Wonderful Tone Control.  http://www.muzique.com/lab/swtc.htm

[waltk]

Try the tone control after the SHO.

Edit: Nevermind.  Just read that you already tried it both ways.  I think the problem is that the tone control has a very low input impedance, and it's sucking tone from the guitar when you put it before the SHO.  It might also be what you like about it - as the tone sucking has the effect of reducing the highs.

[ugly_guitar_guy]

A BMP style tonestack like that loses a lot of volume, so the volume loss is to be expected.  I'd add a trim pot or fixed resistor to adjust the minimum gain of the SHO.  Or use a less lossy tone control.  Have a look at the Stupidly Wonderful Tone Control.  http://www.muzique.com/lab/swtc.htm

Ok, I'll give that tone control a shot and see what I get. Since I'd plan to run the SWTC2 into the SHO circuit, should I put in a trim pot to set a base level going into the SHO? I really don't have the space to add ANOTHER pot to the face of the 1590A.

[Suicufnoc]

Nah with the SWTC you shouldn't need to adjust the gain, it's not nearly as lossy as the BMP stack.  Do use the original SWTC on the top of though page, though, as the SWTC2 may get lossier, and you don't need treble boost anyways, just cut.

[ugly_guitar_guy]

Nah with the SWTC you shouldn't need to adjust the gain, it's not nearly as lossy as the BMP stack.  Do use the original SWTC on the top of though page, though, as the SWTC2 may get lossier, and you don't need treble boost anyways, just cut.

Well that's significantly more simple. I'll wire it up tonight and give it a shot. Thanks!