Tone issue

eightsevenzero · October 03, 2024, 07:31:37 PM

I feel like I'm going crazy. I redrew this schematic in Eagle and had a test board produced. I hand tested every component and triple checked everything was correct. Circuit technically works just fine but the tone is way off, has weird notch to it and the bass frequencies are not pronounced like the original. The knob sweeps from bass to treble but it sounds nothing like the original pedal (which I have), sort of if you turned the presence knob of an amp past zero into the negative. Apart from a few electros with polarities flipped and the order of the cap/clipping diode combos being flipped, both which shouldn't matter too much, everything is the same. Any ideas or see anything I missed on my schem work? apologies for the messy layout, I should have spent more time on it.

GibsonGM · October 03, 2024, 08:14:58 PM

Could be many things, sorry! But one thing I would do is audio probe it - see which circuit blocks are ok, and where the issue starts. That may narrow things down for you!

eightsevenzero · October 03, 2024, 08:22:06 PM

Thanks! I thought about that too, I suspect up to q3 will be ok but who knows!

GibsonGM · October 04, 2024, 06:16:25 AM

Give it a try. If it IS ok up to Q3, then you will have an idea where to look. If the schematic is verified, it's almost always that we have a part in the wrong place, a wrong value (or 2), a solder bridge or something, and it may take looking at it 100 times until you find it. If you post a pic of your build, front and back and of good quality, we can take a look to see if anything jumps out at us!

antonis · October 04, 2024, 06:39:16 AM

Lower end of R24 on your schematic isn't connected..

(R27, C14 & R24 are out of both Q3 output and Q4 feedback loop, dramatically altering TONE control responce..)

fryingpan · October 04, 2024, 07:54:52 AM

Quote from: antonis on October 04, 2024, 06:39:16 AMLower end of R24 on your schematic isn't connected..
(R27, C14 & R24 are out of both Q3 output and Q4 feedback loop, dramatically altering TONE control responce..)

That's the way it looks like in the original "mod" (it's a reworked time section). It does look like a 1:1 copy.

duck_arse · October 04, 2024, 11:57:20 AM

measure your Q2 collector voltage. measure your Q3 base voltage. now reverse your C7 and have that argument with Kitrae.

anytime I see those junction dots and angled lines on an Eagle schem, I get the heebie geebies. did you run the error checkings?

eightsevenzero · October 04, 2024, 03:34:53 PM

All voltages are almost exact to the original pedal, within .03 v in all cases. Error checked both schem

fryingpan · October 05, 2024, 04:30:04 AM

Quote from: eightsevenzero on October 04, 2024, 03:34:53 PMAll voltages are almost exact to the original pedal, within .03 v in all cases. Error checked both schem

Have a look at the passive tone section. Maybe you used some wrong cap or resistor somewhere. This wouldn't alter transistor biasing.

duck_arse · October 05, 2024, 10:44:18 AM

Quote from: eightsevenzero on October 04, 2024, 03:34:53 PMAll voltages are almost exact to the original pedal, within .03 v in all cases. Error checked both schem

alright, get the original pedal, measure the Q2 collector voltage. then measure the Q3 base voltage. which of those two voltages is higher, more positive?

https://postlmg.cc/CzQ97ZG7

there is an image linked here, it's not loading for me at the moment, but it shows these two voltages .

News:

Tone issue