how can i add a mids control to a tube screamer circuit?

[snow123]

i think i kinda fixed the tone control by adjusting some values in the mids control and tone control

tone control (with mids at .9):



mids control (with tone at .5):


ive noticed that R1 at 5k6 (instead of 5k1) and C1 at 39n (instead of 47n) works a bit better.

ok, i just did what i did in ltspice (only difference is that i swapped the 5k1 for a 5k6, added the 39nf, and left the 27k as is and didnt replace it with a 22k), and now the tone control isnt causing or boosting any of the distortion, and the mids control and volume control is only adding distortion at around 80%-100%. so its better now

[snow123]

and when the mids control is maxed, its actually right around where the mids are in a stock tube screamer circuit(around -2db), so theres that.




edit: it turns out if i add the output buffer to the stock tube screamer it lowers the mid peak to about -5db, but if i remove the output buffer to the modified one (the one we're talking about rn) it does nothing, so yea.

[snow123]

also, 9v and 4v5 arent shorting to ground at all, and there arent any shorts on the board itself.

[snow123]

sry about the constant emotional rollercoasters where im like "uhhh i have this weird issue" to "ok i think i fixed it!" to (sometimes) "oh wait that didnt fix it and i have a new issue"

[snow123]

tbh, increasing r1 doesnt seem to be doing a whole lot, and it also looks to be messing up the tone control. and if i increase r1 to the point of it actually removing the distorton, its probably just gonna make the mids control only remove mids and make it not boost at all.

[GibsonGM]

You need to tweak the R1 network...if you double R1, halve C1, and you should get the same performance frequency-wise.

Then listen to the output of the 1st opamp with an audio probe, be sure it isn't clipping. That is now your 'source'.

Then listen to the output of the next active stage, and adjust THAT one to be sure it isn't clipping no matter what tone setting, and so on.

If you do this, there is no way a previous stage can distort the next one once you're done. Finish one stage and move on.

If necessary, re-build the mids section on BB and work on it with no other components involved, get it to where you like it, then adjust the one you've built accordingly.

[iainpunk]

what are the DC voltages you have on the opamp pins right now?

if you are really bothered by this distortion, have you considered running it at a higher voltage, like 12, 16 or 18 volt? a good source for higher voltages is a Laptop charger.

cheers

[snow123]

what are the DC voltages you have on the opamp pins right now?

if you are really bothered by this distortion, have you considered running it at a higher voltage, like 12, 16 or 18 volt? a good source for higher voltages is a Laptop charger.

cheers

i tried using 18v and that didnt do anything.

[snow123]

i just redid everything on breadboard with pcb mount pots so i can actually work on the circuit without worrying about bad solder joints or anything, and so i can freely swap parts out

[snow123]

and i just replaced r1 with a 50k pot on the breadboard, and increasing the value of r1 isnt doing anything other than darken the signal which does help remove the distortion, but its only doing that 'cause its taking away high end.

edit: no, it turns out i had the jumper thats supposed to connect tone 3 to the negative of ic1.2, connected to the output of ic1.2. so increasing r1 does help, but it doesnt really remove the distortion.

[snow123]

and i swapped the 5k6/39n for a 1k/220n and it sounds very similar. so i guess increasing r1/decreasing c1 doesnt do a whole lot

[snow123]

ive tried reducing C2 to 47n and reducing r3 to 100r (both help keep the mids under 0db) and theres still some distortion.

[snow123]

but now the distortion is less high end-y and more like farty low end distortion.

[GibsonGM]

Are we sure that a lot of this 'distortion' isn't what we get from the clipping stage, and messing w/the tone shaping making it more prominent? 
WHERE you are hearing the distortion is the key. 

Sound at the output isn't giving much info..."Right at R1 is has a lot of low end and is distorted; it's not like that before R1" is much more valuable than what you hear on the output...to help we have to know where it is happening, specifically, every time.

BTW, R1 with R2 sets the 'volume level' of the signal hitting your tone controls - I'd say that's 'doing a lot' lol.    C1 adjusts how much high end gets thru that network to the tone controls.   If they're adjusted equally (2x R1, 1/2 C1) then ideally nothing changes except signal level, loading and resistor noise.

[FiveseveN]

WHERE you are hearing the distortion is the key.

Absolutely! I was going to put forward the possibility that whatever is following the effect might be the source of distortion. Easy to check with the volume knob.

Otherwise I'm sticking to my previous recommendation: 20 minutes of learning about proper gain staging could have saved you the last month of troubleshooting.

[Vivek]

Otherwise I'm sticking to my previous recommendation: 20 minutes of learning about proper gain staging could have saved you the last month of troubleshooting.

While it is possible that bad gain staging has lead to the creation of the most iconic distortion pedals that we know !!

[iainpunk]

hey, maybe its like how the ''HIGH'' control on the HM-2 makes the pedal sound more distorted without it actually clipping more?

ow, snow, can you post a full schematic of the current circuit you have please?

am i understanding correctly that you are only cutting mids? if so, have you considered a bridge T filter? its easy, it can scoop the mids or leave them alone with a single potentiometer. there are also some more interesting filters based on a bridge T filter.


cheers

[snow123]

hey, maybe its like how the ''HIGH'' control on the HM-2 makes the pedal sound more distorted without it actually clipping more?

ow, snow, can you post a full schematic of the current circuit you have please?

[snow123]

Are we sure that a lot of this 'distortion' isn't what we get from the clipping stage, and messing w/the tone shaping making it more prominent? 

well before, the tone control was basically making the distortion more prominent (or the tone control was just boosting the mids by alot), but now it just sounds like the mids control is just pushing something too hard, and it sounds bad. before it sounded somewhat similar to a boss ds-1 type of distortion, but now it sounds like farty low end distortion.

[snow123]

theres alot of distortion on the output of the clipping stage (before r1), but thats happening regardless of where the volume or mids control is.