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

[snow123]

And "R2".

nope, just r1

[GibsonGM]

I reposted the schematic, cuz that's what we have to work from.  If you haven't done this...set what you changed back the way it was.   Now, go back and read about putting a pot where R1 is, right after the clipping stage (just below the ".step" command).    Make the pot big enough so that you can get some range from it...50k, 100k...see if you can cut some gain here to not drive the next opamp so hard.  If you find a good value that does this, let us know, we'll help you change the cap right there so the freq response doesn't change.

The distortion is probably due to overdriving the next stage.  This whole thing is about getting enough gain from each stage to keep the signal clean and workable (and for some boost), but if you have too much level, you'll clip any following stage.  As long is it's over unity, you're probably ok.    You check this with an audio probe (if you don't have a scope) at the output of each stage.  You may need to dump gain AT the mid boost stage and put in a recovery stage, perhaps...check this with an audio probe.

See what I mean about this being a big project?     HNY!

[snow123]

I reposted the schematic, cuz that's what we have to work from.  If you haven't done this...set what you changed back the way it was.   Now, go back and read about putting a pot where R1 is, right after the clipping stage (just below the ".step" command).    Make the pot big enough so that you can get some range from it...50k, 100k...see if you can cut some gain here to not drive the next opamp so hard.  If you find a good value that does this, let us know, we'll help you change the cap right there so the freq response doesn't change.

The distortion is probably due to overdriving the next stage.  This whole thing is about getting enough gain from each stage to keep the signal clean and workable (and for some boost), but if you have too much level, you'll clip any following stage.  As long is it's over unity, you're probably ok.    You check this with an audio probe (if you don't have a scope) at the output of each stage.  You may need to dump gain AT the mid boost stage and put in a recovery stage, perhaps...check this with an audio probe.

See what I mean about this being a big project?     HNY!

it seems it starts getting rid of the distortion when its at 2.2k-2.7k, but when the resistance of r1 past 2.7k it doesnt boost the mids at all.

[FiveseveN]

https://www.allaboutcircuits.com/technical-articles/low-pass-filter-tutorial-basics-passive-RC-filter/

[GibsonGM]

It's probably much easier to run an eq pedal after a circuit like this than it is to build in a mids control that has 'big range' and all that, Snow.  More is done in the original by cutting low and high and leaving mids, as you can see.    A little boost of mids goes a long way! 

Without your having more knowledge of how this circuit is operating, it's hard to give advice about what to change.   I mean...if the output of U6 is clipping, then you MUST either decrease the input you're trying to amplify, OR increase the power supply.  So - as Tom was talking about....we can go back and lower the output from the 1st opamp stage at R1, OR we can lower the output of U3, OR we can decrease how much amplification happens in U6.    From where I'm sitting, that's all we got!     And if you increase R1, as stated you'll have to change C1 to accomodate that (double R1, halve C1's value). 

"Clipping" a gain stage happens simply because you are exceeding the amount of amplification that an active component like an opamp can give you...you're asking it to put out perhaps 20v, say, when the power supply is only 10V.   You either lower input or lower the factor that it amplifies by... 

[ElectricDruid]

it seems it starts getting rid of the distortion when its at 2.2k-2.7k, but when the resistance of r1 past 2.7k it doesnt boost the mids at all.

Ok, so say you put a 3K in as R1 to give you a bit off leeway. That fixes the distortion. Now, you've increases the "R" in your RC filter by a factor of three, so you need to reduce "C" by the amount factor. 220n / 3 = 73n. 68n is going to be the closest value. You could also try the nearest values either side to see how you like it, so 47n will let a bit more treble through to the tone control, and 100n will darken it a shade.

[snow123]

after doing alot of tuning, i just set r1 to 3k, and c1 to 68nf, and im super happy with how everything is!

[snow123]

Thanks for all for the help!!

[GibsonGM]

Glad you got it 'tuned' ok!  A very learning experience, ha ha...on to the next project!   

[snow123]

wtf i just got it wired up and stuff and its still distorting. but this time when i max the tone control it gets a bit more nasally. the only things ive done to the circuit are swap the MC1458 for a jrc 4559, and swap the 741 for a TL061.

[snow123]

well i got it wired up about a week ago, but i thought i could fix it but i still havent fixed it.

[snow123]

and, ive tried dialing in R1 again with a pot, but when i have the pot on 1k, it gets rid of the distortion, but when i swap that for a 1k resistor, theres a bunch of distortion.

[GibsonGM]

Honestly Snow, no clue other than what we've suggested.  When I do mods like this, I will use my audio probe to determine EXACTLY where the problem lies.  There just isn't enough data here to tell you "make that R this value and you're all set".   Without hands-on, it's very hard to know what those additional mids do to the stage following it.  You may well have too much gain in stages or thruout, a simulation doesn't tell all!  <<

There is a lot of 'back story' to this stuff...background info you need to know - such as, you are dealing with a 9V circuit...if you ask it to amplify too close or above the power rails, it will distort, among other things.    The only way for ME to know what's up with your mod is for ME to build it and troubleshoot it    I have other things taking my time!   When you decide to re-engineer something, you hit these problems and they are frustrating, I know.

If you used a pot wired as variable R and replaced it with a fixed R, there is no reason it would be any different; something else is going on. Most problems like that are 'user error' on our part...all I can suggest is take it stage by stage and be sure each one is working ok before moving on...

[iainpunk]

did you measure that 1k 'in circuit' or have you removed the pot from the circuit without changing the setting and measure without interference from the rest of the circuit? it can make a huge difference in readings. i have measured resistors in circuit being way way way off, anywhere from a factor 100 to low to a factor 10 to high

cheers

[snow123]

im checking for shorts on the board, and 4v5 looks to be shorted to ground. is that normal?

[snow123]

did you measure that 1k 'in circuit' or have you removed the pot from the circuit without changing the setting and measure without interference from the rest of the circuit? it can make a huge difference in readings. i have measured resistors in circuit being way way way off, anywhere from a factor 100 to low to a factor 10 to high

cheers

well i was measuring the resistance on the pot with the test leads on the lugs on the pot itself, while the pot was wired to the circuit, and the resistance was measuring as if it wasnt in the circuit.

[snow123]

and +9v is shorted to ground

[GibsonGM]

im checking for shorts on the board, and 4v5 looks to be shorted to ground. is that normal?

No. If you follow the schematic, you end up back to the voltage divider where you get 4.5V from.  There is a cap to ground there, which is NOT a short to anything other than AC.   So, that's 'problematic'      Is this built now, all soldered up?

[antonis]

and +9v is shorted to ground

Maybe ground is shorted to +9V..
(just another point of view..)

[snow123]

im checking for shorts on the board, and 4v5 looks to be shorted to ground. is that normal?

Is this built now, all soldered up?

yep