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

[snow123]

i finished building it on vero, but for some reason when i max the volume, it starts to distort. and i have tried swapping IC1 for a 4558 but that didnt do anything.

layout:

[GibsonGM]

Is "it" distoring, or is it overdriving your amp (how's it sound with the amp turned low)?   you had this built & tested on breadboard exactly as you vero'd it, before you built it, and it didn't do that?

I'd audio probe each section and see where the distortion starts. If you jack the mid up, it may not be surprising that the next section distorts...in that case you'd lower following section's gain, and try to make it up from somewhere else if needed. 

[snow123]

Is "it" distoring, or is it overdriving your amp (how's it sound with the amp turned low)?   you had this built & tested on breadboard exactly as you vero'd it, before you built it, and it didn't do that?

I'd audio probe each section and see where the distortion starts. If you jack the mid up, it may not be surprising that the next section distorts...in that case you'd lower following section's gain, and try to make it up from somewhere else if needed.

the pedal itself is distorting, even with the amps volume down. and yes, it didnt do that on the breadboard.

[snow123]

and it seems to start distorting at the output of the clipping amp.

[snow123]

and it seems to start distorting at the output of the clipping amp.

and i should note, that at the very start of the output of the clipping amp (before the 1k resistor) its like this super trebley and spanky type of distortion, but after the 1k resistor into the tone stage, it becomes this much darker kind of distortion. thats the best way i can explain it lol.

[GibsonGM]

You have to go thru it and find where you (likely) made an error, then.  Check the biasing and feedback components in the stage after that 1k....

[bartimaeus]

and it seems to start distorting at the output of the clipping amp.

and i should note, that at the very start of the output of the clipping amp (before the 1k resistor) its like this super trebley and spanky type of distortion, but after the 1k resistor into the tone stage, it becomes this much darker kind of distortion. thats the best way i can explain it lol.

that sounds correct for a tubescreamer? without the tone section, a tubescreamer would be a lot treblier, which is what you're hearing when you probe the output of the clipping stage.

you might want to swap your 68k resistor for a 100k trimpot, at least to test. that way you could back off on the boost to make sure you aren't pushing those LEDs into clipping.

as for the clipping you get from maxing the volume knob, sounds like the transistor output buffer might be clipping, since that's the only active stage after the volume knob. perhaps you're just hitting it with a ton of volume and mids? or maybe it's improperly biased?

also, troubleshooting other people's stripboard layouts is a bit of a nightmare. i think folks would be more willing to offer advice if you included an updated schematic alongside the stripboard.

[snow123]

schem:

[snow123]

i realized that there was supposed to be a cut right after the 27k so it it doesnt connect to the 620k, so that fixed the volume issue, but now it has this weird, very dark kinda overdrive unless the mids control is maxed, and the tone control doesnt seem to do a whole lot when the mids control isnt maxed.

[GibsonGM]

The troubleshoot is going to be the same for the rest of the 'issue', snow...audio probe and try to determine what area has something 'wrong' with it.  But like bartimaeus said, some area DO have a 'odd' sound going on before they're shaped by tone controls. You'll have to go from inputs to outputs and try to figure out what's going on. 

Did all the sections play good with each other when it was on breadboard?  It all sounded good at that time?  If so, then clearly you have a mistake somewhere with a part value, a cut not made - a cut that needs to be made...and so on.  I don't build on vero for those reasons, partially - easier for me to literally go from point a to b, and you can test sections as you build if you want.

[iainpunk]

looking at the schematic, i see you have quite the capacitive load on the 1458 's output, which is something that can possibly cause crossover distortion in those opamps. you can help this by putting a relatively small resistor between the output and ground, to ensure that there's always a positive current flowing from the output stage.

cheers

[bartimaeus]

looking at the schematic, i see you have quite the capacitive load on the 1458 's output, which is something that can possibly cause crossover distortion in those opamps. you can help this by putting a relatively small resistor between the output and ground, to ensure that there's always a positive current flowing from the output stage.

cheers

Though the original Tubescreamer also has that 1uF cap (C6 in this schematic) on the output of an opamp, so probably shouldn't be an issue?

[iainpunk]

looking at the schematic, i see you have quite the capacitive load on the 1458 's output, which is something that can possibly cause crossover distortion in those opamps. you can help this by putting a relatively small resistor between the output and ground, to ensure that there's always a positive current flowing from the output stage.

cheers

Though the original Tubescreamer also has that 1uF cap (C6 in this schematic) on the output of an opamp, so probably shouldn't be an issue?

the 4558 is more resilient to crossover distortion than the 1458.

i think a 10k resistor from the output of the opamp directly to ground would help. it won't impact the tone because the opamp can easily drive the purely resistive load. if the problem persists, going down in resistance can help that, i suggest 3k3 and 1k. if 1k doesn't cure it, you can take away the resistor because the problem probably isn't crossover

cheers

[snow123]

looking at the schematic, i see you have quite the capacitive load on the 1458 's output, which is something that can possibly cause crossover distortion in those opamps. you can help this by putting a relatively small resistor between the output and ground, to ensure that there's always a positive current flowing from the output stage.

cheers

Though the original Tubescreamer also has that 1uF cap (C6 in this schematic) on the output of an opamp, so probably shouldn't be an issue?

the 4558 is more resilient to crossover distortion than the 1458.

i think a 10k resistor from the output of the opamp directly to ground would help. it won't impact the tone because the opamp can easily drive the purely resistive load. if the problem persists, going down in resistance can help that, i suggest 3k3 and 1k. if 1k doesn't cure it, you can take away the resistor because the problem probably isn't crossover

cheers

its not crossover distortion. it still distorts when the mids control is maxed with the 1k resistor.

[ElectricDruid]

it still distorts when the mids control is maxed with the 1k resistor.

How much gain does the mids cut/boost? If the signal level going into that stage is decent, there could well be enough gain to make the op-amp clip. Plenty of tone controls can do +/-15dB or more. That's x5.6, so a 1.5V signal gets turned into something that's too loud for an op-amp on 9V to handle without distortion.

[snow123]

it still distorts when the mids control is maxed with the 1k resistor.

How much gain does the mids cut/boost? If the signal level going into that stage is decent, there could well be enough gain to make the op-amp clip. Plenty of tone controls can do +/-15dB or more. That's x5.6, so a 1.5V signal gets turned into something that's too loud for an op-amp on 9V to handle without distortion.

[snow123]

it still distorts when the mids control is maxed with the 1k resistor.

How much gain does the mids cut/boost? If the signal level going into that stage is decent, there could well be enough gain to make the op-amp clip. Plenty of tone controls can do +/-15dB or more. That's x5.6, so a 1.5V signal gets turned into something that's too loud for an op-amp on 9V to handle without distortion.

rn its more of a scoop control 'cause it starts to distort HEAVILY (almost like a boss ds1) if i let the mids go above 3db.

[ElectricDruid]

rn its more of a scoop control 'cause it starts to distort HEAVILY (almost like a boss ds1) if i let the mids go above 3db.

There's 18dB between the green line at the bottom and the top of that graph, so there's potentially plenty of gain available. The level out of the drive stage will be limited by the clipping diodes, so what's the forward voltage of those LEDs you've got marked on the schematic?

Once we've worked out how much you need to reduce the level to stop it distorting in the tone section, I think the best option might be to tweak the values of R1/R2 since they act as a divider. Increasing R1 will reduce the level, and then you just need to reduce C1 by the same factor to compensate and not change the frequency response.

[snow123]

rn its more of a scoop control 'cause it starts to distort HEAVILY (almost like a boss ds1) if i let the mids go above 3db.

There's 18dB between the green line at the bottom and the top of that graph, so there's potentially plenty of gain available. The level out of the drive stage will be limited by the clipping diodes, so what's the forward voltage of those LEDs you've got marked on the schematic?

how would I measure the forward voltage of the leds?

[GibsonGM]

To a close approximation, you could: 

hook up a 1k resistor in series with one of the exact same LEDs you used and a 9V battery like this     GND --- LED K-A----1 K resistor ---- battery +

Measure the voltage from the LED anode to ground, that's its forward voltage.  If you were doing this in a lab, you'd have a specified test current but for grins and stompbox use, this will be close enough!