ts808 clone !!!!HELP!!!! TONE CONTROL WORKS LIKE LEVEL

[jolly]

ive built a ts808 clone my second one everything is working except the tone control (20kw pot), it acts like a level control. when the tone is turned down it has no sound and as i turn it up it gets louder. the drive and the  level work great the effect works great. ive checked the pot (20kw),the .22 caps, and the 220 ohm resistor, has anybody had the same prob or might know what it is im over looking

[Mark Hammer]

Actually, it IS a level control of sorts.  One leg of the pot adjusts the gain and lowend rolloff of the tone-stage op-amp, and the other leg of the pot adjusts the high-end rolloff after the clipping stage.  Possible you have a problem with one of the legs of the pot?

[Meanderthal]

 Check the wiring to and from the pot... Oh jeeze Mark beat me to it. Yeah- what he said.

[jolly]

i have changed it out with a known working one of the same value and i got the same result, its like it doesnt have a lowend. ive rechecked the wires.

[Barcode80]

sounds to me like one of the legs has a bridge to ground, making one side of the pot a bleed-off, basically making it function like a volume pot. check for solder bridges and groudn outs.

[jolly]

i checked and scratched there are no bridges and still no luck its still doing the same thing. by the way  thanks for all the help guys. also i took this 20kw pot from a working boss sd-1, does anybody know if these pots are diff? wouldnt it work the same way?

[Barcode80]

yeah, should be fine.if you can't find any bridges though, i don't know what it could be.

[Seljer]

maybe try a new pot? I've destroyed a couple pots while repeatedly desoldring/soldering them
or somehow try to confirm that all is well with the salvaged pot

[jolly]

ive done that , i took the pot from the first one i built  and it does the same thing (its a alps 20kw, i robbed it from a broken ts9) i dont think its the pot and i just now re-checked for bridges and didnt find anything. im all out of ideas i dont know what else to check.  could a bad 220 ohm resistor still let it work but only effect the tone pot?

[sfr]

When you say checked for bridges, are you checking with a meter, or visually?  Make sure you check with a meter, just checking visually not's good enough.

Usually bad components is the last thing to worry about.

Perhaps the connections to the pot are mixed up?  Mixing the outside lugs would just change the direction of the rotation of the pot, but if you swapped the wiper with one of the outside lugs, that would mean rotating the pot would change the amount of resistance in the feedback loop, (going through the outside lug to the wiper, rather than staying at 20k going across the two outside lugs) changing the gain of that opamp stage.

I think.

[jolly]

I checked for bridges by just going a scratching in between solder joints with a razor knife, i also check the wiper and still no luck.i know this is going to sound so noob but, how do you check for bridges with a volt meter? has anyone ever had a problem like this one

[jolly]

i know this is going to sound so noob but, how do you check for bridges with a volt meter? or can someone point me in a good direction where i can find info on how to ?

[heyniceguy]

you just set your meter on "continuity/beep" and touch your leads to adjacent pads. if it beeps, you have a bridge.

[Paul Perry (Frostwave)]

As a general rule - I'm not referring specifically to the 808 - one way a tone control can turn into a volume control, is to either remove a cap from the circuit, or accidentally put a 100pF instead of a 100nF or whatever.

[jolly]

well still no luck ive tried all i know to try, its like lug 1 of the tone pot doesnt work from 1 to about 5 (12 o'clock) it acts like a level ,but then from 5 on the rest of the way it does make the sound sharper but it also makes it a little louder like a level. anyone got any more ideas what it could be or something to check ive hit a wall

[jolly]

1.What does it do, not do, and sound like? Tone control acts like a level from 0-5
2.Name of the circuit = Tube screemer
3.Source of the circuit (URL of schematic or project) = www.generalguitargadgets.com
4.Any modifications to the circuit? Y or N = NO
5.Any parts substitutions? If yes, list them.
6.Positive ground to negative ground conversion? Y or N =n
7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? =>8.67
Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead =8.83
Voltage at the circuit board end of the black battery lead =0.00

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
C =8.67   
B =3.61
E =3.13

Q2
C=8.65
B=3.41
E=2.93

IC1 (or U1)
P1 4.31 
P2 4.37     p7 4.25
P3 4.26     p8 8.63
p4 0
p5 4.25
p6 4.25

D1
A (anode, the non-band end) = 4.36
K (cathode, the banded end) = 4.24

D2
A = 4.25
K = 4.24

[johngreene]

well still no luck ive tried all i know to try, its like lug 1 of the tone pot doesnt work from 1 to about 5 (12 o'clock) it acts like a level ,but then from 5 on the rest of the way it does make the sound sharper but it also makes it a little louder like a level. anyone got any more ideas what it could be or something to check ive hit a wall

It almost sounds like your tone pot is a 250K rather than a 25K or 20k. I say this because if the value of the pot was large enough, you would be adding the .22uF in increasing amounts in one direction and the opamp will behave as a voltage follower. As you cross center and move to the other side, you start lowering the resistance from the non-inverting input to ground giving it gain. Which is pretty much how it also works as a tone control but with the smaller value pot, the frequency response of the .22uF cap and the series resistor play a larger role.

I'm pretty sure your problem has to do with how the pot is wired and/or its value.

--john

[jolly]

the pot reads 20kw on the side thats the same as 20k isnt it?

[johngreene]

the pot reads 20kw on the side thats the same as 20k isnt it?

Should be. I can only recommend checking everything connected to the pot and around it.

--john

[Barcode80]

WOAH. i can't think of the article right now but search for "w" taper pots on here. that's probably your problem i am thinking. if the taper is screwy that would explain the odd behaviour. you need a linear pot.