tubescreamer splutter

[luke691]

i've noticed an on and off splutter splutter-esque type of noise in a 808 tubescreamer, i used the tonepad layout. when i use the pedal as notes trail off they will cut out abruptly making a splutter, stuttery sound. ive absolutely no idea looked through everything. the pedal is using a standard 458 chip, nothing special. any ideas???

[R.G.]

Stuttering is one variety of bias problem. You have an internal biasing problem that's not too bad, but does affect the trail off.

Read "Debugging: What to do when it doesn't work" then follow the instructions.

[luke691]

alright, ive looked given it a bit of a touch up... but still the same problem...

here are the voltages

Q1

E-3.11
B-3.62
c-9.37


Q2
E-3.06
B-3.57
c-9.37

4558
1-4.29
2-4.78
3-4.48
4-0
8-9.16
7-4.30
6-4.30
5-4.30

i am using the tonepad layout... transistors seem to be well. but the ic??

[calpolyengineer]

Are you sure you labeled the pins on the IC correctly? They should go like:

1     8
2     7
3     6
4     5

With a 4558 (and many dual opamps), pin 8 is the positive voltage pin, so I'm guessing you labeled the right side with 5 on top. If not, there is definitely a problem with the power. Unfortunately, I can't be of much more assistance with the opamp cause that is pretty much the extent of my knowledge there.

-Joe

[luke691]

yep, sorry. modified that. any ideas??

[calpolyengineer]

For reference, the IC voltages on my TS-9 (not modded) are:

1: 4.74
2: 4.76
3: 4.72
4: 0
5: 4.73
6: 4.73
7: 4.73
8: 9.49

So from that, it seems as though your IC is fine.

-Joe

[Zben3129]

I highly doubt this is the issue, but it is a very simple solution to try, so why not...

Do you have another battery that has maybe been used for a bit (hoping for 9v or less from it). If you do, pop it in and see how it sounds.

Maybe this will work. The IC voltages are all fine, but I don't recall off the top of my head what the voltages for the transistors are supposed to be.

Zach

[luke691]

uhh, ben, tried your idea, no luck... i actually had it going with a bit of a dud battery for a while, and thinking that was the problem bought a new one.. Works slightly better with the new battery,,,???

[luke691]

as, this, new battery has slowly decayed, the stuttering has become more obvious...??

if anyone had reference voltages for the transistors, it would be a big help..

[MikeH]

I don't know exactly what they should be, but I think your voltages are good.  Collectors are at V+, Base and Emitter voltages are reasonable.  There should be a resistor going from Vref to the input of your opamp in order do bias the IC.  Make sure you've got the right value there.  Also check your Vref voltage.