TS-808 problem

[Bobv]

I'm pretty new to building effects - but i have built a Distortion+ pedal and am very happy with that one.

I decided to make a Tube Screamer - following the Tonepad schematic (TS-808 version) building the circuit on a perf board

There is sound coming through, but there is a loud hiss  - that is not affected by guitar volume knob (noise is there even if nothing is coming from guitar)

Minor parts substitutions - used 1N914A instead of 1N914 diodes, 47 pf capacitor instead of 51 pf, .022 instead of .027 cap
used a 1m pot instead of 500k, 25k instead of 20k

I've been through debugging pages and did check voltages on transistors and IC - and they are correct, also checked to make sure everything that needs to be grounded is grounded, and reheated solder joints to make sure everything was attached properly.

my battery reads over 9v, fresh from a costco value pack

for some reason this feels like a common problem, but i can't find a solution.

(audio clip) (oh yeah i can't actually play guitar)

[Plinky]

I've only built the JD Sleep version of the Tube Screamer (www.generalguitargadgets.com). I came up empty on that subject too. Is the effect in an enclosure? It sounds like a level is up really high (like amp hiss). What are the levels on the pedal and your amp when you did this audio clip???

[Bobv]

I'm using an aluminum enclosure, so shouldn't be that...
The gain was near the top, but its hard to find settings where you can still hear the sound and there's no hiss

Tried different ICs so shouldn't be that either.

Is it a problem with the circuit then? is there some change that will fix the problem?

[GibsonGM]

Hmm...you could have a polarized cap in backwards...a bad vol or gain pot would do that, maybe.  Have you audio probed to find the area the hiss begins in?   Could help pinpoint a defective component.  Look on the Debugging link up top for audio probe instructions.
Ground loops are noisy - how are your grounds set up?

It's useful to actually post the readings you've taken, so trouble-shooters can see. What that reminds me of is when 1 section is not working - a level going to some amplification being too low and the noise figure increases....are you sure your trannies and OA pinouts are oriented correctly?  The sound is like low signal, as if your volume was down on the guitar w/ amp turned up.  So, there IS a problem.   Audio probe!

The circuit should sound great, Ive built one.  I'll check back in a couple hours, see how you're getting on )

[Bobv]

Thanks for the quick responses!

These voltages are taken from the GGG instructions:
9 volt power supply 9v
IC Pin 1 4.5v
Pin 2 4.5v
Pin 3 4.5v
Pin 4 0v
Pin 5 4.5v
Pin 6 4.5v
Pin 7 4.5v
Pin 8 9v
Q1
Collector 9v
Base 3.0v
Emitter 2.5v
Q2
Collector 9v
Base 3.0v
Emitter 2.5v


These voltages are taken from my pedal
9 volt power supply 9.1v
IC Pin 1 4.44v
Pin 2 4.74v( uh oh?)
Pin 3 4.35v
Pin 4 0v
Pin 5 4.43v
Pin 6 4.44v
Pin 7 4.44v
Pin 8 9.1
Q1
Collector 9.09v
Base 1.09v
Emitter .52v
Q2
Collector 9.09v
Base .56v
Emitter .11v

Hmm you're right the voltages don't look as good now as they did when i wasn't looking at both sets of numbers at the same time - they still make sense, but are a bit low?



i checked capacitor orientation, and everything seems to be right
circuit said nothing about tantalum capacitor orientation so i just pointed the negative side towards ground

I'm going to look up ground loops because i have no idea what that means

As for audio probe - this noise is there whether or not there's input from the guitar, as long as the circuit is powered


Could this type of noise come from wires being too close together? - it's pretty crowded inside my enclosure

[Meanderthal]

 Maybe a bad opamp? Did you try swapping it out?

A ground loop would be a hum, and even then a hum is usually an unfiltered or poorly filtered power sypply. It's usually a problem in AC circuits only, but I guess with the amp and a power supply, possibly with a direct out hooked to PA/recording gear... I can imagine convoluted ways that ground loops might possibly involve a pedal... but... you have a hiss, not a hum...

I've heard replacing the 1uf tants with film helps too, but I don't think that they cause that much hiss. My TS9 still has the tants, I never bothered modding them out, and it's nice and quiet.

[Stoneham11]

You may have already checked this out but I just built a screamer and substituted c1815 transistors for the one that the schematic called for and it didn't work I did some searching on the internet and found that the pinouts were different the emitter and the base were switched around.
Hope you find the problem

[Bobv]

oh crap i was sure that the 3904 is CBE from top to bottom but i just looked it up and its EBC... i think this may be it... i never would have checked this if you didn't say it, Stoneham, i'm going to go flip them now

[GibsonGM]

Mostly when this happens there's a short somewhere...we SWEAR we found any that could be possible, but time after time - one pops up!   

You say it's on perf...did you test it out before you put it in the enclosure?  I always leave long leads for input/output and jumper jacks to them before I set it up in a box.  That way I know it works before all the switch work.  It's pretty common to mess something up on the switch, another place to look!

Let's say it's the last transistor causing the noise (output buffer).  You'd hear the noise with or without guitar when the effect it on.  You might strum a few chords, listen to the input buffer w/audio probe and find silence....opamp, silence....and then, voila, it's in the buffer circuit.  That would narrow it down - which is what we're trying to do here.   The holy grail of debugging! 
So, I'd go for audio probe...expect nothing but nice clean guitar at input...somewhere after that the trouble lies ;o)   

Hey, I mentioned the backwards transistor first!! LOL  ;o)

[Bobv]

heh for some reason i was so sure that i knew the pinout... i kind of wish i socketed these things now...

[Bobv]

Well that fixed it! That was pretty dumb, but how else do we learn...

The sound is beautiful - except the volume pot isn't doing much, and the tone pot is definitely changing tone but also volume quite a bit - does this sound right?

[GibsonGM]

Happens all the time with pinouts, man!   
Any chance you installed the pots in the opposite locations? That could do that...
Volume definitely will be noticeable when it's working right.  The tone control is a little touchy and can seem not so effective.
So, check the pot's orientation, make sure that wiper is the output, one end to Vr, one to the circuit.  It's easy to make Vr ground by accident sometimes (and sometime it even works!).   These are just wiring errors, and require lots of time to solve, he he he. 
Glad it works!

~Mike

[Bobv]

there was  a stubborn solder joint on the pot - took all the solder off and redid it and that fixed it - now i have a beautiful tube screamer - thank you, everyone

[GibsonGM]

You're welcome, Bobv - I've been doing this for a few years now (and 646 posts!) and STILL catch myself denying there's any short in something I build that doesn't work, asking for help on here, only to find.....a short ;o)   Sometimes going thru everythng and asking gives you the push you need to keep at it, tho!  Solder bridges can be hard to spot.  Good job with the 808, enjoy it! 

[markm]

STILL catch myself denying there's any short in something I build that doesn't work 

Ha!! 
I've been there before!!
Good job GibsonGM and Bobv!