Tube Screamer works, but decays are unnatural...almost gated

[Ponchus]

Hey all,
Sorry if this has been covered before. I tried searching and couldn't find anything, though that's partly due to not being able to explain it well.

I built a TS808, which works but sounds a little...gated. When notes decay, it sounds a little unnatural, a little too "sudden". At one point, I thought it sounded as if the battery was dying, which wasn't the case. It reminds me a little of the artificial sound of an Ampeg Scrambler...in GEOFX's FAQs, he mentioned a blatty, gated sound. That's kinda what I have going on, except in the FAQ example, he's referring to situations where you have to slam your guitar to get any output. That's not the case with my pedal. I can play soft, and it will work.

Anyone have any idea of what to look for, despite my horrible descriptions?

For the record, I built it with a mix of 1% and 5% resistors, the input and output trannies are both MPSA18 (though the same thing was occurring when I had 2N3904s in there), there are 2 1N914 clipping diodes, and a 4558 chip.

Thanks!

[GibsonGM]

Sounds like mis-biasing, Ponchus.
Record and post all your pin voltages;  that might help someone get more specific about what's going on!  Could you have switched resistors or used wrong values when you assembled the board??  Or have a short across a pin or resistor?

A misbiased transistor will do that gating thing. 

[GibsonGM]

2nd thought - a transistor in backwards will do that, too....

[Ponchus]

The transistors seem to be oriented correctly. I checked the data sheets repeatedly at this point. The voltages of the trannys are as follows:

Q1
C- 8.61
B- 3.81
E- 3.389

Q2
C- 8.58
B- 3.8
E. 3.385

[Ponchus]

voltages on the IC are:

1- 4.27
2- 4.27
3- 4.27
4- 0
5- 4.27
6- 4.27
7- 4.27
8- 8.56

[Ponchus]

bump for the morning crew 

[Izzy]

I dont think this is the case but if you had put the diodes back to back in series with the signal by mistake, it will sound like you said.

[darron]

it sounds like you have extremely asymmetrical clipping. like izzy said, maybe one of them is backwards! i got exactly what you are describing when i used a combination of a 1n4004 diode with a germanium diode. that sounded horrible. try measuring both of you diodes, they may just be very different.

by the way, know how asymmetrical clipping sounds in extreme cases, and then lesser cases (horrible, and as described by ponchus), it gives me good reason ot try to keep everything symmetrical. contrary is just a bit of false mojo in my opinion unless you are after the sound of a dying small radio speaker where it sounds perfect.

[Ponchus]

Darron
I've tried both assymetrical and symetrical combinations, and I get this weird decay in all circumstances. I've used combinations of LEDs, a 1N4001 diode, and two to three 1N914 diodes. Right now, I just have 2 1n914 diodes in series (D1 and D2) with a jumper for D3, and the problem is still there.

BTW, if I take the jumper out or if I leave it in D3, I can't hear a difference. I thought that was odd, though I wasn't sure if it is to be expected. I thought that if I take the jumper out and just leave D3 empty, then there wouldn't be any clipping at all? Is this NOT the case?

Thanks again for your continued efforts to get me to rock out! 

[darron]

you can clip with only one diode, and it will only clip one side of the wave. that will have things much louder and the decay will be pretty extreme. if you take all clipping out it will just be a massive boost. what i suggested fits your descriptions perfectly, but i guess it's not that.

[Ponchus]

hmmm, one thing I failed to try is to take out all diodes completely and see if the odd decay still occurs (or put in jumpers instead of diodes). I could try that tonight after work. If that does happen, what does it signify though? Where should I look if I can effectively rule out the diodes as the cause of my problem?

[GibsonGM]

OK, something is wrong, then, LOL.  Good job posting what info you have at this point.  Believe it or not, I've been on here over a year and haven't built a TS!  My friends think they are "too cliche".  I will build one soon just for the experience.  So I am working on theory, altho these things all operate in a similar way (boosts etc).   Quick scan tells me the buffer is probably working (diode drop between B and E, anyway), and you have power to the IC. Output buffer BJT looks ok here, too.  Good battery, and you say the diodes are oriented correctly.  No solder bridges?  I'm sure your cords & guitar jack etc. are in good condition and you've tried your rig without the TS today, right? 
Fear not, we will get your TS screamin', just have to go thru the steps.  You need to Make Sure there are no shorts anywhere; even to the point of using a continuity setting on the DMM and a magnifying glass.

I recommend doing the audio probe.  Run a CD into the input or have someone strum your guitar, and probe from input thru the buffer to the IC input1, output1, input2, output2.  Then output buffer.   If there's a bad cap or something, this is likely to pick it up - you will hear something in the signal path, and then nothing (or a terrible sounding signal) at the next junction - problem is usually with the part in between.

If you haven't done this, see the "what to do when it doesn't work" thread at the top of the forum, and look at the Debugging link up top for probe info.   Make sure to use the cap with the probe; it will click when you hit voltages and that is normal.

Post back & tell us what happens!!   

PS - saw your new post.  My gut thinks something might be shorted in the tone stack, it's an easy place for errors.  You'll know if you get good signal up to there and then crap after!  You want to find what stage it's happening in, and narrow down from there....should have close to the same volume after the input tranny...then a boost at IC1...then the tone stack will drop volume...then it re-boosts at IC2....as was said, the diodes aren't doing all that much (unless they're shorted!).   Try probing...

[Ponchus]

Lots of good info there Gibson, thanks! <sigh> I f-ing hate work, ever since I started building pedals. All I can think about is how my poor pedal is sitting on my desk at home, it's guts hanging out etc. I never used to be in such a rush to get home as when I started on this addictio...oops, I mean hobby 

OK, I will try everything you've said when I get home and will report back.

The only things I can add right now is that the guitar, cord, and battery are all good. I'm sure of that, as everything works perfectly when i plug right into my amp, or when I use other pedals (I was playing around with my PT80 delay last night, for example).

Oh, and build a TS. It's a good pedal, regardless of whether it's cliche or not. Steak and a baked potato is a cliche too, but you won't hear me arguing 

[GibsonGM]

LOL, that is true!  And might help me on my never-ending tone quest, in search of a Strat Paul, ha ha.  The LP is great for fat stuff, then I want to play some skynyrd...better just buy one and save the aggravation   

Seriously, tho, there's only a few things that can be wrong, esp. if you're getting something on the output.  You'll find it!  And each time it gets easier; this is how you learn the in's and outs of how this stuff works.  Block by block, then part by part.  Someone else will ask a TS question down the road, and you'll jump right in and say "A HA, I know what's doing that!" 

Gig tonight, time to pack up.  Good luck debugging!    

[Ponchus]

Hey Gibson, I was on the quest for a Strat/LP mix too! So what I did was build a Warmoth Strat, with a swamp ash body, and a mahogany neck with a Rosewood fingerboard. I figured that the mahogany and rosewood would darken the tone...

It sounds f'ing great, though not LP-ish to tell you the truth. You could take it a step further and get a mahogany body maybe?

[GibsonGM]

I think any ol' strat with a HB in the bridge would fit what I want...tap it off to switch SC to HB.  I get a neat sound with an old Charvel I have, but I hate the sharp 80's headstock, LOL.  Just for the occasional Outlaws song, when you really need some twang.  I'd like to be able to do a lot with it, don't like switching guitars during a set unless I have to. 

The Warmoth sounds sweet, lol...I have an old Melody Maker ('69) with a Dimarzio PAF in the bridge that is all mahogany - it comes close, but is TOO bright/shrill. 

Have a debugging-filled evening!

MP

[Ponchus]

Ahhhh, sweet victory, how your taste blesses my tongue! Against your will I taste thee, as you hid in a poor solder joint by diode #2. But I have found thee, and eradicated thine hiding spot, and now that joint is shiny and bright, and you are mine sweet victory! Yes, you are mine! And now, I must goeth. There is much rocking to be done...

[GibsonGM]

LOL, Ponchus, congratulations on crossing that solder bridge    I knew it was there, but the wisdom that was passed to me by the DIY forefathers told me to let you find it on your own!  Good work.

Played a nice sized gig with my DIY stuff tonight - we kicked some ass!  Great sounding room and people ready to rock, what more could you ask for?  I'll try out a TS soon, seems to be a hole in my knowledge there, ha ha.

Later!

Mike