My TS-808 is a glorified Standby switch...

[Sir_Ian]

So I just finished building my Tubescreamer, and it works in bypass, and the LED turns on when active, but the sound goes away completely. Ladies and gentleman, I have build the most complicated standby switch. Anyways, I guess its off to read the "debugging" topic. Tomorrow I will start taking voltages and seeing what I can come up with.

Given that this is my first build, I had no grand expectations of success. Luckily, someone else was there to keep me from suicide. I followed the layout on General Guitar Gadgets, but I did all my own PCB work. (no etching). So I'm guessing its either a solder bridge or maybe a fried a component (probably a transistor...I'm not too great at soldering). I'm pretty sure I made all my connections. Before I ever tested I took a highlighter to the schematic and traced the whole thing out. But I will not rule this out.

Well, wish me luck.

~Ian

(oh, and I was gonna ask. How heat sensitive are Pots? I don't think I ruined em, but just wanna make sure. I know the technology in them, so I seem to think it's be hard to ruin them with heat. But if there is a way to do it, I'm sure I could find it.)

[GibsonGM]

Pots are probably the least sensitive of the parts in a TS...the transistors the most.  Yeah, the debugging is called for!
With the voltages posted, we can help you to see what went wrong.  99% of the time it's something easy like the switch, or a missed ground connection, etc.  I'd say mine work first time I power up probably about 70% of the time, after 3 years of building them! 
Post and we'll advise - you'll get it working, don't worry )

[gutsofgold]

If you're getting nothing when it is switched on, an 'audio probe' can be very helpful. Just follow the signal in and keep poking at the trace until  the sound goes away then you know where the problem lies!

[m-theory]

Could be as simple as the op amp being installed backwards.  It's easy to do. 

As for pots and heat, I'll add that, with the solder lug type, I've never had a problem.  With the PCB mount type, when I've run the wires through the holes that the rivets holding the mounting pins are installed through, I've damaged every single one.  The only times I haven't fried one of those types of pots is when I've twisted the wire around the mounting pin instead of going for that rivet hole.  The hole is very close to the carbon track, and apparently not much abuse is allowed there.   

[ubersam]

If you're getting nothing when it is switched on, an 'audio probe' can be very helpful. Just follow the signal in and keep poking at the trace until  the sound goes away then you know where the problem lies!

Good call on the audio probe. Even better if you have a signal generator, like maybe one of those 1KHz oscillators. I think there is a schem for a DIY one at R.G.'s site.

[Sir_Ian]

Here we GOES!!!!

Here is the checklist to fill out:
1.What does it do, not do, and sound like? Works in bypass, LED lights up when turned on, but absolutely no sound.
2.Name of the circuit = Tubescream 808. From general guitar gadgets.
3.Source of the circuit (URL of schematic or project) = http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=82&Itemid=26
4.Any modifications to the circuit? Yes. I have it set set to switch between regular diode clipping and LED clipping. I also have a switch to bypass capacitor C3 (.047 uf), which is supposed to give a bass boost.
5.Any parts substitutions? If yes, list them. No....I used all the right values except for CAP C4. It says 53 pf, I used like a 49 pf. This "shouldn't" matter. I also used polarized tants for caps C5 and C9. But thats what the schematic says to do...
6.Positive ground to negative ground conversion? Nope, none of this nasty business.

9 volt power supply = 8.8 volts

Q1
C = 8.78
B = 0
E = 2.95

Q2
C= 8.79
B= 0
E= 2.96

IC1
1= 4.69
2= 5.09
3= 3.65
4= 0
5= 4.65
6= 4.66
7= 4.66
8= 8.8

to see what values I'm supposed to get, i direct you to page three of this pdf.
http://www.generalguitargadgets.com/pdf/ggg_its8_instruct.pdf

As you can see, I'm having a problem (the same problem) with both transistors. (My op amp looks like its in the ball park). I am using 2sc1815, and the collector is in the middle, so I had to bend it up around so it was at the top of the ciruit. My collector value looks correct, but I my base is 0 volts when it should be 3, and my emitter is 2.95 volts when it should be 2.5

So I think the problem is with the transistors, but really, I have NO CLUE what the problem is. The transistors might only be a symptom. I don't know...once again my first build. I'm 97% sure I orientated them right. So maybe I fried them...? I don't know how hard or easy it is. I tried to be delicate....but my knickname is Shreck...

Any help and suggestions are greatly appreciated. Thank you very much.

[zachomega]

I wonder...do you have the transistors oriented backwards? 

-Zach 

[Plinky]

Have you tried another type of transistor? I tried the 1815s but went to MPSA18s when I realized there wasn't much sound difference and it was too easy to put them in wrong.

[petemoore]

Ladies and gentleman, I have build the most complicated standby switch.
  What exactly does that mean ?
  Schematic helps.
  Nice bias on the opamp.
  The base of the transistors needs to be a diode drop above emitter, test the base bias resistoros

[Sir_Ian]

Ok everybody. even after I had double check my transistors, I still had them in wrong...lol. SO I fixed that....

NEW PROBLEM!!!!!!!!!!!!!!!! (I think).

Ok, I now have sound running through, I get sweet sounds. Driver is good, level works, but I get no response from the tone knob. Whether its at low, max, or in the mid...it just sounds the same. Is it supposed to be unresponsive. (note, I am using the 25 linear and not the 20 k eq pot). I check the voltate on all three prongs of the Tone Pot and I got 4.3 volts on them. I measured them with the knob turned to different degrees and got 4.3 volts every single time. I'm not 100% sure something is wrong, but I think so. Would somebody be kind enough to measure their voltage readings on all three prongs of the tone pot for me?

Thanks for all the help already, just a little bit more and I'll be done. Thanks.

[zachomega]

Check for a bad solder joint.  The tone control should be pretty noticeably different from all of the way up to all of the way down. 

-Zach

[Sir_Ian]

I resoldered all the wires onto the pot...that didn't fix it....so it might be a bad solder joint on the pcb. Time to debug.

One more thing. I'm using one of those "superbright" LEDs. But I would like it a lil less bright. On the board, it has a 1 k dropdown resistor. Could I change that to a 20k without affecting anything besdie the LED? Would it do anything to my tone? would it cut down on battery life? Thanks.

[Sir_Ian]

Ok, i checked all my connections for continuity. The tone knob "works". Sound goes in, sound goes out. Now, the middle lug which goes through a cap, resistor, and then to ground....I check it all...they are all connected. So it "should" work. And technically it does.

The problem is, I just can't hear a difference. Now, I don't own any other tubescreamer, so I can't compare, but I'm gonna head over to the music store tomorrow and play one of theirs to make sure.

The last possitbility is that I might not be hearing the difference because I'm playing on a solid state practice amp. I know the pedal sounds best on a tube amp, and it will be played on one. (its a gift for my bro, and he has a nice tube amp). But I only have my wee little brothers guitar and practice amp. (I don't actually play guitar....I play bass....and my big amp (only 100 watt really) is a solid state too.) Do you think if I took my pedal in, they would let me hook it up to their amps. I know if I was them I wouldn't....but I'm not them.

Last thing. Once again...what about the led....can I put a big LED (like 20k) on it? Or am I gonna lose power to the effect?

Thanks!

[rikkards]

What I did as a work around tone generator was create a 404Hz tone in  wav editor and copy and paste it. I have it on my ipod and just repeat it.

If you're getting nothing when it is switched on, an 'audio probe' can be very helpful. Just follow the signal in and keep poking at the trace until  the sound goes away then you know where the problem lies!

Good call on the audio probe. Even better if you have a signal generator, like maybe one of those 1KHz oscillators. I think there is a schem for a DIY one at R.G.'s site.

[GibsonGM]

Good call, Rikkards....I have a CD I set up with 220, 440, and 1K that each run for about 8 minutes.  Line out from the CD player to an alligator clip on the ground line, and a probe on the signal line.   That way you can spend your time testing, not strumming.

Try replacing the 1K LED resistor with something like a 3.3 or 4.7K.  It won't affect circuit operation at all, just the light's brightness.  If that's not enough dimming, go to 6.8 or even 10K!   I wouldn't try 20K first, too much R there.

About the tone stack - they can be tricky. You have to be sure the end is grounded (NOT to Vr!), and there are no solder bridges.  It DOES work, believe me, you'd hear the diff!   Look at all your junctions around there (the in- connections, etc), and the 10K going to Vr, too. 

[Sir_Ian]

bout the tone stack - they can be tricky. You have to be sure the end is grounded (NOT to Vr!), and there are no solder bridges.  It DOES work, believe me, you'd hear the diff!   Look at all your junctions around there (the in- connections, etc), and the 10K going to Vr, too.

Ok. I'll look into it. I went to guitar world today and played around on their Boss pedals setup demo. I played my guitar with just the SD-1 on (a similar circuit to the tubescreamer). Everything seemed to work like mine...except for the tone. Their was a such a clear and distinct range. But I wanted to hear the difference, to make sure it just wasn't my ears being incapable of hearing. I heard it.

I came home, and played a lil and listened, and knowing what to listen for helped, and I could hear a little difference. But not the nice range I heard on the Boss pedal. So, I'm gonna open it up, go through, and make sure everything is okie doorie dandy. Once again. The pedal is very playable...but the tone seems a lil stuck.

Out of curiosity...could it be a broken pot? like the wiper not sweeping well or something? I don't have any other 25ks to test....

[Sir_Ian]

Update. I've been debugging....but no luck. Does the boss's version of the tubescreamer just have a wider tone control?

Could somebody here who has a Tubescreamer play it into a solid state amp and tell me if the tone control still sounds right?

I'm thinking, (more like desperately hoping) that somehow this is because I'm just on a crappy 15 watt.....but I doubt it. I checked all my connections.. they all seem to be ok...

I plugged in and ipod to the input jack and just played some tunes through my box. While doing this...I measured lots of voltages. On the level control, the voltage was at a high at like 4.25 volts and then a low of 3.9 or 3.95 volts with the pot turned the other way. Now whats interesting is that the voltage on my Tone pot decreased from 4.25 volts to 4.21 volts and then increased back up to 4.25 volts. (so with the wiper at either end, it was 4.25 volts, but with it in the middle it was 4.21 volts.) I think that the Tone pot gets these readings because there is power from Vr on either side of the pot. And with the wiper in the middle, it is the furthest away from both pots.

One more question about the Tubescreamer itself....I don't quite understand the function of Vr. Its a 4.5 volt power supply....so is it adding voltage to the signal...or is it providing a different way for voltage to leave the signal and get to ground. In either case, does anyone mind explaining the ramifications. Why would you want to add voltage to the raw signal? or why would you need a second quasi ground? Maybe if I understand this concept a bit better, it might help my debugging.

Once again...thanks for the help. Any ideas and help are much appreciated.

[Sir_Ian]

WOW....I FIXED IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 

I accidently had two wrong resistors in....lol

I had a 100k in for a 100 ohm and a 220k in for a 220 ohm

It hit me at like 2:30. Long story short....i finally noticed the schematic said 220...not 220 k. Then I looked around for others with no k and saw a 100. Realized i had put a 100k in for that too. Well.....alls swell. Spent forever doing this, but its done. Now I got to go to bed. I got to wake up in 4 and 1/2 hours and go to work...but at least this is done!!!!

Thanks everyone for the encouragement and tips!

[rikkards]

Glad to hear you resolved it.
They say you don't learn from thing you do right. 

WOW....I FIXED IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 

I accidently had two wrong resistors in....lol

I had a 100k in for a 100 ohm and a 220k in for a 220 ohm

It hit me at like 2:30. Long story short....i finally noticed the schematic said 220...not 220 k. Then I looked around for others with no k and saw a 100. Realized i had put a 100k in for that too. Well.....alls swell. Spent forever doing this, but its done. Now I got to go to bed. I got to wake up in 4 and 1/2 hours and go to work...but at least this is done!!!!

Thanks everyone for the encouragement and tips!

[Sir_Ian]

thanks...one last minor debug.

I have a lil noise, but no more noise then when in bypass or when the guitar is plugged straight into the lil amp. However. When the tone knob is at like 4 or 5 o'clock (almost max to max) I suddenly get more noise. Its the only knob I have this problem with. And it ain't major. But I was curious as to what the culprit is. My guess is that since i'm boosting the really high frequencies that the static is a really high frequency and it gets boosted. If so....oh well. But I was just curious if there were any suggestions, etc. gracias