ggg ts808

[Devius]

So I built this a while ago and it sounds great. Unfortunately with the volume full cw it sits at unity gain. Is this common?

[rockhorst]

Nope. Read the debug thread, follow those guidelines and post your measurements. Somebody will be able to help.

[Kesh]

Depends what you're inputting.  If you are inputting half a volt peak you'll probably get that out whatever you twiddle.

[Devius]

Okie Dokie, here goes...

I built the ts808 tube screamer. Vero layout by sabrotone http://www.sabrotone.com/wp-content/uploads/2011/10/TubeScreamer.gif
Based on the GGG schematic. http://www.generalguitargadgets.com/pdf/ggg_its8_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

Voltages are as follows.
IC1 4558cn
1 4.41
2 4.43
3 4.41
4 0
5 4.41
6 4.41
7 4.41
8 8.89

Q1 2n4401
e 3.01
b 3.51
c 8.89

Q2 2n4401
e 3.02
b 3.47
c 8.89

Both diode voltages are 4.41 as well. I used 4148s instead of 914s. When I initially built this the volume was very low, I found adding another 4148 in series with the first diode gave me unity gain. I used mono ceramic caps for c2 and c8 instead of non polar. Aside from that everything is the same. I referenced the info sheet from ggg and the ic v's jive and the q's are only a half volt off. Quite perplexing.

[Kesh]

if it sounds fine but too quiet, then perhaps check resistor values are correct? check for shorts? (shorts in some places may just cause a volume drop)

[Devius]

Could the bi polar caps be the issue?

[Kesh]

Voltages look fine.

Did you check resistor values? Particularly R8, R16, R17, R18, R20 and R21 (pots), R15, R13. (That's numbering from the ggg schematic.) It's an easy mistake to make.

And you haven't said what you are inputting into it.

The normal sub for bipolars is film caps, but it shouldn't cause a big volume loss to use ceramics.

[Devius]

I double-checked all the resistors with a dmm. Everything is good, caps seem to be the right values. Took a magnifying glass to the solderside (which I usually do, then hit it up with the dremel with the brush attachment just to make sure) and I couldn't see any bridges.

In terms of input you mean guitars? Jackson dinky with dunc invader, ssl4 and a hotrails. Same result with my gibson explorer (stock p/u). Same with my dean (dunc livewires) and ltd (emgs).

[J0K3RX]

Remove all of the clipping diodes and see if the volume comes up... should get loud(er)  While you have them out maybe think about sticking sockets in there so you can experiment with different diodes without de-soldering every time...

[Kesh]

I double-checked all the resistors with a dmm. Everything is good, caps seem to be the right values. Took a magnifying glass to the solderside (which I usually do, then hit it up with the dremel with the brush attachment just to make sure) and I couldn't see any bridges.

In terms of input you mean guitars? Jackson dinky with dunc invader, ssl4 and a hotrails. Same result with my gibson explorer (stock p/u). Same with my dean (dunc livewires) and ltd (emgs).

Those are pretty hot/active pups. The TS otput is limited by the diodes. It gives out about half a volt for single silicons (as the tone stack etc. takes a little bit off) around double that with two in series each way. This is probably about the same as hot active pups, so I would expect no gain.

I'm guessing your TS is working correctly. Use your amp's volume if you want loud.

Or (and this is what I'd do) get an infra red LED with forward voltage about 1.2 and a red LED with forward voltage about 1.8, and replace your 1n4148s with those.

[Devius]

Cool beans. I'll swap diodes and see what works.
Thanks for the help fellas.