Tube Screamer with different transistors

[JebemMajke]

I've never built tube screamer before, I've sold my soul to the fuzz world. For years I have ignored the TS circuit, and now guys from my band are eager to play some SRV ... well it's pretty much mandatory to have TS 808. I've been looking at the tonepad schematic, also at this SRV special ts http://www.lynx.bc.ca/~jc/srvSpecialMatsumin.gif .

Is there going to be any difference in the sound if I use bc 108's, or bc 109's as q1 and q2? Should i use trimpots to bias collector voltages? And if the answer is yes how many volts?

[Pyr0]

The transistors don't really make much difference, the input buffer is configured for unity gain so Hfe of the transistor won't really come into it.
I would use the BC109's as they have a slightly lower noise level then the BC108's.
You shouldn't have to use trimmers for biasing them either.

[J0K3RX]

I use 2N5088's and I notice a little difference... maybe psychological but hey, whatever

[Kesh]

Use the lowest noise transistor you have to hand for the input buffer, as it's going to get about 100x gain soon after and any hiss will be amplified. I used a MPSA18, but 2n5088 or 2n5089 are the standard. The output buffer is less important, but use the same for ease. Actually I'm half convinced the MPSA18 and the 2n5089 are the same transistor.

The transistors are just emitter followers, and need no bias fiddling. You can't really do anything anyway, the bases are biased from the 4.5V line and you don't want to change that as the op-amps need it, even though 5V might be better. The collector should be to 9V for max emitter swing.

[FiveseveN]

Are you planning to use electronic bypass? If not, just skip the buffers altogether.

[Kesh]

Some people believe the buffers, particularly the impedance character of the output one, give part of the "mojo".

[boogietone]

Everything you want to know about the TS: http://www.geofex.com/Article_Folders/TStech/tsxfram.htm.

[J0K3RX]

Everything you want to know about the TS: http://www.geofex.com/Article_Folders/TStech/tsxfram.htm.

And another..
http://www.beavisaudio.com/projects/ScreamerLab/

[Kesh]

http://www.beavisaudio.com/projects/ScreamerLab/

I built a similar screamer lab to that, not quite so elaborate, but every diode switch was two pole, so switching in and out a diode also changed the level so the two choices of diode gave equal volume (as far as was possible). That way you aren't fooled into thinking louder equals better.

OP, I'd also recommend trying the CA3260 op amp as well as the ones listed, though, to be honest, I didn't find op-amp choice made much difference.

A 1Meg gain control like in the SRV is a good mod so it can go up to 11 (it's a log taper, so 1Meg isn't really a big change from 500k). The SRV using 4.5V (labelled "bias") on the volume control and then not using the coupling cap/bias resistor there seems a good idea, but not such a good idea to leave out the coupling cap and bias resistor after the input buffer.

[JebemMajke]

Well I've asked about transistors because I have plenty of bc series ( ranging from 108 to 550 ) and I'm not eager to order 2n3904 or any other. I was only worried about the hiss or noise from q1 and q2. That's why I've asked about the bias. Thanks, I will read geofex and beavis articles.

[roseblood11]

What's the best choice for a low-noise transistor to replace the 2sc1815 in a vintage TS-808 that is in mint condition? It should have the same pinout, because you eat with your eyes first.

Where the pinout doesn't matter, I use 2n5089 or bc549...

[Kesh]

2n3704, 2n5249