SI transistors in a tonebender

[scotheath]

Sorry if this is a dumb question but having trouble with a tonebender build. I'm putting together a TB on a PCB and have socketed the transistors and using 2n3904 and can't get more than farty noises out of it. The question I have is they recommend hfe for Q1, Q2 and Q3 when using germanium transistor's but is that still the case when using SI transistors? I can get it to bias to the correct voltages but no sound unless strum real hard and it sounds farty and fades out real quick.

[Zerro]

There are more versions of "tonebender", which one do you have? Any schematics? Generally try with audioprobe track signal from very start. Biassing resistors in basis of first transistor. Try to fiddle about resistor basis-ground. Change values.

[benny_profane]

Can you link the schematic you're using? You can easily make an Si tonebender, although you'll have to do some slight modifications to simulate leakage so that it can be properly biased.

[scotheath]

I've attached a screen shot of schematic, its a Tayda board and I didn't mention I am doing an NPN version. I have electrolytic caps reversed as per instructions on site
Still curious about the hfe values. If building SI version is measuring the hfe needed for each position?
https://www.taydakits.com/instructions/tone-bender/pages/designators-and-components--35

[Zerro]

First transistor hasn't bias from plus pole to basis! I would put here cca 680-820k resistor. Set with this resistor cca Ub/2 at collector of Q1. That's for a start.

[benny_profane]

I've also had good results with a 470k resistor from Q1 collector to base.

[Zerro]

That's I wanted to attach now :@(  Another version.

[scotheath]

First transistor hasn't bias from plus pole to basis! I would put here cca 680-820k resistor. Set with this resistor cca Ub/2 at collector of Q1. That's for a start.

Sorry I'm not sure what Hb/2 is.
I think what you're saying is run a 680-820k resistor between collector and base of Q1 ??

[Zerro]

Ub/2 is one half of power supply. Sorry not to be clear. Picture in first post is one solution, and another picture Tonebender III is another. Try both of them and you will see what you get. Both of them will work. Here is another kind of bias setting:

http://www.hawestv.com/transistorize/germanium1.htm

All will work with proper resistors, you must find. Use trimmer and try to set cca 4,5V at collector of Q1 (for 9V power.) Then substitute with resistor with closest value.

[scotheath]

Ub/2 is one half of power supply. Sorry not to be clear. Picture in first post is one solution, and another picture Tonebender III is another. Try both of them and you will see what you get. Both of them will work. Here is another kind of bias setting:

http://www.hawestv.com/transistorize/germanium1.htm

All will work with proper resistors, you must find. Use trimmer and try to set cca 4,5V at collector of Q1 (for 9V power.) Then substitute with resistor with closest value.

That is great, thank you for the help, and now I know what Ub/2 means. I will save link and read through when I have time.
I guess that Tayda build doc should be updated for when people use SI transistors. I can't be the only 1 that has had troubles

[Zerro]

That link will help. Some tips:

[scotheath]

Thanks for all the help. 400k is the resistance I needed to bring collector of Q1 to 4.5v. Don't have that so I ran a 330k + 62k in series and tacked onto the back of the board. sitting at 4.32v on collector of Q1 now and now have a useable circuit !!
new issue the 1kb fuzz pot does very little in the way of changing the amount of fuzz, is the 1kb the wrong value here or maybe change it out. its already attached to the board or i would just try something else

[benny_profane]

Thanks for all the help. 400k is the resistance I needed to bring collector of Q1 to 4.5v. Don't have that so I ran a 330k + 62k in series and tacked onto the back of the board. sitting at 4.32v on collector of Q1 now and now have a useable circuit !!
new issue the 1kb fuzz pot does very little in the way of changing the amount of fuzz, is the 1kb the wrong value here or maybe change it out. its already attached to the board or i would just try something else

Glad you've got it working! B1K is indeed the correct pot; however, it's not a terribly useful control since the distribution of the sweep does not allow for much nuance. If you wanted to change it so that it is more useful (and not just 'not really fuzzy' and 'fuzzy'), try subbing a C1K pot instead.

[Zerro]

Great work! Now only tuning: Try biasing Q2 and especially Q3 too. But now set that 4,5 or better 4,8 V only at Q3 collector. Trimmer Q3 bias try at half setting, and play with Q2 bias trimmer - gating. (In tonebender III that I attached you can see even another resitors around Q2 and Q3. You can try them in your device.)

For a better fun I attached schemas of Suck fuzz - improved Tonebender, where you can play with many settings at breadbord. One for npn and one for pnp transistors. You can rebuild that your machine in to a Hell of fuzz :@)

[scotheath]

Great work! Now only tuning: Try biasing Q2 and especially Q3 too. But now set that 4,5 or better 4,8 V only at Q3 collector. Trimmer Q3 bias try at half setting, and play with Q2 bias trimmer - gating. (In tonebender III that I attached you can see even another resitors around Q2 and Q3. You can try them in your device.)

For a better fun I attached schemas of Suck fuzz - improved Tonebender, where you can play with many settings at breadbord. One for npn and one for pnp transistors. You can rebuild that your machine in to a Hell of fuzz :@)
Confused again. I've got Q2 biased at 1.23v per tayda instructions and Q3 is at 4.51v. Are you saying to bias Q2 to 4.5v as well ?