help me nurse my homemade rat

[challengerdeep]

I've got a homebrew rat I'm working on. I do pretty well with amplifiers, but my pedal work and study can be pretty shoddy. Unlike a tube, I don't have a clear idea of what each of the pinout voltages and outputs should be. Nevertheless I've got this little number running a 1v sine and it delivers me almost half a volt of output.

lm308 voltages
1 - 8.7v
2 - .8 to 2.7 depending on distortion pot
3 - .8 to 2.7
4 - 0 gnd
5 - no reading
6 - 4.1
7 - 9.2
8 - 4.7

2n5458 voltages
s - 3.2v
d - 9.2
g - a couple mV


I didn't realise I was building the compact layout untill it was too late.

[DRodriguez]

Just first look, clean up your soldering a bit. There may be some solder joining tracks. For vero, less solder and tiny leads can be hugely helpful.

[crochambeau]

Measuring the AC voltage of your signal in relation to the actives will give you better idea of where your signal is dropping off.

Shining light through the circuit board is a nice start to visual examination.

[challengerdeep]

I check over traces and cuts for continuity, but there have been no blaring mistakes.

I've got this on the Goldstar. One volt of 1k sine on the input. I see a 2v triangle out of the lm308 then it drops back to 1/2 volt at the diodes. The output appears similar.

[multi_s]

hmm well its not that unreasonable maybe. the output will never be greater than +/- the voltage drop of the diodes used. There is no amplification after the diodes in the circuit shown. Did you use germanium diodes? or schottky perhaps? if they were 1n914s i would expect a bit more at teh output of that stage +/- .6V or so. BUt can you confirm teh scale on your scope? maybe it is already working correctly....

[crochambeau]

Agreed, the level drop looks like diode loss.

Those end curves look soft, does your tone control do anything?

How does this sound with something more complex than sine?

[challengerdeep]

Nope, I just grabbed some beefy 1n4007 rectifier diodes. I'll have to go through and see if I have something suitable on hand.

I don't see any amplification from Q1. After calibrating old Gold I've got a stubby .4 vac


Tone and volume work swimmingly, but gain is suspect.

I've honestly never done this and it's badass.

[multi_s]

what is teh setting on your oscilloscope for that picture? if it is .5 V per vertical bar i would say the circuit is already working properly.

[Dr Satan]

There won't be any amplification by the transistor as it's just a follower aka buffer. Opamp works similar to NFB on an amp in that the less signal you have fed back, the more gain you have. Opamp has to have some feedback to work though. I'd suspect your diode choice to be the culprit. If you have a couple of LEDs, those work really well for a less compressed sound and much higher output volume.

[challengerdeep]

I had to swap the distortion pot. The linear taper was unusable.

All about the diodes fellas. I hooked this up to a breadboard and taste tested about every LED and diode I have on hand. I love the look of some of the lights, but the fast zeners won out on sound.

I'll put in an order for a wider variety of diodes and experiment with the clipping on another build. This rat board is ready to jam.