Random Number Generator - Bad Gain Problem

[niggez]

I found an old thread about this neat thing called the Random Number Generator (By "DD").
I made a vero layout from the schematic:

which looks like this:


So i built it, and its amazing. BUT theres incredible gain. I tried switching volume pot to lower values, but this makes the tone extremely thin. (I had to lower it to an 800 R to get ANY control)
Is there a problem in my vero? (Its the first one ive ever made)
I didnt have the specified transistors so i used

2n3904 in Q1 and 2n2222 in Q2.

I biased Q1 to optimize the effect.

So whats wrong?   

[birt]

did you use a Log pot?

it is supposed to be very loud

[niggez]

Ok, so let me rephrase "very loud"
I had my Amp below 1 when trying it, hardly noticable volume when playing clean. If i turn the 100k (Linear) Pot more than half a milimeter im close to needing ear protection.
If it was only a log/lin problem, i doubt it would be THIS loud..hm...any other ideas?
Maybe biasing the other transistors lower?
Does anyone have "optimum" readings for those transistor voltages? Il lcheck mine.

[birt]

use a log pot.

[niggez]

ok ill try it out...one second

[niggez]

No its not the pot. I put on a 100k log pot and its absolutely NO difference!

its driving me crazy

aaaah...the pain...must...finish..build..aaaah.......

I remeasured most of the components used to build it, and found the 2.2 M Resistor to be 2.4 M. Although I dont think thats going to solve my problem...

[niggez]

Transistor Voltages are as follows:
          C         B      E

Q1:   0.89   0.63      0

Q2:   0.4     0.54      0

Q3:   0.72   0.59      0

Q4:   2.19   0.72      0

[Dragonfly]

Not sure on the volume, though you could try a 100k resistor to ground right before the volume pot...

Anyway, here's another vero layout...

[niggez]

Did you add a 1M resistor from input to ground? what does this do?

[Dragonfly]

Did you add a 1M resistor thats not in the original schematic? The one from input to ground?

yep....pulldown resistor...I also added power supply filtering (47u cap)

[niggez]

Pulldown resistor to avoid popping? I dont have any of that, but ill keep it in mind for later, both of the components...
Still chewing on the gain! Hm.....
Ill try adding a bias pot to Q4 next, since its voltage is much higher compared to the others.

[Dragonfly]

Pulldown resistor to avoid popping? I dont have any of that, but ill keep it in mind for later, both of the components...
Still chewing on the gain! Hm.....
Ill try adding a bias pot to Q4 next, since its voltage is much higher compared to the others.

Did you try the 100k to ground that I suggested ?

Also, you could try putting a resistor "inline" with the output on it...

[niggez]

I soldered the resistor in but will test it tomorrow. its late here in germany and some folks are sleeping...
Too bad im the only one who found out how to live without it 
Will also try the resistor in line -> output. Ive got a few variable resistors lying around that will be perfect for experimenting.

[Dragonfly]

I soldered the resistor in but will test it tomorrow. its late here in germany and some folks are sleeping...
Too bad im the only one who found out how to live without it 
Will also try the resistor in line -> output. Ive got a few variable resistors lying around that will be perfect for experimenting.

remember...if the inline resistor cuts too much high end, you can always parallel a small value (100-470pf) cap with it, so high end still gets through....

[niggez]

Hey...tried the inline, tried the 100k to ground before output. They both seem to work at least somewhat, buth now my modulating has stopped. I removed them...still nothing...i must have touched something wrong, because now its just a sharp fuzz. So im hunting for that right now...

I just dont get it...I cant get it back to the first working state, when it was only too loud, but doing what it was supposed to be doing. Now its just a harsh fuzz, nothing else.

[niggez]

I added a trimmer across the 100k feedback resistor, and across R1 (47k). Now i can adjust the fuzz to be really great sounding.
but what happened to the modulation? Its still gone... great silicon fuzz though...driving me crazy

Is there a part of the circuit that is primarily important for the modulation type sounds?

[niggez]

Im sick of this vero thing. Its the only vero i ever made and its not working.

So i decided to rebuild the whole thing as pcb if i dont get it working by the weekend... Im starting to think it might be a transistor problem tha tthe modulation just wont kick in.

The pcb includes the diode mod suggested by DD. Does anyone see errors on first glance?

[dxm1]

Does anyone see errors on first glance?

Well... If you're using standard TO-92 packages for the trannies, you have the leads reversed. The way you have them on your layout, with the flat side facing left, the emitters are on top...

[niggez]

Ok, i didnt really pay attention to that, as i was goin to check the pinouts when it was time to populate the board. Ill fix it in my next revision.
Any chance someone could give me transistor voltages?
My current readings are

       Emitter  Base  Collector
Q1     0         0.61     2.8
Q2     0         0.54     0.55
Q3     0         0.55     0.67
Q4     0         0.67     1.71


I replaced the 100k feedback resistor with 47k just to see if it would change anything, but im still only getting fuzz, no modulation.

[birt]

The pcb includes the diode mod suggested by DD.

DD?