What's up with C7 on the 2012 Snarkdoodle?

[mgwhit]

Right now I'm thinking about leaving the gain pot as it is, and changing the volume for a 100k, as I like the ridiculous amount of gain. Shame I'll have to de-solder the pot, so proud of how I got the whole deal in there...

To be fair, I have no idea if the A100K Volume pot is actually lowering any volume (although that, C5 and the audio-taper Gain pot are the only changes I have from stock Red Llama values).

I hate desoldering, too, so if you'd like I can compare my current A100K Volume pot with an A25K I've got and then I can tell you which knob position gets me unity gain for each pot.  Also, let's compare voltages on our IC's.  I think I've got 9.5V at the jack and about 5.95V on pin 1.  I'll have to double check, though.

[mgwhit]

Okay, I ran some quick tests.  Most Gain settings that I found usable required a Volume setting somewhere around 10 o'clock.  The lightest Gain setting I found useful (with audio-taper) was just past 9 o'clock and required an 11 o'clock Volume setting.  Gain maxed required a Volume setting of about 9 o'clock.

My pin-outs are a little different since I breadboarded and it was easier to get at the inverters on the right side of the chip, but the basics are like so:

Jack: 9.51V
Pin 1: 5.55V
Pin 8: 0V
Every grounded input pin: 0V
Every unused output pin: 5.54V
Every used input pin: 2.45V
Every used output pin: 2.45V

Hope that helps.

[oldhousescott]

Your voltages look off. Pin 8 (and hence every unused output pin) should have close to 9v. Pins 2, 3, 4, and 5 should have about half that, I would guess. What is your value of R7?

[mgwhit]

Your voltages look off. Pin 8 (and hence every unused output pin) should have close to 9v. Pins 2, 3, 4, and 5 should have about half that, I would guess. What is your value of R7?

You've written "Pin 8", but I think you mean Pin 1.  Pin 8 is grounded...we've been over that! 

I'll have to recheck R7.  I'll admit that I didn't measure it before I threw it in my breadboard, but I distinctly remember clipping it out of a lot labeled 1K, though.  Maybe this is why I'm the only one getting tolerable volume from this circuit!

Edit: R7 = 984R, Brown-Black-Red-Gold carbon film.

[oldhousescott]

Woops, yes pin 1. And, I see now that R7 is 1k in the RL. Odd. 4ma of quiescent current will drop Vcc by 4 volts. With 4 gates grounded, I suppose it could be drawing 4ma. Maybe they do that to get a lower threshold of clipping against the PS rails.

[DutchMF]

I'll try to get some voltages, but I'm cramming for exams (may seventh, so they're approaching fast!) and only have some time to browse the forum now and then....

Paul