Ruby Amp Potentiometer Issues

[Zounds!]

I just built a Ruby amp on perfboard and am having an issue with the pots. I get signal and it sounds good, but the gain pot doesn't do much. It adds very little little grit to the sound through its rotation. By mistake I found that if I disconnect the ground on the volume pot, the sound overall is much fuller and richer, with more bass, more volume, and a ton more grit controlled by the gain pot. It sounds really nice with the volume ground lifted, though the volume pot isn't functional that way. Wired up normal it sounds just ok, and with very little overdrive. The only substitution I made was for the gain pot, which is 5KB instead of 1KB. I'm more familiar with volume pots that go between the circuit out and jack, so I'm not really sure what is going on here or how to troubleshoot it. I imagine the sound I like (volume ground lifted) is how the amp is supposed to sound, and the thinner sound is the result of a short somewhere? Any ideas? Having a blast playing it with the ground lifted, though it's way too loud if I turn up the gain at all!

[mth5044]

Always post the schematic you are working from as they aren't necessarily memorized by everyone and there are many iterations of the Ruby floating around.

What value is the volume pot? Care to share a picture of your wiring?

[slashandburn]

Unless I've misunderstood, the gain pot on a Ruby amp goes  across pins 1 and 8 ofthe LM386. Lug three of the pot goes to pin 8, the wiper (lug 2) goes to pin 1.  I think 2.2K is the optimal value , your 5K pot should work fine. Ignore Lug 1 on the pot.


Data sheet also suggest s a 2.2uf polar cap between pin one (lm386) and the wiper of the pot. (Positive side to the chip.) for maximum gain.
I don't understand your volume pot issue, disconnecting the ground makes it work better you say? Post a schematic if you get a chance. The Ruby brought me here and these guys helped me get it working in next to no time.

Is this the schematic you're using? http://www.runoffgroove.com/ruby.html

Only other lm386 tips I can think of off hand are: 1. I've often found myself putting in a much bigger bypass cap on pin 7.(1 to 10uf, polar)   2. Sometimes I've had chips that play nicer if you run the input to the +in and ground the - or vice versa and 3. Watch out for the suffix on your chip (n1 -n4)

I really don't think any of those 3 sound like they're related to your problem but you never know. Good luck with it.

[Zounds!]

Sorry for the lack of schematic! I am indeed using the Runoffgrove one:



I can post a picture of my wiring later today when I'm off work. Thanks!

My volume pot is a 10kB as indicated on the schematic. And yes, the issue is that the sound improves when the ground is disconnected from lug 1 on the volume pot. The volume pot no longer functions when I do this, but the overall tone is much fuller and the range of the gain pot gets much wider and more usable.

[slashandburn]

Maybe I need more coffee, but I think lug 3 of the volume pot should be ground. Again though I don't think this explains your issue, I think it would just function backwards. I'd try swapping the leads on vol. Lugs 1 and 3 all the same.

The gain pot on the lm386 works in reverse to the volume, (no resistance = Max gain. Putting a jumper between pins 1 and 8 has the same effect.   I think that's the case. I've been known to be wrong.

[blackieNYC]

I believe that shorting pins 1 and 8 gives you maximum volume, so zero ohms.  I could confirm, but I just took apart my breadboard yesterday.
   EDIT - I AM WRONG ABOUT THIS. Data sheet - shorting pins 1 and 8 together gives you 20x/26dB gain.  with a pot you can get 200x/46dB of gain
you've got something wrong with your circuit. Take a look at another 386 circuit and see if it sheds some light.  these are distortion pedals, not amps, but they might help.  Might be worth trying another 386?
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/Krank+Distortus+Maximus.jpg.html
http://www.diystompboxes.com/smfforum/index.php?topic=86389.300

[slashandburn]

I got the feeling the problem lies more around the buffer. Specifically around the volume pot. If the gain pot functions properly when the volume ground is lifted.

Zounds, you mentioned being more familiar with volume controls on the output. While it doesn't explain your problem, you could put a <500ohm pot on the output a-la the Little Gem? That's what I've done. It doesn't explain your issue though. 

[Elijah-Baley]

Zounds, you mentioned being more familiar with volume controls on the output. While it doesn't explain your problem, you could put a <500ohm pot on the output a-la the Little Gem? That's what I've done. It doesn't explain your issue though. 

I'm putting a volume pot a-la Little Gem on my Smokey Amp, a 25 Ohm pot, but I can't low the volume to zero. Maybe I should insert a resistor, but I don't know exactly where.

[slashandburn]

A slightly bigger pot might be a better idea, Elijah. 25ohms on the out put might not be enough to silence it. A resistor in series with the pot would rob you of volume at the other end of the pot I think. 1k would work, the first half of the pot rotation likely won't have much effect, you'll find more happens from 12 o'clock onwards. 100ohms works perfectly for me.

[duck_arse]

zounds - for fun, unwire that offensive 10k pot entirely (measure the resistance across all pins while it's out). connect the free end of the 47nF cap directly to pin 2, where the WIPER connection was. then add a 10k fixed resistor from that same point to ground. this will simulate the volume pot, correctly wired, at full volume.

what happens when you do this?

[Elijah-Baley]

A slightly bigger pot might be a better idea, Elijah. 25ohms on the out put might not be enough to silence it. A resistor in series with the pot would rob you of volume at the other end of the pot I think. 1k would work, the first half of the pot rotation likely won't have much effect, you'll find more happens from 12 o'clock onwards. 100ohms works perfectly for me.

Thank you!
Unfortunately I got a 25 Ohm pot, like Little Gem project, and I pay it more than ordinary pot.
I don't want to lose the max volume, of course. Do you think a 47 Ohm or 82 Ohm resistor between board and pot should be work well?

[slashandburn]

Im not even sure I know what I'm talking about anymore. To get Max volume at full pot rotation (on the output) I dont think you don't want a resistor in series there at all. Any resistance there will lower the overall volume somewhat.

I'm taking a stab in the dark here (I don't know the equations or even the basic theory here) but (assuming your volume knob does work, it just doesn't go silent) could the impedance of the speaker come into play in calculating how much resistance is needed here? Hopefully someone else can step in here, Elijah. I'm out of my depth now I think.

[Elijah-Baley]

Thanks slashandburn.
My problem here is I can't get volume to zero, I got the max volume and I can low about half volume, and the sound come out anyway, even with the pot to zero.

The wiring of the pot is:
Lug 1: ground;
Lug 2: Tip Jack Output;
Lug 3: from the output of the board.

I thought I could use a resistor to low the minimun volume to zero or almost, but I don't know how nor where.
My homemade cab has a 8 Ohm 8" speaker.

[slashandburn]

The wiring of the pot is:
Lug 1: ground;
Lug 2: Tip Jack Output;
Lug 3: from the output of the board.

Swap lugs 2 and 3?  My signal goes into the wiper (2) and out of lug 3.

[Fndr8875]

does your breadboard layout look anything like this? It worked for me...

http://hobby-electronix.blogspot.com/2015/08/ruby-amp-on-breadboard.html