ruby amp mod, gain pot question

remmelt · September 26, 2004, 12:10:04 PM

before i go out and buy one... with the RDV mod on the ruby amp, do i need a 50K reverse taper log pot?

i have a regular log 50K and a linear 50K and i like the clean that gives me over the 1K pot. i don't like the way it stays clean all the way around the pot-cycle and then all of a sudden starts overdriving in the last bit.

i didn't notice this in the "stock" 1K pot. that one's also linear, but doesn't really have that final boost... why not?

thanks!

Peter Snowberg · September 26, 2004, 01:06:42 PM

If you look at the 386 datasheet (google), it shows that the gain pot is in parallel with a 1.35K resistor. Using a 1K pot here will cause the gain to be increased by a fair amount even with the pot turned all the way down. A 50K pot on the other hand will have very little effect until it starts to get close to the resistor value it's bridging.

I would suggest trying a 5K pot in there to give a better range over the rotation. I would also suggest adding a 10uF cap in series with the pot to keep the DC voltage correct for the 386 input stage.

B Tremblay · September 26, 2004, 01:11:40 PM

The 50k pot is used for the Volume control, not the Gain. The 1k Gain pot can be left as-is or connect pins 1 and 8 with a jumper (that's what Ricky did).

Peter Snowberg · September 26, 2004, 01:29:20 PM

Anyone have a link to Ricky's schematic?

B Tremblay · September 26, 2004, 02:27:13 PM

There's separate no schematic that I know of, just his notes that I added to the Ruby article.

http://runoffgroove.com/ruby.html

RDV · September 26, 2004, 02:42:33 PM

:|

remmelt · September 26, 2004, 02:52:14 PM

HO! my bad. i misread that as gainpot! hmm.

i actualy like having the higher value pot in the gain position. it goes cleaner than the standard 1K. the output is still high enough for me. the pot value needs tweaking though.

i like the versatility of the gain pot over a jumper.

i'm now going to try the 50K volume pot.

(RDV: your picture doesn't work!)

RDV · September 26, 2004, 02:55:43 PM

It would sound better with an MPF 102, I just didn't have any. A 2N5457 might be a good sub, I was looking 4 as much clean headroom as possible 4 a more amp-like response. It worked pretty well, but I still like more treble, which I guess is why I love that English Channel. Anything 2 make me sound more like The Edge!

RDV

RDV · September 26, 2004, 02:57:04 PM

Quote from: remmelt(RDV: your picture doesn't work!)

Keep trying. Photobucket is on and off today.

RDV

RDV · September 26, 2004, 02:59:21 PM

RDV

RDV · September 26, 2004, 03:11:04 PM

I also ended up putting a .0022uF across the volume control to fight treble loss, .001 might even be good.

RDV

petemoore · September 27, 2004, 12:37:20 PM

A 10uf can go across pins 1 and 8...forget what schematic I saw that on that uses a 386, but I have one 'dangling' off the perfbaord so I can push it to pin 8 [my idea of a cheeeeep switch]...this increases gain also, maybe a pot between 1 and 8 in addition to the cap would give more variability, or just the pot...maybe someone knows the 'equation' but you can see what it does pretty easy, I started by just bending the leads j'just right and 'poking [draping?] them between the OA pins for initial tests.
I find I like my 386's pretty clean, and use 'pre-distortion' ...internal distortion of a Fuzz or whatever before the amp.

petemoore · September 27, 2004, 12:38:38 PM

Quote from: RDVIt would sound better with an MPF 102, I just didn't have any. A 2N5457 might be a good sub, I was looking 4 as much clean headroom as possible 4 a more amp-like response. It worked pretty well, but I still like more treble, which I guess is why I love that English Channel. Anything 2 make me sound more like The Edge!

RDV

>>>I concur...the English Channel works 'swimmingly' for bright boosted TONE !!!

Steben · September 27, 2004, 03:57:09 PM

Quote from: petemoore
Quote from: RDVIt would sound better with an MPF 102, I just didn't have any. A 2N5457 might be a good sub, I was looking 4 as much clean headroom as possible 4 a more amp-like response. It worked pretty well, but I still like more treble, which I guess is why I love that English Channel. Anything 2 make me sound more like The Edge!

RDV
>>>I concur...the English Channel works 'swimmingly' for bright boosted TONE !!!

RDV and petemoore:
Why not using a treble booster than?
First thing I'll do when I get my 386 amp running...

RDV · September 27, 2004, 04:15:51 PM

Quote from: StebenRDV and petemoore:
Why not using a treble booster than?
First thing I'll do when I get my 386 amp running...

As for me:
Treble boosters boost treble by cutting bass, then boosting what's left. I hate that. I want the full pie, plus more treble. I get that with the EC.

RDV

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ruby amp mod, gain pot question