Help with volume pot

[goldstache]

I've been fooling around with a 2-12ax7 2-6l6 SS rectified design, and need some ideas on how to add mor control to my volume control.
Here's a picto of the topology:

V1A> volume pot> V1B> fenderesque TS> LTP PI> PP 6l6's
             500K

Should I add a grid stopper into V1B?
Or.......
Voltage divide after or before Volume pot?
(Seems strange to have a fixed voltage divider in series with a variable voltage divider?????
There is currently no bias resistor on grid of V1B, just the volume pot. 
The amp is loud and all clean headroom is gone by a 1/4 turn of the volume.  After that it just gets more saturated.  Would like to see it a little more "turnable". I've tried 1M and it didn't help.  All pots are audio.
Thanks!

[shooter]

try a linear pot, but I think another ax7 would help, outta v1B into a CF then TS, then Vol into a gain-stage feeding the PI.  The 1st pot becomes what I call a gain pot, the 2nd I call vol or drive, anyway, fwiw.

[2deaf]

What if you used a dual-ganged 500K audio pot with one pot between V1A and V1B and with the other pot between the TS and the PI?

[goldstache]

Shooter: Thanks for the tasty suggestion.  And I may experiment with TS placement or CF in there at some point, but I have to punch another hole.  And I think i will just call that another build! 
2deaf:  This is a nice idea, never thought about dual control between stages.  I always use those dual gangs for PPIMV, kinda forgot to think outside the box. 


Honestly though, do you all think grid resistor in front of V1B would help soften the blow.  The more I think about it, the more I lean towards it not helping especially pot taper. 
I think Im gonna try and add a 1M grid leak to V1B and start at 100k for the volume pot and see how it sounds?

[eleventeen]

You haven't exactly characterized what it is you don't like about the vol control. A lot of people like reducing first stage gain, for example, with a 12AY7 or 5751. A 12AT7 can be thrown in as a close approximation. Of course, one can never complain about super easy changes like swapping in a tube. Me: I'd try that before getting more complex. 


I just thought of of this (have never tried it) If your PI tube is a 12AT7, perhaps reducing the gain of that stage by swapping in a 12AU7 might get you closer to what you're trying to do.

[shooter]

I just did what eleventeen suggested on my latest build, wasn't getting enough distortion with a 12AU7 for V1, I liked the sound, but the guitar guys wanted more punch, so AX7 and I'm happy with the drive/vol at 5, they're happy at 8.

[goldstache]

Thanks Eleventeen, I designed it around two 12ax7's.  I did try popping different triodes in there.  5751, 12at7, 12au7, Ecc803, 12ay7.  It reduced my gain of course, and the 12at7 was nice in the PI.  But it has a compression artifact that I really like with the 12ax7's. 


The real problem is that it just gets loud as heck right off the bat.  It really sounds like it's on 4 or 5 when it is on 2.  I mean you have to breathe on the thing just to dial it up to with drums volume. 


I will admit, it is a really low voltage 6L6 design.  My B+ is 250VDC and power tubes are biased at 50ma, just trying something different and found a sound I liked so Im exploring it a bit.  PT is Heyboer rated to 400ma so I think everything is cool.  I am gonna try it with other octals sometime this weekend and see what I think.  But before I build a Head Cab, I gotta sort this volume thing out!
Thanks for the help and inspiration!

[goldstache]

Man it sure is hard to find a Dual Gang 500K pot in Akron, OH at this time of night! 

[goldstache]

Tried the dual gang 500KA

Here's the topology

V1A > volume Gang 1 > v1B > tonestack > volume Gang 2 > input to PI

Really strange results, max volume on both pots renders the amp at bedroom volume.

I was expecting a gradual rise in volume out of the volume control. 
Any insight on why output is so lean.  Back to the drawing board on getting a more useable volume control.

[2deaf]

Really strange results, max volume on both pots renders the amp at bedroom volume.

Dual 500K dimed will get you the full volume you had before as long as everything is hooked up right and everything is functioning properly. 

Attached is a quick scribble of what I meant.

[VMS]

My suggestions for your original circuit:

-Remove V1b cathode bypass capacitor.

Try the amp and if there is still too much gain then try this:

V1a>cap>series resistor 470k> vol pot 500k>V1b.....

[goldstache]

Thanks for the effort to clarify 2deaf!!!

That's how I had it wired exactly. 
It was real quiet till all the way up and it was fuzzy, and just above bedroom level!?????
I checked my connections, but did not re wire!!!
Maybe it was the shielded wire I'm using for volume pot.  The amps controls are wired out of the chassis and mounted to a flat face plate. (Think orange)
That pesky shielded wire could be the cause!!!!

VMS- thanks!  That's an easy enough idea!  I will give it a go.
I don't have it written out pretty yet, but here's some info. 
It's a 6l6 (though I've been trying all the octals I can find) PP
 250v b+
Running near class A ( I think)
No NFB
No cathode bypass caps in pre
Fixed bias
Really liking the amp just want a less touchy volume. 
I will try the dual Gang again. The effect of the volume didn't seem to make sense with my last wiring!
Sounds sweet with KT66's

[sluckey]

Do you have a coupling capacitor between the second volume pot and the grid of the LTP PI?

[goldstache]

Sluckey- I do not.  I have only the Coupling cap after the TS
So I guess I don't have it wired like 2deaf proposed!  My cap is after tonestack headed into Dual gang.  Thats gotta be the problem.


So V1b > TS > Coupling cap (.0047uF) > 500K Volume gang 2 > 2nd Coupling Cap > PI????????
or......
V1b > TS > 500K volume gang 2 > coupling cap (.0047) > PI


Is that what you mean?
THAnks

[sluckey]

V1b > TS > 500K volume gang 2 > coupling cap (.0047) > PI

Yes, that's what I mean. You don't need two coupling caps. That coupling cap on the grid of the PI prevents the volume pot (or the tone pots on the orig circuit) from interfering with the bias voltage on the grid of the LTP PI. It must be in that location for proper operation.

[goldstache]

Eureka!!!!!
Thanks guys.  Makes a lot of sense now!  Definitely did the trick!  All the volume is after 5.  Much more volume friendly with dual Gang. 
That being said, there is still a bit of magic with it wide open going into the PI.  I may benefit from having a pre and post volume set up with different pots.  Or at least put in separate pots to tweak where the voltage divider in front of the PI works best.

Can anyone point me to a resource on Fender TB style tonestacks,  I need to tweak things a bit.  Trying to understand the calculations!
Thanks again!