Express and Liverpool Volume Pots

[bcmatt]

How high do you run your volume pot to get the gain you want? Is there a specific point you never really go over?

I use VVR on my Liverpool and Express, so I will have to experiment to see how it alters at full voltage, but I notice that I never push the gain over about 12 0'clock on either amp. But then, if I don't plan to do the typical TW clean to mean and want to use a pedal board in front, I am trying to dial in a very touchy position of around 8-9 o'clock.

Has anyone played around with different values of pots in the volume position?

I haven't removed and measured the actual (Bournes 1MA) pots in my amps yet, but comparing the key positions on another 1MA pot and measuring them... that typical 12 o'clock position is only about 150K into the 1M pot, and the lesser position I struggle to dial in is maybe only 30K or so.

I'm tempted to try either an audio (CTS) or linear (PEC) 250k pot in series with a 750k (or so) resister on the wiper (correction: leg coming from the previous stage). I guess the bright caps would have to connect to the other end of the resister too. Theoretically, this should leave the circuit unhindered electronically, just giving more sweep range within the values I actually use. I suppose what could work against me is perhaps that the taper of the 1MA pot somehow makes dialing in the right values easier...

So, anyone have any experimenting done in this area? Or, does anyone use a certain brand of 1MA pot that gives them an ideal taper?

I also considered playing with 500K pots with a 470K resister...

[RJ Guitars]

I recall reading something by GeetarPicker once where IIRC, the volume pot at 4 to 5 (on a scale of 10) was a sweet spot for him. I can't actually recall the exact scenario but I took this to heart and I began to tweak everything else around this setting and now I kinda like it. Now this is pretty stinking loud so the tone is good but the volume is too much so then you are looking at some sort of power regulation... I've never measured what the actual resistance is but in my case I generally have either CTS or Alpha 1MA pots on most of my High Gain Wrecks. Hope this is helpful...

[bcmatt]

Thanks RJ. Ya, I remember reading Glen's advice about the gain being about halfway up in order to get that versatility with the guitar pots... and it does work great. So I do that sometimes.

The other times I want to find something closer to "just the edge of breakup" when the guitar volume is maxed... so that it can better be used with a whole pedalboard in front of the amp. I find the amp sounds great for this too, but that spot is much harder to dial it in and finding a lower gain first preamp tube only slightly helps. I'm thinking I will do some experimenting with this tomorrow on my day off.

I'll start with the Liverpool and put a 5751 in V1, and figure out the max gain I may want and then measure what that pot position value is at.

[JazzGuitarGimp]

I'm pretty sure you want to place the 750k resistor in the clockwise leg of the pot, not the wiper. With a 250k pot, this will load the previous stage to the same 1M value.

[andresound]

I think this scenario seems to be an EXPRESS thing. Last week I found a NOS old Clarastat 1M pot that measured 80k at 50% rotation. Helped a shit load. Having said that, when using the VVR, amp still comes on quick, especially with HB's. I am on the look out for a NOS 5751 to help matters.

[bcmatt]

I'm pretty sure you want to place the 750k resistor in the clockwise leg of the pot, not the wiper. With a 250k pot, this will load the previous stage to the same 1M value.

Yes, good catch. I think you are right. Thanks.

[Roe]

I'm using a 500k alpha pot in series with a resistor. I rarely turn above midway, although I may add a little extra gain with a strat

[geetarpicker]

Glen here! I mostly run my Express amps at 12-1pm, though sometimes a little higher. This is with 12AX7s in all 3 positions. Still Ken used pots that came on quite slowly, heck my '85 Express actually has a noticeable gain difference between 3/4 and full up. My '89 uses different pots that are a little thouchier but still calmer then most clones with modern day "audio taper" pots. I believe you need volume pots that are no more than 10% resistance at 12pm, and I know for a fact the volume pot on my '85 is even less than 10% at mid rotation. This makes for a much more user friendly response from the controls. The concept of putting in resistors or a 2nd volume pot in series to give you more control sounds like it might be a nice and effective work around.

[bcmatt]

Well, I did it to the Express today. I used at CTS 250KA pot (that only measured around 230K total. Then (because whose ever heard of having 750K resisters in their collection?) I used 3x 470K resisters (2 in parallel and then 1 more in series). I put them between the treble pot and the volume pot. Then the wire that I had going between the bright switch and the volume pot got moved to the treble pot as well.

Anyways, it actually seemed to work quite well, astonishingly. I do suspect it slightly changed the results of the bright switch settings because my total simulated pot value went from about 1.1M to about 920K.
But the main thing is that I have a wide variety of tones between clean and crunch, with the typical "trainwreck clean to mean" spot being pretty much at 80-100% on the new knob. I tested with a Strat, and I was pleased with the saturation level still available. However, this was down at my more typical VVR settings. I do know things tend to clean up a bit more at full plate voltage, so we will see how this plays out in the coming weeks and if I will keep it or have to move to a 500K pot.

I think for the Liverpool I will go ahead and try a 500K pot... I hope to get to it this evening....

[bcmatt]

So, just to update, the 250K pot gave a a fantastic ease of use to dialling in those clean tones, but I felt that it wasn't quite giving me availability of saturation I may want...it's very close, but diming the control seems to hint I may want the option of more. So I did swap to a 500K pot for both amps. That has seemed to work quite well, and they are both much easier to dial in something that sounds full and rich but still clean.

My 500K pots I had seemed a little less than ideal for soldering to and I figure the taper could still be improved... so I've now ordered some Gibson Historic Guitar Pots that I'm curious to see how they would work out... I hope the taper is the right way...

[bcmatt]

My Gibson Historic 500K pots (one measure 504K and the other 506K) arrived at my local L&M and I picked them up today. I installed them in my volume positions on my Express and Liverpool this evening.

I don't think they actually made a huge improvement over the previous 500kA pots I had in there aside from them seeming more durable and better built. My other ones were random ones out of my used parts bin that weren.
I do think the taper is smoother and more predictable now. 9 o'clock on both amps is sort of that spot that remains clean with the guitar volume up and they both hit that clean to mean sweet spot right at about 1:30-2:00 if riding guitar volumes. that's with the VVR set somewhere around 30% Voltage so they are both about the same volume. I imagine I would have to dial up a bit higher if running at full voltage.

So, would I recommend everyone needs to get Gibson Historic pots for their Express and LP? Not necessarily. I like them and they have been the best for me so far... but if someone has found great reasonably priced 1MA pots that have that perfect taper like Ken's, that's awesome. I think just going to 500KA is going to make things a lot easier to dial in than most 1MA pots.
I just find these Gibson Historics are actually some of the easier pots to order (free shipping) to my local (Major Canadian) guitar store (Long & McQuade) and only cost about $11 Canadian. No Canadian with humbuckers should have anything else in their guitar in my opinion.