Importance of pot quality in Lar-Mar master volume?

Info for maintaining and tweaking your amp to perfection.

Moderator: VelvetGeorge

Post Reply
shakti
Senior Member
Posts: 2005
Joined: Tue Apr 05, 2005 9:06 am
Just the numbers in order: 7
Location: Ramnes, Norway

Importance of pot quality in Lar-Mar master volume?

Post by shakti » Sun Oct 07, 2018 12:41 pm

I've tried to search but the Lar-Mar thread is so long I can't really find a definitive answer.

I have only built one amp with a Lar-Mar master volume and used a dual Alpha pot I had. I found out that I actually liked the master volume a lot in that amp, so I'm thinking about adding it to one or two of my other builds for practical purposes. But I am wondering if it makes a significant difference to use PEC pots insted? I know George is a big fan of the PEC dual pots for his master volumes, but IIRC he is using a different type of PPI master volume, is that right? With the Lar-Mar, does it make any sense to buy the much more expensive PEC type? The rest of the pots in these particular amps are Alpha FWIW.

I will try a zero-loss FX loop in these same amps, but that shouldn't have a bearing on my choice, I would assume?
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

User avatar
toner
Senior Member
Posts: 2580
Joined: Sun Dec 03, 2006 7:57 pm
Location: Iowa

Re: Importance of pot quality in Lar-Mar master volume?

Post by toner » Sun Oct 07, 2018 6:36 pm

I doubt it's worth getting a PEC. I have an Alpha (or whatever Metro used to sell) that has worked fine for 11 years of regular use.

danman
Senior Member
Posts: 765
Joined: Tue Sep 10, 2013 9:09 pm
Just the numbers in order: 13492

Re: Importance of pot quality in Lar-Mar master volume?

Post by danman » Sun Oct 07, 2018 7:19 pm

No difference in tone that I have been able to hear. The PEC pot does have a smoother taper, especially on the lower end of the range. Readings between both halves are also much closer on the PEC. Alphas can be quite a bit apart.

shakti
Senior Member
Posts: 2005
Joined: Tue Apr 05, 2005 9:06 am
Just the numbers in order: 7
Location: Ramnes, Norway

Re: Importance of pot quality in Lar-Mar master volume?

Post by shakti » Mon Oct 08, 2018 11:32 am

Thanks guys! I think for my uses (typically keeping it at around the halfway point or a little higher) the Alphas will do the job just fine.
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

User avatar
neikeel
Senior Member
Posts: 7063
Joined: Tue Dec 06, 2005 8:31 am
Location: Suffolk, England

Re: Importance of pot quality in Lar-Mar master volume?

Post by neikeel » Tue Oct 09, 2018 4:56 am

I found a fair amount of variability in the Alphas at different knob settings (I had cause to experiment as I had one pot that was faulty and the MV did not work). As a consequence I have not been fitting PPIMVs recently (just using attenuators) but then most have been restorations as time permits.
Might have to try a PEC some time. CTS do a nice Clarostat type dual pot too.
Neil

Roe
Senior Member
Posts: 5018
Joined: Thu Apr 13, 2006 1:36 pm
Just the numbers in order: 7
Location: Drontheim. Norwegen
Contact:

Re: Importance of pot quality in Lar-Mar master volume?

Post by Roe » Fri Oct 12, 2018 3:41 pm

some dual pots are too unbalanced/assymetric to be usable. One pot reads 220k, the other 270k and the taper also differs
http://www.myspace.com/20bonesband" onclick="window.open(this.href);return false;
http://www.myspace.com/prostitutes" onclick="window.open(this.href);return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

Post Reply