Preamp Grounding

[Funkalicousgroove]

Ok, Here's the deal.... Since the Stackpole pots used in the Original amps are totally unobtanium, I decided to use conductive plastic Clarostat pots which can't be soldered to. In my conversation with Ken Fischer he stressed the importance of the preamp cathodes grounding to the bus wire in the manner they do, my question is: If you can't solder the buss to the back of the pots, where and how are you guys grounding your preamp cathodes, and are you ending up with quiet good sounding amps with your methods??

[rhinson]

hello, funk i hardly ever use the " solder buss to the backs of the pots" method unless i'm just trying to clone exactly. i do pretty much always use a big piece of buss wire (14 or 16 ga.) about 8-10" long and attach one end to a ground lug over on the far input side of the amp and the other to a single terminal strip (not grounded--just used for support) and attach the grounds for each preamp stage (filter cap, cathode, etc.) together all along the buss---kinda like fender does with the brass grounding plane. i run the wire just a little bit away from the pots in the space between the circuit board and the front of the chassis. i just like doing it this way and have never had any problems with it. this is a good way to do it if you want to keep the same concept as the back of the pots method but can't solder to 'em. anyway, i'm sure you've probably already thought of this but just thought i'd throw it in the mix. rh

[Allynmey]

I almost always use a pot buss bar on my builds and they are extremely quiet. On the other hand I have a few that I did like Rhinson and they turned out quiet. Funk you are correct about the cathodes and the rest of the preamp ground need to go through the buss on this one. It has to do with shortening the ground plane to a minimum in order to keep out unwanted noises and parasitics. Rhinson, did you follow "francesca" exactly? if not you may be fine the way you did your amp. I think it has to do with the way KF setup his layout that required this way of grounding it. Funk, you can solder those PEC pots...it's just a real bitch!

Allynmey

[Custom 100]

I used the Clarostat pots and then daisy-chained the grounds on the pots to a ground tab on the chassis by the presence control. I tied the cathode points together and then ran another wire to the same ground tab. Seems to work fine. The input jack is just grounded to the chassis with its mounting nut/washer. Got the ideas from the komet pics that were posted. Is it the best way? Not sure but it worked on this build.

[rhinson]

hello, allyn i've built a couple of express amps but not exact physical clones in terms of layout---this was before we had the pics. but never fear, i've got one in the works! i did not use either the pot buss or bar buss grounding method on either of these and they both turned out great (i do use a nos ge 5751 or the new eh 5751 gold pin in the first position---these sound killer in here). i always in terms of preamp grounding group the individual stage grounds together then run a single good sized wire from that stage to the final grounding point close to the input side of the amp. what ken does it pretty much like the marshall preamp grounding setup, just shorter pieces of wire. you'll notice also the power/output trannie proximity is like the marshall 45 and 50watters---damn close to each other except rotating the output away from the preamp tubes. anyway, off the subject. personally, i don't understand the fascination with the pec and clarostat pots----i'd be afraid that the amount ot heat needed to solder to them would end up damaging them. i just use cts pots---you can solder to them and they're good quality. if you really want to use the pec/clarostat pot and incorporate the pot (really the front of the chassis) grounding buss, just get some of those big, long ground tabs that double as a star washer for the pots---this way you have your grounding plane and don't have to go to the trouble of soldering to those pots. i've never bought any but i've seen 'em on gear before and i know they're out there. rh