Bizarre tone stack in Marshall 4104 combo

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1/6/2001 12:09 AM

Bob S II

Bizarre tone stack in Marshall 4104 combo I just picked up a 1982 Marshall 4104 combo, which is essentially a 2204 in a 2x12 cab. Of course, the first thing I did was pull the chassis. The electronics look fairly unmolested, but the tone stack is the strangest arrangement I've ever seen. Both the mid and bass pots have a free, unattached leg, and the mid pot has a 4n7(4700pf?)between the wiper and terminal 3, which is grounded. This all looks dead stock.         Any of this ring a bell with anyone? I can't find it documented anywhere.         Thanks,         =Bob

 

1/6/2001 12:15 AM
Don Symes	The free legs are at one end, right?         This is a rheostat hookup instead of the voltage divider (all three legs) hookup you're used to.         This is pretty common, often drawn as a resistor with an arrow through it - more often as a pot with one leg no connected.         HTH!

 

1/6/2001 12:54 AM

Bob S II

quote: "This is a rheostat hookup instead of the voltage divider (all three legs) hookup you're used to."         Thanks Don. What I'm trying to determine now is whether this configuration is typical of the Marshall combos of this era, or if this is a one or two year thing. I really like the sound of this arrangement, moreso than my 2204 head - I've just never seen it before in any of the Marshall schematics out there.         =Bob

 

1/6/2001 9:18 AM

Dai Hirokawa

I'm pretty sure it's stock. I have what was originally an '83 4010 (1X12 combo version of a 2204--I'm the second owner and I know for sure that the first guy was never inside the amp), and I don't recall if the mid pot was hooked up that way, but can w/absolute certainty say that there was a a 5000pF cap from the mid pot wiper to ground (an Erie-brand ceramic disc cap). The bass pot hookup is the same as in (prob. all?) Marshalls w/similar designs(variable resistor instead of potentiometer). The other thing that was different was that instead of the 4.7k on the presence pot, there was a 10k. I can't recall where, but there is a factory schematic of a 4010 on the 'net somewhere that shows the cap on the mid pot. There is also a spot for a cap there on the PCBs in the later pot-mounted PCB models, which seems to be more evidence that Marshall did this in some amps. In terms of Marshall history, though, I wonder when this first showed up? Using a cap there adds more mids, I think.         Dai Hirokawa

 

1/6/2001 12:39 AM
Bob S II	my attempt at a drawing " target="_blank">http://websights1.com/stack.gif">

 

1/6/2001 4:23 AM
Don Symes	That actually looks pretty normal.         Compare that with the plexi preamp schematic in the Ampage schematic pile. You could also look at         http://www.obsoleteelectronics.com         HTH!

 

1/6/2001 6:53 PM

Glen H.

maybe that explains... I have a 2204 and 4104 , made in '83/'84, and noticed that, in the 4104, the tone controls have much more of an effect on the volume of the amplifier. When the bass/mid/treble controls are rolled to "0", there is little to no volume even with the volume cranked, but on my 2204, this does not seem to make much of a difference. I like the arrangement on the 4104 better because it is more flexible, however both amps are very nice sounding, and I'll probably keep them until I'm old & gray (possibly very deaf too!).         I bought the 4104 new (for about $900 CDN) in '84 and this was my first "real" amplifier. I sold it in '93 (for $650) and found it in pawn shop 5 years later (scored it for $300!!! haha!). OTOH, my 2204 was just too good a deal to pass up. Some metal-head kid just had to get a JCM 900...         Glen H

 

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