Metropoulos Forum

Ok, so while I'm waiting on a 100k pot to arrive so I can add in a variable NFB control, I have come up with a few ideas for some simple switches to put on the rear panel of my 1959RI. If you guys out there with a boat load more knowledge and experience than I have are able to see any improvements then don't hesitate to make suggestions..

SW1 - VOL1 treble cap switchable from no cap, to 1000pf, to 5000pf. (I already have this switch in lower normal channel input, I want to put that input back in place and move the switch to the rear. I've had no cap, to 500pf to 5000pf on that switch for some time but I prefer the 5000pf or no cap at all.. So I figured I'd try 1000pf this time)

SW2 - V1A cathode bypass cap switchable from 25uf to 10uf.

SW2 - V2A cathode bypass cap switchable from .68uf to no cap.

Currently the preamp is a 2k7/.68 with 2n2 coupler on V1B with a 100pf bright cap on VOL2 - 1k5/330uf with 22n coupler and switched bright caps on VOL1. I have 470k mixers, 470pf bypass on the lead channel mixer. I have a 47k slope resistor, 470pf treble cap. I got some RFT ECC83's in V1 and V2, Sovtek ECC83 long plate in V3. Power valves are Shuguang EL34B's, biased kinda hot. Lar/Mar PPIMV - hence the variable NFB control which I am hoping I will be able to tighten things up a bit.

I'm looking for a bit of versatility; my band is pretty heavy garage rock I suppose. I play a Gibson Firebird and use heavy fuzz (Fuzz Face, Muff and Univox Superfuzz) as well as clean-ish delay and chorus in the front end. I always plug in to the top bright channel and jump to the top normal channel.. to blend in a decent amount of normal channel.

I also play a Strat a lot, so while I think the switches will allow me to dial out a little of the woof for 'buckered fuzz, I can still plug my Strat in and get that beautiful richness of a 1959 on the edge with single coils without having to take it all apart. Thoughts?

You could try a 56k/250pf tonestack with .1 output coupling caps. Should work good with a strat.

I find stock circuit great with Strat.

I've tried many things and always went back to stock.

Here is my 79 Strat straight into my '71 Super Lead. Not well played , but the sound is good
https://soundcloud.com/josecarbia/blues

sickman82 wrote:
SW1 - VOL1 treble cap switchable from no cap, to 1000pf, to 5000pf. (I already have this switch in lower normal channel input, I want to put that input back in place and move the switch to the rear. I've had no cap, to 500pf to 5000pf on that switch for some time but I prefer the 5000pf or no cap at all.. So I figured I'd try 1000pf this time)

Good idea - very similar to what Bogner used as Pre-EQ switch in the Xstasy.

sickman82 wrote: SW2 - V1A cathode bypass cap switchable from 25uf to 10uf.

Not worth doing IMHO. The tonal effects will be minimal, unless you switch to a much lower value, say 2.2uf.

sickman82 wrote:SW2 - V2A cathode bypass cap switchable from .68uf to no cap.

Not something I would want on my amp since I usually prefer one option much over the other but why not.

sickman82 wrote: Lar/Mar PPIMV - hence the variable NFB control which I am hoping I will be able to tighten things up a bit.

You need to be aware of the fact that the further you turn down the PPIMV the less negative feedback you get. At some point there will no longer be a sufficient signal in the NFB loop to correct the input signal - that Is when the feedback loop will collapse and behave like it is not there. At that point the variable NFB control will also no longer work.

Cheers Stephan

Cheers for the replies guys.

The bright cap switch is great.. Particularly when you have guitars with very different timbres.

I did wonder if there would be a discernible difference with 10-25uf.. I'll go with 2.2-25uf as suggested. I had decided on leaving out the V2 cathode cap switch since putting this thread up.. I like variation and options, but I think the two switches I have is enough.

Re the variable NFB.. I am aware that the negative feedback will be out the circuit with low volume use, but it was more an idea to dial NFB in at rehearsal and live situations where the MV is up past 1 o'clock. So we'll see I guess.. I'm hoping it will give decent results for that application.

Ok, so I decided to go with a spdt on-off-on switch with some nice Vishay electro's.. 3.3uf on the centre pin, then 6.8uf and 22uf either side in parallel with the 3.3uf depending on the position to give a decent range.