Debate on Eddie's Plexi

[rgorke]

This:

330u or 250u/820 - .68u/820 split cathode
.0022u bright channel coupling cap
.68u/820 v2a

[StuntDouble]

...

[bob barcus]

Yeah, it looks like a 330uf capacitor across V2's 820 ohm cathode resistor.
When it was added, who knows?

The 820 ohm resistor/.68uf capacitor combo on V1 starts rolling off the bass at around 431 Hz and the 820 ohm resistor/330uf capacitor combo on V2 starts rolling off the bass at 10 Hz or less and has all frequency gain including bass gain.

The 820 ohm resistor/.68uf capacitor combo on V1 starts rolling off the bass around the 5th fret on the 1st string and the 820 ohm resistor/330uf capacitor combo on V2 starts rolling off the bass below the low E string so there is a lot more bass in this circuit.

So the 820 ohm resistor/.68uf capacitor combo on V1 gives a mids/upper mids boost and the 820 ohm resistor/330uf capacitor combo on V2 gives a more bass boost. So there is a fair amount of bass in this circuit.

The original 820 ohm resistor/.68uf capacitor combo on V1 and 820 ohm resistor/.68uf capacitor combo on V2 gives a double mids/upper mids boost with the bass rolloff starting around the 5th fret on the 1st string for both V1 and V2, producing much more mids/upper mids and not a lot of bass. FWIW, this .68uf capacitor on V2 is closer to VH1 IMO and the 330uf capacitor on V2 would be closer to later Ed.

Guitar open string frequencies

E - 82.4
A - 110
D - 146.8
G - 196
B - 246.9
E - 329.6

A 5th fret on 1st string - 440
E 12th fret on 1st string - 659.2

Looks alot like the 93 SLP100W ri.

[leadguy]

Looks alot like the 93 SLP100W ri.

Yes it does.

1959SLP Super Lead (2nd) Plexi Re-issue, 100W head
Introduced in 1993.

http://www.drtube.com/schematics/marshall/1959sprm.gif" onclick="window.open(this.href);return false;

http://www.drtube.com/schematics/marshall/1959spwm.gif" onclick="window.open(this.href);return false;

[RACKSYSTEMS]

You guys are trying to get your amp to sound like the recorded tone. Well just to let you know a lot of eqing was done after the fact in mixing. Your chasing a ghost. If you are trying to do this there are many variables like the resistors you are using in the B+ line and in the circuit. The caps you are using is a huge thing. The .68 with the 470uf on v2 together sound different then just a 470uf. Just the makeup of the 2 kinds of caps changes the sound. Then lets look at wire yes that to sounds different from kind to kind { radically actually}. Then we have the tubes. You must have the real 6ca7s so they can hold up to the cooking bias. Etc etc etc. Oh wait what about the vintage celestions 25s begging for mercy. Oh then the brand of variac changes the sound also. Oh feedback resistor and what tap it was on in the amp. Huh look there also. Have fun

[bob barcus]

You guys are trying to get your amp to sound like the recorded tone. Well just to let you know a lot of eqing was done after the fact in mixing. Your chasing a ghost. If you are trying to do this there are many variables like the resistors you are using in the B+ line and in the circuit. The caps you are using is a huge thing. The .68 with the 470uf on v2 together sound different then just a 470uf. Just the makeup of the 2 kinds of caps changes the sound. Then lets look at wire yes that to sounds different from kind to kind { radically actually}. Then we have the tubes. You must have the real 6ca7s so they can hold up to the cooking bias. Etc etc etc. Oh wait what about the vintage celestions 25s begging for mercy. Oh then the brand of variac changes the sound also. Oh feedback resistor and what tap it was on in the amp. Huh look there also. Have fun

Dave,Whats in your Marsha

[bob barcus]

Looks alot like the 93 SLP100W ri.

Yes it does.

1959SLP Super Lead (2nd) Plexi Re-issue, 100W head
Introduced in 1993.

http://www.drtube.com/schematics/marshall/1959sprm.gif" onclick="window.open(this.href);return false;

http://www.drtube.com/schematics/marshall/1959spwm.gif" onclick="window.open(this.href);return false;

Thats the 2nd RI 1959X made in 1992. The SLP final version was made in early 1993 thats the "good one" The last one has the FX loop and Not as good

[leadguy]

You guys are trying to get your amp to sound like the recorded tone. Well just to let you know a lot of eqing was done after the fact in mixing. Your chasing a ghost. If you are trying to do this there are many variables like the resistors you are using in the B+ line and in the circuit. The caps you are using is a huge thing. The .68 with the 470uf on v2 together sound different then just a 470uf. Just the makeup of the 2 kinds of caps changes the sound. Then lets look at wire yes that to sounds different from kind to kind { radically actually}. Then we have the tubes. You must have the real 6ca7s so they can hold up to the cooking bias. Etc etc etc. Oh wait what about the vintage celestions 25s begging for mercy. Oh then the brand of variac changes the sound also. Oh feedback resistor and what tap it was on in the amp. Huh look there also. Have fun

Yes and more like Sunset Sound etc.

I don't think trying to copy Ed's tone or his playing or any other players for that matter, is very realistic at all. There are too many variables and Ed's already done it.

It is interesting about what gear he did use and basically it was gear that a lot of people used in the 70s and Ed just matched it up his way, but that's as far as my interest goes.

[pfrischmann]

I'm stuck on a couple of things.

Are we sure about the .1's in the PI?
I really like that tone but historically, that is a bass spec. All of the 12 series amps I've seen at amp archives etc...have been .022's. I could never dime the bass with the .1's it was just too much.

I use a .022 as the treble cap. Same reason. To me it looks like all of the 12 series are using a .022 not a .0022. I found .0022's to bright

Are you guys using the 100pf or 47pf fizzy cap?

I think standard for this circuit is 47K for NF and tied to the 8 ohm tap. 4 ohm tap sounds really rough to me. Never tried the 16 ohm tap but I would think you'd lose too much gain.

Man,I love doin this.
If I left it as is...the amp sounds great.

[leadguy]

Where did you get all that from?

I would only take what John Suhr and Dave Friedman say as reliable.

John Suhr says at HC

"The first stage was split cathode Most definitely NO 250pf treble cap, no on the 100pf across the PI plates"

Dave Friedman has said here that there was a slight change in the feedback circuit.

Basically it's these specs and then alter to taste.

It is a bright spec, hence Ed's 2 changes ie fat cap on V2 and the NFB. When he had them done in VH's timeline, well it's up to everyones ears.

Split cathode V1a 250uF/820,V1b .68/820
All coupling caps are 0.022uF,Bright channel coupling cap is 0.0022uF
bright cap on vol pot 0,005uF
470k mixer resistors
470pF mixer bypass cap
Bypass cap on V2a is .68uF
33k/556pF tone stack combo
47k NFB resistor at 4 ohm tap
220k bias splitter resistors
0.1 uF cap on presence control

[pfrischmann]

That's some of the stuff circulating in this thread.
So,
I don't believe there is a250pf cap in the 12 series circuit.
I still haven't found evidence of a .002 cap in a 12 series. 69 spec, yes.
Slight change in the feedback circuit....this means either more or less feedback. 47k would be standard for this circuit...the tap is debatable...4ohm sounds like crap to me. I could see changing this value to tune the amp a bit. My guess would be a little less

[leadguy]

Are you talking about the small blue cap?

I can't see the value, but the small blue cap looks like a different value from the larger .022uf caps and is more than likely to be .0022uf and if the small blue cap was .022uf then I would expect it to look like the .022uf caps.

[pfrischmann]

Gotcha,
I agree, all things being equal, that is probably a .0022 or something smaller than the standard .022.

[vh junkie]

Are you talking about the small blue cap?
I can't see the value, but the small blue cap looks like a different value from the larger .022uf caps and is more than likely to be .0022uf and if the small blue cap was .022uf then I would expect it to look like the .022uf caps.

Good Guest and I kinda agree the blue cap could be as low .001uf(1000pf). It would not be to uncommon to reduce bass early on in the chain, then add it back later. Which brings us to the big brown PI input cap... it certainly larger than the .022uf that was probably there originally... This would be part of adding the bass back in...

You guys are trying to get your amp to sound like the recorded tone. Well just to let you know a lot of eqing was done after the fact in mixing. Your chasing a ghost.

All true... but I am chasing a tone in my head that brings me back to seeing Ed at the Tower in Philly in 1978.

If you are trying to do this there are many variables like the resistors you are using in the B+ line and in the circuit.

Please tell us more! Is it the type of resistors or the the voltages we see at each node? I have been fooling with lower than normal screen and preamp voltages. They give a more VH1 vibe, but lack the grind for VH2 songs like the intro to Beautiful Girls.

The caps you are using is a huge thing. The .68 with the 470uf on v2 together sound different then just a 470uf. Just the makeup of the 2 kinds of caps changes the sound.

This would give you a kind of double hump in the frequency response, right?

Oh then the brand of variac changes the sound also.

Oh! Please don't tell me that! How so?

[Good Guest]

The chocolate cap is a great example of what Dave F. is talking about....That cap variety reacts in a differant way than the later orange drops and the tonal differance is generally agreed upon as real and some say the differance between a white face and black face fender amp.

BUT because it warms up the tone and cuts highs better than identical orange drops of the same value it makes total sense to place that type in a place where you want bass added. Bottom line is values matter but so do the construction of the part itself....like the zozo cap guy pointed out in some write up.....one alternative part (even of the same value) in the entire circuit path can make or break the tone of the entire amp....it's all true.

And it gets worse because of shelf life parts can drift in value up or down...it really takes training to able to tune things up properly.