Debate on Eddie's Plexi

[leadguy]

Could be anything. A small change in the 470k 470pf (500pf) treble peaking circuit but I don't know how much this John Suhr bass mod affects the tone whatever it is, because Ed is treble and mid city on most of VH1 and the low end is not dominant at all.

[motrock]

Just to give you an example... here are 2 clips of a Plexi that John Suhr worked on:

http://www.youtube.com/watch?v=3dmx5MNUtXk" onclick="window.open(this.href);return false;
http://www.youtube.com/watch?v=PLOvYA6ipMQ" onclick="window.open(this.href);return false;

And here is the one that Dave Friedman did for me:

http://www.netmusicians.org/files/94-DaveVariplex.mp3" onclick="window.open(this.href);return false;

Dave and John do the same thing to get the EVH tone. I would listen to those guys! Dave has done all kinds of work for me, and he's got me as close as I think I can get!

[fivecoyote]

Awesome! Can't believe I missed that thread. Thanks for the tip -- and the hour gone out of my day!

[Good Guest]

Yes he did say the .68 uf was on the cathode follower

is a very minor addition that Jose did giving it a slight bit more bass in the treble channel

This is the one that bugs me a little... the supposed pic of ed's amp and the 5153 schematic show a small first stage output coupler (a blue 750 pf to a 1000 pf), this would restrict bass in the first channel. Of course we never were sure what those pics were really of...

I think the reason for the 750pf is to emulate the effects ( mxr 6 band ) he normally used before his plexi to make that @1khz tone shine thru...but yeah in the supposed real Eddie preamp pic that cap looks to be something in that range also , perhaps a .001uf .

Now were being led to believe NO he added bass in the treble channel....

A 330pf across the 470k treble peaker ups the treble also and some players get a pretty good vh tone with that one mod and a cascade , so I'm having a hard time swallowing the stock plexi with increased bass in the treble ...doesn't make sense. Especially now that there saying NO 330uf fat cap on the cathode follower which does add bass and gain.... Even the 2203 mod with the .1 paralelling the 10k increases bass but that's a cascaded circuit also.

The white knob could be anything ...there was a push button half power switch mod that Jose used to do that was in one ebay vh marshall...it could be a line out for preamp slaving....it could be a master volume mod... it could be an interstage volume control ..or it could be a way to dial a cap in and out of a circuit and tune it just right.....(.68uf in series with a resistor or paralell) ...that would make a good experiment..as that sems to be key spot before the tone stack to shape tone. But that would affect both channels not just the treble channel.

If it were etched in stone that a single mod to the treble channel for more bass, the magic mod would be exposed so who knows ..with big bucks in the VH tone business to be had all bets are out the window...maybe there is too much competition out there now.People are buying modded plexi's instead of 5153's ...who knows.

[dazzlindino]

Just to give you an example... here are 2 clips of a Plexi that John Suhr worked on:

http://www.youtube.com/watch?v=3dmx5MNUtXk" onclick="window.open(this.href);return false;
http://www.youtube.com/watch?v=PLOvYA6ipMQ" onclick="window.open(this.href);return false;

And here is the one that Dave Friedman did for me:

http://www.netmusicians.org/files/94-DaveVariplex.mp3" onclick="window.open(this.href);return false;

Dave and John do the same thing to get the EVH tone. I would listen to those guys! Dave has done all kinds of work for me, and he's got me as close as I think I can get!

Cool Vids, and excellent playing on those youtube snippets.....would have a good time seeing you guys live.....

Now back to the VH amp thingy.....
So,to start more controversy......

After trying countless pickups as well as making hundreds of them, all trying to get the classic VH tone...it cannot be stressed enough, the eq of the pickups role in that ulta mid range snarl.....as well as the output smacking the front of the amp, along with a gh-10 / mxr 6 bander.....along with an ep-3....green backs.....
Trying to get it all from the amp is virtually impossible.....if you dont start right you cannot finnish right......
Just sayin' ......

I have tried all sorts of amps, amp mods, dis dat and the other.....
So how was that...tring to hijack a thread?

[Good Guest]

True the plexi is just 1 piece and pickups are a part no doubt especially now that there saying the humbucker had a broken coil in the bridge part so only the neck part worked as a single coil.

You got to admit vh1 does have a single coilish quality too it. Makes me think about the tone Jimi got with his upside down slant of his single coil. It does make a differance.

[dazzlindino]

True the plexi is just 1 piece and pickups are a part no doubt especially now that there saying the humbucker had a broken coil in the bridge part so only the neck part worked as a single coil.

You got to admit vh1 does have a single coilish quality too it. Makes me think about the tone Jimi got with his upside down slant of his single coil. It does make a differance.

This broken coil thing......emm...ya it probably happened once..then that pickup got rewound to his specs.....
If you cant believe what he says about the amp, why are you gonna believe what he says about a pickup?
The single coil tone quality...like I said....the eq of the pickup is absolutely essential.....
try this.....the first d cord in RWTD.....is your g and b strings just as prominent as your d?
I think not.............and that is the missing ingredient.......listening to the recording it is almost as if he is playing
solely on the g and b ( eq wise ) strings, however that is not thick enough, and absolutely needs the d sting, but then, that f ups the eq because that wound string takes over the frequency and masks the brightness / tightness
..... now , will it go round in circles....like a bird up in the sky...I hi......

[dirtycooter]

First off-"its the gear page".

Its not the same as this forum here where everyone is and has gone through every thing and any thing possible for the VH tone alone.

I think I would head toward Rockstah for his "Mod 5" and call it good-not that Dave and John are not great in their own right.

But you simply cannot deny the clips-its all in the clips-the mod 5 Rockstah treatment is "it" in my book and that is not meant to bash anyone elses work or amps.

I have heard some small fender amps pushed balls out wide open get the vibe and similar gain yet they are no more gainier than plexi's.

[leadguy]

"untouched except for filter caps and 1 added part which I prefer to keep to myself (Dave knows it well of course too). It is a very minor addition that Jose did giving it a slight bit more bass in the treble channel"

"It also makes less difference than you think when the amp is dimmed. "

Maybe the capacitor across the volume pot. That's what I'm going for anyway because as the volume pot is dimed the capacitor across the volume pot has less effect but as the volume is turned down it starts having more of an effect.


The 680n .68uf mid boosting capacitor and Ed setting the tonestack etc all on 10 matter to what frequencies are being maxed and gain perception depends partly on what frequencies are being maxed.

[dirtycooter]

[quote="leadguy
The 680n .68uf mid boosting capacitor and Ed setting the tonestack etc all on 10 matter to what frequencies are being maxed and gain perception depends partly on what frequencies are being maxed.[/quote]

I agree-when people do the 10 Band EQ stuff-it only adds gain to those specific frequencies that are boosted-and we all know only a few of them are really boosted while others are left completely alone or even removed somewhat. So the additional gain is not all over the entire frequency spectrum-just where it counts.

[leadguy]

http://forum.metroamp.com/viewtopic.php ... 45#p315945" onclick="window.open(this.href);return false;

[Good Guest]

2 really interesting things leadguy....a 820 ohm/.68 uf instead of the 2.7k/.68uf in the treble channel cathode could be responsibe for the xtra bass in the treble channel and would also give it more gain than the typical plexi 2.7k version.

Second interesting thing is the 556 pf treble cap in the tone stack, but that will affect both channels that would boost the mid to upper mids especially that crucial @1khz vh frequency by a 1.5 db compared to the normal 470pf - 500pf plexi tone cap.

Between the 2 of them would make a really mid boosting higher than normal gain plexi with lots of balls for sure. Someone has to try this and see.

[leadguy]

The circuit is interesting.

The 820ohms cathode resistor with a .68uf is a bigger mid boost and then the other .68uf is also a mid boost and with the treble peaking 470k/470pf that is a double whammy mid boost and a treble boost.

The mids are where all the gain is going on with this circuit.

I think the bass mod is understandable with this circuit and might be the treble peaking cap being altered or something else like the cap across the volume pot being altered or a couplng cap maybe because from the John Suhr bits I've come across the cathode resistors and caps are the original values and the more bass mod is only a small mod.

ie

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

If a cathode resistor/capacitor combo is taken from the below gain rolloff frequency chart and compared to the guitars open string frequencies it's easy to see at what frequencies the gain is going to and the 820 ohm cathode resistor produces more gain than say a 2.7k cathode resistor with a 100k plate resistor.



Guitar frequency for each string in Hz

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

=============================================

From one of my other posts about cathode resistor/capacitors.

http://www.aikenamps.com/GainCalculations.html" onclick="window.open(this.href);return false;

http://www.aikenamps.com/CommonCathode.htm" onclick="window.open(this.href);return false;

12ax7

load resistor = 100K

cathode resistor = 1.5K

Real cathode resistance of tube and cathode resistor is 777 ohms because the tubes cathode impedance is in parallel with the cathode resistor.

The actual -3dB point for this gain stage with a 0.1uF cathode bypass cap is:

f = 1/(2*PI*R*C)
= 1/(2*PI*777*0.1uF)
= 2.05kHz

0.1uf = 0.0000001

Note that the actual cathode resistance value of 777 ohms (as calculated previously) was used instead of the 1.5K cathode resistor value that is commonly (and mistakenly) used.


For a .68uf capacitor

f = 1/(2*PI*R*C)
= 1/(2*PI*777*0.68uF)
= 301Hz

0.68uf = 0.00000068

For a 10uf capacitor

f = 1/(2*PI*R*C)
= 1/(2*PI*777*10uF)
= 20.5Hz

10uf = 0.000010



In this graph the frequency gain gets reduced around 2.05kHz for a 0.1uF cathode bypass cap

For a 0.68uf cathode bypass cap the frequency gain gets reduced around 301Hz

For a 10uf cathode bypass cap the frequency gain gets reduced around 20.5Hz

[Good Guest]

Great research leadguy . Looking at the 12ax7 data sheet there would be actually less gain from the triode with the low cathode resistor but as the gain is now in the mids and highs instead of being wasted in the lows it would definetly cut thru more.…which is really good for a treble boost and tightening up of the tone, especially with the treble peaking cap…provided the lows are added later in the circuit.

There are a few places to add some lows in the treble channel…coupling cap (.0047)….a grid stopper resistor change....instead of 470k maybe it's a higher value…maybe a snubber resistor on the cathode follower plate resistor.Probably wouldn't affect the bass channel but surely the treble one. That would be unconventional in the plexi but I notice Jose uses them quite a bit.

The whole mixer section affects both channels ..it could be something related to where they cross that affects the treble channel. Regardless , that circuit seems to follow the recipe for a high gain amp which is treble first add lows later.

The frequency graph coincidently seems to match the frequency response you see in many of vh1 guitars spectrum analysis where the lows seem to disappear and a nice flat response follows.

Failing all this I guess there are pics around of the suhr and freidman amps so we can cheat

[leadguy]

Maybe this small more bass mod was done just after VH1 because Ed's opinion of VH1 was that it was a bit too bright and if he was using this circuit, I can understand why. Might explain why VHII is a bit different as well.