50w Plexi mods

[Greg_L]

I'd like to get to a point where an amp is just a pile of parts to me - like cars. I don't see cars as a Toyota this or a Ford that. I just see nuts and bolts. They're all the same to me when it comes time to fix one. Each brand has it's own nuances, but ultimately cars are just a pile of parts stuck together with nuts and bolts. They essentially all work the same way. If I could get to a point where I can view amps like that, I think I could be in a position to actually charge people money for it. I'm not anywhere near that yet.

My buddy with the Jubilee also has a JVM. He wants me to put a choke in it. The JVM is like astrophysics compared to a Plexi, but I'm gonna try it anyway. He bought two chokes, one for him and one for me. If we like the choke in his JVM, I can put the other one in mine. Seems like a good little experiment. We both get chokes and I get to try my hand at something like that. Should be pretty easy.

[Bubba]

I'd like to get to a point where an amp is just a pile of parts to me - like cars. I don't see cars as a Toyota this or a Ford that. I just see nuts and bolts. They're all the same to me when it comes time to fix one. Each brand has it's own nuances, but ultimately cars are just a pile of parts stuck together with nuts and bolts. They essentially all work the same way. If I could get to a point where I can view amps like that, I think I could be in a position to actually charge people money for it. I'm not anywhere near that yet.

My buddy with the Jubilee also has a JVM. He wants me to put a choke in it. The JVM is like astrophysics compared to a Plexi, but I'm gonna try it anyway. He bought two chokes, one for him and one for me. If we like the choke in his JVM, I can put the other one in mine. Seems like a good little experiment. We both get chokes and I get to try my hand at something like that. Should be pretty easy.

I was just saying to JD the other day that I can see you winding up as a builder/tech. Now then, what's the choke meant to do?

[JD01]

I hope you're better with a soldering iron than me.

[Greg_L]

I was just saying to JD the other day that I can see you winding up as a builder/tech. Now then, what's the choke meant to do?

A choke helps with the power supply filtering. Here's how I understand it: The shit that comes in from the wall is AC - a sine wave. Positive and negative swinging voltage. The shit in the power supply side of the amp needs to be DC - a straight steady supply of voltage. No ripples. An amp uses rectifiers, solid state or tube, to either cut off the negative swing of AC, or flip it back positive so you get something resembling the straight line of + DC voltage. But it's not perfect. It's better but it still ripples. So then you introduce filter capacitors which help straighten out those ripples by blocking out low frequency and store up reserve power for when you bang a chord hard and starve the power supply. In between these filter caps are usually dropping resistors spec'd to supply the tube plates and whatnot an exact supply of DC voltage. A choke can be inserted in place or in series with one of those dropping resistors to give further smoothing of the power supply. Where the filter caps straighten ripples and block low subsonic frequencies from being a problem, the choke does the same but in reverse. Since it's basically a 1:1 inductor it strongly resists current change (ripple) and acts as a low pass filter. The filter caps block lows and smooth the power supply, the choke blocks highs and smooths the power supply. Any voltage fluctuation at the plate of a tube can impart itself into the guitar signal as noise, so any smoothing of the power supply is a good thing. And what's noisier than a JVM? Nothing. So after all that hopefully the JVM will be quieter, which will allow better use of it's massive gain potential, and it should smooth out the sound and feel of the amp in general. Hopefully.

[WhiskeyJack]

Way to much science in here, i'm gonna see myself out. . .


nerdzzzzzzzzzzzzzzzzzzzzzzzzzz

[Greg_L]

Way to much science in here, i'm gonna see myself out. . .


nerdzzzzzzzzzzzzzzzzzzzzzzzzzz

Yeah, there's that, or you could learn this stuff too and never have to send your own amps out to get fixed ever again!

[WhiskeyJack]

Way to much science in here, i'm gonna see myself out. . .


nerdzzzzzzzzzzzzzzzzzzzzzzzzzz

Yeah, there's that, or you could learn this stuff too and never have to send your own amps out to get fixed ever again!

I overloaded my head yesterday with a whole bunch of stuff and then your last post actually fractured my brain. I have to tap out for a day or two. your point is noted and couldn't agree more.

[Bubba]

I was just saying to JD the other day that I can see you winding up as a builder/tech. Now then, what's the choke meant to do?

A choke helps with the power supply filtering. Here's how I understand it: The shit that comes in from the wall is AC - a sine wave. Positive and negative swinging voltage. The shit in the power supply side of the amp needs to be DC - a straight steady supply of voltage. No ripples. An amp uses rectifiers, solid state or tube, to either cut off the negative swing of AC, or flip it back positive so you get something resembling the straight line of + DC voltage. But it's not perfect. It's better but it still ripples. So then you introduce filter capacitors which help straighten out those ripples by blocking out low frequency and store up reserve power for when you bang a chord hard and starve the power supply. In between these filter caps are usually dropping resistors spec'd to supply the tube plates and whatnot an exact supply of DC voltage. A choke can be inserted in place or in series with one of those dropping resistors to give further smoothing of the power supply. Where the filter caps straighten ripples and block low subsonic frequencies from being a problem, the choke does the same but in reverse. Since it's basically a 1:1 inductor it strongly resists current change (ripple) and acts as a low pass filter. The filter caps block lows and smooth the power supply, the choke blocks highs and smooths the power supply. Any voltage fluctuation at the plate of a tube can impart itself into the guitar signal as noise, so any smoothing of the power supply is a good thing. And what's noisier than a JVM? Nothing. So after all that hopefully the JVM will be quieter, which will allow better use of it's massive gain potential, and it should smooth out the sound and feel of the amp in general. Hopefully.

I see. No, really - I do, in principle. By 1:1 inductor, I presume you mean it's like a pair of transformer coils that don't change the voltage -same number of turns? So they only respond to any residual AC noise in the DC supply and suppress it?

[Bubba]

But hang on - coil pairs aren't physically connected, so there must be a direct line for the D.C. current as well?

[Greg_L]

I see. No, really - I do, in principle. By 1:1 inductor, I presume you mean it's like a pair of transformer coils that don't change the voltage -same number of turns? So they only respond to any residual AC noise in the DC supply and suppress it?

Yup, pretty much. It's kind of like a transformer that doesn't transform up or down. We're not changing voltages or current. Signal just passes through but get straightened out while it's in there.

Some amps have chokes, some don't. I'm not sure yet how or why a designer would choose to implement a choke, but it seems to me like any amp could benefit from having one. All of my favorite amps come with chokes. Maybe the choke is part of the magic sound of certain amps, but I don't know. I'm thinking they're probably a band-aid for a noisy power rail more often than not. Chokes seem to be most common on old-school amps with less capacitor filtering. If it helps with the noise on a JVM, then that's a good thing. If it "softens" the stiff attack of a JVM, that could be good too. If it does nothing, well then lesson learned. It seems though that most people that have added chokes to amps that don't have them like the change.

[Greg_L]

But hang on - coil pairs aren't physically connected, so there must be a direct line for the D.C. current as well?

It's one wire that coils around iron like one half of a transformer.

[Bubba]

But hang on - coil pairs aren't physically connected, so there must be a direct line for the D.C. current as well?

It's one wire that coils around iron like one half of a transformer.

I get you, now - I've seen simple ones in a lot of devices. Often it's just a toroid with one of the conductors wrapped around it?

[Greg_L]

I get you, now - I've seen simple ones in a lot of devices. Often it's just a toroid with one of the conductors wrapped around it?

Yup, it can be. It is literally like one half of a transformer. It's basically a wire coiled around an iron core. The models for amps even look like a little transformer.

This is the one we'll be using:

[rayc]

Ouch. My brain learnt about Bitcoin, Blockchains & Cryptocurrency last night so isn't capable of cogitating this kind of information this morning.
It's interesting that achieving the desired squishy sound of a great break up through pre and power amp tubes is done by smoothing the power supply in various stages, while nuancing and learning from the shortcuts and gap filling of earlier production techniques.
Throwing a Variac into the mix - does the "sag" make those nuances redundant?

[Greg_L]

Ouch. My brain learnt about Bitcoin, Blockchains & Cryptocurrency last night so isn't capable of cogitating this kind of information this morning.
It's interesting that achieving the desired squishy sound of a great break up through pre and power amp tubes is done by smoothing the power supply in various stages, while nuancing and learning from the shortcuts and gap filling of earlier production techniques.
Throwing a Variac into the mix - does the "sag" make those nuances redundant?

To a point, a Variac can potentially create even more "sag" and squishiness. EVH is famous for dropping the voltage going into his old Plexi, and some of those amps were already relatively low voltage and low filtering anyway. They "sag" naturally, and he exacerbated the sag by dropping voltage even more. That's how he got that squeaky grindy saggy squish to his sound. But if you go too low weird things can start happening and probably sound really bad...if it works at all. Supposedly EVH only dropped his incoming voltage to around 90 volts on a 110v amp. That sag happens when you use up the available voltage on the plates with that first hit of a note. The caps basically store extra power to quickly replenish the juice going to the tubes when you deplete them quickly. If the amp is being starved and the caps are small values as well, you can get a crazy squish out of it. That's how I understand it anyway.

I'm not sure how a choke is going to effect any of that. Some people say they sag the amp down a little, some say it stays tight because the voltage is smooth and regulated. Just thinking about it, I can see it going either way. I'm just gonna have to try it and see. JVMs have a tendency to be hissy and can squeal at the crazy high gain settings. If it helps with noise and high end weirdness, I'm all for it.

[JD01]

Interesting (and a bit complicated) got me thinking though...

Marshalls have historically been made in the UK where we have 240V AC coming out of the wall. In the US you have 110C AC? Is that right? They'll have to have differing transformers to deal with this. Do UK and US Marshalls sound different? Can you easily move amps between countries?

[Bubba]

Interesting (and a bit complicated) got me thinking though...

Marshalls have historically been made in the UK where we have 240V AC coming out of the wall. In the US you have 110C AC? Is that right? They'll have to have differing transformers to deal with this. Do UK and US Marshalls sound different? Can you easily move amps between countries?

You can buy a step-up/step down transformer that plugs into the wall, I believe.

[Bubba]

I get you, now - I've seen simple ones in a lot of devices. Often it's just a toroid with one of the conductors wrapped around it?

Yup, it can be. It is literally like one half of a transformer. It's basically a wire coiled around an iron core. The models for amps even look like a little transformer.

This is the one we'll be using:

That's cute.

[Greg_L]

Interesting (and a bit complicated) got me thinking though...

Marshalls have historically been made in the UK where we have 240V AC coming out of the wall. In the US you have 110C AC? Is that right? They'll have to have differing transformers to deal with this. Do UK and US Marshalls sound different? Can you easily move amps between countries?

Modern Marshall power transformers are switchable for either wall voltage. For older amps you'd need to change the transformer or use a step up/down transformer between the amp and wall. Some power transformers have the wiring for either voltage, but often the wires you don't need are capped off inside the amp so you'd need to get in there and move some wires around. US/UK amps don't sound different because of wall power. Any amp is gonna be rectified and the voltage will be dropped to appropriate levels so the tubes see the voltages they need. The first preamp tube doesn't know if it's in the USA or UK.

[Greg_L]

Man this amp fucking kills now. I've been playing the shit out of it. It's fantastic. Good job Greg!