Metropoulos Forum

I know I should know all this by now but it just takes me a bit longer to remember the names. This is a great picture I am going to make it my desk top.

http://forum.metroamp.com/viewtopic.php?t=15719

Yep saw that too.Finally can figure out what you guys are talking about.THanks George!!

Great stuff. It's easy to confuse some of the names, so I think this will help provide a level of consistent terminology.

Thanks a million for posting George.

I been wanting to do that forever. Thanks, G!

You're welcome. Sorry it took so long.

I think we also need a schematic with corresponding component names. Add it to the list.




george

I notice theres no name for that second input cap in the phase inverter. I dont think Ive ever heard anyone refer to that cap by a specific name. Just the second input cap or the .1 cap or whatever.

And probably a cross-reference from your stock Heyboer to MM, Marstran, etc. power and output trannies, too.

That way you won't have to walk some poor slob with Radiospares/Mercury trannies through how to test for the right wire to go "here"... (that poor slob will remain nameless however...).

He he, that's on the list too Jim!

Regarding the .1 in the phase inverter, I've always just thought of that as part of the long tail.
The PI in a Marshall is known as a "long tail" type. Maybe one of the tech types here can explain why. I always assumed it's because of the extra circuitry around the cathodes and grids.

george

Tail capacitor?
NFB Capacitor?

From http://www.aikenamps.com/

The Long-Tail Pair
General
The Marshall/Fender phase inverter is commonly known as a "long-tail pair", or "Schmitt" type phase inverter, or phase splitter (actually, the original Schmitt inverter was a differential pair with a large "tail" resistor; the "standard" guitar amplifier phase inverter is a self-biased version of this circuit that works better with positive-only power supplies and ground-referenced inputs).

Following is a schematic diagram of a typical phase inverter found in some guitar amplifiers:






The basic circuit is commonly known as a "differential amplifier", which means that it amplifies the voltage difference between the two grid inputs. Technically, it is a differential in, differential out amplifier, because it has differential inputs on the two grids as well as differential outputs on the two plates (the two plate signals produce the same voltage signal, but one is inverted, or 180 degrees out of phase, with respect to the other).


It should be noted that there are actually three inputs used in this type of phase splitter. The first input is the obvious one, the left side of C1. The second input (the lower end of C2) is useful as a feedback input, a reverb or effects return input, or as a second channel input. In the circuit shown above, the second input is used as a feedback return input, taking the signal off the junction of the feedback divider.

The third input is not so obvious; it is the lower end of R6. If a signal is input at this point, the phase splitter will produce an output signal on each output that is in phase with the other, rather than 180 degrees out of phase, and also in phase with the signal input at the lower end of R6. This means that if a signal of equal phase is applied to the first input (C1) and the third input (R6), it will subtract from the out of phase output (R2) and add to the in phase output (R1). Likewise, if an equal phase signal is applied to the second input (C2), and the third input (R6), it will subtract from the in phase output and add to the out of phase output (this is because the out of phase output is actually in phase for the signal applied to the second input, C2, and the in phase output is out of phase). This third input is useful for balancing the feedback signal by subtracting from the in phase output and adding to the out of phase output in order to compensate the unequal gains to each output from the feedback input. The gain is much less than the gain into the first and second inputs.

The two outputs provide (nearly) identical signals, except for a 180 degree phase difference between them. This is exactly the type of signal needed to drive a push-pull amplifier, so this circuit is commonly seen in higher-power guitar amplifiers

RE: http://forum.metroamp.com/viewtopic.php?t=15719


Yes! George,
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^
THANK YOU ^^^^^^^^ THANK YOU ^^^^^^^^^^

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Oh, sure... Now you post that. I made my own version a few months ago.

Thanks for the great info and TONE, George!

George, A schematic version would be great for some of us who suck at reading them. There were a few times I would have liked to do a board layout from a schematic and I think that would help alot.

I have to chine in here with my gratitude. This is great for a newb or almost newb, like meself.

George,

I thought the name of "plate bypass capacitor" is a little deceiving. I think it is more commonly (and correctly) referred to as a "coupling capacitor", or more specifically "AC coupling capacitor", as it couples AC signal from the plate of the gain stage to the following circuitry. I believe it can also be correctly referred to as a "DC blocking cap" for similar reasons. Just FYI.