How does this ep3 volume control work?

[walkman]

Can anyone tell me what going on with the volume control on this ep3 circuit? is it rolling off highs as the volume is turned up?

[pdf64]

The 500k variable resistor is acting load the output of the FET.
The output impedance of the FET will be 22k; that acts as the top part of the potential divider.
For the lowest frequency of interest, the 0.1uF cap near enough a short, given the 22k minimum impedance and there being no reason to adjust the 500k control to minimum.
It's rather like the way a 5E3 volume control works.
Pete

[Mark Hammer]

Am I the only one who thinks this might be misdrawn? or at the very least, incomplete.

[52 Bill]

Am I the only one who thinks this might be misdrawn? or at the very least, incomplete.

Yes, it is just the straight signal section of the circuit. I guess that there are a few pedals based on this design, trying to emulate the sound of an EP-3 Echoplex with the echo turned off but still in the signal path.

The grounding pot is not really meant to be the volume control. It is supposed to emulate the load of the recording circuit. I don't really think that it is the correct way to do that, but that's why it's there. The volume is actually controlled by the echo level control.

[walkman]

Yes Bill ,

I believe its taken from this schematic, and has been worked into a pedal format commercially and as a diy project



What i'd like to know is how different a pedal based on the EP3 preamp would be compared to any other jfet buffer , such as the one by don Tillman or ROG Fetzer valve.

On this page on metroamp forum there is a claim that "The output impedance is very important to the phase response of the EP-3 preamp" MetroAmp.com Forum View topic - Echoplex pre-amp.

I'm interested to understand this point. Is this the same as highs being rolled off when going into the low input of a two input fender?

A jfet buffer or booster that smooths that enhances the upper mids and smooths the highs, is something i'd like to build myself.
Does changing the phase response do this? Sorry this is beyond my experience or maybe i'm getting terms mixed up.




edit I might have found the answer myself .. but am still interested in other replies . see ... http://forum.metroamp.com/viewtopic....29716&p=293367