EP-3 compressor questions
Posted: Sat Oct 27, 2012 12:28 am
Hey guys, I finally found time between work and school to put together a layout for the compressor board from the Echoplex.
However I'm running into a few issues putting the schematic together. This is something Good Guest alluded to in the EPPos thread. I noticed there is a mistake in the EP-comp's design vs. the MXR dynacomp. At the output of pin 6 of the 3080 in the EP-3, you can see a simple RC network of a 150k, a 22k, a 1µF and a .001µF. As per ampsnob's corrections there is also a 47k that comes from the 9v rail to this network.
http://forum.metroamp.com/viewtopic.php ... 45#p374235" onclick="window.open(this.href);return false;
if you check the dynacomp schematic this resistor network is set up very differently. There is a 56k (47k in EP3) off the 9v rail that connects to the 150k and .001µF, and this connection continues to the base of Q1. However the 150k and .001µ also connect to the output of pin 6, making this a feedback loop of sorts. Since the 27k (22k EP3) and 1µF also connect directly to the 56k (47k EP3) they are also part of the feedback loop. Q1 for the dynacomp is a buffer, and since this circuit is likely run after the EP-3 preamp circuit then it is probably unnecessary, and was omitted from the EP-3 compressor circuit.
In the Echoplex, all of these components are located off pin 6, more or less. I'm very puzzled as to why they decided to include these components when they are part of a circuit they omitted.
So my question to you guys, is should I bother to include these in my version? I feel they would actually be detrimental to the sound of this thing, even if it was accurate. Maybe I should rework the circuit so they are part of a feedback loop for the opamp? I'm not sure if i want to trade accuracy for perhaps poorer performance or tone.
However I'm running into a few issues putting the schematic together. This is something Good Guest alluded to in the EPPos thread. I noticed there is a mistake in the EP-comp's design vs. the MXR dynacomp. At the output of pin 6 of the 3080 in the EP-3, you can see a simple RC network of a 150k, a 22k, a 1µF and a .001µF. As per ampsnob's corrections there is also a 47k that comes from the 9v rail to this network.
http://forum.metroamp.com/viewtopic.php ... 45#p374235" onclick="window.open(this.href);return false;
if you check the dynacomp schematic this resistor network is set up very differently. There is a 56k (47k in EP3) off the 9v rail that connects to the 150k and .001µF, and this connection continues to the base of Q1. However the 150k and .001µ also connect to the output of pin 6, making this a feedback loop of sorts. Since the 27k (22k EP3) and 1µF also connect directly to the 56k (47k EP3) they are also part of the feedback loop. Q1 for the dynacomp is a buffer, and since this circuit is likely run after the EP-3 preamp circuit then it is probably unnecessary, and was omitted from the EP-3 compressor circuit.
In the Echoplex, all of these components are located off pin 6, more or less. I'm very puzzled as to why they decided to include these components when they are part of a circuit they omitted.
So my question to you guys, is should I bother to include these in my version? I feel they would actually be detrimental to the sound of this thing, even if it was accurate. Maybe I should rework the circuit so they are part of a feedback loop for the opamp? I'm not sure if i want to trade accuracy for perhaps poorer performance or tone.