MODIFICATION Teaser: I've got a Circulator mod in the works


Active member
4. Inserted 10K resistors (R103-R106) in series with pins 1 & 16 on IC1 & IC2. Pins 1 & 16 program the operating current and gain of each amplifier. The way EQD connected them all in parallel, there is no guarantee that they will share current equally. Putting those resistors in forces them to share. Should make for smoother phase sweep. Optional, but highly recommended.
Hey Chuck,

I have a question regarding mod #4.
So am I supposed to clip the 1 & 16 leg on the IC1 and IC2 and solder on a 10k resistor like the paint image below?


Chuck D. Bones

Circuit Wizard
Yes. Don't clip the lead too short, just enough so that it doesn't contact the pad on the board. I found it easier to bend the top lead of the resistor in an upside-down "U" and solder that to the stub IC lead.


Active member
I finally got working on your mods, tbh I was dreading it but here are some pictures of what i did in case any other newbie like me wants some pictures. Not sure if this is bad practice or not but i didn’t have 1/8w resistors to fit nicely.

I’ll report back with how it sounds :)


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Chuck D. Bones

Circuit Wizard
Looks good to me!

Correction: you have the 3.3M soldered to IC1-4, should be IC1-3. It will still work the way you built it, but it's not 100% correct.
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Active member
I was considering ordering this PCB and came across this thread. Was there still a plan for a boneyard edition?


Well-known member
This may have been answered already, but how do the EQD production units avoid the LFO stalling issue? Carefully selected components?!?


New member
Hi everybody,

I've been trying to get this build to work for some time but still no luck.

All the pots are affecting the sound and if I manually turn the sweep knob, I do get a phaser. The PV switch also affects the sound but the rate switch obviously doesn't do anything. I did test that switch for continuity and it does work.
I've already checked all the components in the right spot and polarity (I might still have missed something?) and went through all the solder joints to make sure they were good. I added mods 8 and 9 as described in this thread, it should prevent the LFO from stalling but it still appears to do so in my case.

Somebody posted their voltages somewhere on the forum and they all were quite close except for every pin 2 on IC1, 2 and 3, where I'm only getting 0.1V. Perhaps this could also be a hint to the problem, I'm not experienced enough to figure that out.

I've added some pictures for reference, yes those mod resistors are not pretty but I just put them on quickly for testing.

Any help would be very much appreciated!


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Well-known member
One suggestion is to move your request to the troubleshooting thread where more people might see it and offer suggestions.

I also suggest trying to take better pictures with good lighting and closer focus on both sides of the board. If you look at the schematic in the build document, the part that makes the automatic sweep is in the parts around IC3. You will want to verify the connections between those parts and part values.

What are your measured voltages at all of the pins on IC3?