Electric Mistress Clone - wont bias

[rundgrenrules]

Hey everyone!

I built the Electric Lover project from Guitar PCB Mania. Its a modernized Electric Mistress clone. It is passing signal, but I cannot get it to bias up correctly. There is only a small range of the BIAS trimpot near max-clockwise position that allows signal to pass, regardless of the settings for the CLOCK, T1 (max feedback), and VOLUME trimpots. Here are the directions for the setup:

Set Clock and Bias in the middle, at 12 o’clock.
Set T1 and the Rate knob fully counter-clockwise
Set Range, Volume, and Feedback in the middle, 12 o’clock.
Filter Switch pointing to the right position.
Plugin your guitar and amp to the board, and the DC power supply, this
project works great at 12V, but also could be feed with a standard 9v
power supply. Never plug it on 15v, this would be risky for the MN3007.
Now the signal should be going through the effect, although you may not
hear any flanging yet. If you can’t hear any signal through the effect, double-check all your solder points, components on connections to ensure
everything is okay.
In order to get the flanging effect to show up, adjust the Bias trimpot. This
trimmer is in charge of feeding the BBD MN3007. You don’t need to be
extremely precise with this one, just till you hear the flanging effect and the
BBD working.
Adjust the Clock Trim pot. As we said before, this trimmer is pretty sensitive.
Set it up to the point where you achieve a wide sweep with minimum noise.
If the flange starts to whine or “chirp” at the extremes of its sweep you will
need to do a little more adjustment.
Go back and tweak the Bias trim pot further clockwise until you get smooth
up and down flange without distortion.
With T1, we can control the maximum of Feedback desired, as this trimmer
acts as a limiter to the maximum allowed. Set Feedback at max, fully
clockwise, then start adjusting T1 as you get the maximum desired
feedback.
Once we have almost everything set-up, use your ears to make the final
adjustments on the trimmers while testing the limits of Rate, Range, and
Feedback.

And here is the link to the page with the build doc, schematic, etc.

https://pcbguitarmania.com/product/elec ... r-flanger/

I am honestly not sure what the deal is. I've tweaked and tweaked the trimpots in every order, tweaking this one then that one then this one and then back and forth and all directions. The bias seems to be the one throwing a wrench in getting a good clear sound. There is such a tiny range of adjustment and a lot of that trimpot range completely cuts out the signal and another chunk of it is significantly crunchy in an overdriven way and then there is a small range where there isnt crunch and there IS flanging, but the sound is overall weak and tinny, and then I cant turn it anymore clockwise from there.

Here are some pictures of the build:




And here are the measurements I took with all trimpots at middle position except for the bias which I turned far clockwise:

https://i.ibb.co/k9G36XC/14-35-03.png

Any suggestions would be greatly appreciated!

[The G]

I'd check the voltage at cursor (pin 2) of the BIAS pot reaching around 8V at maximum. If you used an IC socket for MN3007 (recommended), you could take it out (be VERY careful, it is sensitive to static charges like those on your not grounded hand) and measure the voltages again.

The differences at CD4013 and LM324 are not relevant. Those are an unused flip-flop and an op amp (or rather comparator, it has no feedback loop) with inputs tied together, which makes them race to an unpredictible output. My OCD always made me think of tying inputs together like this as lazy, or rather stupid. But it is not usually relevant, the purpose is to stabilize the unused parts somehow.

Oh, and the voltage at pin 15 of CD4049 is not listed because it is connected to pin 2.

[Fender3D]

You can't reach 8V at cursor since bias trimmer is 100k and r10 82k and you're supplying 9V;
there you can get just slightly more than ~1\2 Vcc.
While this should be ok, I guess it's not enough to bias properly with some chip.
Reduce r10 to 68k or less.

[The G]

My bad, I was sure that R10 is 10k. I need to change my cofee brand.

[Fender3D]

Do you read resistor values and schematic early in the morning?

[The G]

At least when is what passes as "early" for me.

[Alesek.R]

I maybe have same issue. I have R10 - 82K Should i change it for less than 68K ?

[Fender3D]

There's no known issues when changing or even shorting R10, since you got R9 you can't burn down anything, the worst case is getting a too much small setting range, but this will be always around the trimmer center position...
If you want bigger setting range, you must add another resistor, with value similar to R10, on the other trimmer pin (1)

[stolen]

Hello!

The issues aren't your fault. The schematic is simply dysfunctional. According to the schematic the gate voltage for the buffers (pin 4) doesn't have defined DC. It may work in some units due to leakage through C5, but this node should really have a properly defined voltage. According to the datasheet you'd want 1V there, you can use a simple resistive voltage divider to generate it and let C5 do the stabilization (which isn't even that critical). Note that VC is a diode drop below 9V when picking values; 4.7k to ground and 33k to 8.3V generate 1.03V, which should be good enough.

Not quite sure where MN30xx tend to bias; if the above doesn't help we'd consider shorting R10 to get the full range.

All the best,
stolen

[Yazoo55]

I apologise in advance if I am stating the obvious - do you know that the MN3007 is a genuine working chip? There are so many fake chips kicking around now. I have had exactly the same experience in the past with a different flanger build.

[Yupnitski77]

I'm having issues with my EM clone build too (the same PCBGuitarMania PCB).
At first I couldn't get the guitar signal through, it got as far as pin-3 of the 3007, but nothing after that. I tried the tricks mentioned above. After I lowered R10 from 82k to 10k I got a faint, distorted signal through and on top of it was the flanging effect, though it was a high pitch phasing...well, actually it was squealing. I even shorted the R10, but it worked exactly like with the 10k. Then I tried making the resistive voltage divider for MN3007's pin 4. I soldered a 10k resistor to pin 1 and 1,3k resistor to pin 5, tested that there was ~1V between those resistors and connected the junction to pin 4. That didn't do anything more, the squeal was still there. I could get rid of the squeal by turning the bias trimmer CW or CCW enough, but then I lost the guitar signal also.
I opened up my know good Madbean Current Lover flanger and (since it's 1:1 the same effect with same schematic) I swapped the 4013, 4049 and 3007 and it would seem all the IC's are OK, so there's something else going on with the circuit(?). Although my voltages are pretty far same as in the original posting, I'll put them here anyways.

[franblanc]

Hi, Did you sort out the calibration on the electric lover? If so, can you say what worked for you. I have 1.5kilo ohm on R10 (down from 82k) and I jumpered the send and receive pads but I am still struggling to bias. There is a very small range of usable movement on the bias trimpot with distortion on either end. One of the Facebook (PCB Mania Pedal Builders) contributors suggested it might be the LM311P. He suggested swapping in an LM311M. The building docs suggest an LM311N in the IC6 position. I notice that you are using an LM311P, like myself. I am not sure if this is the cause of our difficulties however.