Electric Mistress V4 clock noise

[ConnorRMoore99]

Hi all, troubleshooting an Electric Mistress V4 that is having some major clock noise, especially with the range and color turned past noon. Sound clip posted below. I've gone through the troubleshooting, and calibration procedure given at http://www.metzgerralf.de/elekt/stomp/mistress/repair.shtml and nothing has changed.
I measured the ESR and values of the electrolytics which checked out fine, and replaced the 4013 with a known good one.

For context guitar is plugged straight into the pedal and then straight the amp.

Not really sure where to go next, really hoping it's not a friend SAD1024 because I'm not willing to sell a kidney for a BBD today. Any help much appreciated Thanks.

https://soundcloud.app.goo.gl/L6jY91Lvz4Ht7oRw6

[stallik]

In the absence of other, more knowledgeable replies, I've read that the LM741 chip has a habit of going bad in old EM's leading to increased clock noise. Whether this is just internet lore or not, a replacement chip is pretty cheap so it's where I'd start.

[Govmnt_Lacky]

A good place to start would be finding out what the minimum and maximum Clock pulse frequencies are that are going into the BBD.

[ConnorRMoore99]

In the absence of other, more knowledgeable replies, I've read that the LM741 chip has a habit of going bad in old EM's leading to increased clock noise. Whether this is just internet lore or not, a replacement chip is pretty cheap so it's where I'd start.

Thanks for the reply I'll give this a shot! I read something else similar happening in some like-flangers of the era to do with bad BJTs in the circuit so I guess with all else seeming in good operating I'll play a game of swapping 1 part a time

[ConnorRMoore99]

A good place to start would be finding out what the minimum and maximum Clock pulse frequencies are that are going into the BBD.

Good call, I'll take a measurement of this and report back today.
I'll also post a clip of playing guitar through as it actually flanges really well and sounds great but the clock noise is almost louder than the guitar signal. This gives me strong hope that the SAD1024 is fine so must be a fault clock or something else.

[DrAlx]

Is anything before the EM in the signal chain?  You can get aliasing noise (those whistle sounds) if something earlier in the signal chain has any sort of clock or charge pump in it. You can also get aliasing if things after the EM have switching circuitry (e.g. anything that samples, or even a class D amp).

[ElectricDruid]

Is anything before the EM in the signal chain?  You can get aliasing noise (those whistle sounds) if something earlier in the signal chain has any sort of clock or charge pump in it. You can also get aliasing if things after the EM have switching circuitry (e.g. anything that samples, or even a class D amp).

That's a detailed but entirely accurate way of saying that the pre- and post- filtering in the Electric Mistress is crap!!
There are good reasons for a "light touch" in both cases, but in our age of digital and ultrasonic noises, it leaves the pedal very vunerable to all sorts of effects it never expected to see.

[matopotato]

Probably not your issue but adding anyway.
For flanger, chorus, phaser I try to use a shielded wire. At least from input and any wire close to any IC. Only one end of the shield of each wire to ground, but not both ends to avoid risk of ground loops.
The ones I got are a bit of a pain to solder since the inner wire is very thin and even fragile sometimes.
In a duo-phase I made all signal wires shielded.

[12Bass]

Haven't looked at the schematic.  IIRC, the A/DA Flanger had a trimpot to null the clock signal at the output of the SAD1024A.  If present, that's where I'd start.

[ConnorRMoore99]

A good place to start would be finding out what the minimum and maximum Clock pulse frequencies are that are going into the BBD.

Okay so back at it after a little break for the holidays. I replaced all of the electrolytics to be safe and I also replaced the LM741 and 2N5087 which seemed to lower the noise just a tad but it's still very loud compared to others I've seen on YouTube. Clock pulses measured at pin 3 and 8 of the SAD1024 read 44khz to 267khz so this should be about audible right?

[ConnorRMoore99]

Is anything before the EM in the signal chain?  You can get aliasing noise (those whistle sounds) if something earlier in the signal chain has any sort of clock or charge pump in it. You can also get aliasing if things after the EM have switching circuitry (e.g. anything that samples, or even a class D amp).

I wish it was a simple fix like this, it's the only thing in the chain going straight into a Princeton reverb, and I'm using the original EHX wall wart to power it.

[ConnorRMoore99]

Tinkering with it some more, I realized the noise drops significantly if I turn the volume on my strat down. Also helps if I turn the tone knob down. Any ideas?

I know these things are sensitive to RF, is there anything I can do about this? Adding a 10k resistor in series with the input and 150pf cap to ground helps a tiny bit but still loud chirps.