A/DA Flanger high pitched squeal

[BDuguay]

I posted awhile back about these 2 A/DA Flangers I have. The one always worked and I thought I had the other sorted too but now, as soon as it's powered up, there's a high frequency squeal/whistle noise mixed in with the guitar and effect that increases in frequency until it's out of range and then finally gone from the mix.
I have no idea where to even begin. Anyone?
B.

[armdnrdy]

You can begin with a bit more information.

Why don't you supply a link to the post you are referring to.

[Mark Hammer]

1) How long does it last for?

2) Does changing either rate or the manual offset or enhance control modify what the squeal sounds like?

[armdnrdy]

I found your thread: This is a A/DA MN3010 BBD factory Flanger..not a build.

http://www.diystompboxes.com/smfforum/index.php?topic=110383.msg1015041#msg1015041

[Fender3D]

the lowest clock frequency is (should be) 17.4KHz (clock @ pin 13 is double the clock @ BBD's pins), unless you're a bat you shouldn't ear it...

Check VCO range (from.. to..)

[BDuguay]

You can begin with a bit more information.

Why don't you supply a link to the post you are referring to.

I didn't think it was necessary but you're right, it would've have at least given a point of reference. My apologies.
B.

[BDuguay]

1) How long does it last for?

2) Does changing either rate or the manual offset or enhance control modify what the squeal sounds like?

I just checked now and after 2 minutes or so, it's out of range. A big fat Yes to number 2.

[BDuguay]

I found your thread: This is a A/DA MN3010 BBD factory Flanger..not a build.

http://www.diystompboxes.com/smfforum/index.php?topic=110383.msg1015041#msg1015041

Yes, an original late 70's A/DA flanger. I don't think I eluded to it being anything but. Now, if it's not cool to ask for help repairing something NOT diy then please let me know.
F.W.I.W. I'm fixing this for a friend as a favour and using the experience to learn more about this witchcraft known as electronics.
B.

[BDuguay]

the lowest clock frequency is (should be) 17.4KHz (clock @ pin 13 is double the clock @ BBD's pins), unless you're a bat you shouldn't ear it...

Check VCO range (from.. to..)

I was able to calibrate the clock to factory specs using info found on the web. The only thing I have in common with bat's is the need for night life but I do have very good hearing despite my lifestyle and past experiences in bands.
B.

[armdnrdy]

Yes, an original late 70's A/DA flanger. I don't think I eluded to it being anything but.

The problem was...in your first post...you didn't elude to anything! 

It wasn't clear if this were a DIY build, possibly with a charge pump that could have caused the "high frequency squeal."

The more information, the better the chance of solving the issue. 

[Mark Hammer]

1) How long does it last for?

2) Does changing either rate or the manual offset or enhance control modify what the squeal sounds like?

I just checked now and after 2 minutes or so, it's out of range. A big fat Yes to number 2.

So that tells me that something is monkeying with the clock rate.  For the first few minutes on bootup, the clock is below the lowpass corner frequency, such that you can hear it.  Over time, it becomes less audible by virtue of being higher, and better-filtered from the audio path.

If it changes over time, then my spidey-sense says its either a heat-related thing, or a cap somewhere.  I will note that descending squeals are frequently heard when removing power from less complex analog and digital delays, as a cap somewhere drains and the clock rate drops from ultrasonic to audio range.

Assuming it is a cap, the question becomes where and which one.  It cold be somewhere in the clock circuit itself, OR something in the leadup to the clock circuit, that mediates some sort of control voltage feeding the clock.

That's my best guess, anyway.

[Fender3D]

I was able to calibrate the clock to factory specs using info found on the web. The only thing I have in common with bat's is the need for night life but I do have very good hearing despite my lifestyle and past experiences in bands.
B.

Ok Brian,
you know, one starts hearing flangers squealing, then necks biting is just behind the corner.... 

now, check VCO frequency(es) and supply voltage, while it squeals.
As Mark said it might be a capacitor...
Whether VCO's supply is not steady, it will change clock.
If they (freq and voltage) are ok and steady, it might be any capacitor on power supply

[BDuguay]

This one is full of Tantalum caps. Should I look at the scheme at check the caps surrounding the clock timer? Maybe see which one(s) are taking their time reaching full charge?
B.

[snap]

Does the guitarsignal do a pitchbend or runaway as well, during the squeal? In other words: does the delaytime vary synchronous to the whine and not according to the usual LFO-sweep? If not, try this: http://www.diystompboxes.com/smfforum/index.php?topic=110383.msg1025688#msg1025688

[Fender3D]

...Should I look at the scheme at check the caps surrounding the clock timer? Maybe see which one(s) are taking their time reaching full charge?
B.

It may be useful, but we should first realize what is the noise, I mean, if it is a clock issue or not,
check VCO frequency(es) and supply voltages

[DrAlx]

It may be useful, but we should first realize what is the noise, I mean, if it is a clock issue or not,

+1.   

If it were me, I'd use an audio probe to follow the signal through the circuit, starting at the input, and see where the noise first appears.  If you find it on a IC that is before the BBD then audio probe the supply pins for that IC.

[BDuguay]

Does the guitarsignal do a pitchbend or runaway as well, during the squeal? In other words: does the delaytime vary synchronous to the whine and not according to the usual LFO-sweep? If not, try this: http://www.diystompboxes.com/smfforum/index.php?topic=110383.msg1025688#msg1025688

The guitar signal does not mimic the squeal but it seems the delay time is synchronous to the squeal if I understand correctly. The power supply I'm using is a good old fashion transformer type; a Dunlop 18vdc, not a switching type. Do we call those linear?
B.

[BDuguay]

It may be useful, but we should first realize what is the noise, I mean, if it is a clock issue or not,

+1.   

If it were me, I'd use an audio probe to follow the signal through the circuit, starting at the input, and see where the noise first appears.  If you find it on a IC that is before the BBD then audio probe the supply pins for that IC.

That's next for sure. Also, I have a properly functioning A/DA Flanger of the same vintage to compare with. That's my lesser educated go-to for trouble shooting.
B.

[snap]

Does the guitarsignal do a pitchbend or runaway as well, during the squeal? In other words: does the delaytime vary synchronous to the whine and not according to the usual LFO-sweep? If not, try this: http://www.diystompboxes.com/smfforum/index.php?topic=110383.msg1025688#msg1025688

The guitar signal does not mimic the squeal but it seems the delay time is synchronous to the squeal if I understand correctly. The power supply I'm using is a good old fashion transformer type; a Dunlop 18vdc, not a switching type. Do we call those linear?
B.

Godd old=linear, yes. My squealtheory=wrong.

[BDuguay]

I did some digging and found I'm getting 7ish volts on pin 14 of the LM324 quad opamp of the properly functioning unit and 12ish volts on the same pin of the squeally one.
Oddly enough, that's the new opamp I put in awhile ago. Both quads are getting the proper 14+ volts DC feed. The data sheet for this LM324 shows pin 13 as a - input and 12 as a + input that combine to feed the output on pin 14. Both quads have the same 3+ volts at pins 12 and 13.
Can I safely say the quad putting out 5 more volts than the other on pin 14 is bad?
B.