Aargh .. Whine noise from a TAPLFO chip

[drolo]

I am building a tremolo with Electric Druid's TAPLFO.

On the breadboard I was getting a tick in square wave mode from the Vactrols but that's normal. No whine whatsoever despite the uber-messy breadboard.
Now i built up on perf, making sure to separate the grounds of the lfo/vactrol circuit from the grounds of the audio circuit.

What do I get? Whine .....

I have not boxed it up yet. So I don't know if it will disappear once boxed.
I'm still at work so I can't try right now ...

In case it does not go away, is there anything I can do to minimize it? Shield wires? Shielding the DC power cables can help (can it be done?) ?

The clock runs at 20kHz can I filter that out somehow?

[midwayfair]

I am building a tremolo with Electric Druid's TAPLFO.

On the breadboard I was getting a tick in square wave mode from the Vactrols but that's normal. No whine whatsoever despite the uber-messy breadboard.
Now i built up on perf, making sure to separate the grounds of the lfo/vactrol circuit from the grounds of the audio circuit.

What do I get? Whine .....

I have not boxed it up yet. So I don't know if it will disappear once boxed.
I'm still at work so I can't try right now ...

In case it does not go away, is there anything I can do to minimize it? Shield wires? Shielding the DC power cables can help (can it be done?) ?

The clock runs at 20kHz can I filter that out somehow?

Increase the resistance after pin 5. If you didn't use a transistor after pin 5, you're going to have to fit it in somehow. I know, I know, it makes the tremolo less strong and that sucks. But it'll kill the whine if you find the right value. That's part of what the trimpots are doing in the MusicPCB tap tempo tremolo.

And if you did use a transistor ... try flipping it around backwards. Sometimes that works.

[R.G.]

On the breadboard I was getting a tick in square wave mode from the Vactrols but that's normal. No whine whatsoever despite the uber-messy breadboard.
Now i built up on perf, making sure to separate the grounds of the lfo/vactrol circuit from the grounds of the audio circuit.
What do I get? Whine .....
I have not boxed it up yet. So I don't know if it will disappear once boxed.

It may disappear when boxed, but not necessarily. Breadboards are high-capacitance things. Something about the physical change to perf released the whine demon. For high-frequency digital signals, physical construction matters.

In case it does not go away, is there anything I can do to minimize it? Shield wires? Shielding the DC power cables can help (can it be done?) ?
The clock runs at 20kHz can I filter that out somehow?

1. Look carefully at your construction job. Is the perf really, really the same as the breadboard? Are all the components connected the same? All grounds really connected, especially the filtering on the output LFO waveform? Are the components really the same values? I have modest red-green colorblindness, so I sometimes confuse 4.7K and 47K resistors from just reading the color codes, as an example. Reading tiny printing on caps gets harder as I get older...
2. How are your power supplies decoupled? Digital circuits pull short, sharp pulses of current. They need decoupling capacitors to be as close to the IC pins as you can get them. I'm not familiar with the TAPLFO chip, but I believe it's a PIC. Put 10uF and 0.1uF ceramic RIGHT AT THE POWER SUPPLY PINS of the chip. A good test would be to temporarily solder them onto the power pins on the bottom of the board for testing whether this was a problem.
3. Is the LFO output filtered? Check whether the filter is really the way you think it is. Perhaps try the 0.1uF or 0.01uF ceramic capacitor trick in parallel to whatever filtering is there and see if this makes a difference.

If those tricks don't help, it may be that one of your signal wires crosses over the LFO chip or the filtering on the LFO output, and picks up the signal capacitively. In that case, shielding that wire would help.

[drolo]

Increase the resistance after pin 5. If you didn't use a transistor after pin 5, you're going to have to fit it in somehow. I know, I know, it makes the tremolo less strong and that sucks. But it'll kill the whine if you find the right value. That's part of what the trimpots are doing in the MusicPCB tap tempo tremolo.

And if you did use a transistor ... try flipping it around backwards. Sometimes that works.

Hmm actually the whine stays even when I lower the current so much that the LEDS are not reacting anymore.
Must be something else :-(

[drolo]

1. Look carefully at your construction job. Is the perf really, really the same as the breadboard? Are all the components connected the same? All grounds really connected, especially the filtering on the output LFO waveform? Are the components really the same values? I have modest red-green colorblindness, so I sometimes confuse 4.7K and 47K resistors from just reading the color codes, as an example. Reading tiny printing on caps gets harder as I get older...
2. How are your power supplies decoupled? Digital circuits pull short, sharp pulses of current. They need decoupling capacitors to be as close to the IC pins as you can get them. I'm not familiar with the TAPLFO chip, but I believe it's a PIC. Put 10uF and 0.1uF ceramic RIGHT AT THE POWER SUPPLY PINS of the chip. A good test would be to temporarily solder them onto the power pins on the bottom of the board for testing whether this was a problem.
3. Is the LFO output filtered? Check whether the filter is really the way you think it is. Perhaps try the 0.1uF or 0.01uF ceramic capacitor trick in parallel to whatever filtering is there and see if this makes a difference.

If those tricks don't help, it may be that one of your signal wires crosses over the LFO chip or the filtering on the LFO output, and picks up the signal capacitively. In that case, shielding that wire would help.

It's a PIC indeed.
Actually I'm running the PWM signal straight to 2 inverting unity gain opamps that run 2 Vactrols. On breadboard I had tested with and without filtering and (since I had no whine then ) did not notice any difference, except for the sharp edges of square signals to be rounded of, so it sounded, at least.

If i reduce the current enough that the LEDS don't turn on anymore, can I deduce that the whine is not transmitted by the LDR's?

The PIC has a 470nF right next to the power pins and a 100uF an inch away on the other side of the chip. Each of the circuits, the PIC, the LED driving Op Amps and the Audio Op Amps have a separate 33 ohm resistor going to their own filtering Caps. PIC and LED driver Op Amps share the same ground, but Audio ground is separate and touches the other ground only at one point on the perf, where the power comes in.

[R.G.]

OK. Probably not grounding, unless there's a break somewhere. Getting deeper than that would require some on-the-spot testing.

Maybe try audio probing the power supply and ground at different points, searching for the whine.

Got schematics?

[drolo]

OK. Probably not grounding, unless there's a break somewhere. Getting deeper than that would require some on-the-spot testing.

Maybe try audio probing the power supply and ground at different points, searching for the whine.

Got schematics?

Thanks for the advice, I will try that this evening.

Here are the schematics:

http://i1277.photobucket.com/albums/y492/drolobucket/tremolo_zps66c3767d.png

And the layout:

http://i1277.photobucket.com/albums/y492/drolobucket/tremolo-layout_zpsc3fbe233.png

You may recognize some bits of a fender tremolo from your site :-)

The perf on the left is a daughter board with the 6 pots and the rotary switch.
Now I am a bit suspicious of the 3 wires on the top of the main board that connect to the balance pot as they run a long way next to the PICs ground ... is it bad doctor ?

[drolo]

Ok used shielded wire for input and output and the whine was gone after boxing it :-D

Hurray!

Sorry for the false alarm and thanks for the good advice !

[R.G.]

Ok used shielded wire for input and output and the whine was gone after boxing it :-D

Hurray!

Sorry for the false alarm and thanks for the good advice !

Not a false alarm. The whine was real. It's lucky that a bit of shielded wire can fix it. Good work.