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 Post subject: Harmonic Tremolo
PostPosted: Tue Apr 21, 2020 10:02 am 
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Joined: Tue Apr 21, 2020 8:04 am
Posts: 2
Location: Medford, Oregon
So I finished my build. Nothing was working. No LED blink etc.
After some troubleshooting I managed to get mine working. My 7660SCPA was faulty.
I swapped it out and replaced with a 7660CPA that i had available. ( Working for a contract electronics company has it's benefits 8) )
But now while it is working there is a high pitched noise that pulses along with the oscillation.
It almost sounds like a microphonic cap, but in tapping on the caps I wasn't able to find one that pinged.

Is this due to the 7660CPA instead of 7660SCPA?


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 Post subject: Re: Harmonic Tremolo
PostPosted: Tue Apr 21, 2020 10:18 am 
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Joined: Sun Jan 22, 2006 1:39 pm
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Location: Moses Lake, WA
Yes. The "S" is very important.

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 Post subject: Re: Harmonic Tremolo
PostPosted: Tue Apr 21, 2020 12:13 pm 
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Joined: Wed Apr 26, 2006 5:14 pm
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Location: Truckee, CA
You need to use only certain charge pumps in audio circuits. As you've found out, the wrong versions will be too noisy.

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 Post subject: Re: Harmonic Tremolo
PostPosted: Wed Apr 22, 2020 4:37 am 
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Joined: Sat Mar 04, 2006 9:15 pm
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Location: Ohio
You also need to pay close attention to the CP’s data sheet. Particularly the device’s max. input voltage. Some have a low max. input of 10VDC. A generic 9VDC wall wart power supply will typically have an unregulated output of 12 to 13VDC with no load attached to it. This over voltage will fry the CP in an instant. Look for one with a max. input of 12VDC or higher if you can find one.

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 Post subject: Re: Harmonic Tremolo
PostPosted: Wed Apr 22, 2020 8:43 am 
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Joined: Tue Jan 02, 2007 1:24 pm
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Location: Albany, NY
Stephen wrote:
Look for one with a max. input of 12VDC or higher if you can find one.

I'm a big fan of the LT1054. Very robust charge pump (handles up to 15V input) with higher current output (100mA) than the 7660 and 1044.

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 Post subject: Re: Harmonic Tremolo
PostPosted: Thu Apr 23, 2020 6:47 am 
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Joined: Tue Apr 21, 2020 8:04 am
Posts: 2
Location: Medford, Oregon
Thanks everybody for the info! :D

I'll pick up the correct part from my next Digikey order. We only have the 7660CPA available where I work.


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