external VCO clock

Hardware questions and issues with the FV-1

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sandromatik
Posts: 27
Joined: Wed May 18, 2011 11:47 am

external VCO clock

Post by sandromatik »

I would try to clock the FV1 with a simple op amp VCO instead of the knowledge base circuits, as I would like to modulate its frequency via CV.

I have a couple of questions:

-How precise should be the 50% duty cycle of a square wave generator used to clock the FV1?

-Which must be the peak to peak level of the square wave?

thanks in advance for your help!
frank
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Re: external VCO clock

Post by frank »

sandromatik wrote: -How precise should be the 50% duty cycle of a square wave generator used to clock the FV1?
We never tested that parameter but it should be as close to 50% as possible. I expect the PLL to be a bit forgiving.
sandromatik wrote: -Which must be the peak to peak level of the square wave?
Normal 3.3V logic levels so I would target 0.8V to 2.5V minimum and 0 to 3.3V max.
Frank Thomson
Experimental Noize
sandromatik
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Post by sandromatik »

OK Frank!

Can you predict which issues will cause a poor clock symmetry within the audio performance of the chip?

thanks again
frank
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Post by frank »

The primary problem would be the PLL unable to lock to the clock signal, this would cause multiple audible issues in the chip. I expect the PLL will be forgiving to a clock that is not 50%, just not sure how much, but I suggest you make up the circuit and just test it. We did design the FV-1 to work across a wide range of issues and the PLL was designed to lock to a wide range of signals but we never actually worked out min/max duty cycle.
Frank Thomson
Experimental Noize
GaryInThailand
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Joined: Sat Sep 20, 2014 12:01 am
Location: Hua Hin, Thailand

Post by GaryInThailand »

Any luck with this, sandromatik? I'm interested in variable clock, but I think there might be issues with the range of frequency, speed of modulation, as well as (maybe) symmetry. Would love to have the benefit of your experience. Thanks!
Just a little eMusic hacking on the old Malay Peninsula
bradholland
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Post by bradholland »

I'm interested to hear how this sounds, perhaps the LTC1799 would be a good candidate for teh clock signal. what audible effect would this have?

I place ltc1799s into the alesis hr16 drum machine replacing the clock line to the asic, by modulating the clock signal I get an 'overall' pitch control for the machine.
GaryInThailand
Posts: 7
Joined: Sat Sep 20, 2014 12:01 am
Location: Hua Hin, Thailand

Post by GaryInThailand »

TipTop Audio advertise external sample clock as a feature of their FV-1 based ZDSP3000. Their documentation implies that it works over quite a wide range (not exactly defined) modulo aliasing issues.
Just a little eMusic hacking on the old Malay Peninsula
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