Anyone built a VPI-SDS clone? - diyAudio
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Old 7th August 2003, 03:24 PM   #1
BobM is offline BobM  United States
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Default Anyone built a VPI-SDS clone?

VPI's SDS turntable motor controller is more than just a voltage controller. It's a frequency controller that stabilizes what is fed into VPI's synchronous motor. It's $1000 new (about $650-800 used), which is a lot of dough to spend (for me).

Anyone have plans for something like this?

Thanks,
Bob
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Old 7th August 2003, 04:23 PM   #2
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Default YES!

Thought no one would ask!

Bob, I'm designing one right now. Its based arround a pic with the output passing a butterworth filter to turn it into a sine wave. Has the same resolution as SDS (.01Hz) can store multiple speed configurations and accuracy is pretty much dependent on the clock feeding the pic (which can easly go down to 1ppm if you think it's worth it). Has 2 outputs so you can digitally control phase of your motor. Also has voltage ramping and fold-back, cartridge mileage counter.
Heck, come to think of it, its better than SDS. And yes, for the DIYer it should be waaay cheaper that SDS since most of its functions are done in the software domain (err.. I'm a programmer).

Right now I'm aiming at low voltage output since that's what I need for my TT, but if others get interested in it I may extend it for 110/220V output.

At this moment I have a prototype on breadboards with most part of the digital section as well as the software, done. Filtering and output amp is not implemented yet, but I'm getting to it (very little time )


Stay tuned. I'll start a thread on this forum once I have someting worth looking at.

Guilherme.
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Old 7th August 2003, 04:30 PM   #3
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Guilherme

Just curious why you need a butterworth? I've done something similar using a look-up table (100points for a period) and the output after a DAC needs minimum filtering (first order) for a very good sine.

cheers
peter
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Old 7th August 2003, 04:57 PM   #4
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Hi Peter.

Because of resolution. You'll want your 100 slices to have the same duration otherwise you'll introduce distortion. So, when you want to change frequence you have to sum/subtract the same amount to all of them and so the total delta is multiplyed (in your case) by 100.

For example, .01Hz change is a 0.9999 uS change in period. You would have to divide that by 100 to get the right timing for each slice. That would be 9.9 nS. So your counter would have to run at 9.9 nS steps, not an easy thing for a pic or any other mcu for that matter.

Doing it the way i'm doing it I just have two counters with a step resolution of 200 nS which is still almost 5 times lower than what I need.

Guilherme.
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Old 7th August 2003, 05:14 PM   #5
BobM is offline BobM  United States
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Default Cool - someone else is thinking of it

I'm very interested in your project. I'm no engineer, so I can't add ANYTHING really useful to your investigation/experiment, but I am interested in a DIY version if it's simple enough to execute.

Please keep me informed.

Bob
ptmconsulting@att.net
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Old 7th August 2003, 06:55 PM   #6
wrankin is offline wrankin  United States
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Default Me too?

I would also like to be kept posted on your developments. I'm thinking about a similar approach for rebuilding a Rega.

Thanks,

-bill
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Old 7th August 2003, 07:05 PM   #7
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Guilherme

I understand. Didn't notice the .01Hz requirement. I just get fixed frequencies with extra phases to avoid using an external cap. 8515 has enough ports

cheers
peter
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Old 8th August 2003, 12:22 AM   #8
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Guilherme,

I'd also be interested. Hopefully there'll be enough interest to get a PCB made and some PICs programmed.
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Old 8th August 2003, 01:18 AM   #9
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Hi,

Maybe a short class of physics would cure you all ?

It's a massive case of self delusion....

Cheers,
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Old 8th August 2003, 01:32 AM   #10
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Quote:
Originally posted by fdegrove
Maybe a short class of physics would cure you all ?

It's a massive case of self delusion....
I'm willing to listen Professor. Go ahead and enlighten.
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