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8 minutes ago, luvdunhill said:

Just a few more holes here and there - need a fuse holder on the rear panel, then four PCB mounting screws and the transformer - hoping to get the mechanical stuff done during the three-day weekend!


Why not follow the high-end audio industry practice and just use duck tape. They supposed to sound better that way! 

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On 10/19/2016 at 11:13 PM, luvdunhill said:

A small discrete buffer - prototypes have been created, will fire them up tomorrow.



On 10/20/2016 at 11:27 AM, luvdunhill said:


Perhaps something like this?


What connectors are you using in the top pic (buffers), and what are they plugging into in the bottom pic? Bottom pic looks kinda like a torpedo amp, though it isn't.

1 hour ago, luvdunhill said:

Ok, added holes and screws. Next need to make a cable, perform some turntable modifications and then the software side of the project.




I see the micro hanging on the USB port... what is this and the software for? Cool project? What kind of TT?


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Chris, those parts are made by FCI. Search for BergStik. They are rather nice board to board connectors.


Actually, what is hanging on the USB is a cheap USB serial uart bridge, based on the CP210x. You can get them on eBay for a few dollars. It makes for a nice multiplatform software option, as you can get Mac, Linux and even .NET support. There is a three wire connection to an Atmel microprocessor.


Well, now I can change he phase of the outputs via software.








Now the question is how to convert a frequency of the output sine wave to rotational frequency of the platter. That seems to need some maths.


Oh and here is the four pin DIN cable that has way more parts to assemble then it needs. It's kinda nice spring loaded mechanism when it's all said and done. It will interface directly with the connector on my Rega turntable. Crazy Brits.





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  • 2 weeks later...

It's going into a Parasound D/AC 1600. It's still a work in progress-- I needed to replace the DAC power supplies because the stock ones were remarkably derpy. Pulling the I/V stage causes the regulator output voltage to go up. I put in some shunt regs and ripped out approximately a million bypass caps that were to far from the load to do anything.



I don't like GICs/FDNRs. That's what the Parasound had. The big problem I see is that the op amps don't have sufficient gain at frequencies that we care about (352.8KHz and multiples) to actually work. The PCM1702 specs this fellow, which has just 30dB of gain that rolls off very quickly at 300KHz+. Not only is the impedance driving the shunt op amps going to be sort of high, it will also change with frequency.

I like Sallen-Key filters because they can be built around an emitter/source follower. Those are much more dependable. By cascading it with an RC pole, you can build a third order filter with just a current sink and a BJT as active devices, and it seems to work well into the lower MHz without doing anything weird.

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