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C-J HD3: replacement of USB DAC module with more modern HRT model

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Billy Budapest
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C-J HD3: replacement of USB DAC module with more modern HRT model

Post by Billy Budapest » Sun Nov 22, 2015 1:40 pm

The USB DAC module inside of the HD3 looks like a self-contained unit. Kevin Halverson of Muse and HRT designed it. It seems like it could be an OEM version of a HRT Streamer. Because the HD3 is limited to 24/96, would it be possible the replace the USB DAC module with a newer, 24/192 capable HRT Streamer?

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Re: C-J HD3: replacement of USB DAC module with more modern HRT model

Post by plurn » Sat Jan 02, 2016 11:31 pm

That is interesting - I didn't know it was set up like that. I guess that means that all the rest of the stuff in there that is set up by CJ is an output buffer for the DAC module, and a power supply powering part of the DAC module.

internal image http://media.tas.zeitpress.com/articles ... ternal.jpg

I would suspect you could be correct about changing the module with a newer one, though probably not a retail one. I would think it would need to be a custom one set up in a similar way to the original. I am assuming the following changes to the retail streamer:

- bypass the output buffer of the HRT streamer to use the CJ output buffer.
- allow the DAC part of the streamer to be powered by the CJ DAC power supply. The USB input is powered by the computer.

I could easily be wrong about all this.

Anthony

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Re: C-J HD3: replacement of USB DAC module with more modern HRT model

Post by Billy Budapest » Sun Jan 03, 2016 6:06 pm

Based on the complexity of the circuit, I don't think it is a buffer stage, or at least, only a buffer stage. It probably is the entire analog output stage of the DAC.

I actually corresponded with Kevin Halverson who, while not confirming that that the USB module is an OEM version of a HRT streamer, stated that it would take a tremendous amount of work, if it were even possible, to replace the USB module with another 24/192 capable one.

He said that if I wanted to see a 24/192 capable version of the HD3, I should take that up with Conrad-Johnson.
Last edited by Billy Budapest on Mon Jan 04, 2016 9:00 am, edited 1 time in total.

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Re: C-J HD3: replacement of USB DAC module with more modern HRT model

Post by plurn » Mon Jan 04, 2016 6:03 am

When I said buffer, maybe it is more correct to call it a booster/buffer? By that I mean it boosts/amplifies the voltage to the quite high 3.5V and buffers to lower the output impedance.

Not that I really understand it but I don't think the circuit looks all that complicated*. More than half of the circuit board is for the power supplies. From the image linked above, everything from the centre line (if you imagined a vertical line through the middle of the image) where the biggest capacitors are, to the right of the image is all for the two (or three?) power supplies.

From the image you can see the the thicker blue cables leaving the "hrt streamer" going to the motherboard where it says L-in L+in and R-in R+in and to the left of that you have a bunch of resistors, and what looks to me like a couple of opamps, and a bunch of capacitors. That smaller section would be for the analogue output booster/buffer. From there it would go to the RCA outputs.

Part of the analog output stage, the DAC part, would be in the "hrt streamer" and it would feed some sort of analogue signal via the blue cables to what I have guessed is the output buffer.

We can be sure part of the analogue output stage is in the "hrt streamer" because the smaller power supply at the bottom right of the image is feeding power to the "hrt streamer" via the black and red cables, and CJ says "The digital circuits are powered by regenerating power from the USB connection itself, while the analog portion of the dac and the analog audio stage are powered by separate transformers feeding discrete dc voltage regulators".

*I am not putting it down at all when saying that I don't think it looks complicated. It is all quality design and parts.

If I got any of the above wrong - sorry in advance. I am interested in electronics and know a little (enough to be dangerous) but not skilled.

Interesting info from Kevin Halverson. I thought it might have been a fairly easy swap but it seems not. Thanks for letting us know about that.

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Re: C-J HD3: replacement of USB DAC module with more modern HRT model

Post by Billy Budapest » Mon Jan 04, 2016 8:58 am

I defer to your analysis--quite thorough!

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Re: C-J HD3: replacement of USB DAC module with more modern HRT model

Post by Billy Budapest » Wed Aug 16, 2017 9:08 pm

Something else that I noticed: where the thicker blue cables leave the "hrt streamer" and enter the L-in L+in and R-in R+in of the analog output booster/buffer, there is also a small green wire that exits the "hrt streamer" and is soldered onto an unmarked connection between the L-in L+in connections. I assume the green wire is for a ground connection. The curious thing I noticed is that there is an unused connection between the R-in R+in connectors. It is very common for there to be unused silkscreened connections on a motherboard (due to circuit design changes, etc.), but this connection isn't just silkscreened, it's through-the-hole on the motherboard and has what appears to be a metal ring on it, ready for a wire and solder to make a connection. I wonder if there was originally going to be another green ground wire connected to it, and why the wire was omitted from the final design?

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Re: C-J HD3: replacement of USB DAC module with more modern HRT model

Post by Billy Budapest » Wed Aug 16, 2017 9:14 pm

There are also some capacitors missing from the left and right channels of the analog output booster/buffer. They are labeled C13, C14, C19, and C20. Again, I wonder why they were deleted from the final product?

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