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No lock when connecting the 4:1 MUX (SPDIF out) to B32S via GND and D1
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I'm in the process of putting my TPA boards together in a decent housing and my wiring is the following:
4 input SPDIF sources -> MUX (SPDIF OUT) -> OTTO -> B32S (GND, D1)
1 DSD input coming from my Denon SACD -> OTTO -> B32S (works by the way!)
I was under the impression that the MUX output TTL level SPDIF which should be taken by the GND/D1 connections on B32S even with the SPDIF set to off. However I don't get any lock.
Everything is fine when I connect the MUX SPDIF out to the SPDIF in on the B32S (and turn on SPDIF).
I know that I could connect the MUX to B32S via I2S and switch DSD/I2S with the otto but I would like to avoid the as B32S is great with SPDIF.
I have played around with the DIP switches but there is an awful lot of combinations and I have the impression that most should be functional anyway.
Any suggestions?
Nic
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The MUX outputs consumer lever SPDIF. You can remove R2 and you will have TTL level output.
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Taking out R2 went out smoothly but did not make a change.....
Funny enough I find that the pads from which I took of R2 are connected (<1 ohm). What I did looks fine under the magnifying glass.
Hmm...
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You may need to remove the transformer. It is likely too low an impedance to get true TTL. The transformer is the reason you see the low resistance at DC with your DMM. Edited by user Wednesday, July 1, 2009 6:56:08 PM(UTC)
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Rank: Advanced Member
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Removed the transformer and initially I was disappointed as it still did not work. Stupid me, because I realized that taking out the transformer cut the connection to the SPDIF output. I jumpered the SPDIF out to the transformer in and now I get a lock when connecting to GND/D1 with the SPDIF comparator set to off!
I assume the the pulse transformers at the MUX output is of marginal importance.
Thanks Russ!
Nic
P.S. Maybe this mod should be configurable on a v2 of the MUX or described in the manual. I quite clearly recall that there are posts from you or Brian saying that the MUX output TTL level SPDIF.
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Well - kind of works.
When the MUX and B32S are directly connected its fine. When I have the OTTO between I don't get a lock anymore.
Hmm....
Nic
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Ok - issue solved.
When the output transformer is removed from the MUX one of the SPDIF remain grounded. If the MUX and the DAC use the same PSU their grounds are also connected. It is this ground loop that prevents a lock on the signal.
There are two solutions:
1) If the MUX and DAC share ground simply do not connect the "-" SPDIF from the MUX to the DAC.
2) use another PSU for the MUX which does not share the ground with the DAC.
I still wish I could make it work with the pulse transformer in the circuit.
Nic
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You probably can. Keep trying. :) What I would do is try shorting R3 and going direct to the trafo, you can do this by shorting R3, but keep C5. :) Give that a shot. Edited by user Friday, July 3, 2009 3:56:05 PM(UTC)
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Ok. Will try. Fortunately I can work while listening to a Dire Straits SACD over tapped DSD! Spectacular, the music does not come from the speakers - they are doing a live performance somewhere in my workshop! Nic P.S. I assume it is normal that the Sabre chip is really hot (my estimate around 70˚C - sorry I don't recall the Fahrenheit conversion). Edited by user Friday, July 3, 2009 4:58:22 PM(UTC)
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Yes, its normal. The chip is actually not generating that heat, its coming from the PS parts around it.
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No - shorting R3 does not make it work with the transformer in. The transformer has been in and out about 10 times now so I need to verify a few things before being certain.
Nic
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It may be a lot easier on the board to simply short the pins on the transformer, rather than remove it.
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Brian you would still have the load if the trafo in that case, and you would end up with both the primary and secondaries in parallel.
BTW I tried last night just shorting R3 nothing else, and it worked for me into D1.
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Rank: Advanced Member
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Russ White wrote:
BTW I tried last night just shorting R3 nothing else, and it worked for me into D1.
Thats with the R2 in place? I lost that microscopic resistor so I will have to improvise something (93 ohms?). Enjoy your 4th of July, Nic
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It should not matter if R2 is there or not.
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Rank: Advanced Member
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Put back in R2 but still it did not work so in the end I have it working with the trans and R2 out and R3 shorted. I really have no clue to explain why shorting R3 is not sufficient on my MUX.
It works great without the trans so for the moment I wont troubleshoot anymore on this issue.
Thanks for the help.
Nic
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No lock when connecting the 4:1 MUX (SPDIF out) to B32S via GND and D1
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