I assuming that the short piece of green ribbon you are using probably provides some level of stray or gimmick capacitance already - have you mounted a crystal directly on the board without some capacitance?
One other question is I noted the thevenin equivalent source impedance of the spdif out with 75//200 is: 55 ohms - are you using 50 ohm coax? I am planning on using 243 and 110 ohm resistors which results in ~75.8 ohm source impedance for my 75 ohm coax. (Of course I do not have 75 ohm bnc.. :whazzat: I keep looking... ;) ) I'm assuming signal in the range of 3.3Vpp on the processor chip spdif output.
Yes, I installed the crystal directly on the board and it works fine without caps.
The Shigaraki transport uses indeed 200/75R resistors at the output and I had originally 220/75R Caddocks there, but later after some suggestions for another forum member decided to try some other resiustors in that spot. The Caddock 75R was definitely the best choice for 75R shunt, however the series resistor choice was not that clear.
After some experimentation no resistor at all gave most "clean" sound, however I was noticing also some edginess and in a long run it didn't work for me. The Caddock wasn't that good here, and Vishay S102 seemed to give the best results sonically. I tried two values I had on hand: 240R and 62R. The first one added too much veiling and 62R was just about right: more smooth than direct connection and almost no signature of it's own.
Riken is a bit more euforic, but overall good choice too when cost is consideration.
In all test I was using Belkin Synapse 6ft digital intrconnect: by some people regarded as one of the best out there, no longer available though ;)
As to BNC connectors on digital cables, I'm not that crazy about it any longer.
When I got my 6ft Belkin I cut it in half and terminated one end with Vampire BNC, however, I noticed it sounded worse than the original RCA/RCA 6ft cable.
I later found the info about cable length and reflections, and this seems to be more critical than termination itself:
"When a transition is launched into the transmission line, it takes a period of time
to propagate or transit to the other end. This propagation time is somewhat slower
than the speed of light, usually around 2 nanoseconds per foot, but can be longer…
When the transition reaches the end of the transmission line (in the DAC), a reflection
can occur that propagates back to the driver in the transport. Small reflections can occur
in even well matched systems. When the reflection reaches the driver, it can again
be reflected back towards the DAC. This ping-pong effect can sustain itself for several
bounces depending on the losses in the cable. It is not unusual to see 3 to 5 of these reflections
before they finally decay away. So, how does this affect the jitter? When
the first reflection comes back to the DAC, if the transition already in process at the
receiver has not completed, the reflection voltage will superimpose itself on the transition
voltage, causing the transition to shift in time. The DAC will sample the transition
in this time-shifted state and there you have jitter.
If the rise-time is 25 nanoseconds and the cable length is 3 feet, then the propagation
time is about 6 nanoseconds. Once the transition has arrived at the receiver, the reflection
propagates back to the driver (6 nanoseconds) and then the driver reflects this back to the
receiver (6 nanoseconds) = 12 nanoseconds). So, as seen at the receiver, 12 nanoseconds
after the 25 nanosecond transition started, we have a reflection superimposing on the
transition. This is right about the time that the receiver will try to sample the transition,
right around 0 volts DC. Not good. Now if the cable had been 1.5 metres, the reflection
would have arrived 18 nanoseconds after the 25 nanosecond transition started at
the receiver. This is much better because the receiver has likely already sampled the
transition by this time."
Thanks for the insight on the spdif resistor matching, sounds very tweakable so I guess I will just have to experiment to see what works best with the Audio Alchemy DST active data stream transceiver cable I am using.
I've been following this post with interest, having wanted to replace my Pioneer DVD 'transport' for quite awhile. If someone could make a transport kit based on this (or another) mechanism, I would think it would be a good seller. Heck, even a metal plate template ala Front Panel Express would be useful.
Just for the sake of it-I got mine from the link in Sweden, 40 euro... I have a friend there so it wasn't that difficult but it looks like these guys have some units in stock.
And another source - this time Switzerland...
any guidance for the 6 capacitors to be replaced? I suppose the 10nF could be a polypro. Seems that Black Gate N/NX could be used for the rest. I'm not sure for the 47uF if 6.3VDC is enough, etc. so any guidance would be appreciated.
10n is best ERO 1830 (metal film, not metalized foil as 1837)
As to other caps, while I used BG N other types may work too. Maybe Elna Silk?
47uF is on 5V supply so 6.3V might be OK.
|All times are GMT. The time now is 04:06 AM.|
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright ©1999-2015 diyAudio