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#1 |
diyAudio Member
Join Date: Sep 2002
Location: near Milano , Italy
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While searching in my drawers for the 74CH125 specified in Elso's schematic I found out that I have none.
![]() Since it seems to me a ordinary buffer/line driver I started looking for equivalents. I have a lot of boards to salvage that mount the 244 octal buffer in various flavours (HC, HCT, F, AC...), as well as some 74F125 which is twice as fast as the HC. Can I use this or the "F" series carries some issues that make it unsuitable? Among these logic families, which ones can work best? Attached is the schematic I'm referring to (posted by Elso Kwak) Cheers Andrea. Edit: the 5V can be taken from the player(maybe with some LC filtering or I'd better use a separate PS?) |
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#2 |
diyAudio Member
Join Date: Dec 2001
Location: Eindhoven
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Hi
Why adding the buffers ? Suggestion: Place the master clock close to te DAC ad feed it backwards....... Ciao |
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#3 | |
diyAudio Member
Join Date: Sep 2002
Location: near Milano , Italy
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Quote:
I think Elso added the buffers to drive a coax cable for each data line, since the DAC itself is placed outside the CD player housing for RFI reasons(I suppose). Initially I was thinking to omit this circuit and place my DAC inside the player (adding a supply for it), but I experienced serious RFI problems only placing my external TDA1543 DAC on the top of the player (Philips CD931) so now I'm quite doubtful about it. For the clock, what do you mean? I think I'll replace the player's one but AFAIK no other clocks are needed using IIS direct.. ![]() Cheers Andrea Edit: partial answer to my question.. using a TTL buffer followed by a emitter follower greatly degrades the noise margin of the circuit, so I think I must use a HC one. |
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#4 | |
diyAudio Member
Join Date: Dec 2001
Location: Eindhoven
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Quote:
If you use the buffer, then why the E-follower ? Clock should be as close as possible to the DAC, where the party is ! Feed it back to help generating I2S RFI: Weird, shouldn't be a problem to combine a drive and a DAC chip..... Ciao |
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#5 | |
diyAudio Member
Join Date: Sep 2002
Location: near Milano , Italy
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Quote:
So the clock should feed the DAC (like in DDDAC ?) and then be brought back to the transport? About RFI I remember that the SPDIF output of my player wans't considered that well... maybe it's just a problem of that interface... Cheers Andrea |
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#6 |
Banned
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Hi Andrea and Guido,
What, do I have to explain this very simple circuit to an EE? ![]() As Andrea indicated the Masterclock is not needed or used in the NON-OS DAC. So why bring it back? I explained this earlier to Lars Clausen. Is the NON-OS concept so difficult to digest? In your words "there is no party for the Masterclock at the NON-OS DAC". Then the circuit is taken directly from Horowitz page 612 fig. 9.42 in my second edition. Here is also explained why direct logic drive of long coax cables is not feasible. Now for the buffer: why it is there? No, I don't have to explain that....[hint: figure what happens if you short the transistor...] Oh no, leave the buffer away but don't email me helping solving the problem... Andrea I only had at hand 74HC125 in DIL and did not want to fiddle with MC74VHC125 in SMD. Maybe VHC logic works better here, but I have not yet tested that. AC logic should be avoided as the black pest and F logic is obsolete. HCT or VHCT will probably also work. Ciao ![]() ![]() |
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#7 |
diyAudio Member
Join Date: Nov 2002
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The E followers are here to compensate the 0.5 gain of the transmission line, I think.
Guido: the TDA154x dacs have no clock input (except the BCLK from IIS) and this way, no clock output. I don't think that placing the clock near this specific DAC will help |
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#8 |
diyAudio Member
Join Date: Nov 2002
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I went here too late
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#9 | |
Banned
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![]() Quote:
Sorry wrong answer! There are no 50 Ohm resistors at the transmittor end of the cable. In fact the overall gain is close to one but <1. |
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#10 |
diyAudio Member
Join Date: Dec 2001
Location: Eindhoven
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dear all,
EVERY DAC needs a clock to convert the data to something analog, regardless of the level of oversampling. Is DA conversion so difficult to digest ? Needless to say that a 1541 has a clock input. If you use asynchronuous clocking, you can have a free running clock close to the DAC (but I am still not convinced of this principle) Buffers: The example is too complex. I suggest an E follower, current source loaded with a 47 ohm series resistor to the output, to make it a characteristic driver impedance Elso, others, I'd suggest to use true transmission line with proper driving / terminating. The jitter (for example due to non characteristic system) in the I2S signals definitely ripples through the DAC, wasting the sound (regardless of the clock used there). regards |
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