Experience with this DIY DAC ?

[gabrielbecheanu]

What about HDCD decoding? Can we make this DAC to decode HDCD? Also to show us with a led when that kind of signal feed the DAC?.

[Kevin Wood]

These DACs don't do any HDCD decoding themselves. They will accept data with up to 24 bits resolution but it would require the player or an external decoder to decode the 16 bit output of the HDCD and generate the extra bits. That's as far as I understand it anyway. I don't know a great deal about HDCD, to be honest.

Kevin

[johnm]

Google a program on the net called 'hdcd.exe' (also comes as part of the package with dbpoweramp). It will convert 16-bit HDCD encoded files to 24-bit which you can then play back through a DAC such as the one discussed here. I do that myself using foobar2000 and it works a treat

[gabrielbecheanu]

In this case I can use my Panasonic S52 to feed the DAC with the HDCD decoded signal.(hope to be a good transport for the dac)
And the player will show me if is HDCD or not I will use also an Onkyo DX 6850 to compare HDCD signal vs. Redbook signal. I hope to receive the DAC this week.

[ah-luo-ko-ko]

Hi Fred;

I will send you an email with the links from which I got the mod info from in a day or two in order to maintain this specific DAC threads.

Cheers.

[hafp]

johnm,

Opamps; LM4562 sound much better than the NE5532's; faster with more top end.

You should give the OPA2107's a try. IMO, not as digital sounding as the LM4562's, kinda of tube like qualities; but this is subjective, so please don't bash me on this...

Just got some LME49860's which I plan to break in on my small DAC project board and compare to the OPS2107's.

Cheers

[ah-luo-ko-ko]

Hi John;

Sounds like when using the LM4562, you are modding the circuit to a single amp o/p instead of the NE5532 double amp circuitry ?

Hapf; are you doing the simialr mode per John's instruction or the LM4562 is just a direct replacement of the stock NE5532?

[Fenris]

I'm looking at one of these boards as well. I was planning on removing the caps and tapping the signal at that point. I'm looking at building a small "daughter board" with all the analog side components. I'm looking at using a INA134 as a balanced to unbalanced converter followed by a LM4562 used as a lowpass sallen-key filter. Does anyone see any problems with this arrangement? Is there going to be a DC offset to worry about, and if so, how much?

[SoNic_real_one]

Originally posted by gabrielbecheanu
In this case I can use my Panasonic S52 to feed the DAC with the HDCD decoded signal.(hope to be a good transport for the dac)
And the player will show me if is HDCD or not I will use also an Onkyo DX 6850 to compare HDCD signal vs. Redbook signal. I hope to receive the DAC this week.

You won't be able to compare using that DAC, unless you will compare the analog output from your player.
The digital output will not output the 20bit PCM when you play HDCD CD's (that's the equivalent resolution of an HDCD disc). My DVD player has an option to send out PCM (16bit) or bitstream HDCD to be decoded by the receiver.

PS: As software player, any new Windows Media Player can decode HDCD if you have a 24 bit soundcard (MS owns the HDCD from 2002).

[Kevin Wood]

Couldn't resist the urge to have a play tonight:

1) Remove both NE5532s. Insert one (only) LM4562 in the first op-amp socket - the one nearest the center of the board.

2) Remove the following 4 capacitors: L+ / L- / R+ / R-. Replace with wire links.

3) Replace R14, and R17 (both 22k) with 36k.

4) Run a wire directly from the output pins (1 and 7) of the LM4562s to the phono sockets (via the output rely if you prefer this added safety measure).

Step 3 was not required on my board. The 36K resistors have been replaced with 22k so the imbalance that was causing the DC offset is gone.

There is another set of caps between the output of the first op-amp and the input to the second, which is configured as a non-inverting amplifier with a little gain (very little) then there are some more caps down by the phono sockets!

I will draw the circuit in all its' glory when I get a chance but the second Op Amp stage is not worth bothering with, as suspected. You can tap the output from the cap position between the two stages (already a 1k resistor in series with the output here) and bypass all those caps and the mute relay.

Haven't listened to it on anything but my less then great setup in the workshop but it works, minus 8 electrolytic caps from the signal path. There are a few clicks and bangs thanks to removal of the mute circuit. It seems sometimes the DAC ends up outputting a nonzero level when you pause a track, for example, and there's a click when you restart. There's some odd noise on the output if you remove the digital input too, so maybe some kind of mute circuit is a good idea.

Still, looks promising so far.

To Fenris: What you propose sounds like it would work fine. I'm not sure how much you'd gain over the existing first OpAmp stage which doesn't seem too bad as a combined filter and balanced to unbalanced conversion. Only one way to find out. I doubt you'll see any DC offset worth worrying about. After removing the 4 caps on the DAC outputs I saw perhaps a couple of mV of DC on the output of the first stage.

Kevin