DAC board(s) for 3-Way active Speaker

[wgh52]

Hi folks,

this is my first post and I have joined because of the equipment reviews done here. So far I have been reading, now I have an application question. My background is electronics, but I'm not too experienced with DACs.

Anyway, I've been a fan and user of active spreaker for 40 years now, using a DEQX PDC as 3-Way active cross over since about 10 years. The unit employs AD1853 ADCs and has a 3-Way AES3/SPDIF Output board built in. I am wondering about the sense of employing a more up to date DAC solution now. May be in the form of internal boards or an outside DIY box with balanced analog outputs to feed the power amps in the speakers.

For this I'm looking for DAC boards recommendations. Max. resolution on the SPDIF/AES connection would be 24Bit/96kHz. I'd like to keep the budget to ~100€ per board.

This list may help me, but it is sooo long and maybe there are some folks out here who are willing to help me pre-select from it.

Thanks a lot!
Besst Regards,
Winfried

 

[AnalogSteph]

Ha, I thought I knew the handle from somewhere... diyAudio? ... Yup.

Which unit is this, I'm assuming either of the old PDC-2.6 or 2.6P? Found some specs for these guys.

I think you meant to write DAC rather than ADC, given that the AD1853 is one of the former. (Which ADC does it use though? My guess would be perhaps AK5393?) While the AD chip does have some quirks like idle tones and is not quite on par with newer ones, output specs still are a good ways off from datasheet level, indicating that the output stage may be the limiting factor here. Looking at what a modified Behringer DEQ2496 can do, there is little doubt in my mind that the performance of the trusty PDC-2.6 could be spruced up a bit as well. Distortion would be perfectly fine as-is, I'd just want dynamic range above rather than below the 110 dB(A) mark to clear any concerns of audible noise.

The question is at what price, of course. Reverse-engineering the existing circuit (so you know what could be reused and where to tap in), coming up with a new one, designing boards, having them fabbed (possibly twice because of some kind of annoying screwups), populating them and modifying the unit to accept the new board + output jacks (not to mention measured performance verification) all takes time and money.
That said, it's not like inexpensive DACs with SPDIF in and balanced outputs are growing on trees either... you'd have to approximately double your budget for a finished unit, and I'm not sure whether there even are any bare boards available. Those with RCAs are more plentiful but you may easily end up with a passives fail like this... presumably these are being designed and built with very little if any performance verification.

There may be suitable multichannel studio-level converters on the used market as well, but I am under the impression that these are mostly using ADAT, not AES/EBU, and those old enough to fit the budget may not provide DAC performance much better than what you already have.

 

[Kal Rubinson]

Hi folks,

this is my first post and I have joined because of the equipment reviews done here. So far I have been reading, now I have an application question. My background is electronics, but I'm not too experienced with DACs.

Anyway, I've been a fan and user of active spreaker for 40 years now, using a DEQX PDC as 3-Way active cross over since about 10 years. The unit employs AD1853 ADCs and has a 3-Way AES3/SPDIF Output board built in. I am wondering about the sense of employing a more up to date DAC solution now. May be in the form of internal boards or an outside DIY box with balanced analog outputs to feed the power amps in the speakers.

For this I'm looking for DAC boards recommendations. Max. resolution on the SPDIF/AES connection would be 24Bit/96kHz. I'd like to keep the budget to ~100€ per board.

This list may help me, but it is sooo long and maybe there are some folks out here who are willing to help me pre-select from it.

Thanks a lot!
Besst Regards,
Winfried

I recommend the one at the top of the list. He used to sell the DAC board itself which might do the job for you.

 

[Juhazi]

Multichannel version needed for a pair of 3-ways...
https://www.oktoresearch.com/dac8pro.htm

And if one is not so critical, minidsp 4x10HD will do...
https://neurochrome.com/pages/minidsp-4x10hd#

or even a pair of 2x4HDs if one doesn't need balanced out
https://www.audiosciencereview.com/...urements-and-minidsp-2x4-hd-dsp-and-dac.2674/

 

[AnalogSteph]

Multichannel version needed for a pair of 3-ways...
https://www.oktoresearch.com/dac8pro.htm

Excellent device, €989 may be just a tad out of the OP's budget range though.

And if one is not so critical, minidsp 4x10HD will do...
https://neurochrome.com/pages/minidsp-4x10hd#

Then he might just as well stick with what he has now, which has roughly the same noise level and at least 10 dB lower distortion. The CS42528 could definitely do better, it's the implementation in the 4x10HD that lets it down. Tom would have liked to see a better-performing opamp and I do think this would have helped, the results are about what I'd expect when a '2068 is breaking a bit of a sweat.

 

[wgh52]

Hi everyone,

Yes, I actually meant DAC, not ADC., so thanks a lot for all the comprehensive and engaged comments and recommendations!

As we mention ADC anyway: The original 12.288MHz oscillator was replaced by a Tent clock fed by a shunt regulator many years ago which already brought significantly better sounding AD conversion. And at the moment I'm exchanging the Meanwell power supply by a linear one. But all this is off topic ;o)

Your answers confirm what I had heard in some other cases in the past: The output stage may be a better place to start modification efforts. Also, adding an external DAC unit for 1,000€ or more was actualy not the plan, 300€ for internal boards would be OK... ;o)

Maybe to clarify my thinking by an example: Khadash has the Tone board. May be a suitable solution? Potentially, if the board works stand alone, but I don't know that. If that works, I could remove the RCAs from the boards and solder suitable connections to the PDCs Dig Output board (making sure signal levels match).

Well, the PDC-2.6p Mainboard (it's actually the HD version with better OPAs and capacitors) also provides dedicated Headers to plug in DEQXs own balanced analog output board cables. Finding out where these connect to the DACs' electronics should be simple, so suitable balanced output buffers could be done as an initial alternative to new DACs.

I'll give all this some thought... Maybe someone knows/understands the Khadash board...?
Thanks again,
Winfried

 

[wgh52]

Just remembered this thread, so here is the project status:

The (off-topic) power supplies are working well: Separate +/-15V linear for the digital part and separate +/-12V linear for the analog part (the original LM317/337 regulators feeding from the +/-15V SMPS are gone).

In the mean time I followed the advice to not use the digital output board to drive a new internal or external 3-Way-Stereo-DAC solution, but instead tap into the DAC circuitry and implement an improved analog filter and output stage.

The solution being built up right now uses the existing internal DAC circuitry (the AD1853 seems to not be such a bad choice after all...) until after the I>V Stage (OPA2134) and then diverts to an add-on board with OPA1632 doing mutable filtering and balanced output driving of symmetric signal cables to the active balanced speaker inputs. So this way the signal is never referencing GND until it gets into the speakers, The existing (many!) OPAs in the PDC circuitry which were (according to my reverse engineering) "just" filtering and feeding the signal forward (e.g. I'm using the digital volume control anyway) and drive the cinch lines will be disconnected from their power supply, so they don't draw current without doing work .

So far in brief.
Thanks again for all the feedback received here!
Regards,
Winfried

 

[howard416]

What's your source? Any opportunity to get I2S, or limited to S/P-DIF / AES-EBU?

 

[wgh52]

What's your source? Any opportunity to get I2S, or limited to S/P-DIF / AES-EBU?

Hello Howard,

sorry for the late reply! I had missed your question and unfortunately, in the mean time, the now 15 year old DEQX PDC started to work unreliably, cost of repair would be "out of range", so I have aborted the DAC upgrade project for the time being.

Alternatively, I am currently evaluating a miniDSP Flex Eight as PDC successor, but it lacks an ADC for my LP recordplaying. So I'm looking for a decent Phono ADC, not costing a fortune, but this is yet another story

Oh well...
Greetings,
Winfried