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Old 7th March 2004, 09:03 PM   #1
kyrill is offline kyrill  Netherlands
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Join Date: Mar 2004
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Default DeqX -pd 2.6


I just bought the DEQX pdc 2.6, a digital preamp including an USB interface for yr PC. The special software installed on the PC (winXP in my case) makes it able to use the preamp to measure your loudspeakers characteristics (among others) with the matching microphone.

Build in the preamp are 3 digital active X-overs (6 outputs for stereo) with Linkwitz-Riley filters with a maximum of 300 db slope per octave. but the more slope the more delay For instance 4 millisec at 20 hz with 48 db filters. Also included is a DRC (digital room correction)


I could not actually afford it, but I bought one. Finally you can have flat frq response within 0.2 db (!) and room corrected. By itself it would not attract me but add on top of this near perfect phase correction for the different drivers and time alignment for tweeters and (sub) woofers, and it won me over. Especially now I can build speakers with a wide arrange of drivers and not worry at all about crossovers. You acccept the suggested crossover points or you specify yr own ones. within 10 minutes you listen to yr speakers with those crossovers, with no phase distortion. >100 db slope filters make it possible that your drivers can play perfectly the frq range which they are at their best with no overlap with the other drivers in praxis.

I have unpacked the box. The unit has no high end "charisma" at all. It is modern looking like, like ..well a thin satelite receiver for yr TV. It is almost looking female -ish. Like a modern technical unit for in the kitchen, not to intimidate women. No rotating knobs. A silver sleek unit with dark blue-ish knobs that you can push and it is very light weight.
I like the looks of the "Benchmark DAC1" ( a highly good sounding modern dac or the more technical looking Behringer digital equaliser (
The Deqx I expect to better the Behringer.

I opened the unit to look inside:
One pcb fills 50 % of the inner space. It looks completely like a computer motherboard.. No way that an amateur hobbyist who can even solder well, can replace or mod things. You need a binoccular to find the very small SMD parts.

A second PCB is the power supply that looks.. raw. Raw like the PWS of your computer. Probably there is room to mod.

I don;t know how it sounds!
I have it now for a week and the unit is not even connected to the wall outlet. I don't have a second amp to biamp yet. The installation guide is huge and comprehensive (172 pages in total)

I cannot use the filters and so I cannot correct for the phase difference or correct the time alignment. I only have left perfect freq response and the room correction.

but I have ordered an ASPEN 55 watts sweet SS power amp (kit:
and then I can do much more.

I will let this forum know what it will do
A strange property of the unit is that the blue-ish looking knobs glow (in the dark) with all kind of colors!
The volume "knob" according to the installation guide"
Red: -60db to -50 db
Yellow: -50 to -40
Green: -40 to -30
Blue: -30 to -20
Purple/Pink: -20 to -10
White: -10 to ) dB
Isn't that nice?
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Old 7th March 2004, 11:15 PM   #2
ojg is offline ojg
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Congrats! This is a very cool device! I am very curious about what is inside, any chance of posting some pictures? What DSPs and DACs are used?
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Old 10th March 2004, 09:52 PM   #3
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Default User interface, PC software

I would be very curious about your thoughts on the interface and process for setting it up!

I've searched for a manual on this product and/or a software demo but neither seems available.

Looking forward to your posts!
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Old 12th March 2004, 01:52 PM   #4
Sjef is offline Sjef  Netherlands
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I'm using a DEQX PDC2.6 for about 8 months now, it works great.
I have never looked inside. Normally that the first thing I do when I get a new piece of equipment but I didn't want to get the feeling that I could build something like this my self for about one third of the price. After all, a DSP unit only performs and sounds as good as the software it runs on. It's the software you pay for, and the guys at DEQX have done a pretty good job so far.

The PDC does NOT have Linkwitz/riley filters in a two or three way setup. The LR filters can only be used for subwoofer arrangements when you're out of total system delay. The PDC has a max delay of 42 msec wich it uses for the linear phase crossovers and for time/phase/group delay corrections accross the entire audio bandwith. The use of linear phase filters is one of the biggest advantages of digital crossover, after all the Butterworth, Linkwitz, Chebbychev, etc filters where ALL a compromise between flat freq response and phase response. It simply not possible to build a perfectly phase linear crossover with analog active or passive components. With enough DSP power that's not such a problem. The Behringer for instance does not have enough DSP power to do this, that's why it only works with simulated LR or Butterworth filters.

First I have compared the PDC as a stand alone DAC against the (modified) build in DAC of my Marantz CD63KI. No real difference, in fact very hard to hear any difference at all, although they are totally differend types of DAC's, but with the speaker correction filters in place the difference is huge, I'm very happy with it. I used a tube based LR crossover before but this is something completely different.

Is it worth the money. Yes and no. Yes because you get a unit with good sound quality and possibyllities you could only dream of ten years ago, but on the other hand I think that within the next ten years every mid-fi system has something like this allready build in (together with some class D amps) for a fraction of the money. I really see a big future for DSP based systems ones they go in mass production.
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Old 12th March 2004, 02:06 PM   #5
kyrill is offline kyrill  Netherlands
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Default Dag Sjef : )

thanx Sjef for the correction of what kind of filters DEQX is using and for the people who do not want to wait 10 yeard the price (+/_ 3000 US $ is very very reasonable almost a steal, for what you will get., by direct ordering I got the remote control and preamp mode for less than that price)


I am waiting for my AKSA amplifier from Australia so that I can Biamp my speakers and tell you what I found. I am also waiting for my heavily modded Copland CD player and integrated DAC (modded by the sincere integer and friendly Sebastiaan
I don't have a homepage so I cannot (I presume) post a link here where you can download the comprehensive installation and user guide. I have this guide also in adobe pfd format.

As for a photo of its innards, I will ask for permission by its creators, if that is possible.
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Old 24th May 2004, 07:28 PM   #6
kyrill is offline kyrill  Netherlands
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I have not forgotten this thread, but I want to be sure when posting in public.

I am still in progress to get the best sound out of it sans filters or any EQ. I have a highly transparent muscial system (that is why I fell in love with the Aspen amplifiers, "AKSA " from Hugh Dean in the first place)

I have one AKSA in the house and ordered 2 stereo AKSA power amps extra as the DEQX in a 3 way system needs 6 mono amps (3 per speaker).
However I do hear a difference with the DEQX in the chain or not with all its goodies in bypass mode. In the beginning I was not content about its transparency and "quickness" especially when you use the analogue in and activate its AD converters. However after a few weeks of continuously playing the sound opens up much more than I expect it ever would be.
Now I really believe it can become a true high end unit. When you have a good NAD, Rotel, Arcam or similar system the DEQX in standard mode can already be better.
I am still busy to find out how to get the high end transparent sound out of it , way beyond what mainstream recording studio monitor systems will be able to deliver.

When you can without shame put it in the chain with your beloved Decware, Welbornlabs, Pass Labs, Blue Circle or Krell, just to name a few I will let you know
: )
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Old 24th May 2004, 10:39 PM   #7
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Default Its a shame about the sound quality

You mentioned using it with the AD's engaged. Its not surprising the sound quality is a bit less transparent than you expected.

What about using it as a dac with a digital feed? How is the sound quality in that case?
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Old 24th May 2004, 11:32 PM   #8
Sjef is offline Sjef  Netherlands
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Offcoarse you will hear a difference in a good highres system. But that counts for every piece of extra equipment you put into the signal chain. Put in an extra reference quality multibuck preamp between yor pre and power amp and you will hear a difference. And if you want to use it only as a DAC there are better ones out there for this money. Don't judge the DEQX on that part only but compare it between a passive setup an a properly corrected active setup and you will hear the gain in resolution and soundstage, that's what the DEQX is all about.

I seem to be the only one who actually prefers the analog input via my preamp. (wich is also more convenient) Maybe my CD player has a bad digital out, or maybe I just like the tube sound of my preamp more, who can tell, as long as it sounds good to me it's o.k.
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Old 25th May 2004, 10:03 AM   #9
kyrill is offline kyrill  Netherlands
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Hi Jonathan
Dag Sjef : )

On "expensive" mainstream hifi equipment the analogue in at the DEQX is of course less transparent and less 3D than having the DEQX not in the chain. This is unavoidable. The perceptual difference however, is so small that Sjef and others will gladly accept this for the enormous benefits of the DEQX, it was created for. I believe over 80 % of the people in good hifi systems will even notice the DEQX to be a more transparent pre amp than the one you already have.

On carefully configured high end system which are highly "tuned" to get the best musical transparency out of it, you better avoid the analogue in and use the S/PDIF of your stable transport with of course a retrofitted high precision clock. If your SACD or cd player, irrespective of price still has its original clock in spite of its (heavy) mechanical stability, (I think only 0.001 % or less of all cdplayers have a stable clock) than the DEQX will not be a weaker link in your chain.

However if you tweaked and love your system ( cd player, vinyl player) for being relative resonance or jitter "free"
then the DEQX can use some tweaking itself. It is already highly listenable in such a system, but it has some deeper "potentials"

I am in search for these deeper potentials and I will let you know.
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Old 25th May 2004, 11:42 AM   #10
ergo is offline ergo  Estonia
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What is the price of PD 2.6 ?

I just received my Behringer DCX2496 which is the first step to digital crossover land. If it is worthwhile I may consider a better unit some day .... after tweaking a hell out of DCX

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