Multi-amplification and Active Crossover

[Keith_W]

Maybe you have done it this way, but a better assessment would be between the analogue out of the MPS and preamp ...

The whole point of the comparison (for my point of view) was to see how well the DEQX would function in the way I intended to use it. Therefore, it was inserted between the preamp and the power amp.

It was never my intention to use the DEQX in place of my preamp. If it was, I would have performed the experiment you described.

By the way, the software on the DEQX has a level indicator to see what the input level is (and how close the signal comes to clipping). As I indicated in an earlier post, the DEQX has some kind of electrical incompatibility in my system where anything above a moderate volume on the preamp causes the input on the DEQX to clip. I can assure you that at no time did the input level on the DEQX fall to less than optimum

 

[fas42]

The whole point of the comparison (for my point of view) was to see how well the DEQX would function in the way I intended to use it. Therefore, it was inserted between the preamp and the power amp.

It was never my intention to use the DEQX in place of my preamp. If it was, I would have performed the experiment you described.

By the way, the software on the DEQX has a level indicator to see what the input level is (and how close the signal comes to clipping). As I indicated in an earlier post, the DEQX has some kind of electrical incompatibility in my system where anything above a moderate volume on the preamp causes the input on the DEQX to clip. I can assure you that at no time did the input level on the DEQX fall to less than optimum

Fair enough. It certainly sounds like there is some "problem" there; that's a shame. Any A/D - D/A black box has to get extremely close to being transparent; and it's certainly possible to do. Having heard the beast, and reading other reports it is possible for the DEQX to do. Perhaps it's throwing out too much electrical garbage, which is upsetting the preamp.

Anyway, if you have found an overall solution, that's what counts!

Frank

 

[Nyal Mellor]

Some interesting observations!

A couple of factual corrections:

- Actually the DEQX HDP-3 has two analog inputs, one is XLR, the other is RCA.
- It will also accept a 24 bit digital input at 96kHz.

I do agree though with what others have said, it does not make sense to do a D/A conversion out of your Playback Designs, then a A/D and have an extra pre-amp in the signal chain. I have had a few customers who have wanted to implement the DEQX like that and I always say to them yes it is possible but no you are really not getting maximum benefit out of the unit implemented that way.

Fed with a digital signal the unit is extremely transparent. That's how I use it in my system, fed with a digital signal from an AudioPhilleo USB/SPDIF converter. I have done some comparisons of the DEQX used as a pure DAC against similar cost ($4-6k) two channel DACs such as the Weiss and found it to be competitive...slightly ahead in some areas, slightly behind in others, but more a difference of presentation. And certainly a big step up from the Benchmark cost DACs.

I have been multi-channel active for 7 years now, first with the Linkwitz Orions and now with my DIY compression horn 'monitors' which use Radian compression drivers on 18Sound XT1086 horns with Acoustic Elegance woofers. At some point this year I am hoping to have a 'kit' for this design, but it's still in prototype stage....

Once you go active there is no going back in my opinion. Much like I'd never go back to a system without a subwoofer or digital room correction to deal with the below 100Hz issues.

One of the defining characteristics of a mult-amped active system is consistency of sound character with SPL changes. Many passive systems seem to change character as the volume control gets advanced, I guess this is an audible consequence of the power amp fighting to control the bass drivers with a couple of big inductors and capacitors in the way. With an active system you turn it up and it just gets louder!

DEQX are at some point releasing their HDP-4, which according to the people who have heard one, is an advancement over what they have now. I'm looking forward to getting a demo unit when they finally start shipping.

 

[cjfrbw]

Over the years, I have heard of many who have gone toward digital equalization and crossover, including some of the Apogee guys.

However, they eventually have abandoned them due to the sound quality issues.
They would get a TACT or whatnot and marvel at all of the fiddling and adjustments for a period of time until their tinker-philia was exhausted, and then go back to analog active crossovers or combos of analog active and passive.

I would imagine if digital is your main and only source then it might make sense to use digital crossovers exclusively.

My own thought is that digital active adjustment is very useful for surrounds and bass, and that is the way I use it with the Yamaha RX Z9 receiver unit.

However, since I listen mainly to vinyl in my home system, the front two channels are all analog active crossovers.

Tying a viscous lob of capacitors and coils to the outputs of an amplifier in a passive crossover and expecting the best dynamic performance doesn't compute any more.

 

[fas42]

One of the defining characteristics of a mult-amped active system is consistency of sound character with SPL changes. Many passive systems seem to change character as the volume control gets advanced, I guess this is an audible consequence of the power amp fighting to control the bass drivers with a couple of big inductors and capacitors in the way. With an active system you turn it up and it just gets louder!

Yes, this is where so many systems become undone, but the reason for it is not what you say, but still very bassic -- :b

No matter what people "claim", most amplifiers have barely adequate power supplies: this is why companies like Krell always win in certain areas, it is one thing they really throw the money at. Because producing bass sound requires energy, lots of it! Which means that for a normal amplifier and speakers once you up the volume beyond a certain point the power supply starts to lose the plot, and the sound starts to change, begins to disintegrate.

And an easy solution is to completely separate the power supply for doing all the bass work from that doing midrange and tweeter; even better, separate power supplies for the the midrange and tweeter drivers. Voila, active speakers, and genuinely dynamic sound!

Frank

 

[terryj]

- contrary to what many people claim, the DEQX is not as transparent as is made out to be. There is a massive loss of resolution and dynamics. Instruments sound smeared together and the soundstage is noticably smaller. I have a Playback Designs MPS-5 - the DEQX made it sound like a Samsung.
- the auto function on the DEQX produces unbelievably bad sound. A steep learning curve is involved, something I am still working on.

For me, the issues with clipping and insufficient drive were real deal breakers. But even if I didn't have those problems, the unit still kills dynamics and resolution. I am convinced that any digital crossover is not a contender in any high resolution system. They are valuable development tools, but the real solution is an analog active crossover.

Aren't these criticisms phrased just a little bit harshly? Don't get me wrong, that you have them etc is fine, but the wording seems a bit over the top.

Massive loss of resolution? Unbeleiveably bad sound? Kills dymanics and resolution?

In any case, no matter how valid your thoughts are on your system (and they are btw, am only questioning the wording and conclusions that can be drawn from that wording) you feel you can therefore calim that due to your experience you can generalise to all systems?

You are now not completely agreeing with your earlier statement you never know how good a piece of equipment is until you get to compare it against something else in the same system. ? I mean if that were true you could not generalise about ANY piece of gear?

Frantz I will get around to answering the question in my system thread. I know TerryJ well, but I have not heard his system. You have to understand that he comes from what I call the extreme fringe of objectivists. He uses a $100 DVD player as a transport, feeding digital into his DEQX, and using a whole bunch of secondhand amps to power his speakers. By all accounts it sounds good, but ... you never know how good a piece of equipment is until you get to compare it against something else in the same system.

Aww shucks (hangs head in embarrassment and pride):b, thanks man.

Just curious, a second hand amp is an indicator of 'outness'?? Surely you meant 'inexpensive, amps with no audiophile rep'???

In my system, I have the ability to compare my DEQX against a straight wire. If the DEQX is really transparent, then doing an ABX, level matched, against straight wire would be a fair test?

Maybe....if it were a piece of wire. It ain't so then 'not so much'.

I have done this comparison and repeated the experiment for several visitors and they all heard the same thing. The DEQX was simply set up as an ADC-DAC and performed no processing on the sound. It would simply take the signal, convert it to digital, then convert it to analog. The ONLY processing was to level match the output to the cable. Compared to straight wire, the DEQX destroys the sound.

Destroys the sound?? All heard it destroy it? I mean destroy leaves not much wriggle room or doubt.

A bit harsh?

The cost comes from the ADC. If you feed the DEQX a digital signal, your cost would be far lower. Using the ADC destroys resolution and dynamics. Regardless of how it measures or what specs it claims, there is no arguing with the audible result - everyone could pick it and describe exactly the same thing.

It is a very good unit, but for my system - it doesn't work.

Understand.