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Old 19th January 2010, 09:00 PM   #2451
Legis is offline Legis  Finland
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Quote:
Originally Posted by SQLGuy View Post
Maybe, but that's a bit brute force. There are other circuit optimizations that can be done besides just swapping different op amps into the existing topology. For instance, switching from the existing input buffer to the OPA1632 reduces the input path from six op amp stages to the one OPA1632, simplifies the addition of the 2.5V offset, and allows for DC coupling.

Similarly, the output side can be simplified and DC coupled as well. If you're looking at such wholesale changes as swapping out all the 4580's, I'd really consider swapping in Jan's I/O board instead.

Cheers,
Paul
Yep, Jan's mods are quite pricey though. Are these I/O board kits good? Selectronic : Vente par correspondance de composants électroniques

You are right, maybe I should have ordered just two of these kits (if they are any good). But this way I did it I saved the price of the other kit.
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Old 19th January 2010, 09:01 PM   #2452
SQLGuy is offline SQLGuy  United States
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Originally Posted by Legis View Post
Yep, I read that OPA1632s perform well, but, as you said, they don't suit well in the original desing as they run too hot. LM4562s should work fine based on what I have read. Do you have experience of how much changing the input and output op-amps to OPA 1632/LM4562 or equivalent will reduce the hiss?

Interesting comment on the "too hot." Do you have more details on this?

The LM4562 idles at 10mA = .3W.
The OPA1632 idles at 14mA = .42W.

A bit hotter, yes, but not excessive for what I'd expect to be able to radiate from an SOIC-8 package.

FWIW, the NJM4580 idles at 6mA = .18W ... so the LM4562's are already almost twice as hot as the stock IC's... and there are a lot more of them on the board. One OPA1632 replaces three NJM4580's, so final power draw is about the same.
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Old 19th January 2010, 09:04 PM   #2453
Legis is offline Legis  Finland
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Quote:
Originally Posted by SQLGuy View Post
Interesting comment on the "too hot." Do you have more details on this?

The LM4562 idles at 10mA = .3W.
The OPA1632 idles at 14mA = .42W.

A bit hotter, yes, but not excessive for what I'd expect to be able to radiate from an SOIC-8 package.

FWIW, the NJM4580 idles at 6mA = .18W ... so the LM4562's are already almost twice as hot as the stock IC's... and there are a lot more of them on the board. One OPA1632 replaces three NJM4580's, so final power draw is about the same.
It was said that OPA1632 runs (too) hot if used in +/- 15 volts: Print Page - DCX2496 audio mod (Post by: jdbakker on March 10, 2009, 03:19:00 pm)

Last edited by Legis; 19th January 2010 at 09:11 PM.
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Old 19th January 2010, 09:26 PM   #2454
Xoc1 is offline Xoc1  United Kingdom
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Default Optimising the gain structure

Legis
It may be possible to reduce the noise floor of the DCX but please also concider that this is a digital unit, and running it at low signal levels will restrict the resolution of the unit.
The aftermarket modifications for the DCX usually result in a much reduced voltage level for full scale digital input. Replacing the op amps would not optimise this aspect of the DCX performance.
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Old 19th January 2010, 09:29 PM   #2455
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Have I understood it right that the hot and cold is floating on the output(within reason)? (relative to ground)
Could I then just take hot and cold plugging it directly into single ended amp. Hot to + and then grounding cold at the amp side.

Amp will be a simple follower with a gain of little under 1. Driving 100dB speaker.

I think the gain structure should be fine for my use, probably ending up controlling volume at the input. Ether digital or analogue in depending on final setup.


And quick PA related question. Will there be any ill effects if the DCX is powered on and off by removing external power. The amps will receive the same treatment (Yamaha P7000s and P5000s) by the same master switch.
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Old 19th January 2010, 09:58 PM   #2456
Legis is offline Legis  Finland
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Originally Posted by Xoc1 View Post
Legis
It may be possible to reduce the noise floor of the DCX but please also concider that this is a digital unit, and running it at low signal levels will restrict the resolution of the unit.
The aftermarket modifications for the DCX usually result in a much reduced voltage level for full scale digital input. Replacing the op amps would not optimise this aspect of the DCX performance.
Do you mean that it will lose some of it's resolution if LM4562s are used? It would meand that LM4562s would drop the gain compared to stock op-amps, do they? Both have quite the same maximum output voltage swing (this measures the maximal gain?). I think the lower overall noise of LM4562 is the reason for lower hiss, not that it would actually reduce the gain?

If I turn the output's gain -7,5dB from DCX, doesn't that mean that DCX will always have 7,5 db greater dynamic range than the music signal will ever have. Does the "extra" (compared to signal) resolution and DR benefit somehow?

Last edited by Legis; 19th January 2010 at 10:01 PM.
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Old 19th January 2010, 10:08 PM   #2457
SQLGuy is offline SQLGuy  United States
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No. What he's saying is that most output mods also include lower gain in the output stage, which directly results in reduced noise from within the DCX and increased use of the digital dynamic range of the DACs - because you're more likely to drive the DCX near to its maximum signal level.

On the other hand, if you have background noise from your source and/or preamp, having to "crank it up", to make up for the reduced gain of the DCX after an off-the-shelf mod, may negate some or all of your benefit.

If all you're doing in swapping JRC4580's for LM4562's, the gain will be identical to stock.
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Old 19th January 2010, 11:44 PM   #2458
Pano is offline Pano  United States
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Quote:
Originally Posted by David_Web View Post
And quick PA related question. Will there be any ill effects if the DCX is powered on and off by removing external power.
I've done it plenty and never had any problem at all. AFAIK, all the power switch does is cut the AC anyway.

EDIT. I checked. The power switch just cuts the hot wire of AC power. Nothing fancy. Pulling the plug or using a power switch on a remote panel would do the same thing. No worries.
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Old 20th January 2010, 07:12 AM   #2459
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Originally Posted by WiredforSound View Post
Its wll know among PA experts that Bheringer is Low end, the pros use dbx og BSS or Dolby... different pricerange - different sound
Go check dbx 260 or BSS FDS 336...
Neither of those units have a digital input, so are less than useful for some of us. All the filters all these units use are FIR as far as I'm aware, so should be no difference in the digital domain, the analogue I/O are reasonably easily fixed by DIYers and they don't need to withstand the physical rigours of pro use at home, I don't see any benefit to either of them.
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Old 20th January 2010, 09:08 AM   #2460
AndrewT is offline AndrewT  Scotland
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Originally Posted by David_Web View Post
Amp will be a simple follower with a gain of little under 1. Driving 100dB speaker.

I think the gain structure should be fine for my use, probably ending up controlling volume at the input.
assuming 10Vpk from the DCX and using that through a unity gain buffer to feed 100dB/W @ 1m speaker will give ~111dBpk @ 1m. That is loud, if your speakers are capable of going that loud.
The system has sufficient gain.

This is the way to set up the DCX, set the maximum output of the DCX so that the final signal coming from the speakers is not quite clipped.
Then turn down the volume for normal listening levels, preferably after the DCX.
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