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Old 10th January 2011, 06:16 PM   #2921
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Originally Posted by sek View Post
... of course I don't just look at the datasheet.
I like this attitude.

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Are you referring to post #2900?
Yes.

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If the common-mode range of a preceding stage is surpassed and it distorts, going unbalanced in a subsequent stage will cancel out the even order components? I don't think so, but even if it did, there's no point, as the distortion will likely be nonlinear.
That's not what I said. If the common-mode range is surpassed, you're screwed. No argument about that. However, if a differential output driver consists of, say, two op-amps with each even-order distortion, this will become common-mode and will be removed by a good balanced-to-unbalanced stage. And let me tell you, there is plenty of equipment out there where this is the case (so if you would just connect only one signal pin and go directly unbalanced, the signal sounds horrible, whereas with a good diff2se it sounds fine). This distortion is a type of nonlinearity that can be corrected. The odd-order ones will not be corrected, but at least converted to pleasurable even-order by the diff2se.

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By that I was referring to noise caused by high impedance drive and/or bad cabling or signal routing.
Ah, ok. I agree that high impedance drive can cause noise.

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... what I didn't agree with was the remark that single ended drive would affect sound quality badly. It can be worse due to the lost balance in the impedances, but that's also true for the differential buffers.
Ok, fine if you disagree. I still think that going single-ended into a differential stage means the CM loop is way too heavily involved in processing the signal, leading to distortion. Unless of course you use a balun (e.g., transformer - Lundahl or so).

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What can SSM2143 or INA134 do that OPA1632 cannot be made to do, component precision aside (i.e. assume 0.1% resistors)?
Fully symmetrical layout, superior CM-induced distortion, any number of things that are not documented. However, in the absence of common-mode, I believe the signal-distortion performance of your OPA1632 to be superior.


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The disadvantages due to the higher complexity might outweight the benefits. At least for someone without an RF PCB fab...
As someone with commercial interests in RF PCB fabrication, let me tell you that nowadays it is quite easy for a consumer to approach a PCB manufacturing company and get them to produce your design using a state-of-the-art PCB technology. And it's not scary expensive. Just give them the gerber files, wait a couple of days and begin soldering...

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The tradeoff that I see is this: the differential buffers with the inverter in it's feedback loop has a much higher component count, first and foremost a second opamp (in the feedback loop), but also a far higher count of passives (compensation, etc.) with their own tolerances.
This is true. However, better five properly configured opamps in the signal path rather than one badly configured opamp.

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I will try both alternatives.
I look forward to reading your findings.

--
Greetz,
MatchASM
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Old 14th January 2011, 10:44 PM   #2922
sek is offline sek  Germany
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Originally Posted by MatchASM View Post
I look forward to reading your findings.
I'll post as soon as I got something, but unfortunately it's exam time (cs) of the year already!

All of the most significant parts have arrived, though (see pic in fullscreen mode). I'll likely be able to get to it in about two weeks.

Cheers,
Sebastian.
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Old 18th January 2011, 08:41 PM   #2923
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I have been planning to make balanced passive outputs with capacitors to DCX according to these instructions:
- passive output stage for DCX2496
- Blanced passive output stage for the Behringer DCX2496

What functions do I lose, if any? (besides the ability to amplify the output voltage). My logic says that is the only lost function, but am I correct?

I figured since the channel balance (when volume is decreased below 0dB) is made digitally, (and vice versa made by opamps if amplified >0dB ie. +1 to +15dB) so I don't lose the ability to to determine channel balance if I do it by using only the scale between 0dB and -15dB, if you understand what I mean. I'm setting the channel balance currently this way, so it would not be new to me.

What happens if I set channels output level to +1 - +15dB - nothing?

Last edited by Legis; 18th January 2011 at 08:44 PM.
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Old 18th January 2011, 09:29 PM   #2924
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Quote:
Originally Posted by Legis View Post
I have been planning to make balanced passive outputs with capacitors to DCX according to these instructions:
- passive output stage for DCX2496
- Blanced passive output stage for the Behringer DCX2496

What functions do I lose, if any? (besides the ability to amplify the output voltage). My logic says that is the only lost function, but am I correct?

I figured since the channel balance (when volume is decreased below 0dB) is made digitally, (and vice versa made by opamps if amplified >0dB ie. +1 to +15dB) so I don't lose the ability to to determine channel balance if I do it by using only the scale between 0dB and -15dB, if you understand what I mean. I'm setting the channel balance currently this way, so it would not be new to me.

What happens if I set channels output level to +1 - +15dB - nothing?
All these issues are of course solved with my mod - the active, remote controlled level control for the DCX. Balance, amplification, level offset between channels, and IR remote control with a volume display on the DCX.
May not be your cup of tea but hard to beat for functionality and performance. If I may say so myself

http://www.linearaudio.nl/6chan-1.htm

jan didden
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Old 18th January 2011, 09:36 PM   #2925
Legis is offline Legis  Finland
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Originally Posted by janneman View Post
All these issues are of course solved with my mod - the active, remote controlled level control for the DCX. Balance, amplification, level offset between channels, and IR remote control with a volume display on the DCX.
May not be your cup of tea but hard to beat for functionality and performance. If I may say so myself

http://www.linearaudio.nl/6chan-1.htm

jan didden
Thanks Jan. What issues there will be then exactly? Is the ability to amplify output voltage the only function that is lost?
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Old 18th January 2011, 09:47 PM   #2926
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Originally Posted by Legis View Post
Thanks Jan. What issues there will be then exactly? Is the ability to amplify output voltage the only function that is lost?
That's not a great loss. The DCX is originally set up for pro output levels which are too high anyway. So going passive after the DAC is OK level-wise if you don't attenuate. (I also have a passive output mod described in an audioXpress article).
But when you go digital in (and you want to do that, with Frank Oettle's mod), you need a level control somewhere and the DCX has too little range as you noted. So you need an analog control somewhere betwen the DCX and your power amps. You also want to set the levels of the different channels separately as you may have different amps and different driver sensitivities.
That was the point I decided to fix it once and for all

jan didden
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Old 18th January 2011, 10:04 PM   #2927
Legis is offline Legis  Finland
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Originally Posted by janneman View Post
That's not a great loss. The DCX is originally set up for pro output levels which are too high anyway. So going passive after the DAC is OK level-wise if you don't attenuate. (I also have a passive output mod described in an audioXpress article).
But when you go digital in (and you want to do that, with Frank Oettle's mod), you need a level control somewhere and the DCX has too little range as you noted. So you need an analog control somewhere betwen the DCX and your power amps. You also want to set the levels of the different channels separately as you may have different amps and different driver sensitivities.
That was the point I decided to fix it once and for all

jan didden
I have an Yamaha AV-receiver with 7.1 inputs and 7.1 pre outs as a 6ch volume controller after the DCX. It is nice, but maybe not the most hi-fi solution on the market. For the price it's nice though; one can get good deals for couple of years old AV-receivers.

So I think I can go passive without sacrificing anything? The DAC has full amplitude digital signal at it's digital input, I set channel balance by only attenuating channels (between 0dB and -15dB), the final volume is controlled by the AV-receiver and from there the signal is finally taken to the power amps.
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Old 19th January 2011, 12:14 AM   #2928
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receivers tend to have VERY noisy preamps.

I tried using my older yamaha as an amp (using their 'pure direct' mode) and it was quite noisy at 0db gain and only at about -20db would the noise be low enough to use.

it seems their amp sections are not too bad but the preamp is the weak spot.

you will lose a lot of performance going from dcx to a home AVR.
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Old 19th January 2011, 05:11 AM   #2929
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Legis, Jan's passive o/p article is on the Audioxpress website to download free.

As for AVR's having noisy pre sections, my experience doesn't agree; neither my old Pio or newer Onkyo are particularly noisy, even with high efficiency speakers.
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Old 19th January 2011, 09:32 AM   #2930
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[snip]As for AVR's having noisy pre sections, my experience doesn't agree; neither my old Pio or newer Onkyo are particularly noisy, even with high efficiency speakers.
I would agree; while there are always cases like that, it certainly is not common. Maybe the 'noisy' case was with lower-than-usual input signal.

jan didden
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