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Old 24th January 2010, 10:32 PM   #2491
Cobra2 is offline Cobra2  Norway
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After trying a stock DCX, and found it noisy (in 112dB efficient horns!), I bought a dbx DriveRack 260. Just as noisy. Did the full DIY-routine, swapped all opamps to LM4562 (big handfull), some coupling-caps, to BG, and it did sound slightly better, but hardly worth the effort. And still just as noisy.
I sold it, got a new (used) DCX, and the kit from http://www.linearaudio.nl/6chan-1.htm .
After some initial struggle, I got it running, and my analog x-over-project was posponed...
-now I have silence !!! (when wanted). Even without lowering the output-volume. The new front-end is that much better.

Arne K

BTW, I run the DCX with analog inputs...
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Last edited by Cobra2; 24th January 2010 at 10:39 PM.
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Old 24th January 2010, 11:39 PM   #2492
mige0 is offline mige0  Austria
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Quote:
Originally Posted by Cobra2 View Post
After trying a stock DCX, and found it noisy (in 112dB efficient horns!), ....
-now I have silence !!! (when wanted). Even without lowering the output-volume. The new front-end is that much better.

Arne K

BTW, I run the DCX with analog inputs...
Good for you - dont know what output level Didden's mod actually provides - but from mere spec he is at -112 dB for THD & noise - whereas the stock unit is spec'ed at -112 dB for THD & noise - see what I mean ?

Have not measured, but don't think stock spec are way off...
So - what actually is the undistorted max output voltage of your modified unit ?


Michael

Last edited by mige0; 24th January 2010 at 11:45 PM.
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Old 24th January 2010, 11:50 PM   #2493
Cobra2 is offline Cobra2  Norway
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The stock speck must have been (estimated) below 1kHz...
I have no measurements of the Didden-mod, but have plenty of gain to play with...

Arne K
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Old 25th January 2010, 12:32 AM   #2494
mige0 is offline mige0  Austria
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Yes THD+N *is* usually measured at 1 kHz.

What I wanted to make clear - you do not know about output *signal* of your mod.

Again - look at the relation of THD+N with respect to signal - anything else is pretty worthless .

There are two possibilities - disconnect your input (or switch to digital-IN) turn fully up your volume and then tell us if there is lower noise as with stock unit.

If you have more or less the same noise - well...
If you have considerable lower noise - you have to check if you get the same signal strength as with stock unit....

If you have checked back that way - *then* and only then , you can tell how much the mod actually reduced noise of the unit - anything else are the benefits of voltage divider attenuation (or in case of the didden mod - VCO attenuation) - also known as the ominous "gain structure"


Michael
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Old 25th January 2010, 01:27 AM   #2495
SQLGuy is offline SQLGuy  United States
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Quote:
Originally Posted by mige0 View Post
Yes THD+N *is* usually measured at 1 kHz.

What I wanted to make clear - you do not know about output *signal* of your mod.

Again - look at the relation of THD+N with respect to signal - anything else is pretty worthless .

There are two possibilities - disconnect your input (or switch to digital-IN) turn fully up your volume and then tell us if there is lower noise as with stock unit.

If you have more or less the same noise - well...
If you have considerable lower noise - you have to check if you get the same signal strength as with stock unit....

If you have checked back that way - *then* and only then , you can tell how much the mod actually reduced noise of the unit - anything else are the benefits of voltage divider attenuation (or in case of the didden mod - VCO attenuation) - also known as the ominous "gain structure"


Michael
Not sure whether Jan's kit has the same 0dB out, but, regardless, it has a 6-channel attenuator after the DAC's, so, at anything but max volume, it will be attenuating background noise.
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Old 25th January 2010, 05:35 AM   #2496
Pano is offline Pano  United States
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Quote:
Originally Posted by Cobra2 View Post
After trying a stock DCX, and found it noisy
Sigh.... gain structure again.
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Old 25th January 2010, 07:37 AM   #2497
mige0 is offline mige0  Austria
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Quote:
Originally Posted by SQLGuy View Post
Not sure whether Jan's kit has the same 0dB out, but, regardless, it has a 6-channel attenuator after the DAC's, so, at anything but max volume, it will be attenuating background noise.
Quote:
Originally Posted by panomaniac View Post
Sigh.... gain structure again.


You both nail it – again - and again - and again - - - -
- S/N seems to be the most difficult lesson to learn in audio


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Old 25th January 2010, 01:56 PM   #2498
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Quick update. I got my DCX set up to drive my subs (AVR sub out > DCX > Class D amps with low impedance input). I set the preamp output on the AVR sub output at +10db and the DCX input gain at 0 db. I adjusted the balance between the subs and mains by turning down the output levels on the DCX (they ended up at -9 and -12 db for the two subs). Then I just used the receiver to control volume. Works fine. No noise at all when the Reciever volume is turned up loud (I did find there to be a bit of noise with pins 1 and 3 disconnected on the output XLR>RCA cables; this went away when I connected them). So the stock DCX seems to work fine for this application.

- Doug
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Old 25th January 2010, 03:55 PM   #2499
Cobra2 is offline Cobra2  Norway
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The perceived volume is the same, -analog settings are set at +3dB in, max(+6) at output,
All digital-settings are equal (maybe even increased the treble-shelf-lift slightly), -still use the same preamp(buffer), I use the same volume-range as before.
Difference is without "Linear-kit", I had a top-hiss I could hear more than 10m away on the Altec 909(or 299)/& MantaRays.
Now, I have to go closer than 1m just to hear the faint noise.

Arne K
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Old 25th January 2010, 04:08 PM   #2500
mige0 is offline mige0  Austria
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Originally Posted by Cobra2 View Post
...
Now, I have to go closer than 1m just to hear the faint noise.

Arne K
you have cranked up your volume control of the modified DCX to full ?



Sanity check:

usually SPL falls -6dB each doubling of listening distance - so in your case from 1m to 10m its roughly 3 times -6dB = ~20dB

See ? - hard to believe....


Michael

Last edited by mige0; 25th January 2010 at 04:16 PM.
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