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Old 26th December 2005, 02:51 AM   #491
Padel is offline Padel  Greece
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Quote:
Originally posted by Davey


I'm sorry I haven't been following this thread for the past few months, but I've been reviewing it a little bit today. Unfortunately there is quite a bit of mis-information in many of the posts.


I hope not from me

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Old 26th December 2005, 03:05 AM   #492
Padel is offline Padel  Greece
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Quote:
Originally posted by Thmartin


Did I say each on his own ? Yes I did

Thierry

Yes you did!!!

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Old 26th December 2005, 08:56 AM   #493
AndrewT is offline AndrewT  Scotland
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Hi,
now that we are getting closer to the real output impedance of the modified DCX output stage.

Can we estimate the true Zout?
If 10R +33R then 0.1uF is a bit large. 68nF or 56nF might be an option to try.

Thmartin and anyone else,
did you try a range of caps on the output?
How did it sound?
Would moving the RC time constant around help?
What roll off characteristic is ideal following a DAC?

Arcam have used a 3pole Bessel (active) in the past. Also set to the high 40kHz.
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Old 26th December 2005, 09:06 AM   #494
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Hi AndrewT

I am VERY happy with what gets out from the DCX now.

However, just to try a more "universal" solution I'm planning to remove completely the DC blocking caps by using the DACs in balanced mode.

That'll include a 1KR resistor on each leg AOUT+ and AOUT- and a 3,3nF polyester capacitor between them.

This will avoid having to block DC (DC shall be cancelled in balanced mode) and 1KR probably provides a better protection for the DACs.

This solution will be tested in the next weeks, I'll let you know what comes out.

But I insist on the fact that the DCX modified as it is is a pure wonder.

Thierry
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Old 26th December 2005, 09:51 AM   #495
AndrewT is offline AndrewT  Scotland
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Thanks Th,

maybe I will go back to mine and experiment some more.
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Old 26th December 2005, 01:18 PM   #496
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Thanks, Thierry.

Simple solution, I am going to try it myself.

I will try it into a valve output buffer,
so I'll be able to run longish cables,
we'll see how that turns out.

Plenty of other stuff to do first, tho,
so probably won't get it done until late spring ,
by that time others may have tried that allready?

cheers
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Old 26th December 2005, 03:14 PM   #497
Davey is offline Davey  United States
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Quote:
Originally posted by Thmartin
Hi AndrewT

That'll include a 1KR resistor on each leg AOUT+ and AOUT- and a 3,3nF polyester capacitor between them.

This will avoid having to block DC (DC shall be cancelled in balanced mode)

Thierry
Are you sure about that?

Davey.
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Old 26th December 2005, 05:11 PM   #498
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Yup, pretty sure. Let's say 99%.
Anyway I'll measure it before I turn the amps on.
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Old 26th December 2005, 05:19 PM   #499
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As best as I can tell, the opamp circuitry is providing:

- current buffering for the DAC
- a high frequency (above audio range), low pass filtering
(both I presume help stabilize the DAC's audio output)

- a shunt circuit for muting signal
- a differential drive circuit for balanced output

Not knowing what the DAC's current drive capability is, how stable and high freq trash free it is, I would be reluctant to chop the first 2 opamps out of the circuit. If you're always going to run an unbalanced output, the last 2 can more easily be chopped without worries.

If the DAC output checks out clean, the mods as shown will work just fine. The downsides are losing the output mute and balanced drive permanently.

MEB
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Old 26th December 2005, 05:51 PM   #500
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Hi !

You know what, this is funny but the "Mute outs" is still bloody working even if T1 to T6 trannies are out of business !

Still can't figure out what Behringer has done there
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