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Old 15th April 2003, 11:52 AM   #21
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Default DIY ACTIVE CABLE

Hi,

Here's a link to that Dutch company:

SEEC AND YOU SHALL FIND.

Cheers,
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Frank
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Old 15th April 2003, 01:50 PM   #22
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Default buffer is good but...

This circuit can be useful if, for instance, your cd player (or preamp...) has a high output impedance and/or only one op-amp with no buffer.
Let me explain.
I tweaked a Marantz cd-player and one of the mods was changing the two series 100 ohm (for a total of 200) resistors on the output, after the op-amp, by one 47 ohm resistor.
You would not believe the improvement.
The player stays much less sensitive to the quality of the interconnect.
Naim cd players have 10 ohms of output impedance, they shure know what they are doing.
There are cd players and preamps with output impedances of hundreds and even 1k - 2k ohms!
In these cases this circuit may work very well indeed.
But you may not notice anything on a well engineered high-end product like a top of the range cd player with variable output like the top Wadia, or even Mark Levinson.
Do you know why?
Because they have on the ouput OPA2132 and BUF634.
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Old 15th April 2003, 02:12 PM   #23
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Default terminating resistors

No. I have done many and many listening tests, blind tests, switch-box tests. Low output impedance is not enough. The terminating resistor at the second end of output cable is a must. All of the effect disappears in case you do not use it. The best result is: 50 Ohms in series with cable (R10, buffer output resistor) and 50 Ohms as a terminating resistor (R12). Omitt R12 and everything has gone ..
Also 0 Ohms (direct buffer output) without terminating resistor at the cable end gives no sonic result.
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Old 15th April 2003, 02:47 PM   #24
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Hi PMA,

Does it have to be RG58 network cable?
Is there an explanation for this?
I mean, that cable has a 50 ohm impedance (I used to work with that many years ago ), but would a 75 ohm cable and resistor give the same effect?
Have you tried other cable types?

You could use a T BNC plug in the end, and a BNC 50 ohm terminator. That's how it's done in computer networks.
Well... not anymore.
Now it's UTP, SFTP...
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Old 15th April 2003, 02:55 PM   #25
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Quote:
Originally posted by PMA
I am an electronic engineer and I would not believe in the effect of this circuit if I did not build it. For everyone who doubts I suggest: try it and then make a judge.
---------------------------------------------

Depends on your cable and input impedance. Adding something unneccesary changes the sound significantly. May be you are haearing the contributions of the i uf cap, or the opamps.
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Old 15th April 2003, 04:42 PM   #26
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Quote:
Originally posted by fmak

---------------------------------------------

Depends on your cable and input impedance. Adding something unneccesary changes the sound significantly. May be you are haearing the contributions of the i uf cap, or the opamps.
Yes, that is perfectly right until you start to use the buffer. All of that commercial electronics is terribly influenced by the components you have described. Not by the foil cap, but input capacitance of power amp etc. But as I said, nobody who did not try believes. I am sorry guys, this is just waisting my time.
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Old 15th April 2003, 06:10 PM   #27
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Quote:
Originally posted by PMA


Yes, that is perfectly right until you start to use the buffer. All of that commercial electronics is terribly influenced by the components you have described. Not by the foil cap, but input capacitance of power amp etc. But as I said, nobody who did not try believes. I am sorry guys, this is just waisting my time.
--------------------------------------------------------------------
I have exactly the circuit built into the output stage of my DAC. I don't actually find that it sounds that good comapred to other DACs and there are suggestions by others (review magazines) that you should jump it and take the output straight out of the output opamp. The unit is the Assemblage 3.1 Platinum.
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Old 15th April 2003, 06:30 PM   #28
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There may be different experience of different reviewers with different circuits. Reviewers of Audio magazine (the czech one) do mostly use the active cable instead of traditional cable.
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Old 15th April 2003, 07:17 PM   #29
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Default Active cable

Just a comment with no intention to criticize.

Why are you calling this project an active cable? It is really a preamp/buffer which feeds a cable as it should with little or no loss.

An active cable is something different, as far as I know. It's a cable that is polarized in some way using a battery or supply.

Right now I can't seem to find the files I had downloaded on such projects, to mention some URLs.

Synergistic Research manufactures some active cables and charges a lot for them.


Carlos
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Old 15th April 2003, 07:25 PM   #30
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Default Project name

You are right. Several years ago they started to call very similar circuit as an "Active Cable" in the Czech republic. That's probably why it is sometimes called the same way until nowadays.
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