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Old 26th May 2005, 10:17 PM   #1
PMA is offline PMA  Europe
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Default Current loop based link signal transfer

Continuing in my search for high quality link signal transfer, I have developed the current loop transmitter module. It is a voltage controlled current source, operating in pure SE class A. The signal current is 12mA +/-6mA, 2mA/V. Cable terminated by resistor 50 Ohm - 200 Ohm. AC coupled input of following amplifier is needed. The sonic results are more than promising, compared to any previous principles.
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Old 26th May 2005, 10:33 PM   #2
AKSA is offline AKSA  Australia
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Intrigueing, Pavel,

Can you tell us more, such as Zin, Zout, FR, the sort of amp it requires, and how it sounds?

Cheers,

Hugh
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Old 26th May 2005, 10:50 PM   #3
hermanv is offline hermanv  United States
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Default current coupled audio

I have used current coupling for instrumentation and wondered about its use for audio interconnects.

On my home system I need to clean my contacts fairly regularly for best results. I've wondered if the ability of current loop feed to ignore effecitve series resistance (within limits) would impact this problem.

This brings up a second perhaps more interesting question: To wit, no one quite understands the whole issue of why cables sound different. Normally cables are driven by voltage sources. If you drive an interconnect cable between two audio devices with a current source does this change the relationship between exotic expensive cables and sound quality?
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Old 27th May 2005, 12:29 AM   #4
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Is this a preamp? The voltage gain depends on the load, isn't it?
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Old 27th May 2005, 02:28 AM   #5
anatech is offline anatech  Canada
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Hi PMA,
Always wondered what a 4~20mA current loop would sound like. As far as a transmission medium, it works very well for telephones. I am not trying to be funny either. Having a bias will overcome dissimilar metal contacts as well.

I did work in an insturmentation cal lab, and now in telecom. Do you think we can use BIX strips as connectors? Just punch the cable down and you have a gas tight seal.

-Chris
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Old 27th May 2005, 03:44 AM   #6
Leolabs is offline Leolabs  Malaysia
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Is Krell's CAST similiar to this????
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Old 27th May 2005, 06:16 AM   #7
PMA is offline PMA  Europe
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Quote:
Originally posted by AKSA
Intrigueing, Pavel,

Can you tell us more, such as Zin, Zout, FR, the sort of amp it requires, and how it sounds?

Cheers,

Hugh
Hugh,

I do not think that these parameters are of special importance. OK, Zin = 15 kOhm, Zout = very very high, BW = several Hz - 200kHz. BW has been limited from original MHz range. The step response is purely (1 - exp(-t/T)), as for simple passive RC. Zload = 50 Ohm (at the input of following amplifier).

I have made a listening black-box test with 3 listeners (individually written impressions), they have all prefered current loop with basically same description - more clear midrange and highs, better resolution, more natural, non-artificial sound.

Cheers, Pavel
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Old 27th May 2005, 08:35 AM   #8
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I have an old article about this in a Swedish hifimagazine somewhere.
They compared 210 feet of "worst kind of cheap" audiocable driven with a currentloop and 3 feet normal highend cable driven with a low Z-out and high Z-in on the amp. Could not hear any differences that would make the expesive kind of cable worth it in that comparison. The 210 feet of bad cable sounded VERY dull and lifeless and harsch driven with a low Z-out and high Z-in.
I belive wery strongly that the usual approach is a very bad way of using cables.
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Old 21st June 2005, 02:58 AM   #9
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Hi, PMA,

I'm very interested in this. I experimented with non-feedback V-I converter, which the voltage gain is R-value dependant only, it sounds good

Are you going to post the schematic?
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Old 21st June 2005, 04:18 AM   #10
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With current-driven connections vs. voltage-driven ones all you accomplish is to exchange series and parallel R, C, and L. They still matter, just in a different configuration. It all depends on the cable configuration as to what will sound best. Certainly some combinations will beat others with current, but just as certainly others will work better with voltage.
As always, ya pays your money and ya makes your choice.

Grey
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