Jump to content

Prosink?


hungrych
 Share

Recommended Posts

Another one of those things that makes much of the industry really pissed at me.

All cables when improperly used act as filters. You cannot possibly ever say that one is better than the other, all you can say

is that you like the sound of this one over the sound of another one.

Pick a cable, any cable, there are only two ways to use it. The right way, and NOT the right way. The right way is to terminate

the source and destination ends in the characteristic impedance of the cable. Termination to ground at the destination end, and

a value at the source end that when added to the impedance of the preamp adds to the characteristic impedance.

There is only one real way to measure the characteristic impedance and that is with a time domain reflectometer. Of which I have

a few including the latest that can resolve time to 25 pico seconds.

Take any 2 of the most different sounding cables and let me measure and terminate them correctly. I then challenge anyone to

listen to and tell the difference between them. Not even weeks of listening will give a definitive answer.

Some of the fancy twisted and other geometry cables in fact show significant differences in impedance down the length of the cable.

These should be avoided at all cost.

Many preamplifiers with tube output stages present a significant problem as their output impedance is already to high, sometimes way

to high. In which case a passive attenuator must be used to correctly terminate the cable. This can result in a loss of up to 10db.

Link to comment
Share on other sites

Another one of those things that makes much of the industry really pissed at me.

All cables when improperly used act as filters. You cannot possibly ever say that one is better than the other, all you can say

is that you like the sound of this one over the sound of another one.

Pick a cable, any cable, there are only two ways to use it. The right way, and NOT the right way. The right way is to terminate

the source and destination ends in the characteristic impedance of the cable. Termination to ground at the destination end, and

a value at the source end that when added to the impedance of the preamp adds to the characteristic impedance.

There is only one real way to measure the characteristic impedance and that is with a time domain reflectometer. Of which I have

a few including the latest that can resolve time to 25 pico seconds.

Take any 2 of the most different sounding cables and let me measure and terminate them correctly. I then challenge anyone to

listen to and tell the difference between them. Not even weeks of listening will give a definitive answer.

Some of the fancy twisted and other geometry cables in fact show significant differences in impedance down the length of the cable.

These should be avoided at all cost.

Many preamplifiers with tube output stages present a significant problem as their output impedance is already to high, sometimes way

to high. In which case a passive attenuator must be used to correctly terminate the cable. This can result in a loss of up to 10db.

Not being an engineer, that confused the hell out of me, but after about an hour of thinking :P I think I get it. So here's what I think it means

Find characterisitc impedance of the unterminated cable.

On the source end, terminate it using a connector with an impedance that when added with the source's output impedance will total the characteristic impedance of the cable. So, if the characteristic impedance of the cable is 10, and the source's output impedance is 4, then you'd need a connector with an impedance of 6.

On the destination end, terminate to ____ (this is the part that threw me off; if you terminate the signal wire to ground how does the signal get to the other end? Sorry I'm a noob...)

Link to comment
Share on other sites

You are close. At the destination you put a resistor to ground in parallel with the output that goes to the amplifier.

The numbers are as follows.

I have yet to see a cable that is less than 45 ohms impedance. I have yet to see a cable that is more than 150 ohms.

(300 ohm tv twinline, but i've never seen someone use that for audio)

The stuff i use is 50 ohm pure silver very constant impedance over length cable made by gore cable.

There are a bunch of good 75 ohm cables.

High quality shielding is still mandatory for low noise.

Typical solid state preamp output impedance 10 ohms.

Typical tube preamp output impedance as little as 30 ohms (conrad johnson ART) to several hundred ohms (audio research)

Link to comment
Share on other sites

You are close. At the destination you put a resistor to ground in parallel with the output that goes to the amplifier.

The numbers are as follows.

I have yet to see a cable that is less than 45 ohms impedance. I have yet to see a cable that is more than 150 ohms.

(300 ohm tv twinline, but i've never seen someone use that for audio)

The stuff i use is 50 ohm pure silver very constant impedance over length cable made by gore cable.

There are a bunch of good 75 ohm cables.

High quality shielding is still mandatory for low noise.

Typical solid state preamp output impedance 10 ohms.

Typical tube preamp output impedance as little as 30 ohms (conrad johnson ART) to several hundred ohms (audio research)

This works for the output impedance of a dac too right? What about a passive attenuator? Sorry I'm just trying to figure this out, I want to start diying some cables soon, and this seems like the best way. :)

Link to comment
Share on other sites

The easy way:

a) Pick some decent coax. The Risch stuff will work fine. It will probably be 50 or 75 ohm, because it's hard to find anything else.

B) Put a resistor (of value 50 or 75 ohms, cable dependent) from the center pin to ground at the sink (amplifier or whatever) end of the cable.

The KG approved way:

c) Figure out what the output impedance of your source is. If it's less than 50 or 75 ohms, put a resistor in series (with the center pin) to make it 50 or 75 ohms.[1]

Before a): Use a TDR to measure the precise impedance of the cable and make sure that impedance is constant to within the precision of your choice, then pick out 0.1% resistors of the appropriate values for steps B) and c).

[1] If your source has an output impedance >75 ohms, use 300 ohm TV antenna-cable twinline or 450 ohm ham radio nutjob twinline. Decent quality 300 ohm stuff is almost impossible to find, but the beauty of this trick is that you won't hear a difference.

Now go out and buy the most expensive connectors you can find, because they do still affect the sound.

Link to comment
Share on other sites

Now go out and buy the most expensive connectors you can find, because they do still affect the sound.

How about rigging up some kind of super ghetto connector; get a thick enough resistor lead and add some contact enhancing goop so it fits inside the rca jack and add some kind of locking barrel around it, and use bare wire connection ala 47 Labs OTA on the other side. >:D

Link to comment
Share on other sites

Hey Dr. Gilmore, thanks for posting the details of this process. I am going to have to try this out very soon. I had a few thoughts spring to mind:

1) This is true for digital cables as well, I take it?

2) Does the same idea still apply to cables that are connected from amps to transducers? If so, does the effect of raising the impedance shown to the transducer basically ruin the amps' dampening factor/ability to drive the transducers? If this method works, I see some funky headphone recabling in my future.

3) How much power/current do the resistors used need to be rated for? Does their quality (outside of matching%) matter to the eventual sound quality?

Link to comment
Share on other sites

Two questions:

1 - the resistor -- should we get the best one we can afford, or are they all the same?

2 -

c) Figure out what the output impedance of your source is.

Is there an acceptable way to do this, besides looking it up in a manual or on the manufacturer's site or something? 2b - isn't this a function of frequency?

This site rocks.

Link to comment
Share on other sites

Sources and destinations for digital use are already properly terminated. Otherwise at those data rates, it would

never work. spdif is 75 ohms, and aes/ebu is 110.

Speakers are not a constant impedance by any means. The only cable out there that even approaches the impedance

of a speaker are the goertz cables. And the capacitance of those cables is so high, it drives many amplifiers into distortion

or oscillation. The best way is to have monoblock amplifiers absolutely close as possible to the speakers and then use

the lowest impedance and shortest distance cable you can.

As for headphone cables probably the same thing applies. I don't have a real solution for this other than to velcro

a gilmore lite to the back of your head.

1/4 watt resistors are all you need. The quality of the resistors definitely make a difference.

Figuring out the impedance of your source is not really so hard. You insert a resistor into the line and then a load to ground.

Measure the voltage on both sides of the resistor and you can calculate the source impedance. Many manufacturers specify

output impedance. All krell preamps and cd players are 10 ohms for example.

Link to comment
Share on other sites

Speakers are not a constant impedance by any means. The only cable out there that even approaches the impedance

of a speaker are the goertz cables. And the capacitance of those cables is so high, it drives many amplifiers into distortion

or oscillation. The best way is to have monoblock amplifiers absolutely close as possible to the speakers and then use

the lowest impedance and shortest distance cable you can.

As for headphone cables probably the same thing applies. I don't have a real solution for this other than to velcro

a gilmore lite to the back of your head.

Interesting... that could be part of the reason that recables make such a big difference. I measured the impedance on my K340's [recabled with Headphile BlackGold] and they measure at 337 ohms. Stock they are supposed to be 400 ohms, though I didn't measure them before the recable.
Link to comment
Share on other sites

Alright, since I've 10 thumbs, no solder iron and no urge to make my own cables, who do I contact for 2x XLR F/M terminated cables made "the right way"?

And while we're at it, is there an "ideal" cable length? The units I want to connect (my AQVOX D/A and my Singlepower amp) will be able to reach each other with as little as 2 feet of cable.

Link to comment
Share on other sites

There have been some studies that seem to say that 1 meter is the ideal length for a coaxial spdif digital cable... though I'm not sure of the science behind it. Generally I would assume that for analog cables shorter is better as long as there is a constant impedence down the length of the cable.

Link to comment
Share on other sites

Guest wrote:

Hi Dan, could you tell me what the output impedance of the DA10's XLR output is (I only need to know the value considering one output pin, for unbalanced operation)? I love my DA10, thanks a bunch!

----------

Regarding the output resistance for the XLR's:

There is 75Ohms in series to each XLR active pin. The circuit impedance is less then 1 Ohm, so why 75 Ohms in series? Long cables are capacitive load at "low frequencies" (into the many MHz). Active circuits driving long cables may oscillate at high frequencies. It is common practice to prevent such oscillations (which will be heard as distortions) by use of small series resistors.

For XLR's the load is most often very high (such as 100K, 10K or similar) so the series resistors do not cause attenuation. There are a few cases, mostly unbalanced, where the load is as low as 600Ohms, and the series resistance will cause some signal attenuation (1dB at 600Ohms).

At 10Kohms load, the loss is only about .12dB.

The output voltage of the XLR is very high (24dBu) so a 75Ohms is a good value - plenty of margin for stability (no oscillations) and not much loss.

Regarding the output resistance for the headphone:

With headphones, the parameters are different. The current for some headphones is very high, the load is not always capacitive... so one needs a strong driver with very low series resistance. The series impedance is 0.69 Ohms so that a 600 Ohm load will cause only 0.07dB loss.

Regards

Dan Lavry

----------

philodox - Ok, WTF? Does he actually state the output impedance anywhere here?

Link to comment
Share on other sites

philodox - Ok, WTF? Does he actually state the output impedance anywhere here?

Yup, in the first line. "There is 75Ohms in series to each XLR active pin. The circuit impedance is less then 1 Ohm, so why 75 Ohms in series?" Circuit impedance under 1 Ohm, plus 75 Ohm on the (+) & (-) pins on the XLR. So roughly 75 Ohm, in theory, I think...

Link to comment
Share on other sites

Thanks Eaphan... so if that is true, am I correct in assuming that if I used 75ohm cable to make my cables that connect from the Lavry Black DA10 to my amp I would not need a resistor at all? 75 + 0 = 75

Prosinked by default?

I'm going to be buying some 75ohm cable already to make my digital cable, so if this is true I could get it all at once.

PS. Anyone know of a good BNC connector and a good BNC socket and where to buy it?

Link to comment
Share on other sites

KG can correct me if I'm wrong, but I think for your cable to be prosink-ed, you'd still need the parallel resistor from signal to ground at the amp end of your cable. The fact that the Lavry's output is 75ohm simply precludes the need for a series resistor in the signal path at the source end, since the Lavry basically has one built-in.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...