No it isn't that simple, but I wanted to mimic the setup that started the discussion and it is the most easy to do.

A proper one would involve extra series resistance at the nos1 cable's end (42 ohms). This is for a later moment.

Regards, Coen

Terminating the 75 ohm video cable with 75 ohm resistors in the RCA plugs.

Similar to using two bnc-rca adapters with 50 ohm resistors buid in for a 50 ohm cable.

Regards, Coen

Hi Mani,

You're right. I have misscounted the number of digits on my unscientific calculator. 1nF was for the entire cable.
Anyway in the mhz range other stuff becomes important as wire induction, and of course the hf transmission characteristics.

So thanks to the low source impedance cable capacitance still doesn't matter at 10m. This was actially my first point  .

I didn't make it to the box tonight and i wonder if I did not throw away all my scr*p token ring coax. if so I could start with a simple video cable and do the 75 ohms in the connectors. (Did anybody try this allready?).

Regards, Coen

I just looked at it:

Source impedance is with 33 ohm series resistor and 50 ohm the first adapter: 19 ohm. This is low enough for a 1 nF cable: -3 dB on 830kHz. The second adapter containing also 50 ohm even improves on this.

Regards, Coen

Ps. audio signals have very long waves (>10km for 20 kHz) so the hf characteristic impedance does not apply. We must take the capacitance  into consideration.

10m?

For killing reflections/resonances no problem, but cable capacitance will become more significant (this is relevant for audio frequencies) so ymmv...

regards, Coen.

Can't touch this!

Peter, the link provides excellent information on the -loudspeaker-cable resonances. Allthough I think the resonance picture with the simulated Proac is a little misleading since a computer model will assume an ever rising impedance for the tweeter induction (rising of the impedance on the right side). This will not be the case in practice.
How did they solve it? I guess by placing notch filters parallel to the cable.

Nevertheless it is a real phenomenon and the resonance energy can creep into our precious audio signals. Also there is a likely source of UHF because of the NOS character of the DAC specifically designed for very wide bandwidth square waves. Not to forget USB noise creeping into our cable.

Hmmm, I wonder if this is how the Bybee products work: just eating -excess- HF energy (do they work on digital too?)?

There's more ways to skin this cat, yet the simple termination solution sounds excellent to me.

The discriminator between professional telecom cables and boutique audio stuff is the tight tolerance for the characteristic impedance. These cable's intended use is for much longer distances then in our home environment and you cannot have your impedance vary much otherwise it won't work and you invested a lot of money for nothing.


So the NOS sees 33 + 50/2 = 58 ohms for LF and 33 ohms for HF    and seems to be comfortable with it.

from the article:

If the amplifier is not designed to drive very low-impedance loads, say 1-2 ohms, it may saturate, causing distortion. Even if it does not saturate, the circuitry that eliminates crossover-distortion in most amplifiers may not work optimally at high loads. In fact, the crossover distortion in most amplifiers increases with load.

This is what I was referring to. This is true for any class AB amplifier, including opamps. Seems to be a non-issue.

Now let's have a look what's in my cable box tonight.

regards, Coen

Ok Peter,

The 33ohm output impedance is the result of a series resistor? That makes my cable capacitance point somewhat less relevant.

Regards, Coen

What about both? !

I do think that distortion -for a 'voltage source'  output- will increase with current; at least that's what I've seen in most amp/preamp test reports. Is this audible or important? That's another question. You must be able to measure this.

BTW this is the 'impedance mismatch' Joachim pointed out in his last post, like my tube phono output preamp playing into 25 ohm with gross distortion (way to much current needed), loss of gain and HF (high output impedance) and finally loss of LF (too small output caps).

No doubt either that the phase angle of the output load has an influence on the performance of the DAC's output opamps. These must be in some feedback arrangement (Inverted or not) which will be sensitive to phase twists. This corresponds with anecdotal evidence on this forum that lower capacitance cables sound better.
A rule of thumb 1:10 ratio, that would mean a happy NOS1 at a load of 330 ohms?

The point where cable capacitance becomes important in this setting is determined by the load at the end of the cable.
Now we shift the frequency by increasing the load (=lowering the resistance) this point is moved at least three decades upwards, making the load for the DAC resistive for the whole audioband.
This is the good stuff, again: is it measurable and important? I don't know it's audibility is speculative but plausible.

Unlike for the very high frequencies, audio signals encounter the plain parallel cable capacitance and series inductance (which is very small) and not the characteristic impedance. Joachim's snip points this out clearly. This should be taken care of in USB transmission lines for instance (proper termination, short cable?).
Yet there could still be HF energy in the relevant spectrum on the DAC's output that would remain undamped in a normal setup potentially causing unwanted interference.

I see enough good stuff to offset the bad so in the end you can call me positive .

regards, Coen

two adapters: terminated at both ends with 50 ohms. That's a properly terminated transmission line. Mind you that the imperfect 75ohm RCAs are still in service (!).

Here's one for you: what about the shift from a capacitive to a resistive load for the NOS's output?

With a terminating load of 100kOhms and a cable capacitance of 60pF the cable capacitance starts to dominate from 1/(2*pi*R*C) = 26,5 KHz. No doubt this will do something for the phase of the signal. Now with a 50 ohm resistance this will be 2000 times higher (MHz), with 25 ohms 4000 times.....

regards, Coen

R u guys kidding us?

Correct me if I'm wrong but 2 adapaters, 50 ohms each that's a load of 25 ohms for the NOS1(a), output and terminating impedance not taken into consideration. You are just listening to the extra distortion of the output stage. I have speakers here with a higher impedance.

You must have had a loss of gain.

It could work but what impedance was the NOS designed for? Irrc most audio cables and RCAs are about 75 ohm, terminate both sides with that and you will eliminate reflections as well.

Please don't think I am sceptic about the idea, it was on my todo list as well but the output stage needs to be designed for it.

regards, Coen

Hi Jachim,

I am Reading correctly that you are running the NOS into 50 ohms? Or is it just extra plugs rca-Bnc * 50 ohm cable *Bnc-rca?

Regards, Coen

I am demanding with 9z9 SFS=2 (AP of course). sfs=6 with 1.186i. Looking for the static.

Regards,  coen

No, not that I specifically listened to it. The static I know is the small random ticks in quiet and organic music (classical). This is rare and usually my indicator for a poor USB connection.

I will put attention to this later this day.

I had a hunch that it might have a thing to do with the processing of the WAV files that is different from FLAC. I noticed that already played tracks are less inclined to have a drop-out.

I understand better now that samples and bits get messed up by the OS and USB interface. I am also realizing that my current PC is not fit for purpose. Who'd thought that you need a top of the line setup to get a few crunched bits correctly over a wire. And even then..

Regards, Coen

I think so, but it happens unnoticed by the driver error counters. I mean it just crashed while I was having a sandwich upstairs and after a restart, I swear it sounds different. No I am shure. Before the mono recoding sounded like a mono recording, now it could be mistaken for a (narrow) stereo one. Much much less focus. Nothing to see in the panel and absolutely no changes except for a restart.


That was the goal of attaching the Mac. The PC cable connection is lousy and the Mac's better but not much better.
 
Now I have to wait longer for the crash to happen (I got hungry so I wasn't even there ). Now I'm in my second track. No additional errors above the "start" ones (see comment below).

Maybe I just touched the USB cable while starting up the PC. Just enough to cause some *unmonitored* buffer to fill and cause the system to go unstable.
I did reconnect it two times yesterday though, maybe I had better luck today with connection...


It is not very repeatable. Today it was several times 35 seconds on all starts except for the one that went without an interruption (). Oops there just was another interruption 18 minutes playing and another one at 25 seconds after a restart...
These interruptions seem to be win7 and WAV related, so far no interruptions with FLAC...

The DC offset stays rock solid: -4,4 and 3,4 respectively.


AC between USB cable shield and Chassis USB ground is 5,3V.

So of course today no crashes observed by me yet (Murphey?). The stops remain and might be related to the crashes but that would be another topic.

regards, Coen

about 45 seconds. After a driver buffer adaption (4->8msec) 1 minute, 45 seconds.


I will report later.

FWIW: on the mac no "crash" observed.

regards, Coen