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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 22nd September 2018, 04:25 PM   #8061
Max Headroom is offline Max Headroom  Australia
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Location: West Australia, near to the beach, natural ambient sounds mostly.
I have run a set of loopback tests and have interesting results.
Comparing three runs of the same conditions enables pretty good cancellation, ie good record events matching.
Comparing Both Normal to Both Reversed gives lousy cancellation.
Comparing Left Normal/Right Reversed to Left Reversed/Right Normal gives really good cancellation.
I will also compare swapping L and R cable positions next round of tests.

There are still some latency issues as I had to closely time align each recording, this needs closer inspection.
These results repeat what I obtained a week ago, more in the next few days.



Dan.

Last edited by Max Headroom; 22nd September 2018 at 04:37 PM.
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Old 22nd September 2018, 05:25 PM   #8062
DPH is offline DPH  United States
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Originally Posted by Jakob2 View Post
But that is much easier to write down as to concede in reality that someone else was able to demonstrate.......

Unfortunately we lost that thread, but without stating (before) what criterion/criteria has to be met by experimental results it will most likely not work as intended.

Thatīs what the "we act like Bayesians (often) without realizing it" implies, if you - deep in your heart - set the prior belief at zero, there will be nothing able to convice you that the opposite is true.
That's pretty unfair to many of us who have to revise deeply seated opinions in the face of new evidence pretty often as our respective fields of research evolve. But as Bayesian analyses imply, it's going to require a very substantial amount of evidence to move the needle.

Now, ask John or Dan to revise their belief systems in the face of abundant fundamental evidence to the opposite. Do you realize how ridiculous this all is?!
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Old 22nd September 2018, 05:27 PM   #8063
DF96 is offline DF96  England
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Quote:
Originally Posted by Max Headroom
How is this so when the only changes are cable direction and minimal, hopefully nil positional change.
If the cable is of sufficient length then you can do things like vary the characteristic impedance along the cable. Then it behaves differently in the two directions - but of course the cable is now asymmetric so this is unsurprising. The same trick does not work for short cables (e.g. domestic audio).

Quote:
In metallic conductors, impurities, crystal boundaries and dislocations are causes of noises.
They are causes of resistance, which is a cause of thermal noise. I have seen nothing to suggest that they are sources of excess noise, which seems to be very small in metals. Given that thermal noise in an interconnect is negligible, anything smaller than this must be super-negligible.

Quote:
What does annealing and cryo treatment really do to metals etc ?.
It can make a significant difference to some mechanical properties, and an insignificant difference to electrical properties like resistance.

Quote:
Originally Posted by indra1
Were you not saying that there could be defects in cables (wire and connectors) that may result in directional property within the understanding of physics?
Only if the cable is long enough that transmission line behavioir becomes apparent, and only if these defects are asymmetric.

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I hope some of us can work together like the people of CERN to find a reliable way to obtain hard data on the subject. Tasking the onus of proof to cable proponents has been so far unproductive.
When you find some evidence we will be pleased to consider it, especially if a plausible explanation can be offered too.
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Old 22nd September 2018, 05:56 PM   #8064
jneutron is offline jneutron  United States
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Quote:
Originally Posted by Max Headroom View Post
I have run a set of loopback tests and have interesting results.
Comparing three runs of the same conditions enables pretty good cancellation, ie good record events matching.
Comparing Both Normal to Both Reversed gives lousy cancellation.
Comparing Left Normal/Right Reversed to Left Reversed/Right Normal gives really good cancellation.
I will also compare swapping L and R cable positions next round of tests.

There are still some latency issues as I had to closely time align each recording, this needs closer inspection.
These results repeat what I obtained a week ago, more in the next few days.



Dan.
Time align???

Just hearing that phrase tells me you have no control over your experiments.

You should be using a single mono source, you should be using the amp output difference as the metric. That is as sensitive as you are going to get.

Oh, and use dummy loads. If you are using speakers, the room reflections will impact the difference signal due to room reflection patterns, and you in the room alters that pattern as well.

Without the knowledge base, you are not going to be able to build an accurate test.

I'm glad to see you trying something, but you do not understand the confounders that ruin your tests.

Jn
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Old 22nd September 2018, 05:57 PM   #8065
cbdb is offline cbdb  Canada
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Originally Posted by anatech View Post
Hi cbdb,

I'm agreeing - right?
Yes fully agree.
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Old 22nd September 2018, 06:19 PM   #8066
cbdb is offline cbdb  Canada
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I wonder why the expensive audio cable manufacturers have no real test results on directionality. I'm sure they are aware that real proof would help them sell more cables (and maybe even get them on the list for a Nobel prize ). The only reasons I can think of all point to there being no such phenomenon.
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Old 22nd September 2018, 09:53 PM   #8067
indra1 is offline indra1  Indonesia
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Originally Posted by DF96 View Post
... When you find some evidence we will be pleased to consider it, especially if a plausible explanation can be offered too.
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Old 23rd September 2018, 09:01 AM   #8068
KSTR is offline KSTR  Germany
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Quote:
Originally Posted by Max Headroom View Post
I have run a set of loopback tests and have interesting results. [...]
Quote:
Originally Posted by jneutron View Post
[...] I'm glad to see you[Dan/Max] trying something, but you do not understand the confounders that ruin your tests.
I mentioned similar issues to Dan in posts # 7670 and 7691.
Prerequisites, in my view are: one single plaback channel, one single record channel, loopback connection with the DUT cable, sample-sync'd recording, time alignment. With ASIO driver the TASCAM US-122/144-MkII is capable of all that with most any audio software.
The only thing that changes between runs is the RCA cable's direction (the interface has RCA outputs and TRS inputs, so with an RCA-to-TRS Adapter this is also really easy). Make 10 runs minimum, changing direction after each, so you have 5 sets of A and five sets of B and then compute the differences as described.

Alas, IME (and I do this kind of tests for quite some years now, sometimes even using that same soundcard), we will not find anything of significance in the residuals as they are still much too noisy. And clock and ref-voltage drifts also quickly start to dominate the residual once you try go deeper with heavy time domain averaging, can be mitigated by interleaving of the data to be subtracted and that needs some automatic synced switching of the cable direction. Further, the null must be fine-trimmed manually (because of the remaining drifts). Lastly, a much better soundcard than the TASCAM is very favorable. This is the level required to get down as deep into the details as needed for any directional differences which sure must be very small, very likely smaller than, say claimed copper vs. silver "character" (with same RLCD params, of course) . If they are readily apparent without effort (both in a simple diff test as well as by listening) I would suspect a "setup error" somewhere else.
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Old 23rd September 2018, 09:21 AM   #8069
gerhard is offline gerhard  Germany
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Quote:
Originally Posted by scott wurcer View Post
When I read the stuff posted here I get a laugh remembering that Dr. Weiss and I had a discussion on whether 1/f noise is a fundamental property of all processes. I told him that in my experience, for semiconductors, it was and I have measured it down to 10 micro-Hz. He said that he was not convinced that was true for all processes.

LIGO is limited by the thermal noise (motion) of the gold atoms coating the mirrors (it is a big parametric amplifier after all). That puts wire directionality pretty far down on the list.
Do you think that there is 1/f noise in analog switches like ADG819 when used in a
chopper? Are there frequency ranges that have been shown to be 1/f-free in this application?

Cheers,

Gerhard
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Old 23rd September 2018, 10:08 AM   #8070
gerhard is offline gerhard  Germany
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Quote:
Originally Posted by simon7000 View Post
RF network analyzers will often show a lower SWR using a cable with attached connectors in one direction versus the reverse.
Given that any decent network analyzer has elaborate 12-term error correction that
makes definitely sure that S21 == S12 and S11 == S22 across the port cables,
this would mean nothing but sloppy calibration.

regards,

Gerhard
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Last edited by gerhard; 23rd September 2018 at 10:28 AM.
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