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Townsend Isolda cable

Purité Audio

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#1
Help required, someone posted this video, which purports to show the lower distortion of this cable,
I know you don’t see an analogue oscilloscope very often these days, and Isolda cable has I believe high capacitance is Max and the video correct?
Keith
 

SIY

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#2
FUD. Pure FUD. There would be more difference if he uncoiled the wire.
 
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Thread Starter #3
Yes I did notice that ,coiled cable and a square wave , crafty old Max.
Keith
 

solderdude

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#4
The spikes are showing some minor roll-off (around -0.6dB) from 50kHz. This is linear 'distortion' and while he claims it shows 'distortion' in audio frequencies a slight roll-off at 45kHz can hardly be called "visible distortion in the audible band".

The 'better' cables do extend a bit further in frequency range but will that really be audible ?

A High capacitance cable might not be the best idea for some amplifiers.
This might make some amps unstable and may ring/oscillate at very high frequencies with some speakers.
 

Soniclife

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#5
This might make some amps unstable and may ring/oscillate at very high frequencies with some speakers.
I've seen this reported before with this cable, how often it happens with normal amp designs I don't know, but things like old Naim amps should be kept well away from it, they need low capacitance and high inductance.
 

amirm

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#6
He is using a square wave generated by a Lodestar AG02601a. THe specs for it show a rise time of 0.5 microseconds. We can convert that to bandwidth and get 680 kHz. In other words, the source square wave is running at 680 kHz! The generator has a bandwidth limit of 1 Mhz so way, way higher than audio band.

Because the bandwidth of the square wave used is so high, it of course becomes sensitive to cable characteristics. No digital or analog format we have can produce a 680 kHz bandwidth square wave.

And yes, he also conveniently coils the competitor cables while not showing how short his cable is.
 

SIY

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#8
I'm up for preliminary testing of said device, max seems a suitable candidate.
Chances of him sending it are close to zero. The chances of him agreeing with the conclusions of honest measurement are less than zero.
 

Max Townshend

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#9
Keith. The video was made 12 years ago.
High capacitance and low inductance is mandatory for speaker cable to get square root L/C near 8 ohms to eliminate reflections. see
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/characteristic-impedance/

SIY It doesn't matter if the PAIR of wires are coiled or not, as there is no net external field, electric or magnetic. The results are identical if coiled or uncoiled. Try it yourself.

Keith. See above. Also, square waves are quite good for analysing the dynamic performance of electrical circuits.

Amir All wires are 10 metres in length, except for the long coil of Monster. The short one is 10m.

Solderdude. The spikes are due to to multiple reflections giving the appearance of rolloff. The results when playing music are shown here
I will be posting a video soon where you can listen to the difference. Quite alarming!

We modelled the class AB transistor amplifier and found it to be stable with zero capacitance and 2 microfarads, but maximum instability with about 10 nanofarads. When my colleague Jack Dinsdale designed the first transformerless transistor amplifier he observed this and so he included the 3 microhenry inductor in series with the output to compensate for this to make the class AB amplifier unconditionally stable. In the 70s, John Farlow of Exposure Elecronics left this inductor out of his designs to make sure you used his widely spaced, high inductance, low capacitance cable for marketing purposes. 3. 5 metres of Exposure/Naim/TQ/DNM etc cable provides the 3 microhenries to stabilise the amplifier. He taught Julian Verica of Naim this trick, hence the proliferation of widely spaced cables with these conditionally stable amplifiers. To allow the use of our high capacitance/low inductance cable (sq rt L/C=8R) with these amplifiers. It works!

Amirm. Yes, the Lodestar AG02601a has a rise time of 0.5 microseconds, but what you have conveniently avoided observing is that the signal is passing through a severely band-limited, normal Cambridge Audio amplifier. The distortion is clearly audible!

Thomas Savage Typical flat-earther comment.

Max Townshend B.E. (Communications)
 

solderdude

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#10
Thanks for your reply.

The fact that a specific amplifier remains stable under simulations does not mean all amplifiers connected to certain speakers remain stable.

Also the 8 Ohm argument is nonsense as no speaker cable reaches anywhere near 8 Ohm at audio frequencies. Also there are no speakers that have an 8Ohm impedance >100kHz they may well be hundreds of Ohms or even lower.
Also amplifiers have a close to 0 Ohm output R and have to deliver current into complex (inductive/capacitive) loads and not in a nice resistive 8 Ohm load. So there is no impedance matching at all as the output R of the amp is not 8 Ohm.

Can you zoom in on those squarewave peaks to actually show they are reflections.

It is quite easy to see if they really 'distort' the signal by doing measurements and/or nulls at the begin and end of the cable (connected to a real load)

The second video seems to show resistive differences (given the low frequencies) and cannot possibly come from reflections. The wavelenghts simply are too long for audio frequencies.
 
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SIY

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#11
For a wire carrying a signal whose wavelength is several orders of magnitude longer than the wire, characteristic impedance is meaningless- it is a lumped LRC system. And unless the LRC are pathological, any engineered amplifier will work fine with it.

This was settled, from a non-commerce standpoint, over 35 years ago with the work of Fred Davis and Dick Greiner, and (no surprise) no cable-peddlers have been able to produce listening tests to refute their data and analysis in the intervening years.
 

amirm

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Amirm. Yes, the Lodestar AG02601a has a rise time of 0.5 microseconds, but what you have conveniently avoided observing is that the signal is passing through a severely band-limited, normal Cambridge Audio amplifier. The distortion is clearly audible!
That amplifier seems to be the Cambridge Audio Topaz AM10. I can't find a measurement of it but the specs say it is down -1 dB between 5 Hz and 50 kHz. That tells me its actual bandwidth is quite bit better than this. So my point remains. Square wave with wide bandwidth is not a proper test unless it is band limited to the audible frequencies.
 

amirm

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#13
Amir All wires are 10 metres in length, except for the long coil of Monster. The short one is 10m.
10 meters? Roundtrip would be 20 meters or 60 feet. That is one heck of a long speaker cable for typical hifi listening. And you went even higher lengths for Monster? 3 meters would be a much more typical cable length.

Any speaker cable testing should have the cables in exact same condition. When I did my speaker cable testing, I actually put them in a jig, keeping them all flat and absolutely the same length. You can't coil one and not the other, etc.
 

Max Townshend

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#14
We have modelled it with SPICE. see attached

Solderdude. My suggestion is to use unconditionally stable amplifiers (99% of all amps).
We make Isolda cable 8 ohms, it is easy. Note, there is no frequency component in characteristic impedance and it applies for DC attached. Yes, the DC resistance of the cable becomes significant below 5kHz, but it is at the higher frequencies that it becomes significant. See the parameters in the cable simulation document.
Note the equivalent circuit of the speaker is predominantly resistive (the DC resistance of the speaker coil)
The amp has zero ohms impedance and we never suggest otherwise. It is only necessary to have source R and Load R equal when the transmission is duplex i.e. analogue telephones where communication is both ways. Amplifier to speaker is simplex transmission, only one way where the load is to be matched (forward matching). The other case is typically with video where the source is matched to the cable (back matching).
The theory here is for SHORT transmission lines (wavelength much shorter than the line), not to be confused with LONG transmission lines (line longer than the wavelength).
Some some zoomed-in reflection pictures are attached.
If you don't like the transmission line concept (blue traces in simulations) then lumped analysis yields similar results (red traces in simulations).

There is a good analysis on reflections in interconnects. Deletraz This clearly explains that the slow rise-time of the step at the load is not due to simple RC filtering (the most common mistake) but to the slow build-up because only a small amount of the signal is absorbed in the load at each reflection and it takes hundreds of reflections to reach stability.

See another simulation TymsCables.
 

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Max Townshend

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#15
10 meters? Roundtrip would be 20 meters or 60 feet. That is one heck of a long speaker cable for typical hifi listening. And you went even higher lengths for Monster? 3 meters would be a much more typical cable length.

Any speaker cable testing should have the cables in exact same condition. When I did my speaker cable testing, I actually put them in a jig, keeping them all flat and absolutely the same length. You can't coil one and not the other, etc.
The only coiled up cable was the 60 metres of Monster. All the others are scattered over the bench.
 

SIY

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#16
Man, that cable theory "white paper" is just begging for an annotated version.:D

For those of us who use cables for audio rather than shortwave transmitters, regular wire works just fine.
 

amirm

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#17
The only coiled up cable was the 60 metres of Monster.
60 meters? Why was that relevant to any home speaker/amp testing as shown in the video?
 

SIY

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#18
60 meters? Why was that relevant to any home speaker/amp testing as shown in the video?
For that matter, how are nanosecond effects relevant?
 

amirm

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#19
See another simulation TymsCables.
I looked at the first doc and noticed this:

1553284181614.png


The "and more" is the problem here. An impulse signal has infinite bandwidth. You can't use it to simulare what an audio circuit does for a listener that can't hear above 20 kHz. The gap between 20 kHz and infinite is well, infinite. :)

We all know that if you make your signal high bandwidth then cables matter. Audible signals are not that so showing what happens with square waves, impulses, etc. is not relevant to our ears.
 

amirm

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#20
I also see this table of measurements:

1553284476893.png

You then say:
We make Isolda cable 8 ohms, it is easy.
How did you get to 8 ohms? I don't know which one of the above is yours but taking the highest one at 88 milliohms/meter, 10 meter length would be 20 meters roundtrip = 0.088 * 20 = 1.76 ohms, not 8 ohms. How did you get to 8 ohms for DC?
 
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