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Exposure amp with Van Damme speaker cable - What mm size?

As a rule of thumb, the Farlowe era amps should be used with Exposure cable (or Cable Talk 3 which is the same). The Tony Brady designed amps (anything from the original 2010 on) don't require it.
 
1. WTF is a Zobel Network?

Typically a resistor and a capacitor, used to compensate for the speaker impedance (to make it easier to drive).

2. Why did NAIM and Exposure feel that they could manage without one

Because loudspeaker cables with enough capacitance act as a zobel network.

and to what.. if any advantage... apart from pushing customers into also buying 'approved' cable, which in effect replaces the Zobel?

Here I run out of answers, as I don't want to speculate.
 
Older Exposure and Naim amps have intentionally no zobel network on the poweramp output!
This is compensated with de electrical specs of the Exposure and Naim cables

With other cables, the amps can become instable and heat up > so... no nonsense, but technical talk!

No it is nonsense! i wouldn't have mentioned it if it wasn't so....

The amp would have to be actually oscillating for it to get hotter. This is a fault condition and all sorts of other symptoms would accompany it. If the oscillation was of a high amplitude it could even blow tweeters and likely destroy the amp due to cross conduction in the output stage.

They do have Zobel networks but the output inductor is replaced by a small resistor, which is not really a very good idea....
 
As a point of infinite pendantry, Naim and Exposure amps do in fact have Zobel networks (the series RC to ground from output). They do NOT have Thiele networks though (parallel LC, placed between the Zobel network and the output of the amp circuit). The use of certain speaker cables like NACA5 etc allows for stable operation without a Thiele network. "Zobel" gets wrongly used as a general term for output networks quite a lot.

I suppose one advantage of this approach is that there is one less inductor and resistor in the signal path, thus pleasing the audiophiles. Personally, id' rather have a Thiele network and be left to choose my own cable (Les had the right idea when he added the Thiele network to the NCC200). Also Naim get to sell loads of NACA5 cable too, which back in the day when it was cheap was not too big a deal for customers. But look at what it costs now - that's what happens when you sell out to Focal!).
 
to last remark of Julf:
to have complete control over the impedance value from Amp/LScable till the speakerterminals....
With a Zobel/Thiele network in the output plus any LScable, the impedance value till the speakerterminals is undestined?
 
to last remark of Julf:
to have complete control over the impedance value from Amp/LScable till the speakerterminals....
With a Zobel/Thiele network in the output plus any LScable, the impedance value till the speakerterminals is undestined?

There is just somewhat excessive capacitance, but at the impedance levels we are discussing it shouldn't have an audible effect.
 
Wikipedia: Boucherot cell

A Boucherot cell (or Zobel network) is an electronic filter, used in audio amplifiers to damp high frequency oscillations that might occur in the absence of loads at high frequencies. Named after Paul Boucherot a Boucherot cell typically consists of a resistor and capacitor in series, that is usually placed across a load, for stability.

It is commonly seen in analog power amplifiers at the output of the driver stage, just before the output inductor. The speaker coil inductance of a loudspeaker generates a rising impedance which is worsened by the output inductor generally found in analog power amplifiers; the cell is used to limit this impedance.

The documentation for some power operation amplifiers suggests the use of a "Boucherot cell between outputs and ground or across the load".

Additionally, Boucherot cells are sometimes used across the bass driver (and mid-range) of a speaker system, in order to maintain a more constant driving point impedance as "seen" by a passive crossover. In this specific arrangement, the Boucherot cell is sometimes also known as a Zobel network.

Some loudspeaker crossover designs aim to stabilize impedance at high frequencies by including Zobel networks.
 
Well thanks to our more electronically 'savvy' contributors for the explanations. The only thing I can add is that having worked with and made up more than a few cables using NAC 5 and even a bit of 4.. it is a bloody awkward animal, being very inflexible. Most wires will naturally hang from horizontal speaker connections such as banana plugs, with a smallish radius and while having any wire hanging vertically is probably a marginal improvement, with NAC 5 it's a requirement.. I'd assume this is why the NAIM speaker plug exists. I have to say it's a neat and quite elegant solution to a problem that probably shouldn't exist. ;)
IIRC, when I sold a couple of NAITs back around 2000, I was amused to find that the left speaker outputs were on the right rear of the amp and vice versa. Very odd.
 
Typically a resistor and a capacitor, used to compensate for the speaker impedance (to make it easier to drive).



Because loudspeaker cables with enough capacitance act as a zobel network.



Here I run out of answers, as I don't want to speculate.


Nope....

A Zobel network (or Bucherot Cell) is not there for any reason to do with the speaker load or to make it easier to drive or anything like that.

A negative feedback amplifier with voltage feedback tends to show an inductive output impedance, with associated phase shift. This is often accompanied by a speaker load which due to voice coil inductance can have a steeply rising impedance at HF which is less and less of a load for the amp as frequency rises. In the case of a common emitter output stage (before feedback) the gain of the output stage itself is proportional to the load impedance and so the open loop gain varies hugely with frequency, as, therefore does the loop gain and the amps stability. It is less awkward with an emitter follower output stage but the phase shifts are still present.

The Zobel network puts a capacitive load on the output of the amp which tends to counteract the inductive output impedance of the amp and its resulting phase shifts and hence helps to stabilise the amp. The resistor in the network shelves the response to prevent the capacitor looking like a dead short at a very high frequency.

The output inductor and resistor (I don't call it a Thiele network. It was in use a very long time before his 1975 article!) are there to ameliorate the effect of capacitive loads on the amp and the resulting phase shift and falling impedance with frequency on the amp.
It is the inductance and not the capacitance of the speaker cable that can help it to form part/all of this network. A value in the range 2 - 10 uH will usually be chosen and must be optimised for a particular amp design of course. The resistor in parallel with this inductor is there purely to damp the "Q" of the output inductor... With a typical feedback amp using an output inductor it is very instructive to feed it some square waves and observe the ringing at the output... The ringing is often due to the inductor and not due to HF gain peaking in the amp! I tune my output networks for best overall response in my power amp designs;)

A few companies, including Naim and IIRC Exposure (there are several others) place a small value resistor of usually around 0.22 Ohm in series with the amps output, in place of the inductor and resistor usually used. The amp then feeds the speaker via a resistor of often higher resistance than the speaker cable!
The idea is that this resistance is enough to isolate the amps output from the load capacitance but in the case of Naim it can be not enough on its own and need some inductance from the speaker cable. It's a bad idea! IMHO anyway. Its only possible benefits being to give a more constant output impedance with frequency from the amp (hence more constant damping factor... same thing)... but achieved by nobbling it so it's much worse at all frequencies! Another possible advantage is the resistor acting as a load for speaker back EMF but this is fairly tenuos and again highly frequency dependent.

What it definitely will do is add 0.22 Ohm in line with the speaker cable and reduce damping factor to a theoretical maximum (assuming a perfect amplifier and perfect zero resistance speaker cable) of 36 into an 8 Ohm load and 18 into a 4 Ohm load....

For those with an amp which doesn't use an output resistor of around 0.22R you could try putting one in line with the speaker cable and see what it does to the sound;) Even if you have a Naim or similar you could add an extra 0.22R (or more) to give a idea of what it's doing. I think you'll find it to be very audible and not in a good way.... more "confused", less separation between instruments, less control etc. In some cases, depending on amp and speakers used, some may find a "sweetening" of the sound and that it can sound less "relentless" and "hard" but this is the exception rather than the rule and the loss of control and precision should be evident at the same time.
 
The output inductor and resistor (I don't call it a Thiele network. It was in use a very long time before his 1975 article!) ...
As found in the Armstrong 600 series amplifiers and receivers - a tiddly 10uH coil with a 10 ohm resistor neatly inserted through its middle, wrapped in tape and soldered to the positive terminal of a whopping output capacitor, providing unconditional stability into any load above 2.5 ohms and available to buy in early 1970s high street shops alongside the washing machines, refrigerators, et al. Stuff that matters.
 
As found in the Armstrong 600 series amplifiers and receivers - a tiddly 10uH coil with a 10 ohm resistor neatly inserted through its middle, wrapped in tape and soldered to the positive terminal of a whopping output capacitor, providing unconditional stability into any load above 2.5 ohms and available to buy in early 1970s high street shops alongside the washing machines, refrigerators, et al. Stuff that matters.

Yes indeedy. Some interesting takes on output networks can be found in a paper by E.M. Cherry but you'll have to search for it... He of Nested Differentiating Feedback Loops...
 
A few companies, including Naim and IIRC Exposure (there are several others) place a small value resistor of usually around 0.22 Ohm in series with the amps output, in place of the inductor and resistor usually used. The amp then feeds the speaker via a resistor of often higher resistance than the speaker cable!

I bow to your much greater expertise with Naim amps (I have tended to avoid them), but yikes, with a 0.22 ohm resistor in series with the output you can indeed forget talking about damping factor...
 
I bow to your much greater expertise with Naim amps (I have tended to avoid them), but yikes, with a 0.22 ohm resistor in series with the output you can indeed forget talking about damping factor...

I avoid them as well! The example I gave is just one reason why... The recent stuff seems to be good but the classic Naim gear is another matter... Take a look at the schematic for the NAP250 power amp and look at the price... When you've stopped laughing tell me what you think...
 
Thanks I’m having difficulty understanding and out of curiosity if Van Damme specs mean mm2 or just mm and how that converts to 4mm2

Thanks!

Sorry ‘Balance’, I’ve only just seen your post. The Van Damme 4mm means four millimetre squared and is the same cross section area as Linn K20, NacA4, A5 and Exposure.
 
speaker-cables.png
 
DNM cable is so bad as to be unusable IMHO. Even "bell wire" would be slightly better! Put a 1R resistor in series with your speakers to replicate it!

I also completely disagree with that article. And no I'm not going to say why... life's too short!
 


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