[aldavey]

Triodes and Horns + 1

 

[Jawed]

I wonder if the power pulse array amplifier is nearly ready for launch.

I've been thinking that it would be possible to have a version of this with an M Scaler built in. This would be a product that has a broader appeal, since it is no longer restricted to systems where there is a DX output available (currently DAVE or Blu 2 are the only such compatible products). I think there are many people with streaming systems who would like to just drop a power amplifier into their system, and for it to take USB input and that is all the hi-fi they need. Similar to Devialet (though that is a far more capable product in terms of input options). It's hard to argue with the simplicity and attraction of system building when there's a single hi-fi product between a server and the speakers.

Anyone who runs a DAVE direct into speakers already knows what that's like. (Not to mention us headphone-only guys.)

And, if the idea is that 2 PPAs are used in a dual-mono configuration, it would be possible for one PPA to have M Scaler processing and then send one channel of digital audio to the other PPA using DX output. Again, this would be like the system setup seen with Devialet: dual-mono consists of two boxes, one of which is fed a digital output from the other.

Obviously an M Scaler PPA would cost considerably more than a "simple" PPA, but the number of potential customers goes up quite dramatically.

Now playing: Joy Division - Shadowplay

 

[Babysnake]

I've always pondered the same questions on EQ for room correction and have concluded, based on principle and not necessarily from empirical research, that one either does it before it hits the DAC or stay in analog after the DAC as additional ADC/DAC will inevitably use inferior reconstruction filters.

DEQX do room correction/speaker correction kit with a digital out, so it could be implemented before the DAC. That leaves one needing some sort of non-DSP crossover between preamp and power amps but at least there is only one DA conversion going on

 

[ecwl]

DEQX do room correction/speaker correction kit with a digital out, so it could be implemented before the DAC. That leaves one needing some sort of non-DSP crossover between preamp and power amps but at least there is only one DA conversion going on

I used to run my video system through miniDSP parametric EQ digital output into DAVE/Blu2. The problem is that the 44kHz/48kHz goes through ASRC in the miniDSP and then goes through parametric EQ into 96kHz output. As you can guess this is a low-tap length process. So there is significant sonic degradation in my system, particularly to transient timing which was the whole point of having DAVE/Blu2. I now just accept the minor bass peaks (because I did do physical room optimization first) and run straight through Blu2 for watching movies. For my music playback, I use Roon's parametric EQ which preserves the original bit rate to tune out the subtle bass peaks.

 

[Babysnake]

I used to run my video system through miniDSP parametric EQ digital output into DAVE/Blu2. The problem is that the 44kHz/48kHz goes through ASRC in the miniDSP and then goes through parametric EQ into 96kHz output. As you can guess this is a low-tap length process. So there is significant sonic degradation in my system, particularly to transient timing which was the whole point of having DAVE/Blu2. I now just accept the minor bass peaks (because I did do physical room optimization first) and run straight through Blu2 for watching movies. For my music playback, I use Roon's parametric EQ which preserves the original bit rate to tune out the subtle bass peaks.

So running the digital signal through a low tap process first (some sort of DRC) loses you the subsequent benefit of going through the high-tap process in the Blu2/DAVE?

 

[rayl]

So running the digital signal through a low tap process first (some sort of DRC) loses you the subsequent benefit of going through the high-tap process in the Blu2/DAVE?

This doesn't sound right -- minus the SRC part. I suspect SRC is the primary culprit in the miniDSP chain.

As I understand it, the point of a large number of taps is a better approximation of the sinc function for interpolation/reconstruction. Digital domain filtering at original sampling rate (or an integral upsampling), and with sufficient resolution, should impact the effects of the filtering w/o affecting subsequent reconstruction into analog.

It's possible that there are round off issues -- so if there's a chain of filters, hopefully internally, they will be performed at a greater bit depth so you pay the round-off penalty only once.... But filter length should not matter. If you are willing to go minimum phase with IIR (zero taps), even that's OK (except, of course, you are accepting the phase shift behavior of the filter).

 

[Babysnake]

This doesn't sound right -- minus the SRC part. I suspect SRC is the primary culprit in the miniDSP chain.

I'd be interested in Rob's take on that specific point, whether you lose the 1M tap benefit by feeding the Blu2/DAVE with anything other than the original source

 

[JaZZ]

I'd be interested in Rob's take on that specific point, whether you lose the 1M tap benefit by feeding the Blu2/DAVE with anything other than the original source

Note that the WTA filter with the 1 million taps is a component of the digital-to-analogue conversion. Modifying the signal in the digital domain (in DSPs) doesn't involve any (inferior) anti-aliasing filter, hence bears no risk of losing the benefit from the WTA filter.

 

[ecwl]

Note that the WTA filter with the 1 million taps is a component of the digital-to-analogue conversion. Modifying the signal in the digital domain (in DSPs) doesn't involve any (inferior) anti-aliasing filter, hence bears no risk of losing the benefit from the WTA filter.

I agree except we are first assuming that there’s no sample rate conversion which a lot of DSP devices, like miniDSP or Behringer would do. And I think the second you’re assuming is that the DSP applied by the computer uses a good algorithm with sufficient accuracy that wouldn’t lead to errors (which is a very reasonable assumption but Mr Watts has said that’s not always true). I use Roon parametric EQ daily for DSP and I’m happy with the results. But I’d be slightly reluctant to say it’s okay to use DSP generically together with the WTA filter with no loss of quality because there are so many ways to apply DSP. With all that said, when I did need more DSP in my system with the miniDSP, the Chord DACs with the WTA filter, even receiving the DSP altered 96kHz signals still sound better than other DACs. You still get some benefits of the WTA filter and Chord DACs aren’t just about the WTA filter.

 

[JaZZ]

A tricky question to Rob:

Which conductor material for analogue signals (or generally) do you consider the best – and why?

Personally I favor silver since quite a while, but my experience with cables (especially of the high-price sector) is relatively limited. In terms of geometry I experimented a lot with multiple ultra-thin isolated wires (magnet wires). However, although they left conventional no-name cables behind, they couldn't exactly compete with some well-respected buyable cables – I guess due to my lack of access to high-quality wire.

 

[Rob Watts]

I haven't tried solid silver, but prefer silver plated OFHC copper. But you must use silver bearing LMP solder with silver. Also, the insulation, use of solid core against stranded, no. and thickness of insulated solid cores, vibration immunity, and RF characteristics play a bigger role. For loudspeaker cable, impedance and inter conductor rigidity are extremely important factors.

 

[JaZZ]

With extremely thin wires (in the interest of low skin effect) insulation boils down to lacquer. Is this a bad concept? Vibration immunity: against external or self-induced vibration? (I'm asking this as a headphones-only listener.)

Finally: Why does silver sound different than copper?

 

[Rob Watts]

The issue of solid core being better than stranded is due to non-linear contacts at the surface of each strand; when skin effect comes into play, the current moves towards the surface; this behaviour gets disturbed by the nonlinearities of the strand to strand contact. Copper oxide is a semiconductor with diodic properties, and this is the source of the non-linearity (silver is too but is less likely to oxidise).

But even with solid core you get similar effect with the metal crystal boundaries, hence why thinner individually insulated strands is better than thick ones (with the total impedance the same).

On vibration, with loudspeaker cable it's more induced due to current flow (Lenz's law); for interconnect it's less important and is of course external. For loudspeaker cables rigid clamping of the conductors is important.

 

[Triode User]

The issue of solid core being better than stranded is due to non-linear contacts at the surface of each strand; when skin effect comes into play, the current moves towards the surface; this behaviour gets disturbed by the nonlinearities of the strand to strand contact. Copper oxide is a semiconductor with diodic properties, and this is the source of the non-linearity (silver is too but is less likely to oxidise).

But even with solid core you get similar effect with the metal crystal boundaries, hence why thinner individually insulated strands is better than thick ones (with the total impedance the same).

On vibration, with loudspeaker cable it's more induced due to current flow (Lenz's law); for interconnect it's less important and is of course external. For loudspeaker cables rigid clamping of the conductors is important.

Rob, I know that you have done quite a bit of work with cables so I bow to your superior knowledge but here is my 2p worth.

What you say is certainly the classic description of the effect of stranded cables but the cable manufacturer QED has published a paper on the science behind cables. Much of it is vague and either intentionally or unintentionally confused but on the stranded vs solid issue they say,

"It has been claimed that multi-strand cables introduce ‘diode’ effects due to current jumping between strands within the cable and thereby crossing very many metal/oxide/metal junctions. This is sometimes said to be caused or worsened by skin effect as a result of it pushing the current towards the conductor surface at high frequencies.

Making the assumption that the current does ‘jump’ as suggested, we put signal in via one strand of a multi-strand cable and measured the signal from a different strand. Even using the Audio Precision AP1 test set to its maximum capability, no increase in distortion compared to using all the strands could be found, as shown in Figure 22. This graph overlays curves for the two cases – they are so close that they could as easily be repeat tests of the same measurement. It seems that interstrand diodes do not exist, or if they do they are shorted out by the many good conductors pressed together over the cable’s length."

Of course their experiments would probably have been with new cables but the use of good quality OFC ought to minimise oxidation over time. One might even argue that in practice TPC is just as good as OFC for corrosion resistance where the cables are not in a severe environment. And unless anyone is running their speaker cables in a high vacuum similar to a magnetron it is unlikely that outgassing will be an issue because of not using OFC!

On speaker cables in general, I have been doing my own private assessment of various speaker cables for a few months now. For me the single most important factor seems to be length. Keep speaker cables as short as possible and if necessary shift equipment to achieve this. I have moved my kit to achieve 1m speaker cable lengths, down from 3m, with an instant and stunning improvement. After that my conclusion is that the overall thickness of conductor is the next most important factor. This seems to completely overwhelm other considerations such as copper vs silver or litz vs stranded. Sure, if one has two identical cables (same thickness, same geometry, same dialectic etc etc) and change from say copper to silver conductor then there is a very slight betterment essentially due to the slight (~5%) reduction in dc resistance but this is easily and cheaply improved by going to greater cumulative cross section of copper. Personally I have found that one of the best ways of improving speaker cables is merely by doubling cables up in parallel. For the 1m length of my cables there was improvement up to about total 12mm2 cross section before the diminishing returns factor set in but even so I have found it worthwhile to use 18mm2 total.

I freely admit that all of this is assessed by my own self appointed 'golden ears' but it does seem to be backed up by my own version of blind testing which was for me to either change the cables or pretend to change the cables whilst a trusted friend listened. He had no way of seeing which cables were used as they were all set out together whether in use or not.

 

[Rob Watts]

I agree - you will absolutely not be able to measure it, I tried in the 80's.

But that does not mean that the effect is not audible - I can measure (using simulation) the effect of a noise shaper at -330dB, and a -350 dB noise shaper has easily noticeable improved depth perception - it's just the ear/brain is very much more sensitive than what we can measure.

Agreed on loudspeaker cables - you can hear down to milli-ohms, that's an inch or so. In the past my amps had feedback around the loudspeaker cables, and this is the only way of eliminating the issue.