The "re-birth" of MF A1

Stereo Mic said:
Rob,

amps don't need to be universal - they just need to be suited to the partnering loudspeaker.

Geez having switching distortion right at the power level used for typical listening sucks. Talk about having the worst of all worlds. ;-)
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Agreed if we are talking power requirements but all amps should have as low distortion as possible regardless of the partnering loudspeaker.

As for switching distortion, find it within the 0.002% THD (worst case) and you get a gold star :)

Let's just say I see no reason to worry in the slightest.
 
Tenson said:
The designer would agree hence he built the 'XD' topology, which from what Rob told me has a sliding bias rather than a defined switching point. I really don't think there is much to dislike about the 840a.
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Would be interesting to hear the implementation of this circuit design in a model not constrained by a Richer Sounds manufacturing budget. HFW thought it sounded a bit bright (haven't heard it myself), which might be down to cost saving on the components side, rather than intrinsic sonic flaws of the technology itself.

DT
 
I don't think it really was that budget limited. Its supposed to be Cambridge Audio doing their thing without the usual budget limitations I thought! Inside it is clearly not a cut-back design.
 
Dynamic Turtle said:
Would be interesting to hear the implementation of this circuit design in a model not constrained by a Richer Sounds manufacturing budget. HFW thought it sounded a bit bright (haven't heard it myself), which might be down to cost saving on the components side, rather than intrinsic sonic flaws of the technology itself.

DT
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Noel Keywood thought it a little bright though no other review (there are plenty) has echoed this, but Noel is a valve head and thinks most SS amps are a bit bright.

If you get the chance, look inside one.
24 separately regulated lines, 1KVA transformer on the power amp, 100VA transformer on the pre, relay controlled stepped attenuator, balanced inputs, cast base plate and side panels, dual mono throughout following the transformers..... I could go on.

It costs £750 for three reasons.
It's made in China, doesn't carry a premium brand logo on the front and CA don't take the piss. That's why I have a lot of time for them.

The Richer Sounds thing needs clarification. RS sell CA exclusively in the UK only and the product is available worldwide through regular hi-fi dealers.
They are quite different companies, not that it really matters.
 
Good amplification can make huge differences - I used to doubt that. Sadly most people don't ever seem to experience that it seems. Points of reference and all. I'd be delighted to one day do a blind comparison between the likes of the 840 and some truly transparent electronics to demonstrate my point. I am very confident on that.
 
What would you want to ABX the 840a against? I'm sure you could hear the effect of something like the Berning, since the output Z alone could change the response enough to be audible. Do you have something else in mind?

So do you not consider an amp that measures very well in most every department to be 'truly transparent'? I would put the 840a in that category I think. I'm not sure in what area it turns out a bad performance. (and don't say musicality SM, your better than that!)
 
Stereo Mic said:
Good amplification can make huge differences - I used to doubt that.
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Huge differences?

Sadly most people don't ever seem to experience that it seems. Points of reference and all.
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Just like some unenlightened folks never experience the difference cables make I guess? Sorry my bad, I wouldn't put amps in that category, its easily established that they do make a difference.

Its probably important to quantify 'huge'. For me that's the difference between a good room vs a bad one, a 15" sub vs a 4" and so on. Maybe your definition is different.

I'd be delighted to one day do a blind comparison between the likes of the 840 and some truly transparent electronics to demonstrate my point. I am very confident on that.
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Would love to see the results of that. I'd buy you a frosty one if you convincingly passed.
 
Tenson,

provided the output impedence is less than half the loudspeaker impedence, FR variations will be minimal. The Berning comfortably matches that with well designed loudspeakers without massive impedence swings.

What is interesting is that both amplifiers running into highly efficient loudspeakers will demonstrate THD figures way below audibility yet do sound remarkably different. It is quite usual at this point for someone to intimate that valves are distorting the signal but of course this is not the truth, nor are they limiting bandwidth in many cases. Anyway, I'm quite convinced of a certain level of amplification that makes the likes of cambridge and Bryston etc sound broken by comparison. I'm lucky enough to have attended enough comparisons, some of which were blind, to have established that a truth in my mind. As many of you will know, I'm an independent thinker.
 
Stereo Mic said:
Tenson,

provided the output impedence is less than half the loudspeaker impedence, FR variations will be minimal. The Berning comfortably matches that with well designed loudspeakers without massive impedence swings.
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All dynamic speakers have a big impedance swing at resonance, and depending on the design of the driver may rely more or less heavily on electrical damping. So while the response may not vary much above the bass range, it will likely change audibly around FS. Especially so when you look at CSD, not just FR, where the damping factor plays a significant roll. You only need compare a small and large gauge inductor on a woofer to hear the effect. Its largely why active sounds so good IMO.

The difference could also be a number of other things like IMD or PSRR, all of which the 840a does pretty well at.

I looked at the user guide for an old Technics tuner amp a while ago trying to see what the tape-loop output Z was. It didn't say, but I did notice that while it had something like 0.02% THD it had about 0.5% IMD. I seem to remember someone saying this is quite common in the 'jap crap' amps and is the main reason why they sound a bit poor despite low THD.

So while I have no issues with you liking the sound, I'm not surprised the difference is clearly audible, and I would be hesitant to put it down to the other amp being more transparent than the 840a.
 
Ok, lets clear up this myth about output impedance and also deal with the the question of amplifier transparency.

Most solid state amps have output impedance in the region 0.01-0.1 ohms at low and mid frequencies, rising a little at HF due to the output inductor and falling NFB. Typically you will see around 0.2 ohms at HF. This has practically no effect on frequency response (<0.1db) and ensures good electrical damping at driver resonance.

Now look at a range of tube amps and you'll see anything from 0.5 ohms to perhaps 7-8 ohms for SETS, low/no feedback designs or unusual stuff like Berning. Simon has rightly pointed out the effect high output impedance has on damping but that is only half the story. Look at the other half and all notion that these amps can offer high levels of transparency evaporate very quickly. Such amps are only viable if the impedance curve is flat and I'd argue that they should also be limited to use at MF/HF due to the lack of damping ability and often gross response manipulation at LF.

Some examples will show the effect and I've chosen the Prima Luna PL7 tube power amp as it's different transformer taps give different output impedance and so neatly illustrate the point.

These are response plots of the PL7 driving a simulated speaker load, ie something approximating reality rather than a simple resistor dummy load. The graphs show the effect of 8, 4.5 and 2 ohm output impedance:


1206PLPFIG09.jpg


1206PLPFIG07.jpg


1206PLPFIG08.jpg


With 8 ohms output impedance you can see that response variations reach +/- 3db and even at 2 ohms we are looking at +/- 1.6db.
These are broad response variations and far more audible than narrow glitches. It blows any notion of transparency of faithfulness to the original signal out of the water unless your speakers have a flat impedance characteristic.

Now let's look at a different tube amp with 0.7 ohm output impedance. Benign you might think?
Oh no:

307ROGFIG01.jpg


Here we see +/- 0.4db - better but still clearly audible as these are broad errors.

Now contrast all this with a Bryston 28B-SST amp at 0.06 ohms:

108Bryfig1.jpg


Much, much better!
 
Hi Rob,

Which lines on the graph should we be looking at? I assume you are looking at the quite wild line on each, that looks as though it follows a typical speaker impedance. What are the other quite flat lines, various resistive loads?
 
Tenson said:
Hi Rob,

Which lines on the graph should we be looking at? I assume you are looking at the quite wild line on each, that looks as though it follows a typical speaker impedance. What are the other quite flat lines, various resistive loads?
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Spot on Simon.

Looks like their simulated real load approximates a 2 way sealed box with crossover at around 3-4khz.
 
Thanks for posting that Rob. Nice information.

I didn't realise that tube amps were doing such interesting things to the signal. A FR doesn't tell the whole picture but its damning enough to raise an eyebrow when claims of transparency pop up. I think the appeal for folks is because they're coloured and obviously different. Nothing wrong with that.

I've not had a great deal of exposure but almost every time I hear one it feels like the system is trying to run whilst knee deep in syrup. On the other hand tube aficionados don't mind bashing SS amps for various perceived sonic flaws so it all rounds out nicely. :)

Boring story alert:

Have you heard anything up beat and bass heavy through a tube amp? Two years ago at the Manchester show, I had the opportunity to play Imogen Heap' "Speak for Yourself" CD through Audio Research reference series gear hooked up to what I *think* were ML speakers, they might have been Final can't really remember, they were e-stats anyway. I and the others in the room sat through what was an obviously coloured but enjoyable playback. It was as if the midrange had swelled up and slightly swallowed the high frequencies so things seemed overly lush and smooth. Definitely not what you usually hear from e-stats. I only got the chance to play a single track before the guy ejected the disk - guess he didn't like Imogen Heap :D As he passed the disc back he asked what I thought. I told him pretty much what I've said here. I can't blame him when he replied it wasn't music that played to strengths of the system and that the recording quality wasn't up to showing the full capabilities of the kit. Like I said I can't fault him for his reply, he is trying to sell the kit after all and was pretty diplomatic about it all.

I've played that same CD through a few other systems and it always sounds great. The common denominator here is quality SS amps. If you want transparency that where the meat is IMO.
 
Surely very much dependant on speakers, if you have inefficient speakers I just can't see the point of valves, on the other hand efficient speakers really come alive with competent valve amps.
 
Robbo said:
Different strokes for different folks. people should simply buy what they enjoy.
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I'd tend to agree Neil. People will always believe what they want to believe first and foremost. I obviously refute pretty much every word of Rob's post - it's full of innaccuracies,generalisations and assumptions. But I'm past bothering to argue the point. I'll continue down my path thanks - I've tried yours :)
 
SM, you had a Lyngdorf setup previously, with parametric EQ, so you must be aware of the impact that such variations in FR would have on the sound.
 

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