I think they can also become quite hot.
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boXem Arthur 4222/E1 Amplifier Review
- Thread starter amirm
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I think they can also become quite hot.
Ok, you’ve got me on that. I’d still say the small, incremental differences presents an even smaller value in some of these Purifi amps, this one being an example.Not really, there is the design of the buffer board and some other features like auto on and gain selections and general build quality and care in the assembly .
Here all options are slightly different, you choose
Fidji
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Out of curiosity- what would make analogue multichannel preamp a viable business proposition?I hope it will be multichannel and not only plain old 2.0 stereo and that it will not be deprived of some useful features, that are to often lacking in current analogue preamplifiers.
But perhaps I have to much expectations and I am asking for to much for a début in this field.
I do not see any reasonable application for such type of device (as compared to proper AVP) in the days of immersive audio.
This amp does not represent a "small, incremental difference" with "an even smaller value". The SQ is actually also marginally inferior to the 1ET400A. But it DOES represent a significant higher value for the customers that need the higher current output on lower loads. If you do need the latter, then it is just not the amp for you.
Well, we need to go from digital to analog to drive loudspeakers, and we need to control gain. Multichannel is no different from stereo in that respect (just > 2 channels). But as we can decode multichannel formats (including Dolby Atmos) on a source device, upstream of said DAC/pre-amp, we don't necessarily need/want an AVR/AVP. Especially as they don't usually measure well (with some exceptions at higher prices).
For a while I relied on source device software to adjust gain (in the context of playback volume) but doing that you are just one software glitch or user error away from a blown speaker so I'd say don't do that. When my existing stereo DAC failed and I decided to give myself the option of multichannel there were roughly two choices—exaSound or Okto—apart from pro audio interfaces (and only one you could actually buy). At least one more choice now, I'd say more is better.
Now I'm happy to have the DAC and pre-amp functions in one box, but separate boxes are also functional. From a Mac source it's straightforward to aggregate a number of stereo DACs for multichannel (Mr Rubinson did and wrote about this at length). Then you want something to control overall gain into the power amp stage.
But that remains a small market niche, so I'll not be expecting same from BoXem out of the gate.
Edit: added use case for analog box.
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Hum... Is it?
Fidji
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I am into multichannel so this would be actually of interest to me - do you know any producer of mulchannel analogue preamps fit for today 16-20 channel setups?
Now I feel like a politician in front of an interviewer
.So, since you both kindly asked, let me tell you about these points
.- active common mode rejection: to transmit a signal, two potential V+ and V- are needed. Differential voltage is defined as (V+ - V-), common mode voltage is defined as (V+ + V-)/2.
To simplify, common mode is perturbations, differential is signal. All the game is to avoid perturbations to mix with signal, that is called common mode rejection.
To do this, the idea is that the amplifier input presents an impedance as high as possible to common mode signals. With adequate topology and resistors tolerance, this is relatively easy to do. Until you add an EMI filter with it's capacitors whose impedance will dramatically decrease with frequency. 2 x 100 pF at 20 kHz is équivalent to 40 kOhm, far away from the MegOhm that we want to reach.
Then enters Mr. Bill Witlock whose capacitive bootstrap technique patent is now in public domain. We can now have both excellent CM rejection at audio frequencies and good EMI rejection. Since this technique uses active components, we called it "active" common mode rejection. - ultra low noise buffer: for various reasons (bigger FETs but also modulator topology) the 1ET7040SA is 40% noisier than the 1ET400A.
For the 4215/E2 we chose OPA1656 opamps for the buffer. Their low bias current allows both low DC at amplifier output (no thump at power on/down, less speaker distortion) and input impedance while their noise is low enough to allow excellent THD+N and SNR values.
Since we knew that the cost per channel would be multiplied by two for the reasons that I explained previously, performance of the new amp had to be at least equal to the 4215/E2. Buffer noise had to at least decrease as much as the module noise increased.
So bye bye OPA1656, hello OPA1612, a lot of work on the choice of resistors and the layout, then target was achieved. As shown by the measurements, the buffer has no footprint at low and medium gain.
Some will notice that I didn't talk about low noise regulators. In addition to be in unobtainium, they are completely useless with modern opamps. So we don't use them for this application. - high pass response: OPA1612 has a quite high bias current, so if you mix it with an elevated input impedance, you will get a lot of DC at the output. Since we want our amps to be easy to drive, even with tubes, high input impedance is not negotiable. And high DC output is not acceptable. The solution was to AC couple the buffer to the module.
- u-shaped buffer: I will leave some mystery here, but the members having followed the discussion around the glorified ribbon will understand.
I wasn't sure when you said analog if you specifically wanted something without a DAC function. If not, then look into audio interfaces (which is what they call them in pro music/audio) from say Motu or RME, you'll find devices with high channel counts and master volume control. You'll have to trawl through the model range to narrow down to something suitable (you need to consider physical connections for example) but they can be had a fair bit cheaper if you don't need all the functions of a Trinnov for example.
I almost bought this RME instead of above-mentioned DACs, there are similar models with more connections in the range.
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I attended one of her concerts.
Really nice.
There are some nice Belgian rock/pop artists.
For blues or jazz as well...
Yep I saw Puggy in concert, they were pretty good.
Arno (well, unfortunately, he's gone now), Ozark Henry, Selah Sue,...
But also my friends JF Foliez, Johan Dupont, Étienne Plummer (Steppe, ...), Music 4 a while, Jean-Philippe Collard-Neven (with -or without- Jean-Louis Rasinfosse and José Van Dam), Boogie Beasts (not exactly the same style), Yves Teicher (sadly, also gone),...
and so many others...
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That's it.
I acknowledge that analogue multichannel preamplifiers is a niche (dream ?) market, but an appealing one for those who, like me, do have hundreds of multichannel materials playable on an analogue ouput only source and are eager to give said materials a listen.
Higher current output on lower loads based on it being a mono amp rather than two channel ? If so, wouldn’t a like for like comparison between this amp and the lesser priced VTV mono amp’s make the same point?
The audio multichannel interface product type I mentioned in reply to @Fidji have analog in (they do ADC/DAC) so can be used in that sort of application, barring a (more) simple pre-amp. Not sure if you can bypass the digital stage and do analog through though, if that matters.
*I enjoyed typing through though
Thank you Fred for your explanation. A little light more in the tunnel now. I could learn more. What is the actual input impedance in buffer mode of your Amps?Now I feel like a politician in front of an interviewer
So, since you both kindly asked, let me tell you about these points
- active common mode rejection: to transmit a signal, two potential V+ and V- are needed. Differential voltage is defined as (V+ - V-), common mode voltage is defined as (V+ + V-)/2.
To simplify, common mode is perturbations, differential is signal. All the game is to avoid perturbations to mix with signal, that is called common mode rejection.
To do this, the idea is that the amplifier input presents an impedance as high as possible to common mode signals. With adequate topology and resistors tolerance, this is relatively easy to do. Until you add an EMI filter with it's capacitors whose impedance will dramatically decrease with frequency. 2 x 100 pF at 20 kHz is équivalent to 40 kOhm, far away from the MegOhm that we want to reach.
Then enters Mr. Bill Witlock whose capacitive bootstrap technique patent is now in public domain. We can now have both excellent CM rejection at audio frequencies and good EMI rejection. Since this technique uses active components, we called it "active" common mode rejection.- ultra low noise buffer: for various reasons (bigger FETs but also modulator topology) the 1ET7040SA is 40% noisier than the 1ET400A.
For the 4215/E2 we chose OPA1656 opamps for the buffer. Their low bias current allows both low DC at amplifier output (no thump at power on/down, less speaker distortion) and input impedance while their noise is low enough to allow excellent THD+N and SNR values.
Since we knew that the cost per channel would be multiplied by two for the reasons that I explained previously, performance of the new amp had to be at least equal to the 4215/E2. Buffer noise had to at least decrease as much as the module noise increased.
So bye bye OPA1656, hello OPA1612, a lot of work on the choice of resistors and the layout, then target was achieved. As shown by the measurements, the buffer has no footprint at low and medium gain.
Some will notice that I didn't talk about low noise regulators. In addition to be in unobtainium, they are completely useless with modern opamps. So we don't use them for this application.- high pass response: OPA1612 has a quite high bias current, so if you mix it with an elevated input impedance, you will get a lot of DC at the output. Since we want our amps to be easy to drive, even with tubes, high input impedance is not negotiable. And high DC output is not acceptable. The solution was to AC couple the buffer to the module.
- u-shaped buffer: I will leave some mystery here, but the members having followed the discussion around the glorified ribbon will understand.
2 x 47k to GND
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PS Audio
S.M.S.L
Nuprime
Topping
Hattor
Loxjie
T+A
Rouge Audio
NAD
Jeff Rowland
Monoprice
Elipson
Cambridge Audio
Peachtree
Even McIntosh (Multichannel amp)
And so on...
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