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In Reply to: RE: Sony Class A, think not posted by AbeCollins on July 24, 2014 at 15:10:04
It's the output transistors working in class A mode. Huge transformer and heats sinks are necessary only to support the power is being WASTED while the amp is idling or running well below its rated output.Various makes have produced "sliding bia" amps over the years. Another one of the current crop is Cambridge Audio's Azur 851A integrated amp, (120 wpc @ 8 ohms).
I love the music of ... ... Gustav Mahler
Edits: 07/25/14 07/25/14Follow Ups:
To make a reasonable amount of Class A power, it requires both big trafos and big heat sinks and/or forced air cooling. Even a modest 50 watts requires substantial amounts of both.
This sliding bias is and always was a kind of a gimmick unless the amp can sustain those bias levels for a significant amount of time (like the Krell Sustained Plateau bias schemes), which STILL requires big power supplies and heat sinks (again like Krell KSA-S series and FPB series and probably there newest stuff too).
This Cambridge may be 120 watts but it will never, ever achieve that in Class A without meltdown. It is for sure AB or even B by that power. I would give it max 15 watts in Class A before it moves over to AB or B.
...but huge idle power consumption in a relatively low power amplifier is one indicator of Class A operation.
I have large 300wpc monoblocks each with 2000VA transformer an large heat sinks. They are Class AB and draw about 65-watts idle.
I have the Pass Labs X150.5. According to its specs, it idles at over 200 watts. Pass says its class A operation is up to 16 watts (at 8 ohms). Also, Pass says it take up to an hour of operation before it sounds its best.Because of the long warm up, I sometimes just listen to my Schiit Asgard 2 headphone amp rather than switch on the Pass amp. Incidentally the Asgard 2 is class A and runs very hot -- it consumes 30 watts continuously.
I love the music of ... ... Gustav Mahler
Edits: 07/25/14
Sounds about right. I had a Sphinx Project 14 that was drawing 240 watts at idle and was delivering just over 20 watts in Class A...180 watts total on tap.
My NAT is single ended 100 watts Class A and draws HUGE power (around 800 watts). It takes more than 2 hours before it sounds the best and the shift is not subtle. It goes from being damn good to OMG good. Practically hallucinogenic but you have to wait and wait and wait.
I think the wait is too long with some hot running Class A SS amps. It could be due to thermal mass and everything needing significant time to reach thermal equilibrium.
In fact, I believe hot running tube amps come up to optimal operating temperature - and sound - quicker than many solid-state amps.
I like an amp that needs maybe 10 minutes or so to be 95% there, and maybe another 20 minutes tops to be 100%.
"I think the wait is too long with some hot running Class A SS amps. It could be due to thermal mass and everything needing significant time to reach thermal equilibrium."
Absolutely! My Nak. Amp. takes a good hour to really settle but it's reasonable after twenty minutes. Thermal mass is indeed the culprit. Probably.... May be some capacitors too but most likely it's the bias point that's the main thing.
It's a stupid amplifier for me since I doubt that it ever hits 10W on the peaks but I like the clear mid-range and I need the low Zout. I do still have my Citation 12 that I built as a kit back-when and may work it over some day. Pass has a Mod. for them that replaces the bipolars with FETS of some nature but I bet that I can clean it up quite a bit by focusing on the lower-level stages.
It's tempting to bi-wire my speakers and run the woofers from SSPP (how's that for an acronym?) and the rest from an SE something as I tend to listen at rather low levels. But I wonder if getting the time-domain clean at crossover wouldn't be a problem. The folks using the fancy digital crossovers seem to have the right idea. Hmmm.
Rick
Much quicker in my experience. My Nat is like 140 lbs and it takes a long time to get full warmed up. The heat sinks get hot pretty fast but the rest just slowly builds up and then BLAM amazing sound.
My KR was singing optimally in about 20 minutes. My other current amp, the JJ 322 (parallel 300B SET) takes about 30 minutes and at first it doesn't sound very special at all. Then it opens up and clears up and the sound is pretty darn nice.
I was reading about your NAT as well as the KR 350i. I read from the NAT website as well as your review posted on the Asylum last yer.
"To avoid unnecessary heat from pure class A operation, Symbiosis Se use automatic adaptive bias - mean if the listening level is not so high then dissipation drop due to lower consumption of power."
In any case, do you know approximate MSRP in USD for these amps?
I don't know the US prices but the KR is 10,000 Euro and the NAT 11,500 Euro.
I know the NAT claims to be sliding bias but I don't see/feel any difference in the heat sinks...they just get damn hot after about 30 minutes regardless of what level of music is playing (or just idling).
It must run Class A all the time though because it is single ended. The four big heat sinks all have ONE transistor slapped on the bottom. The back two amplify the signal and the front two regulate the back two.
14k for the VA350i, which doesnt even have an active preamplifier component.
I believe prices rose 30% last year. There also are lots of questionable issues with this company over the years- see the 'gon thread.
Well, I owned 3 of them and they never had any serious issues and now two of my friends have ones and they love them.
I believe they are currently 10K euro here in Europe.
Nice amps but the pricing is almost 10x more than I want to drop on my 'office system'. ;-)
I'm not even remotely suggesting that the Sony is in the same league as the NAT but the similarity in design philosophy doesn't seem that far apart. The Sony also uses a form of 'sliding bias'. It's heat sinks appear to be the same temperature running idle as they do when playing music. And Sony also attempts to minimize the number of output transistors in it's push-pull output stage.
The power amp, meanwhile, uses a simple push-pull design, with a single pair of transistors driving the speaker: as Kingdon’s white paper explains it, ‘In many cases large output amps employ a power amp stage with multiple transistors to achieve high current output volume, but transistors do not perform identically and emitter resistance is used to stabilise transistor variations.
‘In this amp however, the power amp stage features only one pair of transistors and a design that eliminates variations in each channel at the source, enabling elimination of variation-controlling emitter resistance as well.’
The amplifier is also designed to change its bias according to the volume setting, with the result that most users – unless they’re total volume-level maniacs and/or have extremely hard-to-drive speakers – will find the Sony is actually working in Class A for most of their listening.
The idea is that this technique keeps the output devices working in their most linear range, but without excessive heat.
Abe,
Is there a thread where you describe the setup or software used to interface your Mac mini and your Ipad?
I am thinking about replacing my Windows laptop with a Mac mini using my ipad Air as controller/keyboard/monitor but was not sure how well this would work? Thanks.
I wasn't really suggesting one of them for your bedroom system. I might suggest something like the Pathos TT or Classic one though. Both are pretty darn nice sounding hybrid integrateds.
"'m not even remotely suggesting that the Sony is in the same league as the NAT but the similarity in design philosophy doesn't seem that far apart."
That is stretching it quite a lot don't you think? One is a single ended hybrid with no compromise (or almost no compromise) design and the other is pure SS, push pull and clearly built to a price point. One weighs 40 lbs the other 140...
The only two other amps I know of with something like the same design is the old Blue Circle Audio BC-2 and the curent Ypsilon monster monoblocks.
No one else besides these three companies I know of has ever made a single ended hybrid design.
Warm up times, exactly what my Class AB Prime Design A100 amp achieves, I found the Sony TA-1AES to sound very poor when I compared the two side by side. Most suprising is that the pre can not be separated from the power section. Although Abe (excellent photos) has mentioned the not so good bass I am suprised he does not hear the overall artificial sound ( probably due to the FET input) of the amp neither did the two main stream reviewers Words & Music & HFN & RR. This amplifier should not be purchased without first having an audition at Home which is easy to achieve with Sony's 30 Day money back trial offer.
Edits: 07/26/14 07/26/14 07/26/14 07/26/14 07/26/14
"... my Class AB Prime Design A100 amp achieves, I found the Sony TA-1AES to sound very poor when I compared the two side by side. "
Never heard of it. Can't find anything on it. What is a Prime Design A100? I'm not arguing that you like your amp better. I like my Rogue better than the Sony but that doesn't make the Sony a bad amp.
The Sony amp actually sounds very nice to me. No where did I say or describe the amp as having 'not so good bass'. Those are your words, not mine.
"Most suprising is that the pre can not be separated from the power section."
Why is that still 'most surprising' to you when the answer was presented to you when you asked in the comments section following the Words and Music online review? Besides, what does that have to do with how the amp sounds, and why would separating the pre from the power amp section be important to someone who intends to use the Sony strictly as an integrated amp? There are several integrated amps on the market that do not offer access to the pre and power amp sections separately.
"I am suprised he does not hear the overall artificial sound ( probably due to the FET input)" .
And there is consensus that FET inputs sound artificial? Tell that to all the owner's of world class high-end gear that use FET inputs. ;-)
It seems that yours were the only negative remarks about this amp in the comments section after a stellar online review by Words And Music. I saw your remarks there and only AFTER complaining about all it's alleged faults without actually experiencing them, did you decide to audition one. It appears that you didn't want the Sony to sound good.
I already bought the amp. I'm quite happy with it. I don't use 30 day trials knowing ahead of time that I will return the product.
Prime Design A100 is a 18 year old integrated amp with a pre that can be separated from the power section only 100 were manufactured due to manufacturer having problems including a bad review plus a stupid rush to get on to market before it was properly signed off. Mine has been extensively modified hence the excellent performance. I have previously posted part of the spec. 11O watts into 8 ohms, 200 wpc into 4 ohms ,damping factor 200 measured at 40Hz THD 0.005%, 500 VA transformer 80,000 mfd capacitance. Words & Music told me that the TA-1AES could still be used as a power amp despite having to use it via two line stages, the pre-out of the excellent Sony DA5400ES AVR (UK version). Being delighted with my Sony combo DA5400ES/XA5400ES the idea was to use a all Sony system but the new Sony amp was a big disappointment. My TL speakers full range Jordan drivers are not bi-wired so I can not use the Sony AVR in bi-amp mode, the A100 driving front speakers gives a better bass performance than the AVR. I was completely misled by the TA-1AES OTT reviews. I took the Sony amplifier for a second opinion to a loudspeaker designer that I know, he is also an audio electronics engineer and he completely agrees with me over the sound of this latest Sony amplifier. He is also the person who told me that FET inputs in power amps should not be used for lowest distortion especially at HF. Apologies if I miss read you re the bass issue but read it somewhere.
Edits: 07/26/14 07/26/14
The 'true Class A' amps that I have personally owned include the Krell KSA-50S, Pass Aleph 3, and Pass Aleph 30.
The KSA-50S had a stepped Class A system that Krell called Sustained Plateau Biasing. At high volume levels, it would draw 800-watts continuous, and when the volume level was reduced or signal removed, it would continue to draw 800-watts for a while until it stepped down to a lower demand level.
The Pass Aleph and Aleph 30 are 30wpc amps but they each drew over 200-watts just sitting there idle.
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