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Old 13th March 2012, 05:52 PM   #3361
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by dvv View Post
Wayne, with a peak output current of 200 A, it not only doubles down, it goes way beyond that.

When you halve the load impedance, an amp may still be able to deliver the same nominal output voltage, but NOT with the same THD and IM specs.

More of this anon, in VERY practical terms. Stay tuned.
It goes into protect driving CLS's and I understand thd increases when you lower the load. When viewing this phenom one can see there is an signature thd vs load vs output .

I will post up some graphs when I'm at my desk ......
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Old 13th March 2012, 05:52 PM   #3362
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T., I can perhaps offer an example or ten of halving up.

I have had the pleasure of demonstrating an old Grundig integrated amp to quite a few Far East/N. America audio fans, and, much to their surprise, it came out far better than they would ever have given it credit for.

It actually outshone quite a number highly touted, very sexed up Japanese integrated amps, all to the one with at least one sexy technology, like Sansui's DD/DC and all that jazz.

The trick was, as you may have guessed off hand, that I purposely used my refreshed AR 94 speakers for the demo, precisely because of their naughty impedance modulus and its tendency to drop below 8 Ohms by not a little.

Only a few people realized the catch - the Grundig was designed to drive 4 Ohm speakers, and then two pairs in parallel (although their statement has it that this should not be done, in practice, many of them actually could do it). So, its nominal 110 Watts into 4 Ohms (it used two pairs of BD 249/250 C per channel) became something like say 70 W into 8 Ohms, but beacsue it was initially designed to deliver considerable currents, it never saw the ARs as any special problem or such. Whereas the Japanese amps did see it as a problem, some of them as quite a problem.

No matter what anyone says, and despite the fact that Grundig was usually flippantly dismissed as a low end of the low end, I thought, and still do, that they were grossly underestimated. Those boys knew more about real world sound than most others, and their 20 wpc amps usually sounded more authoritative and in charge than many a fancy Japanese brand and/or model.

In many ways, this is true of most of Germany's audio companies, most of which never made it outside Germany at all. Germans were great to design and build it, but they were absolute cretins when it came to marketing their gear. That, plus their blind insistence on 5 pole DIN plugs and standards cost them their industry.

The ASC LV5000 integrated amp, a spin-off of Braun, is still No.1 on my shopping list.
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Old 13th March 2012, 05:59 PM   #3363
dvv is offline dvv  Serbia
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Originally Posted by john curl View Post
DVV, you can NEVER completely duplicate the maximum drive voltage between 8 ohms and 4 ohms. You just have to leave some room by providing slightly more
power supply voltage than is absolutely necessary.
Agreed in absolute terms.

HOWEVER, you do two things: 1) you let the 8 Ohm specs go to say 30 Vrms, so with 4 ohms it should be just about right when you do 2) you add fully regulated power supplies.

And you don't skimp, either - if your output stage uses say 3 pairs of transistors X and Y, you use just as many of the same in your electronically regulated power supplies. You do NOT save by saying - aha, two 250 W trannies will be nicely powered by just one 250 W trannie.

And just because you are using full electronic regulation, you do not take that as an excuse to reduce your filter capacitors - you use just as many and just as much as if you didn't have any regulation at all.

Of course, when all is said and done, you do end up with a nasty bill. But hey, whaddaya want, to drive a Rolls Royce for the price of a Mini? When you sit in your Porsche, and want to remind yourself of what it can do between say 4,500 and 6,000 rpm, is the petrol bill what you think about?
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Old 13th March 2012, 06:16 PM   #3364
a.wayne is offline a.wayne  United States
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In mine I'm more interested in what it does between 1.2 bar and 2 bar ......
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Old 13th March 2012, 06:18 PM   #3365
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Congratulations; now we are back to dynamic distortions, about 150 pages ago.
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Old 13th March 2012, 06:36 PM   #3366
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Quote:
Originally Posted by dvv View Post
[snip]And you don't skimp, either - if your output stage uses say 3 pairs of transistors X and Y, you use just as many of the same in your electronically regulated power supplies. You do NOT save by saying - aha, two 250 W trannies will be nicely powered by just one 250 W trannie.[snip]
It's not that bad though - a single pass transistor can feed two or three pairs in the output. The pass device only sees a relatively small Vce so will not be SOA-challenged; the SOA being the reason why the output stage needs two or three pairs.

jan
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Old 13th March 2012, 06:38 PM   #3367
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Hi,

Quote:
Originally Posted by a.wayne View Post
Yang Wang size room , bad SS amp ....
The room is indeed modest, but I used the speakers and Amp in around 60m^2 as well and they did splendid there as well. The SS Amp does not lack power or control etc., it just sounds for want of a better word "boring" and "uninvolving". It's actually not bad at all, as far as solid state goes.

Speakers are ~90dB/2.83V 3-Way (1st order series crossover, timealigned) with a 270mm Woofer and a pretty much flat 6 Ohm impedance above the bass loading peaks with the Bass minimum at 7 Ohm, what we call a "undemanding load", so even fairly load intolerant SS Amp's have little trouble driving these.

Ciao T
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Old 13th March 2012, 06:45 PM   #3368
dvv is offline dvv  Serbia
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Click the image to open in full size.

This is what I'd like to make for myself - not as a commercial project, with the prospect of making it public domain once I have compiled a true list of materials, notes, instructions, etc.

Please do not ask me why I did something the way I did - obviously because I thought that would be best. Which may or may not be so.

But, I have my point of view, and others have theirs. So, this is an invitation to one and all to make their suggestions as they see fit, if they feel so inclined. Publically or in private messages, as they prefer.

Just a few initial words.

The I/V protection circuit is about as classic as it can be, but still with two twists. The first is that it will sleep out even 2 Ohm loads and will activate at 1.8 Ohms. The second is that before it activates at all, it has a delay of about 40 milliseconds, or twice the IEC impulse strandard.

The model assumes two fully electronically regulated power supplies. The one for the voltage stages is set at +/- 55V, and the one for the current stages at +/- 48 V. These voltages have been chosen so that in both cases, the supplies should be very tolerant towards possible line variations, each with about 4V reserve (after stabilization). The basic voltages will be provided by custom toroidal transformers, separate for each channel for current and voltage stages. I'm gonna hog this one.

The ciruits at the bottom are clear enough and are known well enough. The right part protects the amp from too much DC (it will sleep until about 150 mV DC) and from overheating, with indicator LEDs in both cases.

Initial measuring within the simulator are as follows:

35 mV at the input will produce 29 Vrms at the output with no overall NFB;

Closed loop, it takes 95% of 1.5 V to get 29 Vrms at the output; the input pot is tentative. It will be there if the amp goes as is, but it will be removed if I decide to install a discrete, fully complementary buffer; however, the buffer can be used in its adjustable mode. I insist on being able to adjust the actual volume of both channels to below 0.1 dB because it is my feeling that this imbalance is one of the important reasons why much spatial information could lost in case it is too great, and I've seen it be as much as 0.5 dB on commercial products;

Speaking of which, what are your experiences with buffers, good or bad, yes or no?

At full rated power (28.3 Vrms), THD measures as follows, 20...20,000 Hz:
8 Ohms: 0.015%
4 Ohms: 0.025%
2 Ohms: 0.06%

(Note: regarding above measurements, actual output power into 8 Ohms is 29.1 Vrms, 28.9 Vrms into 4 Ohms and 28.1 Vrms into 2 Ohms).

That's as far as I got so far, and I have only just begun. It seemed logical to me to ask for your views now, before most of the work is done, rather than later, when any change will incur more changes downstream.

The only completely non-negotiable part of this are the output transistors. I just went through some hell to get hold of really, honestly, cross my heart and hope to die Motorola/ON Semi original trannies, in a population which should allows for decent matching, meaning I plonked down a healthy sum of bread, and I am not about to go through that again.

There are several aspects I have not made up my mind yet. I also have another version of it, minust the cascode transistors at the input (just plain differentials), which measures practically the same. In terms of electronics, I don't really NEED the input stage cascodes, all I have to do is use BC 546/556 B trannies, and I am tempted to keep it as simple as possible.

I have a yet third version, which uses a cascode as its second and final stage of voltage amplification, combining a BC 546 or 556 and BF 720 or 721. This yields a VERY low distortion factor, 0.009% for 8 Ohms at 1 kHz under the same conditions as above, but forces me to use the BF trannies, which while readily available and with reasonable prices, are SOT-223 packages, for SMT mounting (tricky soldering, but it can and has been done).

Full power bandwidth exceeds 300 kHz into 8 and 4 Ohms. This will be regulated with the inpit RC filter, cut down to say 250 kHz.

OK - hit me.
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Old 13th March 2012, 06:49 PM   #3369
dvv is offline dvv  Serbia
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Quote:
Originally Posted by janneman View Post
It's not that bad though - a single pass transistor can feed two or three pairs in the output. The pass device only sees a relatively small Vce so will not be SOA-challenged; the SOA being the reason why the output stage needs two or three pairs.

jan
You are right, I know, but somehow, I'm in the trip of saying if it's a ball, let it be a ball under masks and with plenty of champagne.

Actually, I was thinking of using plastic pack 2SC5200/2SA1943, three pairs, as regulators feeding the three pairs of MJ 21195/21196.
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Old 13th March 2012, 06:54 PM   #3370
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Hi,

Quote:
Originally Posted by bcarso View Post
Yep, that's consistent with the shutdown of Andy's program in February of 1990, when I joined Harman as an employee.
More like 10 years apart actually. John gave us more of the inside dirt...

@ John, I have no idea what went on between You, Matti, Silver and HK, but the lower aimed units of the X series indeed look a lot like your circuitry. The original XX and XXP DO NOT. This may be very well Matti's circuitry, it is some freaky mirrored and rail symmetrical Rush cascode thing, really quite strange looking and probably faster than greased lightning on snow.

@ Dejan, I have incomplete schematics, but I do not think I can pass them on.

As for halving up or doubling down, please read the specifics of my challenge/contention.

Ciao T
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