HCC, Harman-Kardon and Amplifier Weight

[DVV]

That's exactly how they do it. No amplifier can achieve the theoretical ideal of 'doubling down'.

Dig up IEEE publications from the second half of 1972, and find the text by one Dr Matti Otala, related to first time ever mentioning and identifying the mechanisms of TIM. Look carefully at the schematic of his proposed zero TIM power amplifier provided there. It is rated at 25/50W into 8/4 ohms, and works in pure class A up to 2.9/5.8 W into 4/8 ohms.

That is THE cornerstone text for amps. What we have today, ALL of it, is based on that one text, which was subsequently followed by several more, ending with one in 1975 related to driving extremely difficult load impedances, with highly reactive components. Examples provided were AR3a Improved and Yamaha NS-1000.

If you should want to make it, you will be surprised at the quality of sound it affords. That I will guarantee, or I'll be happy to pay your bill for making it.

Cheers,
DVV

 

[PENG]

The voltage drop is NOT proportional to load current, excpet on such poorly made units as I have never seen in my 35 years in audio.
DVV

For all intents and purposes, volt drop, however small, (I specifically single out the transformer itself), is proportional (may not be exactly in direct proportion but pretty close) to the load current. Well made ones drop less because its winding impedance is low.

There is a voltage drop, to be sure, but on decently done stuff, it will be less than 1 V.
DVV

I can agree with your number, but just because its low, it does not negate the fact that it is proportional to the load current. It is 0 under no load condition (once the caps are charged) but will rise with current to a low value under full load condition. I was not talking about losses. Core loss is more or less fix, winding loss varies with load, as is volt drop.

For a nominally 100/200W into 8/4 ohms amp, I use a 500VA toroid; you think it will sag at 200W/4 ohms? Well, it won't - try it and see. Each power supply line is fed by a separate full wave bridge rectifier (a good US high end practice!), two per channel, each feeding 3x10,000uF capacitors (60,000 per channel). Sag? What sag? My typical sag is below 0.5V.
DVV

Yes it will still sag, but I agree with you that it may be below 0.5V, but still sag. If you use a 500VA toroid in this case, you set yourself up to potentially understating your 8 ohms output (100W). For argument sake, capacitors take care of most needs in real life, i.e. playing normal music, movies etc., when the capacitors provide the intermittently needed high current, buying time for the transformer/rectifiers to charge them back up quickly, but I assume we are talking about continuous rating here. BTW, there are not too many amps that use 60,000 microfarads per channel. Amps that do, are better than just "good amps".

Any self-respecting amp manufacturer will say 100/200W into 8/4 ohms. When measuring under specified conditions, you will very likely find it delivers say 110W into 8 ohms and say 205W into 4 ohms. Nobody in their right mind will forget to include some tolerance because you can't escape small variations in production no matter what you do. They would want to be sure you get what you paid for, although I must say this practice of old is not quite so popular these days.
DVV

No comment on this one.

As for Bryston, my experience with them is not very extensive, but the three units I did get onto my lad bench did, all of them, very happily double their output into 4 ohms. And one of them is now 15-16 years old, never had its caps changed! Bryston is about the worst possible example you could have given for sagging, but about the best you could come up with ideal doubling. Bryston, Krell, Levinson, Kensonic Accuphase - these people do it routinely without batting an eyelid.
DVV

I used Adcom and Bryston as examples because I have the manuals for my two amps. They do not double their outputs into 4 ohms. 200W/350W for the Adcom and 300W/500W for the Bryston. Again, just examples, I did say the best ones could come close to doubling down, I meant, really close.

It is nice to finally have people knowledgeable in audio engineering like you to post here and I learnt something from your posts. I thought you might have misunderstood the point I was trying to make in my post. I was only responding to Buckeyefan1's post that implies any good amps will put out double the output into 4 ohms. In fact he was actually talking about quadrupling down to 2 ohms. He's really stretching to the point I was sure he was trying to stir things up here, right Buckeye?. That said, Buckeyefan1 posts often and I know he's open for discussion and disagreements.

I think most "good amps" (if I may borrow Buckeyefan1's expression again) get you around 1.75 times their 8 ohms output into 4 ohms. That's all I have to say, thank you for responding.

 

[PENG]

Sorry to digress once more, but I do have a question for DW, or others.

Let's assume an 100W/8 ohms amp can tripple down to 400W into 2 ohms. On continuous basis (I know its not possible with music/movies), that would result in a draw of 14.14A or 28.28A with 2 channel driven simultaneously. What would be the typical rail voltage assuming the impedance is in fact 2 ohms with a test tone signal?

I am just wondering what would be the draw on the transformer primary side, i.e. the 120V outlet, and the resulting line volt drop.

 

[DVV]

Sorry to digress once more, but I do have a question for DW, or others.

Let's assume an 100W/8 ohms amp can tripple down to 400W into 2 ohms. On continuous basis (I know its not possible with music/movies), that would result in a draw of 14.14A or 28.28A with 2 channel driven simultaneously. What would be the typical rail voltage assuming the impedance is in fact 2 ohms with a test tone signal?

I am just wondering what would be the draw on the transformer primary side, i.e. the 120V outlet, and the resulting line volt drop.

Since in voltage terms, 100W/8 = 200/4 = 400/2 ohms, the effective minimum being sent out must be 40 V peak in pure theory, in my view at least 42 V peak. To this you need to add the voltage drops across all of the transistors the signal passes along the way, and there's no telling how many that may be. If we assume one input stage, one voltage gain stage, predriver, driver and output devices, that makes 5; worst case is that all are PNP, so that's (0.7V x 5) 3.5V.

Consequently, your absolute minimum rail voltage must be (42+3.5), say +/-45V.

But this is theory only, NOBODY wants to cut it cloase, so you are likely to see rails of +/- 48...55V across the current gain stage alone, or more like +/-52...60V across the entire amp, if if uses single rails for the works.

On the sagging subject - I tell you have ZERO sag. You see, just as you start from the nominal power into 8 ohms, so I start from the nominal power into 2 ohms. Hence, I design everything for 2 ohms, and the voltage required to get me where I want to be with 2 ohms will by defualt be the least possible. Therefore, into 4 and 8 ohms, my supply voltage will not sag, but in fact quite the opposite, it will rise because the power supplies and output stages will be off-loaded rather than on-loaded.

Point is, this is a matter of your viewpoint, although we are talking about exactly the same thing.

Also, please remember that with fully regulated power supplies, sag will be in the vicinity of 10 mV or less - realistically speaking, no sag at all.

As for the draw on the primary side, on my last sample, at full load on (i.e. 405 watts into 2 ohms), the transformer drew just under 2 amps from my wall socket (at 220 VAC, 50 Hz). I hasten to note that this is only one of many possibile values, because it depends on many factors, from the line voltage, via the transformer convesrion factor, to the absolute quality of the transformer itself, and that alone will vary wildly from case to case.

Cheers,
DVV

 

[DVV]

I note I forgot to finish the story ...

When he identified TIM and TID, in 1972, Professor Otala (Finnish) was working with Jan Lohstroh, himself a most capable designer, in the Dutch Philips labs. He stayed there until late 1975, and rounded off his TIM study.

Next, 1975-1985 he spent working with Richard Miller in the labs of one Harman/Kardon. That was when we saw Citation XX, capable of prodigious 500 (no typo, you read it right, five hundred amps!) of instantaneous current capability (whatever that means, because I for one never saw any explanation of it whatsoever). That's when H/K's wide bandwidth approach reached its pinnacle, when most of what is sold today was first concieved; modern designs are merely further developments of what was designed then.

Richard Miller is still head of design in H/K; Matti Otala has slipped away from public eye, more's the pity.

Cheers,
DVV

 

[PENG]

Okay, I really don't think we are arguing any more, especially on the electronic side, you obviously have the hands on knowledge that I don't have. Thanks.

 

[PENG]

As for the draw on the primary side, on my last sample, at full load on (i.e. 405 watts into 2 ohms), the transformer drew just under 2 amps from my wall socket (at 220 VAC, 50 Hz). I hasten to note that this is only one of many possibile values, because it depends on many factors, from the line voltage, via the transformer convesrion factor, to the absolute quality of the transformer itself, and that alone will vary wildly from case to case.

Cheers,
DVV

Wait a minute, 2 amps from a 220 VAC, 50 Hz wall socket gets you 405W output, efficiency will have to be over 90% and power factor will be unity?

 

[DVV]

Wait a minute, 2 amps from a 220 VAC, 50 Hz wall socket gets you 405W output, efficiency will have to be over 90% and power factor will be unity?

2 amps, yes. The line voltage is nominally 220 VAC, but since the local power company is slowly moving up to general European standard of 230 VAC, the real volatge is 224-227 VAC.

I should also mention that it is well filtered.

What's so surprising about that? Krell's integrated amp some years ago, I forget its designation, rated at 150/300W into 8/4 ohms, used just ONE 400VA toroid for both channels! And delivered the goods, for a short while at least, but that only because of overheating, it had very small heat sinks for a 2x300W/4 ohms amp.

My own Karan Acoustics KA-i180, rated at 180/250W into 8/4 ohms, uses one 680 VA toroid for both channels, with 20,000 uF per supply line (80,000uF in total).

Cheers,
DVV

 

[Buckeyefan 1]

Check out the specs on this amp. Sure, it's car audio, but it's only spec'd at 11 volts. JL is known for conservative ratings.

www.jlaudio.com/amps/3002.html

There are dozens of more amp examples in the car audio industry.

 

[DVV]

Check out the specs on this amp. Sure, it's car audio, but it's only spec'd at 11 volts. JL is known for conservative ratings.

www.jlaudio.com/amps/3002.html

There are dozens of more amp examples in the car audio industry.

Good point, although these amps are constructed on an entirely different technology.

Just take a look at PC speakers these days, about 99.9% of them coming from China. Well over 1 kilowatt P.M.P.O. (Peak Modulated Power Output, whatever that means) is the norm, for something costing less than a half-decent interconnect cable. How is that possible? Tesla must be turning in his grave! As are Ohm, Volta, Faraday and a slew of others.

Cheers,
DVV

 

[PENG]

but it's only spec'd at 11 volts.

"but" ?? given the low impedance, and the fact that you don't get much more than that in a car, I am not surprised.

 

[Buckeyefan 1]

"but" ?? given the low impedance, and the fact that you don't get much more than that in a car, I am not surprised.

Most car amps are spec'd at 14+ volts. That's a plus for JL Audio. Like you said, you don't get much more than that in a car. That's why $100+ caps are so popular. Only in a large truck do you average over 14 volts. My F150 puts out just under 15 volts on a constant basis. The larger battery and alternator don't hurt either in comparison to what a tiny civic puts out. Luckily I don't need a cap, and still push my amp at 1 ohm levels. Love that class D - never gets warm.