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Old 19th February 2013, 10:30 AM   #8421
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I am so loaded down with work right now that my plans to knock together a simple high current op amp booster will have to wait . It seems to me that any amp that can raise 15 V rms in bridge and drive 1 ohm is a winner .

My previous research into this said that any amp that can offer 5 watts class A and then jump into class AB ( the much criticized bad type AB that looks like class G ) will be a winner . It will not have the gutless sound of many class A designs .

My other experiments were very surprising . When the OPA 604 was replaced with 2 transistors ( 3/4 is better ) the control of distortion became easier !!!! Low distortion at 50 kHz with some cunning was possible . At -70dB 50 kHz I was happy ( 5 watts down to noise ) . 2 transistors was a stupid caprice . What it did prove was the following .

Bootstraps work .
Bootstraps are mostly wrongly thought out .
Single input is not a source of excessive distortion .
High DC stability is possible with a single input .
LTP input is not a source of instability to any great degree .
Single VAS is a bad idea
A small VAS emitter resistor is a fine tuning aid . It can do more good than harm .
Complimentary feedback pairs work well without obvious problems .
Class A to 5 watts is ideal because it requires no special bias system if heatsink is suitable .
I would say 5 watts regardless of load is practical and advantageous . No need for class A to increase with load .

I have to say when I turned down the bias it still was as sweet as I could hope for . The scope said it should be . The difference was the reality of voices with sensible class A .

I do think " wrong " class AB has an advantage . It gives the correction system two places to correct . OK it will produce more THD . The thing is the distortion is where we already are not able to turn down ear distortion . The amplifier now tells us detail is important and the thrill of loud is available on demand . With bad amps I just listen loud . " Good class AB " puts the distrotion where it dose most harm, makes me know it is amplified music .

It is often quoted that to our ears 10 watts is half of 100 watt , it is a quarter of 1000 watts . The reason most 10 watt amps sound gutless is a serious lack of current .

Dvv . I had a Naim Nait . 90% of the time I could hear what it did wrong . All of the time it was fine and had a feel good factor . It was like Burger King ( one shouldn't like it ) .

Last edited by nigel pearson; 19th February 2013 at 10:32 AM.
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Old 19th February 2013, 04:57 PM   #8422
dvv is offline dvv  Serbia
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Nige, Frank,

It's all economics, NONE of it is electronics.

The industry wanted to make as much money as it could, so it did its best to create the idea that power equals quality. To reaffirm that, more powerful was also given extra faclities, so it would even look richer. Far too few people even dared think outside that box.

The few that did gained world fame.

I'm not sure whether our American friends had an opportunity to see Hiraga's legendary little amp. Just in case I'm right, the schematic is attached. Note the simplicity and right down to business approach. I have heard tens and tens of version of it, and most sound from very good, to outstanding, low power notwithstading. King of the road is a guy who ran his from two 22,000 uF caps - per channel.
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Old 19th February 2013, 05:28 PM   #8423
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Quote:
Originally Posted by dvv View Post
I'm not sure whether our American friends had an opportunity to see Hiraga's legendary little amp. Just in case I'm right, the schematic is attached. Note the simplicity and right down to business approach. I have heard tens and tens of version of it, and most sound from very good, to outstanding, low power notwithstading. King of the road is a guy who ran his from two 22,000 uF caps - per channel.
Wonder what the d.c. offset was? Rarely are PNP and NPN matched well enough, even when alleged to be complementary pairs, to have that current-mode input stage have low offset voltage.
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Old 19th February 2013, 05:38 PM   #8424
a.wayne is offline a.wayne  United States
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Two notes here.

You are absolutely right when you say we blamed the amps for what had nothing to do with them. Also, speaker designer didn't give a hoot what the amp saw of their impedance modulus, they simply passed the blame on to the amp designers.

Secondly, some years ago, just before they were shut down, Son Audax published a catalog of their own speaker drivers. Some 15-20 years ago, they produced a soft domw tweeter which could be found in at least 50% of British speakers at the time. Their own waterfall diagram showed that the driver was intermodulating like crazy, yet people swore by it. Their titanium dome, on the other hand, had an exemplary clean waterfall diagram up to +1.5 dB above nominal power, yet people shunned it because it was made of metal, claiming it sounded sharp and shrill.

I own two pairs of speakers from the same stable, and whichever amp I plug in, the titanium dome is much more clear and defined than the "legendary" soft dome. To someone accustomed to the sound of the soft dome, this may appear to be shrill, but give it a few days and I doubt you'd want to go back to the soft dome.
Yeah , keep blaming me ..

Build a true voltage source and its all over, build a compromised amp and then in turn blame the speaker designer ...

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Originally Posted by fas42 View Post
Just to echo dvv's comments: well sorted out 20W amp into 90dB sensitivity gives one all the sound volume, and quality, that one could want in a conventional living area.

And, yes, shortfalls in engineering application are the reason why this, and nominally much more powerful setups typically don't do the job ...

Frank
OK, now do that experiment again with a 200w amp, obvious game changer
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Old 19th February 2013, 05:52 PM   #8425
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Not really blaming you Wayne, I have no idea what you do, so how can I blame you?

But you have to admit there were some downright irresponsible designs around.
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Old 19th February 2013, 06:03 PM   #8426
a.wayne is offline a.wayne  United States
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Not really blaming you Wayne, I have no idea what you do, so how can I blame you?

But you have to admit there were some downright irresponsible designs around.
It was tongue in cheek and rhetorical DVV ........

Irresponsibility comes from bad sound, if the sound is good, then its a good design coupled to a bad amp ...

I hate toy amplifiers, despise them really, there is no reason mass produced amplifiers cant have enuff outputs and transformers for proper current protection without reverting to dumb down circuit protection.

Much better to have a 50watt per channel amp that is load tolerant than a 200 watt per channel 8 ohm only amp loaded down with sonic degrading protection ..

Hence i stay away from dinky toy designs ......
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Old 19th February 2013, 06:39 PM   #8427
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It was tongue in cheek and rhetorical DVV ........
So was my post.

Quote:
... Much better to have a 50watt per channel amp that is load tolerant than a 200 watt per channel 8 ohm only amp loaded down with sonic degrading protection ..

Hence i stay away from dinky toy designs ......
Completely agreed. Power is not half as big a point as load tolerance is. Some have never figured this out, and others have a long time ago, like Harman.
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Old 19th February 2013, 10:04 PM   #8428
fas42 is offline fas42  Australia
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Originally Posted by a.wayne View Post
OK, now do that experiment again with a 200w amp, obvious game changer
With a conventional 200W amp there would be no point, I've just listened to a suite of such beasts at a hifi show, and there was only one there that had the goods, the top of the line Bryston.

If the 200W was as well sorted as the 20W there would be no difference, except that I could go louder, assuming the speakers could take the sustained drive at those levels; like having a top notch PA system and standing a foot away from a cabinet vs. 6 feet away ...

Frank
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Old 19th February 2013, 10:30 PM   #8429
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Originally Posted by fas42 View Post
With a conventional 200W amp there would be no point, I've just listened to a suite of such beasts at a hifi show, and there was only one there that had the goods, the top of the line Bryston.

If the 200W was as well sorted as the 20W there would be no difference, except that I could go louder, assuming the speakers could take the sustained drive at those levels; like having a top notch PA system and standing a foot away from a cabinet vs. 6 feet away ...

Frank
Not so, has nothing to do with playing louder, the 200 w amp will better the 20 watt amp with all being equal. I have done the comparison so many times over the years, there is no way to reproduce 20 db of dynamic range above listening Din with 20 watts.

Even high sensitivity speakers benefit from the extra power ....
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Old 19th February 2013, 11:06 PM   #8430
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Not so, has nothing to do with playing louder, the 200 w amp will better the 20 watt amp with all being equal. I have done the comparison so many times over the years, there is no way to reproduce 20 db of dynamic range above listening Din with 20 watts.

Even high sensitivity speakers benefit from the extra power ....
Not quite sure what you mean by "listening din" ... as said earlier, I can go cleanly to around 106dB at a reasonably close listening position, which is plenty. With something like Foo Fighters my ears can start ringing in a matter of minutes, no trouble. The ideal is to go to say mid 120dB's cleanly, which is equivalent to standing a couple of feet in front of the brass section in an orchestra, as another player.

The key thing is, you have to be 100% certain you're comparing oranges with oranges -- why a normal 20W unit is, sounds flimsy is because the power supply is under-engineered. If you took a massive power supply, from a 1000W amplifier, and attached it to the 20W unit then the latter would sound like a 1000W unit. It's all about, and always is, engineering ...

Frank
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