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Old 25th November 2005, 06:40 PM   #11
anatech is offline anatech  Canada
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Hi Kanwar,
If you commutate the supply rails linearly, you can't hear it in the output signal at all. Therefore, it should sound the same as a normal A-B amp of the same design with huge savings in heat, size and weight.

The commutated AC in Carvers was used to further stabilise the operation of the amplifer and increase efficiency. The only problems that arose were when fools and technology came together. They could run the supply rails closer to the capacitor breakdown voltage by doing this. The operation of the amp was more defined as it was the same as having the same AC voltage, all the time.

When these amplifiers failed, the damage was normally limited to the defective output transistor (except the one plugged into 550 VAC). djk, you might want to ask me about that one. No, it wasn't worth repair. Almost never did a defective Carver amp take out a speaker. They would happly bake one under normal operation if the operator turned them up too high. Loved those guys.

-Chris
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Old 25th November 2005, 09:45 PM   #12
djk is offline djk
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"If you commutate the supply rails linearly, you can't hear it in the output signal at all. "

Absolutely right!

Being insane, we used the M1.5 on compression drivers. It sounded cleaner than L-MOS class AB amps with high bias (300mA).

If the bias was set wrong and they dropped into class B on the lower tier, they could sound 'etched'.

Considering that at 4R they were driving way beyond the continous Ic, right at the bonding wire limit, we had very few failures.

IIRC, only six $2 outputs per channel. Might have been indestructable for another $5 (per channel) if they had used the M1.0 output scheme and doubled up on the outputs.
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Old 25th November 2005, 09:50 PM   #13
anatech is offline anatech  Canada
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Hi djk,
True, but they didn't break that often. When they did, there wasn't much blown.

Now the generator guys - that's a different story. We have Carribana in Toronto. They'll kill anything.

-Chris
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Old 26th November 2005, 06:48 AM   #14
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Hi Anatech,

Would you please ellaborate more on "commutations"...

Secondly, isn't Early Effect comes into play when collector is subjected to instant voltage switch over from one Tier to Another....


If both Class-AB & Class-H amp with same ratings in Wattage are Clipped or working near the full voltage swing, isn't the Efficiency would be the same in both of the amps..


regards,
K a n w a r
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Old 26th November 2005, 07:26 AM   #15
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Quote:
Originally posted by Workhorse

If both Class-AB & Class-H amp with same ratings in Wattage are Clipped or working near the full voltage swing, isn't the Efficiency would be the same in both of the amps..


regards,
K a n w a r
Sorry to butt in.....

I would think you have more loses in the class H amp at clipping since you generate heat in both the class H switch and output tranisistor. In class AB you only loose power in the output stage.

I also guess that the glass H amp will clip before the AB amp since there is a voltage drop in the class H switch.

Is class G (modulated rail voltage) better compared to class H or is the result more or less the same?

Thanks for an interresting thread

\Jens
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Old 26th November 2005, 10:29 AM   #16
djk is offline djk
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Hi Jens,

I will use your nomenclature for consistency. The saturated rail switch will be referred to as class H, and the linear follower (modulated rail voltage) as class G.

Prior art on class G (3772606):

http://patimg1.uspto.gov/.piw?Docid=...y=637608C562C2

An earlier example for CRT deflection (3622899):

http://patimg2.uspto.gov/.piw?Docid=...y=2E6E84FB42ED

Early class H (3319175):

http://patimg2.uspto.gov/.piw?docid=...6RS=PN/3319175

'Commutation' was Bob Carver's nomeclature for a rail switching design. I believe he coined this term for the diode on the lower rails, also refered to as an ORing diode (as it allows the output stage to use power from either the lower, or the higher supply, as needed). These diodes switch, or commutate as needed. The fast switching, soft recovery types, or newer high voltage Schottky type are best here.

The theoretical class B efficiency is 78.8%, a three rail design like the M1.0 is 87% (after Pol HSU). When you consider bias in a class AB design, 60% is more in line. Pol HSU found that the rail switcher showed even higher efficiency driving reactive loads vs resistive.

At full power, class G and H are slightly less efficient than class AB. However, the majority of the time we are not at full power.
Worst case for the class AB would be at about 50% voltage out, where the rail switchers are king.

Most Carver are three rail designs, most Crest are two rail designs. AB International has an interesting two-and-a-half rail design. Instead of a third set of transformer windings, associated rectifiers, and filter caps, they use 0V as a rail in class H. No improvement on a resistive load line, but much better into a reactive load line, and a reduction in the Vce required for the outputs.

IMO class G sounds better than class H. One example of this is the QSC MX2000, a 1KW per channel design. The original was class G, the 'A' version class 'H'. The original sounds better, and the used market value is higher for that very reason.

Why do any class H?

Cost, it is much lower for class H.

The later Carver M1.0 is an interesting hybrid, being class G on the lower rail, and class H on the higher rail. Good sonics at a reasonable cost.

The Early Effect doesn't seem to be a real issue.

An early example of the 'Tracking Down Converter' or 'BASH' type (3426290):

http://patimg2.uspto.gov/.piw?docid=...6RS=PN/3426290
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Old 26th November 2005, 11:19 AM   #17
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Great info - thanks

\Jens
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Old 26th November 2005, 06:51 PM   #18
anatech is offline anatech  Canada
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Hi djk,
You went into more depth than I would have. And yes, I agree with you 100%.

The biggest issues with class H and G designs is that most repair techs can not properly repair them. So there are service issues that need to be addressed. In short, these need to be labled clearly that there is a basic difference in design.

There are also "use" issues in that many pro and semi pro installers would use a lighter amp for mids or highs only. The belief being that the heavier amp is better for bass. Another lable.

-Chris
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Old 27th November 2005, 03:52 AM   #19
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Quote:
Originally posted by djk
'Commutation' was Bob Carver's nomeclature for a rail switching design. I believe he coined this term for the diode on the lower rails, also refered to as an ORing diode (as it allows the output stage to use power from either the lower, or the higher supply, as needed). These diodes switch, or commutate as needed. The fast switching, soft recovery types, or newer high voltage Schottky type are best here.

The theoretical class B efficiency is 78.8%, a three rail design like the M1.0 is 87% (after Pol HSU). When you consider bias in a class AB design, 60% is more in line. Pol HSU found that the rail switcher showed even higher efficiency driving reactive loads vs resistive.

At full power, class G and H are slightly less efficient than class AB. However, the majority of the time we are not at full power.
Worst case for the class AB would be at about 50% voltage out, where the rail switchers are king.

Most Carver are three rail designs, most Crest are two rail designs. AB International has an interesting two-and-a-half rail design. Instead of a third set of transformer windings, associated rectifiers, and filter caps, they use 0V as a rail in class H. No improvement on a resistive load line, but much better into a reactive load line, and a reduction in the Vce required for the outputs.

IMO class G sounds better than class H. One example of this is the QSC MX2000, a 1KW per channel design. The original was class G, the 'A' version class 'H'. The original sounds better, and the used market value is higher for that very reason.

Why do any class H?

Cost, it is much lower for class H.

The later Carver M1.0 is an interesting hybrid, being class G on the lower rail, and class H on the higher rail. Good sonics at a reasonable cost.


Hi DJK ,


THANKS, THANKS, THANKS, very much for the State of Art Info....

Yeah the Class-H amp were really efficient when the output voltage swing is about 60% of Full output.....
I have Just Designed a Class-H Rail Switcher Mechanism and its working very good and it has much higher efficiency when driving reactive loads....But the Complexity is Lot.. Double Supplies, Caps, Rectifiers....

But the Efficiency when Driving at full output is just the same with what we had with class-AB.....

In our Indian Sub-continent people usually drive the amps near their Max output and therefore Class-H doesn't seems to be a worth in implementing...but good for the guys who crank the amps moderately.....

regards,
K a n w a r
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Old 27th November 2005, 10:00 AM   #20
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Hi Djk & Anatech,

In my opinion , Class-G does the commutation more linearly than Class-H ......But it uses More Devices whereas in Class-H the Switching element may be a high power Mosfet with lower RDS , and is much cheaper to implement then Class-G...what do you think.....

The Spikes originating from the switching phenomena might have their impact on the sonics what are your views.....

regards,
K a n w a r
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