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Old 23rd August 2006, 10:34 AM   #1
Flavio88 is offline Flavio88  Italy
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Default MORE power from this one

hi everybody
i have two of this modules, can i use this module with supply rails higher than +/-50 v???
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Old 23rd August 2006, 10:48 AM   #2
sreten is offline sreten  United Kingdom
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The simple answer is no.

The more complex answer is perhaps with high impedance speakers,
but come across a pair of low impedance speakers and the probability
of self-destruction will be much higher.

Having had similar circuits in a bass amplifier running off 50V rails,
3 different versions of similar circuits have self expired. Might be OK
for hi-fi but IMO an unreliable circuit for heavy duty use @ 50V rails.

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Old 23rd August 2006, 11:14 AM   #3
darkfenriz is offline darkfenriz  Poland
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I agree, these mosfets are only of 7A Idmax, so 50V into 8ohm nominal impedance is on the edge of its abilities. If you are dead sure, that your speaker's impedance doesn't go lower than 8ohm at any frequency, than 55-57V might be 'safe' too.
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Old 23rd August 2006, 04:44 PM   #4
parsecaudio is offline parsecaudio  Italy
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Default power increasing

For more power the solution are to add another pair of mosfets.In case of this,you must to verify if the circuit are stable whith a scope.
Ciao Flavio.
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Old 23rd August 2006, 09:37 PM   #5
ilimzn is offline ilimzn  Croatia
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100-150W? Not even by accident!
For an 8 ohm nominal speaker with reasonable reactance margin, perhaps 50-60W would be the maximum safe power. It should also be noted that the amp will lose about 7V off the power rails at maximum power, so efficiency will be lower than expected, and good cooling will be needed even for this safe power level. The design is, as seems usual for kits, a stripped down version of the original Hitach MOS application schematic. I always wonder how one justifies the 0.2$ saving in a proper tail current source and current mirror transistor (instead of diode)...
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Old 24th August 2006, 01:34 AM   #6
quasi is offline quasi  Australia
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Oh well I may as well add my bit.

I would not even run them at the specified rails. I havn't done a SOAR v Load analysis, but I just know it would fail for a typical 8 ohm speaker. Still for a home situation it could survive, but definately not for extended high power use.

I would not even modify this cct for greater power because it actually aint that good. You are better off starting a new cct.

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Old 24th August 2006, 03:08 PM   #7
Leolabs is offline Leolabs  Malaysia
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A very classic design during the introduction of Hitachi's audio power MOSFET.
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Old 24th August 2006, 06:52 PM   #8
djk is offline djk
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Back in ther day, Hafler made a model like that. With ±52V it could do 60W/8R and 90W/4R. It will require very large heatsinks to do it.

The Hitachi L-FETs have 1 ohms RDS at room, 1,7 ohms over temperature. At near 100W/4R you are at maximum drain current (7A) and RDS is maximum (1,7), and you will drop about 12V across the device from drain to source.

Hafler originally used two pair of outputs at ±63V for their 100W/8R design, later increasing to three pair. Driver transistors were added to handle the extra gate capacitance.
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Old 30th August 2006, 06:17 PM   #9
Flavio88 is offline Flavio88  Italy
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ok, i have buyed 4 pairs of irf640/9640, can now increase the supply rails?
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Old 30th August 2006, 07:15 PM   #10
MikeB is offline MikeB  Germany
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I don't think so, the poor T4/5/3 TO92 devices are already dissipating ~370mw. This means they are already too hot to touch. Further increasing the voltage will make them smoke.
Replacing the mosfets with IRF type will make you need to replace the trimpot r13 with a vbe/vgs multiplier as the IRFs need thermal compensation.

What makes you believe you can take some simple amp and increase power output by simply increasing voltage supply ? There is a reason why high power amps are more complex...
Quasi's amps are about the minimum complexity necessary for reliable high power amps.

Is your subwoofer 4 or 8 ohms ? What is your targeted power output ?
I doubt that 4 pairs of TO220 mosfets will allow more than ~200watts.
What is your targeted voltage supply ? Are you experienced enough to handle lethal supply voltages ?

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