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Old 21st October 2003, 02:19 PM   #1
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Default Class A sound/AB Heat Dissipation

Has anyone seen or built this circuit? I have and it sounds incredible. I have used Hitachi's 2SK1058 and 2SK162 devices at the output. The Gate resistors are changed to 1.2k and 820E, I forget which value for which Mosfet. Rail voltage is about + -42.

During transients/crescendos, the amp clips quite annoyingly, but only in the mid frequencies; even while clippling (popcorn like sound) the low and high frequencies are as clean as ever. Is the rail voltage too low or is it a problem with the drive stage?

If someone here can mop up the parts, just try it out. I think the Exicon and Semelab Mosfets can be used as well and since these have a higher rating than the Hitachi device that I am using, you will be able to give it a + -50 volt supply and derive 100w into 8E.

Any views on this phenomenon and expert comments on the circuit.
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Old 21st October 2003, 04:07 PM   #2
Vigier is offline Vigier  Netherlands
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Hi,

- Do you have a readable schematic? This one seems to be resized!

- If you bass and tweeter are clear and your mid sounds clipped, then I think that can have 2 reasons:
1) Your mids are damaged (usually the woofer uses more power from the amp than the mids. And if it's clipping, you'll definitely hear it through your tweeters also)
2) is the impedance of the mid lower than the tweeter and the woofer? Then the amp can get problems with the outputcurrent, and yes, then it will clip; If the transformer doesn't have enough current-capacity, the output-voltage will drop, so the amp will clip at a lower volume.

Grtz, Joris
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Old 21st October 2003, 04:32 PM   #3
PMA is offline PMA  Europe
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Probably oscillating and/or wrong value of the quiescent current. Do you have an access to the oscilloscope?
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Old 22nd October 2003, 01:48 PM   #4
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I am using a 2-way QWL (Quarter Wave Loading) enclosure; hence, the question of a bad mid-speaker does not arise.

I have also checked the Iq, it is 100mA. Although there is no preset to change the Iq, the 330E resistor can be reduced to increase the current. I have tried this also, but to no avail.

I tried to attach a more readable picture withing the 100KB limit but simply did not succeed. I am using MS Photo Editor. May be someone can help here too.
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Old 22nd October 2003, 02:42 PM   #5
PMA is offline PMA  Europe
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Try not to resize (minimize) original picture in order to maintain resolution and readability. You might like to try *.bmp format, which will appear as a link here.
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Old 23rd October 2003, 12:34 PM   #6
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Default JPEG's are only ok for photos, not drawings.

Use a GIF or a PNG file. Way better than JPEG's for line drawings. Lots smaller too.
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