Class A sound/AB Heat Dissipation

Samuel Jayaraj · 21st October 2003, 03:19 PM

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.

Vigier · 21st October 2003, 05:07 PM

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

PMA · 21st October 2003, 05:32 PM

Probably oscillating and/or wrong value of the quiescent current. Do you have an access to the oscilloscope?

Samuel Jayaraj · 22nd October 2003, 02:48 PM

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.

PMA · 22nd October 2003, 03:42 PM

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.

Circlotron · 23rd October 2003, 01:34 PM

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

22nd October 2003, 02:48 PM	#4
Samuel Jayaraj diyAudio Member Join Date: May 2001 Location: Bangalore, India	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. __________________ Sam

23rd October 2003, 01:34 PM	#6
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	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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21st October 2003, 05:07 PM	#2
Vigier diyAudio Member Join Date: Nov 2002 Location: Netherlands	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

21st October 2003, 05:32 PM	#3
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Probably oscillating and/or wrong value of the quiescent current. Do you have an access to the oscilloscope?

22nd October 2003, 03:42 PM	#5
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	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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