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Old 29th January 2003, 10:34 AM   #1
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Default Slone low distortion amp problem

I've constructed four of slones low distortion (BJT) 80 watt amps from his high power audio manual, and due to the diagram its hard to see what way around Diode three goes. Unfortunatly as Sods law would have it I put them in the wrong way around. So much to my dismay two of the channels I've built have now stopped working with a huge DC offset present in the output (this is with the diode round the right way). With the diode round the wrong way I got a huge DC offset present in the output as it was. This DC present was (and still is) however one the supply rails shunted straight to the output (i cant remember which one atm and im at college so cant exactly go check).

I know the circuits work fine as I have one of the other two channels up and working (will be getting the other one too when i get home) with the problem located and the diode polarity fixed.

Now ive got the task of seeking out the destroyed components in the half baked amps. I dont think that its the predriver, qbias or output stage as even with the problem I could still adjust vbias and when the quiesent went up the trannies got hot as youd expect. But I was just wondering if any of you experts out there know what the problem could be and how to go about fixing it. Im a novice (ive only just turned 18) in the field of amp design and construction so any help would be apreciated, up till now ive spent all my time and energy on loudspeaker design to great success. So having built an excel(seas that is)lent pair of loudspeakers need a good amp to go with them.

Cheers Matt.
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Old 29th January 2003, 10:49 AM   #2
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Default sloane

Matt,

If you say that one of the rails is at the output, but you are still able to adjust qbias, that is strange. If you turn up bias, is only one of the output xsistors heating up? The other one may have a CE short. Try to disconnect the two output emitter resistors. If that clears the problem (without load) one of the outputs is gone.

Jan Didden
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Old 29th January 2003, 01:05 PM   #3
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Maybe you could tell us more precisely which of the amps you
have built? I would guess that you mean design no. 3, Fig. 11.4,
although I cannot find any power figures for this amp. If so, I
wonder if there is some printing problem in your copy of the
book, since D3 is very clear in the diagram.
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Old 29th January 2003, 01:33 PM   #4
halojoy is offline halojoy  Sweden
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Quote:
For specific questions or concerns, please feel free to contact us at sealelec@eastky.net, or use the information provided on the "Contact" page.

"With GOD, all things are possible."

This website owned by G. Randy Slone, owner, Seal Electronics. Wednesday, January 29, 2003
http://www.sealelectronics.com/index.html

5th element
Why don't you send Randy an email. Describe your problem.
As being a Good christianI am sure Randy Slone
will do what he can, to help a guy,
who has built an Amplifier Slone has designed.

/halo - will never design, as good as Randy Slone does
- even Mr Pass respect this Slone-guy
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Old 30th January 2003, 10:58 AM   #5
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Ok Ive just sent and email to Mr. slone and am awaiting a reply however I'll respond to each one of your messages at a time. I did do this yesterday but it didnt post anyway here goes again.
Now tho I have two channles up and running as I said I would and the results are nothing short of superb.

Jan - Both the output trannies heated up on adjusting of vbias and none the out put trannies are fried.

Christer - I made a mistake in my last post and it was d2 and not d3 either way the problem still stands. Yes its the 11.4 design which is rated at 80wpc (page 10 of the book). I was refering to the layout diagram without the tracks in the back of the book and not the circuit diagram if this helps understand why I put the diode in the wrong way.

Halo - Ive just sent a message to slone and am awaiting a reply.

Matt
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