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Advice for improving professional vintage GDR power-amp
Advice for improving professional vintage GDR power-amp
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Old 17th July 2019, 03:39 PM   #11
franzm is offline franzm
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Quote:
Originally Posted by sgrossklass View Post
Besides, no idea what R8 is supposed to accomplish - some sort of failsafe in case R13 burns up?
Philips patent.
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Old 18th July 2019, 12:07 PM   #12
seasound is offline seasound
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Thank you sgrossklass (and franzm), my tech told me that
he is going to answer here directly soon.
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Old 19th July 2019, 02:27 AM   #13
nigelwright7557 is offline nigelwright7557  United Kingdom
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Be careful with the Baxandall diode, it can sometimes cause oscillation in output stage.
Then lower driver will need a cap between base and collector.

I designed a very similar amp and didn't put local decoupling on the power rails.
The first time I turned something off the glitch on the mains blew up the amp.
So maybe 100uf and 100n close to output transistors.

I also found I needed a couple of ohms degeneration between driver transistors and output transistors to stop oscillation.
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Old 19th July 2019, 07:54 AM   #14
seasound is offline seasound
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Thank you for this advice nigelwright7557. This could be very helpful.
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Old 21st July 2019, 03:15 PM   #15
seasound is offline seasound
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Sgrossklass, all capacitors have been renewed. At the moment there is the original transformer balanced input which sounds good but has it's disadvantages (impedance problems, distortion). I am going to test an electronic balanced input-curcuit soon.
Also to mention is the completely renewed power-supply with toroidal transformer, high-quality capacitors and fast diodes.
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