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Old 15th October 2003, 03:28 AM   #11
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I'm using Anthony's boards and there still is a little bit of hum. I have imperfect power supply wiring myself. The problem may not be specific to your PCB layout. I'd look at perhaps isolating the earth grounds with a diode bridge, or ensuring a good power star ground[?]
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Old 15th October 2003, 05:29 PM   #12
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Hi,
Running fb from SPKR is good. But move R11 close to R10 - otherwise you have a long aerial on the base of your diff pair.

Where is your Zobel network? This is an HF load for the amp.
BAM
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Old 16th October 2003, 07:11 PM   #13
naula is offline naula  Finland
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Quote:
Originally posted by traderbam
Hi,
Running fb from SPKR is good. But move R11 close to R10 - otherwise you have a long aerial on the base of your diff pair.

Where is your Zobel network? This is an HF load for the amp.
BAM
I think I will move the SPK connector to center of the board, next to C12. This will shorten the feedback circuit.

There is no Zobel network in the Anthony's design.

- Antti
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Old 16th October 2003, 07:43 PM   #14
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Quote:
think I will move the SPK connector to center of the board, next to C12
Yes you could do that, but my point is that the length of the track off the base is critical not the length of the whole feedback path. In fact I'd say leave the spkr term as far away from the input stage as you can to minimize inductive feedback - the currents in the speaker wire will be very large, or rather the transconductance of the amp will be very high compared with the voltage gain.

IMO the circuit should have a zobel. Otherwise, what is providing damping for the output stage at high frequencies?
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