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Old 25th February 2012, 10:50 PM   #21
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More progress on the head phone amp. I've been busy wiring and soldering. The power supplies are providing power, the inputs are wired up, and heat sinks are drilled, tapped, and screwed in place. Absolutely no drama. I adjusted the power supplies for +/-15VDC and that was that. Nothing gets warm either. Hopefully this will turn out good. I'm using silver wire with teflon insulation for most of it.
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Old 26th February 2012, 03:40 PM   #22
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OK, It's all wired up now, but I have a problem with it. It plays fine, but there's no bass. I don't understand that. There's no coupling caps in the circuit at all, so no RC filter. The transformers are supposed to be good to 10Hz. They are loaded by 10k ohm pots, just as required by Jensen. The DC offset on the output is about 1.5mV per channel, so I'm not sure that would have anything to do with it. I'll have to do some more investigating to figure this out. I used my old Sennheiser HD540's to listen.
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Old 26th February 2012, 04:13 PM   #23
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This is the schematic for the amp. It's bone simple to me. I added the two small capacitors and in the process deleted a 100k resistor from input to ground. The input is directly connected to the wiper of the 10k pot. There is some scratching when ever I move the volume knob, but I guess that's normal with this arrangement.

Maybe I need to let it run for a while to get all those power supply capacitors formed? I dunno what's up... feeling like I'm
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Old 26th February 2012, 04:36 PM   #24
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something is definitely up, because the wire, which although has superior layout should be similar, has some of the best bass ive ever heard with headphones
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Old 26th February 2012, 06:06 PM   #25
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It's broke now. Only one channel is working. I'll investigate when I have time. I suspect the power supply. I'm planning on changing the input circuit to include a DC blocking capacitor.
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Old 26th February 2012, 09:33 PM   #26
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I have a theory that I bought the wrong power transformers. I got secondaries with 2x15VAC, so since I don't know the dropout for the regulator, I may not be able to get +/-15VDC out of them. I turned the regulators down to +/-14VDC but haven't had time to test them. I measured about 4 volts across the series power transistors in the regulators after dropping the outputs by 1 volt.
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Old 27th February 2012, 07:39 AM   #27
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Details you have disscuss here are great and helpful ..It's going to be tricky and it helps to do work a lot easier.
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Old 28th February 2012, 12:14 AM   #28
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Quote:
Originally Posted by andrewscott View Post
Details you have disscuss here are great and helpful ..It's going to be tricky and it helps to do work a lot easier.
Thanks for the support.

I figured out the problem. It was not the power supplies after all. I wired the potentiometers incorrectly. Then I found that I had way too much gain. So, I swapped the 20k resistor for a 1k. Still a lot of gain, but I guess the HD580's are fairly sensitive. The amp does sound really good now.
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Old 28th February 2012, 03:47 PM   #29
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You should have the input resistor to ground, because if your pot somehow loses connection to ground, you could have maximum input level and damage something.
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Old 28th February 2012, 06:27 PM   #30
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Quote:
Originally Posted by Redshift187 View Post
You should have the input resistor to ground, because if your pot somehow loses connection to ground, you could have maximum input level and damage something.
Yeah, thanks. I was thinking of putting some kind of high value resistor there. I'm just glad I got it working now.
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