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Old 21st April 2009, 08:05 PM   #1
Artie is offline Artie  United States
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Join Date: Jul 2007
Location: Jax, FL
Default Some questions on the Gilmore headphone amp.

I think I'm going to build this Gilmore headphone amp, but have a couple questions:

1. I'm not sure I understand why he's using eight output transistors per channel. Each of those transistors can handle up to 150ma. Seems excessive for a headphone amp. Since I'm going to use this to drive 250-ohm Beyerdynamic DT-770 Pro's, (20ma/100mW max), could I get by with just one transistor pair per channel?

2. Is there any particular reason for +/- 16-volts per se? +/- 15-volt supplies are fairly common. (I have a few lying around.) Is that 1-volt going to matter?

Btw: I would have asked this over at Headwise, but their forum is down. Thanks all.
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Old 22nd April 2009, 12:08 AM   #2
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1. I think Glimore used 4-output pairs because: a) he believes using one pair of large output transistors does not sound as good as multiple pairs of small signal transistors; b) the outputs are the same 2SC1815/2SA1014 transistors used in other stages - its already in his parts bin; c) multiple outputs means very modest Tj temperature changes and this removes the need for a Vbe temp comp circuit(diodes or Vbe multiplier) and the need for heatsinks; e) these are only 400 mW transistors

2) I think this circuit would work fine at +/- 15V without any component changes. You can always run a Spice sim if you want to fine tune any resistor values.

This Gilmore headphone amp gets consistent excellent reviews, and I would try to copy it as closely as possible. The main cost is the power supply.
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Old 22nd April 2009, 12:21 AM   #3
Artie is offline Artie  United States
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Thanks LS. And I agree, it would probably be best to build it verbatim, and make sure it works right, before I start messing with changes.
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