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Old 28th May 2003, 06:08 AM   #1
jwb is offline jwb  United States
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Lightbulb Aleph headphone amp

Just about the only way to improve on <a href="http://www.diyaudio.com/forums/showthread.php?s=&threadid=2451">tortello's beautiful Zen headphone amp</a> is to go for an Aleph headphone amp. The advantages are the balanced FET front-end and the DC-coupled output. This design is specified to put 500mW into Grado headphones, or other phones with about 32&Omega; impedance. It should also drive a small speaker, and indeed has done so in a breadboard incarnation.

Right now the only thing I'm not liking is the high value of the current sense resistor. I used it in my breadboard mockup but I might change it for something smaller.

One channel shown.
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Old 28th May 2003, 09:10 AM   #2
Nicke is offline Nicke  Sweden
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Default Missing component ?

Shouldn´t there be a resistor between R14 & R15 coupled to ground ?

Nicke
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Old 28th May 2003, 09:45 AM   #3
akira is offline akira  France
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Would it be OK to drive HD580 Sennheiser Headphones with this amp ? The input inmpedance is much higher ... 300 Ohms.
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Old 28th May 2003, 01:16 PM   #4
jwb is offline jwb  United States
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Default Re: Missing component ?

Quote:
Originally posted by Nicke
Shouldn´t there be a resistor between R14 &amp; R15 coupled to ground ?
All that junk on the left is for the input coupling. I didn't draw it because it isn't that interesting.
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Old 28th May 2003, 02:08 PM   #5
paulb is offline paulb  Canada
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Default Re: Missing component ?

Quote:
Originally posted by Nicke
Shouldn´t there be a resistor between R14 &amp; R15 coupled to ground ?

Nicke
What Nicke means is, you're showing 100% feedback. A resistor where he suggests would reduce feedback, adding actual gain.
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Old 28th May 2003, 03:09 PM   #6
Nicke is offline Nicke  Sweden
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Default Re: Re: Missing component ?

Quote:
Originally posted by paulb

What Nicke means is, you're showing 100% feedback. A resistor where he suggests would reduce feedback, adding actual gain.
Thats right ...
Is it unity gain stable as drawn ?
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Old 28th May 2003, 07:00 PM   #7
jwb is offline jwb  United States
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"As drawn" is incomplete. Trust me, those resistors over on the left really do go in the circuit. I just got tired of clicking the mouse. You obviously get the idea.
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Old 1st June 2003, 01:12 AM   #8
jwb is offline jwb  United States
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Take 2. The front-end doesn't have enough headroom with that 9.1V reference, so reduce to 5.7V via an LED string. Switch to 2sj109 monolithic FET pair. Increase idle current to about 220mA. DIscard C3 and C4.
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Old 15th June 2003, 10:00 PM   #9
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How is it going?

I have some kristian PCB boards lying around for an Aleph 4 which I like to turn into a headphone amp for my Sennheiser 580!

Edwin
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Old 16th June 2003, 12:00 AM   #10
jwb is offline jwb  United States
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Hi Edwin. It's going well. I got a Sun 411 SCSI case to put the amp in and modified it for XLR connectors. I'm still in the process of drawing the printed circuit board. Hopefully I will finish it next weekend.

I also increased the design rail voltage to 14V.
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