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Old 13th April 2016, 03:14 PM   #1
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Default No-gain diamond buffer headphone amplifier advice

Hello all,

I came across a nice, simple circuit for a low distortion buffer that I'm thinking of using as a unity-gain headphone amp. I already have most of the parts in my bin, and it's straightforward enough for me to tackle.

My DAC output is pretty juicy, so I really don't need gain. I've attached the schematic below. What do you guys think of it?

The only thing I'm unsure of is what D1 and D2 represent. Are they constant current diodes? If so, what is the "2.0" likely to mean? Surely not amps . Is the 47uF input coupling cap a bit much? From what I've read it doesn't need to be anywhere near that big.
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Old 14th April 2016, 12:42 PM   #2
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I think d1 d2 are LEDs. 2.0 means 2V forward voltage, it's a green led i guess.
In addition, 2 pairs of 8A current rating output transistor might be overkill

Last edited by hta95; 14th April 2016 at 12:47 PM.
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Old 14th April 2016, 01:02 PM   #3
Mooly is offline Mooly  United Kingdom
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They will be constant current diodes, probably 2ma. LED's would just turn on J3 and J6 destructively. They could be replaced by resistors but you would have to calculate and simulate it. It would work though.

These are basic circuits and you will find big differences in simulated values and real world components. The DC offset could be disappointing without individual tweaking or adding a servo.
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Old 14th April 2016, 02:13 PM   #4
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Hmmm..., parallel output transistors and 24V supply voltages, I would estimate output power about 30W in 8 ohms. IMHO plenty oversized for a headphone buffer.
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Originally Posted by Mooly View Post
They will be constant current diodes, probably 2ma. LED's would just turn on J3 and J6 destructively. They could be replaced by resistors but you would have to calculate and simulate it. It would work though.
O.K., but why zener diodes in forward direction are used?

47µ for electrolytic coupling cap isn´t that unusual, but you will find a lot of different and controversial opinions and discussions about this topic.
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Old 14th April 2016, 03:05 PM   #5
Mooly is offline Mooly  United Kingdom
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Its a zener symbol although the polarity is correct for a current diode though. Maybe the software doesn't have the correct symbol for a current diode.
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Old 14th April 2016, 03:24 PM   #6
jam is offline jam  United States
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Something else to try if you don't have current diodes.
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File Type: png diamond buffer design 4.png (16.1 KB, 269 views)
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Old 14th April 2016, 05:17 PM   #7
mlloyd1 is online now mlloyd1  United States
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hi jam;

just for grins, why not a little bit of cascoding, tying Q4 collector to Q20 (or Q1?) emitter and Q3 collector to Q19 (or Q2?) emitter.

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Old 14th April 2016, 07:03 PM   #8
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30W you say? Hmmm... since I lack constant-current diodes, and don't yet have plans to strap a pair of full-size speakers to my head I'll give jam's circuit a try . What supply voltage would be best?

Are there any other headphone buffer recommendations? I'll also do some searching.

Last edited by BuckarooBanzai; 14th April 2016 at 07:06 PM.
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Old 14th April 2016, 07:34 PM   #9
jam is offline jam  United States
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Michael,

That should work if you want to try it.

Hi Buckaroo,

15 to 18V split rails should work fine.

Jam
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Old 14th April 2016, 07:39 PM   #10
jam is offline jam  United States
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Michael,

Since you like complexity how about this...............

or if you are really into pain the second one.

Jam
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File Type: png 2753625016_f735b88b31_o.png (14.9 KB, 243 views)
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