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Class A Headphone Amp; OPA827 and IRF610/9610
Class A Headphone Amp; OPA827 and IRF610/9610
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Old 9th July 2019, 08:51 PM   #31
Carl_Huff is offline Carl_Huff  United States
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All good points Patrick. Thank you for that.

I have been looking at your F5-HA Headphone amp. It looks very nice! I think that I would like to build one.
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Old 11th July 2019, 09:14 AM   #32
lineup is offline lineup  Sweden
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This is a simplified version.

Uses resistors R3 and R5 instead of current sources.
The performance is just as good.

I recommend setting like 100 mA idle current using R1.
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Old 11th July 2019, 05:26 PM   #33
xrk971 is offline xrk971  United States
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Class A Headphone Amp; OPA827 and IRF610/9610
Sort of related in its simplicity is the ESP HPA:
ESP HPA

I have built it and it sounds very nice.

Click the image to open in full size.
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Old 11th July 2019, 09:58 PM   #34
Bare is offline Bare  Canada
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Then there is This one
"WHAMMY" Pass DIY headphone amp guide
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Old 12th July 2019, 07:19 AM   #35
EUVL is offline EUVL  Europe
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One can find many many variants of headphone amplifiers being made up of an opamp driving a emitter or source follower.
Apart from opamp rolling, the major difference is in the output devices being used, the biasing method, and the thermal stabilisation.

One can of course use TO220 (or larger) BJTs or MOSFETs.
But one could also use a number (say 10x) of TO92 BJTs or JFETs in parallel.
These will require matching and degeneration to ensure equal current sharing.

If the output devices have positive tempco, they will run away thermally, which can be mitigated with :
sufficient heat sinking
emitter / source degeneration
some form of thermal compensation (such as NTC's)
some form of auto-biasing circuit (such as in the WHAMMY or JLH headphone amp)
Auto-Biasing Circuits for Complementary Followers

Or better still, you use a device with negative tempco at bias, so that it is self stabilising.

The other major difference in the biasing circuits is how much of a AC or DC load they present to the opamp.
A current source based design in post #1 is e.g. a much easier load for the opamp than the 2-resistor solution in post #32.
There are ever simpler biasing circuits but these are not self contained and relies on the opamp to correct for everything.
An example can be found in Fig 4 :
https://www.diyaudio.com/forums/atta...fer-public-pdf

They will all have their own different sonic signatures, be it minute.
But they will all have the characteristic sound of a high NFB circuit.
(And nothing wrong with that. All personal taste.)


Cheers,
Patrick
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Old 12th July 2019, 08:22 PM   #36
martin clark is offline martin clark  Europe
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^ +1 a fine summary!

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