|Headphone Systems Everything to do with Headphones|
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|9th July 2019, 08:51 PM||#31|
Join Date: Dec 2004
Location: Bakersfield, CA
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.
|11th July 2019, 09:14 AM||#32|
Join Date: Dec 2005
Location: the north
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.
|12th July 2019, 07:19 AM||#35|
Join Date: Oct 2003
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 :
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.)
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