Proprius As Headphone Amp

I know a few have tried the Proprius as a headphone amp but until today I had not.

The music source is always going to be whatever is being tested in the workshop, and currently it's Bluetooth, or more exactly the Huawei Ascend playing albums from a mem stick via Winamp and transmitting using SBC to the Bluetooth module I'm trying out, which is set to output SPDIF. Without any buffering the module is driving a 6 metre (20 foot) coax to a coax input on the Majestic. From there it's going to the pair of Proprius amps via the Majestic balanced outputs using the R3 single-ended cables. I am driving my HD250II's and there is a 15 Ohm resistor in series with each leg on the headphone adapter lead I made up for the test.

I don't know if I am in order saying this but it's the best I've heard on headphones yet!

The only downside being hiss between tracks, and that's exactly what I expected from a power amp intended for speakers. I could easily accept the little amount of hiss, but I know there are some fussy people out there.

I reckon if I work out a passive attenuator circuit to reduce the full volume to something that doesn't burn your ears out instantly - which it could mine - then the hiss will go down with it.

I know there are those who reckon passive attenuators decrease damping factor but most wouldn't know Kirchhoff from their elbow - source impedance can be made as low as you want.

I think there is some considerable mileage in using the Proprius for headphones and this is going to be quite some fun (for me).

I once did this before some years ago when developing the MA230 studio power amp, and I'd forgotten how open doing it this way sounds. That was on some of those black foam earpad Senny's.

Ash, you're right, it's the balanced input stage input impedance that's the source of the hiss, and turning the levels down attenuates it. Obviously resistors are noise sources and add FET inputs and you'll have plenty, because that's what FETs do.

OK for speakers because the hiss is unnoticeable: except in your case with your near-fields' and highly attentive listening.

The great thing about inverting inputs is they don't suffer common mode distortion, and FETs have stacks more headroom (than BJTs), which means you can throw anything at them and the music will swing (and "It don't mean a thing if it ain't got that swing" to me).

But, as I keep trying to educate this world, electronics isn't perfect - most people mistakenly think it is - but it is man-made from the very stuff we walk upon (rocks and clay). There are trade-offs, and in this example it's hiss.

As I've been saying since the very start, low-noise = boredom. Musical fun comes from timing, and timing requires fast electronics, and fast electronics has large slew-rates, and anything having a large slew-rate isn't low noise (as all the data sheets say).

Anyway, that out of the way, the reason I've been trying this is because I'm having a go at designing an integrated - an all-in-one amp. Your opinion, Miguels' opinion, and those of a few others, is that the Proprius plays headphones well. So I tried it for myself and I agree.

Rather than trying to shoehorn a separate headphone amp circuit into the box, it makes sense to me to use the power amp for headphone duties, provided it's good enough - which this obviously is.

The age-old problem is in attenuating the output to the right sort of level - the attenuation required often making headphones sound unmusical - or that's the rumour everybody latches onto.

Your explanation of your findings have given me the answer. Although the source driving the power-amp (yes, the power amp will be Proprius) might have a different level of hiss, putting the attenuation at the input instead of the output removes the need for output attenuation!

The headphone jack has separate contacts which detect when the plug is plugged in, and they can be used to switch a relay which places an attenuator at the power amp input, effectively doing the same as turning the pots down on the Proprius.

Solution!

Right now I can't be the only one wondering how the Solo ULDE stacks up against the suitably attenuated Proprius . . . can I? 

miT wrote: morris_minor wrote: Right now I can't be the only one wondering how the Solo ULDE stacks up against the suitably attenuated Proprius . . . can I?  I believe the answer is not quite as good...

It's probably like asking how a Madras stacks up against a Jalfrezi... different tastes, both equally good!