Aspen Headphone Amp

[jam]

Bigun,Gaetan,

I was kidding Hugh as we had this debate years ago........my contentention is that to get the current source to work on the differential we need to run more current in the diff. (with suitable changes in the collector resistor) before a fair comparison can be made as a current source can also be a current limiter...........the VAS is up for grabs at this point...........

I do not mean to take anything away from Hugh's great design nor do I want to turn this into a Blowtorch thread. .... and hope that the gods from down under don't send a bolt of lightning this way....

Regards,

Jam

[Bigun]

I'm going to have to have a play with some of these new Spice tricks. I like the ac source in the nfb loop, in the past I'd disconnect the nfb and then greatly reduce the input signal to stop clipping as the only means to explore open loop ...

What about headphones - I've focussed on amps driving speakers all my audio life (less than a year !) but headphones come in different impedances and have different characteristics. Any special requirements we have to address with this amp ?

Jam - current sources are a good topic, wanders into the objective vs subjective debate very quickly but your suggestion was still a good and necessary one so that we know from the first what we're aiming to do here.

MJL21193 - use an op-amp ? hmmmm, probably quite a sensible option, but it feels wrong. The signal flows through the load, the output stages of the amplifier and the regulator. Putting an op-amp into the psu is not much different than using one for the amp. Since we decided on a discrete amp, I think it means we need a discrete regulator. I like the idea of a simple shuntie.

[ostripper]

This might be what the doctor ordered...

Read about it here : http://www.rason.org/Projects/discreg/discreg.htm

Only 4 components and it will match a 7815 IC regulator , I would guess by reversing everything (pnp for npn) ,the negative half could be made.(7915)
OS

[ikoflexer]

This is a series regulator, and just because the page says high performance it doesn't mean it is. Any 7815 should not be taken as the target to beat. The salas regulator is classes above the regulators mentioned so far. I've built it, measured it, and lots of people listened to it. While this thread is not about the regulator, especially for a headphone amp you want the best psu you can get.

There have been many threads on regulators and super regulators in this forum, all you have to do is search. My recommendation is based on testing many of the "super" regulators.

Just my 2c.

[Bigun]

I agree, there is the danger that this project could turn into a regulator design exercise.

And it has been suggested that we could instead, pick from one of the many highly regarded (discrete) regulators available and use it as-is rather than try to redesign it. I think that approach would be more in keeping with the goals of this thread and doesn't mean we don't get to learn about regulators along the way.

If you'll agree, the next step would be to compare the choices of regulator and decide which one to use ???

[AKSA]

Iko,

Why do you think a HP amp needs a good power supply? I'm sure you have a good reason. I have never done regulated supplies for my power amps, and frankly don't believe they are necessary because the headroom is better on transients - a little more voltage at the leading edge.

The trick with loop gain is useful, thanks to GK and Andy_C, very useful way to figure stability.

This amp is not intended to offer lowest possible distortion. It is, however, designed to bring out the music. I expect this will be controversial, but the design is public domain from Aspen and building it is not compulsory!

Hugh

[MJL21193]

Originally Posted by Bigun

MJL21193 - use an op-amp ? hmmmm, probably quite a sensible option, but it feels wrong. The signal flows through the load, the output stages of the amplifier and the regulator. Putting an op-amp into the psu is not much different than using one for the amp. Since we decided on a discrete amp, I think it means we need a discrete regulator. I like the idea of a simple shuntie.

Hi Gareth,
Is opamp a dirty word?
The Jung regulator uses the opamp to linearize the regulator by monitoring the feedback - the current still flows through a discrete part (the MJE15030 in my schematic). It has some real advantages over a shunt reg, efficiency being just one.
For my time and money, I'll go with the Jung.

[ikoflexer]

Originally Posted by AKSA

Iko,
Why do you think a HP amp needs a good power supply? I'm sure you have a good reason. I have never done regulated supplies for my power amps, and frankly don't believe they are necessary because the headroom is better on transients - a little more voltage at the leading edge.
Hugh

My apologies to everyone for another OT.

Hugh, the short answer is because with a good pair of sensitive HP one can real hear any nasties coming from the psu. It's interesting that you mention transients. That's where a good shunt regulator will shine, hence increasing greatly the dynamic of the sound. A series regulator cannot do that, by its inherent design. The shunt reg will give current on demand, if it's fast enough. Besides that, a black, silent background doesn't hurt either. There are many other theories, including that it eliminates the large caps influence (and therefore doing away with the need of boutique caps in the psu).

However, don't listen to me. IMHO you owe it to yourself to try it, I think you're in for a pleasant surprise. There are a few variations of a basic "ccs feeds shunt" topology, simple circuits, but highly optimized for performance and sound. You can find more info in the shunt reg thread. It contains low/high current versions of the circuit, pcb designs, etc.

The simplistic Salas low voltage shunt regulator

Yes, the inefficiency of passing the shunt current is something that we accept, just like we accept a class-A amp, for the other benefits it offers.

OK, I'm starting to feel like prozelityzing which is certainly not why I joined this thread. If anyone is interested I can continue either privately or in the shunt reg thread.

Regards.

[T in AZ]

Originally Posted by Bigun

I agree, there is the danger that this project could turn into a regulator design exercise.

And it has been suggested that we could instead, pick from one of the many highly regarded (discrete) regulators available and use it as-is rather than try to redesign it. I think that approach would be more in keeping with the goals of this thread and doesn't mean we don't get to learn about regulators along the way.

If you'll agree, the next step would be to compare the choices of regulator and decide which one to use ???

I agree, I like the sims on this amp and want to build it. Wall wart, battery, shunt, 7815 I don’t care. We all have our own Ideas of what is the best PS. Lets stick to the amp and then I’m sure we’ll figure out how to get power to it.

[Bigun]

Headroom, how much do we need, the power levels are so very low for headphones that these considerations aren't the same as with a power-amp. We need voltage swings, but low currents. This is new territory for me.

If I understand though, the summary is that we don't want to commit to full regulation, but some level of regulation/filtering is going to be a good idea because we're playing into a headphone that has a very high sensitivity - these guys measure in dB per mW, not dB per W. Plus, if we decide to go with a single supply for both channels, some precautions for channel isolation might be good.

So, I would ask again about a simple capacitance multiplier - it's public domain, simple, cheap and very effective in lowering ripple. Put a single device on each rail to each amp and you have good channel isolation. Put a good storage cap after it and then you partly remove the cap. multiplier from the signal path because the a.c. currents will flow through the output devices, the load and the 'last' capacitor. ???