• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Millett Hybrid headphone amp.

Hi all,

Well after trying a chip amp based headphone amp, I was left wanting more. Have thought about getting the MF X-Cans V2 or doing a clone. But then stumbled across the Pete Millett Hyrbid amp and it looks rather good.

I have seen two versions, one is the "max" version and the other is the starving student version.

If you were to build one, what would you chose and why? I like the simplicity of the starving student one.

Or are any better designs to be had for not much money to build?

Will be designing a regulated PSU for either one.

Headphones I will be using have a 40r and 32r impedance.
 

ericj

Member
2008-12-08 10:24 pm
I have a mosfet max i built, plus the old version, which i built a diamond buffer board for.

They're . . . . alright. If you want tube coloration they deliver it.

I hear that the Starving Student is a bit better, though it sure did a number on 19j6 tube prices. No board required - way simple to build.

You might also consider Alex Cavalli's SOHA II. Glass Jar Audio sells the board. B+ on these is about 100v if i recall right. They use common preamp tubes including 12at7, 12au7, or 6dj8 types unless i'm confused.

Alex's website seems to have some issues with the images, but you can read about it here:

SOHA II – Cavalli Audio
 

ericj

Member
2008-12-08 10:24 pm
I wouldn't call them hard to get. 12ae6 are $4 each, 12fm6 are $3 each, as are 12fk6. All from esrc.

But the fm6 and fk6 are said to sound better than the ae6, and the amount of voltage gain you end up getting from the fm6 and fk6 is so low as to beg the question of why you are bothering.

19j6 are $8 each, for the starving student.

If ecc82 and friends are more to your liking, see the SOHA II.

Or, for a simpler build, there are many variations on a design where a 6922 or 12au7's heater serves as bias for output mosfets. A diyer who went by the handle Sojosae published several designs. Called them "multi hybrid headphone amp"

.:Sent by pneumatic tubes
 
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Showed both circuits in work today, and my boss ruled the max millett straight away saying good luck with the tubes, and the starving student one, we contacted our valve guy in the UK who doesn't stock or can get hold of them. So that kind of killed that, I can order from the states but I would rather use parts in stock or obtainable.

The next design we looked at was this. Hope I can post links.

NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier

Everything to build it is at hand, but concerns were mentioned towards the PSU saying it won't be enough to deliver the volume I want. Unless someone knows different?

Will have a look for the schematic for the SOHA II, just wanted something nice and simple to build point to point for a first attempt see if I liked it, then look at making some PCBs.
 

ericj

Member
2008-12-08 10:24 pm
Ah, the 12au7 circuit you linked to looks a LOT like the MHHA. With the exception that the MHHA was a 24v design, and that one is 12v.

I hadn't realized that you were in the UK - that would make American car radio and tv tubes hard to get

.:Sent by pneumatic tubes
 
Yeah this is why my boss ruled the two designs out straight away. He said getting the tubes would become harder and harder plus none were on hand to order from the UK.

Do you have a link to the MHHA, the 12au7 we have in the workshop and I can quickly build one up, but everyone in the shop (with far more experience than me) all questioned the supply voltage.
 

ericj

Member
2008-12-08 10:24 pm
Oh, here we go:

????(sijosae) - [DIY] MHHA v3.0 (Multi-Hybrid Headphone Amp)

Machine translation of korean is nearly impossible, but his diagrams are very clear.

He was using a 24v switcher that was intended for an inkjet printer, iirc. A linear regulated supply would work too though.

These were very popular 10 years ago. I never finished mine - got distracted by other projects.
 
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Okay, looking at it, slightly confused by the battery. Faultfinding and building is my thing, understanding the design of the circuit is not my strong point.

Regulated PSU won't be a problem I can just manage them haha. Any other designs worth considering? I have a chassis that will do nicely but it is W:300mmH:20mmmD:200mm with a nice perspex window at the front.
 
What sort of output would I be looking at? I am dissapointed with a chipamp LM380, and the starving student one seemed ideal. Unless a similar EU tube could be used?

Want to build one with a regulated PSU as it will be my main source of music for some period of time at home. Would like some headroom if I want to go loud.

Thinking this design will not go loud and is more of a portable design?
 

ericj

Member
2008-12-08 10:24 pm
What sort of output would I be looking at? I am dissapointed with a chipamp LM380, and the starving student one seemed ideal. Unless a similar EU tube could be used?

Want to build one with a regulated PSU as it will be my main source of music for some period of time at home. Would like some headroom if I want to go loud.

Thinking this design will not go loud and is more of a portable design?

I can't find a gain spec but i am under the impression that the MHHA provides plenty of gain and power.

It idles at about 480mA and runs hot, so no, not portable. The 9v batteries just increase the b+ by 9 volts, but the current drawn to accomplish that is tiny.

.:Sent by pneumatic tubes
 

ericj

Member
2008-12-08 10:24 pm
Anyway no, there is no direct equivalent of the 19j6 used in the starving student amp.

The sijosae design works on similar principles, just with a lower voltage and different tube.

It would be possible to build a more complex version of the starving student that uses 6j6 tubes. You'd have to add a 6v supply for the heaters, and bias the mosfets with a different load, like a resistor or an lm316 configured as a constant current source/sink.
 
Anyway no, there is no direct equivalent of the 19j6 used in the starving student amp.

The sijosae design works on similar principles, just with a lower voltage and different tube.

It would be possible to build a more complex version of the starving student that uses 6j6 tubes. You'd have to add a 6v supply for the heaters, and bias the mosfets with a different load, like a resistor or an lm316 configured as a constant current source/sink.

Will see what the people with the knowledge say tomorrow, but I know they will question the 9v battery like me and ask why it can't be driven from one PSU if I understand the design correct.

Have seen a few headphone amp designs using a few hundred volts, seems overkill in my opinion.

Sijosae seems ideal, just want to make sure gain would be enough.