UTHAiM -- Just for Fun

UTHAiM stands for Universal Topology for Headphone Amplifier with Current Mirrors.

This is a project I built for fun, using components I readily had in my drawers. Surprisingly, amongst all the DIY projects I had done over the years, I had never used a current mirror before. It is no attempt to break record for lowest distortion. But based on this simple topology, one can try out a variety of configurations, and see how that affects the sonic results. Which is why it is a project, just for fun.

Of course it is only fun if you understand what you are doing. And therefore definitely not for beginners.

To support the GB effort of Nikon1975 to raise fund for Dave of Planet 10 which is seriously ill and in need of financial help, I made a “Planet 10 Special” edition of the PCB, and sent the Gerber files to Nikon1975. He will take care of everything of this charity GB from then on, with no interference from me. I only urge you to give him support over at the GB thread (to follow later at his convenience), for a good course. I have built two channels with negative feedback based on exactly the PCBs that Nikon1975 ordered. So we can be sure that they function as intended.

For technical questions related to the design, you are welcome to raise your questions here and I try to answer as I can. I also attached the basic Spice files here for you to play with. Please feel free to experiment in both simulation and in hardware, and share your experience with us.

Above all, have fun while supporting a good course. And of course you can also build this with a Vero board, as I did initially to proof the circuit principle.


Patrick

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  • UTHAiM Public 170407 Part4.pdf
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On the PCB there are a number of locations requiring jumpers.
These are required to enable flexibility on circuit configurations.
They are show here in red.

One can use 0805 0R SMD resistors as jumpers.
Or one can simply use the leads of the transistors and bend them over as required.


Patrick

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Very nice. I have a few questions...

1. Are the gate-drain jumpers on Q3 and Q5 drawn incorrectly on the schematic in post two? They are gate-drain connections to Q4 and Q6 in the Spice file.

2. What do you suggest for trimming offset? Looks like a combination of R8, R21+R22, and R31 is used?

3. Any reason for MOSFET current mirrors over BJT?
 
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1. Are the gate-drain jumpers on Q3 and Q5 drawn incorrectly on the schematic in post two? They are gate-drain connections to Q4 and Q6 in the Spice file.

NO. See Fig. 1 of Reference 6.
https://www.researchgate.net/publication/3975456_Noise_performance_of_classical_current_mirrors

You can also see from the photo that the PCB proto is built this way.
But it works both ways, as described in Ref. 6.

2. What do you suggest for trimming offset? Looks like a combination of R8, R21+R22, and R31 is used?

R6/R8 without output stage, then R21/R22 with output stage.
R31 is for Yfs mismatch, as described in article.

3. Any reason for MOSFET current mirrors over BJT?

Less distortion.
If you believe in Spice.


Patrick
 
The initial impression from the independent audition was that, even with ZGF,
"control of the entire spectrum is remarkable, and most evident in the bass region"
which corresponds with my own impressions.

That makes me curious how it might perform as a "power" amp driving 8-ohm speakers.
Like e.g. a HiVi B3N.
http://www.diyaudio.com/forums/full-range/249372-mini-dcaav-dayton-nd91.html#post3782570

Well, actually much better than I thought, using all the NFB I can get, but still with a bias < 200mA.
So more fun options to try out.

:)


Patrick

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I did in fact have the opportunity to audition the UTHAiM headphone amplifier as recently hatched
by Patrick. I am always all ears when there is a new concept of a headphone amplifier to try out,
so I "quickly" built a pair of them on the boards I got from Patrick, and he also borrowed me a
version he built sporting global feedback.

Both were quickly rigged up on a breadboard and powered by a pair of the cap multiplier psu's I
initially used for the F5 HA, with a quick change to output the suggested +/- 24V.

My first impression was that both versions sound almost like power amps... with power in abundance,
a full tonality and with very good control over the entire spectrum. When you like deep and hard bass,
look no further. ;) Mids and Highs do sound like a good ZGF amplifier... natural with a total absence
of harshness or other artifacts that I remember from my first forays into solid state territory
(long before I built the DAO or F5 HA).

Switching over to the version with feedback (using the same psu) I initially was surprised that it sounded
quite the same, but concentrated listening to well known tracks revealed that there are differences.
To my ears, and in my subjective perception, everything sounds a bit harder, the tonality of instruments
gets shifted slightly, and bass precision is now bordering brutality.

I, personally, prefer listening to the UTAiM with zero global feedback as it is more natural sounding.
You pick your poison.
 

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BTW, if you have a high impedance phone (>100R), or you want less output control, consider to replace :

Q11 with 2SK216 (pin compatible, just need to bend the legs)
Q12 with 2SJ79 (pin compatible, just need to bend the legs)
R31 with 2R

R21, 22 would have to be adjusted accordingly.
Nominally they should have about 1.2~1,4V across them, depending on the Vgs of Q11, 12.
When biased to 70mA, the output impedance without feedback is about 5 ohm.
Distortion will decrease significantly, due to lower capacitances of the output FETs.
You can always add 30dB or so NFB if you must have low Zout.

;)


Patrick
 
Oh, perhaps you care to tell us what phone(s)you were using for the listening tests ?

Sorry, I forgot to mention this.

Music was coming from the Pono Player and listening was done with either Sennheiser HD800 or Hifiman HE-500.
Those two do sound quite different although their frequency response resembles each other quite a bit,
with the Sennheiser sounding more analytical (but not troublesome with ZGF amps :p) and the Hifiman sounding
warmer and more relaxed.

For me it's more a question of the personal mood which one I pick for listening... although I was under the impression
that the UTHAiM liked the low impedance Hifiman a little bit more ( it can deliver all the required current, and then some...).
 
Now that I have signed up for the GB, I would like to know what would be the preferred power supply for the UTHAiM? Stixx had used a +-24V cap multiplier, I suppose that could be a good starting point. Is there boards/schematics available for suitable cap multipliers?
 
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