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UTHAiM -- Just for Fun
UTHAiM -- Just for Fun
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Old 8th April 2017, 07:27 PM   #1
EUVL is offline EUVL  Europe
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Default 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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Attached Images
File Type: jpg 170407 UTHAiM NFB s.jpg (218.6 KB, 2148 views)
Attached Files
File Type: asc UTHAiM NFB THD.asc (6.7 KB, 138 views)
File Type: asc UTHAiM NFB Freq.asc (6.7 KB, 61 views)
File Type: pdf UTHAiM Public 170407 Part1.pdf (950.7 KB, 564 views)
File Type: pdf UTHAiM Public 170407 Part2.pdf (959.5 KB, 433 views)
File Type: pdf UTHAiM Public 170407 Part3.pdf (793.8 KB, 383 views)
File Type: pdf UTHAiM Public 170407 Part4.pdf (552.9 KB, 317 views)
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Old 8th April 2017, 07:35 PM   #2
EUVL is offline EUVL  Europe
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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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Attached Images
File Type: png UTHAiM Sch Public 170408.png (222.7 KB, 2110 views)
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Old 8th April 2017, 09:04 PM   #3
needtubes is offline needtubes  United States
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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?

Last edited by needtubes; 8th April 2017 at 09:13 PM.
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Old 9th April 2017, 12:13 AM   #4
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by needtubes View Post
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.
I would very much assume so, at least that's the usual method of stacking current mirrors (for high impedance on both legs).
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Old 9th April 2017, 04:12 AM   #5
EUVL is offline EUVL  Europe
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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/publica...urrent_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
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Old 9th April 2017, 06:06 AM   #6
EUVL is offline EUVL  Europe
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There are many articles on the net that compares
a cascoded MOSFET current mirror to a modified Wilson MOSFET current mirror.

For example :
Difference between simple cascode current source and modified Wilson current source

The comparison is not the same as a BJT current mirror, due to the lack of gate (base) current.


Patrick
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Old 15th April 2017, 03:42 AM   #7
Hikari1 is offline Hikari1  United States
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Nice work Patrick. Might be next on my list...
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Old 15th April 2017, 07:47 AM   #8
EUVL is offline EUVL  Europe
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Give Nikon1975 some time to finish his protos first.
Not everyone has all the parts in his drawers.
He can then tell you how it sounds.

AFAIK Dave (Planet 10) has been released from hospital.
So wishing him a speedy recovery.


Thank you for your interest,
Patrick
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Old 15th April 2017, 08:11 AM   #9
Nikon1975 is offline Nikon1975  Austria
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I'll be in duty travel until 25/4. I hope that upon my return I'll find all the parts on my desk. After the first build, I'll start a GB for the boards to n stock.

D.
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Old 15th April 2017, 03:33 PM   #10
EUVL is offline EUVL  Europe
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The 4 prototypes have gone to a long-time member of the forum for an independent audition.
You will hear from him in a week or two.




Patrick
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