Once again - Small headphone amplifier - ty.ytka

Each time, I am impressed by the aesthetics and refinement of the design.
What is a U3 circuit in an oblong housing? The output protection?
And a second question - do you mill the front panel in-house or do you have someone where such can be ordered?

Another very nice design, I'm very curious to see the measurements and how they compare to the previous, heavily developed version, how much the performance has deteriorated (or improved?).

You, when you throw something in, it's always a masterstroke, your designs are top notch

It is a pleasure to look at each of your projects, the attention to detail of workmanship is exemplary in DiY.
You have improved the design by what you deemed worthy of correction.
Obviously a big plus from me.

I'm not a gadgeteer by nature and always attach headphones to the jack on the unit.
Your amplifier would be complete for me if it included an RIAA EQ circuit, enabling me to listen directly to real analogue recordings from the 'asphalts' of the era, without a heap of other 'blocks'.
Please don't take this as a criticism, it's just a loose, non-committal comment.

You are already approaching the level at which I would spend the money to buy. A little more refinement to the lettering on the front panel and we have a commercial level of workmanship.

I see the paper under 230V is .

I'm impressed with the design and aesthetics. It looks great and probably works just as well.



I noticed a little zonk in the schematic but that's probably a Czech error.

Something wonderful. There is no denying that some users are waiting for the ty.tyk presentations with baked goods!
I guess you haven't received the goodie kits from Elektroda yet, send a Parcel Post, it will be a pleasure.

Thank you very much for your comments.

Of course, I'm aware that the level of my projects is still not up to par with the commercial ones, but for the time being, that's all I can afford.
And also considering the workshop I have (or actually don't have), the end result, gives me some moderate satisfaction.

And referring to your posts:

- "What is the U3 circuit ?" It is a protection circuit. It delays the switching on of the headphones, and automatically disconnects them if any DC voltage is present at the output.

- "Do you mill the front panel yourself ?" Yes I did the machining myself. Only the lettering was milled. The holes were made with a table drill and refined with a mini grinder.

- "Two parallel amplifiers in the first stage ?" Apparently not necessary in this case, although they have their advantages. But note that the board is the same as in the original version, so there was no other option.

- "An operational amplifier in a 'global feedback' loop?" Well, it's well known that DC-servo circuits probably have as many opponents as supporters. I am, let's say, in the middle, but in this project I decided to use it.

- " A 6R8 resistor at the output?" Maybe its value seems high. I used it to protect the outputs of the circuits in case of a possible short circuit of the amplifier output. And to be honest, I personally don't use low impedance headphones. Of the ones I own, the least is 44 ohms.

- " likewise the resistors on the output of the secondaries" I there, would not dare to give up those 1 ohm resistors.

- "The amp would be complete for me if it included an RIAA equalization circuit" Very interesting and inspiring comment. I won't change it anymore in this amp, but I am thinking of upgrading, my tube OTL. I will strongly take this under consideration.

- "The paper under 230V is" In the previous version there was a foil, but supposedly wrong, not enough etc.

- "I noticed a little zonk in the schematic". This is a result of the fact that I had a transformer of the same dimensions in the library, but without the split primary winding. And at the moment, it was quicker to do such a myopic than to add a new component to the library.


I promised to post the measurement results of this amplifier.
There will be some curiosity here, you will see how the PCM2705 chip, turns out to be quite a bottleneck in terms of the measurement results obtained.

Here is a report of measurements of the amplifier driven from the line input:

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And this report, is the result of a test carried out, when driven from the digital input:

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It appears that I have not achieved the parameters declared in the PCM2705 note .

If I'm not mistaken, this simplified version has slightly better performance than the previous, more elaborate version, especially the THD, which is almost halved. I'm already overlooking the fact that this is probably beyond the limit of perception in either case.

tytka wrote:

It appears that I have not achieved the parameters claimed in the PCM2705 note

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Interesting... You must have something wrong. I would expect a lot more from analogue too.
Can you give measurements of the card/interface itself?

In fact, this version came out slightly better in the tests carried out. But this may be partly due to the slightly changed measuring conditions.

It doesn't look like anything is wrong.
It's just that the PCM2705 surprisingly comes out poorly in the tests I ran. I also tested it on another device.
Maybe I'll give it another go.

And if you want to see the card's measurement, here you go:
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Where did you get this enclosure from? I ordered some from the net, it was supposed to have these dimensions, it arrives and here's the trick, the dimensions are given for the outside and it's not possible to put the board inside. This would have been ideal.

wiorekw wrote:

If I'm not mistaken, this simplified version has slightly better performance than the previous one

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Today I had a moment, so I tested the original/more elaborate version (as it sits in a drawer one without a case) under the same conditions as now this revised, or simplified, one.
For the line input:

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For USB input:

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Unfortunately I am not able to achieve better results in measurements with this PCM.
The situation is similar with my other battery-powered headphone amplifier ( Link ).
There I accidentally achieve virtually identical performance.

siewcu wrote:

And where did the colleague get this enclosure from?

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And from Alie...
I bought a few months earlier, but now I checked and the auction is still active. So if you want it, get back to me on priv and I'll provide you with a link.