DIY Power supply for a Szekeres headphone amp

[Bricolo]

Hi all!
I'm new here. This forum looks great I hope I'll find my answears here.


I'm going to build my first audio DIY project: a szekeres amp


First: I choose the szekeres because of it's simple design, and I've heard it sounds good. I'll use it for a Sennheiser HD565 on a computer (with sblive).
Is this a good choice? Or do better amps exist (better and not really more complicated) ?



Do you have some advices on the szekers model that sound the best? (DC coupled; CCS...)
My first choice is to build the latest one that is on headwise's site: (if nobody tells me it's a poor choice)

http://headwize2.powerpill.org/proje...szeke1_prj.htm




Now, I'm working on the PS. I've heard the szekeres are very sensible to ps quality, anr ripples. So I'm going to buils th PS myself, and not buy a regulated PS (a friend gave me a torroid transformer 2 days ago, so I haven't to buy the main part)

I'm thinking about using this model:



It's a ZenV4 PS. IMHO the design is good. But the values (especially for the condensers) are to be changed.

The problem is: how much will be good?

The transformer is a 230V (primary) 12V (secondary) 50VA. Will it be enough to drive a stereo szekeres?

What do you think about all this?
Can you give me some good values for the condensers?



Thanks a lot

[Jean]

I like that amp, it sounds really good and very simple. I am currently reworking it to make it more symmetrical take a look.

picture

[Bricolo]

great

thanks for answearing so fast!



Your amp looks really good!
I sea (at least) 5 capacitors per channel. What are they for?
The picture i've posted only recommends 3

What kind of PS are you using, Jean?

[Jean]

Two caps in the middle are C2 1000uF Elna caps. Four blue caps are ps caps 4700uF caps. I am going to use regulated PS, 50va avel tranny 18volt x 2 and 2 LM317T (to220 package) voltage regulators. Regulators and misc components should arrive soon

P.S. I used a cheap 12 volt power supply for testing the board.

[Lligior]

Your transformer looks good to me but I have no experience with class A power supplies.
At 15 volts the max current draw is 1.26A (by my calculations) This is low enough that you may be able to get away with a simple IC voltage regulator. I don't know how it will sound, but it seems to me as good or better than the radioshack power supply. 15V may be a little close to the transformers output (with rectifier diodes factored it) and mains droop may do you in. If you go with 12V supply the current demand drops to about 1A. This should be possible with the regulator on a fair sized heat sink. Those regs have huge ripple rejection and since the current requirements should be fairly constant that shouldn't create a problem either. I would look something like an lm7812.


(next post was up befoe i finished mine)
edit:

lm317 is in the same family as the lm7812, but is adjustable. It takes a few more external parts, but any output voltage is possible. Seems like this would be the way to go.

[halojoy]

Here is Tomo version
in an earlier post at Diyaudio forum.
Szekeres a la Tomo

This picture is also on Headwize.

[trwh]

Hi Bricolo,

Have a read of this article:

http://sound.westhost.com/project36.htm

before you construct the Szkeres amp.

The distortion of such a basic circuit is likely to be very high - around 2%. Maybe you could consider Rod Elliott's revised project instead:

http://sound.westhost.com/project70.htm

Hope this helps,
Tim.

[MWP]

On the topic of this amp, im finding the IRF510/512/513 hard to find.
Can anyone sugest a commonly found MOSFET to replace them?

[halojoy]

IRF610 is easier to find, I hope.
And of course such an amplifier can be designed with some TO220 Bipolar,
like MJE15030 (or is it MJE15031, being NPN?)
Should in my opinion not sound any worse,
more probable better, I guess.(lower distortion)

[paulb]

Originally posted by Bricolo
The transformer is a 230V (primary) 12V (secondary) 50VA. Will it be enough to drive a stereo szekeres?

The Szekeres you've shown should draw (I think) around 350 mA per channel, 0.7A for two channels. At 15VDC, this would be 10.5 watts DC. A rule of thumb is to double DC watts to get AC VA, so you need 21 VA. Your 50VA should be more than enough.

You need a reasonable sized heatsink, and mounting of the transistor is critical to ensure good thermal contact. Headwize should have plenty of examples of Szekeres amps.

You can experiment with adding regulators, but my preference is a capacitance multiplier. You don't really need regulation, you need smoothing. See www.sound.au.com for one such project. I suggest one multiplier or regulator per channel.