The Aleph-X

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#462
PSRR?

OK, maybe I'm covering old ground here, but I just can't bear re-reading this entire thread, and the search tool is no help... 🙄

I'm pondering the power supply in preparation for building my Aleph-Xs. The possibility of doing a pi-filtered supply is in the back of my mind, but wether or not this is even necessary is what I'm wondering...

The balanced nature of the circuit should give it excellent PSRR :up:, but I really want this amp to be absolutely SILENT when not playing music. If this means the added expense of a pi filtered supply, then so be it, but I'd prefer to avoid the avoid it if possible. I'd also like to make a compact chassis, so if I can build it without leaving "expansion space" for extra chokes and caps, then that's good too.

So, who's got theirs built and running, and what are your experiences with power supply noise in the outputs?
 
#463
I second hifizen's power supply questions. I am really interested in building this amp too and was wondering if choke regulation is a viable alternative to a pi filter for this power supply. Does anyone here know how the Musical Fidelity choke regulation works?
 
#464
choke input filters in general

As long as the choke has sufficient inductance for the output voltage and current draw, the output voltage of the choke filter will be limited to the average value of the rectified wave at the input to the choke.

The Radio Amateur's Handbook (1970 edition that I have here, anyway) offers the following equations, where L is in henries, I is in milliamps and E is in volts:

L (crit) = E / I

At the same time a certain minimum current needs to be drawn for an output of a given desired level and a choke of size L henries:

I = E/ L

(I is in milliamps again, here)

The equation for output voltage is summarize below:

E = 0.9 Et - I (Rchoke) - Er

Et is the RMS voltage of the transformer secondary
I is the total current draw in amps
Rchoke is the resistance of the choke itself
Er is the total voltage across the rectifier.

The book gets to the point that the higher the current, the smaller the choke can be and still act like a choke-input filter. It goes on to discuss swinging chokes, which I haven't actually ever seen. (Though maybe I don't shop in the right places. *grin*)

Hope that helps a little,
eLarson
 
#471
John,

Thanks for the reply...

Dos 8.3 format simply means to save the file in a format such as

aleph.bmp

The first portion of the name not being longer than 8 characters and the second half being the file extension separated by a period.

I know you Mac folks have never had to deal with this stuff, but when posting for other pc folks to use it's easier for everyone if this format is used. This way the file can be opened by most systems regardless of age or operating system...

Also, in the dialog box that pops up when you save the file usually there is a drop down list near the bottom that allows you to save the file in various formats. Make sure to save it as a bmp, jpeg or tif if at all possible...

Thanks for your efforts! 😀
 
#475
Hi Guys

Not a bad layout... However I would like to make a small suggestion.

The closed loop ground track is not such a good idea in power amplifier PCB layouts. It can be the cause of circulating ground currents, which can cause Hum loops. I would suggest that you cut the track between the node or R19 and R29.
This will fix this small problem.
🙂

Have Fun!

Cheers

Anthony Holton
 
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