Zalman mini-Aleph

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ojg

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A couple of years ago I bought some of BrianGTs mini-Aleph boards. A few months ago I finally built them. And here is the result.

They use a Zalman CNPS 7000B-Cu LED as a heatsink. It's very efficient even with the fan at minimum, and works as a nice power-on LED to boot :)

The power supplies are two 12V/50W switch mode units.

The casing is an IKEA pencil holder, 10cm on each side.

The pictures are taken while doing the first power-on test so please ignore my test-speaker :)
 

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ojg

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1W, 7kHz into 8ohm

I should also add that the board is very easy to assembly and get to work. The circuit behaves nicely, no power on/off thumps, very little offset and output noise level at -90dBV. Great first-time or second-time build.
 

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ojg

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They are working very well. In my opinion SMPS are much better suited for this kind of class-A amplifier than transformer-based supplies.

I used two 12V supplies in series to make +/-12V. I made sure they had only a 2-pin power cord to avoid any grounding problems.
 
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I'll go OT and hijack this thread, so read on...

Wow, nice amp. Small, simple, neat. But say, did you mutilate the IRF9610s? They look kind of...short?
And I especially like your implementation of fancy parts, like the pencil holder, great idea.

To go a little OT, here's my favourite casing so far:
http://diyaudioprojects.com/Chip/Synergy-LM3875-Gainclone/index.htm

I came across this amp while I was trying to decide whether I shall build a gainclone or a Mini Aleph (so it's not that far OT).

I've decided to go with the Mini Aleph, so I'll kind of hijack this thread (well, I just have to, there's the right people watching...).
I'll be using GRollins's original circuit with the following modifications:

- Resistors of 221 Ohms at each and every gate
- protective zeners for Q1 and Q3
- a 1µF MKP cap across D1
- a 10pf Styroflex cap across R8

The external PSU will be CLC and it won't be built in a Pepsi can, sorry Grey. But it will be P2P.

Now I have four questions:

1) Can the output's DC-offset be adjusted by varying R4?

2) What happens if one varies R12?

3) What is achieved by increasing R8 (e.g. to 100k)? More gain?

4) How sweet does it sound (maybe compared to a Zen lite)?


Oh, one, no, two more questions.
ojg, why do you think that SMPS are better for this kind of amplifier? How much power can they deliver?
 

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well here we go: (may need correction)


1. low DC offset is achieved by close matching of Q1, and Q3

2. R12 sets the AC current gain, if you raise this value, you lower the AC gain and vice-versa. I believe there are roughly hundreds of posts on how to set it. In the end it comes down to personal preference. 50% supposedly being optimal.

3. R6, and R8 form a voltage divider that sets the feedback. I believe the gain is set by R1, and R2.


4. I've never built/heard the Zen Lite (its on my build list), but the Mini-A is tops on the sweetness scale. With the low output of the mini, you will probably get the best results with efficient speakers. Of course you can build a gainclone in a pepsi can, but IMHO the sound doesn't compare.


-john
 

ojg

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SMPS are better here because:
A) the mini-Aleph is a class-A amplifier so it draws a constant current.
B) the mini-Aleph has less-than-excellent PSRR so it benefits from a regulated supply.
C) SMPS are physically smaller so it fits with the mini in mini-Aleph :)

One comment to the measurements I posted earlier: I really think these are excellent results for such a design. After all it only has 7 transistors total including protection!

The cut-off TO220 I believe is called a TO262 package.
 
ojg said:
SMPS are better here because:
A) the mini-Aleph is a class-A amplifier so it draws a constant current.
B) the mini-Aleph has less-than-excellent PSRR so it benefits from a regulated supply.
C) SMPS are physically smaller so it fits with the mini in mini-Aleph :)

One comment to the measurements I posted earlier: I really think these are excellent results for such a design. After all it only has 7 transistors total including protection!

The cut-off TO220 I believe is called a TO262 package.

I don't think point A is always correct.

In balanced class A circuit, like one of the X series, the current drawn form the power supply is constant, as it is steered from one side to the other, via the load.

In a single ended class A circuit, the changing current in the load has to come from somewhere, and the only place it can come from is variations in the current drawn from the supply.
 
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