Merry Aleph-X-Mas !

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WAX, FAX, MAX, SAX, TAX, I miss the words !

Just let me introduce my anticipated Xmas presents.
For anybody here, it's just another pair of Aleph-X,
but for me two marvelous monoblocks of pure class A,
that just arrived in time to warm the freezy winter nights :).

As I said, I just miss the words... Don't know how to call them :

WAX - Wonderful Aleph-X ?
FAX - Fabulous Aleph-X ?
MAX - Marvelous Aleph-X ?
SAX - Superlative Aleph-X ?
TAX - Tremendous Aleph-X ?

Just don't know. Any suggestion ?

Anyway, a HUGE thanks to Nelson and Grey :drink: :drink: :up: :up: :up: !!!
May all your Aleph-Xmases be white !!!
Thanks for sharing such a great design !

I began with a pair of Zen V2, 30W, so I was tempted to say I knew
something great, especially about the "heavily biased mosfet
sound"... Was desperately wrong !! I couldn't believe my ears. The
new twins make me rediscover every record I own. Never experienced
such a multilevel listening. Everything is new to me, perfectly in
place and pace, nothing added, nothing removed, everything's
unveiled. Tigh and perfectly controlled bass, unreached medium
clarity, tremendous highs. Silences are silences, every recording
room characteristic is present, natural reverberations and
instruments extinctions are just perfect and natural. And the
imaging... Sorry, my english's too poor to describe what I feel.

Just WOOOOOOOOOOWWWWW !!!!!
And No, no Blue LED... Sorry, too cold color for such hot beasts.

And thanks again to Santa Nelson :hohoho: and Grey Claus :santa3: !

May be you would like to see a picture, so here it is :
An externally hosted image should be here but it was not working when we last tested it.

Oooops, sorry, it's just the prototype, with messy wires everywhere...

So just let me introduce WAX (Left) and MAX (Right)
 

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Rear view ?

Nice hefty babies : almost perfect cubes, 25x25x25cm
Just heatsinks with aluminium addons :) Ready for biwiring.
Unbalanced and balanced inputs, with a switch for selection
between them. At the bottom, mains switch, standby/full power
pushbutton (the small red point :) ), plus a 3.5mm stereo jack
input for external remote control.

WAX (Right) and MAX (Left)
 

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From the inside...

Well, from the practical pont of view now, some characteristics
for the interested ones :

Differential DC offset around 10mV for both, and absolute DC
offset 'round 100mV.

8xIRPF044N per channel (4 per half-side), biased @ one small Amp,
950mA more exactly. I matched the mosfets for this current,
and even matched them on transconductance. Lot of time here,
since I had 60 of them...

Supply : a 2x18V / 250VA toroid, discrete double bridge of MUR1560
from OnSemi, followed by 2 x 22000uF/35V, followed by 2 x 2.2mH air
coils, followed by 6 x 22000uF/35V caps (THSA series from Panasonic).
Each electrolytic is bypassed by a 100nF Polyester SMD 2824 from Wima,
mounted on the copperside of the PCB. All of this giving a rough
+/- 21.9V rail voltage after the coils.

For the circuit itself : Nothing fancy here. I used the "TL431 current
source" ala Netlist ;) for the front end Mosfets, the BJT being
a MJE15030 (just 'cause I have a bunch of them). The "critical" resistances
in the front end are Welwyn RC55 0.1% with low tempco, Ian's magic resistors
;) being 3K65. Feedback resistors are 150K, and I didn't find on the scope
I had to use a small cap in the feedback path, although I had planned room
for it on the PCB.Power resistors from output to ground are 100R/7W, quite classical.

The power resistors gave me food for thought. I was somewhat reluctant
to use 5% or more power resistors with all the time I spent matching all
the mosfets. Dunno here if I was thinking right... So I began to look for
precision and low tempco power resistors. I found some, but the price
wasn't compatible with me. May be a kind of allergy... So I tried to
overcome this by paralleling low power low tempco 1% metal film resistors
(MRS25 from Philips, 0.6W @ 70°C). As I planned to bias the mosfets around
1 ampere, the theoretical dissipated power was only 0.5W. Thus I used 4x2R
small resistors as a 0.5R power resistor. Large safety margin, but it gives
a total of 128 resistors for the two channels :) More time to solder them,
but much much more cheaper than the 32 required power resistors !

I couldn't resist adding a "Cheff touch" to the design :) ... I added a
standby mode for the beast. Two relays add a 47K resistor in // with the
R11/V1 (and R33/V3) in Grey's original schematic. At standby, the total
resistance here is decreased, thus lowering the bias. In my configuration,
the mosfets idle at 250mA, keeping the monoblocks gently warm, and it lowers
the time to reach the cruise level when powered on.

All this stuff is controlled by some glue logic I designed. There's a mains
switch (and a soft start circuit for the power section), plus a very small
pushbutton that toggles the standby/full power mode. When actionned (from
standby to On), it immediately switches on the standby relays (removing the
additional resistance in the circuit), and 5 second later, the speaker relay
(God, I forgot to say there's a speaker relay...) is activated, just to let
the circuit the time to eliminate the transient behaviour when changing the
bias current. When switching from On to standby, the speakers relay is
immediately switched off, and 100ms later, the bias current is decreased.
In my case, the ridiculously small pushbutton is useless, since the
Monoblocks are triggered from and to standby by the preamp though a
5V pulse.

I first tested a "spaghetti" version, with wires everywhere, and it worked
fine (no listening...). Then I designed a PCB, trying to remove almost all
the wires, and trying to maintain the marvelous symmetry of the design. As
I previously built ZEN V2 monoblocks, idling at 4 amps, I knew how hot it
can be... So the PCB is designed with many many holes in it (almost 200
if memory serves), to allow a natural convection INSIDE the beast. I tried
to have all the components rated for high temperatures (105°C elecrolytic
caps for example) with a low tempco. The "equivalent power resistors" are
standing 3 or 4 mm above the pcb, not touching it, and a concentrated
"hole zone" is drilled underneath them. Although not quite necessary,
heathsinks have been used for the front end mosfets and current source,
just to help them to reach the global thermal equilibrium faster,
and to have a higher thermal inertia.

Here is a photo of the main PCB...
 

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Building the perfect beast (copyright Don Henley)

The base plate, 6mm thick, with holes for the air flow inside.
The "little" PCB here includes the soft start circuit, plus
the standby and relay logic. Heatsinks with lots of holes too,
but they were previoulsy used in my ZENs...
 

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Gentlemen, thanks for the kind words :)

Nothing special here, I just took the time... No special tools, just a press drill and a belt sander. And a lot of "elbow oil" as we say here...

I just hope that it can give people the willing and desire of making their own A-X. A thousand times worth the time spent !
 
Congrats Cheff,


very nice work!:up: :up:

I hope mine will look as nice as when they are ready.

Nice to see that someone else has already tried the trick using small resistors in parallel for the sources.

Do you have some more measurements / values? For example
sec. voltage of the transformer, dc after bridges (wich diodes do you use?), dc after chokes, ripple before and after chokes, value of chokes. Amount of caps before and after chokes etc.
Wich ac current gain do you use and what maximum power do they deliver?

william
 
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Joined 2002
Paid Member
Wow!

Cheff,

Your amps are really beautiful!

I'm wondering how you cut the holes on the top plates.
They give the amps a funky look.

I didn't notice any power devices mounted on the front heatsink.
Does it get warm at all?

I'm also curious if you needed to do anything special to get a
good thermal interface between the metal pieces with the
mosfets mounted and the heatsinks.

Merry X-mas,

Dennis
 
Re: Wow!

Thanks all !

wuffwaff said:
Nice to see that someone else has already tried the trick using small resistors in parallel for the sources.

Do you have some more measurements / values? For example
sec. voltage of the transformer, dc after bridges (wich diodes do you use?), dc after chokes, ripple before and after chokes, value of chokes. Amount of caps before and after chokes etc.
Wich ac current gain do you use and what maximum power do they deliver?

william

Yes, the standby trick is great ! Works like a charm.

About the components, did you read post #3 ;) ? DC after the bridge is about 24.5V (loaded), and the DC resistance of the coil is about 0R7. For the measurements, I have not measured the ripple. I used the same arrangement in my previous ZEN, and there was no audible hum. And I still hear nothing ! Dead quiet.

The AC sensing resistors for the current sources (R12/R34 on Grey's schematic) are 931R. It was obtained by simulations I made, to get an AC current gain of 50%. I had hard times measuring the experimental value, since I don't have a true AC voltmeter. I did it on the scope, and get a rough 52%, modulo the errors. But it doesn't worry me a lot :D

And finally, concerning the output power, I actually didn't measure it. It plays as loud as I want, and I don't wanna go deaf :). Both simulations and your spreadsheet gave a rough 55W/8R in theory.

Dennis Hui said:
Cheff,

I'm wondering how you cut the holes on the top plates.
They give the amps a funky look.

Just with this kind of tool (38mm in diameter)
hole-saw.jpg



I didn't notice any power devices mounted on the front heatsink.
Does it get warm at all?

I'm also curious if you needed to do anything special to get a
good thermal interface between the metal pieces with the
mosfets mounted and the heatsinks.

Merry X-mas,

Dennis

First question, yes, they do get hot ! Only the bridge rectifiers are mounted on this heatsink, but there's a 1" aluminium square rod with multiple screws joining the heatsinks, and it's hidden by the triangular aluminum corners. This rod allows a heat transfer between the lateral heatsinks and the front one.

Second question, second answer. I used a graphite thermal film between the mounting plates and the heatsinks. Characteristics are here. It's a bit messy to work with (dirty and fragile), but it helps to fill the gaps between the two metal surfaces.

may I know how are made the aluminium corners?

That was the trickiest part for me. As I said, there's a square rod at each corner. Its length is the total height of the heatsinks, minus 2x6mm, the thickness of the two triangular "captions" at the top and bottom. These rectangle triangles are drilled in their thickness (perpendicular to the rectangle sides) to be bolted on the two heatsinks they join, with M2 screws. Two other holes are drilled (perpendicular to the hypotenuse :confused: ), and M3-threaded, to welcome the front screws. A 1/8" aluminium plate with bevelled edges (very very time consuming to do only with a belt sander....) hides the square rod.... Am I clear enough ? Should do a drawing, but I'm too bad at this game :(


Thanks again, and merry X-mas :)
 
Re: Gloria in Excelsis Deo!

moe29 said:


(what could you possibly build after that?)

A GainClone? ;)


But seriously, very well implemented design. Just looking at the pictures, I'm developing desire to build another Aleph X (and I will definitely do).

I've been using that hole saw tool to cut 1" openings in 1/4" panels with very good results, just use some lubricant.
 
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