Merry Aleph-X-Mas !

[CheffDeGaar]

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 !!!
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 and Grey Claus !

May be you would like to see a picture, so here it is :

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

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

[CheffDeGaar]

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)

[CheffDeGaar]

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...

[CheffDeGaar]

And from the copper side, with the small SMD bypass caps under the big
'lytics...

[CheffDeGaar]

Another view of the main board, with the thermistance for ground to
chassis connection (near the bal/unbal switch).

[Duck-Twacy]

Very, very neat.

And a merry Aleph-Xmas to you too!

[CheffDeGaar]

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...

[CheffDeGaar]

Almost completed...

[CheffDeGaar]

And the speaker relay arrangement... Not enough room on the main PCB
without destroying the symmetry...

[grataku]

OH LA LA! Cheff!!

That's probably the best realization of an amp ever. It rivals the real thing. It's what I always wanted to do but never been able to! Congrats!