Aleph 5 sound?!

[tortello]

Hello all
I've just finished to build the definitive version of an Aleph 5 amplifier
(with 6 x IRFP240 HexFets) biased at 3A.
I've tried several preamplifiers, among these an Audio Research SP16 and a
Bride of Zen. Best results I obtained from a DIY SS preamplifier with a low
output impedance.
The loudspeaker systems are Tannoy Cheviot, with HPD AlNiCo components.
The sound is extremely clear, precise, my impression is to listen for the
most focused sound in my experience.
The differences between records is not only
noticeable, but really dramatic.
The soundstage is very tall, deep and absolutely precise, the instruments
nailed in their "supposed" position, the loudspeakers (very) often
disappear: highest precision and rigour here too.
But... but the bass region seems to be too timid, a little recessed, so the
musical involvement fails, when rhythmic contents are essential features.
This is the only, but for me important, flaw of this amplifier.
I don't know if this is a peculiarity of the A5 design too, or only a
speaker lack of compatibility.
Any suggestion?
Thanks
Marcello

[stefanobilliani]

First time I ear the aleph sound the first thing that comes in my mind was the lack of compressions rather than lack of bass region.

Most important (for me) is the balanced line at its imput: this lets the amplifier take fly...

[Nelson Pass]

If you want to improve the Aleph 5, you raise the bias
current.

[jeclk]

Hello
It is a ridiculous question for you , but if you can say to me how you raise the bias current?
Thanks
escuse my english
i'm french.
BYE BYE

[macka]

Hi Marcello,

Congratulations on your Pass Aleph 5.

In reference to your perceptions thus far it may pay to do some objective analysis.

What power amp are you comparing the Aleph to?
Conventional amps can appear muddy in the bass when compared to say class A.

The speaker......

The overall balance of the Tannoys may now need some realignment via the high frequency controls. Perhaps the previous power amp was less pro nounced in the highs?

Even a subtle shift in the overall frequency response , that is a tilt in the lows verus highs can create the impressions you speak of.

Try attentuating the high frequency roll off slightly or even the high frequency shelfing control, but only a small amount.

The Tannoys in my experience are a little timid in the bass compared to say a JBL monitor which I use so try moving the speaker box near the rear wall for more low frequency room gain.

Also, is the box vented?

If this is the case the output impediance of the amp will have some impact on the lows. This is because the RX of the amp is a component of the speaker's overall QTS, which in turn govens the low frequency alignment. (ie QB3 ------ B4)

A Japanese amp for argument sake, with less control in the bass will make the bass sound for full and pronounced, but with false scale so the amp sounds more powerful than it really is.

However, an amp with well controlled bass will sound perhaps leaner, dryer and tighter in the bass. This is why audiophiles think some speaker wire is better than others, Mr Pass has a great article on this subject my the way.


The Aleph ...........
My view is the Aleph 5 is fairly flat in tonal balance, but this subject to the power supply.

Tell us about the Aleph power supply you have made and how it is configured, this can have a marked impact on the dynamics and low frequency projection.

Seperate power supplies for both left and right will most likely give the best results and the take off point for the negative supply to the input pair should be close to the output stage.

After a lot of experiementation I ran seperate power wiring from the driver board and the power fet boards to the positive and negative of the filter bank. Thiis seemed to work best.

macka

[fcel]

Jeclk,
Check out this thread to get some idea of how to adjust bias Aleph5....it works!!!

[tortello]

Hello all, thanks for your opinions.
I'll try to translate my perceptions, these are extremely subjective considerations, and must not be taken as truths.
I'll try to explain myself as better as I can.
The bass behaviour should be considered as "dynamic timidness", at least this is my opinion, since
the tonal balance is quite neutral.
In my opinion, the lack of punch could be caused by a not optimal synergy between the amplifier and
the loudspeaker, but really I don't know.
My A5 version has a monophonic building, in two separate chassis, the power transformer is a nice
Talema 500W piece (per channel), the smoothing bank is made by 6 x22000uF computer grade capacitors.
With 3A bias current, the heatsinks' temperature is about 25 degrees (measured, 26 calculated...) above the room's one, so I can't run the HexFets hotter.
In my opinion, tilting the "energy" or the "level" controls is not a good practise, the tonal homogeneity of the Dual Concentric faints even with a single click from the "level" position.
And the problem of this configuration seems to be the DYNAMICAL behaviour of the bass range...
Paradoxly, with a far cheaper Hafler amplifier, the tonal profile seems to be more balanced, even if
the class gap is immense (there is a sort of low-level slime, while with the Aleph every small detail
is fixed in the most natural way).
But now I can't do without the Aleph's natural precision... so Help me!!
Since I can't enhance the total power dissipation without a complete re-building, do you know if a 12
devices configuration, but with the same total dissipation figure ( = Aleph 60) could be a bit "more
expansive" towards the bass region?
Thanks again
Marcello

Post Scriptum: The interconnect wires are Furukawa and Audioquest stuff, Lapis and Emerald models.
For the power connection I use some, such as Straighht Wire ( an old MR32 model), Exposure and Kimber
cable models

[macka]

Marcello,

Hmm I must haul my Aleph 5 out for a listen, I cannot image why this is!!

Are yo running balanced input drive?

Have you checked / re adjusted the current share for 50/50 % as per the Master's instructions?

I recall that this alters all things merry and good in the Aleph.

If the current share is out , the amp will sound detailed by rather anal.

This is quite an easy test if you have a 1k sine wave source and 10 watt 8 ohm dummy load.

Just allow the amp to warm for 1 hour, then apply a 9 volt signal to the load and measure the vac across the negative side source resisters and at the same time the vac across the 6 x .47 ohms output bridge. Then derive the relative ac current from the measurements. The split should be 50 % current , so the ac current via the negative side should be about 0.562 amps, if this is not the case adjust the value of R21 with a 2 K trim pot.

What brand of capacitors are you usingin the amp.. Black Gate, Silmic?

Failing this, change all the cables/ interconnects for run of the mill cables and see what happens, they could be making the Halfer sound okay (when in fact is sounds like a brick layers cement mixer)

You could add more output devices aka Aleph 60, but I doubt if this is the problem.

Cheers

macka

[wuffwaff]

Marcello,

the sound you describe just about fits my Aleph 5 too.
What you can try to get a bit more dynamic in the bass is change the ac current gain to 60-65% or so.

This will improve power delivery into lower impedances and somehow makes the bas more punchy/lively.

At the moment I´m quite satisfied with the sound of my 5 but I will try to improve bass further by building an X........

william

[tortello]

Hello Macka, hello William, thanks for your replies.
Yes, my Aleph(s) are running ok, with a 50% (un)costant current source gain.
About the CCS regulation, I wrote a post here one year ago or so.
My only interconnect cables are unbalanced, but I suppose that an XLR cable could refine the sound, not change the tonal approach: no direct experience about this, only a personal idea.
The NFB capacitor is an Elna Starget piece, quite good in my experience; the PS caps are Kendeil 105° stuff, and seems to be high quality ones.
I'll try to unbalance the active side/current source ratio, I have only to set a trimmer for this.
Anyway, the tonal behaviour is such even at low power level, say 3-4 Wpeak: the Tannoys are quite efficient, at least respect to the other hi-fi common gear.
Marcello