Aleph 30 -> Aleph X?

[dieringe]

Hi

I have an Aleph 30 clone (as 2 monoblocks) and think about trying Aleph-X...
The easiest thing for me would be to modify the existing aleph30, keeping the case, transformer etc.
So I tried the excel sheet and put in the aleph-numbers:
25V rail
2 Amps total current
6 FETs total per channel
50% aleph...
...makes 100W dissipation and I could keep the whole setting.
But I see that the plotted curve is far from optimal.
What would the sound be? Is it promising in any way?
If not, what is the way to go: more transistors, lower voltage...?
I don't want more dissipation, but can live with 20W into 8ohm or so.
(speakers are 8ohm).

thanks,
martin

[Andypairo]

I assume you used the spreadsheets floating around on the forum (but which one?) , but you probably missed some points:

1- the fets can only be multiple of 4, since the Aleph-X is made of 2 "balanced" amps

2- Don't know the topology of the power supply you are using, but if it's the "standard" one (Caps only) I'd suggest to lower it (maybe using a CLC or CRC filter) in order to be able to raise the idle current. Being the X a balanced (some would say bridged) amp it needs lower voltages and higher currents.

3- Keep in mind that the PS will be more stressed, especially the diodes, provide enough cooling for them and eventually switch to Schottky types

4- Provide better ventilation to the inside of the case, since the trafo and the diode bridge will generate much more heat.

Cheers

Andrea /who has a Aleph 30 and is building (well, has built but still looking for a good solution for the cabinet) a Aleph-X

[dieringe]

hi
thanks for the quick answer!

I used the spreadsheet from the wiki page. Should be the latest?

Ok the multiple of 4 got clear to me in the meantime...
The total number is only a question of power per transistor, isn't it?


CLC is probably a good idea.
Why is the powersupply stressed more given I keep the same dissipation?

Well I guess I have to enlarge my heatsinks anyway...

Btw. how do I cool a discrete schottky bridge?

Have you already listened to your -X?

martin

[Andypairo]

Let's try to give a good answer to every question...

The spreadsheet on the wiki is probably the latest, surely it is a good one.

The total number of fets (4, 8, etc) depends on the power/fet but also on the thermal resistance of your heatsink.
If your heatsink can keep quite cool (oversized) you can use higher power per fet, on the contrary if it is on the smallish size the use of multiple devices allows you to keep the junction temperature lower given the same heatsink temperature.
Not being sure about the °C/W of my sinks (good enough for my Aleph30+) I use 8 fets with rails 14.5V and Ibias=5A per amp (I intend to use a 4 ohm speaker, so I'm more on the "current" side).

The supply is more stressed given the same output power, if you keep the current the same it won't probably be stressed further.
But to optimally use the resources you have I'd suggest to use a CLC /CRC to lower the rail by 3-5V and to raise the current accordingly. I believe that with the settings you are willing to keep you'll be constantly current-starved, even on a 8 ohm load.

Schottky diodes come in T0220-To264 plastic packages, which can be easily heatsink-mounted.

I haven't had the occasion yet to listen to my Aleph-X (at least on good speakers.. at home I have a 3-way active system so...) but when I'll be able I'll let you know.

Cheers

ndrea

[dieringe]

I kept nearly everything. Bought parts for a few Euros.

I now run it with +-25V and 2Amps total current (0.47Ohm source resistors), 4 transistors.

It sounds absolutely wonderful... like zero distortion... (I wonder how the Aleph could be so bad... )

But I have problems with output offset. The absolute offset constantly rises with warmup. I have about -10V when fully warm.
(warm means you can't touch the sink anymore but that's like before )
There is no way to turn this down with the currentsource pot.

And the relative offset starts with about 15-20V and goes down very slowly. I end with .5V or so when hot (which is completely acceptable)

I started with the potentiometers in minimal settings for the aleph source, as described somewhere in the A-X thread. I have left them there, because I thought it 1. sounds better, 2. makes less heat.

But how do I get the offsets right? Do I have to turn up the aleph source in order to achieve this?
Or will I always have to wait 30 minutes after turn on to get 0V relative, but have to live with 20V on startup, and -10V absolute?

thanks
m.

[dieringe]

that's how it looks (what a mess!)

[dieringe]

Originally posted by dieringe
But I have problems with output offset. The absolute offset constantly rises with warmup. I have about -10V when fully warm.
(warm means you can't touch the sink anymore but that's like before )
There is no way to turn this down with the currentsource pot.

Correction: I can get absolute offset to zero.
But I think I get problems when the amp is cold. It wouldn't do down again while warming up. At least last time I tried this...

m.

[Nelson Pass]

Incidentally, I built the first XA from an Aleph 60, which was
just about ideal.

The issue of absolute offset has four things to note:

1) It's not that critical, particularly while the amp is still cold.
Just get it down to a reasonable figure.

2) Output resistor loading to ground is a big help, say 50-100
ohms.

3) Resistors from the outputs back to the Sources of the input
diff pairs provide some common-mode feedback. Use these
sparingly - only as low a value as you need to help stabilize
the offset.

4) Resistors to ground at the inputs are important in reducing
common mode drift. Typically 20 to 100K.

[macka]

Mr Pass,

I did a similar modification to the Aleph 2 using a 25volt dc supply, it works well enough, like a pizza oven

Do you recall if you used any compensation capacitors?

Ian

[JDeV]

Originally posted by dieringe


Correction: I can get absolute offset to zero.
But I think I get problems when the amp is cold. It wouldn't do down again while warming up. At least last time I tried this...

m.

I also can't get abs. dc lower then 6V. If it is cold or warm , not much differance. How did you manage to get it down ?