Alphe 2 Vs Alphe 4

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Has anyone built and compared either of the Alphe 2 and Alphe 4?

I am curious as I would like to scale up from the Alphe 5 in the new year so I can use some smaller (more female friendly) speakers and would like to understand the virtues of each design.

Despite both amps being rated at 100 watts / 8 ohms the Alphe 2 is abviously a mono block style and appears on paper to be geared for 4 ohms from 45 volt rails, while the Alphe 4 is a stereo design and runs from 48 volt rails. (no power rating into 4 ohms is stated for the Alphe).

Both biased at 3 amps use the 12 output devices and have different source resister values and current values.

The Alphe 4 also uses the Zetec ztx450 tranisters.

It is my feeling the Alphe 4 may offer slightly more linear performance in 8 ohms, the trade off being limited current delivery into 4 ohms.

Can anyone explain the differences?

best regards

What's it all about...Alphe?
I've got a pair of Aleph 2's, and am nearing completion on a second pair so as to be able to do some experiments. I'm not sure I understand how using the 2 or 4 relates to smaller speakers, but that's up to you.
The difference between the two is contained in the monoblock vs. stereo chassis observation. Due to thermal constraints, the Aleph 4 was biased somewhat less than the Aleph 2 (about 2.5A vs. 3A), leading to less heat being generated so that two channels could be put in the same chassis.
Lower bias current means reduced ability to drive low impedance loads (i.e. 4 ohm), and a whisker less sonic performance.
In that part of the circuit the MPSA18 (45V NPN) or the ZTX450 (100V NPN) makes little difference. I went ahead and used MPSA18s, since they're something I keep on hand, anyway. The resistor value changes fall out from the lower bias current.


Thankyou for your prompt clarification, after Xmas l will have a go at the bigger amp.

Land of the Giants

The point about smaller speaker ... my current boxes are 10cu feet large format JBL monitors @ 96 db sensitivity and you can run them with 2A3 SE amp.

So when I mean smaller.. about normal size boxes!


I know there were various versions of the schematics around, due to errors and whatnot, but the one I've got here next to me shows .6V across 1.5 ohms...i.e. 400mA per pair. That times six would be 2.4A. I was rounding up when I said 2.5A. Also, the power dissipation was listed as 500W for the 4. Three amps on 48V rails, times two channels would give about 575W, not including the dissipation from the front end and rectifier, etc. which would round it up to circa 600W. Using the lower figure gives a dissipation near 500W, which is what the manual says.
I dunno.
Somewhere around here I've probably got all the various versions of the schematic; I'm not even sure which one this is, offhand. Have you got one that indicates a higher bias?


I notice from Mr Pass comments that the bias voltages on the schematics may be incorrect as he points out the drawings were cut and paste.

I have just been looking at a print out of Mark Finnis Alphe 4 construction PDF and he confirms the Alphe 4 is bias for 3 amps.

Mark found this out when he made the amp with 3 pairs using 1.5 ohm source resisters and discovered the total bias was only about 1 amp. So Mr Pass suggested using 0.68 source resisters @ 0.6 volt for three pairs, hence 3 amps.

So based on this the Alphe 4 must run 3 amps or 0.5 amps per device (x6) @0.75 volts across 1.5 ohms.


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