Aleph 1 modification

[lubbie]

I was wondering if the aleph 1 would be able to handle larger voltage. I'm looking at running it with +-80 Vdc.

The schmatics of the Proximity amplifier are unavailable. So i was looking at pressing the dual transformers mounted in a 19" rackmount to good use.

[Nickolas K.]

Well, I think IRFP240's can handle 80 volts.
But what are you going to do with the bias?
Aleph 1.2 runs on 4 Amps @ 60 Volts.
Can you imagine the size of the heatsinks you
are going to need if you keep the bias at 4 Amps?
And I don't think it would be wise to lower the bias.
In the original Aleph 1.2 each mosfet (of the 12 used) draws about 330 mAmps (330 x 12 = 3.96 Amps).
When I built mine I used 10 mosfets and placed a 100K trimmer in place of R19 just to see what happens with bias trimming.
With 300 mAmps per mosfet the amplifier sounded harsh and aggressive.
With 400 mAmps per mosfet it really sings.

Good luck anyway!

Nick

[Nelson Pass]

The answer is yes.

[lubbie]

Originally posted by Nelson Pass
The answer is yes.

Thanks for the quick response. The heat won’t be a big problem, the proximity was forced air.

Now on to building this animal... Whats the differance between the 1 and 1.2 ??

Anyone know of a supplier of PCB's? groveling will accompany if required.

[Nelson Pass]

Big difference between 1 and 1.2. The 1 has 3 gain stages and lower distortion and higher output into low impedances.

The 1.2 has 2 gain stages, and is the more familiar Aleph design. I recommend this, particularly as you will find more support for it here.

[lubbie]

Originally posted by Nelson Pass
Big difference between 1 and 1.2. The 1 has 3 gain stages and lower distortion and higher output into low impedances.

The 1.2 has 2 gain stages, and is the more familiar Aleph design. I recommend this, particularly as you will find more support for it here.

The main reason i picked the 1 over the 1.2 was because of the lower distortion and higher voltage supplies. I thought that modification of the 67Vdc supplies to 75-80Vdc would be less troublesome then the 60Vdc. The Horns are going to be a complex load for this amp so it should be interesting.

I plan on running this amp on a pair of klipschorns with 120db+ sensitivity. I've been looking for a nice clean amp to run on these speakers. The reveiws said that a well designed single ended tube amp sounds nice on these speakers. Seeing as fets and tubes are "simular" in the way they handle sound, i thought i'd give this a try.

Any assistance would be great.. Thanks everyone.

[Nickolas K.]

Hey, you don't need 200 Watts @ 8 Ohms to drive 120+db Horns.
Why don't you go for ZenV4????????

[lubbie]

I agree that 200watts from the aleph 1.2 would be to much. The aleph 1 was only rated at 150w and i prefer to run just a little more then speakers can handle.

I've always done this, and i've never blown a amp and never smoked a woofer. I still currently run speakers i designed 15years ago. Although the new klipschorn replicas should be a nice change.

The speakers will handle 100Wrms with a peak of 400w.. So the match sould be really good.

[Franz]

Hey!

please don´t feel offended but 120 dB /1W sensivity means much more than 100 % efficiency !!! 100 % equals 112 dB/1W1m

Although I know what al Khorn is capable of, I recomend to stay on the ground with any ratings!

I also feel that it´s senseless to specify sensivity at a single frequency which might just coincide with a strong resonance as it´s often done.

Franz

[lubbie]

you were correct.. the rating i gave was wrong... the correct rating is.

SENSITIVITY: 104dB @ 1watt/1meter