Best Pass Design Zen, SOZ, Aleph 30??

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What is the best amp to go for Zen or Son of Zen, or an Aleph 30? I'm only interested in the relative performance with music, power is not an issue, nor is the need for a balanced source for SOZ. has any one built all three?
Finally (and sneakilly!) Nelson when do you expect the next Zen installment to appear? (to say I can't wait is a vast understatement!)

Unless you have very efficient speakers, I would have to say ZEN or SOZ are really lacking in the power output department even though you said power is not an issue. I'm still trying to find a reason for myself to built SOZ.

I have a ZEN and it sounds wonderful on efficient speakers and it can play as loud as you want it be but not if you hook it up to, say Magnaplanar speakers. To me, it would be like listening to background/elevator music on inefficient speakers. The sound quality is there but I can not get excited if it can not play loud .... & I don't listen to rap music.

So, aside from sound quality and I know you said power is not an issue, among the three that you mentioned, I would go with Aleph 30 simply because it'll be able to drive more variety of speakers.

If you do go with Aleph 30, why not just go for Aleph 5? Isn't Aleph 5 just a couple more output transistors (& slightly bigger heatsinks) and a bigger power supply than a Aleph 30?
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It really depends on what you want. The Aleph 30
has more power and accuracy.

The SOZ has no damping factor, but if you can get past
that, it is very interesting. Most suitable for horns or
efficient mid/high frequency drivers.

I listen to my Zen-lites all the time at about 20 watts,
and they are a bit weak on the bottom with 87 dB speakers,
but they still play loud enough to create neighbor problems
in your typical apartment.
More power on Zen


You can increase Zen's output power "simply" by paralleling two stages (Gain device & current source). Increase also supply voltage, and you've got it. I've done that with no huge problems, except heatsinking :) (photo here), resulting in about 30 gorgeous watts :p. Thanks again, Nelson.
SOZ and 4 Ohm speakers

A response I gave from similar thread.

I have a pair of variable power output SOZ mono blocks driving large three way 4 ohm 87 dB efficiency dynamic speakers. Ten watts is just barely enough. On big orchestral climaxes or other very demanding spikes in music with the volume turn up the sound would compress or in a worst case situation the midrange cone would start to break up a little. At 15 to 20 watts the problems went away. In fact you think your listening to much larger amps.

New info:

I found the lack of bass control is a function of the amount of capacitance used. The more capacitance I added the better the bass became. Using 60,000 uF 6.2 mh choke and another 60,000 uF "fixed" the bass control and power supply noise. I think I can improve this by using 40,000 uF 6.2 mh choke and 80,000 uF. I am also going to try a choke input. This is a choke after the bridge rectifier. There just is not enough time in the day.!

Those big computer grade caps of more than 10,000 uF do not sound good to me. Use 10,000 uF caps or less.
Do you think 4 of these heat sink from Electronics Surplus are sufficient for a 20W SOZ monoblock? I plan to stick one IRFP244 on one heat sink, maybe with one or two resistors. The other piece will be for resistors only. I hope 20W per channel could drive my 86 dB loudspeaker (it is just a book shelf one). How do you guys say?

Re: More power on Zen

ftorres said:

You can increase Zen's output power "simply" by paralleling two stages (Gain device & current source). Increase also supply voltage, and you've got it. I've done that with no huge problems, except heatsinking :) (photo here), resulting in about 30 gorgeous watts :p. Thanks again, Nelson.

Hello, would you tell me in detail how to increase the power of Zen amp ? is first i build two Zen amps , then parallel the two amps of input "+ -" and parallel the output "+ -" that's all?


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Resistor R7 has very little load and does not have to be mounted on any heat sink. I used a 1 ohm 50 watt R7 and it runs cool. The other resistors run very hot as does the mosfets. Mount the other resistors on a separate heat sinks from the mosfets. SOZ makes a lot of heat. Those big heat sinks you plan on using look fine if you use enough of them. They should be mounted vertical for best heat dissipation. This will make your amp very tall. How many ohms are your speakers? Speakers are very tricky. A speaker manufacturer may quote 4 ohms but it could dip below this at times. The only real way to tell is to try it out. But, with twenty watts you have a good chance. Ten watts or less is more of gamble.
Tall amp is cool

Yes, I planned to put the heat sink vertically, two at each side, totally four for a 20W monoblock. I don't mind it tall, actually I love it this way. You know, I love the Mark Levison 300 series very much. I try to imitate it.

My loudspeaker is 8 Ohm with 86 dB sensitivity. I used an integrate Class A amp (20W, 25W? not sure) for it. But it had a hard time to drive it happily. Actually, the speaker is ProAc Response 1S. I'd love tube amp for it but can't afford that. I heard mosfet has similar sound as tube, so I want to give it a try. Like you said, i feel more comfortable to have 20W to drive it. But a 20W dual channel in a single chassis will be very big and hard to move. So I came up with monoblock idea like many other did. I wonder the chassis and heat sink contribute the major cost of SOZ. How much did you spend on yours, gnomus?


86db sensitivity is consider to be pretty inefficient speakers. IMHO, 20W is inadequate to drive it ... as you have stated too. You might want to consider building other amps by Nelson Pass, say Aleph 5 or at least Aleph 3. By your monoblock heatsink construction description, I take it that this is not an amplifier to built it cheap. You don't want to find out the lack of loudness/bass after you built it. So you might want to consider the alternative.

But .... if you listen to your ProAc speakers in a small room most of the time, then I would say 20W is sufficient.
I have heard the Proac Response 2.5's driven by a VAC Ren. 30-30, a 30 wpc 300B tube amp and they sound excellent. The 2.5's are also only about 86 db efficient. Tube amps have a lower damping factor than most solid state amps and some people say that this is why they sound more powerful. I think your 1S woul sound great with an Aleph 30 or 20 wpc SOZ. Just my opinion.
SOZ sounds and acts bigger than it is. The bigger the power supply the more control it seems to have over the speakers. SOZ sounds like what you drive it with. I use an old CJ pre amp and it sounds tube like. I run my cheap cd player direct and it sounds solid state. I listen mostly to LP. You can build SOZ and if its not what you want then those heat sinks will do fine for an aleph. I spent quite a bit on SOZ because I experimented a lot with power supply and different parts. I made several different versions and I am still experimenting. I thought in a few months that I would have the final version but, now I read threads on adding X therory to SOZ. The good news to add X is not a lot of new parts. The power supply is the same. And this is where I spent the most time experimenting.
Re: More power on Zen


sorry for late answer, took a little vacation...

I simply paralleled two active gain stages. Starting from the Zen Revisited schematics, the following components have been doubled :

R1, R3, R4, R6, R7, C5, Q1, Q2, Q3

Apart from +V and GND, the only common connections are the drains of the mosfets (the four drains tied together), and the two gates of the gain mosfets (before a 221R gate resistor - not on the schematics). Mosfets have been matched.

Transformer is a 36V 300VA (2x18V), leading to 45-46V of positive supply. Take care to match the capacitors' voltage to this value (63V in my case)

Hope this helps
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