Hybrid Aleph- anyone buit this??

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I read an article about this design in AudioXpress a few years back and I have been itching ever since to build it. This will be my first amp project and I was wondering if anyone has built this or something like it?? I post this here as it is based on NP's aleph circuitry.

http://digilander.libero.it/essentialaudio/hybrid_circuit.htm

The other project that I'm considering is an Aleph 30
Either of these will be run with a Rogue Audio 66 tube pre or a BZLS that is nearing completion.

Any input appreciated!

Nate
 
The idea of a tube front end for the Alephs comes up two or three times a year. It's been about three or four months now, so I guess it's time again.
To begin with, I should note that the schematic you linked to is not an Aleph. Second, I'd suggest that 35V (note that the majority of the negative rail is taken up by the CCS) is a bit low for linear operation of a tube. Third, given that tubes can go through some gyrations as they wake up, I'd like to see some sort of protection for the Gates of the output MOSFETs. Fourth...oh, never mind...a friend of mine has an expression that covers circumstances such as this, but crucial portions of his saying would be rendered as asterisks and the flavor of the thing would be lost.
Suffice it to say that it can be done, but to be done well you're going to need to use a more robust front end, DC blocking caps, and a method of handling the output stage bias. Assuming that you're wanting an Aleph amp, you'll need to redesign the output anyway, so you're looking at a whole new project no matter what.

Grey
 
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nate said:
I read an article about this design in AudioXpress a few years back and I have been itching ever since to build it. This will be my first amp project and I was wondering if anyone has built this or something like it?? I post this here as it is based on NP's aleph circuitry.

http://digilander.libero.it/essentialaudio/hybrid_circuit.htm

The other project that I'm considering is an Aleph 30
Either of these will be run with a Rogue Audio 66 tube pre or a BZLS that is nearing completion.

Any input appreciated!

Nate


besides all answer you're already given, its worth to mention that at broskie's site you'll find some (if I remember well - good ones) musings about this schmtc
 
You should spend a couple weeks reading Tube Cad Journal.

John Broskie has many hybrid amp designs, many of them excellent. He also deconstructs many published designs, such as this article that shows an Italian DIY design:

http://www.tubecad.com/march2001/ (look under the "email" section in this particular article)

Some other good ideas, which I have built and tried, are:

http://www.tubecad.com/2006/04/blog0058.htm

Here are some thoughts on the Zen.

http://www.tubecad.com/2007/03/blog0099.htm
 
Thanks Kashmire,

There is quite a bit of info on the tubecad pages.....
Broskie's comments on the Italian hybrid design are pretty interesting. His explanations and modifications seem to be based on some serious knowledge.

The tube cad version of this circuit seems to be a little more based on common practices (higher voltage on the tube side and better safety on the mosfet side). I like this and I think that I have a busy summer ahead of me..... though I may need some help along the way.

Does anyone have any input on the advantages of the BUZ900db/905db versus the IRF9540/540? I think that my current speakers could use the extra power, but I can always build different speakers....

I welcome any comments or suggestion on the tube cad design that I've attached.

thanks
nate
 

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I do not agree with Broskie on everything--probably more like 80-90% of the time--but he is someone who puts more than the average amount of thought into his circuits. I always read his reasoning before rejecting something he posts--he often has a very good reason for giving something a thumbs up or down. Just glancing at his version of the circuit, I'd say give it a shot. I particularly like the higher rail for the front end. You'll get far more linear performance out of the tube with a 100V rail than with 35V. (What was the original author thinking? Yes, you can run tubes that low, but it's like casting Andres the Giant in a role where one would normally cast Warwick Davis--the height disparity should set off alarm bells in the casting department; using a part designed to shine at higher voltages in a low voltage circuit isn't something I would choose to do except as a stunt or in an emergency.)
Over time, I have suggested or posted quite a few circuits that use more than the simple +- rail customary in the solid state world; most recently the New-Tron. My experience is that solid state folks are flustered by more complicated rails. Tube guys are used to such things--after all, any decent tube amp has at least three rails: The main high voltage rail, the filament supply, and the bias supply (assuming fixed bias). Frequently there's another, lower rail for the front end. I see that Broskie has proposed four rails: 105V, +-35, and the implied filament supply. I approve. However, hard core solid state people are turned off by such things and I've nearly quit suggesting them. If you have the courage to build the circuit, I'm with you all the way. Show them solid state critters a thing or two.
As far as MOSFET selection goes, it's an arcane art. You want something that can withstand the voltage, current, and heat. Another thing to keep in mind is the difference between lateral and vertical MOSFETs (the IRF parts are vertical). Depending on the circuit, substituting vertical for lateral or vice versa may give you biasing problems. Off the top of my head, I don't remember if the BUZ parts are vertical or lateral. But rest assured that there are any number of parts that you can substitute for the IRF540/9540. Spend a few minutes looking at the datasheets for some candidate output devices and see what looks good. The IRF parts are readily available, as are Fairchild parts. OnSemi had only N-ch devices the last time I looked. IXYS might have something useful...if they have P-ch devices...actually I'm not sure that they do, but it's worth checking. Etc.
See what's available. Make a list of, say, ten or fifteen possible substitutions, then post here and let people weigh in. It may turn into a food fight as folks argue for their favorites, but nobody says you have to listen if the static gets too loud.

Grey

EDIT: Incidentally, the New-Tron could easily be altered to use a bootstrap, but not one person suggested or requested it. It's always interesting to watch peoples' reactions to posted circuits. I think of it as an ongoing survey of DIY attitudes. Not much has changed on that front.
 
Thanks Grey,

The power supply is the only thing that doesn't scare me.... Though I do have the appropriate level of respect for things that might hurt me!

The low voltage tube supply was one thing that I questioned from the beginning. In audio, I am a firm believer in using the right tool, or piece of equipment, for the job. Don't expect a minimonitor to sound like a gargantuan 4-way....

I will take your advice on the mosfets. The Italian guy recomends the BUZ and IRF mosfets. I have the datasheets around somewhere and I will do some searching and post my findings. I just finished my last final for the quarter today and I will have a little more time to devote to hobby type stuff.

thanks for taking the time to add your thoughts.

Nate
 
Hi !
Well, one advantage of the original design is that it is direct coupled. 2 caps less in the signalpath. The first stage is differential and with the currentmirror on top, it should be able to deliver rather low distortion. It is only asked to give a small signal voltage out, as most of the voltage amplification takes place in the P-channel MOS FET.
Thorsten ( another one )
 
Well,
I decided against the hybrid. I am currently up to my eyeballs with parts for Aleph 5 monos. The only item that has not been ordered is the transformers. I'm trying to talk myself out of dropping a couple c-notes on Plitron toroids.....

With all the discussion lately on CLC and which inductors to use. I am buying 2.2mH perfect layer 14awg air cores from Zalytron.

I have 8 x 47KuF caps ordered from apex jr as well. I hope they work out!

Nate
 
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