Aleph J versus Aleph 3

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It is certainly possible to build an Aleph J that is capable of handling lower impedance loads quite well. Using the diyAudio PCBs, I substituted a 10V zener diode for the current source about the 'J74 JFets and adjusted R8 to get the diff pair current back to 8 mA. I also put a 200 Ohm resistor in R30 to drop the voltage a little more and provide an easy way to measure that current. I used a pair of 300VA transformers with 20V secondaries. Rail voltage on the boards came to +/- 24.2V using LVB2560 bridge rectifiers. I built the amp to support LT4320 based rectifiers, which would have given another 1.5 Volts or so on the rails, but haven't made that change yet. As long as the diff pair in the front end is protected from excessive voltage, the amp should handle 26V rails just fine.

When setting the bias current for the output stage, I slowly brought it up to 1.8A total on each channel. Having listened to the amp for some time I am very pleased with the sound, and don't plan to raise the OS bias any further. My chassis is just nice and warm to the touch and could easily handle 2.0 or 2.2A bias. The heat sinks are about the same size as the Modushop Dissipante 4U, 400mm deep chassis. I took the extra step of adding an aluminum L bracket along the bottom edge to help spread the heat into part of the base plate. I've done that with all of my bigger amp builds lately.
 
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look for Babelfish J thread

several powerful bstrdz were made

powerful - multiply outputs , crank Iq

Well, aehm, I am not sure which thead you are referring to. I found this one, but I have a hard time to absorb all the goodness. I simply don't understand what your're writing. Donuts, critters, bstrdz. Whaaaat?

Is there plain English description of the Babelfish, with a schematic, parts values, explanation how it works, and description of how it is different from the Aleph J?


It is certainly possible to build an Aleph J that is capable of handling lower impedance loads quite well. Using the diyAudio PCBs, I substituted a 10V zener diode for the current source about the 'J74 JFets and adjusted R8 to get the diff pair current back to 8 mA. I also put a 200 Ohm resistor in R30 to drop the voltage a little more and provide an easy way to measure that current.

Not sure which schematic you are referring to (R30?). However, I believe your changes relate to the frontend, not to the output stage. How does that make it more capable of driving low impedances? I seem to miss something, but I don't get it...
 
Official Court Jester
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......
Is there plain English description of the Babelfish, with a schematic, parts values, explanation how it works, and description of how it is different from the Aleph J?




....

it is there , on very end of first post , under condition that link isn't ooked in meantime

though , you'll need to manage with ZMengrish and slang , generally

:rofl:

anyway , that's not so important , how important is - I already gave you (loud and clear) recipe for 4-ohms capable Aleph - multiply, crank it

no replacement for displacement
 
anyway , that's not so important , how important is - I already gave you (loud and clear) recipe for 4-ohms capable Aleph - multiply, crank it

Yes, sure, that works.

However, I would like to understand what's going on between the Aleph 3 and the Aleph J:
- The Aleph 3 is specified as 30W @ 8 Ohm and 60W @ 4 Ohm
- The Aleph J is specified as 25W @ 8 Ohm and 13W @ 4 Ohm
Looking at the output stages of the Aleph 3 and the Aleph J, they look almost identical. Why do these amps have such different behaviour at 4 Ohm, even though they share the output stage? What am I missing here?
 
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Not sure which schematic you are referring to (R30?). However, I believe your changes relate to the frontend, not to the output stage. How does that make it more capable of driving low impedances? I seem to miss something, but I don't get it...
The schematic I'm using is the one in the first page of the Aleph J Illustrated Build Guide
My first paragraph is about the input stage of the Aleph J. The second paragraph refers to the output stage. There is more than one way to improve the current capability. As ZM has already mentioned, increasing the bias current helps. It also helps to increase the Vds across the output stage transistors, either with original IRFP240s, or better yet, Mosfets with higher transconductance. IRFP140, IRF150, etc. The improved transonductace is only realized significantly with increased Vds.
 
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6L6

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Aleph 3 has 3rd parallel transistor per stage and higher bias, which is why it can put more current into 4ohm.

Unless you listen at very loud levels regularly, you will find the AJ to have enough power. It's a fantastic amplifier. :yes:

If you want to build something bigger, that's also a great idea. Use Toshiba 2SJ313 in the diff pair and it will get you a huge dose of the AJ sound.
 
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There was an Aleph power calculator once - a little Excel sheet that allowed you to calculate power into 8R and 4R at different rail voltages and bias currents, along with showing the dissipation and MOSFET temperature.

I have it on my computer at home, but am away for a few days. Maybe somebody else remembers this handy little sheet.

Mostly responsible for the power at 4R output load is the overall bias current per side, whereas for 8R, the strongest relation is to rail voltage.

Best regards, Claas
 
Please help me find a malfunction.
One amplifier channel started working immediately; in the second, problems started. The sound is poorly audible with noise. The quiescent current of the output transistors is adjustable and set to 0.4v Thank you very much.
 

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it is there , on very end of first post , under condition that link isn't ooked in meantime

There is a "link to final schematic and parts placement", but that link just takes me to page 4 of the "About possible Babelfish J interest" thread. I don't see the documentation there. Can you provide a link to the documentation?

It also helps to increase the Vds across the output stage transistors, either with original IRFP240s, or better yet, Mosfets with higher transconductance. IRFP140, IRF150, etc. The improved transonductace is only realized significantly with increased Vds.

Ok, thanks, that's useful!

Aleph 3 has 3rd parallel transistor per stage...

Are you sure? The Aleph 3 Service Manual shows only two transistor pairs.

There was an Aleph power calculator once...
...This one?

Ok, that makes a lot of sense. Output voltage is limited by the +/- rail voltage (minus some residual voltage drop across the MosFETs), and output current is limited by bias. Normal Class A stuff as we know it, easy.

Now I am just trying to understand what I found about the Aleph 3 and FirstWatt Aleph J so far:

Looking at the Aleph 3 Service Manual it looks like each transistor pair is biased at approximately 1 A (0.5 V across the 0.47 Ohm resistors), giving a total of 2 A for both transistor pairs. With +/- 25 Vdc rails, thats 100 W heat dissipation at idle.

What's the bias current the rail voltage of the Aleph J as it is/was sold by FirstWatt? I guess the current was quite a bit less than with the Aleph 3. The lowish 4 Ohm power rating suggests the bias current was quite a bit less. Why is that? Maybe the FirstWatt chassis gets too hot at a higher bias current?

What is the recommended max. bias current per transistor pair with the Aleph J, assuming the heatsinks are not the limiting factor?
 
Official Court Jester
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There is a "link to final schematic and parts placement", but that link just takes me to page 4 of the "About possible Babelfish J interest" thread. I don't see the documentation there. Can you provide a link to the documentation?

#138

if you read first 200 or so posts in linked thread , you'll have most of your questions answered

besides , when Aleph circuit is in case , always take in account so called Aleph AC Gain , which represents amount of Aleph CCS current contribution in output current

so , Aleph is an Aleph is an Aleph , only some are more Alephy than others

:clown:
 
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