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Aleph J  versus  Aleph 3
Aleph J  versus  Aleph 3
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Old 9th September 2019, 02:26 PM   #21
Zen Mod is online now Zen Mod  Serbia
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Aleph J  versus  Aleph 3
look for Babelfish J thread

several powerful bstrdz were made

powerful - multiply outputs , crank Iq
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Old 9th September 2019, 03:21 PM   #22
TungstenAudio is offline TungstenAudio  United States
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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.

Last edited by TungstenAudio; 9th September 2019 at 03:24 PM.
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Old 9th September 2019, 04:16 PM   #23
mbrennwa is offline mbrennwa  Switzerland
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Aleph J  versus  Aleph 3
Quote:
Originally Posted by Zen Mod View Post
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?


Quote:
Originally Posted by TungstenAudio View Post
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...
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Old 9th September 2019, 04:21 PM   #24
Zen Mod is online now Zen Mod  Serbia
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Aleph J  versus  Aleph 3
Quote:
Originally Posted by mbrennwa View Post
......
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



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
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Old 9th September 2019, 04:49 PM   #25
mbrennwa is offline mbrennwa  Switzerland
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Aleph J  versus  Aleph 3
Quote:
Originally Posted by Zen Mod View Post
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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Old 9th September 2019, 04:50 PM   #26
TungstenAudio is offline TungstenAudio  United States
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Quote:
Originally Posted by mbrennwa View Post
...
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.

Last edited by TungstenAudio; 9th September 2019 at 04:53 PM.
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Old 9th September 2019, 05:04 PM   #27
6L6 is offline 6L6  United States
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Aleph J  versus  Aleph 3
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.

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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Old 9th September 2019, 08:13 PM   #28
chede is offline chede  Germany
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Aleph J  versus  Aleph 3
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
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Old 10th September 2019, 01:59 AM   #29
mpmarino is offline mpmarino  United States
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Quote:
Originally Posted by chede View Post
There was an Aleph power calculator once .....................
Best regards, Claas
This one?
Thanks to Wuffwaff
Attached Files
File Type: zip Aleph-Power.zip (6.4 KB, 20 views)
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Old 10th September 2019, 06:20 AM   #30
chede is offline chede  Germany
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Aleph J  versus  Aleph 3
Yes, exactly ...

Thanks, mpmarino, and thanks to wuffwaff !
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