Aleph J illustrated build guide

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#1,261
jacco vermeulen said:
In my experience, a power amp will require a maintenance job long before it reaches end of life. (as a car, a washing machine, yacht, airplane, or anything military)

Ever seen what the goop under power devices in a class A power amp looks like after 15 to 20 ?
Click to expand...

I used Keratherm insulators 😉

That and the diyAudio PCB's have pots for bias and offset. I left mine in ... in the HOPE that I only ever need a screwdriver for maintenance!

But this is all just wishful thinking after all ... 😛
 
#1,262
A overheated amp (read undersized sinks) will eventually break the output devices.
No one knows how the device fails,
It might just as well send a huge voltage offset (rail voltage) down in the direction of your expensive speakers.........

Well thats prob. just negative thinking from my side..🙄
 
#1,273
due to working principle of said first stage , value of R1 is input impedance of stage , ratio and values of these two are replicated/mirrored on negative input (R3 and R4) ...... so just imagine it as simple operation amplifier with those two resistor pairs

not easy task to fiddle there , without unnecessary phase altering and tone control effect

add there , spicy isn't it , correlation of C5 with R4 ....... and fun is complete

:clown:
 
#1,274
just as little illustration - remember that nice little amp - Musical Fidelity A1 ?

I really like(d) it ; besides miniscule temperature arrangement , beancounter's PSU capability , actual power amp schematic is pretty damn good

but , there is something fishy else - OP based preamp stage was made with ALPS pot in nfb path - resistor value from output to input is made variable

so , besides screeching pot after some time , there wa free equalizing effect

result - toss everything active preceding power amp stage and amp is suddenly half decent

sell it , buy some parts and make it as proper Papamp and you're having ton of fun
 
#1,275
Thanks a lot for your answers Zen Mod 🙂

I considered the pot/attenuator as I'm going to feed the amp from SE source and I focused myself on 'in+' input and totally omit the 'in-'

Theoretically using a quad ladder to keep R1 equal R3 and R2 equal R4 could help a little bit. But the C5 constant value problem will remain.
 
#1,276
Zen Mod said:
but , there is something fishy else - OP based preamp stage was made with ALPS pot in nfb path - resistor value from output to input is made variable

so , besides screeching pot after some time , there wa free equalizing effect
Click to expand...

I have a Telefunken Empress II console that I restored that also did this. It seemed they wired the feedback into the bottom of the volume pot so as volume decreased, feedback increased to help at the lower volume levels. Interesting design ala Peter Baxandall! 😎
 
#1,278
I just finished to read the complete thread. Thanks for all the usefull informations shared.

I'm planning the build an Aleph J and I, despite reading the full thread, still have some questions.
-This will be my first DIY project (except the crossovers of my speakers and and a J-Fet RIAA preamp kit). Do you think this project is within reach for a newbie?

-My speakers are Altec 414-8B in Petite Onken enclosures with Altec 808-8B on 811 horns. Do you think the AJ will be able to drive it?

-My goal is to build the AJ as a kind of integrated amplifier, by just adding a source selector and a pot. Is there enough gain for that and how do I choose the pot impedance?

-Concerning the PSU, with a single primary transformer, how to use the CL60 thermistor?

Thanks a lot.
 
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