Aleph J for Universal Mounting Spec

[Marra]

I did exactly the same changing from an F5 to the J and mine is the same but it is only a relatively gentle thump.
Nelson says in the manual that " switch on /off noise is gentle in this amp " although how that equates to actual noise level...?
It will be interesting to see if removing the 2k2 resistor helps.

 

[Zen Mod]

it really depends of actual RC constants and mechanismus .......

Alephs are generally thump-ier than F5 , not being completely symmetric in nature ;
though - please clarify - what's big thump , for your ears ?

is it Badaboom ...... or Biiig Badaboom ?

 

[WalterW]

Before I start cutting my resistors , here is a movie of the thump:
I switch off with a rockerswitch at six seconds. Also hear the "craaahhh" sound...

MVI 5123 - YouTube

Walter

 

[WalterW]

I found some cheap 500VA, 2 x 22V donuts, at the surplus store, is it possible to run this Aleph J at around 30 Volts ? Or do I have to change some things? I have a 4 Ohm load...

Walter

 

[6L6]

The first, most important thing is to make sure that the capacitors are all 35V or better.

Then you need to watch your total bias in Watts, but other than that, you should be fine.

 

[ticktock]

What are the pros and cons of lower and higher voltages?

 

[Zen Mod]

22Vac is in ballpark , really ; no need for wasting time for analysis

only if you're interested in higher voltages .......... in that case just search for various amps from Aleph series , and imagine each of them with Jfet FE (cascoded where needed , due to higher PSU voltages)

 

[bfg4wd]

RE: video

In response to that video of turn off thump.


OUCH!

I have collected all the parts for this amp, but would not want to do that to my speakers. Sorry for not being helpful to your issue, but I am watching hoping you get a good solution.

Good Luck.

 

[Zen Mod]

WW
take exact Aleph J schematic you're using

measure everything* and write down values on that schematic and post here

*current through input LTP , all voltages etc.

that Badaboom is really Big one

 

[ticktock]

What are the pros and cons of lower and higher voltages?

I do ask cos PSU design (CLC vs CRCLC with several R values) does affect DC voltage.
Better filtering (resulting in +-22.5 V) vs higher voltage (say +-24 V)? I was just playing
with PSI designer.

 

[henryve]

Hi

I just want to get some feedback. Are there any issues on the BOM that needs attention? Are those that used it happy?

 

[WalterW]

Hi ZM, here are the voltages... left and right measure identical. Everything is measured against ground.
PSU is between 24.0 and 24.2 volts. Bias is 0,38 volts over 0.47 Ohm. meausured with a warm 49C amp.

Maybe the thump is high because of the current limiter I left out?
Thanks, Walter

 

[Zen Mod]

..........

Maybe the thump is high because of the current limiter I left out?
Thanks, Walter

there is just one way to solve a dilemma ....... put it in

even if I think that culprit is exactly there .....

 

[WalterW]

Thanks.
There is one voltage I don't understand....the 0,58V at the connection of R24 and C3...
Can you explain?

 

[Zen Mod]

that node is sort of floating - not having DC path , except when you connect 10M of your DVM ...... which is pretty meaningless

so - just ignore it

 

[WalterW]

Ignored!

I understand now why I can use 22V AC: with + and - 24V PSU I have 20V over the JFets, so with 30 Volts PSU around 25V, which is the official max for 2SJ108 / 74. Dissipation will be exactly the 200mW for the small JFet

 

[william2001]

Hi

I just want to get some feedback. Are there any issues on the BOM that needs attention? Are those that used it happy?

I made a comment way back here...

http://www.diyaudio.com/forums/pass-labs/224881-aleph-j-universal-mounting-spec-42.html#post3579550

 

[Zen Mod]

Ignored!

I understand now why I can use 22V AC: with + and - 24V PSU I have 20V over the JFets, so with 30 Volts PSU around 25V, which is the official max for 2SJ108 / 74. Dissipation will be exactly the 200mW for the small JFet

Q1b ?

you still can ....... but correct that logic

 

[henryve]

I made a comment way back here...

http://www.diyaudio.com/forums/pass-labs/224881-aleph-j-universal-mounting-spec-42.html#post3579550

Confirm: the fact that R5 dissipates 300mW, and that R5 should be specced as 1/2 Watt resistor?

I myself used an RN60D there, which is Mil-Spec 1/4 Watt, but is really a 1/2 Watt resistor (basically same as CMF60). If we get consensus I can change the BOM.

 

[didiet78]

My calculations, R5 disipates 380mW.
So R5 should be 1/2 watt minimum

Didiet