AlephJ Mimi! (Mini)

[lykkedk]

Hey here.

I am collection part from my messy shop

Only thing i miss is this 50K trimpot. -I have an 100K trimpot, and i think i can use it instead, if i short the 47K R27 resistor.

Stupid or good enough for testing ?

Jesper.

 

[didiet78]

Keep r27, for safety reason

 

[Zen Mod]

you can use 100K , you'll just have half of useful turns

presuming that you're using multiturn

only Papa is versed enough to use simple turn pots , everyone else is sissy

 

[lykkedk]

Yes...

I am using 25x turn one's- I will just put maybee 5-10K in front of the 100K trimmer for avoiding "0" ohm. - Well maybe just i use a short, i allways place such trimmer halfway anyway

only Papa is versed enough to use simple turn pots , everyone else is sissy

Speaking of sissy... guess what's used when painting the big Cu traces

Jesper

 

[Zen Mod]

?

 

[lykkedk]

?

 

[lykkedk]

Stuffing board up a bit this evening

Jesper.

 

[Zen Mod]

be careful with mosfet mounting

it's easy to pill out traces , when mosfets are soldered like that ( no support from above)

 

[lykkedk]

be careful with mosfet mounting

it's easy to pill out traces , when mosfets are soldered like that ( no support from above)

Yes... I see you are right. Thanks.

Jesper.

 

[maiko]

Hello Jesper, seems like a nice build!
One question though, what is the function of adding C3 and C6??

 

[lykkedk]

Hello Jesper, seems like a nice build!
One question though, what is the function of adding C3 and C6??

I cant tell; but the 220uF is in original schematic.

Jesper.

 

[didiet78]

C3 , C7 functin : fill empty space of pc board

 

[maiko]

Ok, I think I found the schematics in Jespers earlier post.
http://www.diyaudio.com/forums/pass...j-whatever-maybee-jfet-input.html#post4933856

It is a schematics of First Watt Aleph J (C)2005, there is Q4, if I understand the function of it, is to current limit the output transistors to roughly ~1,5A, but C3 seems to modulate the current limit?
I am lost, maybe you are right Didiet haha...

Mr. Pass, please explain C3!

 

[Zen Mod]

Aleph current source

 

[maiko]

Thanks ZM!
I found a good description how it works, easier reading than patents (# 5,710,522).
https://www.passdiy.com/project/amplifiers/zen-variations-9

 

[lykkedk]

I assume -In have to be connected to GND for test/best performance?

Jesper.

 

[Zen Mod]

when testing/setting - ground both inputs , no load on output

when singing - if you use RCA , ground neg input

 

[lykkedk]

when testing/setting - ground both inputs , no load on output

when singing - if you use RCA , ground neg input

Ohh yea! i remember now... thanx.

Jesper.

 

[lykkedk]

Testing

Hello.

I assume that this is the right procedure, when testing/powering up ::

Short -IN and +IN to GND

Plug in mains (Variac, lightbulb is only for Sissy )
PSU is +18 - "0" -18 VDC

Meassure voltagedrop across R16 (Source resistor Q5)
This is BIAS, but howto calculate this ???
I expect this voltage to be around 0.5V for Bias >1A ???
Bias is adjusted with R27 trimmer.

When everything is good, also adjust DC-offset with R7 trimmer.

Normal procedure after that, let amp. warm up and settle, then readjust and see if everything is stable and temperature is not to hot (>55C)

Jesper.

 

[lykkedk]

So everything is stuffed up now...

Just have to prepare my PSU... maybee test this betabuild in next few days?

Have a good weekend all.

Jesper.