Aleph J illustrated build guide

[Zen Mod]

Here is the question: mouser did not send me 22K for IN - input. Can I run amp without it if I do not use balanced input and connect In- to the gnd?

Dodo

put temporary 2 x 10K in series instead

cuttin' resistor from Pa's schematic is usually tough challenge

 

[PKI]

Thanks ZM! I am not that bad ;-) one local guy asked me to come and help him to fire up his amp. There are no other resistors at his place. That's the thing. I will go and check local radio store tomorrow.

If it was my amp I would try to improvise and probably fire it up without the resistor, but the amp is not mine

 

[lykkedk]

Setting bias, choosing inputs ?

Hi.

Speaking af inputs, i was wondering the following ::

1. Do i have to short both +IN ans -IN to GND when setting ?, or does it matter at all ?

2. What is the difference of using -IN or +IN and GND for normal RCA inputs ? (I see a C1 cap at -IN, whats the use of that)

// Jesper

 

[6L6]

1. No
2. Use +IN and GND for RCA inputs. Jumper -IN to GND .

 

[lykkedk]

Thanks

So i leave - in and + in open when setting bias and dc offset ?

// Jesper

 

[Zen Mod]

everything just cobbled together , when setting bias

meaning - + input , -input and ground

just tie them together ..... in one big knot

 

[lykkedk]

Okay....

I thought so.. Making sense to me

I am not there yet ... Have to solder a bit more.

// Jesper

 

[lykkedk]

It's ALIVE

Who cares how it sounds ?

Okay... Jokes off... At least i think the pcb, parts is working.
--- the bias settles fine, and dc-offset is also easy to adjust




// Jesper

 

[6L6]

Wonderful! Congratulations!'

Let it sit for 1/2 hour and see if anything needs adjustment.

Those are beautiful heatsinks - they should run fairly cool (for an Aleph...)

 

[lykkedk]

Aleph J fro, scratch part II - Stuffing and testing

Hi..

Please look at direct link to photobucket, as the pictures are getting weird, when linked direct here.

I must say, that i am a little impressed by this amp. I tried to give it 1v/pp ~1000Hz sine, at the input. Looking at the output, it (gains) 8 times the input.

I tried to crank up the inputvoltage, giving it more volts, ended up with the Aleph J clipping at approx. 30-35v/pp

This is excatly what the manual says...

Next part is to listen to it.

// Jesper

Aleph J From Scratch Slideshow by Jesperlykke | Photobucket

 

[Zen Mod]

8 times ?

time for ophthalmologist ....... .or brain doctor .......... or Magura

you choose .......

 

[WalterW]

yes, I thought gain was around 10 times (9.6) 19.6 dB...

 

[lykkedk]

As a matter of fact.

I was seeing approx. 8v/pp sine (not accurate) at the scope, when feeding it with 1v/pp...

The sine was fine, so to me, everything looks normal.

//Jesper

 

[JohnGeneva]

Jim, for the Aleph Will it be an issue using 74GR instead of BL fets, Supplier has lots of GR and can match at .1.

 

[Zen Mod]

use 2+2

 

[6L6]

The Greens are low on the Idss scale, so not ideal. With a few mods to the circuit they could be made to work, but if they have the Blue, then use those.

Edit - I just saw Zen Mod's post - paralleling greens is a perfectly good idea. You just need more of them.

GR - green
BL - blue
V - violet

That is Toshiba's code for Idss range

 

[JohnGeneva]

thanks

 

[JohnGeneva]

Zen, to make sure I understand, 2 plus 2 would simply be putting two GRs in parallel, gate to gate, drain to drain, and source to source, and then installing them together in the pcb board instead of one 74BL? Is this correct.

Thanks, John

 

[Zen Mod]

either like that , or piggy-back ( underneath the pcb )

as one of our Dodo's is sayin' - If it's not Boeing , I'm not goeing .....

in other words - better more xconductance than eeny weeny ...

 

[JohnGeneva]

Good idea! Thanks.....