Aleph J Schematic

[Zen Mod]

Papa Nelson, or Papa Choky?

even if I'm blushing now , I'm still Papa just for one child

can I even hope of possibility to reach - even 10% of Papa's helping hand length ?

naah .....

OK - let's be practical - Papa is nearer to you ........

 

[carpenter]

You're a wonderful fellow, Choky.

With all the beauty that Nelson's amps posses, I wonder if this piece would have a place in his repertoire.

We'll have to see.

 

[korben69]

I haven't seen informations about 4 x IRFP240 matching.
Does they need to be or not ?
Thanks

 

[Nelson Pass]

I haven't seen informations about 4 x IRFP240 matching.
Does they need to be or not ?

The devices in parallel are best matched to better than
.1 V Vgs.

 

[korben69]

Thank you Mr PASS, usefull hint for the BOM !

 

[bobodioulasso]

I need help in analysing Aleph J schematic.
How Q7 and Q8 are biased?
Is it only from the voltage across R7?
Is Q3 participating to the bias or is it a current limiter only?

I did not succed finding any answer into this thread neither reading articles.

 

[Bill Fuss]

I need help in analysing Aleph J schematic.
How Q7 and Q8 are biased?
Is it only from the voltage across R7?
Is Q3 participating to the bias or is it a current limiter only?

I did not succed finding any answer into this thread neither reading articles.

For greater understanding it would be best to study the Zen articles. They take you through every aspect of an Aleph circuit piece by piece.

Q7 & 8 are biased strictly by the voltage across R7. Q3 is used only for current limiting.

Best, Bill

 

[bobodioulasso]

Thanks, Bill.

 

[mthoi]

I need some help - whether I would have any problems. I recently powere-up my AJ without installing the IRFP240 (Q5, Q6, Q7, Q8). I am using matched J74s. Some measurements are as follows ;-
i. PSU's V+ = 24.35VDC, V= -24.33VDC
ii. Voltage across R8 = 8.9V (Schematics shows 8.3V)
iii. Voltage across R7 = 8.8V (Schematics shows 4,3V)
iv. Voltage at Output ref Ground = 22.6VDC
v. Voltage across Q4 (ZTX450) Ves = 230mVDC (Schematic shows 4.3V)

I have rechecked the values of the resistors, orientation of the J74, ZTX550/450s and they are placed corretly. Are these figures faulty? Should I install the IRFP240 and re-measure?

Tx for any assistance.

 

[Zen Mod]

....... Should I install the IRFP240 and re-measure?

Tx for any assistance.

yes .

use light bulb in series with mains - for first powering up .

 

[mthoi]

Zen Mod - thank you for your response.

I have connected the IRFP240 (q5-8). My first set of 240s generated some smoke and high heat on Q7/Q8. I think Q7 shorted out - resistance across Gate/Source became 9R. Q5, Q6, Q8 seems OK but I changed all four new 240s and powered-on again.

This time no heat on any of the 240s (stone cold). V+ is 25.33V, V- is 25.29V. I have connected negative input to ground. I took some measurements :
i. Voltage across R7 = 3.45V (Schematics shows 3.4V)
ii. Voltage across R8 = 8.71 (Schematics shows 8.3V - I think it should be OK since I am on a slightly higher rail voltage)
iii. Voltage across Q4 Vse = 3.484V (Schematics shows 4.3V)
iv. Voltage across source resistors R16 = 0.030V, R17 = 0.140V, R18 = 0.596V, R19 = 0.44V
v. Voltage at output ref ground = 21.54V.

I think the voltage across the source resistor is suspect. I am keen to change Q3 (ZTX 450) but that is only for protection and should not affect the function Q7/8. The voltage at output should be near zero - what may be the cause for such a high DC voltage?

What am I doing wrong? Any suggestion is much appreciated. Tx.

 

[Zen Mod]

seems that your 2SJ74 (are they BL grade or ? ) have slightly lower Idss , so current flowing through input LTP , and down through R7 isn't enough to open lower IRFPs .

replace R8 with series connected 510R resistor and ~ 500R trimpot .

lowering resistance of that chain will give you more current through input LTP

look at this great schematic . made by Algar_emi - you'll see many details explained ; don't be puzzled with another Aleph type - they're pretty much similar

 

[mthoi]

Zen Mod - Tx for the prompt reply. The 74s are BLs - I would put in a trimpod as suggested and re-measure the voltages based on Algar's A30 schematic.

 

[Zen Mod]

dunno - will this help you more :

 

[mthoi]

Thank you Mr Pass for sharing your incredible design for AJ.

Thank you ZenMod for your assistance to help me debug the AJ ciricuit. I finally got one channel working and is playing music. i have traced the error to Q6's (IRFP240) drain connection to V+. I changed all the jfets, mosfets and some resistors - viola! it is playing music. I would spend some time during Christmas break building the 2nd channel.

2009 is drawing near and we are all looking forward to a much better, exciting 2010. May I take this opportunity to wish you and the family

MERRY CHRISTMAS

And

HAPPY NEW YEAR !!

May everyday of the new year greets you all with Peace, Joy, Health and Fortune.

 

[mthoi]

I have both channels working and started the burn-in process. The sound is fantastic - great clarity, sounstaging and "airyness".

I need some suggestion to rectify the turn-off "thump" sound coming from the speakers when I switch-off the AJ.

Merry Christmas.

 

[mach.88]

Hey mthoi,

congrats on your working J!

I have a original J and a clone and there is no way I would have succeeded to get rid of this nasty turn off thump. Its just there and so you should learn to live with it.

Papa once mentioned something about the thump to be there and it seems, he just left it where it was.

Over the time I got used to it.

Merry christmas!

 

[Rodeodave]

I think I remember it has to do with the fact that two voltages from the PSU don't decrease equally fast when the amp is switched off. Maybe play with different bleeder-resistors?

 

[bobodioulasso]

You could use a relay to disconect the speakers when switch off. Though i fear that in't in the Pass line.

 

[Tea-Bag]

lift the speaker grounds with a DPDT?