The Aleph-X

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#2,005
My Aleph X works!

Ok,I am back been very busy.

My prototype works,but I would like feedback on several points:

1) V rails +/- 22.8V
2) actual draw on V+:3,93A
3)actual draw on V-: 3,84A
4)offset vs ground: 543mV and 500mV approx.
5)offset between speaker outputs:40-58mV approx.Now,30mV.It is hot...

I have a total of 8 IRFP 240.Source resistors are 0,47 ohms.The reading on those is correct assuming draw

I must say that I had to deal with the famous resistors from outputs to Source pins of the differential.
I started at 2k2.Offset to GND was- 8,9 V or so.
I went for 4,7k.Even worse:-21V offset to GND!
With 1k I went to -2V,which was better.
To balance the circuit,I opted for 867 ohms.That way I got 500mV offset or so.The circuit is almost balanced between the current sources and the output stages.Is it a bad value that 867 ohms?

Input has a capa 4,7uF film series.

Gain is 20 or 26 dB,anyway like Alephs.

The PSU is 1000VA with 2 diode bridges and a Pi filter of only 88.000uF-0,97 ohms-88.000uF.

When I hooked up to the speaker I thought it wasn't working;I have NO NOISE at all on the 97dB/W/M speakers !But it works quite fine.

The 2 9610 of differential pair are not thermally linked together.Shall I do so ?

Sound is close to original Alephs.However,I have the impression that medium and treble are cleaner and more subtle,a wider variety of sounds.More different colours.

The bass is cleaner I think.Less round and more focused.I have to build the second prototype to know it really.

I would like to increase bias,but I will have to add more sinks !!!

Nelson ? Is my baby OK ? Or am I dreaming ?
:cannotbe: :bigeyes:

Thanks for feedback,

Best regards to you all

Anael
 
#2,006
I have forgot to mention that R series with the 220uF cap (gain in current allowed to CCS) is 1k5. I should try to go for 750 ohms maybe,to allow more current for peaks.

Tonight I will rise a bit bias,to get to 4.2 A total.

Accordingly,if I calculate

V out peak = 22.8- 2.5 X 2 (remember my outputs seat 500mV below GND)=40.6V peak

Peak current is actual bias,so 4A

P=40.6 X 4 =162.4 W peak,so 81.2W RMS

Am I right? Please guys tell me !!!

Maybe I will search for less absolute DC offset,so I propose to get the Magic Resistors from outputs to Source pins of the differential a lower value,let's say 600 ohms or so.

Nelson,you vanished...:ghost:

Where are you ? :devily:
 
#2,007
Nelson Pass said:
I have taken output-to-differential-Source resistors
down to 2.2K without seeing any problems. Probably
they could go lower, but between this and ground
loading of the outputs and adjustment of the current
source for the diff pair, you should be able to nail the
absolute DC.
Click to expand...

Nar , you do not mention VR2 for the diff pair current source variations , why ?

I set the absolute dc at fiew millivolts this way .

Total current / channel at 3.8 A.
 
#2,008
Stephanobilliani,

The VR doesn't seem to vary enough DC offset for me.

Looking at Grey's original schematic,I made a mix from Rtirion and

V2 is now 250 ohms

R26 is 470 ohms

R24 is 221 ohms

What are the values you use for those resistors ? Thanks.And which is your latitude for offset ( VR at max,DC offset and VR at min,DC offset ? )

Maybe I can't vary bias diff.pair enough

Which is your value for the Magical Resistors ?

In your version,how many power mosfets ( i.e P240 ) do you use for the whole amp ? ( I don't think about the 9610s )

Great thanks for reply.

Regards,
 
#2,010
It will go to 300.000 Mr Pass!

Thanks very much for coming on the diyaudio.com.

Have you seen my results?What do you think about this strange value of 867 ohms for output-to-source resistors ? Only way for me to get acceptable absolute DC.

I guess something is wrong with values of resistors for varying bias into the diff. pair :devilr:

Regards
 
#2,011
nar said:
Stephanobilliani,

The VR doesn't seem to vary enough DC offset for me.

Looking at Grey's original schematic,I made a mix from Rtirion and

V2 is now 250 ohms

R26 is 470 ohms

R24 is 221 ohms

What are the values you use for those resistors ? Thanks.And which is your latitude for offset ( VR at max,DC offset and VR at min,DC offset ? )

Maybe I can't vary bias diff.pair enough

Which is your value for the Magical Resistors ?

In your version,how many power mosfets ( i.e P240 ) do you use for the whole amp ? ( I don't think about the 9610s )

Great thanks for reply.

Regards,
Click to expand...

The need for changin imput to ground rsistors (R19 R29) from 10k to 68k was the first thing when I tested the circuit, as the absolute dc wasn't good .I say 15 or so volts.
The resistors from the output to the sources of the diff pair are 4.7k and for me is hard taming the dc offset varing this ones .
I notice large variations of dc as you report , changin this resistors.
VR2 give large variations also but the position depends by the current trough the output mosfets.
For me R24 is 475, VR2 220, R26 330.4 mosfets/channel R5 R6 etc. 0.33 ohm.
Setting VR1 and VR3 for the max current VR2 voltages variations are from -11 to + 5 volts.
Rails : +/- 15 volts

Stefano
 
#2,012
Ok,so I changed a lot of stuff.

I went to 2k2 for the famous magical resistors.

I got 475 ohms for R24,332 ohms for R26 and a 200 ohms trimmer,like in Grey's version.

I re-ran the circuit,and this time I can adjust absolute DC to 0V !

But varies + and -,I have to wait for temperature equilibrium for

precise 0V.Around 0V,the offset goes - 30mV and then to +30mV,and again.

My bias is now a little over 4 A. Sink temperature is OK.

I have to wait 2 hours.Listening !

What a pleasure
:nod: :nod: :nod: :nod: :nod: :nod: :nod:

Thanks Staphanobilliani !!!

PS:The draw of the Aleph Current Sources seems higher than the output stages.In other terms,more draw on V+ than on V-.I have no explaination.The values for R 39 and R 35 are 221 and 100 ohms respectively...

:idea: If the to92 NPN for output stage sense was limiting current...I have no clue yet however.

Regards
 
#2,018
AC current gain adjust in Aleph X

Hi everyone,

Could someone give me the recipe to adjust the AC current source gain to 50 % ???

I have a BF generator non balanced out,and a good multimeter but non True-RMS type.I have no scope :bawling:

But I guess it must be simple to adjust when having clear explanations :nod:

Thanks for feedback

Regards

Anael
 
#2,020
Re: AC current gain adjust in Aleph X

nar said:
Hi everyone,

Could someone give me the recipe to adjust the AC current source gain to 50 % ???

I have a BF generator non balanced out,and a good multimeter but non True-RMS type.I have no scope :bawling:

But I guess it must be simple to adjust when having clear explanations :nod:

Thanks for feedback

Regards

Anael
Click to expand...

Been covered in several threads but essentially I think you could do this:

Disconnect R10 (or whatever the resistor is called that feeds back to the current source). Run a signal into the amp driving a constant load and measure the voltage variations on the source resistors of the output stage. Now connect R10 (...) and adjust until that variation is half of the original value. Then the contribution from the current source is half.
 
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