new born aleph 3 need help Dr. Pass

[jeapel]

hi
supply = +-25
irfp140n +irf9610 +mpsa18

my new aleph 3 is under test all dc voltage are ok just
change 2 things:

1-my aleph current source was unstable but with 1nF
on mpsa18 base and collector it s rock stable now

2-my bias was 1.7A change R113 for 47.5k + 30k and
now my bias is 2.1A cold and 2.05A hot

first good news

- very good 200khz @ -3db maybe because my input
stage is 25ma not 20ma ccs
- 10khz square wave test is good just a very small overshoot

bad news :-(

I m lost to check aleph current modulation

-test no 1 :
-------------------------
F=1khz
Vout=45v peak to peak
load = 8ohm power resistor
my scope is on one .47ohm (upper aleph source resistor)

with vout=0 volt on .47 = .5v
with vout=45vpp the voltage swing between .05v and .92v

.92 / .47 = 1.95A x 2 for aleph 3 =3.91A peak
is it normal or normal is 3A or 3.5A or ???

-test no 2:
--------------------------
F=1khz
Vout=45vpp
scope on AC position

650mVPP on rout .1175 (4 x .47)
870mVPP on one upper aleph .47 source resistor
450mVPP on one lower irfp140 .47 source resistor

but no idea what to do for check my 50% modulation
with these voltages

thanks

 

[Zen Mod]

nice table underneath that ugly amp


http://www.diyaudio.com/forums/showthread.php?postid=438837#post438837

 

[jeapel]

hi choky

I give you the table or alpeh make your choice

your url post is speaking remove some resistor to test

but must be possible without remove.

please confirm :

aleph 3 bias=2A max peak current on .47 with
45vpp is ??

thanks

 

[Zen Mod]

hehe- I think that both-the table and aleph are perfect where they are ...
in any case- seems that English is not native language for both of us,so it's maybe easier to quote Master of Latheral Thinking And Vertical Mistfets :

" you generally want to set the gain so that
the AC variation of the current source is about 1/2 the output
current. It can be more or less, but 50% gives the optimal
energy efficiency figure.

You will note in the Aleph schematics that the Base of the NPN
transistor which controls the current source attaches to the
output of the amplifier through an RC network. The value for
C is set arbitrarily high so that it does not interfere with audio
frequencies, and it is the value of R which is the most convenient
spot to adjust the gain of the current source. For the purpose
of this discussion, I'll call it R0.

If you set the amplifier driving a sine wave into a load (let's say
16 Vrms into 8 ohms at 100 Hz), you can measure the current
variation of the gain N channel Mosfets (whose Sources attach
through power resistors to the - supply rail) with a cheap AC
voltmeter placed across one of these Source resistors. With
R0 taken out of the circuit, you will get one AC value across the
Source resistor (say 470 mV, for example). As you put a value
for R0 in the circuit, this will decline, and when it measures 1/2
the value without R0, you have reached 50%. If it measures
1/4 the value, the current gain of the Aleph source is 75%, and
this figure is too high for a standard Aleph. Most listeners like
the Alephs at 50% or lower, so I recommend between 50% and
100% of the AC voltage value compared with no R0"


if you read that slowly ,you'll realize that sayed R0 is nothing else than that little resistor in series with 220UF-going from output rail;if we look at same pdf -that's R114 =750 ohms
trust me-or trust Master - lifting one leg of sayed resistor in measuring purpose is easiest way for testing current gain of Aleph CCS....besides-that resistor is exactly one you need to decrease or increase for adjusting sayed current gain

from top of my head- sum of upper 0,47 resistors AC current modulation must be exactly half of AC current modulation through output 0,47 resistors....but-you must know that I do my typing on the end of pretty long day........my brain is not exactly capable for simple equitations in this moment

 

[Zen Mod]

650mVPP on rout .1175 (4 x .47)====(0,65/0,47)x4=5,53A

870mVPP on one upper aleph .47 source resistor====(0,87/0,47)x2=3,7A

450mVPP on one lower irfp140 .47 source resistor===(0,45/0,47)x2=1,9A


seems that your goal is 5,5A/2 ~ 2,25A or less for CCS or-even easiest to say- same AC voltages at lower 0,47 and upper 0,47 resistors

for start-increase that R114 to 1K and then measure again



I must go to sleep..............

 

[jeapel]

ok no choice to remove 750ohm to do a good test
i will do next possible day and give you feedback

thank you very much choky

 

[jeapel]

hi choky i just finish the test and it s work great

test no 1 for volt on lower .47 :

R=750 F=1Khz

Vout=10VPP without=300mVPP
with=105mVPP
---> 105/300=35% ---> 65% AC gain

Vout=20VPP without=600mVPP
with=205mVPP
---->205/600=34.17% ----->65.8% AC gain

I m surprise the AC gain is constant with variable Vout

with 1Kohm test i fall right on 50% AC gain

after reading test no 2 for AC gain test without remove resistor
but not sure check that choky:

Ac gain ??=I upper .47 (x 2 for aleph 3) / I out

I upper=(.87/.47) x 2=3.7A
I out= .65/.1175=5.53A (.1175 = 4 x .47 )
3.7/5.53=67% ~= 65%

my next step will be to update my tube preamp to lower gain
but do you have a opinion on tube preamp for aleph 3

and for you what is the best preamp , tube or boz or boboz or aleph P or ?

thanks

 

[Zen Mod]

hi choky i just finish the test and it s work great

test no 1 for volt on lower .47 :

R=750 F=1Khz

Vout=10VPP without=300mVPP
with=105mVPP
---> 105/300=35% ---> 65% AC gain

Vout=20VPP without=600mVPP
with=205mVPP
---->205/600=34.17% ----->65.8% AC gain

I m surprise the AC gain is constant with variable Vout

with 1Kohm test i fall right on 50% AC gain

after reading test no 2 for AC gain test without remove resistor
but not sure check that choky:

Ac gain ??=I upper .47 (x 2 for aleph 3) / I out

I upper=(.87/.47) x 2=3.7A
I out= .65/.1175=5.53A (.1175 = 4 x .47 )
3.7/5.53=67% ~= 65%

my next step will be to update my tube preamp to lower gain
but do you have a opinion on tube preamp for aleph 3

and for you what is the best preamp , tube or boz or boboz or aleph P or ?

thanks

if I undertand you corectly-with 1K as R114 you have on upper 0,47s exactly half of output current?
if that's case-you made it.....

besides-this calcualtion looks OK to me:

"I upper=(.87/.47) x 2=3.7A
I out= .65/.1175=5.53A (.1175 = 4 x .47 )
3.7/5.53=67% ~= 65%"

but only as example just because your goal is 50%....


preamp?
I dunno really-somebody else must give you advice about that...I made just BOZ 'till now,and I have doubts that I'll made some other ,just because in preamps that's not my cup of tea...you can always look at my site what is my cup.....

maybe one of this days I'll play a little with BOZ variation with some nice piece of iron in output-that's why I made it in first place

BTW -which tube preamp you use?

 

[Zen Mod]

I m surprise the AC gain is constant with variable Vout

why you are surprised?

its basic premise of NP's patent of Aleph CCS...Constant DC current,but also constant AC current gain......

 

[jeapel]

if I undertand you corectly-with 1K as R114 you have on upper 0,47s exactly half of output current?
if that's case-you made it.....

------sorry my english is so so yes with 1kohm volt on lower .47
20vpp without=600mv and with=300mv

3.7/5.53=67% ~= 65%"
but only as example just because your goal is 50%....

-------yes only for example

BTW -which tube preamp you use?

--------6SN7 supply=300v bias=5ma transistor ccs load
+6AS7 supply=150v cathode follower for zout=100ohm but i
need to remove the first 6SN7 because the gain is too high
for aleph but the problem with my design is fc -3db is
only 50 khz maybe a boz project for next winter

why you are surprised?

---------my first impression was very wrong something like
current modulation 50% a full power 25% at half power

thanks