Aleph P1.7 first pictures

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#21
Clarkcr said:
Where is the universal ground? Doesn't the circuit need a ground?

Nice looking setup.

C
Click to expand...

Hi,
maybe i don´t understand your question.

Ground:

both channels have separate ground.
powersupply too.
The controlboard too.
The volume control relay shared a 12VDC supply and are switched to Control-gnd via transistors, see pic. Left and right channel are not an common ground. As i buy an second transformer, are both channels fully separate.
All pcbs are made with Ground plane at bottom. Maybe is it not a best? But singlesided layout with a straight star ground wirng is not so easy... This should be realise by next project (AX) :smash:

greetings

Adam
 
#25
rsbay said:
...Which type of MOSFET's
you have used in your design ? The original types are not available
at my favorite dealer (Reichelt)....
Click to expand...

Thanks Ralph!

Reichelt is too my favorite. 😉
I used IRF510 (SEC) and IRF9610 (Fairchild) both from Reichelt.I bought 50+50 piece , selected these from equally lot and matched in pair to 1mV. See my matching-circuit. At Reichelt you can´t buy a original sealed tube from producer, only mix.
But you can buy more and send what you don´t need back.

thx
Adam
 

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#26
Hallo Adam,

I take a look at the datasheets of the 610 and 9610 at
International Rectifier and I think about giving the 630 and 9630 a
chance. They have nearly the same data's, but the Rds_on of the
630/9630 are a little bit lower. These MOSFET's are available
at Reichelt.

Greetings from Titz

Ralph
 
#27
I wouldnt use the 630/9630. In a preamp the Rdson is of no
importance and as these Mosfets are primarily designed as
switches they dont perform too well in an analog circuit.

You may read some of the background literature by NP as well
as the construction articles about A75 by NP and Norm Thagard.

Uli

:nod: :nod: :nod:
 
#30
Hello,

I followed your tips and bought IRF610 / IRF9610 (50 pieces each)
at Conrad Elektronik. A little bit more expensive than my prefered
supplier Reichelt, but I get the "original" from International Rectifier.

In the next step I have to select the right MOSFET's for my Aleph P.
Which MOSFET should be equal ? I think the two upper current source
transistors, the two lower current source transistors and the two
amplifier transistors in the middle should have the same values, so that
both sides of the preamp are identical.

Regards

Ralph
 
#31
If I see mosfet data sheet, the input capacitances are indicated at the conditions of Vgs=0, Vds=25V and f=1MHz. Is this meaning the input capaitances are different also at different frequencies lower than 1MHz? I am wondering because the top audio frequency is considered at about 20kHz.

Hmm... IRF240 has the input capacitance of 1275pF at the above conditions. :bigeyes:
 
#32
jh6you said:
If I see mosfet data sheet, the input capacitances are indicated at the conditions of Vgs=0, Vds=25V and f=1MHz. Is this meaning the input capaitances are different also at different frequencies lower than 1MHz? I am wondering because the top audio frequency is considered at about 20kHz.

Hmm... IRF240 has the input capacitance of 1275pF at the above conditions. :bigeyes:
Click to expand...


Hi,
at higher capacitance you need more current to change voltage level at the gate (music signal). Therefore you need a driver before high power FETS.
/adam
 
#34
jh6you said:
If I see mosfet data sheet, the input capacitances are indicated at the conditions of Vgs=0, Vds=25V and f=1MHz. Is this meaning the input capaitances are different also at different frequencies lower than 1MHz? I am wondering because the top audio frequency is considered at about 20kHz.

Hmm... IRF240 has the input capacitance of 1275pF at the above conditions. :bigeyes:
Click to expand...

Actually, the first Aleph P's used IRF230's which have somewhat
less capacitance than that, and they worked fine. They did
sound a bit different than the IRF610's used later, but I've
never heard anyone express a particular preference one way
or the other.

Remember that the big capacitance figures being quoted are
Gate to Source, whose voltage changes very little. The real
capacitor to watch out for here is Drain to Gate.

😎
 
#35
Nelson Pass said:
The real capacitor to watch out for here is Drain to Gate.
Click to expand...

From your comment, I understand that the concern is capacitance between input and output (as a kind of bypass capacitor). If the amp is Source follower, then to watch out is Source to Gate?

By the way, I played BOZ and BOSOZ with different IRF numbers and, yeah, hardly detected my preference. 🙂


------
Want to see that John Travolta and Uma Thurman dance Twist of Goldfrapp............
 
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