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help designing preamp
help designing preamp
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Old 11th April 2003, 12:10 PM   #1
strulon is offline strulon  France
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Location: island of reunion / paris
Default help designing preamp

hello, my name is fred i just discovered this forum i think it is going to be one of my favorites right now

well, i need your help please

here you can see one ECL86 mu-follower stage preamp schematic

Click the image to open in full size.

i ve been told it was a very good one
so i ve been badly challenging me trying to make a basic 6 channel preamp with it, putting three of them in serial.
I ve already been able to design the circuit, but some questions remain unsolvable for my pour skills:

for the stereo preamp, the alim transfo characteristic is:
primary 220V
secondary: 2*220V 40mA
1*6.3V 1A

so i need a transfo with 2*220V 120mA and 3*6.3V 1A secondary,
i know i could use a single 6.3V 3A but like this it is easyer to build the circuit

what i would like to know is, if someone can explain to me:

what component values are going to change?
i think R25, and C7-R27-C8 pi filter, but what will be their values?

please help!

thank you
frederic awaoki

you will find the schematic and the list of components here for an easier overall view


of course i give you the original values of all components:

- Résistances ħ5 % 1 W
R1 - 2,7 KOhm
R2 - 150 Ohm
R3 - 220 kOhm
R4 - 1 kOhm
R5 - 180 Ohm
R6 - 15 kOhm (2 W)
R7 - 470 kOhm
R8 - 150 Ohm
R9 - 150 Ohm
R10 - 22 kOhm
R11 - 10 kOhm
R12 - 2,7 kOhm
R13 - 150 Ohm
R14 - 220 kOhm
R15 - 1 kOhm
R16 - 180 Ohm
R17 - 15 kOhm (2 W)
R18 - 470 kOhm
R19 - 150 Ohm
R20 - 150 Ohm
R21 - 22 kOhm
R22 - 10 kOhm
R23 - 47 Ohm
R24 - 47 Ohm
R25 - 150 kOhm
R26 - 47 kOhm
R27 - 2,2 kOhm (2 W)

- Condensateurs non polarisés
C1 - 0,22 µF / 250 V
C2 - 10 µF / 250 V
C3 - 2,2 µF / 400 V
(ou électrolytique 2,2 µF / 450 V)
C4 - 0,22 µF / 250 V
C5 - 10 µF / 250 V
C6 - 2,2 µF / 400 V

- Electrochimiques
C7 - 100 µF / 400 V (ou 385 V)
C8 - 220 µF / 400 V (ou 385 V)
C9 - 100 µF / 100 V
C10 - 1000 µF / 16 V
C11 - 1000 µF / 16 V

- Divers
T1-T2 : ECL86
P1-P2 : pot 22 kOhm or 47 kOhm Log
D1-D2 : 1N4007

TR1 : primaire : 220 V
secondaires :
- 2 x 220 V / 40 mA
- 1 x 6,3 V / 1 A

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Old 11th April 2003, 05:54 PM   #2
Elkaid is offline Elkaid  Canada
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2 threads were talking of this preamp in the past so here's one :

I built it and I'm not disapointed at all. However, I don't understand how you're ending up with 2X220V 120mA and 6.3V 3A.

On mine, I simply use the suggested 2X220 40mA and 6.3V 1A and everything's fine.

You should try to build the preamp as it is on the schematic and try some tune-up once you know it is working fine.

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Old 16th April 2003, 10:13 AM   #3
strulon is offline strulon  France
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Join Date: Apr 2003
Location: island of reunion / paris
hi elkaid, i m ending up this power because it s a 6 channel preamp i want to build, so three times more power in fact...
but i found answer to my question, it s evil simple...
so i ve ended my circuit design after lot of troubles and now i have to make it build, the difficult thing is to get it to come under a certain surface corresponding to the maximum size my electronician can build the circuit
to be continued..., i ll post some pics by the time
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