Moding this phono preamp ?

[gaetan8888]

Hello

A friend bring me a RCA phono preamp, I will recap it and mod it for him.

Any suggestion of better transistors than the 2SC2240 for higher gain and lower noise ?

The schematic was in the cover of this preamp, it's a quite simple one, but can it be modified a bit to be better ?

Thank

Bye

Gaetan

 

[gaetan8888]

Hello

How about the MPSA18 to replace the 2SC2240 ?

Thank

Bye

Gaetan

 

[syn08]

Hello

How about the MPSA18 to replace the 2SC2240 ?

Thank

Bye

Gaetan

MPSA18 will only worsen the noise. 2SC2240 is a very good low noise device, Made In Toshiba.

The original design has negative feedback, so changing the trasistors will barely impact the gain. Besides, you don't want to change the gain, anyway.

Leave it as is on the transistors side.

 

[gaetan8888]

Hello

I have lot of MPSA18, and I have also lot of BC546 and 2N5551 but they are a bit noisyer than the 2SC2240.

Looking at the schematic, the gain are maby too low for a stand-alone phono preamp, so it could be a kind of phono adaptor who would be plug into the input of a line preamp, since lot of preamp or integrated amps today do not have a phono input.

At least it have a voltage regulator.

Thank

Bye

Gaetan

 

[mjf]

hello.
the power supply cap (c 107 220uf/50v) is really small...........i would use a bigger one (1000uf or so.....).
the volt rating of the filter cap c99(100uf/25v) is to low.......i would use a cap with 35v or so........
output cap c 56(0,22uf) is small..........2,2uf or more.
input cap c 54 (4,7uf) could be substituted with a film cap 1uf (quality of filmcaps is better than elco's).
greetings................

 

[gaetan8888]

Hello

I agree about those cap, that's why I was intend to recap the preamp and ps.

So, even with only two transistors, (after changing those caps)that preamp circuit are good ?


Thank

Bye

Gaetan

 

[gaetan8888]

Hello

After a close look at the preamp board, I've found one 1K resistor who was not on the schematic, so here is a revised schematic with that 1K resistor between the power supply and the right and left channel of the preamp.

Thank

Bye

Gaetan

 

[mjf]

hello.
that is a simple standard circuit.it was very often used in amplifiers and receivers (my old beomaster 1000 uses it too...).minimalistic but it works........

 

[mjf]

there is annother example for that kind of phonopreamp.......they all are similar...........
greetings...............

 

[homemodder]

Gaetan

Have a look at the adressing John curl concerns on low noise design, theres some good input there concerning transistor selection in the last 2, 3 pages.

 

[ticknpop]

Change the resistors to metal film, change the input and output caps to Blackgate or Muse, the small caps to polystyrene, and recap the power supply caps , change the diodes to 1n4936 fast /soft recovery type. That's about all you can reasonably do with this simple unit.

 

[gaetan8888]

Hello

I've just try it today, sound good but there is a small hiss noise wen I use a head-phone.

I will look for replacing caps and some resistors.

Thank

Bye

Gaetan

 

[ticknpop]

the 1% metal film resistors will be noticeably quieter (less hiss) than the 5 % carbon films that I expect are there now - if that's what you need to improve .