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Old 7th October 2014, 03:32 PM   #1
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Default Gain Issue

I have recently gone mono block and passive pre amp route and whilst I am very happy with the results it as caused a moderate gain issue .

My moving coil is very low output ( 0.12mv ) so whilst the desired volume is okay for most occasions i would like to increase the volume for those rare occassions when i am home alone .

a Cambridge 640p feed the passive pre amp. I will shortly be replacing the cartridge and the phono amp , so i need a temporary solution .

does anybody know of a quick mod i can do the phono amp to increase the gain . changing a resistor or capacitors for example ?

thanks for any help .

p.s - I am a numpty and would appreciate if you could identity said part that requires changing based on my level of ignorance

Last edited by Daniel quinn; 7th October 2014 at 03:34 PM.
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Old 7th October 2014, 03:36 PM   #2
rayma is online now rayma  United States
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Quote:
Originally Posted by Daniel quinn View Post
My moving coil is very low output ( 0.12mv ) so whilst the desired volume is okay for most occasions i would like to increase the volume for those rare occassions when i am home alone . does anybody know of a quick mod i can do the phono amp to increase the gain . changing a resistor or capacitors for example ?
It is said that adding 18 or 22 Ohm resistors in positions R82 and R49 will increase gain by 6dB. The sound may suffer, though.
If you wish to try this, I would solder receptacle pins in these locations, so you can plug and unplug resistors there. Be sure that your power is off.

Last edited by rayma; 7th October 2014 at 03:51 PM.
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Old 7th October 2014, 04:21 PM   #3
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Now you know why conventional preamps are active and have some gain, around 16 dB typical. That gain is simply lacking in this case. You're best advised to borrow some kind of preamp. Got a headphone amp floating around that's not too noisy?
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