Problem with Preamplifier...sound like junk. (NJM4558) - diyAudio
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Old 4th November 2007, 10:06 AM   #1
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Join Date: Sep 2004
Location: Binyamina
Default Problem with Preamplifier...sound like junk. (NJM4558)

Hii.

I have Car amplifer with Preamp that integrated with actice crossover, and all the opamp's is made from NJM4558,

and hear the background noise...... and sometimes with the background noises there are radio noises...

the preamp-crossover build from 8 parts of NJR4558,

the power supply is max 16V +\- ... why max ? because of the power supply out between 20V +\- up to 28V +\-

(DC to DC supply that be fed from 12-14.4V)

so the preamp-crossover get power from 2 resistor and 2 zener diode .. that Vlimiter to 16V +\-.

so now i replase the supply to 15V+\- from 7815 and 7915...

and now i want to replace the opamp.. with something better !

what you suggest ?

i think the only problem it the opamp case : i add a picture.
(what the name of this case ?)

thanks
tamir
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Old 5th November 2007, 01:32 AM   #2
dangus is offline dangus  Canada
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Join Date: May 2004
Location: Vancouver Island
I'd call that a SIP: Single Inline Package
I don't know if there's any better op-amps available in that package. Your best bet is to make up a little circuit board to adapt an 8-pin DIP. Or you could do something ghetto like bend the leads of an 8 pin DIP op-amp flat, stick one side of the opamp in the board, and solder wire jumpers to the other 4 pins.
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Old 5th November 2007, 02:08 AM   #3
janusz is offline janusz  Australia
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Join Date: Oct 2004
Tamir,

You can use Brown Dog adaptors (now Cimarron Technology: http://cimarrontechnology.com ) - SO8/DIP8 to SIL adaptor. Then you can replace your junk op-amp with lm4562 from National Semiconductor.

Similar junky op-amps are used in yamaha c series preamps. I bought one of these preamps (c-65) a year ago on EBay and apart from having to fix the preamp I have recently replaced all op-amps in audio path. That together with thorough recapping improved the sound quality considerably.

But in your case check the Power Supply first - I bet it is very noisy and any PS to work properly must be very quiet (not so easy to achieve in a car - interference from fireing spark plugs etc). If PS is too noisy upgrading op-amps will not improve anything.

cheers,
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Old 5th November 2007, 06:01 AM   #4
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Join Date: Sep 2004
Location: Binyamina
thanks... i will work on this and will update you.
My car is a diesel... so i have no sparks...

tamir
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