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Old 22nd March 2012, 02:43 PM   #1
tabams is offline tabams  Netherlands
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Default OPamp 4558 replacement

Found a safe replacement for my 4558 chips in my Technics SH-9010 equalizer (12 pieces)
It's NJM2068 from NJM2068|LOW-NOISE DUAL OPERATIONAL AMPLIFIER|Semiconductor Selection Guides|New Japan Radio(New JRC)
Low Noise Voltage (0.56V (FLAT+JISA))
●High Slew Rate (6V/μs typ.)
●Gain Bandwidth Product (27MHz(f=10kHz))
Want to be on the safe side, because I read on this forum someone had problems with OPA2604 and newer ones, like the LM4562.
Had to do something with the anti-parallel diodes on the inputs.
The NJM2068 has a Slew rate of 6V/uSec, the 4558 has 1V slew.
Also the Bandwidth has increased from 3 MHz to 27MHz.
Want to cut the old pins of the 4558 and solder the new 2068 on the old pins.
Want to prevent stray inductances and (oscillations?) by this method.
From a supplier in Asia I ordered 50 pieces for $ 28.00.
Here in Europe, also Mouser, you have to order more than 1000pcs.

Regards Tabams
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Old 22nd March 2012, 05:29 PM   #2
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Moderators may move this to the proper analog line level thread.
I upgraded a disco mixer from 4558's to a part with equivalent specs to the 2068, the 33078. I had oscillation afterwards and had to 1. put disk caps (0.1 uf) across the power supplies near the IC's 2. Put disk caps across the feedback resistor (22 pf). 33078 quieted the hiss right down. Farnell was selling 33078 in singles for $.38 . I considered the 2068 but didn't find any stock.
I also had to remove the resistor dropping the +- 15V supplies to +- 5, because the 33078 used more power than the 4558. I believe Herald installed the dropping resistor to reduce hum. I had to remove the AC power switch and the AC power transformer from the steel PCB enclosure to get the hum down. I'm using +-8v now, off an 18VDC race car wall transformer.
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Last edited by indianajo; 22nd March 2012 at 05:44 PM.
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