anyone suggest a good quality replacement for NJM2115 [3028U] OP AMP - diyAudio
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Old 24th March 2008, 05:25 PM   #1
at77 is offline at77  Canada
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Default anyone suggest a good quality replacement for NJM2115 [3028U] OP AMP

hi there,
i'm contemplating modding an audio recording unit that i have.
in the input section it uses NJM2115 op amps. from what i've read so far online i think an OPA2134 will work well as a replacement, but i'm not experienced in this regard so i'm looking for advice and help as to not ruin my unit (if i can avoid it).
basically looking to open up the sound of it a bit.

the output stages use the NJM4580 [2 kinds (i think) labeled 2215U and 2218 U] and again from what i've read, either the AD8066 or the OPA2227 or OPA2228.
any experienced feedback would be appreciated, including advice for replacing the op amps as i have never done it before though i have moderate experience with electronics and a decent handle on soldering.
thanks
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Old 24th March 2008, 05:41 PM   #2
Mooly is offline Mooly  United Kingdom
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Hi. NJM2115 is optimised for low supply voltage of 5v and works down to 2Volts supply, possibly using single ended supply rather than dual + & - . You might have problems swapping this one. The 4580 is more conventional, but think you need to find out what supplies your unit runs on. Is it a DAT recorder ? Also what package are they, DIP8 , or surface mount.
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Old 26th March 2008, 07:43 AM   #3
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thank you Karl,
the unit is a MOTU 828 mkII firewire recording unit.
I'm not 100% sure on the power or how to discern it rightly. haven't pulled out the multimeter to take measurements yet... not sure how to discern otherwise the voltage to these op amps. that being said, there is writing by the transformers indicating 3.3v. and looking at a few other parts some are rated at 6v max, i'm lead to believe that 3.3v is the voltage for the entire board save the 48v transformer that i assume is dedicated to the 48v phantom power supply for the two microphone inputs.
as for mounting, both the NJM4580's and the NJM2115's are surface mounted 8 pin units.
from what i can discern, the 2115's are the input op amps and the 4580's are the output op amps.
any guidance or input is appreciated.
thank you,
adam
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Old 26th March 2008, 08:49 AM   #4
Mooly is offline Mooly  United Kingdom
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Measure from signal ground to pin 8 of opamp (positive supply) and pin 4 (negative supply) . If your not sure just measure across pins 4 and 8 to get the total supply. If it's low you might be best leaving well alone, those OpAmps are optimised for use at low voltages.
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Old 26th March 2008, 07:16 PM   #5
at77 is offline at77  Canada
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Hello again,
thank you for the guidance Karl.
I took some measurements - both units just because - and here they are. They seem a bit high for the NJM2115 compared to its data sheet parameters, but this is what I measured:
*for signal ground, by the way, I plugged a TRS cable into an input at the back and used the sleeve as signal ground. I assume that's correct.

NJM2115
16.63v from terminal 4 to 8
10.61v signal ground to terminal 8
-5.9v signal ground to terminal 4


NJM4580
21.1v from terminal 4 to 8
10.7v signal ground to 8
10.0v signal ground to 4

Adam
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Old 26th March 2008, 07:16 PM   #6
at77 is offline at77  Canada
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correction on that last measurement for the 4580. signal ground to terminal 4 is -10.0v, not positive of course.
adam
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Old 27th March 2008, 12:59 AM   #7
at77 is offline at77  Canada
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hey all,
did more research - it looks to me like the THS4032 would be a very good replacement for the NJM2115 in this situation. looks like there's enough voltage (requires minimum 4.5v+-) and the pin layout is the same.
can anyone tell me if this is one will likely work or not?
would it also work as a replacement for the NJM4580?
any thoughts are welcome.
thanks,
adam
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Old 27th March 2008, 07:51 AM   #8
Mooly is offline Mooly  United Kingdom
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Hi , The THS4032 is a very fast OpAmp and may not be stable in your application particularly if used at unity gain. You need to see circuit to see how they are configured. Also current consumption is much higher, important on battery powered equipment. Sorry to sound a bit negative, but I think you might end up worse off on this one. Those supply voltages are fine for most OpAmps, even the unbalanced one. Have you ever unsoldered surface mount components by the way ?
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Old 27th March 2008, 04:55 PM   #9
at77 is offline at77  Canada
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Hey Karl,
thank you again. That's helpful information.
I have not soldered or un-soldered surface mount components before. My understanding is that i need to be sure that: 1) I do not use too much heat (which will fry the op amps), 2) the old solder is well removed (perhaps with solder vacuum, perhaps braid), 3) to use only high quality silver solder and 4) to 'tin' the contacts on both sides before joining them. Anything else?

The unit is not battery powered - it runs on AC (switchable from 100-240v) with its own transformers (one for the circuit board and one for the phantom power for the microphones).

So my questions then are:
1) Is there harm in trying (ie soldering in and running some tests) the THS4032 to see if it will work by trial and error?
2) Any other good OP AMP recommendations?
3) Any other suggestions or tips regarding unsoldering and soldering surface mount components?

I'll send along a jpg of the section of the board that i'm looking at.
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Old 27th March 2008, 06:22 PM   #10
at77 is offline at77  Canada
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here's a jpg of the analog input section.
adam
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File Type: jpg 828input.jpg (79.9 KB, 768 views)
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