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Old 23rd November 2006, 12:58 PM   #1
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Default Low voltage opamp recommendations

Hi,

Any suggestions for a decent low noise, high input impedance opamp that'll run at <9V (ie a NiMH PP3)?

Doesn't need huge output current but must be transparent. The application is for a unity gain buffer to be fitted in an electric guitar belonging to a _very_ fussy musician.

Thanks!
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Old 23rd November 2006, 03:44 PM   #2
lineup is offline lineup  Sweden
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Default Re: Low voltage opamp recommendations

Quote:
Originally posted by bremen nacht

Any suggestions for a decent low noise,
high input impedance opamp that'll run at <9V (ie a NiMH PP3)?

Doesn't need huge output current but must be transparent.
The application is for a unity gain buffer to be fitted in an electric guitar
belonging to a _very_ fussy musician.

There are many new dedicated low voltage op-amps. From any manufacturer.

This one is not for audio, but for general use:
LM324, and the very low supply current version LP324.
324 is 4 op-amps in one device and can operate as op-amp or comparator
in good way down to +-1.5 (=3V) and I think even will function as low as +-1.3(=2.6V)

LM324 is very low price, have 4 amplifiers in one little chip
and good to have at home for any circuit that is not directly hifi audio.
Extremely useful!

----------------------------------------------------------------------


Most used audio diy-audio op-amps are most often restricted to
MIN +-5V operation( = 10 volt ) with recommended use of 30-36 volt.

But .... Some fairly good and cheap audio op-amps have minimum voltage +-3.0V (=6V)


This is one additional feature of the famous, very useful and pretty good for audio
Op-Amp NE5534 from Texas Instruments.

NE5534 is today very low price, compared to other AUDIO op-amps.
It has been used in many commercial as well as diy audio circuits
and many loves this chip.

==========================================

I am one NE5534 lover.

(NE5534 should not be confused with 5532.
5532 is another chip with a bit less good performance.)

NE5534 has got its own dual version!!!
NE5533 !!! is the dual version of NE5534, but not much seen or used..

==========================================

NE5534 can be used +-3.0(=6V) but draws a bit more current (to consider fro battery operation)
than other more dedicated low voltage op-amps.



==========================================

Op-amps, dedicated low voltage, low power and rail-to-rail voltage output, there are plenty of.
Not all are suited for audio (too much noise).
But some are!

At the big operational amplifiers manufacturers websites
you will have Selection Guides and Selection Tree Menus,
where you can specify what you are after.
... there is an operational amplifiers chip for any possible application we can think of ....

LINKS:
TI, Texas Instruments Amplifiers Selection Guide.
http://focus.ti.com/analog/docs/ampl...linearhome.tsp

LT, Linear Technology Amplifiers Product Tree:
http://www.linear.com/pc/viewCategory.do

National Semiconductor, Amplifiers Product Tree
http://www.national.com/appinfo/amps/

AD, Analog Devices Amplifiers Parametric Search
http://www.analog.com/en/pSearch/



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Old 23rd November 2006, 04:18 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
with just +-4.5V available on fresh battery and likely to work on +-3V when the battery led should be flashing, you will probably need to specify rail to rail output.

This spec usually (always) compromises the performance, but there are very many low voltage low current opamps out there and many are specified for MAX +-5V supplies and of necessity (well usually) will be R2R.
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Old 23rd November 2006, 06:16 PM   #4
jcx is offline jcx  United States
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more info would be helpful, improve answer quality

magnetic pickup?

pickup impedance?

max signal amplitude?

cable length/capacitance?

amp/mixer input impedance?

accetable battery life? - more power hungry low noise op amps cut run time for improved quality

willing to use surface mount parts? - many of the better new op amps are only available in surface mount

# of channels? - probably want at least a dual for active ground, or is a coupling Cap acceptable?

cost? - options range up to ~us$20 per op amp

from google, "high impedance" magnetic guitar pickups seem to be >10KOhms, definitely fet/cmos op amp territory

the needed V swing could make rail-rail input desirable but some parts have poor linearity
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Old 24th November 2006, 09:05 AM   #5
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Quote:
Originally posted by jcx
more info would be helpful, improve answer quality

These are all good questions.

The guitar in question belongs to a workmate. He's going to bring it in Monday and we'll make some measurements.

Thanks!
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