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Old 10th December 2006, 08:53 AM   #1
Nordic is offline Nordic  South Africa
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Default OPA2228 what can it be used for

I made the mistake of ordering some opa2228 chips in stead of opa2227, which is unity stable and therefore much easier to integrate.

Its not a bad chip, and if I understood the application docs, TI suggests using opa2227 for input impedance of under 10k, opa2228 from 10k to 100k, and opa2132 above that. SO, its simply a matter of horses for courses I guess.

Anyhow, I hate to let stuff go to waste, so I tried the chip in my cmoy, but it sounded awefully thin. Then I saw in the datasheet is a circuit for 2x gain (ps how do I convert that to db?) and one for 1/2 x gain (dunno what one would do with that).

I build the 2x gain circuit and it sounds very smooth very likeable.

I just tested with headphones but it didn't play terribly loudly. Possibly due to slightly under power battery I used to test it with... Oh well datasheet says it works fine vrom 5V upwards.. I suppose fine for other things, less fine for audio...

Can I put 2 of these 2x gain stages in series for 4x gain, or would that still not be worth it as a preamp stage for a GC?. My main source puts out nearly 2V full scale so I have gain to burn I think...

What would the synergy be like combining it with a valve based cathode follower as output stage.?
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Old 10th December 2006, 10:13 AM   #2
lineup is offline lineup  Sweden
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Thumbs up Opa2227 Opa2228 Opa227 Opa228 Opa4227 Opa4228

OPA2227 OPA2228 OPA227 OPA228 OPA4227 OPA4228
are variants of the same OP amp circuit.
High Precision, Low Noise Operational Amplifiers

they are all excellent for audio
-------------

OPA2228 is a dual of OPA228.
As you say, unity gain stable variant.
This means you can use it for gain= +1 or -1 and any other normal gain you like,
without adding any compemsation caps for stability.

Just like any normal Op-Amp.
Like OPA2134 or whatever.

You can use each one of the two for x4 or x10, if you like.
So getting 2 channel stereo left-right preamplifier with your desired needed gain.
As both channels are in same package, you can get preamp very compact at a small PCB.

These Op-Amps are so good, you need a well regulated supply
for utilizing best performance.
LM317 + LM337, as usual for Op-amps will do very well.
High CMRR = 120dB!!!
Which tells us this device will suppress ripple & noise from power supply to a very high degree.


You may use these chips for most anything within highest quality hifi audio.

Congratulations, Nordic.
Audio Op-amps do not come very much better than this.
Than this OPA circuit:
OPA2227 OPA2228 OPA227 OPA228 OPA4227 OPA4228
Product Page, info and datasheet
at Texas Instruments
http://focus.ti.com/docs/prod/folder...t/opa2228.html


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Old 10th December 2006, 10:51 AM   #3
Nordic is offline Nordic  South Africa
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Thanks, so its not just my imagination, it was much more pleasant than opa2132/4
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Old 10th December 2006, 11:05 AM   #4
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Hi Nordic,

Your mentioned Opa 2134 (which has a fet input) has a higher input impedance than Opa2228, but I guess that will only be an advantage in a few cases...

The OPA228 could be externally compensated for gains lower than 10, but it's only a hint for the future, I wouldn't really do that 'cause it's already available as OPA227.
I like these chips a lot, they're very good performance, as lineup stated. Also, whenever I switched several op-amps in the same circuit, they were always among the best behaving, so they're rather easy to use!

Cheers,
Dominique
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