Topic: interesting DIY preamp kit

[keith]

Also the slew rate on the 5534 is 13uS the opa is 2.3! much better this chip is also stable at low voltages.

You seem to be saying that a lower slew rate is better.  The 5534 is around 13V/uS, the OPA227 is 2.3V/uS.  Are you saying lower is better?  Please explain.

[Church-Audio]

Also the slew rate on the 5534 is 13uS the opa is 2.3! much better this chip is also stable at low voltages.

You seem to be saying that a lower slew rate is better.  The 5534 is around 13V/uS, the OPA227 is 2.3V/uS.  Are you saying lower is better?  Please explain.

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Man I think I misread the spec sheet I thought the 5534 has 13mV not 13v Sorry in this case the slew rate of 13 volts trumps 2.3 volts I stand corrected.. Dam I still think the burr brown sounds better.. 

As we all know the higher the voltage = better performance / reaction time with the input signal..

[keith]

Man I think I misread the spec sheet I thought the 5534 has 13mV not 13v Sorry in this case the slew rate of 13 volts trumps 2.3 volts I stand corrected.. Dam I still think the burr brown sounds better.. 

Obviously slew rate is not the only measure of how an opamp will sound... 

[Church-Audio]

Man I think I misread the spec sheet I thought the 5534 has 13mV not 13v Sorry in this case the slew rate of 13 volts trumps 2.3 volts I stand corrected.. Dam I still think the burr brown sounds better.. 

Obviously slew rate is not the only measure of how an opamp will sound... 

Thats true what opamp do you like?

Chris

[keith]

Obviously slew rate is not the only measure of how an opamp will sound... 

Thats true what opamp do you like?

I do like the Burr Brown opamps.  I used an OPA37 in a design a number of years ago - I think the OPA227/
OPA228 are newer cousins of that one.  I'd be inclined to try an OPA228 where I had the OPA37 before.

The OPA228 is the decompensated version of the OPA227, so it isn't unity gain stable.  If the gain is 5 or higher of the circuit the 228 would probably be better, IMO.  Less than 5 the 227 is appropriate.

[Church-Audio]

Obviously slew rate is not the only measure of how an opamp will sound... 

Thats true what opamp do you like?

I do like the Burr Brown opamps.  I used an OPA37 in a design a number of years ago - I think the OPA227/
OPA228 are newer cousins of that one.  I'd be inclined to try an OPA228 where I had the OPA37 before.

The OPA228 is the decompensated version of the OPA227, so it isn't unity gain stable.  If the gain is 5 or higher of the circuit the 228 would probably be better, IMO.  Less than 5 the 227 is appropriate.

Interesting how about supply voltage and current draw? always factors when we are talking about battery life.. I use a OPA 2227PA and a ic based rail splitter design for my 9100. It works quite well.. But I am always looking for lower current and more gain with less noise.. Right now I am about -99db at +20 db of gain from 20hz to 80khz.
I am thinking of putting a cap in the feedback loop and bocking off anything about 40k... maybe squeeze more gain out of the amp that way.. I dunno its hard I am not a real electronics guru. I built things mostly out of trial and error luckily I know guys like Sparkie and a few other talented guys who have helped me with some of my designs. In electronics when your trying to build a preamp its not as simple as it seems... For me anyway.

Chris

[Church-Audio]

One thing to keep in mind with slew rate is how fast do you need to slew?  And that question has to be answered by the application.  If you are building a high-headroom pro-level (+4dBu) preamp, then you need more slew rate than for a few extra dB in front of a -10dBV portable recorder.  Actually, you'd need something like 8+ times the slew rate.

On the other hand, you have issues like current consumption and noise.  But again, what is your application?  Most people here are using condenser mics with a reasonably hot output.  If you are using small diaphragm condensers, especially the weensy ones, those by their nature will have a higher noise level than nearly any quality opamp you'd stick them into.  And if you are powering it with a battery, you'd be more concerned with current than noise.  If you are using unbalanced microphones, you might have enough induced noise to not even care.

I am using OPA2277 in a new mic I'm working on that will end up with total current ~2.5mA.  If you look at that chip, it isn't the quietest, it isn't the fastest, has a low GBW, but at 0.8mA/channel, it's incredibly efficient.  The slew rate is just fine when you consider the capsule's FET can't swing much more than 2V peak to peak before it clips, and the circuit is unity gain.  Note that slew rate is measured in microseconds; a 20kHz signal takes 25 microseconds (somebody check that math please) to go from peak to peak.

If I were building a general-purpose pro-level preamp, I usually use OPA2134.  OPA2277 uses a little less current, with less noise, but slower.  There are even sexier ones . . . OPA211, OPA627, and we still haven't left TI's range; there are a few other well-regarded chip makers out there.

But you could drop any of those in a particular design and not hear any difference, if the application did not test the limits of each chip's strength and weaknesses.


On the other hand, you might drop in OPA627 to a circuit that was designed with a 5534, and it might oscillate horribly . . .

That is one thing I have learned just because its pin for pin compatible does not mean it will work in your circuit.. but thats part of the fun of designing.. Its hard for guys like me and Jon because if your like me your so busy building you dont have as much time as you would like to try new things.. Thats the hard part for me anyway..



I would like to thank you for your contributions here!

Chris