I'm looking for a preamp build for my dynamic mic and I already have an OPA2134PA that I don't use. Is there a build that I can use this opamp? Is it suitable for this application?
I'm guessing (maybe wrongly) that you only want to use the opamp and not add any extra stages... however for something really good:
CordellAudio.com - Dynamic Microphone Preamp
If you are just experimenting then the OPA on its own is OK although far from optimum in terms of noise for this kind of application (which is different to Bob Cordells approach).
Most opamp circuits will translate to the OPA devices with little or no changes.
Project 122
CordellAudio.com - Dynamic Microphone Preamp
If you are just experimenting then the OPA on its own is OK although far from optimum in terms of noise for this kind of application (which is different to Bob Cordells approach).
Most opamp circuits will translate to the OPA devices with little or no changes.
Project 122
I'm really new into electronics and yes, I'm just experimenting. I'm not sure what staging on amplifiers mean to be honest. On last couple weeks I've been reading a lot of blog posts and I'm really interested into electronics and audio stuff.
When it comes to performance even the dynamic mic that I use is a DIY one. So I'm just trying get things to work 🙂 All I'm trying to do in this project is getting the mic input via XLR and outputting the signal to my computer via 3.5 mm jack. If I didn't get them wrong both audio designs do exactly that right?
When it comes to performance even the dynamic mic that I use is a DIY one. So I'm just trying get things to work 🙂 All I'm trying to do in this project is getting the mic input via XLR and outputting the signal to my computer via 3.5 mm jack. If I didn't get them wrong both audio designs do exactly that right?
Most mic amps need a lot of gain, that's your main challenge. But just about any opamp will be fine to experiment with.
Staging... stages 🙂
Bob C's design uses quite a bit of extra circuitry in front of the opamp (extra stages) that add considerable complexity if you just wish to experiment.
The simplest possible circuit would be a single high gain opamp stage where you just alter the gain setting resistor suit. Just tie the mic between ground and the input of the circuit.
You could then develop that and split the gain between two stages (the two opamps in the package)
This runs on a single supply... you might even get away with 9 volts from a battery. Watch the pin outs, this is for a 741 type opamp.
The gain is set by changing the 22k and/or 1k and equals (R2/R1) +1
Attachments
Or you could just use a single IC designed for the purpose:
http://www.ti.com/lit/ds/symlink/ina217.pdf?&ts=1589182623692
Thousands upon thousands of professional mic preamps have been built with this, and it's predecessor, the SSM2017.
http://www.ti.com/lit/ds/symlink/ina217.pdf?&ts=1589182623692
Thousands upon thousands of professional mic preamps have been built with this, and it's predecessor, the SSM2017.
For some reason I thought "Stage" as an electronic term instead of taking it literally 😀
Thanks a lot for the explanation and all other resources you shared. I learned a lot.
In this application there is relatively little benefit from the JFET frontend suggested by Bob Cordell, and the bipolar one in P66 should work just about as well at lower parts cost. You could also tweak its performance for even lower noise e.g. with a 150 ohm mic (like the SM7B), while perhaps also using the lower-rbb' ZTX550 as an upgrade to 2N4403.
I would suggest the following alternate part values for P66:
R9 - 10R
VR1 - 5k
R10, R11 - 100-330R
R12, R13 - 10k
C2, C3 - omit and replace by single C on the output.
R2, R6 - 2k2
R4, R8 - 1k
If your power supply is nothing special noise-wise, 100R resistors in series with +VE and -VE may be well-advised.
That said, if you want good results and a minimum of hassle, an INA217 or similar based solution is almost a no-brainer - it's still at least as good as the above, and can potentially do even better.
http://www.thatcorp.com/datashts/AES129_Designing_Mic_Preamps.pdf
I would suggest the following alternate part values for P66:
R9 - 10R
VR1 - 5k
R10, R11 - 100-330R
R12, R13 - 10k
C2, C3 - omit and replace by single C on the output.
R2, R6 - 2k2
R4, R8 - 1k
If your power supply is nothing special noise-wise, 100R resistors in series with +VE and -VE may be well-advised.
That said, if you want good results and a minimum of hassle, an INA217 or similar based solution is almost a no-brainer - it's still at least as good as the above, and can potentially do even better.
http://www.thatcorp.com/datashts/AES129_Designing_Mic_Preamps.pdf
PS - in the P66 input stage you have to take care of thermal coupling of input transistor pairs yourself. It looks like Rod Elliott's own P66 rev A board may be coupling each PNP & NPN per side, which doesn't make that much sense to me - the critical match relevant to offset voltage drift / 1/f noise is between the PNP inputs. So it should be Q1 + Q3 and Q2 + Q4.
I guess the issue went unnoticed as an amp like this would generally be inhabiting its own little enclosure with precious little internal airflow. Out on the bench, the output may get a bit nervous. When you're trying to amplify a few mV of signal and transistor tempco is -2 mV/K, it doesn't take that much.
Circuits with an integrated input pair do not have this particular problem for obvious reasons.
I guess the issue went unnoticed as an amp like this would generally be inhabiting its own little enclosure with precious little internal airflow. Out on the bench, the output may get a bit nervous. When you're trying to amplify a few mV of signal and transistor tempco is -2 mV/K, it doesn't take that much.
Circuits with an integrated input pair do not have this particular problem for obvious reasons.
P66 looks really good for my case.
Seems cost would be pretty low too which is desirable cause there is a high chance that I may mess this up 🙂
I see INA217 everywhere but I would rather use it in a more serious project.
Also, K. Herbert's tutorial looks really educational thanks a lot for sharing!
Think for a moment...why do you see it everywhere? Because it works, works very well, is simple to use, and the overall implementation is low cost. Simply put...you can't beat it. I have no idea why anyone would fight with anything else, unless higher parts count and more difficulty have some sort of weird appeal.
I built a bunch of mic preamps once, in practically another lifetime, with Jensen JE-16 input transformers, 990 for gain and another 990 to create a differential output. Two channels per card (that's 4 990s, 2 xfmrs, $600 in just those parts), 10dB stepped input gain control with integral pad for line in, custom boards, phantom, on-card regulators...blah blah blah. Expensive as all getout. And they sounded great. The INA217 also sounds great, and a bit quieter and a whole bunch cheaper. They didn't exist at the time.
Edit: Oh by the way, the figure nobody talks about is common mode rejection. The INA217 and a JE16 transformer are surprisingly similar, with around 120 @60Hz, better than 85dB @3kHz. There's no way the Cordell circuit will be even close, doing well if it makes 70dB with a lot of hand tweaking.
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I didn't specifically mention it but my main reason for not using INA217 is I can't find one in my country, so I have to import it which increases the cost of the project drastically.
I understand INA217 is perfect for this project. If I can find one for reasonable price it will be my go to.