I want to build a dynamic microphone preamp. Do any one of you has any tested good quality circuit diagram of dynamic mic preamp? The circuit should be simple and must have an option to control gain. Thanks in advance.
This link
Microfoonversterkerontwerpje voor de liefhebber - forum.zelfbouwaudio.nl
points to the schematics and a description in Dutch of my home-made microphone amplifier, which works well with both dynamic and phantom-powered condenser microphones.
Microfoonversterkerontwerpje voor de liefhebber - forum.zelfbouwaudio.nl
points to the schematics and a description in Dutch of my home-made microphone amplifier, which works well with both dynamic and phantom-powered condenser microphones.
An OPA1611 (single) or OPA1612 (dual) is the best op amp available for microphone preamplifier applications. Their noise, distortion, common-mode, and speed specifications can't be topped. Here's a link to some circuits using it:
https://sites.google.com/a/vt.edu/amp_lab/projects/high-gain-low-noise-microphone-preamplifier
https://sites.google.com/a/vt.edu/amp_lab/projects/high-gain-low-noise-microphone-preamplifier
The op-amp is pretty good, but the amplifier design isn't. At least to me it doesn't make much sense to buy a 1.1 nV/sqrt(Hz) op-amp and then connect a 4 nV/sqrt(Hz) resistor in series with its input. A noninverting amplifier topology with very low-ohmic feedback network would be much better, especially for dynamic microphones.
This one is pretty simple & inexpensive. I would substitute an OPA1612 for the NE5532, but either would be fine.
Project 122
Project 122
I'm no expert, but I've read great things about the THAT 1510 and 1570, for high gain audio applications. IIRC, THAT has some circuit diagrams on the website.
Other chips that get raves for audio, but not specifically mic pres:
LT1469
ADA4898
TLE 2082 Excalibur
Other chips that get raves for audio, but not specifically mic pres:
LT1469
ADA4898
TLE 2082 Excalibur
THAT 1510/12--- awful THD specs
ADA 4898----good noise & distortion specs; high current draw; low maximum output voltage swing
TLE 2082---very fast, very noisy, high distortion. A JFET device==not optimum for microphone preamps
The OPA 1612 is much superior in all respects.
ADA 4898----good noise & distortion specs; high current draw; low maximum output voltage swing
TLE 2082---very fast, very noisy, high distortion. A JFET device==not optimum for microphone preamps
The OPA 1612 is much superior in all respects.
LT 1469--- very good distortion, very noisy, fast.
I should also mention the OPA 1662; VERY good performance at only $0.99 per opamp.
I should also mention the OPA 1662; VERY good performance at only $0.99 per opamp.
What on earth is so awful about 0.005 % distortion at 60 dB gain? It is about 200 times less than the threshold of audibility. Admittedly, this is at 1 kHz with no indication what happens at higher frequencies.
The noise of a THAT1510 or THAT1512 at high gain settings is lower than that of your favourite op-amp, especially when you use two of those op-amps to make a balanced amplifier.
Well, there's probably nothing wrong with 0.005% THD. Except that it's about 50 db worse than an OPA 1612. Is that (THAT?) audible.....I don't know.
At 60 db gain, THAT's noise is 1 nV/√Hz; the OPA 1612 is 1.1nV/√Hz. It's interesting that the 1512's noise density figure varies so much with gain---all the way up to 34 nV/√Hz at unity gain. I've not seen that on other datasheets.
Let's see......005% THD is ~-86 db; 200 times is 46 db. So you are saying that the threshold of audibility is -40 db?? I think it's a LOT lower than that.
At 60 db gain, THAT's noise is 1 nV/√Hz; the OPA 1612 is 1.1nV/√Hz. It's interesting that the 1512's noise density figure varies so much with gain---all the way up to 34 nV/√Hz at unity gain. I've not seen that on other datasheets.
Let's see......005% THD is ~-86 db; 200 times is 46 db. So you are saying that the threshold of audibility is -40 db?? I think it's a LOT lower than that.
Find an example of any audio console and start from it. You don't need phantom power, nor an attenuator switch. Any good opamp would work if you add a pair of nice transistors up front. Look at Zetex medium power transistors, they are better on inputs than so called "low noise" transistors.
Aren't you comparing the the that1512 at 60dB gain vs the opa1612 at 0dB gain ?
At x1, the that1512 is -100dB thd+n (0,001%). That's 36dB worse than the opa1612, not 50.
At a gain of 60dB, the THAT is only down to -82dB. What do you think will be the opa1612 distortion now that the available amount of feedback at 1khz has lost 60db ?
Well, I'm not sure what the performance would be at 60 db gain; the datasheet shows the same distortion specs at 20 db of gain as at unity, and doesn't show anything for higher gains. But if the THAT 1512 starts off 36 db worse than the OPA 1612 at unity, I doubt it outperforms at 60 db gain.
Outperforms, probably not. But the benefits might not be huge nor easily audible. Especially in the context of ESP project 122. As the source impedance into the + input of the opamp wouldn't be 0R, the opa1612 won't perform at its best either and this will narrow the gap.
All I know is, top designers who work with professional recording gear for a living, recommend this chip VERY highly. It can't possibly suck.
Of course, there may be something better. Things change all the time. - But"better" and "100% drop-in compatible" do not always co-exist, either. One has to watch out for current draw, impedance & other factors.
Again, I'm no expert, just passing along some info.
Also note that high THD (even if it existed) is not always a bad thing. Some types of distortion end up sounding GOOD to our ears. And other factors can be more important, like slew rate. If you don't understand that, then you know nothing about audio component design.
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