Hello All!
I was researching on some preamps when I found this site, and I got to say this website is a wonder resource. Anyway, I am a computer engineer who is getting back into electric circuits after many years. I want to make a micro mic and preamp setup to record the voice of a person who is within your vicinity(around 1 meter). After researching a bit, I have settled at these two electret microphones:
1. PUI Uni Mic 680 Ohms AUM-5247L-R PUI Audio, Inc. | 668-1321-ND | DigiKey
2. CUI uni MIc 2.8 KOhms CMI-4537-SN69 CUI Inc | 102-2191-ND | DigiKey
It seems 680Ohms is preferred by people.
I have designed a preamp based on THIS circuit with some changes. But it seems that you have to be way too close to the mic for it to register useful signal. I am wondering now if the problem is with preamp or this mic can not be used for the purpose. I was also thinking about using TL971 instead of LM471
Another alternative that I have been thinking is pre-packaged IC's for eg. LMV1012 | Microphone Preamplifier | Audio | Description & parametrics or THAT Corporation 1583 Low-Noise Differential Audio Preamplifier IC. Am I on the right track? If not any suggestions are welcomed.
The signal from Pre-amp will go to an ADC then to computer for some signal processing.
Thank You for your time. Sorry if query is too naive.
I was researching on some preamps when I found this site, and I got to say this website is a wonder resource. Anyway, I am a computer engineer who is getting back into electric circuits after many years. I want to make a micro mic and preamp setup to record the voice of a person who is within your vicinity(around 1 meter). After researching a bit, I have settled at these two electret microphones:
1. PUI Uni Mic 680 Ohms AUM-5247L-R PUI Audio, Inc. | 668-1321-ND | DigiKey
2. CUI uni MIc 2.8 KOhms CMI-4537-SN69 CUI Inc | 102-2191-ND | DigiKey
It seems 680Ohms is preferred by people.
I have designed a preamp based on THIS circuit with some changes. But it seems that you have to be way too close to the mic for it to register useful signal. I am wondering now if the problem is with preamp or this mic can not be used for the purpose. I was also thinking about using TL971 instead of LM471
Another alternative that I have been thinking is pre-packaged IC's for eg. LMV1012 | Microphone Preamplifier | Audio | Description & parametrics or THAT Corporation 1583 Low-Noise Differential Audio Preamplifier IC. Am I on the right track? If not any suggestions are welcomed.
The signal from Pre-amp will go to an ADC then to computer for some signal processing.
Thank You for your time. Sorry if query is too naive.
Your open-electronics.org mini microphone amplifiers is okay, but a 741 op amp is fairly noisy, hissy. I'm not going to look up the TL971, I have enough choices, but at gain 480 you can use ne5534 (for a single op amp or 5532 for a dual) which is quieter. 5532 does not like unity gain, which you are not at. 5534 has a weird pinout, so if you are buying blank boards you may want to watch that. 4558 a dual amp is a little less hissy than 741, but I'm using MC33078 which is quite quiet at gain 50, to drive a 6' coax audio cable.
You have to pick an output drive current depending on how long your cables are to the DAC. 600 ohm drive is useful, even more drive current is useful for 100' runs. Peavey uses the JRC4580 in their pro mixers.
If your ADC is in the same package as the preamp drive, then a 2000 ohm drive current op amp is okay. Lots of people experiment with TL072, but they latch up if you bang into either rail, so I don't like them for my hobby projects. TL082 is reputed to not latch up. You have to keep the input 1.5-3 v away from the + and - power supply rails to keep the op amp from clipping, which sounds awful. All the op amps listed after the 5534 are standard dual op amp pinout. If you don't have a board, tubelab.com used to sell a nice dual op amp gain board for $10, although he leaves off the positions for the power supply bypass capacitors. You can nail the other half of the op amp to ground if you don't need it.
Most bands prefer a super-cardioid mike for the vocalist, to keep the vocal mike from picking up the instruments. These are designed to be used about 1/2" from the singers mouth. The classic Shure SM58 comes to mind. The non-radio versions are usually available used on craigslist because bands are moving to mikes without cables. This device you found may be a cheap substitute. Flat wide frequency response is not wanted for vocal mikes, to keep the pickup in the voice frequency range. Hand holding particularly makes some low frequency rumbling sounds that you don't want transmitted.
The power supply of the mini-mike circuit is a bit primitive with two resistors, but could be driven by a DC wall transformer in the voltage range. I pick these up for $1 at the Salvation Army resale shop - my favorite for op amps is an 18v car race version. This gets you +-8v which fits nicely with the 1n5322 zener diodes I use for voltage regulation.
Zener diodes of course each require a resistor to keep the current within the power rating of the diodes.
I'm experimenting with a $2 bargain bin dynamic mike I bought 40 years ago, and find the voltage out is much lower than that which I get from the pro condensor mike on the other channel. This makes the hiss a lot louder with the mixer gain jacked all the way up. You get what you pay for, the KSM27 condensor mike cost $80 and was a bargain at that. You don't want that one, it is a full frequency cardiode mike for recording several instruments in a band - or my organ in my living room.
Have fun.
You have to pick an output drive current depending on how long your cables are to the DAC. 600 ohm drive is useful, even more drive current is useful for 100' runs. Peavey uses the JRC4580 in their pro mixers.
If your ADC is in the same package as the preamp drive, then a 2000 ohm drive current op amp is okay. Lots of people experiment with TL072, but they latch up if you bang into either rail, so I don't like them for my hobby projects. TL082 is reputed to not latch up. You have to keep the input 1.5-3 v away from the + and - power supply rails to keep the op amp from clipping, which sounds awful. All the op amps listed after the 5534 are standard dual op amp pinout. If you don't have a board, tubelab.com used to sell a nice dual op amp gain board for $10, although he leaves off the positions for the power supply bypass capacitors. You can nail the other half of the op amp to ground if you don't need it.
Most bands prefer a super-cardioid mike for the vocalist, to keep the vocal mike from picking up the instruments. These are designed to be used about 1/2" from the singers mouth. The classic Shure SM58 comes to mind. The non-radio versions are usually available used on craigslist because bands are moving to mikes without cables. This device you found may be a cheap substitute. Flat wide frequency response is not wanted for vocal mikes, to keep the pickup in the voice frequency range. Hand holding particularly makes some low frequency rumbling sounds that you don't want transmitted.
The power supply of the mini-mike circuit is a bit primitive with two resistors, but could be driven by a DC wall transformer in the voltage range. I pick these up for $1 at the Salvation Army resale shop - my favorite for op amps is an 18v car race version. This gets you +-8v which fits nicely with the 1n5322 zener diodes I use for voltage regulation.
Zener diodes of course each require a resistor to keep the current within the power rating of the diodes.
I'm experimenting with a $2 bargain bin dynamic mike I bought 40 years ago, and find the voltage out is much lower than that which I get from the pro condensor mike on the other channel. This makes the hiss a lot louder with the mixer gain jacked all the way up. You get what you pay for, the KSM27 condensor mike cost $80 and was a bargain at that. You don't want that one, it is a full frequency cardiode mike for recording several instruments in a band - or my organ in my living room.
Have fun.
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The capsule used has a sensitivity of -47 dBV / Pa - the other one, while requiring higher input impedance, would have been a fair bit hotter at -37 dBV / Pa.
So in order to get a 1 Vrms output at 94 dB SPL (which is = 1 Pa), you'd need 47 dB of gain. You are probably interested in more like 60-70 dB SPL.
What sort of signal levels do you need? I wouldn't want a single opamp to perform more than about 50 dB of gain, they do tend to run out of GBW then. (5534 is a good idea btw, you could also use LM4562 if you're feeling fancy, but do observe its pitfalls in single-supply operation.) A line-level input of decent dynamic range should be sufficiently low in noise for the remaining gain to be performed in the digital domain though.
So in order to get a 1 Vrms output at 94 dB SPL (which is = 1 Pa), you'd need 47 dB of gain. You are probably interested in more like 60-70 dB SPL.
What sort of signal levels do you need? I wouldn't want a single opamp to perform more than about 50 dB of gain, they do tend to run out of GBW then. (5534 is a good idea btw, you could also use LM4562 if you're feeling fancy, but do observe its pitfalls in single-supply operation.) A line-level input of decent dynamic range should be sufficiently low in noise for the remaining gain to be performed in the digital domain though.
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