Need Advice for a Weird Project

I'm glad it works! I expected it to work, but have designed electronics long enough to know it doesn't always do what is expected of it.

Regarding your question, yes, you can get in-between high-pass filter responses by just switching off some of the switches SW2...SW4:

SW2, SW3 and SW4 all on: 130 Hz third-order Butterworth high-pass

SW2 off, SW3 and SW4 on: 1 kHz first-order high-pass cascaded with a slightly peaking 130 Hz second-order high-pass, so approximately 1 kHz first order

SW2 on, SW3 and SW4 off: slightly peaking 1 kHz second-order high-pass cascaded with a 130 Hz first-order high-pass, so approximately 1 kHz second order

SW2, SW3 and SW4 all off: 1 kHz third-order Butterworth high-pass

Any combination with one of SW3 and SW4 on and the other off: some weird over-damped response, not sure what it looks like
 
The filter consists of a first-order section controlled by SW2 and a second-order section controlled by SW3 and SW4.

So when you only switch off SW2, you switch the first-order section to 1 kHz and get a first-order response between 130 Hz and 1 kHz. Below 130 Hz, the other section kicks in and you get a third-order response.

When you only switch off SW3 and SW4, you switch the second-order section to 1 kHz and get a second-order response between 130 Hz and 1 kHz. Below 130 Hz, it is again third order.

When you switch off SW2, SW3 and SW4, you switch both the first- and the second-order sections to 1 kHz and get the combined, third-order 1 kHz high-pass response.

When you switch on SW2, SW3 and SW4, you switch both the first- and the second-order sections to 130 Hz and get a third-order 130 Hz high-pass response.
 
Hey there, getting some preliminary data in and it looks very promising. I noticed we are getting some sort of ground loop or interference. It may be how I have the solar panel charge controller wired into the battery, but haven't experienced this before. It appears as bands of noise at 2, 3, and 4 kHz. Link to download a sample file is here: WeTransfer. The wiring for the preamp to the raspberry pi power supply and 3.5mm jack is a mogami W2534-06 4 wire with shielding. I didn't connect anything to either end of the shielding as I don't really know what to connect it to. The filters appear to work great and the setup seemed to have survived hurricane Laura.

Any thoughts or advice are greatly appreciated. Thanks!
 
You could try connecting the shield to signal ground on both sides and/or changing the sample rate of the sound card, just in case what you hear is an alias of a harmonic of the switching frequency of a switched mode power supply. Your charge controller is a switched mode power supply if I remember well.
 
I have no experience with condensation on printed circuit boards, so I can't help you much. All I know is:

1. There are substances called conformal coating meant to protect PCBs from moisture, chemicals and scratching. I know nothing about them except that they exist. See Conformal coating - Wikipedia and Blocked

2. Flux residues can become electrolytic conductors when they get damp, so I would advice you to remove them (before applying any coating). I usually do that with cotton buds and isopropyl alcohol, but I never get the PCBs really clean. Ray a.k.a. nautibuoy has more success with the procedure he describes here: https://www.diyaudio.com/forums/dig...-linear-audio-volume-13-a-41.html#post6261302 See post #400 of the thread for the stuff he uses and #403 for the procedure.
 
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I wanted to circle back to this thread and post some results. I was able to successfully conduct a fall season of night flight call monitoring using this preamp design and microphone setup. I ran into moisture issues that I remedied with some conformal coating products and installing a moisture vent. Once I was able to configure the recorder correctly to the preamp it worked perfectly. The attached photo shows some of the many spectrograms that were processed from the collected data using this setup.

I have a question about using electrets in parallel in order to help the SNR on this setup. Would using 2 or 3 mic elements work with the current preamp design and would there be any advantage in using multiple elements for reducing self noise?
 

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Great that you managed to solve the moisture issue and that it has all worked out well!

Regarding your question, in the circuit of post #97, you could scale down R1, R2 and R3 by a factor of n, scale up C3 and C4 by a factor of n and connect n microphone capsules in parallel. This will result in non-standard component values, but you can round R1 and R2 to the nearest E12 value, R3 to the nearest E96 value and C3 and C4 to the nearest E3 value.

As long as you manage to mount the capsules such that the bird or frog sound reaches the n capsules essentially in phase, you will get about the same signal level as with n = 1, but with almost 10 dB*log10(n) less noise. So that's about 3 dB with two microphones and 4.7 dB with three microphones. The difference in path length from the bird or frog to the various microphones has to be much less than a quarter of a wavelength.

There is more that needs to be changed when you want to use 100 microphone capsules or more, but it will probably be difficult to keep the acoustical signals in phase then anyway.
 
Thanks Marcel! In this case n is the number of mic elements that I would divide or multiply the resistor and capacitor values by? So, if I wanted to add 3 mic elements in parallel I would need to change R1 and R2 to 220 Ohm, R3 to 732 Ohm, C3 and C4 to 680 uF? My plan would be to cram them into the parabolic dish to be as close as possible to each other and hopefully allow for the signals to be in close phase. Thanks again for your help!
 
Thanks Marcel! Another dumb question. I am having a tough time sourcing the 680 uF capacitors that will fit in the pcb footprint that has the same voltage rating as the other capacitors I used (12-19 volts). The ones I found are rated at 6.3 volts. Do you think that’s alright? Thanks again!
 
Hello all, first time poster here. A little background on me and my project. I am a wildlife biologist that is currently pursuing bioacoustic projects. The specific project I currently need help with is night flight calls given by migrating birds. These sounds are are usually concentrated in the 5-8khz range with outliers on both sides (black-billed cuckoos are very low and some sparrows are over 10khz).

My setup uses a raspberry pi with a sound blaster play 3 audio interface as the recorder. I am using the POM-2730L-HD-R (http://www.puiaudio.com/pdf/POM-2730L-HD-R.pdf) and use the recommended drive circuit in the datasheet. I currently use a preamp designed by old bird, Inc (Old Bird 21c), but they are expensive and hard to get as a stand alone item. I don't know much about how that preamp works other than it runs off 9-12V single supply and passes on 5V to an electret element. The preamp is balanced too. My setup runs off a 12V solar powered battery that powers the raspberry pi. The raspberry pi sends out 5V to a 9V step up converter that then powers the preamp.

I am in need of a preamp design that I can make at home (have some skill in putting components together) or purchase one that would suite my needs. What I am looking for is an ultra low-noise, balanced, linear, single supply (12 volt preferably) electret preamp that I can build myself or buy. I would prefer it have set gain levels to limit variables when setting up the "Night Flight Call Stations". Gain could then be set using the audio interface.

Any advice and criticisms are greatly appreciated.
Hi Hal,

Sorry for the weirdness of this but perhaps I can do something about that CZM item you are interested in on ebay. Any way to send a private message on here?