Fitting microphones to my Weltmeister Perle 48

[Rosie C]

My summer holidays are finally here, and one of the things I've been planning to do is fit microphones to my Weltmeister.

Earlier in the year I bought a bag of old stock 3-wire microphone capsules. The seller helpfully provided a note explaining the wiring colour code. I'm thinking to make it very low-key - no volume knobs visible, just the jack socket. I can have a couple of the 'trimming' potentiometers that can be adjusted with a screwdriver inside, but otherwise rely on my amplifier to set the level. Battery can be switched on automatically when the jack is inserted.

First though, can any advise whether I'm on the right track with my circuit? I tried to copy it from my Hohner, but that seems to use 2-wire capsules so has a capacitor and resistor, but I'm thinking that's not necessary?

 

[debra]

I think you're on the right track, but I'm not an expert in any way. It's hard to say beforehand how well it will work. The positioning of the mic capsules is important, and you need to find out whether the signal is clipping when you play loudly or not. The sound of an accordion can be quite loud under the grille. The voltage may have an imfluence on that as well. 2 batteries in series, providing 3V may work better than a single 1.5V battery. Another point of attention is how well the mics will work when used in parallel (without any resistor between the signal output and the "common rail" that goes to the potmeter and then jack.

 

[Rosie C]

Thanks Paul! I'm thinking maybe build the circuit and try it out. Maybe blutack the mics in place or something and experiment. Should be a fun project anyway

 

[Caps]

This is the circuit I used for mine and it worked fine. I used a 9 volt battery and an opamp to provide more gain and balance the mics. Without the opamp the output of the mics is really low, barely above the noise level.

 

[Rosie C]

This is the circuit I used for mine and it worked fine. I used a 9 volt battery and an opamp to provide more gain and balance the mics. Without the opamp the output of the mics is really low, barely above the noise level.

Interesting. My Concerto III came with mics pre-installed. I'm assuming it's a DIY job. But it works well and the output level is good. As far as I can see there's just four 2-lead capsules in parallel, with a capacitor and resistor.

Of course I don't really know how the microphones on my Concerto compare to the ones I've bought.

 

[SteveBox]

The positioning of the mic capsules is important, and you need to find out whether the signal is clipping when you play loudly or not. The sound of an accordion can be quite loud under the grille.

A good point. I originally had electret microphones (similar to yours) installed in an accordion that had very little space between the grille and the pallets. The mics were so close to the pallets that they distorted. As an experiment, I placed a sound pressure meter right on top of the pallets, then played a single note with high bellows pressure. I got a reading of 122.8 dbA. With more than one note, I got 124 dbA. That is PAINFULLY loud, and some microphones will distort at that level.

The good news is that the sound pressure level drops off very rapidly as you get further away from the sound source. This is why an accordion does not sound painfully loud to your ears. If your accordion has enough space under the grill such that the microphones can be placed an inch or more away from the pallets, then you will probably have no problem. Also, the further they are from the pallets, the more even the sound pickup will be.

 

[dak]

Frankly I'd rather go for 2-wire microphones: the dedicated 3-wire mics may have higher noise tolerance but are usually wired as source followers which makes combining them a bit of a headache. Two-wire microphones essentially act as current source and you can just parallel them.

3-wire mics can reasonably easy be used in 2-wire mode: you just tie the output wire to signal ground, and the power input will then drain current proportional to the signal. If the gain is too large then, you can experiment with not directly tying their output to ground but with a resistor of a few hundred ohms.

 

[Rosie C]

Frankly I'd rather go for 2-wire microphones: the dedicated 3-wire mics may have higher noise tolerance but are usually wired as source followers which makes combining them a bit of a headache. Two-wire microphones essentially act as current source and you can just parallel them.

3-wire mics can reasonably easy be used in 2-wire mode: you just tie the output wire to signal ground, and the power input will then drain current proportional to the signal. If the gain is too large then, you can experiment with not directly tying their output to ground but with a resistor of a few hundred ohms.

Oh, don't say that! Someone else here recommended 3-wire mics and it took ages to find them!

 

[Dingo40]

Oh, don't say that! Someone else here recommended 3-wire mics and it took ages to find them!

No matter what the topic is, if there's more than one option, there will be champions for each of the various options .
Until you develop some personal experience in the matter, "you pays your money and takes your choice!"
Be happy !

 

[dak]

Oh, don't say that! Someone else here recommended 3-wire mics and it took ages to find them!

They are lowest distortion and low sensitivity (which is nice for accordion) but combining multiple microphones is more of a hassle. Simple circuits (like paralleling them) will lower the sensitivity even more and will negate the low distortion advantage, and if you parallel the outputs using resistors, you get higher noise again.

By the way: the easiest way to get 3-wire mics these days is to get suitable 2-wire mics and cut a trace on their bottom PCB and solder an additional wire there. But if they clip acoustically, changing the circuit will not help. So you need to start with low-sensitivity high-dynamic-range two-wire mics anyway. The low-sensitivity bit may mean that you are better off with cheaper mics and/or voltages below spec. One of the annoying cases where it is entirely likely that the cheap cobbled together prototype will work better than when you redo things "right" with quality parts.