Magnetic to Piezo

Thread Starter

Nanophotonics

Joined Apr 2, 2009
365
Hello,

I'm currently working on an audio project and one of the various tasks is to find out a way of making a magnetic pickup to sound like a piezoelectric one. I couldn't find the relevant information on the web. If you know any links/advice at all, please let me know.

Thanks.
 
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Thread Starter

Nanophotonics

Joined Apr 2, 2009
365
Hello,

Thanks for the link.

Yes, I meant it literally. I'm thinking of using an electronic circuitry that will adjust the magnetic pickup's response and make it as close as a piezo one. Would a proper filter do the job?
 

beenthere

Joined Apr 20, 2004
15,808
Skipping over the completely differing mechanisms of producing the electrical outputs, yes, sort of.

You need to determine the magnetic pickup type - moving magnet or moving coil - make a preamp to accommodate the low signal level, and apply a RIAA network ( http://www.glass-ware.com/audiogadgets/AG_RIAA_Eq_Networks_Design.html ) to adjust the frequency responses over several areas to the audio band to remove the funny non-linearities on the record due to the funny characteristics of the cutter head.

After that, you will have an output with similar levels to that of a ceramic cartridge. The last bit - obtaining that public telephone-like quality to the reproduction - may only be possible with an old 45 RPM record.
 

Thread Starter

Nanophotonics

Joined Apr 2, 2009
365
Hello,

Thanks for the reply. It makes sense to me. Actually, it's for a guitar pickup, more precisely a humbucker.
 

rjenkins

Joined Nov 6, 2005
1,015
I don't know if it's so much the pickups 'sound' different, as the sound they detect is from different sources?

A magnetic pickup is directly detecting the movement of the strings, where a piezo pickup is (I think) normally an add-on for an acoustic guitar and is detecting the soundboard vibration with all the extra resonances that gives.

If that's what you are trying to do, then I would guess what you want is something along the lines of a reverb or chorus type effect pedal to give additional depth to the sound.

(I've built and wired electric guitars and effects, but I know absolutely nothing about acoustic guitars & their pickups etc., so apologies if I'm wrong).
 

Thread Starter

Nanophotonics

Joined Apr 2, 2009
365
A magnetic pickup is directly detecting the movement of the strings, where a piezo pickup is (I think) normally an add-on for an acoustic guitar and is detecting the soundboard vibration with all the extra resonances that gives.
Hello,

Thanks for the post. That is correct. However, I'm trying to use only a magnetic pickup, feed its output signal into an electronic circuit such that upon listening to the resulting sound produced via a loudspeaker, you would think that only a piezoelectric pickup was used.
 
Not sure why you'd want to do this, but if you must: Neuter the bass and introduce horrendous peaks and troughs into the remaining frequency response, and if you can, introduce some unpleasant ringing. That's your piezo sound right there. If you can find a datasheet for a guitar piezo pickup then the frequency response graph would be a good starting point.

Piezos are normally used for augmenting a soundhole mic on an acoustic guitar; on their own they sound thin and nasty.

This reminds me of respected ex-colleague Allan Bradford who once designed the fantastic "CD Spoiler" for ETI magazine. Its purpose was to make a CD player sound like an old Dansette record player, so it used a noisy, distorting amplifier IC, mixed it down to mono, and thanks to the unique "flabby earthing" system, introduced lots of mains hum. For best results he recommended placing the finished circuit inside a toaster.

Allan's circuit was meant as a joke for the April issue, but I was quite serious in my first paragraph above, that really is why piezos sound like they do. It won't be an easy task at all to duplicate that frequency response as it looks like the Himalayas on a bad hair day. If you've got access to studio equipment, then you could try playing around with a parametric equaliser, as some of those piezo spikes have a high Q, hence the tiresome resonances.
 

Thread Starter

Nanophotonics

Joined Apr 2, 2009
365
Hello,

Anyone knows a typical single supply opamp I could use to design a Sallen-Key 2nd-Order Active Low-Pass Filter for this application? I will be using a 9 V battery, but adjustments can be made if lower voltage levels are required.

I've got a few options, but please suggest any better solutions you may have.

LMC6035
OPA341
LMV321
 
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