Violin preamp

Status
Not open for further replies.
Jump to Latest
E

eala

Member
Joined 2018
#1
Hi folks,

My kids play violin and they recently played a gig where "somebody" forgot a microphone.
:violin:

I thought I would look around to see if I could acquire a preamp for some small microphones I have that could be mounted on their acoustic violins:
JK MIC-J 044 Lavalier Lapel Clip On Omni-directional Condenser Microphone For Computer Voip Skype Laptop Voice Amplifier (Mono 3.5mm Plug): Amazon.ca: Musical Instruments, Stage & Studio

I came across these which seem to be exactly what I was looking for, alas, I can't afford $200 each:
Myers Pickups —Myers Instrument Pickups and Instrument Microphones Feather

I have no issue soldering and I would love to be able to make something small and battery powered {prefer to use lithium ion batteries (3.6V to 4.2V)}.

I have been looking through the threads in this subforum for a couple days and have found a million circuit ideas with very technical descriptions of how they work most of which are over my head. Could anybody recommend a build (or cheaper product) that would achieve my goal here? I am not looking for the amplification part, just enough of a signal bump to get it to the point where the sound can be recorded or amplified.

Thanks a million.

eala
 
#5
Oh they do look really good and a much better price than the Myers ones. I don't understand why they don't require a preamp. There is no power source in there. Could you plug that directly into a small amplified speaker?

eala
 
#6
Hello:

I have used two different pickup methods on my daughter’s traditional acoustic violin, and she just bought another type for her mandolin, which has approximately similar pitch range.

A microphone potentially can give the most realistic results, but cost + preamp & feedback present challenges.

The latest could also work on violin, but we haven’t tried it yet. (Don’t need to, but I’m sure I will want to know).

The latest one is the least costly, so let’s start there. AGT100(G) from Canadian company EPM. They have what looks like a well thought out product line.
It is a piezo transducer hot-glued into a bottle cap with a decently ruggedized molded cord/jack (1/4” TR). It uses a sticky putty material to adhere to a instrument body. It’s mot supposed to harm most finishes but if the violin has a delicate oil finish ask a knowledgeable expert. The normal version uses beer bottle caps donated by breweries. The like price may vary from US$27-40 depending whether you have a local retailer or mail-order.

Piezo sensors are capacitive and thus form a high pass filter in combination with the input impedance of the amp or preamp they are plugged into. If the input impedance is not high enough low frequencies suffer loss of volume.

I immediately measured the capacitance so I could think what impedance was suitable. It was about 4100 pF including the cord.

Violin is easier than guitar for piezo pickups as the lowest fundamental string frequency is about 190 Hz (guitar with standard tuning ~82 Hz).

For 190 Hz to not suffer signal loss, approximately 200 kOhm or higher is desirable. For standard acoustic guitar with standard tuning this pickup would like to see about 470k or higher input impedance. Many instrument amps have 470k-1M input impedance & thus probably will work well directly without a preamp. That was the case for us with a random guitar amp.

It was not compatible with an Audio-Technica mic preamp I brought along: 30 k unbalanced input Z is too low, and has XLR connectors. Piezo output signal level can be too high for a mic input but thise problems are solvable (not on the spot...)

The amplified speaker things I have tried to repurpose were about 10k input Z and agreeable to line level signal typical of a decent size, so the input Z is the problem with those.

There are unbranded (no name) guitar piezo/preamp/EQ boxes online in various configurations. I bought an EQ-7545R years ago for $12 shipped. Mounts in the side of an acoustic guitar. Has a 9V battery holder and comes with a 6-rod piezo saddle pickup wired with a tiny (3/32”/2.5 mm?) plug, and a 1/4” output jack. I cut off the piezo and wired the tiny cord to a 1/4” jack.

I am awaiting delivery of another ($4.94 shipped!). May take a week or two months...

There are other stick-on pickups for acoustic instruments with small stick-on sensors...sone with three.

We also used a rubber RODE violin mic mount (~$15) because I already had a small (6 mm) lapel Sony ECM. It has two slots and hangs from the two outer strings between the bridge & tailpiece (this part of the violin family instruments is called the ‘afterlengths’ and doesn't produce sound. Acoustic bass mics sometimes exploit this). The Rode ECM is tiny-4mm. I (carefully) opened the rubber 4 mm hole with slits on one and (extra carefully!) drilled another to 6 mm. I have also jammed a Shure ECM (W?-93?) that goes with a
wireless belt-pack transmitter.

Lastly, if there is interest and she gets a job, there is a Velcro-attaching triple-sensor system that wraps around the instrument...”The Band”, made by British company Headway (Electronics). No preamp ‘necessary’ for reasons discussed above, but all such systems benefit from them). Years ago it was about $160. Who knows, might find one used for less.
 
#7
eala said:
Oh they do look really good and a much better price than the Myers ones. I don't understand why they don't require a preamp. There is no power source in there. Could you plug that directly into a small amplified speaker?

eala
Click to expand...
They use the piezo electric system and supply around 50mV output. They are exceptional and I fit them under the bridge on acoustic guitars, cello and double bass. On a violin, they should be fitted on the bridge or speak to JJ, they are very helpful.
Cheap Chinese versions require a high impedance pre amp, these perform well into about 100k.
 
#8
eala said:
I don't understand why they don't require a preamp. There is no power source in there.
Click to expand...
When you bend or vibrate a piezo sensor, it generates a tiny voltage. The power source is the violinist!

eala said:
Could you plug that directly into a small amplified speaker?
Click to expand...
If the amplified speaker has a high input impedance (say 1 meg) and high voltage gain, probably yes.

In practice, this means that a acoustic guitar amplifier would probably work with no modifications; a little powered computer speaker would not.

If, however, you had a preamp between this pickup and the powered computer speaker, that would work too. The preamp would have to provide the high input impedance the piezo needs, and the additional amplification lacking in the computer speaker.

You can think outside the box on the preamp - for example, there are some guitar FX pedals that would be sufficient to do the job. I've used a $25 Danelectro Fish-n-Chips graphic EQ pedal as a preamp many times. It gives you not only high input impedance and up to 20 dB or so voltage gain, it also gives you powerful tone-shaping abilities.

-Gnobuddy
 
#9
JJB might be who I was thinking of for the multiple-sensor types.

The Marcato caught my eye then I realized OP had mentioned it...but I hadn’t clicked on it.

They are very reasonably priced, and it looks like there are multiple great options.

Next time someone asks me that’s where I’ll send them...I just never do anything the easy way...can’t help myself.
 
#10
If the JJB sensors are repositionable, I suggest experimenting with body locations as well as the bridge. If it works on the bridge, great. A friend builds contrabasses & he doesn't like the sound of pickups that are on the side of the bridge...but he’s pretty fussy about what he’s wishing for. My theory was that most of the string vibration goes through the feet of the bridge and not alot perpendicularly. Ceramic piezos can have different responses in their 3 axes.

If you can experiment with 2 or more stick-on sensors, one on either (outer) side of the bridge feet or somewhere you like the sound of near the bridge. On the body you’ll get both string and body sound. The soundpost area could possibly be good or bad...it’s complicated. I’ve always stayed away, but I’ll bet the instructions and Jon are better than all of what I just said.
 
#11
I’ve been using polymer ribbon piezo sensors but that’s another detour.

B-Band, the Finnish company, uses polymer electrets (don’t ask) and on a bass model, wedges at least one in the ‘wing’ of the bridge (the flexible slotted hole area).

They absolutely need very high input impedance preamplification, which gets too complex.

I am not sure if their self-adhesive ribbons for guitars have that restriction but suspect they do. Cool, but pretty much a ‘system purchase’...don’t try this at home kind of territory.
 
#13
I really like the look of this:
The_Marcato

It might do the job here nicely.

Is the Carpenter Jack the part that clamps onto the violin? It looks like they have a standard 1/4" mono-connector for the cable but I want to make sure that the cable connector is not something strange called a "carpenter jack".

Thanks,
eala
 
Status
Not open for further replies.
Top Bottom