Getting 1 megohm input impedance for a piezo pickup.

[Whoops]

Another aside - just sticking a piezo element onto the soundboard will sound awful

That depends on the pickup itself, I recently acquired an Ehrlund pickup and it sounds great attached to the soundboard of the Doublebass or Cello.
The best sounding system I've tried for Doublebass was the Yamahiko pickup but that requires a permanent installation by a Luthier.
The EhrLund is easier and more pratical to use and achieves excellent results on the soundboard.

https://ehrlund.se/product/pickup/?v=f003c44deab6

 

[TheGedi]

The K&K type pickups are just little glue on limpets and usually three of them in parallel, each encapsulated on the back with epoxy - apologies I originally wrote in series but corrected the post within minutes, I meant parallel. Indeed a Fishman element sits under the bridge saddle and relies on string pressure over the saddle (no pressure = no signal, and often uneven pressure hence bad string balance) as mentioned earlier they get their signal too early - they are part of the transfer between the saddle and the bridge, the sound then propagates into the top, this type of pickup ignores the timbre of the instrument body. It is the best compromise for stage work but isn't the true sound of the instrument.

If the element is sat in the bass bridge I would recommend jamming it in somehow to get pressure on it, it really isn't the best place to pick up bass frequencies.

Out of interest - here's a link to some research I found twenty years ago while researching guitar design. The bodies are basically resonators with a fundamental frequency and the tops have positive and negative phase signals all over so experimenting with pickup placement is a good idea - Chladni patterns of guitar plates

 

[TheGedi]

That depends on the pickup itself, I recently acquired an Ehrlund pickup and it's sounds great attached to the soundboard of the Doublebass or Cello.
The best sounding system I've tried for Doublebass was the Yamahiko pickup but that requires a permanent installation by a Luthier.
The EhrLund is easier and more pratical to use and achieves excellent results on the soundboard.

https://ehrlund.se/product/pickup/?v=f003c44deab6

I doubt they are piezo transducers, a dynamic mic element would work very nicely in that situation. I did the sound for a guy called John Jorgensen years ago, he had a cheap lavalier mic stuffed into a foam donut holding the face of the mic head on to the soundboard - it worked a treat.

 

[ccaudle]

Indeed a Fishman element sits under the bridge saddle

I have not looked inside a guitar with a Fishman pickup, do you know if they have any that also incorporate a pickup glued onto the underside of the soundboard? Seems that would be feasible if you wanted both styles of pickup. Fishman have both soundboard transducers and undersaddle piezo pickups.
I cannot find on their web page a pre-amp that blends both undersaddle and soundboard, but they do have one which can blend piezo and an included microphone (the microphone seems to pickup from the interior of the guitar, not sure how good that sounds).
Actually now that I think about it, the pickup in the Martin guitar I referenced above may even have that microphone included. I vaguely remember the guitar owner referencing a blend control, but I didn't have time right then to pursue the details. Sounds good whatever it includes.

 

[abbey road d enfer]

I doubt they are piezo transducers

Why would you think that? There are many examples of piezo pickups used in a simialr fashion. In addition, the input impedance of 4.7 megohm for the dedicated preamp seems to corroborate.

, a dynamic mic element would work very nicely in that situation.

I don't see how. There have been dynamic transducer (e.g. National Westwood), but they are rather bulky.
AKG still have a dynamic transducer, the D411. It's 9.5 mm thick.

I did the sound for a guy called John Jorgensen years ago, he had a cheap lavalier mic stuffed into a foam donut holding the face of the mic head on to the soundboard - it worked a treat.

That's the basis for many of the hybrid systems that combine a saddle transducer and an electret mic. The former brings level and feedback resistance, the latter brings timbre naturalness.
Some systems have dual outputs, the piezo output being directed into the monitors and the mic into the FOH.

 

[Whoops]

I doubt they are piezo transducers,

So you need to read the product description, it's in the link I posted

a dynamic mic element would work very nicely in that situation.

Like Abbey I also don't see how.
Anyway the Ehrlunf pickup it's not a dynamic microphones

I did the sound for a guy called John Jorgensen years ago, he had a cheap lavalier mic stuffed into a foam donut holding the face of the mic head on to the soundboard - it worked a treat.

That might work, but it's not related in anyway or similar to the Ehrlund pickup.
The problem with that setup is that you will not have much headroom before feedback in the stage monitors, while with the Ehrlund pickup, or any piezo pickup actually you have a lot of volume in the monitors before feedback.

Different tools, Different outcomes

 

[TheGedi]

I have not looked inside a guitar with a Fishman pickup, do you know if they have any that also incorporate a pickup glued onto the underside of the soundboard? Seems that would be feasible if you wanted both styles of pickup. Fishman have both soundboard transducers and undersaddle piezo pickups.
I cannot find on their web page a pre-amp that blends both undersaddle and soundboard, but they do have one which can blend piezo and an included microphone (the microphone seems to pickup from the interior of the guitar, not sure how good that sounds).
Actually now that I think about it, the pickup in the Martin guitar I referenced above may even have that microphone included. I vaguely remember the guitar owner referencing a blend control, but I didn't have time right then to pursue the details. Sounds good whatever it includes.

I think they do indeed do a mic blend system with their undersaddle pickup. Interestingly years ago I asked a guy at a famous brand guitar factory why they used Fishman, the reply was "they always worked when installed and never came back", I didn't hear anything about how they sounded or reacted to volume on stage but they do work on stage - a good compromise. My experience of a mic inside a guitar is you turn them off if you are working with a drummer as you cannot get the levels - try putting your mouth round an SM57 with some gain on it, it howls round for fun. If you are a solo artist on your own or a small acoustic ensemble the mic will work but any hint of reasonable volume and you get howlround, your separate volume for the mic is you rescue button.

 

[abbey road d enfer]

I have not looked inside a guitar with a Fishman pickup, do you know if they have any that also incorporate a pickup glued onto the underside of the soundboard?

Indeed they do. They call it Powertap, because it picks up not only the strings sound but also the taps that are part of avant-garde picking.

I cannot find on their web page a pre-amp that blends both undersaddle and soundboard,

My understanding is it's part of the Powertap system, but doesn't sell separately.

(the microphone seems to pickup from the interior of the guitar, not sure how good that sounds).

Many players consider it an improvement over the undersaddle alone, but it cannot rival with a good SDC in terms of sound quality.

Actually now that I think about it, the pickup in the Martin guitar I referenced above may even have that microphone included. I vaguely remember the guitar owner referencing a blend control, but I didn't have time right then to pursue the details. Sounds good whatever it includes.

Blend almost inevitably pertains to undersaddle+electret mic inside. There are exceptions of course, but they are custom jobs.
A quite popular alternative to an inside electret mic is the AudioTechnica ATM350, for which a number of specific mounts are available, for guitar, piano, violin, brass and woodwind.

 

[TheGedi]

Apologies guys, the thread started off discussing the input impedance of the preamp and I realise the only thing I have done is dragged it somewhere else - my initial point was if you stick multiple piezo's together in parallel it reduces the necessity of a high input impedance of the thing it is plugged into. I've done this and it works, the signal is full, you get more coverage of the soundboard because you are picking it up from multiple places, and you can bang it into a standard guitar input or Di without needing excessive eq.

If someone wants to open up another thread about piezo guitar systems I can probably add quite a bit of input, I have worked as a luthier most of my adult life and fitted and used most systems commercially available - none of them are perfect but they get very close and are usable on a noisy stage.

 

[abbey road d enfer]

Anyway the Ehrlunf pickup it's not a dynamic microphones

It seems like they've taken their idea of a triangular diaphragm, which they use in their condenser mics, and adapted it to piezo transducers.

 

[abbey road d enfer]

Apologies guys, the thread started off discussing the input impedance of the preamp and I realise the only thing I have done is dragged it somewhere else -

No need to apologize, we love it when it goes OT and opens up to something different.

my initial point was if you stick multiple piezo's together in parallel it reduces the necessity of a high input impedance of the thing it is plugged into.

Indeed. In my piano I have two piezos. They are rather large (about 40mm diameter); I have measured them at 2500pF. I put two in parallels for 5nF. I use a 1Megohm DI, but I have tried direct into the line input, that is about 50k. Of course the LF response is not that good, but nothing that a small amount of EQ can't overcoime.

I've done this and it works, the signal is full, you get more coverage of the soundboard because you are picking it up from multiple place

I have put the transducers in the most extreme locations, full left and full right, and I was surprized that they sound very similar; the balance between left and right hand is not as separated as it is when using mics. It looks like the soundboard does a pretty good mix! I also tried in stereo, there is some width to the soundscape, but it's not coherent. It sounds more like pseudo-stereo.
The overall sound quality is not extremely good. It's for rehearsals, not for recording.

If someone wants to open up another thread about piezo guitar systems I can probably add quite a bit of input,

We don't have a musical instruments section, so I guess it's ok to continue here, unless the OP takes umbrage.

 

[JohnRoberts]

Its all physics and electronics

JR

 

[abbey road d enfer]

Its all physics and electronics

JR

Amen...

 

[iampoor1]

Most of my favorite threads here are the ones that veer offtopic and contain nuggets of wisdom, knowledge and experience! Learned alot from this one!

 

[CJ]

Loading down the piezo might actually help to knock off some of that ice pick hi end,

 

[cyrano]

1 mega is the standard input impedance in most Active DI boxes but you will see that DI boxes specifically made for Piezo pickups have an input impedance of 5 to 10 Mega.

I like to use 10Mega for all piezo pickups, I find 1 Mega to be too low

As I'm lazy, I used an old instrumentation preamp with a 10 Mohm input impedance when I was experimenting with piezos. Not DIY, but cheapness, as you can often get those for 20€ or so...

 

[VanGenz]

Thank you for this wonderful discussion in an area I love. I "forgive" you all for going outside my original question. I have been a gigging musician for 55 years an have tried most of piezo's (K&K, Fishman, LR Baggs, etc and have made my own several times from piezo transducers, and they work quite ok, and are almost free). I have tried a lot of the magnetic soundhole pickups. I use two Fishman Rare Earth on my weissenborns (one normal tuned in D and a barytone tuned in A) the have a little "electric" sound but works very well on the weissenborns and you can also have quite distorted sound and sound more like a lap steel. I have two Taylors with the first magnetic expression 1 system, liked them at first but got a little tired of the "a little bit too much electric sound". But it works very well and is very feedback resistant. have two Taylors with the new piezo expression 2 system which sounds very good. I also have an older Taylor with an under saddle Fishman system and this has been my "work horse" guitar for many years. I also have under saddle piezo in my octave mandolin (also called Irish bouzoki). It s a cheap Fishman system but works ok. I also have a IR system - Audio Sprockets tone dexter. These products can get a piezo system sound very close to a condenser in front of your instrument. But its to stressfull to bend down and change prestes each time I change instrument (which I do all the time...) during a concert while I also have to talk, retune a guitar and etc. I have a Boss GT1000 that I also use for my acoustic instruments which have the possibility to load IR speaker responses. I suspect I could have made IR responses for my different instruments and could have them automatic loaded with different presets for different instruments. But you also need some kind of blend control between the IR sound and the direct piezo sound so I have not looked into this yet. L.R Baggs has a dual system with piezo and a small condenser as described further up called L.R. Baggs Anthem system. I have this system in a beautiful handbuild guitar, but I rearly use this instrument live. I guess Fishman has similar sytems and I have installed a system from K&K in a key fiddle that works very well. This system has 3 small piezos in parallell and a small condenser to be able to blend in a little more acoustic sound. I also have installed a Roland GK hex pickup in one of the Taylors and a similar piezo based hex pickup system from Richard McClish/RMC RMC Pickups installed in a Lowden guitar. I use this to run my Roland VG-99 which I also used for acoustic guitars many years. Thats another story...

​

 

[Egor Reshetnikov]

tl;dr.

i build "charge amplifier" piezo preamp (for upright piano standing right near the loud drumset) from elliot sound website. With some changes\mistakes. i didn't use input capacitor so thers like 1 volt
on the pickups - i dont care. Also changed some resistor values for bax equaliser for my taste, made the circuit run from 48v phantom mic input and 8:1 chinese transformer (which turned out to be pretty clean and flat) for tl072 output . For pick-ups i used chinese 30mm cheap piezo. Two of them glued togheter like a sandwich: 1st is for pickup, 2nd - as a back shield (crystal layer not connected, copper grounded). The thing is that back shield is glued to actual pickup with rubber spacer in between on the copper edge not touching working pickup crystal layer - it sounds much better when nothing is touching it. After all it sounds awesome (for a piezo), lots of low-end with not a trace of 50hz hum. THis "charge amp" maybe a little hissy compared to other designs (i had tried some few of usual fet-opamp high impedance designs) but IMHO is able to get better sound from those piezos

 

[Whoops]

Hi argot,
Can you please post the link from Elliot sound that you used for that circuit?

thanks

 

[deedee]

Hi argot,
Can you please post the link from Elliot sound that you used for that circuit?

thanks

https://sound-au.com/project202.htm