taming a Rod Piezo

[MarkusBass]

Piezo pickup requires a high impedance buffer. And such a buffer requires a battery. So your idea to avoid battery in the instrument is very difficult to fulfill. I would rather search for circuits with very low current consumption.
Also, it's good to know that many companies make such circuits. The one that I know is Powerchip from Fishman: https://www.fishman.com/fishman-equipped/powerchip-oem/ . It's a mixer of piezo/magnetic signal. Of course, it requires a battery.

Mark

[David King]

There's a piezo preamp that's powered by a super capacitor. You charge the cap via the output jack using a 9V battery for 30 seconds and you get about 18 hours of run time. Russian fellow in Montreal, MiSi is the company.
The main issue you'll have with mixing piezo with magnetic is that your signals will never be in phase (piezo pu is at the bridge node, magnetic pu is some distance from the bridge) so you'll always get some signal cancelation which you might like or you might hate. The higher up the neck you play the more obvious that cancelation becomes. No one ever speaks of this so maybe it's not a problem for them.

[J M Fahey]

Agree about the unavoidable phase difference.
Anyway you may try it both ways and choose what you like best .

But I guess any 2 pickup guitar has similar issues; maybe not that strong but anyway noticeable.

[eschertron]

A blend pot comes in handy there, especially for wildly different sources. Even a two-volume instrument like an LP gives a lot of nuance. I end up tweaking the blend via pickup height on instruments that don't have relative volume control built in. A bit limited in control range, but I'm compelled to do it.

[shortcircuit]

Appreciate all for the input and ideas , pointers to available products a lot of great items, most are a little pricey for what I'm doing (again with Leo's nothing cheap & easy) Darn it !!!!!! But I'm still all in , processing the options . Do thank all here at the forum !!

[shortcircuit]

plan #1 is leaving the Alumitone set up as is , piezo to a 10k pot both sent to a TRS stereo out jack , stereo Y cable out, send the piezo through a pre-amp(tech 21 is on the way) to one amp , Alumitone out to another amp . I have more than one build, so I'd still like to have an internal blend set up , haven't decided which way to go on that yet. JM if you are still contemplating on providing a sketch please do , this is not a push!! so please don't feel it is , would like to try a DIY/w help something.

[Helmholtz]

plan #1 is leaving the Alumitone set up as is , piezo to a 10k pot both sent to a TRS stereo out jack , stereo Y cable out, send the piezo through a pre-amp(tech 21 is on the way) to one amp , Alumitone out to another amp . I have more than one build, so I'd still like to have an internal blend set up , haven't decided which way to go on that yet. JM if you are still contemplating on providing a sketch please do , this is not a push!! so please don't feel it is , would like to try a DIY/w help something.

It is no good idea to connect a 10k pot to the piezo. A piezo PU is a high impedance capacitive source, a typical capacitance value being 1.5nF. Connecting this to a 10k pot produces a high pass filter with a corner frequency of above 10kHz! This means that all frequencies below 10kHz will be strongly attenuated.

The minimum load resistance should be 1M. But a 1 M pot will noticeably reduce highs at lower vol. settings.

There is actually no good passive solution to your problem.

[J M Fahey]

Ok, hereīs the very low consumption (0.2mA meaning 4000 playing hours from a typical 9V alkaline ) chopped to the bone Piezo/magnetic preamp.

Fails safe, IF battery dies (which by itself will take Months or Years ) you simply turn Balance pot fully towards the Magnetic pickup and continue playing.

[shortcircuit]

Thank you JM , very nice design, I will start gathering components , will have to order a few , I'll give it a go and let you know.
Thanks again really appreciate it.

[Helmholtz]

Ok, hereīs the very low consumption (0.2mA meaning 4000 playing hours from a typical 9V alkaline ) chopped to the bone Piezo/magnetic preamp.

Fails safe, IF battery dies (which by itself will take Months or Years ) you simply turn Balance pot fully towards the Magnetic pickup and continue playing.

[ATTACH=CONFIG]52978[/ATTACH]

Nice circuit!

One remark: The 100k balance pot will load the magnetic PU. With typical high impedance PUs this results in reduced highs, similar to partly engaging the tone pot. I am not familiar with the Matchbox PU, but it might make sense to experiment with higher pot values (250k or even 500k) to preserve most of the treble response.

[shortcircuit]

Nice circuit!

One remark: The 100k balance pot will load the magnetic PU. With typical high impedance PUs this results in reduced highs, similar to partly engaging the tone pot. I am not familiar with the Matchbox PU, but it might make sense to experiment with higher pot values (250k or even 500k) to preserve most of the treble response.

I will breadboard the circuit before I assemble anything permanent , will keep this in mind,as well as your #37 post for the other project, thank you for the input.

[J M Fahey]

Nice circuit!

One remark: The 100k balance pot will load the magnetic PU. With typical high impedance PUs this results in reduced highs, similar to partly engaging the tone pot. I am not familiar with the Matchbox PU, but it might make sense to experiment with higher pot values (250k or even 500k) to preserve most of the treble response.

True, but real life decisions force us to compromise.

The preamp I make commercially uses a TL062 (double Op Amp) and both the piezo and the magnetic pickups are buffered (1M the magnetic, 3M3 to 10M the Piezo) *BUT* this one is simplified for shortcircuit, specially avoiding him the trouble of printing and etching a PCB.
As shown it needs no PCB at all, not even perfboard, can be built point to point or even dead bug style.

When choosing the balance pot value, I had to compromise, because "half the circuit is active, half is passive" and to boot, since I chose NOT to use Op Amps here, maximum "gain" I can hope for is unity gain (source follower).

* A 250K and even worse a 500k pot will attenuate signal way too much, specially because Volume and Tone pots are 250k each.

* a 10/25/50k one will load Magnetic too much and even more at higher frequencies.

* so I chose halfway 100k as a "least bad" compromise: signal loss is reasonable (a couple dB) and treble loss in practice is irrelevant .... since the Piezo will provide a Ton of highs anyway .... way more and specially way higher range than anything a magnetic pickup can even dream of.

In general I try to see circuits not as a bunch of independent parts but as a whole system

[Helmholtz]

Makes sense, thanks.

[shortcircuit]

True, but real life decisions force us to compromise.

The preamp I make commercially uses a TL062 (double Op Amp) and both the piezo and the magnetic pickups are buffered (1M the magnetic, 3M3 to 10M the Piezo) *BUT* this one is simplified for shortcircuit, specially avoiding him the trouble of printing and etching a PCB.
As shown it needs no PCB at all, not even perfboard, can be built point to point or even dead bug style.

And shortcircuit appreciates it !!!!!!! Will build as posted , out of respect for you taking time to post it, hopefully it isn't bug ugly .

[J M Fahey]

Oh, donīt worry, "dead bug" because parts are usually mounted "legs up" is a tried and true build technology for minimalist projects or even to fit a non-pin-compatible IC replacement, in that case itīs mounted legs up and thin wires connect legs to proper holes.