Hi,

I have fitted a piezo pickup under the saddle of my classical nylon strung guitar.

My plan is to build the following : a 3 channel parametric eq followed by a fuzz box. All will be mounted into the guitar and powered by a 9V battery.

As a beginner I have many questions and in order to start off on firm foundations I guess it would be sensible to understand output and input impedances. So, as I have assumed that I would need a basic preamp for my piezo pickup before feeding the signal into other places I built the attached single transistor amp.

The output impedance of the piezo is simple I guess, I measured the resistance between the 2 electrodes to be 2MOhms or more. The output impedance from the amp is not so clear to me as there are currents and voltages and frequency dependent impedances due to the capacitor etc...

Question 1: what is the output impedance of the circuit in the attached file
Question 2: Do I need the attached preamp if I then have a parametric eq which must contain amps
Question 3: Does anyone have a good schematic for a parametric eq, preferable using transistors
Question 4: is this post breaking the etiquette rules of length and number of questions?

thank you in advance

 

Odd transistor choice and odd transistor symbol.

Have you googled Guitar Piezo Pre-amp? Quite a few to choose from, no point reinventing the wheel.

It's a good idea to put a pre-amp before the eq stage because it probably won't be designed to be driven directly from a guitar pick-up and may only have unity gain and too low an input impedance.

Probably best to go for an op-amp based parametric equalizer as it's likely to be easier to build.

 

hell of a waste to use a 2N3055, use a fet or BC109 ....etc here


https://www.montagar.com/~patj/gindex.htm

 

Odd transistor choice and odd transistor symbol.

Have you googled Guitar Piezo Pre-amp? Quite a few to choose from, no point reinventing the wheel.

It's a good idea to put a pre-amp before the eq stage because it probably won't be designed to be driven directly from a guitar pick-up and may only have unity gain and too low an input impedance.

Probably best to go for an op-amp based parametric equalizer as it's likely to be easier to build.

Thanks for the reply. I will normalise my transistor symbol.

I used the circuit that you show here but it gave a voltage gain of only about 2 so just tried something else to hand and it gave me a gain of 25...?
What is it that is odd about the transistor I used? It says it's general purpose and amplifier...

 

hell of a waste to use a 2N3055, use a fet or BC109 ....etc here


https://www.montagar.com/~patj/gindex.htm

What should the 2n3055 be used for? Why not in this circuit?

 

The 2N3055 is a power transistor, for handling heavy currents. It has a poor frequency reponse for audio use.

 

The 2N3055 is a power transistor, for handling heavy currents. It has a poor frequency reponse for audio use.

ok, its out. thanks.

 

hell of a waste to use a 2N3055, use a fet or BC109 ....etc here


https://www.montagar.com/~patj/gindex.htm

Maybe he wants to drive a speaker directly out of the pickup.

 

What should the 2n3055 be used for? Why not in this circuit?

i would use a Jfet for a piezo pickup, like a 2n3819, or MPF102,

http://m.instructables.com/id/Building-JFET-Preamplifiers-for-musical-instrument/

 

i would use a Jfet for a piezo pickup, likea 2n3819, or MPF102,

http://m.instructables.com/id/Building-JFET-Preamplifiers-for-musical-instrument/

I used the exact circuit that Blocco gave in #2 using a j201 but only got voltage gain of about 2, i think I have some MPF102 as well but can I get larger gain or should I put a few in series?

 

i would use a Jfet for a piezo pickup, like a 2n3819, or MPF102,

http://m.instructables.com/id/Building-JFET-Preamplifiers-for-musical-instrument/

The 3055 is a high power transistor....like 100 watts! You want a low noise signal transistor.

 

I used the exact circuit that Blocco gave in #2 using a j201 but only got voltage gain of about 2, i think I have some MPF102 as well but can I get larger gain or should I put a few in series?

You may not want a lot of voltage gain. The main point of the onboard preamp is for equalization and impedance matching.

 

a good op amp for high impedance is a Ca3240,
its best to use stages, so use Jfet transistors or op amps.

 

Anyway looks like its the jfet no doubt.

hell of a waste to use a 2N3055, use a fet or BC109 ....etc here


https://www.montagar.com/~patj/gindex.htm

thanks for this link

 

You may not want a lot of voltage gain. The main point of the onboard preamp is for equalization and impedance matching.

so that brings me to my other question, namely what is the output impedance of this for example:

is it simply 51K?

 

Should the load impedance always be higher than the output impedance of the source?

 

Should the load impedance always be higher than the output impedance of the source?

Yes. in just about all modern audio circuitry. The load impedance should be 10 x or greater than the source impedance.

 

so that brings me to my other question, namely what is the output impedance of this for example:

is it simply 51K?

It would be something under 6.8k. R3||R4||Rout of the transistor.

 

so that brings me to my other question, namely what is the output impedance of this for example:

is it simply 51K?

The output impedance is around 6k as R4 is effectively in parallel with R3. If you need a lower output impedance, just add an emitter-follower stage.

Oops, Veracohr got there before me