I would like to understand a bit about how a standard preamp effects pedal works? I was particularly interested in how they interact with the speakers? Does the preamp make for example, an overdrive type effect by upping the input to the speaker? Or is it all done on a circuit in the preamp? You can probably tell from the questions and terms I use that I am no electronics whizz-kid, so take it as if I know nothing . . . Which is pretty much the case.
All the best from Bill. :D
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1.) As you play your guitar with a mag pickup, the impedance will change. it is not like resistance, in that it is a moving target. It is all interacting depending on volume and note as the coil in the mag reacts to the rest of the circuit.
2. One problem with disk piezo is the fact that it will act as a capacitor - it will self filter some frequencies. I do not know how the actual size of the disk affects this or whether multiple piezo's of different sizers will correct it.
3. Pictures of piezo installation on violins and cellos that I have been able to find usually had multiple piezo's (2 or 3) and they were pretty much just stuck on in various places. There did not seem to be a great deal of isolation. They were depending on the preamp for correction.
Piezo disks are not just used for CBGs. They are also used on things like violins and cellos where the strings are not steel so an electro magnetic pickup cannot be used. On these instruments fidelity is important, so the corrct preamp is important and if store bought, expensive. The classic DIY preamp for disks is the Tilman preamp. It is a junction field effect transistor preamp, JFET preamp for short. It has a minimum of parts, six I think. There is almost no gain. Its purpose is only to match impedances.
The problem with this preamp is twofold. 1. It uses a really old JFET that is hard to find locally and 2. That particular JFET is not always of consistant quality. However, if you google it, the schematic will show you a basic preamp circuit with the impedance input set right at the start by and external resistor. Then, if you go through some of the other threads here on preamps, you will see that the circuits shown are very similar, but using more accessible JFETs.
As for why piezo materials are so high impedance, my understanding is that they are not acting as a coil or a resistor but as a capacitor instead.
I am no electronics wiz. This is just some of the stuff I have picked up trying to get piezos to sound better and building a few of my own preamps. And believe me when I say I am not sure if I have the actual electrical theory straight here.
Just talking pre amps here. A preamp has two functions. One is to amplify the signal so that the main amp can deal with it. This is exactly the function of the pre amp on a stereo amplifier on the turntable input. The magnetic cartiege signal is faint and must be brought up to power. The other function is impedance matching. The standard guitar amp is designed for electromagnetic pickups. These have an impedance of 3 K Ohms up to about 1 M Ohm for an over wound humbucker. Piezo pickups, especially disk piezo, have a very high impedance. It will be in excess of 1 M Ohm and may be in excess of 10 M Ohms. Disk pickups have a high output and have no need of pre-amplification. They do need impedance matching. The preamp will take a piezo with a high impedance as an input and put out an output to the amplifier of an impedance closer to that of an electromagnetic pickup. Then the amp can deal with it without distorting it. With rod and cable piezo, the impedance problem is similar and they need pre-amplification as the output is not near as strong as a disk piezo.
In terms of distortion pedals, from what I understand, they are playing with setting impedances and pre-amplificarion that may or may not match the amp to give the desired distortion affect. Reverbe and flange etc are probably different again.
A standard preamp boosts the power of the signal. Say your using a piezo. You plug your guitar into the input of the preamp. The volume knob adjusts how much more power you want to add to your week piezo.
Let's call your natural output of your piezo equipped guitar 1. And the natural output of a standard single coil electric guitar pickup at 4. Then the standard output of humbucker a 6. Now to make your guitar output match the more powerful or louder pickups you would turn up the preamp. The preamp using the energy it gets from a battery to add energy to your natural signal. Thus matching the energy or power you would get from a single coil or humbucker.
Yes you can overdrive an amp with a preamp pedal. But be careful with a piezo. If you go all the way up to 11 you'll get uncontrollable feedback. to control this you'll have to turn the amp down. If your just looking for a distortion or overdrive I'd take your piezo equipped guitar to a music store and try out a few distortion and overdrive pedals. You'll be able to get distortion at a very low volume. Remember. When using distortion LESS is more.
Replies
A couple of things:
1.) As you play your guitar with a mag pickup, the impedance will change. it is not like resistance, in that it is a moving target. It is all interacting depending on volume and note as the coil in the mag reacts to the rest of the circuit.
2. One problem with disk piezo is the fact that it will act as a capacitor - it will self filter some frequencies. I do not know how the actual size of the disk affects this or whether multiple piezo's of different sizers will correct it.
3. Pictures of piezo installation on violins and cellos that I have been able to find usually had multiple piezo's (2 or 3) and they were pretty much just stuck on in various places. There did not seem to be a great deal of isolation. They were depending on the preamp for correction.
The problem with this preamp is twofold. 1. It uses a really old JFET that is hard to find locally and 2. That particular JFET is not always of consistant quality. However, if you google it, the schematic will show you a basic preamp circuit with the impedance input set right at the start by and external resistor. Then, if you go through some of the other threads here on preamps, you will see that the circuits shown are very similar, but using more accessible JFETs.
As for why piezo materials are so high impedance, my understanding is that they are not acting as a coil or a resistor but as a capacitor instead.
I am no electronics wiz. This is just some of the stuff I have picked up trying to get piezos to sound better and building a few of my own preamps. And believe me when I say I am not sure if I have the actual electrical theory straight here.
Thanks David. I forgot about the impedance. This is Very a important feature to look for when choosing a preamp.
In terms of distortion pedals, from what I understand, they are playing with setting impedances and pre-amplificarion that may or may not match the amp to give the desired distortion affect. Reverbe and flange etc are probably different again.
A standard preamp boosts the power of the signal. Say your using a piezo. You plug your guitar into the input of the preamp. The volume knob adjusts how much more power you want to add to your week piezo.
Let's call your natural output of your piezo equipped guitar 1. And the natural output of a standard single coil electric guitar pickup at 4. Then the standard output of humbucker a 6. Now to make your guitar output match the more powerful or louder pickups you would turn up the preamp. The preamp using the energy it gets from a battery to add energy to your natural signal. Thus matching the energy or power you would get from a single coil or humbucker.
Yes you can overdrive an amp with a preamp pedal. But be careful with a piezo. If you go all the way up to 11 you'll get uncontrollable feedback. to control this you'll have to turn the amp down. If your just looking for a distortion or overdrive I'd take your piezo equipped guitar to a music store and try out a few distortion and overdrive pedals. You'll be able to get distortion at a very low volume. Remember. When using distortion LESS is more.