piezos, pres, and wireless

[aZnrockstar]

Do high input load preamps lose their effectiveness on a pickup's response on the other end of a wireless system? Violin pickups typically benefit from input impedance above 1 Meg ohm, and potentially up to a 10 Meg load. Assuming I were using a non-companding digital wireless system with such a pickup, should I be.looking for a belt-worn preamp like a Gigpro to plug in before the 1.2 Meg input transmitter, or would it not make a difference? I guess the real question is does a preamp physically affect the response of a piezo pickup, or does it only affect the signal that is passed on to the signal chain?

[RockViolin]

 

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aZnrockstar wrote:

 

Do high input load preamps lose their effectiveness on a pickup's response on the other end of a wireless system? Violin pickups typically benefit from input impedance above 1 Meg ohm, and potentially up to a 10 Meg load. Assuming I were using a non-companding digital wireless system with such a pickup, should I be.looking for a belt-worn preamp like a Gigpro to plug in before the 1.2 Meg input transmitter, or would it not make a difference? I guess the real question is does a preamp physically affect the response of a piezo pickup, or does it only affect the signal that is passed on to the signal chain?

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 I'm no expert on such things. I just play 'em. But I'd guess that the only thing that affects what the pickup itself is doing is the volume knob on the instrument.

I remember thinking my rig sounded better wireless at times, back when I had a reason to use one. The wireless system I used to use went up to 16khz.- and I supposed it was because of that. 

[RockViolin]

  If you're looking to tame the piezos, the Sansamp Acoustic DI was designed with that in mind, has an input impedance of 4.7megOhm, and works as advertised with my Barbera transducers. It's small enough that you might be able to affix it to yourself in some way. I also use an Avalon U5 sometimes. 

 (These days the Sansamp is usually doing marvels with a snare channel, and the U5 is on bass. I'm mostly plugged straight into my Roland GP8 with the outputs going to an ADA MicrocabII. The pass thru outputs on the Microcab go to line in of a couple of Line6 units, Microcab outputs to stereo tube mic preamps. I've Y'ed out of the Microcab pass thru at times and have had 8 lines to the recorder including the line outs from the GP8, all coming out with no added hum or noise issues. But that's usually too much to mess with. Quite happy though!) 

 

[MikeRivers]

 

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aZnrockstar wrote:

 

Do high input load preamps lose their effectiveness on a pickup's response on the other end of a wireless system? Violin pickups typically benefit from input impedance above 1 Meg ohm, and potentially up to a 10 Meg load.

 

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You definitely don't want connect use a pickup that expects a high impedance load to a preamp (wireless or wired) that's designed for a low impedance microphone. You'll lose level and high frequencies. There are wireless transmitters designed for guitars that have a high input impedance. That's what you should be using with your violin pickup.

[philbo]

 

Yeah, Mike is right. I bought a piezo for my dobro, and it sounds terrible into a guitar amp. The level is weak, though I didn't lose highs at all.  In fact the treble will make your eyes bleed.  If I zero the treble and dime the bass controls it starts sounding ok, though.

 

I've designed some electronics to EQ the piezo, add 12 dB of gain, and drive an amp input properly. I plan to lay it out on a 1 square inch circuit board. Eventually I want to add an XLR jack and set it up to run off phantom power so I can run it into the PA direct, but right now I'm shooting for just using it with my guitar amp. It's my project for this winter...

[dboomer]

Well everything makes a difference ... But is there any distinction? Line 6 digital (I assume you are talking about) has an input impedance of 1.3 meg. So considering that you'll probably be using a 2foot cable to get it to the transmitter think about what effect your 20foot cable had before. I think you'll be way ahead

[aZnrockstar]

What I have now is an input impedance of 3.5 Meg. I'm possibly going back to that 1.3 Meg input if I start using my wireless again. The output of the wireless is most likely standard line level. So my 3.5 Meg input won't have the same effect on my tone, right? I think that's the conclusion I'm coming to. So what I'm wondering is, is it going to be worth it for me to get another preamp to wear on my belt for when I use the transmitter? I don't think the there's a way to get around that without degrading my tone. And this is a guitar wireless system that I'm using.

[MikeRivers]

 

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aZnrockstar wrote:

 

What I have now is an input impedance of 3.5 Meg. I'm possibly going back to that 1.3 Meg input if I start using my wireless again. The output of the wireless is most likely standard line level. So my 3.5 Meg input won't have the same effect on my tone, right? So what I'm wondering is, is it going to be worth it for me to get another preamp to wear on my belt for when I use the transmitter? I don't think the there's a way to get around that without degrading my tone. And this is a guitar wireless system that I'm using.

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The output of the wireless system is the output of the receiver which is totally isolated from the transmitter input. Are you saying that you're using a wireless guitar system now and don't like the tone from your pickup?

I wouldn't think that the difference between 3.5 megohms and 1.3 mehohms would matter much, but you may be comparing fish to fowl here. A fair comparison would be how the violin sounds when using the wireless guitar system verssus how it sounds using the preamp with the output going directly to your sound system or recording setup rather than hearing it from an instrument amplifier.

Or have I missed something here? I'm not quite sure what, if anything, you've actually compared, and how you've done the comparison.

[aZnrockstar]

I'm not trying to solve a big problem, or necessarily fix my sound. I'm just trying to find some impedance theory, as it applies to this situation. Call it trying to get the last 5% out of my rig. My actual questions: 1. Do preamps lose effectiveness when accepting line level versus instrument level? 2. Do preamp input load values do something of consequence at the pickup level, or is it just the way they process the incoming signal? 3. Do high load buffers have any effect on the signal out of a wireless receiver, other than adding noise?

[MikeRivers]

 

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aZnrockstar wrote:

 

Do preamps lose effectiveness when accepting line level versus instrument level?

The purpose of a preamp is to provide gain. I suppose that if you put in a line level and get out a line level, it could be characterized as losing effectiveness because it's no longer doing what it's intended to do. But that's probably not a very satisfying answer relative to your other questions. One problem is that putting a line level signal into a preamp that's expecting instrument or mic level may overload the input stage and result in distortion. That would certainly be ineffective, unless you like that distorted sound. The other thing (and I think another of your questions leads into this) is that the input impedance of the device is independent of the level going into it. So as a high input impedance buffer, input level doesn't change this characteristic.

 

Do preamp input load values do something of consequence at the pickup level, or is it just the way they process the incoming signal?

The pickup is affected by the load impedance it's working into. An instrument pickup, particularly a piezoelectric one, has a high source impedance. The source impedance acts as one leg of a voltage divider circuit with the preamp input impedance being the other leg. The higher the load impedance, the less voltage coming out of the pickup is dropped (lost) through the pickup's own impedance and the more voltage there is that can be amplified by the preamp. If you have a preamp with a 1 k? input impedance and feed it from a source with a 1 k? impedance, half the voltage from the source is dropped across the source impedance and the other half is available to the preamp's amplifier circuit. But if the source impedance is 1000 k? (1 megohm) 99.99% of the pickup's output voltage will never see the amplifier since it's all dropped across the impedance. This is why it's important, when amplifying a high impedance source, it's important to have a high input impedance. The goal to shoot for is to have the input impedance by 10 times or more higher than the source impedance, but this isn't always possible. There's an article on my web site that discusses what all of this means in greater detail.

 

Do high load buffers have any effect on the signal out of a wireless receiver, other than adding noise?

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I'm not sure I get this one. The buffer is between the instrument and the transmitter, in the form of a high input impedance. Most instrument pickups have a fairly high open circuit output level, so it's not necessary to amplify them very much to get them to line level (or to the working level of the transmitter), but a high input impedance is necessary to get as much of that open circuit voltage to the transmitter as possible. If you lose a lot of voltage you'll need a lot of gain, and will then likely amplify noise more than you'd like. The signal coming out of the wireleess receiver is probably coming out at line level (or maybe instrument level if it's intended to be connected to a guitar amplifier rather than a PA mixer). The receiver probably has a source impedance of 100 ohms or less.

[JeffLearman]

 

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aZnrockstar wrote:

 

1. Do preamps lose effectiveness when accepting line level versus instrument level?

 

Yes.  The purpose of the preamp is to amplify a very weak signal to line level, where you can plug it into other gear.  Do not connect your pickup to the wireless transmitter.  Plug the pickup into a preamp, and plug the preamp into the transmitter.  Of course, this only makes sense for a battery-powered preamp.

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2. Do preamp input load values do something of consequence at the pickup level, or is it just the way they process the incoming signal?

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Matching impedance is important for weak signals like microphones and piezo pickups.  Matching impedance maximizes power transmission across the interface, which maximizes signal-to-noise ratio.  It's unimportant for beefy line-level signals (as long as the impedance is high enough not to overload or short out the output.)