Understanding impedance and preamps

[static0verdrive]

Hi all,

I'm hoping you can help me sort this out - may just be a brain fart. Disclaimer: I've done a lot of recording over the years, just never with acoustic guitars that can plug in (should I call them acoustic electrics or semi-acoustics?). I just picked up a Roland Octa-Capture but I also have an old Yamaha mixer, and by reading the instructions and other assorted info online, I think I've gone and confused myself.

Here's what I think I know:

• High-impedance (Hi-Z) sources include passive electric basses and guitars and usually use mono / TS cables, under 20' to prevent loss of high-mids & highs
• Low-impedance (Lo-Z) sources include DI out, microphones, etc and usually use XLR or balanced TRS cables
• Before you can plug into a mixer, you need a preamp unless it has a Hi-Z input

Before I say much else I wonder if by writing the above I answered my main question here - obviously preamps amplify the signal, but do they keep the impedance the same?

In other words, I was under the impression that I need a preamp for anything going into the mixer. Then I read the preamps built into most acoustic guitars are very Hi-Z, so that made me think I'd still need a DI of some kind despite them having a pre.

What say you? Even with an active bass or acoustic guitar with a preamp, I'd still need a DI to plug into the mixer or use a Hi-Z input?

Thanks in advance, any info will be greatly appreciated!

 

[static0verdrive]

Update: I just remembered that last night I tried a preamp into a regular input (just preamp, not DI) and it worked - which just makes me more confused because I thought I'd just figured out that a preamp doesn't change the impedance!..?

 

[Dima B]

Low-impedance (Lo-Z) sources include DI out, microphones, etc and usually use XLR or balanced TRS cables

Can be unbalanced too.

Before you can plug into a mixer, you need a preamp unless it has a Hi-Z input

Or any another device which can reproduce correct signal.

Then I read the preamps built into most acoustic guitars are very Hi-Z

Because piezo pickups which use in acoustic strings instruments require the extreme input impedance of the preamp/buffer. Input, not output.

obviously preamps amplify the signal, but do they keep the impedance the same?

No.

Even with an active bass or acoustic guitar with a preamp, I'd still need a DI to plug into the mixer or use a Hi-Z input?

Depends. I know that it isn't the answer what you want but there is so many options... But usually you don't in this case.

 

[static0verdrive]

Can be unbalanced too.


Or any another device which can reproduce correct signal.


Because piezo pickups which use in acoustic strings instruments require the extreme input impedance of the preamp/buffer. Input, not output.


No.


Depends. I know that it isn't the answer what you want but there is so many options... But usually you don't in this case.

Well I really appreciate the response in any case - we're supposed to record tonight and it'll be my first time screwing with an acoustic with a preamp. I suppose as long as nothing explodes it won't hurt to test a little keeping the above in mind. Cheers!

 

[Dima B]

Nothing's gonna explode It's just about sound quality. But I think the instrumental inputs in your interface is enough for the appropriate result anyway.

 

[Mark Reccord]

Preamps will typically have high input impedance and low output impedance. Acoustic preamps would usually have very high input impedance because they have to interface with piezo pickups which have very high output impedance, but they should have pretty low output impedance to interface with other audio gear. There shouldn't be any issue plugging a guitar with an on board preamp into a high Z input on a mixer, but the better way to do it would be to use a DI to turn it into a balanced mic-level signal (also low impedance).

 

[static0verdrive]

Awesome. So would pedals with gain (boost, OD, distortion, etc) act like a preamp and switch a passive hi-z signal to lo-z as well?

 

[Dima B]

Awesome. So would pedals with gain (boost, OD, distortion, etc) act like a preamp and switch a passive hi-z signal to lo-z as well?

It's very common.
Impedance bridging - Wikipedia, the free encyclopedia

 

[Mark Reccord]

Awesome. So would pedals with gain (boost, OD, distortion, etc) act like a preamp and switch a passive hi-z signal to lo-z as well?

Pretty much 100% of them, when they're turned on. True bypass pedals would be a special case because when they are turned off, the signal is switched so that it completely bypasses everything in the pedal and as such will not change the impedance.

 

[J.M.Sutherland]

Hi all,

I'm hoping you can help me sort this out - may just be a brain fart. Disclaimer: I've done a lot of recording over the years, just never with acoustic guitars that can plug in (should I call them acoustic electrics or semi-acoustics?). I just picked up a Roland Octa-Capture but I also have an old Yamaha mixer, and by reading the instructions and other assorted info online, I think I've gone and confused myself.

Here's what I think I know:

• High-impedance (Hi-Z) sources include passive electric basses and guitars and usually use mono / TS cables, under 20' to prevent loss of high-mids & highs
• Low-impedance (Lo-Z) sources include DI out, microphones, etc and usually use XLR or balanced TRS cables
• Before you can plug into a mixer, you need a preamp unless it has a Hi-Z input

Before I say much else I wonder if by writing the above I answered my main question here - obviously preamps amplify the signal, but do they keep the impedance the same?

In other words, I was under the impression that I need a preamp for anything going into the mixer. Then I read the preamps built into most acoustic guitars are very Hi-Z, so that made me think I'd still need a DI of some kind despite them having a pre.

What say you? Even with an active bass or acoustic guitar with a preamp, I'd still need a DI to plug into the mixer or use a Hi-Z input?

Thanks in advance, any info will be greatly appreciated!

Most newer mixers and interfaceds have an input that is switchable and labeled "guitar or inst input" whitch switches an impedance matcher. If your studio isnt equipped with a DI, you are missing a very needed and critical piece of gear that can be a problem solver, you can get a behringer for 20 bucks to do the job, I could try to explain the ELECTRONIC THERORY behind what impedance is and why matching is important but youd leave more confused than you are now..... you just wanrt to always make sure your input level (IE: +10db or -4db are also the same, ) higher end gear will always be matched but some "consumer" level gear with have the +10 and that will always agrivate the process.

 

[EastCoastThump]

I've done a lot of recording over the years, just never with acoustic guitars that can plug in (should I call them acoustic electrics or semi-acoustics?).

Those on-board pickups and electronics are a convenience for stage use. Some sound (a lot) better than others, but I've yet to hear one that sounded convincingly like an *acoustic* guitar. When recording, if you want the acoustic guitar to sound like an acoustic guitar, mic it.

Note: If you have to record via the acoustic's onboard pup, a parametric and compressor can help dial down and limit quacking transients.