Double Bass I Need an Input Impedance Primer

[Steve Freides]

I could use a bit of electrical education here. I own two different AI setups and I'll explain why I'm asking these questions.

My first setup, where I teach, is an original series AI Clarus connected to a Series III Contra-EX. It has a high-gain and a low-gain input, both quarter-inch, and the low-gain input has an impedance switch - push the button down for low input impedance, up for high.

My other amp, usually what I gig with, is a Series III Ten2 where, if I read the manual correctly, the input impedance switching happens automatically based on whether I plug in a quarter-inch or XLR connector. I'm thinking that maybe I need a quarter-inch-to-XLR adapter to get the right settings when I use the Ten2 - but you folks tell me, please.

My motivation in trying to understand this is simple enough - I tried the two different impedance settings on the Clarus and they sounded different. My test instrument to date isn't an upright but an acoustic/electric Ibanez AEF18 guitar from a few years ago. (For an upcoming performance at my wife's school, I recorded the guitar track and will play live on electric bass along with the recording - gives the phrase "playing with myself" new meaning. )

I recorded by plugging the guitar into the Clarus/Contra, using the high impedance setting, and put a Zoom H2 on the music stand a couple of feet from both me and the amp, so what I recorded was a combination of acoustic and amplified sound - I liked the results.

My upright has a SixRounds pickup, an inexpensive piezo transducer with a quarter-inch jack which I've always connected to the Ten2 with a standard guitar cord. I'm wondering what would happen if I switched to using a quarter-inch-to-XLR adapter.

Could someone please explain this to me - what am I hearing that's different when I switch between high- and low-impedance using my guitar - I think the response is flatter on the low impedance setting but I like the sound better on the high setting - and what implications does this have for other instruments, e.g., my upright, which uses a piezo without a preamp, or my amplified classical guitar which has a K&K setup that includes a little preamp mounted inside the guitar?

Many thanks in advance for the education.

-S-

 

[drurb]

Perhaps this will help. Follow the links within. Here's a supplement.

 

[Steve Freides]

Thank you. After reading all that, it sounds like the answer is always going to be, "It depends."

But it also makes me thing that getting more than just the first piece of the signal chain from the people who make the first piece, e.g., buying the preamp from your pickup maker, gives you at least a chance of getting something relatively flat going into your amp.

It also suggests that I ought to try the quarter-inch to XLR adapter for anything that I plug into my Ten2 since it might change the sound.

-S-

 

[drurb]

Thank you. After reading all that, it sounds like the answer is always going to be, "It depends."

But it also makes me thing that getting more than just the first piece of the signal chain from the people who make the first piece, e.g., buying the preamp from your pickup maker, gives you at least a chance of getting something relatively flat going into your amp.

It also suggests that I ought to try the quarter-inch to XLR adapter for anything that I plug into my Ten2 since it might change the sound.

-S-

Whether it's a good idea to buy the pre-amp from the pickup maker "depends" as well. For specialty pickups that are matched with their pre-amps, I think that's a good idea. For others, it may not be optimal at all. There's no harm in experimenting with the different inputs. As for "flat" frequency response, well, that's a nice goal but it just isn't going to happen. My own approach is to use a pre-amp that has a flat response in that it is not "voiced" in any way. My choice is the fdeck pre/HPF. The pickup is not likely to be flat at all. Neither is your cab. Then there are the interactions with the room. I believe in having as flexible a tone-shaping system as possible, knowing how to use it well, and setting it in each venue to get as close as possible to my desired sound. That's also why I use parametric tone-shaping (on the EA iamp200).