Geek Pre-Amp question OHMs

[Perry]

Red-Eye Twin specs:

Input: high-impedance, 1 million ohms, maximum 1 volt peak-to-peak level.

Grace BiX specs state that the input is 10M Ohms and that can cause a problem with K&K pick-ups which I use. See #7 from BiX manual excerpted below.

Is this an issue I really need to worry about? I don't want to start messing with special cables.

[vince f]

yes it matters. best results are achieved with matched impedance (particularly with impedance this high) Do as they suggest with special cable. consider yourself lucky that they provide the option, some pre-amps do not.

[Br1ck]

Use the TRS cable work around or get a device with the proper input impedance. Why Grace would design a pre that would be a pain for such a large segment of their market is perplexing.

[Mandobart]

Here's my take on it as a former navy electronics tech who dealt with a few signal attenuation problems due to improper impedance matching issues:

At every interface in a signal path, the greater the impedance mis-match the greater the signal fidelity will suffer. That said, the function of a preamp or DI is not so much to match its input impedance with the pickup output impedance; its function is to match the high output impedance of the pickup (in the million ohm range) to the low input impedance of the mixer or amplifier (in the thousand ohm range). That is a huge difference (a factor of 1000!). A difference of 1 megohm vs 10 megohm is nothing in comparison. I wouldn't worry about it. My Carvin AG300 has a HI Z function for the input channels that the manual says is intended for pickup impedance values of 500 kohm and larger. It works just fine with all my JJB equipped instruments plugged straight in without using any DI or preamp. For those times I play through anything else I use my RedEye.

Like a lot of audiophile discussions, some of the tech info and "issues" published only affect sounds in the range outside of human hearing - most of us need an o'scope to tell there is any difference. No one can honestly tell me there is an audible difference when going from 1 Mohm to 10 Mohm. Now plugging a high impedance pickup straight into a low impedance channel designed for something 1000 times lower results in the tinny piezo quack were all familiar with. I have no idea why they say K&K have low impedance. ALL passive piezoelectric pickups have an impedance in the megohm range. They *might* be referring to a system that has an integral preamp built into the endpin jack.

[dang]

I used my Grace Design Felix on 10mOhm for a while before I realized there was a switch on the back, it didn’t effect anything I could hear. Ymmv

[Perry]

Thanks everybody. I A/B'd my guitar with BiX vs. Red Eye and if anything I was getting more bass with the Red Eye. Go figure. Still need to try the mandolin which I would expect to be less of an issue since there is not much low end to begin with.

I did reach out to Grace and they sell a 1/4" female to 1/4" male* adapter which will turn your ordinary cable in to the TRS they suggest above.


* how is such terminology tolerated in this PC world

[pops1]

I think the extra bass you are hearing is from a perfect impedance match rather than one that is 9 million ohms off. Electronics says a factor of 10 is ok, but right on is better in my opinion.