Impedance matching for the tech minded

[DoryDavis]

I asked this question in another way but haven't got any responses. For the tech minded: I have a Platinum Pro preamp with an output impedance of 600ohms, from the xlr output. I am plugging that into the mic input on a Fishman mini. That input impedance is 2kohms. Is this asking for problems? Thanks! I appreciate ANY perspective!

[Ed-in-Ohio]

You should be fine. The lower impedance output going into the higher impedance input is not a problem at all.

Moreover; the impedance range 600Ω to 10,000Ω is considered "Medium Impedance" and all components in this range will generally "play well together", especially when one goes from "lower into higher" (like you plan to).

[DoryDavis]

Thanks Ed-in-Ohio. That is what I thought, with research, but I don't trust myself to understand as well as I could/should.

[pieterh]

If I remember correctly, the idea of impedance matching (or at least optimising) is so that the equipment is question reduces the risk for actual current (as opposed to signal) flow. A higher impedance at the input would limit the risk for current (however small) travelling along the signal cable which would negatively affect the signal quality. So in other words, a higher impedance at the amp or mixer input is not a bad thing.

But I'm not an electrician or electronics expert and if I have got it totally wrong someone chip in here and put me right!

[sam.spoons]

The XLR output on most preamps, and certainly on your Fishman is designed to send a mic level signal to a mixing desk mic input. 600 ohms is a 'nominal' figure and most mics and DI outputs have an actual impedance of around 150ohms. Best practice is to have the 'load' impedance (i.e. the Loudbox's mic input) at least 10x the source (Platinum Pre) impedance. You have this with 150 ohms/2kohms so you'll be fine.

If anybody is interested there is a very good article here explaining impedance in relatively straightforward language.

[Mischief]

So is my sound being effected plugging my 3.6k ohm Lyric into my 1 Mohm acoustic play?

Cheers


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[guitaniac]

Originally Posted by Mischief

So is my sound being effected plugging my 3.6k ohm Lyric into my 1 Mohm acoustic play?

Cheers


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There's no impedance mismatch, since 1Mohm is about 277 times as high as 3.6Kohms. On the other hand, I'm surprised the Lyric's output impedance is that high. 1Kohm is more typical for an active pickup system. I'm curious as to where you found the info on the Lyric's output impedance. I couldn't find anything beyond an installation manual in the Support section of the Baggs website.

[Mischief]

Okay thanks for that. That was my fear because the lyric is so high.
I am happy with my final sound but I made some radical EQ cuts on some frequencies and if it was impart to some impedance issues I would try to address that first.

Thanks for the quick reply.


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[jonfields45]

Impedance matching is something often misunderstood. For maximum power transfer and minimum noise from external sources, a matching source and load impedance is best. For sources with reactive impedances (series capacitance for a K&K style pickup and series inductance for a passive electric guitar pickup) it is usually better to optimize minimizing the effect of the source impedance by having a relatively high load impedance. A K&K pickup is unique in that there are three heads and if the load impedance is too high, the heads load each other which again lets the source impedance rear its ugly head :~). Microphones are typically "low" impedances, and so are the outputs of most mixers, but one is a very low voltage signal and the other quite a bit higher. So even the best impedance match can fail if the source is too low or too high an output voltage.

Bottom line is try it and if it sounds good then use it.

[myersbw]

I'll 2nd Jonfields45 on this one. Yes, there is an impedance "mismatch" and yes, impedance matching will effectuate "maximum power transfer". But, that's not what you want in all circumstances.

In some motor and power transformer circuits, close matching is ideal to avoid efficiency losses. In audio signal transfers, you often find some mismatch and NOT loading the source renders the ideal tone. And, sometimes LOADING the source produces the ideal tone.

A good example of the latter is the pots used in some passive guitar pickup sets. In that case, not going for large value control pots reduces the signal and associated harmonics to a tame and enjoyable level.

The only time you REALLY don't want to go a large impedance mismatch is pushing your tube amp into too high an impedance device...like 4 ohm head into a 16 ohm cab. You could get away with it depending on the levels...but, you run a huge risk.

When you scale down to devices producing a line level or mic signal...you don't run much of a risk even if you inadvertently short a connection out. I won't say "all" devices are without risk...most are not though.

Cheers!
Brad

[Marty C]

Hi Jonfields and Myersbw,
Thanks for the information on impedance. I have a K & K mini and had bad results with LR Baggs para DI, which I had used many years on my under saddle pick ups and was happy with the results. I actually thought my cheaper guitars sounded much better than my Martin dread with K & k - when plugged in. When I did some research, I found the impedance mismatch a possible reason, but never really knew what this means. After many trials and almost changing pickups, I found a TC Helicon product (Play GTX and Play Acoustic) that was a match. The result was/is much better. Do you guys think adding a better match of the K & K pure preamp would help? Just looking to get a little more EQ in my chain.

Or As Jonfields said, "just try it and if it sounds good, use it".

[jonfields45]

The K&K sounds great into most amps, mixers, and preamps. But it will sound terrible if you put it into a mixer's line or mic input (too low an impedance which turns the K&K's series source capacitance into a nasty high pass filter). Now that problem is easy to avoid, however there is a more subtle problem with very high impedance loads of some amps, mixers, and preamps. If the input impedance is approaching 10M ohms, then the heads act as strapping capacitance on each other and bleed off the highs. There are relatively few devices with a high enough impedance to sound bad, but count my ZT Lunchbox Acoustic among them. Rather than buy an expensive new amp/mixer/preamp, here is the cheapo solution I keep in the gigbag with my K&K equipped Taylor:







A handy 1M ohm shunt resistor.

[guitaniac]

Thanks, Jon. Its very relevant to me that there's such a thing an an excessively high input impedance (for a particular passive pickup or active pickup system) which is detrimental to one's sound. Perhaps that explains why my passive PUTW I/O UST sounds better to me through the BBE Acoustimax preamp (2.2Mohms input impedance) than through my 1st generation Fishman Platinum Pro EQ (10Mohms input impedance).

I'm not a fan of the Acoustimax's Sonic Maximizer (I keep it turned off), but the preamp works very well with my passive pickups (I/O UST and Baggs Hex).

[myersbw]

Jon...LOVE the improv using the 2nd jack & 1M resistor!!!

[Ed-in-Ohio]

Originally Posted by jonfields45

The K&K sounds great into most amps, mixers, and preamps...snip...however there is a more subtle problem with very high impedance loads of some amps, mixers, and preamps. If the input impedance is approaching 10M ohms, then the heads act as strapping capacitance on each other and bleed off the highs...snip...

Interesting. I was never crazy about how my K&K equipped guitars sounded through the Baggs Para DI preamp. They always sounded "just okay" to me. I wonder if the Baggs' 10MOhm input impedance had anything to do with that?

On the other hand, they sound great to me through the Fire-Eye Red-Eye preamp (1M Ohm input impedance), and even better to me directly into my Carvin AG200 amp set to Hi-Z (input impedance spec'ed as "greater than 500K ohms").

I think the takeaway is that although impedance matching is quite important, it is also quite complex, and is very much a "moving target".

Bottom line...Our ears don't lie. If it sounds good, it works.