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  #31  
Old 03-25-2017, 06:01 AM
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Originally Posted by sdelsolray View Post
…I don't but into the K&K "impedance matching" urban legend. Any preamp with an input impedance of about 900k or greater will work just fine.
Hi sds…

K&K actually started the bru-ha-ha by suggesting on their site (and if you chatted with them by phone) that your sound would be seriously affected/degraded if you didn't use a preamp with precise and accurate impedance.

Some people bought into it.

The rest of us just plugged our K&Ks into whatever preamp we had around (ParaDI, mixers, or 7 channel EQ pedals mostly)…and they sounded great.



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  #32  
Old 03-25-2017, 06:45 AM
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Originally Posted by rmconner80 View Post
Love the RedEye

Don't love the Baggs Para DI
Same here. I also bought the K&K preamp that supposedly is made for the K&K and it is ok, I still like the RedEye best. I have the K&K pickups in my Martin HD-28V and Gibson J-45TV.
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  #33  
Old 03-25-2017, 06:47 AM
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Originally Posted by ljguitar View Post
Hi sds…

K&K actually started the bru-ha-ha by suggesting on their site (and if you chatted with them by phone) that your sound would be seriously affected/degraded if you didn't use a preamp with precise and accurate impedance.

Some people bought into it.

The rest of us just plugged our K&Ks into whatever preamp we had around (ParaDI, mixers, or 7 channel EQ pedals mostly)…and they sounded great.



This is true, That is what the folks at K&K told me also. The Red Eye works fine.
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  #34  
Old 03-25-2017, 08:02 AM
guitaniac guitaniac is offline
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FWIW, here's a link to Doug Young's impedance matching experiments with the Grace Design Felix (which has five input impedance options).

http://www.acousticguitarforum.com/f...tch+Doug+Young

Its safe to say that there isn't a large difference between using a 1 Mohm input impedance and a 10 Mohm input impedance with the Pure Mini equipped guitar (in this particular experiment). Nevertheless, I think K&K's Dieter makes a good point in his observation that some competitors' preamps were designed to optimize the sound of pickups which are very different than the Pure Mini. There are likely multiple factors which differentiate those preamps from a preamp which is optimized for the Pure Mini.


Its interesting to note that the passive Baggs Element/DTAR Wavelength transducer needs an input impedance "in the neighborhood of 100 Mohms" for optimum sound, according to DTAR's Rick Turner. I found this out the hard way when experimenting with a Wavelength transducer which I'd disconnected from its DTAR preamp and installed passively. It sounded incredibly brittle and tinny with any preamp that I tried it with. I bring this up to illustrate how radically different piezo pickups can be with respect to their optimum input impedance. I say "optimum" input impedance because I've been informed that there are reasons why excessive input impedance is a bad thing (though not as obviously bad as insufficient input impedance).

Last edited by guitaniac; 03-25-2017 at 08:08 AM.
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  #35  
Old 03-25-2017, 09:40 AM
Mandobart Mandobart is offline
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Don't think of impedance as excessive or insufficient - the key is the output impedance of the pickup should be matched to the input impedance of the PA/amp. Back in my navy submarine days we used a Time Domain Reflectometer to test long runs of nuclear instrument cables (similar to the coax used for cable TV) for problems. Cables have a characteristic impedance that the rest of the instrument loop needs to be tuned for in order to maximize signal transmission and minimize noise and attenuation. Any time there is a connection, termination, discontinuity, etc. there is an interface where some of the signal will get reflected back (and not in phase with the original signal) and some will continue on. We minimize the reflected signal as much as possible by matching impedance at this interface. Pretty important when you need the radar, communication or nuclear equipment to function correctly on a warship. For a gigging musician the stakes aren't quite so high.

Now how much our pu signal is going to be affected by a few megohms difference is easier to determine by trial and mistrial than by analytical methods that have to take into account the actual amplitude of the signal, the characteristic impedance of your cable, the length of cable, etc. I've found that several different preamps (or no preamp at all sometimes) work fine for the piezo pu's I use (mostly JJB, with a couple K&K).
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  #36  
Old 03-25-2017, 10:47 AM
RustyAxe RustyAxe is offline
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I've tried a few ... but honestly, I find the K&K Pure and Pure XLR just fine, and they don't break ... or break the bank. I looked at the RedEye, but the lack of real EQ control was a deal breaker. You're looking for an input impedance of around 1megOhms, on whatever you choose, for a good match.

I'm about to purchase an Empress ParaEQ for greater control over EQ (semi-parametric on three bands, with adjustable Q on each).
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  #37  
Old 03-25-2017, 11:01 AM
sdelsolray sdelsolray is offline
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Quote:
Originally Posted by guitaniac View Post
FWIW, here's a link to Doug Young's impedance matching experiments with the Grace Design Felix (which has five input impedance options).

http://www.acousticguitarforum.com/f...tch+Doug+Young

Its safe to say that there isn't a large difference between using a 1 Mohm input impedance and a 10 Mohm input impedance with the Pure Mini equipped guitar (in this particular experiment). Nevertheless, I think K&K's Dieter makes a good point in his observation that some competitors' preamps were designed to optimize the sound of pickups which are very different than the Pure Mini. There are likely multiple factors which differentiate those preamps from a preamp which is optimized for the Pure Mini.
...
Gary,

Yes, Doug's recent thread has the added benefit of being a scientific test because it removes other factors that could have an influence (e.g., different preamp design, different guitar, etc.).

Here's an earlier one from Doug from about 6 years ago:

http://www.acousticguitarforum.com/f...d.php?t=210280

Again, the only thing that changed was the impedance and performance, all else remained the same

Here's a post of mine from over ten years ago with a similar test:

http://www.acousticguitarforum.com/f....php?p=1026511

Yes, Deiter is the original source of the 'The K&K pickup requires a 1 MegOhm input impedance' statement. Keep in mind though that when Deiter first said this there was no K&K Mini pickup, only the K&K Standard pickup.
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  #38  
Old 03-25-2017, 11:06 AM
Buc-a-Roo Buc-a-Roo is offline
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Originally Posted by RustyAxe View Post
I'm about to purchase an Empress ParaEQ for greater control over EQ (semi-parametric on three bands, with adjustable Q on each).
I looked at that one as well.....but then it occurred to me that if I need that much EQ control something must be wrong with the pickup or the amp/board it's plugged into. Overkill in spades if everything else is good.
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  #39  
Old 03-25-2017, 11:55 AM
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Originally Posted by guitaniac View Post

I've had mixed results with the two preamps which Dieter mentions. The Baggs PADI (10 Mohm input impedance) gave me way too much bass when EQed flat. The Fishman Platinum (10 Mohm input impedance) was more balanced.

That should tell you a lot, Gary. The problem with this impedance question is that a lot of people compare apples and oranges and make a conclusion about pears from it :-) In this case, you have two preamps with the same impedance with different results, which should be a clue that it's not the impedance that's affecting the results. If you try a preamp with variable impedance (like the Grace Felix), you can do an apples-to-apples comparison and hear the effect of impedance without the unknowns of all the other circuitry that's involved. (Hint: K&Ks sound indistinguishable to me with 1M or 10M or even 20M)

The impedance behavior is actually fairly simple, tho there are some complexities if you really dig in - the "match" acts like a passive tone control. Feeding a passive source into an input with lower impedance tends to reduce the bass (it may also have more complex behavior, especially when you have things like a guitar cable that has a capacitance involved into the equation). Above a certain impedance, you won't get bass loss (but you won't get boost) A passive circuit cannot "boost" anything, so there is never the big bass boost that people talk about, just due to the impedance. There could be a cut to other frequencies, or a relative lack of cutting the bass, and then you turn up everything, which *sounds* like a bass boost (which is what I think all the K&K stuff is about - the pickup is naturally bassy, so using a lower impedance can tame some of the bass by cutting it - but you have to get below about 500K to really hear it).

The area where things get more complex is that with high impedances, you run the risk of other interactions. Plug a passive pickup into a high impedance input with either a crappy cable or a very long one, and all the capacitance and other aspects of the cable come into play. That's why, for the best sound, especially over long distances, you want to use a low impedance cable and input (like running a DI to the PA)

Back to the original question, Larry gave a good answer, IMHO. I've played K&Ks and other pickups thru a lot of preamps. I've not come across one that has some special pro/con with respect to the K&K specifically. Preamps are of varying quality, have different features, and may have a different tone. Depending on your taste, you may like the tone of one vs another. Most preamps these days aim for "flat" and with the state of electronics these days, there's little reason for even the lowest end preamp to not achieve that to some degree. I don't know of any preamps that deliberately add a bass boost to the "flat" sound. There are some preamps that set out to "color" the sound, (the Session DI, and AER Colourizer come to mind), but these generally promote the fact that they aren't flat as a feature.

The highly regarded red-eye is a very nice, clean, quiet and flat preamp, that raises the gain with almost no other features, and if that's what you need, it's great. (Personally, I tend to use very little EQ, so the Red-eye, with its simple treble control is more than sufficient). Other preamps give you more features that you may like. Many are central "hubs" that route your signal to both a PA and a stage amp, while providing an effects loop, mute switch, boosts, and so on. Some have great EQ, if you need that. The SPS-1 with 3 fully parametric bands per channel is hard to beat there. I like dual-channel preamps that can power and blend in a mic, because that's a feature I like to use.

One preamp that I like for SBTs in general is the Grace Felix - my favorite feature is the high pass filter, which you can turn up just enough to get rid of the annoying "thump" that comes from all SBT-type pickups, even active ones (it doesn't come from the impedance, it seems, to me, at least, to come from being in direct contact with the body of the guitar). The high pass filter can really clean up the sound, and tho Felix also has very nice EQ, the high pass filter is often the only one I actually need.

So my advice on "what preamp?" is to think about what features you need - what your setup is like, or how you like it to be. You can get anything from a preamp that clips on your belt or plugs into the end-pin jack of your guitar to ones that require a full rack, and anywhere in between. Then there are features: do you need EQ? a 2nd channel? a mute switch? a tuner output? etc. Between those kinds of choices, your budget, and checking a few out to see if you like the sound, your choices should be narrowed down to very few - and virtually any of them will be fine with the K&K.
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  #40  
Old 03-25-2017, 12:02 PM
RustyAxe RustyAxe is offline
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Originally Posted by Buc-a-Roo View Post
I looked at that one as well.....but then it occurred to me that if I need that much EQ control something must be wrong with the pickup or the amp/board it's plugged into. Overkill in spades if everything else is good.
Not necessarily. If you play out enough, you'll find that rooms are NOT created equally (I could have gone for the pun). More precise control over equalization can eliminate or reduce wolf tones, feedback, phase issues, and more. It's not just about tone. I play acoustic and upright basses as well as acoustic guitar, these things mean a lot to me.
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  #41  
Old 03-25-2017, 01:49 PM
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Originally Posted by Mandobart View Post
Don't think of impedance as excessive or insufficient - the key is the output impedance of the pickup should be matched to the input impedance of the PA/amp. Back in my navy submarine days we used a Time Domain Reflectometer to test long runs of nuclear instrument cables (similar to the coax used for cable TV) for problems.
I assume this was radio frequencies? Takes me back to the T-Lines class in college. Exact impedance matching is important at radio frequencies. What (mostly) matters (from a tone and power-transfer perspective) at audio frequencies is just that the destination has a higher impedance than the source, to avoid rolling off lower frequencies (unless you actually want to roll off the low end, as the early full-sized K&Ks tended to need)
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  #42  
Old 03-25-2017, 02:40 PM
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Doug's reply was quite comprehensive and I concur with the points he made. One thing I would add is that perhaps one of the reasons folks may be overly concerned with input impedance stems not from K&Ks, but from passive USTs.

Electrically, a piezo pickup looks like a voltage source (the signal) in series with a capacitor. The capacitance works with the input impedance of your preamp to determine the low frequency roll off point. It's a first order high pass filter. For KKs, as Doug mentioned, once you get to 1Mohm and above, it all sounds the same. There is no bass loss that you can hear.

However, for USTs, the situation is different. Their effective capacitance is much smaller, on the order of one tenth that of a KK or so, it varies. But in this case, you'll get more bass response with a higher input impedance. That's why you see 5Meg and 10Meg input impedances in some designs. This does come with a potential penalty however. It will make the input circuit more susceptible to power line noise pickup if your cable and connections aren't very well shielded throughout. I was under the impression, but don't know this for certain, that some preamps made specifically for a particular UST had some bass boost built into them to compensate for this general issue with USTs.
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  #43  
Old 03-25-2017, 05:38 PM
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Originally Posted by Doug Young View Post
I assume this was radio frequencies? Takes me back to the T-Lines class in college. Exact impedance matching is important at radio frequencies. What (mostly) matters (from a tone and power-transfer perspective) at audio frequencies is just that the destination has a higher impedance than the source, to avoid rolling off lower frequencies (unless you actually want to roll off the low end, as the early full-sized K&Ks tended to need)
The radar gear is in microwave frequencies, the comm gear RF, but the NI's vary. The detectors have a high voltage applied and they are counting ionizing neutron interactions with the fill gas. The resulting signal is a current spike that ranges over several decades from counts per second on up as reactor power is raised from shutdown up to 100%.
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  #44  
Old 04-01-2017, 07:56 AM
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ive tried em all, and found the best for me is the headway edb1. ive written extensively on why, but to boil it down, the biggest problems with the k&k come from bass frequencies getting out of control. the edb1 has a high pass filter that allows you to completely kill all bass below a selectable frequency point depending on what works in a given situation. this can be much more effective when you are facing feedback than a notch filter, and what i realized in using it is that good realistic acoustic tone doesnt include as much bass as one would expect especially in a band situation where there may already be a bass, and where louder volume levels bring on feedback problems. cutting out low bass cleans up a lot of what will cause problems, at their source.
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  #45  
Old 04-01-2017, 10:07 AM
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This is one of those questions like, "what's the best acoustic guitar?"

My favorite preamp for the K&K is the Radial PZ-Deluxe. I can dial in a pleasing tone very quickly with it and it has the set of most useful features for me. Another set up that I like a lot, that also works with practically anything, is

Boss TU-3 >> Empress ParaEQ >> Radial J48 >> amp and/or mixer.

Kinda like pickups, for every option there are lovers and haters.
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