We recommend impedance-matching preamps...

[joeguam]

...but don't tell you the impedance your supposed to match.

I'll admit, the topic of impedance in guitar pickups, preamps, amps and mixers is not straight forward or easily understood. However, the Fishman website has a disclaimer about impedance-matching preamps plastered all over their site. But, nowhere do they disclose the impedance for which you are supposed to match.

Anyone know how to determine the impedance of a pickup or preamp if its not disclosed in the manual or spec?

...
Joe

[philjs]

Originally Posted by joeguam

...but don't tell you the impedance your supposed to match.

My guess is a pretty sure bet...it's because they want you to ALSO BUY their preamp rather than anyone else's. Some companies seem to even go so far as to make their pickup match just about nothing else except their preamps (and I'll also bet that you know who I'm talking about here...)

Phil

[Bob Womack]

Typically, instrument transducers are high impedance. Knowing this, most onboard instrument preamps are also high impedance*, though they have a much higher output. So, for example, the Fishman Prefix Pro Blend is listed as having a 3.5kohm output impedance in its owners manual on the site. Also, most guitar systems feature an unbalanced out. The typical P.A. or recording console has low impedance (200 ohm) mic inputs. So, the impedance figures of merit are between 2k and 10k for a transducer and 200 ohms for a mic input on a console. What is typically used is either an impedance matching transformer or a preamp or direct box that has the ability to balance the signal as well.

You can do it on the cheap with a passive Shure inline "hypo" 1/4" to XLR converter with an impedance transformer inside. There are better active units that do nothing except balance and buffer and provide a ground lift. However, many people take the opportunity to add some flexibility by using a preamp that does all that but adds some EQ and other facilities.

I think this is a case of an industry growing so ubiquitous that it is eventually assumed that everyone knows what signal parameters they are dealing with so less experienced folks get lost in the assumptions. Sorry about that.

Bob

* The Taylor Expression System's balanced out is specifically excluded.

[joeguam]

Originally Posted by philjs

My guess is a pretty sure bet...it's because they want you to ALSO BUY their preamp rather than anyone else's. Some companies seem to even go so far as to make their pickup match just about nothing else except their preamps (and I'll also bet that you know who I'm talking about here...)

Phil

Phil, and what if the same company sells preamps with different input impedances? How would you choose then?

[joeguam]

Originally Posted by Bob Womack

Typically, instrument transducers are high impedance. Knowing this, most onboard instrument preamps are also high impedance*, though they have a much higher output. So, for example, the Fishman Prefix Pro Blend is listed as having a 3.5kohm output impedance in its owners manual on the site. Also, most guitar systems feature an unbalanced out. The typical P.A. or recording console has low impedance (200 ohm) mic inputs. So, the impedance figures of merit are between 2k and 10k for a transducer and 200 ohms for a mic input on a console. What is typically used is either an impedance matching transformer or a preamp or direct box that has the ability to balance the signal as well.

You can do it on the cheap with a passive Shure inline "hypo" 1/4" to XLR converter with an impedance transformer inside. There are better active units that do nothing except balance and buffer and provide a ground lift. However, many people take the opportunity to add some flexibility by using a preamp that does all that but adds some EQ and other facilities.

I think this is a case of an industry growing so ubiquitous that it is eventually assumed that everyone knows what signal parameters they are dealing with so less experienced folks get lost in the assumptions. Sorry about that.

Bob

* The Taylor Expression System's balanced out is specifically excluded.

Bob, I respectfully disagree, I don't think your suggestion that "it's assumed by more-experienced people" is valid. Here's an example to explain why:

Let's say I purchased a passive pickup from Fishman, we'll just choose one of their SBT's for this example. It has the impedance-matching disclaimer listed in its features section on the product page - you don't even have to go into the manual to be hit with it. Now lets say 6 months down the road you realize you need a preamp, so you go back to the SAME COMPANY to try to avoid any incompatibility issues, which FISHMAN preamp are you supposed to buy to adhere to their disclaimer? Your example of the Prefix pro blend has an input impedance (because this is the spec you'd need to match to your passive pickup, not the output impedance) of 20MOhms, but if I didn't want an onboard installation, the Pro-EQ II option has an input impedance of 10MOhms in its manual and specifically says "for all acoustic instruments".

So, which preamp should I get to ensure I abide by their disclaimer and recommendation to match impedances?

According to your statements above, typically "more-experienced" people know that SBT's are "high impedance", does that mean 10MOhms or 20MOhms would be the correct "matching" preamp? How would us "less-experienced" people know how to define "high impedance" because surely there's a big difference between 10 million and 20 million Ohms.

Thoughts? Appreciate any advice the "more-experienced" people can provide, thanks.

...
Joe

[Bob Womack]

I meant nothing by the phrase. Perhaps it was poorly turned, and I am sorry for the offense. Typically, inputs and outputs aren't too picky, in a general sense. If you can keep the output impedance of the transducer to no more than ten times the input impedance of the preamp, they will be happy. That would be no more than 2k on the transducer output for a 200 ohm input. If you are in search of the perfect combination there's a degree to which it is all subjective and you'll have to rely on others' opinions or a lot of trial and error. There are some outliers, but you can usually get a working and reasonably euphonic signal from a well-built active direct box with preamp with most of these transducers and preamp systems.

Bob

[Side Man]

Originally Posted by joeguam

So, which preamp should I get to ensure I abide by their disclaimer and recommendation to match impedances?

According to your statements above, typically "more-experienced" people know that SBT's are "high impedance", does that mean 10MOhms or 20MOhms would be the correct "matching" preamp? How would us "less-experienced" people know how to define "high impedance" because surely there's a big difference between 10 million and 20 million Ohms.

Thoughts? Appreciate any advice the "more-experienced" people can provide, thanks.

...
Joe

ANY ONE of Fishman's preamps - either onboard or outboard - will handle the input requirements of passive piezo pickups. While there certainly may be a difference between 10 megaOhms & 20 megaOhms. The ceramic-type SBT pickups need anything over 10 mOhms, while the newer polymer / copolymer UST's like to see 20 mOhms.

The key is to buy the preamp from someplace where you can return it if you aren't happy with the results. Then you can go for a different option.

Now all you kids get off my lawn!

[joeguam]

Side Man, where did you get this info, is it on Fishman's site anywhere?

I'll leave the reasons why I'm unable to take advantage of return policies out of this thread, that's a whole different thread on its own, haha!

...
Joe

[ljguitar]

Originally Posted by joeguam

...but don't tell you the impedance your supposed to match.

I'll admit, the topic of impedance in guitar pickups, preamps, amps and mixers is not straight forward or easily understood. However, the Fishman website has a disclaimer about impedance-matching preamps plastered all over their site. But, nowhere do they disclose the impedance for which you are supposed to match.

Anyone know how to determine the impedance of a pickup or preamp if its not disclosed in the manual or spec?

...
Joe

Hi Joe...

Fishman isn't alone. K&K makes similar allegations.

The reality is I own 5 different brands of preamps, and they all work fine with any passive undersaddle or bridgeplate transducers which we've run through them for the past few years.

I seriously doubt that any but the matching-name-branded ones would qualify as a 'perfect' impedance match for the pickups.

I treat these statements with the same seriousness I do when a product from Sony or Panasonic suggests that I must use their brand of batteries and even offers order blanks and product numbers to get them. My grandmother is the only person I ever knew who actually ordered batteries from them for her small recorder.

[joeguam]

Larry, when you say they all work fine, does this mean without needing more than normal/average EQ correction? Just a flat EQ?

If so, this is very promising.

...
Joe

[guitaniac]

Luthier/pickup designer Rick Turner used to tell us that the rule of thumb was that the input impedance of the next gain stage needed to be at least ten times the output impedance of the passive pickup (or previous gain stage). A 10 MegaOhm input impedance is enough to handle most passive pickups which are designed to be sold in their passive form.

The B-Band pickups require a 50 MegaOhm input impedance, and the Baggs Element (in its passive form) requires an input impedance of around 100 MegaOhms (according to Rick Turner) for a proper impedance match. I presume that's why both of those pickups are sold as part of an active system. (You can buy a B-Band UST by itself, but its designed to plug into an active B-Band system.)

I once experimented with wiring a passive Element pickup (salvaged from a broken DTAR Wavelength system) to a strap-jack and using it with a variety of different preamps (Baggs PADI, Fishman Platinum, DTAR Mama Bear) which I owned. The results were very tinny and shrill, due to insufficient input impedance (10MegaOhms for the PADI and the Platinum) at the preamp. Generally speaking, however, a 10MegaOhm input impedance will provide an effective impedance match for pickups which are designed to be sold in their passive form.

Gary

[ljguitar]

Originally Posted by joeguam

Larry, when you say they all work fine, does this mean without needing more than normal/average EQ correction? Just a flat EQ?

If so, this is very promising.

...
Joe

Hi Joe...

I don't know what 'more than average EQ adjustment' means. Perhaps with a perfect sound system (or amp), a perfect pickup, a perfect installation, in a perfect guitar, with a perfect preamp you could run it flat.

I've yet to encounter one of those. That is probably why manufacturers put tone controls on their preamps.

I really don't care how much I have to adjust the tone. I just set it so it sounds natural and I'm good to go.

I'm not saying I don't care about tone, I'm saying we run different pickups with a variety of preamps through our systems, and whatever EQ/tone/shape we use to adjust it with a particular guitar, if we change preamps, that same shape will still apply.

My goal is not to not have to touch controls, but to setup and get a decent sound quickly so I can focus on the music instead of the gear.

Some claim the impedance causes out-of-balance-tone, but I've not experienced that. At any gig between my gigging partner and I, we will have 4-5 preamps at our disposal, and we can set up any of them with any guitar to sound really nice through either an amp or PA system in just a minute or two.

What fear specifically are you struggling with in regards to impedance matching?

[krisls]

I've read more than a few of these type of 'arguments' over time and it always seems to be a search for perfection, which is somewhat doomed, but possibly worthy in an abstract sense. Then there's marketing....

My own experience with two acoustics, one 000 K&K mini equipped and a Tak Nex w' pre. Both work just fine into assorted amps or PA's or through an EQ pedal or more recently a PZ Deluxe and then into whatever. Sure the settings are slightly different but not radically so.

So I can only conclude that most such guitars will work just fine with most gear with tweaks to levels and EQ. There are possibly exceptions but everything I have tried will do the job pretty well.

Kris

[lschwart]

Originally Posted by joeguam

...but don't tell you the impedance your supposed to match.

I'll admit, the topic of impedance in guitar pickups, preamps, amps and mixers is not straight forward or easily understood. However, the Fishman website has a disclaimer about impedance-matching preamps plastered all over their site. But, nowhere do they disclose the impedance for which you are supposed to match.

Anyone know how to determine the impedance of a pickup or preamp if its not disclosed in the manual or spec?

...
Joe

One thing worth adding to this discussion is the fact that in my experience Fishman customer support is very responsive and will tell you the specs if they're not printed in the manual. I had a question once about the output of the Presys Blend because I was thinking of buying a guitar with one in it, and they told me by email.

Louis

[sdelsolray]

Originally Posted by joeguam

...but don't tell you the impedance your supposed to match.

I'll admit, the topic of impedance in guitar pickups, preamps, amps and mixers is not straight forward or easily understood. However, the Fishman website has a disclaimer about impedance-matching preamps plastered all over their site. But, nowhere do they disclose the impedance for which you are supposed to match.

Anyone know how to determine the impedance of a pickup or preamp if its not disclosed in the manual or spec?

...
Joe

Many acoustic guitar pickup/preamp makers are skimpy on standard pro audio specifications. Some are not. I like printed specs because I can use them to see how well other gear will work with it. That way, if there is an incompatibility, or a non-optimal issue, I can avoid an item and (more importantly) avoid the "buy it and see if it works" method. I'd rather "buy it knowing that it will work", at least insofar as something as mundane as optimizing my signal chain in the first place.

Here are two examples of robust specifications provided by two acoustic guitar preamp manufacturers. This is hardly novel. Pro audio specs for thousands of products are at this level of disclosure and transparency.

Pendulum Audio SPS-1 Published Specifications

Rane AP13 Published Specifications