Question about UST Input impedance & ohmic output

[Mbroady]

First, I want to thank Doug Young. He had an older k&K power-pro blend 3 channel preamp that he sent to me.

Second, my understanding of electronics is that of a 5th grader, so keep that in mind when responding (open to an education).

I already have a guitar with the K&k Mini and mic installed and wanted to experiment with adding the 3rd source, a UST

According to the folks at K&K, both the mini and UST channels are 1 meg with a low ohmic output

Should I be concerned about using another brand UST (fishman, LR baggs, etc)?
..are there other USTs that match the 1 meg and low ohmic spec?

Thanks, looking forward to learning something new

[Doug Young]

Originally Posted by Mbroady

First, I want to thank Doug Young. He had an older k&K power-pro blend 3 channel preamp that he sent to me.

Second, my understanding of electronics is that of a 5th grader, so keep that in mind when responding (open to an education).

I already have a guitar with the K&k Mini and mic installed and wanted to experiment with adding the 3rd source, a UST

According to the folks at K&K, both the mini and UST channels are 1 meg with a low ohmic output

Should I be concerned about using another brand UST (fishman, LR baggs, etc)?
..are there other USTs that match the 1 meg and low ohmic spec?

Thanks, looking forward to learning something new

Glad you're getting around to trying that! I think the answer is "it depends". With impedance, what you want is for the input impedance of the preamp to be greater than the impedance of source (pickup), usually by a multiple of 10X, as I recall. I suspect most USTs will be similar to the K&K UST, and that 1M will be fine. But it's not a spec that's easy to find - no one tells you what the impedance of the transducer is, they'll just recommend an input impedance. And for pickups that aren't sold as passive, they just view the whole thing as a closed system, so you are just supposed to use the preamp they supply. I seem to recall Rick Turner saying that one of his (might have been the Highlander?) expected 100M! (And presumably his preamp supported that)

What will happen if you plug into an impedance that's too low is that you'll lose bass response. Pluging into an impedance that's higher than needed should have little or no impact.

There's also the issue of output level - if the pickup is low-level, will the preamp have enough gain? If the raw pickup is really hot, will it overdrive the preamp? If I recall correctly, the K&K UST is pretty hot.

[Rudy4]

Originally Posted by Mbroady

First, I want to thank Doug Young. He had an older k&K power-pro blend 3 channel preamp that he sent to me.

Second, my understanding of electronics is that of a 5th grader, so keep that in mind when responding (open to an education).

I already have a guitar with the K&k Mini and mic installed and wanted to experiment with adding the 3rd source, a UST

According to the folks at K&K, both the mini and UST channels are 1 meg with a low ohmic output

Should I be concerned about using another brand UST (fishman, LR baggs, etc)?
..are there other USTs that match the 1 meg and low ohmic spec?

Thanks, looking forward to learning something new

Your inquiry was titled "Question about UST Input impedance & ohmic output..."

One of the reasons why you won't find manufacturers of piezo transducers listing a specific "impedance" figure is that it's not really the correct verbiage to use as a parameter specification for the device. Impedance, within the field of electronics is "opposition to AC current flow", and the only time you would normally see a piezo material with that description used is when it is used as a speaker.

Yes, if you excite a piezo transducer with an electrical signal it works fine as a speaker. A raft of all those early piezo disk musical instrument pickups were often re-purposed "speakers" or vibrating alarms.

Since piezoelectric musical instrument transducers are operating to PRODUCE electricity as they are physically stimulated the transducer has an OUTPUT.

Since the piezo material usually has an impedance of 1 meg ohm (or often FAR higher) when used as a speaker, you'll find the same general values used to specify the INPUT impedance for the device that it is attached to. The reason for this is simple. Although the output voltage of a piezo transducer is really quite high, that counts on the load seen by the transducer (what it is plugged into...) being low. When we talk about circuit loading, the higher the impedance (in ohms) of the device the transducer feeds the less it serves as a load to the transducer's output.

If all of that is confusing, here's an easier way to understand it. If NO wire is attached the impedance seen by the transducer is essentially infinite, so there's no load. If you could attach a measuring instrument with a very high input impediance you'd see a very high voltage produced by the transducer.

I've been working with electricity and electronics for close to 60 years and I have never seen the term "ohmic output" used anywhere so I'm of no help there.

If your preamp specification is 1 meg ohm or greater you can plug any piezo transducer into it, although some may offer a higher output if the preamp impedance is higher.

[Doug Young]

Complicated topic. I think what OP meant by "ohmic output" is the output impedance of the raw pickup. I understand, that may not be something easily defined for a piezo element, but you see output impedance on electronic devices (like preamps) all the time, so it seems reasonable to a lay person at least to think of the piezo in the same way - one stage of the chain.

I think the basic question, as I understand what he's asking, is" "can I plug just any UST into the K&K preamp without having problems due to impedance?". My guess, lacking specs on all raw USTs, is "probably" but maybe, maybe not :-) Easy enough to try and see, other than needing to buy some UST. As I mentioned, I'd be more concerned about headroom and gain, tho there again, it probably won't be a problem, the signal will just be weaker or stronger.

There are a few USTs out there that seem to be different. I may be misremembering this, but I think there was some replacement preamp that said it would work with all USTs except B-Band. What was different about B-band? I don't know.

[sdelsolray]

The output impedance of a passive piezo pickup varies with the particular frequency being tested.

There is a difference between "matching impedance" and "bridging impedance". Matching impedance requires the same impedance for output and input, was used in the past in some old analog telephone systems and is in little use today. Bridging impedance is what is used these days with virtually all sound reinforcement and studio gear, which would include any discussion about passive pickups and preamps in guitars. Generally, the input impedance should be between 5 and 10 times (depending on the circuit) the output impedance of the passive pickup for the signal passage to remain unimpeded.

[Mbroady]

Originally Posted by Doug Young

I think the basic question, as I understand what he's asking, is" "can I plug just any UST into the K&K preamp without having problems due to impedance?". .........:-) don't know.

Yep that’s what I’m asking. The K&K UST has a one 1/8th inch width. The guitar I want to experiment with has a 3/16th saddle slot.

Thanks all for the education

Any suggestions for a safe bet?

[Howard Emerson]

Originally Posted by Mbroady

Yep that’s what I’m asking. The K&K UST has a one 1/8th inch width. The guitar I want to experiment with has a 3/16th saddle slot.

Thanks all for the education

Any suggestions for a safe bet?

It's totally safe if it's going into a slightly wider slot. If you have some sort of 'shim' material that you could put in front & back of the UST so that it was absolutely centered it would be a good thing.

It would mainly be to keep the UST immovable when changing strings, etc.

If the K&K UST is round/tubular like the LR Baggs it will be a bit challenging, but it's pretty simple. The most important thing with UST is that the saddle bottom, and the slot bottom, be dead flat.

Regards,
Howard Emerson

[Mbroady]

Originally Posted by Howard Emerson

It's totally safe if it's going into a slightly wider slot. If you have some sort of 'shim' material that you could put in front & back of the UST so that it was absolutely centered it would be a good thing.

It would mainly be to keep the UST immovable when changing strings, etc.

If the K&K UST is round/tubular like the LR Baggs it will be a bit challenging, but it's pretty simple. The most important thing with UST is that the saddle bottom, and the slot bottom, be dead flat.

Regards,
Howard Emerson

Meant to say 3/32 not 3/16.
So I would have fill and redo the saddle slot. Rather just get a a preparer fitting UST.