Minimal preamp impedance for Pure Mini

[myersbw]

Ok, so I ended up buying the JJB Prestige 330 system (actually minus the jack, etc.). It's a 3 pickup array and I'm looking for a little input on user's experiences with preamps...and their respective input impedances.

With an EET background, I'm fully aware of max signal transfer when impedances match. I also know that ideal matching doesn't always account for ideal tone, nor do we always want to max the transfer...might need to cut levels at times due to overload, etc.

That said...and since not too many seem to have experience with the JJB product...I'd like to get some feedback on what preamp (or home-brew build) you may have tried with the K&K Pure Mini and what, if you know, the input impedance on the circuit or preamp was.

I do have the Martin GPCPA4 with the lesser Analog system (vs. Aura). I've thought about inputting the JJB unit direct into the Analog, but what I may do to utilize both is just add the JJB to the unused ring as others have suggested and have both present at the same jack.

Thoughts?

Thanks!
BradM

[pitner]

I use a JJB into a Baggs Para DI with no problems whatsoever. Same with the K and K no issues. The Baggs came be had used for $120 or so and is a real swiss army knife of a DI. Built like a tank and plenty of options and knobs to tweak. always get a great acoustic sound with mine. Also can use the phantom voltage from the PA to save batteries.

[McShepherd]

Jesse recommends Archangel preamps, as they were designed, at least in part, to match JJB specs (that is, 1Mohm input impedance). I found the product to be solidly built, near-noiseless, but with somewhat darker tone than I prefer.

Now I'm using a Red-Eye (same advertised input impedance) - only a treble boost for eq, but I've found that to be more than satisfactory to get what I need.

[donh]

Ideal impedance for the K&K products is 1meg-ohm, which is what their preamps and the RedEye have.

[jcmccorm]

I run my K&K Mini into a DTAR Solstice which has 10MOhm input impedance. I was curious about the impedance issue so just recently added a 1Mohm resistor across the tip and sleeve of the cable at the end that plugs into the Solstice. No difference.

I even recorded a little diddy twice; once with the 1Mohm and once without. I ran the spectrum analysis on each of these in Audacity. They were nearly identical.

The low end *should* start to roll off as the impedance (or in this case, resistance) gets less but 10Mohm to 1Mohm isn't it. It didn't do anything. I'm going to keep adding a 1Mohm in parallel with the first until I start to hear the lower frequencies reduce. 1Mohm, then 500Kohm, then 333Kohm, then 250Kohm etc. Eventually that K&K Mini will start to feel the squeeze

Cary

[Doug Young]

Yeah, I did that experiment and posted A/B recordings here years ago, and no one believes it still :-) I've also tried the K&K thru some variable impedance preamps. I found you could start hearing some bass loss around 100K, tho it still sounded fine, maybe even what someone would want. 50K down to 5K, you definitely start hearing significant bass loss and a not so useful sound. Plug directly into a low impedance mixer input (like maybe in the hundreds of ohms) if you really want to hear what an impedance mismatch sounds like. Let us know what your experiments show.

[joeguam]

I use both K&K pure minis and JJB 330's with my LR Baggs Venue DI that has a 10MOhm input impedance. In each case, I have to considerably cut around the 500-800Hz about 10-15 dB's, but get great tone out of it.

In the rigs where I don't go straight into the Venue DI, I use a Boss TU-2 or TU-3 tuner pedals which have 1MOhm input impedance that match.

[sdelsolray]

Originally Posted by Doug Young

Yeah, I did that experiment and posted A/B recordings here years ago, and no one believes it still :-) I've also tried the K&K thru some variable impedance preamps. I found you could start hearing some bass loss around 100K, tho it still sounded fine, maybe even what someone would want. 50K down to 5K, you definitely start hearing significant bass loss and a not so useful sound. Plug directly into a low impedance mixer input (like maybe in the hundreds of ohms) if you really want to hear what an impedance mismatch sounds like. Let us know what your experiments show.

Well, I support the results of your testing because I had similar results. Urban legends can have a life of their own.

[Doug Young]

Originally Posted by sdelsolray

Well, I support the results of your testing because I had similar results. Urban legends can have a life of their own.

Yeah, "no one" was an exageration. But we still get posts here all the time claiming 10M vs 1M is an enormous difference. I keep hoping someone will post a recording demonstrating it.

[sdelsolray]

Originally Posted by Doug Young

Yeah, "no one" was an exageration. But we still get posts here all the time claiming 10M vs 1M is an enormous difference. I keep hoping someone will post a recording demonstrating it.

The preamp input impedance issue of 10 v 1 MegOhm was an issue with the K&K Standard version of the pickup which was discontinued many years ago. Due to the higher ratio of surface area of the three transducers to the thickness of them, the -3dB corner frequency point was much lower than the K&K mini, whose ratio was less. That corner frequency point was down to about 20 Hz, Deiter (of K&K) needed an impedance load at the preamp input on the K&K Standard of 1 MegOhm to reduce that bass response of the Standard pickup. At least that is how it was explained to me by Greg Gualtieri of Pendulum Audio. Greg also said that the Pendulum SPS-1's preamp module (which has an input impedance of 10 MegOhm) was not affected because the SPS-1 has a built in non-modifiable compliance limiter which took care of the near sub-sonic bass of the K&K Standard pickup.

[varmonter]

Dang you guys are technical ....i can't explain it like that.. but I know what i hear..Perhaps my k&k is one of the older models(was installed in the d28 when i bought it) ..But I struggled with this guitar for awhile.I used a pendulum hz-10
and it sounded ok...just ok..I tried a solstice and a para di and none of these
made much difference. they all sounded just ok.So reading about the impedance mismatch thing here on agf i bought a K&K pure xlr.(cheap enough )
This alone plugged into the board sounded better than the pendulum.
I know the hz-10 is worlds above this Little k&k..But the pure xlr just seemed to open up the sound.I find it's eq is somewhat lacking so i added a really nice recording 1/2 rack para eq to the insert channel of the board.Man does that ever sound good.(speck asc)..So again I can't explain it other than it was the input impedance issue..I am waiting(ever so patiently) for archangels new releases.

[sdelsolray]

Originally Posted by varmonter

...
So again I can't explain it other than it was the input impedance issue..I am waiting(ever so patiently) for archangels new releases.

Well, it can be easily explained other than the impedance issue. You used different gear with dozens of non-equal elements. To claim the difference is solely related to the input impedance of the preamp, when so many other variables are present, is a mere assumption.

[myersbw]

So, from what you're stating, Doug...looks like getting to the under 100K load can start to show audible differences. That's good news as what I may do is design a simple 2 stage tube pre with a tone stack with a 150K front end and maybe a 1K or so out.

For that matter, it sounds like I may already have a good candidate to try in a Fulltone GT-500 where the FET boost side has a 500K impedance. Won't hurt to start there, eh? And, it includes some EQ shaping.

Thanks for the input, folks! You've given me quite enough to get a start.

BradM

[myersbw]

Originally Posted by sdelsolray

Well, it can be easily explained other than the impedance issue. You used different gear with dozens of non-equal elements. To claim the difference is solely related to the input impedance of the preamp, when so many other variables are present, is a mere assumption.

To add to that, as far as variables go, the question of how the transducers are affixed is a huge factor, too. I.E. For that years ago install, did you use thin double-sided stickies? Super glue? Or, Lactate gel?

Now...that said...I'm going to deviate my OP to raise another observation/question. While snapping some photos of the inside of my Martin GPCPA4, I noticed when zooming that the inside is in a rough-sanded state. Basically, it looks like there was small degree of sanding (or just machine planing?) and, unlike the finished top, the interior of the soundboard has texture.

Now, from what we know about acoustic vibration, might this lack of a better finish sanding actually reduce the top vibration? Might it perform better if I sand or 0000 steel wool it? Or, does the very slight unrefined state prevent cancellation standing waves in the top?

The question leads me to the bigger question - will a more refined smoothing degrade or enhance the current acoustic imagery it produces? At present...I like what it provides me....but, I'm torn with the idea that..."hmmm, maybe it can be just a bit better!" LOL

Help... ? (btw...on resommendation, I did get the 15mm transducers, give the guitar's liveliness.)

BradM

[Doug Young]

Originally Posted by myersbw

So, from what you're stating, Doug...looks like getting to the under 100K load can start to show audible differences. That's good news as what I may do is design a simple 2 stage tube pre with a tone stack with a 150K front end and maybe a 1K or so out.

For that matter, it sounds like I may already have a good candidate to try in a Fulltone GT-500 where the FET boost side has a 500K impedance. Won't hurt to start there, eh? And, it includes some EQ shaping.

Thanks for the input, folks! You've given me quite enough to get a start.

BradM

Well, that's what I recall. It's hard to find an easy way to smoothly vary impedance from 10M down to something low, so we only have a few data points. I tried the K&K into a 100K input at some point, and thought I noticed some bass rolloff there. Might also happen higher. I think I have tried 500K with no issues. But if you're designing a preamp for use with acoustics, I'd follow the lead of all those who have gone before you and make it at least 1M, so you can plug passive pickups in. K&Ks aren't the only game in town, and although they work well with lower impedances, probably because there's 3 of them in parallel, most manufacturers will tell you to use higher (like 10M) with passive transducers.