JJB Marcato pick-up question.

[soliver]

Hey gang, I just received my JJB Marcato (http://jjb-electronics.com/The_Marcato.html) external mount pick-up for my mando, and got with the Tech director at the church to try it out today and after having to fiddle with it a little, we figured out that you have to leave a standard 1/4 inch cable hanging out of it a little to get anything out of it (2 clicks is fully inserted, only makes noise with 1 click). My Tech buddy said that it it may need a TRS (Tip Ring Sleeve) cable to plug in to the DI. Leaving it hanging out like it did have it a low hum which he said indicated a grounding issue.

Does this sound right? Do any of you have experience with this? What do you recommend to use with this style of pick up?

The church uses JDI passive direct box.

[colorado_al]

Have you contacted JJB to ask them?
It is possible that the jack needs TRS cable, but most mono unbalanced jacks just use a TS cable. Also possible that the jack they use is a stereo jack and that they connected the piezo leads to the "wrong" terminal for a TS cable to work. The problem with this is that your DI might only be wired for a TS cable, so you'd need a TRS to TS adapter.

[mandroid]

JJB is one of the many using a Piezoelectric wafer for the signal source., just + and ground, TR on those....

most people use a Pre Amp next in the signal chain,

get one with a piezo 'handshake' buffer (very high impedance).. from some of the several companies that also sell piezo pickups.

need a DI to go to the house mixer?, the Baggs PA DI is both a Pre Amp (line level 1/4" out put)

and a DI, (Direct Input)
that is Microphone level to feed the Microphone Pre Amp in the house Mixer Channel XLR to use Mic Cables,

in the same box..





.....

[soliver]

Regarding the JJB pickup... I googled “Does a JJB pickup need a TRS ... ?” And found on the Acoustic Guitar Forum a Post regarding a hum (which I experienced) and down a ways read this:

“Now...about what you're doing with a mono cable. By inserting it into the stereo jack...you're now shorting the other pickup. It may seem like it's a non-issue, but what you've effectively done is to create a 1/4 wave dipole antenna out of that second onboard pickup system...and it's feeding itself right into the ground-side of an unbalanced system. Not what you really want to do at all especially in your passive system. Might be how the hum is being picked up. And, if you do only wire the tip...it's still there as an antenna into the ground-side....”

a link for posterity: http://www.acousticguitarforum.com/f...d.php?t=426040

Just bought a TRS cable @ GC for $13 ...we’ll see what happens

[soliver]

That did the trick and it sounded really good!

So let it be known that if you buy a JJB Marcato, you have to use a TRS cable... and of course a compatible DI

[soliver]

Hey gang, I just wanted to follow up on this as I found out that I was actually incorrect about the TRS cable.

I went to my first band rehearsal at the church on Tuesday and had A LOT of trouble with the pickup and the system at the church. Again there was a hum. So I emailed Jessie at JJB and he said that I should NOT need a TRS... His email said this:

"I'm not certain if it is the issue here, but you would only need a mono (TS) cable as this isn't a stereo (TRS) jack or pickup configuration. I would start working through the variables here. Do you have access to a basic guitar amplifier with a standard mono cable? If so, plug straight into that and see if the problem persists. If you don't have easy access, is there a guitar store in your area that you could pop into to "demo" an amp?"

That worked just fine, so I asked what may have been the problem at my initial test on the big system and he replied with this:

"I would play around with all of the settings on the DI (particularly the polarity reverse and merge functions), if you haven't already. It doesn't look like there are many. It shouldn't take long to try them all. Is the DI set up to only run a stereo cable, by chance? I am not too familiar with this particular unit.

I am sure there is a solution here that wouldn't require bypassing the DI and not using it. It seems like a quality unit so I am sure there is no reason why it won't work with the pickup. Possibly even an email to the DI manufacturer explaining what is going on? They would know the in's and out's of the unit better than I would. You could just tell them that you are running a passive piezo pickup and ask if they have any insight on why it is behaving in this manner with the DI. http://www.radialeng.com/contacts.php"

Needless to say, I am still in a little bit of a holding pattern as our Tech director is out because his wife just had a baby, but I wanted to update this thread because I was incorrect in my previous findings: THE JJB PICKUP DOES NOT NEED A TRS CABLE!

[pops1]

I read about the direct box on their web site. First of all the input is for an instrument with a preamp, it is a line level signal. Second I am wondering if your PA is using phantom power which would be coming in from the back side and making it hum. The Phantom shouldn't make it hum tho as it should be able to be used with the phantom on. If you have access to a preamp go straight to the PA and don't use the direct box.

[colorado_al]

I'd try a different DI and XLR cable to the board. Inexpensive DI can be had for less than $50.
Try something like this in passive mode:
https://www.amazon.com/BEHRINGER-V-T...dp/B000KITQK2/
And see if it resolves. Not much of an outlay and a good piece of kit to have in your bag for other gigs.
Here's a power supply for it if you want to not rely on 9v battery
https://www.amazon.com/Behringer-PSU...dp/B000T9L7W2/

[dang]

Isn’t there an impedance mismatch? You need something that takes 10Mohm for a piezo to go into a PA and sound decent

[pops1]

Isn’t there an impedance mismatch? You need something that takes 10Mohm for a piezo to go into a PA and sound decent

1M ohm is suitable for most piezo pickups, 10M is the factor of ten in electronic that will work for anything up to that high. I don't think most are more than 1M. K&K is at 1M and so is the input of their preamp. The OP's direct box is designed for a line input and I am sure an lower impedance.

[dang]

1M ohm is suitable for most piezo pickups, 10M is the factor of ten in electronic that will work for anything up to that high. I don't think most are more than 1M. K&K is at 1M and so is the input of their preamp. The OP's direct box is designed for a line input and I am sure an lower impedance.

So they need a different direct box right? because that JDI isn't 1M

[pops1]

So they need a different direct box right? because that JDI isn't 1M

Aaccording to the website the JDI is designed to accept a guitar with a preamp or a line level singal, which means the signal is already lower in impedance and ready to go into a PA. A line level singal is not what a mandolin with a piezo is putting out, nor is the impedance a match for this device. The JDI will tame the singal, but I don't think it is needed in an instrument that is already compatible. The input of the JDI after going in deeper to their site is 140K ohms, and is really designed for less than that according to all there tables of use. It is more to stop ground loops and tame a hot signal. It is not a high to low impedance device like a preamp designed for a piezo. The OP should try a preamp straight into the PA and I am sure would solve the problems.

[Br1ck]

May be more than you'd like to spend, but a RedEye preamp makes a piezo pickup sound it's very best. It!s my favorite piece of gear by far.

[MontanaMatt]

May be more than you'd like to spend, but a RedEye preamp makes a piezo pickup sound it's very best. It!s my favorite piece of gear by far.

I'm a fan of the Triton piezo bigAmp, it's 10Mohm, small, simple. No adjustments, so all tone controls must happen at the board.
$100.

[colorado_al]

If you're limited on budget the Behringer ADI21 will do the trick. $30
If you're after the best sound, the FyreEye RedEye is great. Also battery powered or can power from phantom power on the board. $195 It also has a boost switch for changing your level for solos.
https://www.amazon.com/Fire-Eye-Deve.../dp/B0089EUZ4A

I like the Radial StageBug SB-4 Piezo DI for $80
https://www.amazon.com/Radial-StageB.../dp/B00EIS6VX0
Has great inbuilt tone for violin and mandolin. No EQ required for me.
It will need phantom power from the board, or a phantom power injector.
https://www.amazon.com/InnoGear-Cond.../dp/B00KAPGLQC

[soliver]

You guys have gone way over my head... but I am gathering that you guys think that I either need a different DI or a piezo compatible preamp... yes, no, maybe so?

[colorado_al]

You guys have gone way over my head... but I am gathering that you guys think that I either need a different DI or a piezo compatible preamp... yes, no, maybe so?

I think you need a different interface than is provided to you by the current setup. Ideally, you would have your own DI that has the correct impedance for a piezo pickup. And that would have its own XLR cable to the mixing board.

You could also go with something like the LR Baggs GigPro.
https://www.amazon.com/LR-Baggs-Belt.../dp/B001E95KEW
It is a discrete preamp and would probably provide the correct signal to the existing DI. I'm not 100% sure that it would, because I'm not familiar with the box that your current system is using.

[soliver]

Thanks guys, I’ve reached out for more input from the guys at JJB. I’ll share what Jessie says here.

JJB has developed and now sell their own preamp that is in the $120 range, so if I do need to get a preamp, I’ll likely save up for one of those.

[soliver]

Hey guys, as I said, I emailed Jessie at JJB and here was his response:

Having an impedance mismatch like the one you mentioned isn't exactly ideal, but it also isn't known to cause the particular problems that you have had. Generally, with a mismatch like this one (it's not too uncommon), the low frequencies are boosted more than usual and they have to be rolled off by external means (at the amp, mixer, etc). A weak output and a lot of hum isn't something that generally occurs in this situation. Like someone mentioned in the thread, the Baggs Para DI works extremely well with piezo systems like ours. The input impedance of those is 10M ohm, and our systems like to see 1Mohm.

The addition of a good preamp can absolutely help you to get the most out of this (or any other) piezo system. Having said that, there is no reason why you couldn't just plug it into an amplifier and get a good workable result without a preamp at all. Like you mentioned, it worked when you plugged it straight into a guitar amp with a mono cable. A decent preamp is a good piece of gear to have though.

What I gathered is that A. The impedance issue is not that big a deal and highly unlikely to cause a hum and B. A preamp is good but shouldn’t be a requirement.

Question: is the Baggs PARA a preamp and DI?

[almeriastrings]

Isn’t there an impedance mismatch? You need something that takes 10Mohm for a piezo to go into a PA and sound decent

No. You don't. Not always.

With large diameter piezo discs and instruments that put out a lot of low frequencies, often yes. With the small discs and mandolin/fiddle, almost never. They'll work just fine into 1M.

[almeriastrings]

You guys have gone way over my head... but I am gathering that you guys think that I either need a different DI or a piezo compatible preamp... yes, no, maybe so?

Yes.

The JDI is a nice transformer based (passive) DI box. It works great with electric guitars with magnetic pickups (it is not just for line level signals). However, it is a very poor match to a piezo transducer. The input impedance is only 140K.

[almeriastrings]

I will write this up in more detail shortly (I am waiting for a batch of 'bare' transducers to arrive from China for additional tess), but this matter of impedance.... there are several variables that influence what is going to sound 'best'. It is also not just impedance, but the ability of the DI or preamp to handle the very large voltage swings than can occur with piezo elements. Example: let't take a 20mm disc and connect it to a volt meter. Now, whack the thing with a hammer (the disc, not the meter! ) - look at those voltages! Now, do the same with a 10mm disc. Much lower voltages, but still pretty high. The harder you whack them = the more volts they generate.

Piezo discs work on the compression principle.

Again, there are various things that can change how they respond. The adhesive they are fixed with... the presence (or otherwise) of any backing plate or coating.... and the instrument. Put one on a violin, and the vibrations are pretty 'smooth'. Put one under a 5-string banjo head or on a bluegrass mandolin top and the vibrations are much more severe and 'sudden' This changes the voltages produced and the WAVEFORM of the voltage too, especially the initial peak after the string is picked.

Not all preamps or DI's handle these 'harsh' and sudden 'peaks' well. Some do. Some don't. This is a very big reason why some sound better than others.

Then, impedance itself. This impacts the frequency response that is transmitted from the sensor to the mixer or amp. Again, there are variables including disc size and the resonant frequency of the disc itself. If you plug the sensor into a too-low impedance, say, 50K it will sound thin.... if you plug it into say, a 20M input, you might find too much low end present - so the trick is to find a happy medium or one that works best in your situation with your instrument. A string bass player will have different needs from a mandolin player. This is why opinions tend to be all over the place on this topic. There is no 'best', merely the 'best' for you.

[soliver]

Thanks for that explanation but is that what is causing the hum? I've yet to get back in there and retry the pickup with a TS cable, but I'm wondering if we are in the weeds here from the tee off of with the original humming issue (I hate golf so not sure why I used a golfing metaphor ).

Long and short, it sounds like I need to fork over some more bucks and get my own DI thats more Piezo friendly. GC has several of th LR Baggs PARA DI's used for around $110... thats not bad, but I'll have to set money aside for it, but will this solve the "problem"?

The church will provide a clip on mic that that i can use in the meantime. I have used it before, but I found it too fiddly, it fell off too easily and it picked up EVERYTHING else on the stage (Drummers [rolling my eyes]) which is why bought the pickup.

[pops1]

If you plug into the board directly, it may not sound as good as with a pre, but does the hum go away. You could also plug into any amp and see if it hums. If it does it may be in your cord or pickup. Since you have already tried a different cord that should rule out hum from the cord. Could there be a wire in the jack on your mandolin touching, they are small and hard to see. I look very close when I install a pickup to make sure a strand of wire is not loose and can touch and cause hum.

[almeriastrings]

What Pops1 says.

Process of elimination. Try several different cables. Standard TS, but they need to be well shielded and not more than about 10ft long for a passive transducer. Plug it into an acoustic amplifier's passive input directly. Try a different (active) DI box. Take it with you to a music store or friend who has this stuff. Try it there. If it is coming from the mandolin, get the PU installation checked. Make sure the core+shield on the coax is soldered correctly to the jack.