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Thread: Thumping sound when playing through amp

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    Default Thumping sound when playing through amp

    My mandolin has twin K&K pickups installed under the bridge (I bought it that way several months ago). I can't see them because I don't have a little mirror, but it looks like they are directly under the outer part of the bridge feet.

    I just tried plugging it in for the first time and I'm getting a percussive thump sound on every pick stroke. Chords or single note. The sound has a soft, puffy quality to it. Sort of like tapping on a mic with a foam cover.

    I was going direct into my friend's Schertler Unico. I know it has something to do with the mandolin because it happened when I was playing it and when he was playing it. We then plugged his mandolin in and it didn't make that noise when either of us were playing his mandolin.

    Any ideas? Is this the sort of thing where it could be one of a number of issues or is it likely one thing? I'm thinking maybe the pickups are not installed in the right spot?

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    Default Re: Thumping sound when playing through amp

    If I remember the Schertler is a contact microphone, while the K&K is a piezo transducer. A difference of impedance would be what I think you are hearing. I am not remembering what the impedance of the Schertler is, but the K&K is one million ohms. You need an impedance match to transfer the sound accurately. An amp with a high z input or a preamp for your pickup. They are horses of a different color and won't sound the same plugged into the same input of an amp designed for an input that is, I just looked it up, 4.7 thousand as compared to one million. Hard to sound good with that much of a mismatch.
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    Registered User almeriastrings's Avatar
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    Default Re: Thumping sound when playing through amp

    Normally an impedance mismatch would result in a lack of low frequency presence, rather than too much. You often have to roll off the low end really hard with these pickups - you actually don't need almost anything there under 196Hz with a mandolin. You need to cut those very low frequencies where the 'bumps' and 'thuds' are occurring.

    The 'soft' sound part of the problem could be either incorrectly installed transducers, or impedance mismatch, or both.

    Some more info would be useful.

    What mandolin do you have? What does your friend have and which transducer is he using with it?

    Which socket did you plug your mandolin into on the amp?

    I would go and try your instrument into an acoustic amp that has a genuine, normal, true hi-z input suited to passive piezo transducers - such as a Fishman Loudbox. That will give you a much more accurate indication of where the issue really is here.

    The Schertler's, while nice amps, are somewhat idiosyncratic and work best with their own range of fairly unique pickups, or with instruments have have active onboard electronics rather than passive piezo transducers.
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    Default Re: Thumping sound when playing through amp

    I tried two different sockets with both mandolins. One was the instrument socket (1/4") the other was instrument/mic which was a combo xlr and 1/4". My mandolin sounded the same through both of those input jacks and so did his.

    I have a Summit A style (2008 I think). His is a Griffin (local builder Dave Griffin). I can't remember what kind of pickup he has, but I don't think it's a passive peizo like the K&K. I think it's a contact mic or something like that. I'll ask him about that.

    Thanks for the info guys! I'll take it somewhere where I can plug it into a Fishman Loudbox and see if it still happens.

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    Default Re: Thumping sound when playing through amp

    If it is a contact mic, such as the Schertler, that is perfectly matched to that amp, and they sound quite different from a K&K to begin with. That said, the K&K's are normally fine through a suitable input (around 1M unbalanced with high headroom) or if testing with the Schertler, a suitable active DI box into the XLR 'mic' input.
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    Default Re: Thumping sound when playing through amp

    Often the low transducer thumping is related to bumping the bridge. In my experience, it's more likely to be an issue with bridge-based transducer systems. These days when I plug an acoustic mandolin in I'm using a K&K Twin Internal through a Red-Eye pre-amp and am not having the problems you describe.

    The very possible culprit comes down to technique: if your right hand technique is such that you're bumping the bridge or mando top with your right hand while you play then that could cause the thumping you describe -- might have to smooth things out. It's at least worth observing if this might be an issue in your situation. Good luck!
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    Default Re: Thumping sound when playing through amp

    Quote Originally Posted by pops1 View Post
    If I remember the Schertler is a contact microphone, while the K&K is a piezo transducer.
    Pops, to clarify, the K&K is the pickup I'm using and the Schertler is the mini-amp/PA I'm trying to play through (Schertler may also make a contact mic but that's not what I'm talking about).

    I just talked with my friend and he says he's assuming it's a "positive microphonic pickup" on his mandolin but he doesn't know what it is for sure (he bought his used as well).

    Pglasse, I thought about bumping the bridge as a possibility so I made sure to play with absolutely no contact with the top of the instrument or the bridge and I'd still get the effect.

    I'll rule out there being a problem with the pickup by taking it to a local store to play through a Fishman Loudbox and see if it goes away. I may have to get a pre-amp or get my own amp with a built-in preamp. Not sure what a DI is but I'll look into it...

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    Default Re: Thumping sound when playing through amp

    Quote Originally Posted by Stevo75 View Post
    Pops, to clarify, the K&K is the pickup I'm using and the Schertler is the mini-amp/PA I'm trying to play through (Schertler may also make a contact mic but that's not what I'm talking about)..
    I knew you were using the K&K, but I put the reference in there because you were playing thru the Schletler amp and that is what that amp wants to see, not what the K&K is putting out. As far as the losing the low's with a mismatch that is more noticeable in a guitar that actually has some lows, but not as noticeable in a mandolin without any real lows. I feel the thud is from the mismatch, as a mandolin has some pick noise most of the time and you may be hearing a real amplified pick noise. I will be interested in what you find playing thru a preamp or an amp like a Fishman designed for a piezo.
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    Default Re: Thumping sound when playing through amp

    I think I am hearing amplified pick noise, at least that's my guess after reading what y'all have written above.

    I'm going to take my mandolin to the Pickin Parlor and play it through an amp designed for a passive piezo. I'll let you know what I find out.

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    Default Re: Thumping sound when playing through amp

    I have the same thumping issue with my LR baggs radius/para DI unless I completely dial out the lows.

    This completely goes away with a mic (clip on or stand) and the baseline (no eq) sound is way better.

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    Default Re: Thumping sound when playing through amp

    Because there is a direct mechanical connection pick>string>bridge>soundboard>pickup
    It will hear a lot of what the pickup is attached to..

    where Mic on a Stand is not connected, it hears variations in sound wave pressures reaching it..

    yea maybe you need the Pre amp designed around the Mega Ohm impedance of piezos .

    since you are still borrowing gear consider trying a Fishman Loudbox,
    fishman being another Piezo pickup maker It may handshake better ,

    My Roland AC-60 has a Piezo/magnetic input switch on the instrument Channel..
    so they may run the piezo signal thru a better impedance match depending on which way the switch is flipped.



    Yea Schertler makes their own pickups , but none are Piezoelectric..

    1 is dynamic the other electaret-condenser .


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    Default Re: Thumping sound when playing through amp

    As Mandroid says... when you attach a transducer physically to a mandolin's top, you turn the entire thing into a kind of microphone membrane. So, any handling, touching, pick noise will be 'translated' into electrical energy, and amplified. The only thing you can do to mitigate this is to try to EQ as much of the unwanted noise out as possible. It is the nature of the beast... how it is... basic engineering and physics... all contact transducers are susceptible to this. Some are worse than others, however, and transducer position, playing technique and "what you plug them into" (gain, impedance, headroom and EQ facilities) will make a big difference to subjective results. FWIW, I found the Baggs radius one of the more difficult transducers to eliminate this from too - really takes some drastic EQ there. The more basic K&K type were less of a problem in this particular regard.

    With a separate, isolated, microphone you don't have this problem at all, of course. Magnetic pickups are also pretty immune - but are not really the sound most of us look for.
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    Default Re: Thumping sound when playing through amp

    As AlmeriaStrings says, the very best thing you can do is cut everything below 196HZ (frequency of the open G string). This will cleanup a good portion of the handling noise, bumps, thumps, etc...

    This is not something that most amps or preamps will be able to do on there own. You will probably need a stand alone EQ, or have someone make a filter.
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    Default Re: Thumping sound when playing through amp

    I have a very similar set up. But I use a Loar 600 with the same pickup and a Schertler jam200. I had the percussive sound at first. Contacted Cumberland that installed the pickup, and suggested what others did here. Reduce the low end on the amp. Turn down the bass. And some of the mids. I also use the k and k preamp. It allows me to do this with more control. Although I get a excellent sound plugging directly into the amp. Just play with the eq settings until you get a happy medium. It's the nature of those pickups, they make the whole sound board a mike so to speak. Makes a great percussive back up. Fwiw, I had the same thumping when plugging into a Bose T1 mixer, into a Bose compact and a full L1 tower. Made me realize it's the pickup not the amps.
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    Default Re: Thumping sound when playing through amp

    Funny, I have a K&K in my mandolin, using a preamp into the PA and I don't get that thumping at all. I have plugged into several amps and several different PA systems and have never gotten the thumping, so I would say it is not the pickup necessarily.
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    Default Re: Thumping sound when playing through amp

    I agree that it is rarely the pickup. I have installed hundreds of pickups in mandolins and this same situation comes up all of the time. With just a few exceptions, all of the mandolins were shipped off, so it ends up being troubleshooting over phone or via email. It is a very common problem, unless you work it out with EQ.
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    Default Re: Thumping sound when playing through amp

    I've had that happen on a few instruments with K&K pickups. Use a preamp and roll off some low end. Simple and effective.
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    Default Re: Thumping sound when playing through amp

    I haven't been able to get to the music store to test things out yet, but it seems like a common problem and the solutions seem to be the same: use a pre-amp and/or play through an amp that is better matched for passive pickups.

    I have read that some amps have built in pre-amps. What does that even mean? Every amp has stages before the final amplifying stage. How is that different than an amp that says it has a built in pre-amp? Is that just marketing. Do I need a true pre-amp and an acoustic amp as well?

    Thanks

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    Default Re: Thumping sound when playing through amp

    Quote Originally Posted by Stevo75 View Post
    What does that even mean? Every amp has stages before the final amplifying stage. How is that different than an amp that says it has a built in pre-amp? Is that just marketing. Do I need a true pre-amp and an acoustic amp as well?
    Normally - no. Not if it really is an amp that is well designed and offers a true Hi-z (1 meg Ohms +) passive instrument input. It is important to check the specifications, but you are on safe ground with the Fishman Loudbox range, for instance. There might be other reasons a person prefers an external preamp or DI box, but certainly with many genuine acoustic amps, they are not necessary as the correct impedance matching and suitable EQ options are already there.
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    Default Re: Thumping sound when playing through amp

    After reading this thread my curiosity created the necessity to plug in my nearly never used acoustic electric f-style and find out if I too have the mystery thump. Sure enough, 'thump,' thump. Some could be attributed to 'pick' thump. I then lifted the heel of my picking hand off the bridge and strings between the bridge and tail piece, and the thumping was considerably less. Could be the pick-up was not only picking up the pick on th string but also the motion of my hand? Not saying I've discovered the actual 'thump,' but it was different. Maybe I'll try the pre-am, even though the mando has an onboard pre-amp? Let the mystery prevail!
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