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Thread: Question about Acoustic Amps and PreAmps

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    Default Question about Acoustic Amps and PreAmps

    I'm just in the curiosity phase of amplifying an acoustic mandolin. I read in the description of one of the popular pickups that it's very important to use a good preamp meant for acoustic string instruments. But looking amplifiers, it seems like many have a first stage has many of same features, three-band EQ, notch filters, etc. What I wonder is if you have an acoustic amp with the necessary first-stage features, do you really need a preamp? Or, if you have a really nice preamp, do you really need an acoustic amplifier or would just a power amp and appropriate fullrange speaker work?
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    Default Re: Question about Acoustic Amps and PreAmps

    1) Not necessarily, give it a try.
    2) No; but you might find an acoustic combo amp more convenient for carting around.

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    Default Re: Question about Acoustic Amps and PreAmps

    Power amp and full range speaker works but Ray is right. Acoustic guitar amps don't have the bass that the first option has but mandolins don't need it and most of the weight of the former is to get the lower bass.

    Another option is a small powered PA speaker. Individual used units can be found fairly cheap. I got mine for $30 and it originally sold for $1200. Also got a single Mackie HR824 for $10, original price $850.

    IIRC guitar preamps' purpose is to provide a strong enough signal so that the noise picked up in the connecting cable is small by comparison and isn't noticeable coming out of the amp/PA. If you need a long cable, a short one to a booster preamp pedal, then the long one should work.
    Last edited by Greg P. Stone; Jul-08-2019 at 9:13am.
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    Default Re: Question about Acoustic Amps and PreAmps

    A preamp is not to boost the signal from a transducer pickup. The pickup has plenty of power on it's own. It does however have an impedance of 1 million ohms and a PA wants to see somewhere between 800-1200 ohms. The purpose of the preamp is to match the output impedance of the pickup to the input impedance of the PA. The new acoustic amps have a channel that matches the impedance of the pickup so it is not necessary to use a preamp. Some plug into the acoustic amp and then line it into the PA which also works fine. I use a preamp into the PA.
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    Registered User John Bertotti's Avatar
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    Default Re: Question about Acoustic Amps and PreAmps

    I don't have an electrified mandolin yet but my martin 000-18 has the K&K pure western mini in it. I use it with a QSC K10. Sounds great but it is a bit feedback prone. I do not have a soundhole cover. However, be warned I liked the QSC K10 so much I wound up with two.
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    Default Re: Question about Acoustic Amps and PreAmps

    It amazes me that people who put pickups in guitars or mandolins don't bother to educate their customers about the importance of an impedance matching devise. I became more involved in an open mic and had realized how many people with $5000 guitars equipped with K&Ks would just plug into a mixing board. The host at the time was an electric guitarist and didn't much care. I listened week after week to piezo mismatch. I used a RedEye, and with few exceptions was alone in this.

    Fast forward to a new host and I fill in. We were both concerned about poor sound and have upgraded almost everything. I had SunnAudio build me a blender so we could have a proper impedance match on at least two piezo equipped instruments. The quality of sound improved greatly. Even the cheapest undersaddle piezo pickups sound tolerable now. But now comes the reality. People don't really care. I'm talking about the more casual player. But my ears don't hurt anymore.

    An acoustic amp really needs to be a full frequency devise. Most acoustic guitar amps have a tweeter. My well loved Carvin AG 300 has a 12", 5", and tweeter. The speaker part of it is close to a PA cabinet. I can take it out to a small gig and put a mic through it and it is a simple no fuss solution. More and more acoustic musicians are using powered PA speakers as they provide flexibility. Two powered speakers and a small mixer and you can take one or both speakers to a gig depending on need. Add a couple more small powered speakers for monitors and you can power a small band. I'm seeing more mixers with an input impedance switch these days.

    We had an issue with the mains one time and just turned the Behringer 8" monitors around and filled a good sized room with sound, and I believe these are around $180, so you don't need to spend a ton. But like everything else throwing money at QSC will make you very happy.
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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by Br1ck View Post
    It amazes me that people who put pickups in guitars or mandolins don't bother to educate their customers about the importance of an impedance matching devise. I became more involved in an open mic and had realized how many people with $5000 guitars equipped with K&Ks would just plug into a mixing board. The host at the time was an electric guitarist and didn't much care. I listened week after week to piezo mismatch. I used a RedEye, and with few exceptions was alone in this.

    Fast forward to a new host and I fill in. We were both concerned about poor sound and have upgraded almost everything. I had SunnAudio build me a blender so we could have a proper impedance match on at least two piezo equipped instruments. The quality of sound improved greatly. Even the cheapest undersaddle piezo pickups sound tolerable now. But now comes the reality. People don't really care. I'm talking about the more casual player. But my ears don't hurt anymore.

    An acoustic amp really needs to be a full frequency devise. Most acoustic guitar amps have a tweeter. My well loved Carvin AG 300 has a 12", 5", and tweeter. The speaker part of it is close to a PA cabinet. I can take it out to a small gig and put a mic through it and it is a simple no fuss solution. More and more acoustic musicians are using powered PA speakers as they provide flexibility. Two powered speakers and a small mixer and you can take one or both speakers to a gig depending on need. Add a couple more small powered speakers for monitors and you can power a small band. I'm seeing more mixers with an input impedance switch these days.

    We had an issue with the mains one time and just turned the Behringer 8" monitors around and filled a good sized room with sound, and I believe these are around $180, so you don't need to spend a ton. But like everything else throwing money at QSC will make you very happy.
    Interesting. I don't know what difference I would hear with a preamp into the QSC but it does currently sound very representative of its unplugged sound. I wonder if using my audio interface and the preamp output to the QSC would do the required impedance matching so I could hear the difference?
    I have tried it through an RNP and it sounded great but a bit different, not better nor worse just different. I think a bit rounder or darker however you want to put it. It is a mic pre so I don't know if the K&K was a good match for the RNP.
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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by John Bertotti View Post
    Interesting. I don't know what difference I would hear with a preamp into the QSC but it does currently sound very representative of its unplugged sound. I wonder if using my audio interface and the preamp output to the QSC would do the required impedance matching so I could hear the difference?
    I have tried it through an RNP and it sounded great but a bit different, not better nor worse just different. I think a bit rounder or darker however you want to put it. It is a mic pre so I don't know if the K&K was a good match for the RNP.
    Look at your specs and find input impedance. If it is around 1 million (1Meg) ohms then it will work fine. If it is close either way it will work fine. You may not hear as much difference with a mandolin as there are not as many lows, but you will sure hear it with a guitar.
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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by pops1 View Post
    Look at your specs and find input impedance. If it is around 1 million (1Meg) ohms then it will work fine. If it is close either way it will work fine. You may not hear as much difference with a mandolin as there are not as many lows, but you will sure hear it with a guitar.
    Xlr or 1/4" input impedance is 2260Ohms so 2.2K set to mic, but I do not know what the pure mini is.
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    Default Re: Question about Acoustic Amps and PreAmps

    To continue my uneducated "IIRC", a long cable will kill the treble, so a preamp corrects that problem. Perhaps cables are made so well today that noise which the cable picks up is no longer a problem. If it is still a problem in some parallel universe a preamp helps.
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    Default Re: Question about Acoustic Amps and PreAmps

    The pure mini is 1 million ohms. A long ways away from 1 Meg.
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    Default Re: Question about Acoustic Amps and PreAmps

    Virtually any acoustic pre amp or acoustic amplifier will have the correct input impedance. Where you need to be careful is if you use a Di instead. Many other devices use DI boxes, keyboards and electronic drums for example, and they don't require this, so you'd need one with a 1 Meg ohm input impedance.

    A high impedance switch is showing up on many mixers these days.
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    Default Re: Question about Acoustic Amps and PreAmps

    Well, it turns out my RNP is 1Mohm input impedance so I am going to give it another look. I tried it with the K&K equipped 000 once but never really messed with it after that. This bears some more experimenting.
    Thansk everyone!
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    Default Re: Question about Acoustic Amps and PreAmps

    All the technical talk about impedance matching and ohms is great, but as I am not an electrical engineer, I like this quote from the Grace Designs Felix preamp user manual:

    Both Ch1 and Ch2 line inputs have 3 input impedance settings,
    selectable from the toggle switch labeled ‘Z’ . The settings are:
    Ch1: med - 1MΩ / hi -10MΩ / low – 10kΩ
    Ch2: med - 1MΩ / hi -20MΩ / low – 332kΩ
    Some pickups or sources are more sensitive to preamp input
    impedances than others. For example, if you use a ‘Sunrise’
    magnetic pickup, they prefer to connect with an input
    impedance of 1MΩ. If you have an onboard preamp or a lower
    impedance pickup, the input impedance setting will probably
    make less of a difference. In any case, we encourage you to try
    different settings with your pickup or source. The difference
    may be noticeable or not, and should be set accordingly to
    what sounds best to you. Always what sounds best to you!

    The "Always what sounds best to you" make the most sense to me. :-)
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    Default Re: Question about Acoustic Amps and PreAmps

    A nice feature offered by Grace. It is only the pizeo pickups that have such a high impedance, that I know of. A magnetic pickup would be nowhere near that. 6K-12K would be more like it. Nice that Grace offers the 10K input, but then a pre is rarely used with a magnetic pickup.
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    Default Re: Question about Acoustic Amps and PreAmps

    You can certainly go from a good 'acoustic' preamp direct into a high quality full-range powered speaker. The QSC K10's and K8's are ideal for this. It essentially gives you an all-in-one 'acoustic combo' but in two pieces. This does give you quite a bit extra flexibility and redundancy.

    Obviously, if you need to add other instruments or vocals, you'll need to insert a mixer between them.

    There are several valid ways of approaching this. Indeed, you can use some 'acoustic combos' as a mini-PA...
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    There are certainly many ways to go here. I've seen guys doing a solo gig with a Fishman mini. Wouldn't do that myself, but in reality, no one cared.

    I've seen guys doing a solo gig with a digital QSC mixer, two QSC k 12s , and a thousand dollar mic. In reality no one cared, except for the one sound geek in the audience. Thanks dude.

    It comes down to how much you care about your sound.

    A friend is doing a solo gig at a venue with no sound reinforcement at all. People have to listen.
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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by pops1 View Post
    The pure mini is 1 million ohms. A long ways away from 1 Meg.
    Ummm, no. 1 megohm = 1 million ohms. Just like 1 kilohm = 1000 ohms.

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    Default Re: Question about Acoustic Amps and PreAmps

    A guitar playing buddy of mine goes thru a Boss acoustic preamp pedal into the Tonematch for his Bose S1. It sounds so great he went out and bought another S1.

    On the other side of the spectrum, I recently plugged the Rigel straight into a Fender Passport 250, and it sounded surprisingly decent.
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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by Mandobart View Post
    Ummm, no. 1 megohm = 1 million ohms. Just like 1 kilohm = 1000 ohms.
    Thanks Bart, that was supposed to be 2.2k
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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by pops1 View Post
    Thanks Bart, that was supposed to be 2.2k
    That had me a bit confused as well but yes I see what you are saying the 2.2k on the QSC input is a long ways from 1M. I can't wait to get home and play with the RNP some more. I haven't had it out for some time since I got my Zen Tour. I was brushing up on it and it is very versatile, at least for my needs.
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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by Br1ck View Post
    But now comes the reality. People don't really care. I'm talking about the more casual player. But my ears don't hurt anymore.
    Yep. Non-musicians listen with their eyes. But better sound will improve the overall experience, so they will like it better. They just won't be able to tell you why.

    I use an Orchid Electronics Pre-amp. Very popular among the folkies in the UK for guitar and mandolin. It's not terribly expensive, it's built like a tank, and it works like a charm. I could go into a full spectrum amp, but I generally go to the PA from it.

    The lack of experience with mandolins and acoustic instruments in general among 'engineers' here in the north of France has influenced my efforts to go full electric. At least that way I have control over my tone.

    Daniel

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    Default Re: Question about Acoustic Amps and PreAmps

    Piezo pickups, a company like Fishman also makes amps, and the pickups , so I expect they have inputs with right impedance.

    I have a Schertler Dyn* Pickup It is a contact microphone , so acoustic amp preamp in mic channel works..

    It has a strong signal , so with a common impedance matching transformer , I can Plug into Guitar amps too....

    * now there is an active 48v phantom power, and a passive.. model , I only have the older Dyn Passive,

    impedance matching transformers, input is XLR but output is TR 1/4" (minus and ground combined..)







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    Default Re: Question about Acoustic Amps and PreAmps

    Quote Originally Posted by Daniel Nestlerode View Post
    I use an Orchid Electronics Pre-amp. Very popular among the folkies in the UK for guitar and mandolin. It's not terribly expensive, it's built like a tank, and it works like a charm. I could go into a full spectrum amp, but I generally go to the PA from it.
    Orchid DI's are really excellent. Their technical performance is up there with the very best at a fraction of the price.
    I've used their stuff for years. Never had a failure.
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    Default Re: Question about Acoustic Amps and PreAmps

    I use the RedEye, still have my Orchid, but too many places I play either don't have phantom or it is not 48 volts so I don't use it much anymore. Liked it while I used it tho.
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