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View Full Version : Acoustic Amp?? Why do you need one?



Dan Uke
10-13-2011, 12:56 PM
Hello everyone

I've read several threads on amps and I am confused on what an acoustic amp is vs. a regular amp? It seems like acoustic amps tend to be more expensive and when people talk of amps, they don't distinguish them.

Does that mean that an electric guitar or ukulele will not sound as good on an acoustic amp? Very confused

Thank you

PhilUSAFRet
10-13-2011, 02:04 PM
As a general rule of thumb, electric instruments sound better on instruments made fo them and acoustic instruments sound better on acoustic amps which tend to produce the true "acoustic sound" of the uke much better. The better the uke sounds, the greater benefit from having an amp that will make sound as good plugged in as it can.

Dan Uke
10-13-2011, 03:49 PM
thanks Phil

Tor
10-14-2011, 12:07 AM
Amps made for electric guitars are different from acoustic guitar amps in several ways, the two main ones are:
1) The equalization is totally different. The acoustic amp will try to be as linear as possible, while the electric guitar amp will e.g. have a boosted mid range.
2) The acoustic amp will have as little distortion as possible, while the electric amp will often use distortion as part of the sound itself. Even the 'clean' channel on an electric amp will let you overdrive the signal (=create distortion). This would be unwanted in an acoustic amp.

Another way to look at it is that an amp for an electric string instrument will try be part of the sound while an amp for an acoustic instrument will try to not affect the sound at all - i.e. be as transparent as possible.

-Tor

consitter
10-14-2011, 12:37 AM
And besides, it just sounds cool to say, "I have an acoustic amp." It just kinda rolls off the tongue. ;)

joejeweler
10-14-2011, 05:42 AM
Simply put,....an acoustic amp is much like a portable PA System. (Public Address System) Often traveling acoustic performers will plug into a venue's PA system rather than use a separate amp. The house unit is often higher powered, and wired to the house speakers often placed to best advantage in that setting. (not always though :o)

You want clean amplication generally for best vocal presentation, and the same for acoustic instruments, although at times some effects are added to an acoustic performance.

The strictly electric instrument type amp colors the output, so never the best choice for vocals or acoustic instruments.

raecarter
10-14-2011, 06:29 AM
Its worth noting that many acoustic amps have feedback detection to eliminate feedback

Dan Uke
10-14-2011, 06:38 AM
Very interesting...I would think for a uke, you would want the cleanest sound but lots of positive comments about amps w/ effects and the ones with a mic input. It's good to know that if there is a good PA system, you don't need an acoustic amp. I am getting a pickup in my uke and don't plan on playing in public but want to be ready just in case. :)

Thanks everyone

OldePhart
10-14-2011, 10:55 AM
1) The equalization is totally different. The acoustic amp will try to be as linear as possible, while the electric guitar amp will e.g. have a boosted mid range...


Actually, that's a common misconception. If you actually graph the response of most electric guitar amps you will find that they have a fairly pronounced mid scoop. Obviously it varies somewhat from model to model but in general "Marshal type" amps the scoop is a little deeper than on most "Fender type" amps.

I used to design and build tube amps for guitars and I honestly can't tell you whether the scoop was originally intentional or was simply the result of the first amps being designed by people who were anything but electronics experts (most of the early designs were lifted straight out of the RCA and other tube manufacturers manuals). There are four factors that determine the amplitude of the signal from a magnetic pickup. Two of them - the size of the ferrous element being vibrated and the speed at which it vibrates - end up being frequency dependent. The result of all that mess is that the signal actually has a hump in the middle range. At the low frequencies you have large strings but they are vibrating very slowly. In the high range you have much faster vibration but the strings are smaller. Across the guitar's midrange you have a "perferct storm" where the string size and vibrating frequency result in a stronger signal.

Obviously, exactly how much depends on way to many factors to predict with precision - but basically it's safe to say that an electric guitar with magnetic pickups is going to have some natural "mid boost."

If anybody really cares that much I can post graphs of typical Marshal and typical Fender tone stack response... I kind of suspect, however, that I've already exceeded most folks' interest in the topic. LOL

John

Brad Bordessa
10-14-2011, 03:56 PM
I'd be stoked to see the graphs.

ricdoug
10-14-2011, 05:35 PM
Acoustic amps are designed to produce cleaner, wider bandwith and a more natural sound. A passive piezoelectric pickup works better if an outboard device, like an LR Baggs Paracoustic DI is used before plugging in. The speakers on an acoustic amp are structured more like those in a home entertainment system. They usually have foam surrounds and stiff cones. Acoustic amps generally have a tweeter, coaxial tweeter or a whizzer cone to expand the bandwidth of the frequency response. This accommodates a more natural movement of the cone.

Electric guitar amps are built to amplify the frequency range and overtones of magnetic pickup/active electronics in a narrower frequency bandwidth for more efficency and acoustical output. The speakers, from companies like Eminence and Celestion, have more slop in the cones. The cone and the surround are one piece and of the same material. The surround is usually coated with a rubbery substance for more strength to prevent tearing at the cone edges.

Acoustic amps are generally closed back. This creates a flatter response as the output is quasicomplementary - push push.

Electric guitar amps are generally open backed. This boosts the acoustical midrange, as the acoustical output is a slightly out of phase - push pull - push comes out of the front of the amp and pull comes out of the back of the amp. This phasing delta cancels some of the bass and treble.

Electric guitar amps are designed for mor midrange. Play your uke through an electric guitar amp and then through an acoustic guitar amp. It sounds more natural through an acoustic guitar amp.

I can explain input biasing, if anyone is interested. Ric

ricdoug
10-14-2011, 05:40 PM
I'd be stoked to see the graphs.

Google Eminence Speakers or Celestion Speakers and look at the speaker graphs, Hippie Guy. Ric

mealfrog41
10-15-2011, 10:45 AM
I currently use the LR Baggs Paracoustic DI straight through the PA for gigs. I am in the process of shopping for an amp and was curious what you guys thought about running through a tube amp vs acoustic as well. Hippie Guy, I've read your article on the Roland AC-90 and was highly considering that but I was told by a couple people that I would be better off going through a tube because the acoustic DI was already taking care of whatever the acoustic amp would've done for the sound. Hopefully that makes sense, any advice on this would be much appreciated. I am playing with a six piece band with acoustic and electrics guitars, bass, and drums so I need a good amount of sound if that makes any difference. I also use multiple effects pedals. Thanks for your input!

Dan Uke
10-15-2011, 11:54 AM
Haha..I just bought the Baggs Para DI as well without knowing how it works. Someone recommended it as I am getting K&K Twinspots. The next step is buying an affordable acoustic amp.

ricdoug
10-15-2011, 12:09 PM
Mealfrog41, I second the Roland AC-90. It's a powerhouse that can be used by itself as a personal P.A. and also as a personal monitor to hear yourself on stage. I use my LR Baggs Paracoustic DI with my Roland Acoustic Chorus series amps to broaden tonal control and reduce feedback like a fine art. Ric

jackwhale
10-15-2011, 12:15 PM
Wow! This thread is great. I have several amps (guitar and acoustic) and never knew the physics behind the different amps. I'd appreciate anything you 'experts' have to say--definitely not boring.

I'm fairly new at this, but it takes a LOT of tinkering with tone controls and strumming 'technique' to get a uke to sound truly 'live' and 'acoustic'. It's easier to get the tone I like at home but those settings don't always apply to other playing environments. i.e. playing in a larger and acoustically lively room is always disappointing. Keeping the uke sounding live while playing with other instruments is very challenging.

ricdoug
10-15-2011, 12:15 PM
Nongdam, what price do you consider affordable for an acoustic amp? Ric

Dan Uke
10-15-2011, 12:32 PM
I would prefer not to spend more than $200 and willing to go up $300 if it's that much of a difference in quality. Since I haven't been to a store yet, I don't know the sizes of these amps but prefer a small one as it's mostly for home use.

ricdoug
10-15-2011, 12:57 PM
Here's my Roland AC-33 Acoustic Chorus amp. Notice the foam surround around the speaker cone. Also look at the smaller cone in the middle of each speaker. That's called a "whizzer cone" and it's purpose and function is to extend the high frequency range:

http://www.hunt101.com/data/500/RolandAC33Speakers.JPG

Following that is my Acoustic AG30. It also has a foam surround around the speaker cone. You'll also see two braided wires coming from the speaker cone into a coaxial mounted tweeter, which also exxtends the high frequency range:

http://www.hunt101.com/data/500/AcousticAG30Speaker.JPG

In this third photo is my Vox DA20 electric guitar amp. The speaker cone and the surround are one piece. The surround is rubbery coated to prevent tearing at the edge of the cone. It has no high frequency device, just a domed dust cap:

http://www.hunt101.com/data/500/VoxDA20Speakers.JPG

mealfrog41
10-15-2011, 12:57 PM
Mealfrog41, I second the Roland AC-90. It's a powerhouse that can be used by itself as a personal P.A. and also as a personal monitor to hear yourself on stage. I use my LR Baggs Paracoustic DI with my Roland Acoustic Chorus series amps to broaden tonal control and reduce feedback like a fine art. Ric

Thanks a lot Ric, really appreciate it. Can you think of any benefit in using a tube amp? The person that recommended it over the acoustic amp is a very accomplished producer and I respect his opinion greatly. I am completely open to either option though, and I'll probably try both out. Just curious if there might be pros and cons you might be able to point out. Thanks again!

ricdoug
10-15-2011, 01:06 PM
I would prefer not to spend more than $200 and willing to go up $300 if it's that much of a difference in quality. Since I haven't been to a store yet, I don't know the sizes of these amps but prefer a small one as it's mostly for home use.

I have an Acoustic AG30. It has two channels that have both 1/4" and XLR inputs with their own seperate volume controls. You can any combinition of microphone/instrument through it's two channels. The effectsill be the same on both inputs, though. It also has an 8 inch woofer with a coaxial tweeter that gives it a wide and flat frequency range. It's not small, but angled up. This allows you to hear what's being played, similar to a floor monitor and gets the sound out into a room. All for $199 bucks:

http://www.musiciansfriend.com/guitars/acoustic-ag30-30w-1x8-acoustic-guitar-combo-amp

The Acoustic AG30 acoustic amp is perfect for performing singer/songwriters looking for an easy and excellent way to amplify their instrument and voice without having to cart around multiple pieces of gear.

The AG30 is designed to maximize projection, with its angled, floor-monitor-style cabinet. For warm, full frequency sound, the cabinet features an 8" studio monitor style speaker for strong mid and low-frequency response and a coaxial tweeter for ultra-clear, sparkling high end. Each of the two channels has a combination input that allows you to plug an instrument into the 1/4'" unbalanced plug or a microphone into the XLR balanced plug. The 3 band EQ with sweepable mid band provides satisfying control over your tone. Also included is a selectable effects section, with 16 high-quality digital effects, including reverbs, delays and choruses. A chart detailing each effect is located on top of your the amp, so you'll never lose it.

For quiet practice, use the 1/8" stereo headphone jack, and for pre-recorded accompaniment, the AG30 amp has an 1/8" stereo aux input. Plug in a CD or MP3 player and play along. Finally, a Line Out affords you the opportunity to send your signal to a PA, for amplification in larger spaces.


Features
16 high-quality digital effects,
Two channels - combination inputs accept 1/4'" or XLR cables
1/8" stereo headphone jack
1/8" stereo aux input
Line Out
Heavyweight cloth grill
Heavy-duty 8" coax studio monitor-style speaker
Angled monitor-style cabinet projects sound upward
Rugged and comfortable handle
Easy-to-read control panel
Protective, long-lasting covering

http://static.musiciansfriend.com/derivates/6/001/268/849/DV019_Jpg_Regular_500133.001_black_R.jpg

http://static.musiciansfriend.com/derivates/6/001/268/848/DV019_Jpg_Regular_500133.001_black_front_angle.jpg

poppy
10-15-2011, 01:31 PM
i am glad to see the acoustics are making a comeback (talking brand here lol) they were once the king of the hill for bass and guitar (the old 360/361 was a killer). The really big misconception I'm seeing here is once you use a good preamp any "good" amp will produce the sound pretty well as the preamp is biasing the input to give you the desired out put. The reason so many old rockers like tube amps is the ability to drive them into distortion (past class "A") and get the old hard rock sound , but with the new amps they literally create the old sound by designing circuits to imulate particular amps.
With a uke or acoustic you are looking for a good class "A" amp that reproduces an input precisely on the output stage with a speaker system capable of producing that sound in many cases that requires
POWER, A pure class "A" amp uses about 2/3 more power than an AB or class B amp. but it is true reproduction of sound from front to back so in reality look for a good Class A amp for BEST reproduction most amps do not operate class A.

Dan Uke
10-15-2011, 01:42 PM
Thanks Ric for the advice...I actually tried to PM you a couple of days but your box was full at that day so I started this thread. I knew you would respond to an amp thread. I will look into the AG30 as that's the price range I am looking for.

ricdoug
10-15-2011, 01:48 PM
Thanks a lot Ric, really appreciate it. Can you think of any benefit in using a tube amp? The person that recommended it over the acoustic amp is a very accomplished producer and I respect his opinion greatly. I am completely open to either option though, and I'll probably try both out. Just curious if there might be pros and cons you might be able to point out. Thanks again!

The tube amps have a "warmer" sound when they are clipping into saturation at high volume Mealfrog41. When they distort, the waveforms peak at even order harmonics - octaves. This is a pleasent "violin type" sound. Solid state amps clip at saturation at the waveforms look very similar to square waves. This is a very harsh sound. When playing an acoustic instrument through a tube or solid state amp, you DO NOT want to drive either amp into saturation. It no longer sounds natural at this point.

I'll use a Fender Hotrod Blues Deluxe (My favorite amp for my Strats) and the Roland AC-90 (The Roland AC "Acoustic Chorus" are my favorite acoustic instrument amps):

http://www.musiciansfriend.com/guitars/fender-blues-deluxe-reissue-40w-1x12-combo-amp/483718000000000

http://www.musiciansfriend.com/guitars/roland-ac-90-45wx2-acoustic-chorus-guitar-combo-amp

Fender Hotrod Blues Deluxe/Roland AC-90

Initial cost - $749/$649

Cost to replace tubes - $150/No tubes in solid state amps

Weight - 45 lbs/25 lbs

Tweeter - no/yes

Separate microphone channel - no/yes

Reverb - yes/yes

Chorus - no/yes

Delay - no/yes

Anti feedback circuit - no - yes

A/C power consumption - 180 Watts/30 Watts

Stereo - no/yes

Size - 23-1/2"W x 18-3/4"H x 10-1/2"D /// 18-5/16"W x 12-7/8"H x 11-15/16"D

Stand mountable - no/yes

Designed for acoustic instrument amplification - no/yes

ricdoug
10-15-2011, 02:03 PM
The really big misconception I'm seeing here is once you use a good preamp any "good" amp will produce the sound pretty well as the preamp is biasing the input to give you the desired out put. The reason so many old rockers like tube amps is the ability to drive them into distortion (past class "A") and get the old hard rock sound , but with the new amps they literally create the old sound by designing circuits to imulate particular amps.

Ditto, Poppy. I love my tube amps for electric guitar, but often perform electric guitar with digital solid state amps. Just the shear weight of tube amps keeps me from lugging them around, except for certain occassions. Ric

poppy
10-15-2011, 02:10 PM
Seems they have changed the way the modern amps are rated Ric. The super reverb was rated at 90 watts had 4 10's and could hold its own in any venue. Our lead used one while the rythm player used a Sun 260 solid state that oddly had killer distortion for a solid state. I had the 360/361 combo 440 watts 1-18 it could hold 4 for a total of 1720 watts but truly 1 cabinet would play dodger stadium. It was a great class AB with zero distortion which is why I bought the roland bass RX I think ukes sound very good through a bass amp with no modeling.
And I do under stand the weight problem finally got tired of lugging the acoustic around ,that was a heavy bugger LOL. Got a Kustom 200 with 2 D-140Fs while no light weigh it was more approiate for the Country band I ended my short career in !

ricdoug
10-15-2011, 02:34 PM
You're correct, Poppy. Amps used to at least state whether the wattage was RMS or Peak to Peak. Most of my performing is done with minimal equipment nowdays:

http://www.ukuleleunderground.com/forum/showthread.php?5333-Battery-powered-ukulele-amplification...

Things have come a long way since James Burton:

http://youtu.be/zLkCWT2neuI

poppy
10-15-2011, 07:36 PM
We were a long way then , this is the stuff we were doing lol
http://www.youtube.com/watch?v=0x6chChxzV0&feature=related
a little zeplin and sabath thrown in for chillin lol.
mel is the reason I use a pick today he was probabaly one of the only bassmen around using one and he really kinda pioneered bass lead ,believe it or not this band is still not in the rock n roll hall of fame !

ricdoug
10-16-2011, 09:53 AM
You're an enabler, Poppy! I just broke out one of the Paul's through a Fromel modded http://fromelelectronics.com/modifications/Amps-Epiphone-Value-Jr Epiphone Valve Jr.. The 70's blues bands (commonly dubbed classic rock) are my favorite musical era. Thanks for that blast from the past. Ric