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Author Topic: Battery Amp  (Read 1152 times)

Bob Burke

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Battery Amp
« on: May 06, 2014, 04:58:04 pm »

Hello all.

  I have an unusual problem that I'm sure you guys can help with. We bought a Crate Taxi Limo to use as a bass amp when busking:

http://www.crateamps.com/products/pindex.php?prodID=26


  The stock speaker would not reproduce the low freqs very well, so I replaced it with an Eminence:


http://www.sweetwater.com/store/detail/LegendBP102


  Big improvement BUT now, the darned thing is distorting/rattling when I increase the volume to a useable level. I've checked inside for loose connections, and tightened all the screws no joy. Anyone have an idea how I can remedy this situation?



Thanks,


Bob

John Roberts {JR}

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Re: Battery Amp
« Reply #1 on: May 06, 2014, 05:49:52 pm »

Does it work properly with the stock speaker?

What is Z of both?

JR
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Bob Burke

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Re: Battery Amp
« Reply #2 on: May 06, 2014, 06:02:10 pm »

Does it work properly with the stock speaker?

What is Z of both?

JR



Yes, but not low enough. I don't know what "Z" is.  ;D

John Roberts {JR}

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Re: Battery Amp
« Reply #3 on: May 06, 2014, 07:37:51 pm »

4 ohm 8 ohm speaker?

JR
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Bob Burke

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Re: Battery Amp
« Reply #4 on: May 06, 2014, 08:11:25 pm »

4 ohms. The amp is 50 watts (so they say) and the Eminence is a 200 watter. The tech at Crate said it should work.

Art Welter

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Re: Battery Amp
« Reply #5 on: May 07, 2014, 10:48:03 am »

4 ohms. The amp is 50 watts (so they say) and the Eminence is a 200 watter. The tech at Crate said it should work.
Bob,

Test the speaker with your PA amplifier (disconnect the Taxi amp) or normal bass amp to determine if it sounds OK in the Taxi enclosure. The only reason it would distort badly with  50 watts of clean power is if the voice coil is rubbing, possible if the magnet shifted from a bad drop in shipping, though usually that causes the coil to become locked and the speaker would just make a low level midrange when played.

The Taxi amp is rated 50 watts at 10% distortion (not clean, but not terrible) with 13.6 volts, about what you get from a car battery when the engine is on and the alternator keeps voltage up. A small lead acid battery as used in the Taxi can only provide about 12.6 volts when fully charged and used at low levels, if you try to pull 50 watts from it as needed for the low notes in a tiny enclosure, the voltage drops and the amp will distort at a lot less power output (probably less than half), the new speaker probably reproduces the low frequency amp clipping more accurately (sounds worse) than the original.

If we figure the amp really can only deliver around 25 watts of low bass when battery powered, the low "E" (40 Hz) would only be about 88 dB at one meter with a 10" in the Taxi enclosure. My voice with no amplification can hit that level easily, but it would only take around 70 dB in the midrange to sound as loud as 88 dB at 40 Hz.

So unless your new speaker is shot,  the only recourse for getting more clean bass is better batteries (like Lithium Ion Iron Phosphate, LiFePO4) which are far more expensive, (but lighter) and can deliver near full power till they run out of juice (which can ruin them) or a larger, more efficient (and heavier) cabinet.

Art

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Bob Burke

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Re: Battery Amp
« Reply #6 on: May 07, 2014, 12:10:50 pm »

Mr. Welter,

  Thanks for the detailed explanation. I think you're right about 10% distortion - that's not too great.

  I pulled the speaker again and checked for anything loose, then I cut up some foam and stuffed the enclosure with it. I also sandwiched some foam between the speaker flange and the enclosure. That reduced the rattle quite a bit. Now it's only distorting when I max out the level control. It sounds pretty good at 75% power - no rattle. We'll just have to be satisfied with that. It's still a great little amp for busking outdoors.

  Thanks again.

Art Welter

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Re: Battery Amp
« Reply #7 on: May 07, 2014, 12:21:44 pm »

Mr. Welter,

  Thanks for the detailed explanation. I think you're right about 10% distortion - that's not too great.

  I pulled the speaker again and checked for anything loose, then I cut up some foam and stuffed the enclosure with it. I also sandwiched some foam between the speaker flange and the enclosure. That reduced the rattle quite a bit. Now it's only distorting when I max out the level control. It sounds pretty good at 75% power - no rattle.

Bob,

At full power without being plugged in, the 10%@ 50 watts probably reduces to more like 100% distortion at 25 watts.

Rattles and distortion are two entirely different issues. Stuffing the cabinet with foam may eliminate some rattles, but the fill reduces LF output by about 3 dB, equivalent to cutting the already low power in half.

Art
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Bob Leonard

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Re: Battery Amp
« Reply #8 on: May 07, 2014, 12:26:06 pm »

Bob,
I have to agree with Art on this subject, but I'll also add that the Crate may not have been your best choice. To be honest I say that because I have not heard anything good about the Crate portable amps, and the Crate portables I have used have sounded horrible. I don't know if you can return the amp, but if you can (or not), you may want to look at the roland portable battery powered solutions for your needs. Roland has a full line of portable amps / PAs, etc. and they all sound great. The power specs are also very misleading as these amps seem to out perform their own specs by a large margin.

http://www.rolandus.com/products/details/940/504

Pignose, Orange and others also make some quality portable amps.
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Bob Burke

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Re: Battery Amp
« Reply #9 on: May 07, 2014, 01:47:04 pm »

Hi Bob,

  We also have a Roland Cube Street that I love.  Roland doesn't make a battery bass amp though, so we went with the Crate. Never been a Crate fan either, but this little thing sounds pretty good. We also have a Pignose Hog 30, and it's useless.

  I believe the best battery-operated bass amp is the Phil Jones, but it's really expensive.


BTW, I'll be trying out your mains behind us technique at a gig on Monday night. I have a real problem getting my monitor loud enough without FB.


Regards,


Bob
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