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Old 7th December 2010, 11:24 PM   #1
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Default Medium power Class D battery bass guitar amp

Hi,

A friend of mine has been asking about a light portable bass amp that he can lug with him and use for around 4 hours. I want to build this as a christmas present.

So far I have come up with the following:

Using 4x 60W/hr 6 cell notebook batteries for the supply
Using 1x 60W/hr 6 cell notebook battery as a reserve supply (switchable)
Using a 45-55 litre max fibreglass enclosure with a 10" driver and 4" mid
Using 2x 41hz.com Amp 11 (60w RMS@32V) (one for a switchable backup with a 2 ohm resistor in series with the speaker as a "limp mode" backup).

I know this will not blow the house down, but with a speaker around 92db 1w 1m am I safe to assume it will be quite loud? Also it has to have bass extension to 41.2hz.

Can anyone suggest a suitable speaker? Is there anything that screams failure in this project?

Are the 41hz amplifiers up to this task, if someone unplugs a guitar and it makes a high level pop sound will the ampifier take it? Should I add input protection (such as 2 lots of opposed polarity banks of 3x diodes in series to clamp the input level)

Thank you for your help with this.
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Old 8th December 2010, 05:33 AM   #2
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What type of use would be most normal? Indoors or outdoors?

Bass extension to low E is a pretty big task for a single 10" woofer indoors, outdoors it's next to impossible. What driver do you have in mind?
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Old 10th December 2010, 12:18 AM   #3
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Hi,

He does a bit of street performing. I do see what you are getting at and my choice in woofer would be:
http://www.eminence.com/pdf/legend-bp102-4.pdf

If required I will use 2x 41hz AMP11 with two of these speakers, I may use mild equalisation to bring the bottom end up (3db centred at 60hz). If I use 2 amplifiers and speakers I will be using 6x 6 cell liion (from 60W/hr notebook packs) for 360W/hr energy storage capacity.

At the moment I am seeking advice with regards to the sound output level and speaker selection - I haven't had to build a bass guitar speaker before, Would using a sensitive 4R home hifi woofer / car subwoofer be better at the expense of a small degradation of sound quality?
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Old 11th December 2010, 08:21 PM   #4
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Any type of electric guitar will use distortion as a musical effect, so you shouldn't be concerned with how good the driver sounds - rather with how sensitive and how tough it is. Avoid high excursion drivers in such an application, they will sound muddy.
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Old 12th December 2010, 01:36 AM   #5
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Quote:
Originally Posted by SEclassA View Post
a light portable bass amp
This is a bit of an oxymoron.

A good bass combo is heavy and large.

This looks like a good (cheap) battery: DealExtreme: $12.70 Mystery 11.1V 2200mAh Lithium Polymer Rechargeable Battery

I haven't tried this battery, but I have bought other lithium batteries from DX with no problem. The Amp 11 will be OK with 3 of these if you get the version with 50V caps (#28)

You've also got a charging problem. You might want to look at something like this balancing charger: Inwood Models : LIPRO QUAD 6 BALANCER CHARGER [FCH005] - 109.99

...you'll need some switching to break the battery down into 3 individual packs unless you can find a charger that will cope with them in series. I think the pack shown has connections for charge balancing, but this is something you need to check. You can probably source a charger closer to home, electric flight is the source for this one.

I'd go for a more efficient speaker, I see some Celestions out there with 99dB, this is more than twice as loud, or the same volume for less power, which is a significant consideration.

Fibreglass may be light but you'll probably find it easier to construct a resonance free cabinet with MDF.

w
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Old 14th December 2010, 11:01 AM   #6
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Your friend is probably thinking of the classic small bass combos like the Gallien-Krueger MB150 or some of the Genz-Benz stuff. I suspect both makers use proprietary drivers to get things so ridiculously small, but maybe you can find some info on the driver used in the MB150 over the years-- it has a strong cult following.
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