How hard is it to convert a regular mains powered amp to 12V battery? I know I could just buy a Crate Taxi or Limo but they sound terrible with my classical guitar, a bit to thin and glassy. So many good-sounding amps around but very few running on batteries. Any ideas?

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Be or don't be....don't pretend!

The only practical way is with a 12V inverter. These are now really quite cheap, around £30.00 for a 400W unit.

There is a reason battery powered amps tend to sound crap. They are designed to run off batteries! Ok smart A you say! But the fact is to get low current drain and hence a reasonable battery life with batteries of reasonable size, weight and cost, something has to give and what gives is sound quality.

Modifying an existing transistor amp (don't even THINK valves!) is impractical. Apart from the inherent dangers of messing with the power suppy section, even a fairly low power amp, 30W say, will have effectively two 25V+ supplies.

If you go down the inverter/car battery route do consider...
100W from a 12V l/acid, 10A near enough. Typical 1.8L car batt'~50Ahrs. That will last a long time for intermittant use but at full drive only a few hours.

I have no experience of these cheap inveters and so the output could be as mucky as hell and guitar amps are not designed to keep such poo out.

"Mains" volts from a battery is JUST AS LETHAL as the stuff from the wall!

Dave.

Well depending on how much you are looking to spend - Aer Compact Mobile

AER have a good rep and this little amp would probably be just the thing.

The battery +inverter + amp is a good idea and fairly easy to implement. I have also used a Hiwatt Busker (similar to the taxi) didn't like the sound - no top end opened it up and sure enough just 1 driver and no tweeter..... bit of rewiring, a jigsaw and a tweeter made it sound quite good!

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Crazy guitar beating - www.myspace.com/dalecampbell

A TWEETER in a guitar amp thinks I!

Then I see you are one of those acoooostic persons Dale.

That AER looks very nice but who'se going to give a drink to a busker with a £1000 amp?!

Have fun,
Dave.

Indeed - it won't sound good with an electric and distortion now : ) !

I have seen busters/street performers with DB battery powered PA speakers with built in wireless address the crowd from headset mics..... Depends on the crowd and the performer.
If I was looking for a small acoustic amp I would consider dropping a bit more for the AER if its just for occasional busking then not worth it unless you only busk for fun, (and have spare cash!).

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Crazy guitar beating - www.myspace.com/dalecampbell

Hah!
'Twas tongue in cheek Dale!

I have seen guys downtown even in jerkwater Northampton with some pretty handsome rigs. I still chuck 'em a quid or two, still takes balls to do that!

Dave.

Having once done such a conversion I would never do it again

Depending on time/money/ability, these days I would suggest you get one of the loverly new class D amp modules.

Then power it with a 12V -> 24V+24V DC-DC converter from RS or Farnell.

With a suitable effects unit you can then dirty it up as much as you like.

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It wasn't me!
(Well, actually, it probably was)

This isn't difficult or problematic. You need to use a TRUE SINE WAVE invertor, others are not designed to power audio equipment so you may get unwanted noise or cause damage to components. The first rule with batteries is to put a fuse in the +ve line right next to the battery terminal - if there's a short, batteries can deliver a huge current which can cause fire/burns if you don't have a fuse. The 2nd rule if using mains electricity is to avoid wet situations, so best not to play in the rain etc.
Use your normal mains lead (power cord) between the invertor and your amp. It's true that a 100 watt amp may need a big beefy battery to run at full power, but if you want quality, not volume you can get it at much lower power, so experiment with smaller batteries to see what works. If your sound gets distorted it's a sign that the battery is going down & if it happens too soon abviously you need a bigger battery.
I'm surprised to hear you say the Crate battery amp sounds harsh - maybe you could try using am EQ pedal to cut down the top end ? That'd be a lot easier than altering a mains amp. I play a Yamaha LL11E thru a Crate Limo & it sounds great. There is a 3rd option: If you use a battery mixer or preamp,with a good quality car amp like jbl, plus speakers you can get a fantastic sound for a reasonable price.

In my last post I mentioned "mains electricity" when I meant to say "mains voltage" from a battery to mains voltage invertor - sorry ! Another thing I thought is that some classic rock guitar amps use only 10 or 12" speakers - no tweeter. If you found the Crate Limo harsh, you could just disconnect the tweeter, this wouldn't alter the speaker load impedance significantly, and the 10" speaker alone would probably give a big enough frequency range and be a lot mellower for a classical guitar, though the volume will be a bit less than before. You just need a friend who has a Limo and will let you give this a try. It is easily reversed and absolutely safe as long as the amp isn't plugged into the mains when you do it !

Looking at the Crate's specs, it seems pretty generic (an "instrument" input with a woofer/tweeter setup).

So, it may well not serve your classical well without further assistance. A dedicated acoustic processor would be worth a try, something like the Zoom A2, Boss AD3/5 etc should lift your tone back. Extra cash, but well worth the investment.

The other option would be a battery powered PA system (Maplins and other PA based retailers offer examples) but again, you may well find that your classical needs extra help from an outboard unit.

I saw a guy busking in Cambridge last weekend with a Zoom G2, Boss RC2 and what appared to be a Crate Taxi (it was hard to get a good look) and I have to say, the tone was very very good for the setup. Very nice Gretsch he had too (and quite an amazing quiff!!).

Hewesy

Strange to relate I have been without mains power since 7.40am today till about an hour ago.
This prompted me to buy a Maplin 600W inverter. With a not bang up 12V car batt' it ran my laptop/BT modem/router fine for about ten minutes, then I shut it down. It also ran a Sony 32" Bravia for about the same time. Wifes' 600w hair dryer made it squeal (low batt).

I shall charge the battery fully then see what the noise performance and life is with my son's 100W Laney line backer.

Dave.

Just to hijack slightly, the invertors I have bought state they cannot run anything that generates heat (e.g. an electric heater, hair dryer etc). Its "only" 150w though so perhaps thats why?

Hewesy