What is the best way to boost voltage (from 12v)

[T4P]

i have never heard of a 12v-18v car adapter

http://www.ebay.co.uk/itm/DC-DC-10-32V-to-12-35V-Converter-Boost-Charger-Module-150W-/360510166840?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item53f0149738

[Zero999]

Yes, a home made amp, using the TDA2005 chip. The speaker impedance is 4 ohms.
And what do you mean, single ended?

Do you have it configured for stereo (single ended) or as both outputs driving a single channel (bridged)?

[vk3yedotcom]

Another battery is out of the question, since lead batteries are heavy, and my amp is portable, so I want to minimize the weight.

A problem though is with a converter you'll double the current drain (actually mor than double as it's not 100% efficient). 

Is there scope to use 2 x 12 volt batteries in series that are half the size/weight?  That will do as well (if not slightly better) than the existing battery plus an upconverter.

[cepa]

Yes, a home made amp, using the TDA2005 chip. The speaker impedance is 4 ohms.
And what do you mean, single ended?

Do you have it configured for stereo (single ended) or as both outputs driving a single channel (bridged)?

It's a bridged amp

[ivan747]

Yes, a home made amp, using the TDA2005 chip. The speaker impedance is 4 ohms.
And what do you mean, single ended?

I thought those were designed to be in cars with 12V batteries.

[ivan747]

Have you noticed you are trying to power the IC on it's absolute maximum operating voltage? I think it is cheaper and more practical to make a bridge amplifier, one that uses two amplifiers with opposing phases to get twice the power into the speaker without increasing the voltage.

And make sure you heatsink them properly! They are not thermally protected. One blew up on me when I was presenting my cool amplifier!

[T4P]

It was intended for a car wth a peak voltage of 14.4V and 12V nominal and running silicon right on the edge is not exactly ... ah well.
If you try to push the rated wattage you will get 10% distortion anyway.

[cepa]

Have you noticed you are trying to power the IC on it's absolute maximum operating voltage? I think it is cheaper and more practical to make a bridge amplifier, one that uses two amplifiers with opposing phases to get twice the power into the speaker without increasing the voltage.

And make sure you heatsink them properly! They are not thermally protected. One blew up on me when I was presenting my cool amplifier!

Any Ideas how I can make this happen? I'm pretty new at electronics.

[mariush]

see my previous post, and the datasheet i linked to in it, for tda2040.

the pdf has a schematic for making a bridge amp using 2 x tda2040

tda2005 is already a stereo amp, with the option to bridge the two channels and get one mono channel. It's just a weak chip. The datasheet for this chip should also have a schematic for bridging the channels, or you should find one online.

[Harvs]

As it doesn't seem like anyone else has mentioned it yet, if you're amp is now drawing an average of 2 amps at 12V input, if you increase the voltage to say 18V, the current will go up to 3A.  In audio applications you're driving an impeadance that for the most part doesn't change with applied power.  V=I*R, increase V, leave R the same and therefore I has to increase proportionally.

[vk3yedotcom]

i have never heard of a 12v-18v car adapter

http://www.ebay.co.uk/itm/DC-DC-10-32V-to-12-35V-Converter-Boost-Charger-Module-150W-/360510166840?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item53f0149738

(bump!) Ordered one of these units to provide 30 volts to power a 30 watt MOSFET RF power amplifier.  Results were good and the heatsink got hardly warm (though I was using it below ratings). 

When DC was applied but no current was drawn there was a small amount of RF interference which increased when I touched the heatsink.  That was with no shielding or bypassing - both fixable. 

A video is at

[joe 90]

Maybe you're tackling the problem the wrong way.
You don't need more volts input, just more current output.

[vk3yedotcom]

Maybe you're tackling the problem the wrong way.
You don't need more volts input, just more current output.

That has all sort of implications for things like amplifier performance and output impedances etc (need to transform it up to 50 ohms for the low pass filter and antenna). 

MOSFETS prefer more than 12 volts if you want more than a few watts out of them.  Easiest to give them the volts they work best at, and this is much easier/cheaper now than it used to be.

[rx8pilot]

I would go with two smaller batteries in series for an amplifier. Why? Cheap boost converters are noisy and generally have modesr step response which is what an amplifier needs. Two smaller batteries would be the same weight or very close, very simple, and therefore reliable.

Sent from mobile device.... Keeping it short and mis-spelled

[vk3yedotcom]

I would go with two smaller batteries in series for an amplifier. Why? Cheap boost converters are noisy and generally have modesr step response which is what an amplifier needs. Two smaller batteries would be the same weight or very close, very simple, and therefore reliable.

I did seriously consider this but discarded the idea given I already had a suitable battery (8400mAH) and charger.  I had no other batteries (so purchase would have cost much more than the DC-DC converter).

As you mention a two battery solution with no DC-DC converter delivering equivalent watt hours will be weight competitive (ie 2 x 4200 batteries should weigh as much as 1 x 8400 mAH).

However if you have multiple applications where some times you only need one battery, and for that application it needs to be 8400 mAH then you'll end up with 3 batteries which takes up space at home and is a charging hassle (especially assuming the smart chargers are only good for charging one battery at a time). 

Another possible complication with two batteries is in use - power draw from one battery will be much more than the other since one will be powering other parts of the gear other than the power amplifier.  So they may need to be swapped in the field near the end of their charge.

Another benefit of 12 volt powered gear with its included DC-DC converter is easy use in a car (with 12v) and at home (if a high current 13.8v supply is available).

[Audioguru]

The TDA2005 feeding a 4 ohm speaker with a 12V battery over-charged to 14.4V produces 20 Whats with horrible distortion when its channels are bridged into 4 ohms or 16 Watts at clipping. With its maximum supply of 18V its power is trying to be 32 Whats or 25.6 Watts into 4 ohms but the efficiency graph in the datasheet shows it stopping at 22W when it overheats.

[Stray Electron]

Another battery is out of the question, since lead batteries are heavy, and my amp is portable, so I want to minimize the weight.

   I strongly suggest that you reconsider that.  Adding a convertor is not going to add any ENERGY to the system and will in fact cause the loss of some energy.  You could use two batteries, each one half the size of the current one, and not gain any additional weight but your total run time would be, at best, approximately 1/2 as long.   Which brings up a couple  of things;  How long is your current run time and how long does you modified amp need to run?  Also if you double the voltage into your amp, how much does the current increase?   In a purely resistive load it would double and the total power demand would be four times greater than now so even two of your current size batteries might be inadequate. The biggest factor in this is going to be (1) how long your run time needs to be.  Also (2) what is the maximum possible run time currently and (3) how does increasing the voltage affect the current consumption.

   We need to know more about your situation before making an intelligent recommendation.

[Audioguru]

An audio amplifier is not used at full output all the time, unless you play acid rock noise or people screaming. Music and speech have momentary peaks of at least 10 times the average output power so the average current from the battery will be much lower than the peak current and the run time will be much longer than expected.

[davelectronic]

I use two converted xbox 360 power supplys (bricks as there known) in series for cb radio and amp use, there rated at 175 watts each, so i get that total current as if it was one unit at 24 Volts. I drop my use of these back down to 12 Volts over a long cable run, but using the 24 Volts is certainly feasable option. I'm it the uk and pick them up for as little as £5 each off facebook sale groups. You can find a tutorial on the indistructables web site to convert these. They make very hardy power supplys.