I am looking for amp otions for a few small little boomboxes I want to put together and I have run across some of these just raw board type amps. I keep seing prople refer to running them in BTL mode. WHat is btl mode and can you suggest other good amp options for it the 30 to 80wpc range and maybe some that will run off 12v or AC or both? Thanks
BTL = Bridge Tied Load. It means the the amplifier has two outputs per speaker - one inverting and one non-inverting, the speaker being connected between them. This gives double the voltage swing across the speaker and therefore 4 times the power for a given power supply voltage - assuming the amplifier can supply enough current. These are common in car audio where the amplifier runs from 12V, but higher power is required than can be got "single ended" i.e. +/-6V peak.
HTH,
Brian
HTH,
Brian
There's a lot of chips made for car stereos that accomplish this with a minimum of parts and complexity. They represent a huge bang for the buck for an application like this. 40 watts a channel (at a higher than hi-fi distortion rating) is a typical claimed specification. 25-30 watts a channel "medium-fi" is easily achievable.
Sometimes the external parts consist only of a power supply decoupling circuit, a few capacitors, and maybe a couple of resistors. You need a big heatsink though.
Sometimes the external parts consist only of a power supply decoupling circuit, a few capacitors, and maybe a couple of resistors. You need a big heatsink though.
With say a 12v battery supply and a BTL IC, you will get only around 12 watts of unclipped power into 4 ohm loads and 7 or 8w into 8 ohm loads. With an IC that can handle 2 ohm loads and a 15v supply, you might crack into the 30 watt low end of your desired power range.
There is an IC with charge pump caps that is rated for high output but it is not clear to me if it can do this continuously or just for high transients in music. Of course, with 12v, you can use a switchmode PSU to boost the voltage for a higher power IC, such as the LM3886 which is well in your desired power range.
My philosophy is to use higher efficiency speakers when power supply is limited. A speaker with a sensitivity of 94db will require only 10 watts to play at the same level of a speaker rated 88db driven at 40w.
There is an IC with charge pump caps that is rated for high output but it is not clear to me if it can do this continuously or just for high transients in music. Of course, with 12v, you can use a switchmode PSU to boost the voltage for a higher power IC, such as the LM3886 which is well in your desired power range.
My philosophy is to use higher efficiency speakers when power supply is limited. A speaker with a sensitivity of 94db will require only 10 watts to play at the same level of a speaker rated 88db driven at 40w.
A single channel amplifier working on 12Vdc can only give out <=4Vrms into a highish load. That equates to ~2W into 8r0.
Increase the voltage to that found in automobiles, or ~13.8V, gives ~2.6W into 8r0.
Use two channels in bridge arrangement and you get ~5.2W into 16r.
If you decrease the load resistance/impedance you will find that the voltage available to the load will also drop.
You will not get 5.2W into 4r0 from an amp that gives 2.6V into 8r0. The worse the amplifier design and implementation the more the load impedance current delivery deteriorates.
At best expect ~3times the single channel when bridged into the same load resistance/impedance.
i.e. that 2.6W into 8r0 amplifier becomes ~7.8W into 8r0 from two bridged channels using 13.8Vdc. How much you can hope for into 4ohms depends so very much on the implementation that you could get anywhere from 8W to 15W into 4r0 when on 13.8Vdc. Expect much worse running on a 12V battery that droops to 11.5V when under load.
The arithmetic is simple.
The science is simple.
Don't let unscrupulous retailers con you into believing impossible science.
Increase the voltage to that found in automobiles, or ~13.8V, gives ~2.6W into 8r0.
Use two channels in bridge arrangement and you get ~5.2W into 16r.
If you decrease the load resistance/impedance you will find that the voltage available to the load will also drop.
You will not get 5.2W into 4r0 from an amp that gives 2.6V into 8r0. The worse the amplifier design and implementation the more the load impedance current delivery deteriorates.
At best expect ~3times the single channel when bridged into the same load resistance/impedance.
i.e. that 2.6W into 8r0 amplifier becomes ~7.8W into 8r0 from two bridged channels using 13.8Vdc. How much you can hope for into 4ohms depends so very much on the implementation that you could get anywhere from 8W to 15W into 4r0 when on 13.8Vdc. Expect much worse running on a 12V battery that droops to 11.5V when under load.
The arithmetic is simple.
The science is simple.
Don't let unscrupulous retailers con you into believing impossible science.
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