Sure-Electronics.com class d amps

[col]

Have just ordered one off ebay. Has anyone tried powering it on two X 12v car batteries wired in series? I think I read earlier that there is a risk that the voltage could go over the 26v max. I guess I could check that with a multimeter first? I want to use it on camping trips

[TheMG]

Fully charged 12V lead-acid (car) batteries actually measure around 13.5V, so you'd be getting 27V with fully charged batteries, which is over the limit.

[col]

Just ordered the 24V DC14.6A 350W Regulated Switching Power Supply from the Sure-Electronics site. I will run that with an inverter from my 12v battery stack. Will still be more efficient than using car amps, they suck juice bigtime.

[MikeHunt79]

Originally posted by col
Have just ordered one off ebay. Has anyone tried powering it on two X 12v car batteries wired in series? I think I read earlier that there is a risk that the voltage could go over the 26v max. I guess I could check that with a multimeter first? I want to use it on camping trips

Originally posted by TheMG
Fully charged 12V lead-acid (car) batteries actually measure around 13.5V, so you'd be getting 27V with fully charged batteries, which is over the limit.

This is not a huge problem, simple add a diode or two to drop the voltage. This is what I would do if i wanted to power this from SLA's.

Does anyone know if this amp has overvoltage protection?

Also, the zobel resistors... They're the ones near the speaker terminals aren't they? I'm just about to replace them with some 7w resistors. They are a bit bigger than I expected!

[TheMG]

Yeah, I thought of using diodes to drop the voltage some time after posting. That would definitely work, just got to put enough in series to drop the voltage.

I have no idea if they have over-voltage protection, it's not stated in the datasheet, and I'm definitely not going to test it.

Are you sure you need 7W for the zobels? Seems a little overkill I think. Some 1W or 2W would probably have been fine. I haven't had any problems with the zobels on mine, although I can't say I'm driving it hard, the surround on my very old speaker's woofers started to rip apart so I had to turn it down, damned foam surrounds that dry out and become brittle as hell.

[col]

It will be more flexible with the 24v PSU and I have a 600w inverter so will follow that path.

I have a pair of JBL SB-2 Control subs with dual voice coils rated at 120WRMS 8ohms each voice coil. They have a pass through that you can connect satellites to which works really well. I am going to try running one of them with both voice coils in parallel which should be 240w 4ohm on 2 of the amp channels paralleled and will see how it copes. If it doesn't completely overheat I will try the other SB-2 on the other 2 channels, that should max it out

Also, I have a pair of JBL GTO937 6x9" car speakers which are 2ohm 94db 100WRMS. I will try them too as the 2ohm load might extract some more power.

OK, will now wait for it to arrive.

[MikeHunt79]

The inverter will work fine, just remember you will probably get les runtime compared to the diode route... Also, I've found this amp to work really well with 2 and 1 ohm loads - just make sure you parallel everything that should be paralleled.

Originally posted by TheMG
Yeah, I thought of using diodes to drop the voltage some time after posting. That would definitely work, just got to put enough in series to drop the voltage.

I have no idea if they have over-voltage protection, it's not stated in the datasheet, and I'm definitely not going to test it.

Are you sure you need 7W for the zobels? Seems a little overkill I think. Some 1W or 2W would probably have been fine. I haven't had any problems with the zobels on mine, although I can't say I'm driving it hard, the surround on my very old speaker's woofers started to rip apart so I had to turn it down, damned foam surrounds that dry out and become brittle as hell.

I think someone in this thread said he had this amp running at 27v or so... I think it may have shut itself down on overload, but don't quote me on that. It's an amazing amp for the money, that's for sure...

The 7W resistors were the only ones I had that were more than 1/4W, so I managed to (messily) squeeze them in...

I've also leaned over two of the inductors, as I need to squeeze this in a car amp chassis... This shouldn't negatively affect things tho should it? I also need to move the 4 large caps to somewhere else, so I'll have to have them on extended cables from the PCB.... Again, will this cause any problems?

[TheMG]

Generally speaking you want to leave leads on capacitors as short as possible. Long leads add inductance and resistance.

You could probably solder the caps to the other side of the board. Even get some new caps (longer leads) so you can tilt them 90 degrees, flat against the board.

I'm assuming what you're trying to do is get enough clearance to mount the IC directly onto the chassis as a heatsink?

[col]

Yeah, I thought of using diodes to drop the voltage some time after posting. That would definitely work, just got to put enough in series to drop the voltage.

Any idea what diodes I would need? Good to have this option for longer run time on batteries.

[error401]

Originally posted by col


Any idea what diodes I would need? Good to have this option for longer run time on batteries.

Any standard diode that can handle the current/power dissipation will be fine. There ain't no free lunch though, and these diodes will burn a fairly significant amount of power, so take that into account. They need to be thermally up to the job. Schottky types will have too low Vf to be useful (though they can help spread the power dissipation if you're dealing with lots of current).

Let's be conservative and estimate 66% efficiency for the class-D module, and say we're driving 100W/ch at most. 200W x 1.5 = 300W load, and that we want to run on 24V supplies.

300/24 = I = 12.5A current draw

Diodes in this current range have Vf about 0.9V. If we estimate max battery voltage at 28V and aim for 25V into the amp, we need 4 diodes. Each diode has power dissipation of 12.5*0.9 = 11W (!). This is too much for most packages without a heat sink. TO-220 or stud diodes with heat sinks capable of it would probably be sufficient, or bolted to the car's chassis (with insulators of course!). Get at least 15A rated diodes.