New to Chip Amps

[skidave]

Hi Group,

I have never tried to build any Chip Amp projects. Can you give me some advice on what a decent kit would be for a project. I'm used to tubes and transistors...

Also, what is the average power output of Chip Amp?

Thanks,

Dave

[sharpi31]

Try Peter Daniel's basic kit (or Premium version if you have the funds). I've used both and they are excellent.

The power output will depend on transformer VA rating, rail voltage, PSU capacitance etc. I'd guestimate 20-50WPC RMS depending on spec.

Good luck - the kits are very easy, as long as you can solder.

[AndrewT]

Hi Ski,
I recommend keeping speaker at 8ohms.
Chipamps need a lot of care and attention to detail to get good performance into lower impedance speakers.
Try to avoid 6ohm and 4 to 8ohm speakers as well as 4ohm.
An LM3886 can manage 60W into 8ohms using a 100VA 25-0, 25-0Vac transformer. For stereo buy 160VA.

Most importantly download the manufacturer's datasheet for the chip you intend buying and read it thoroughly (it might be 20 pages). Any bits you don't understand then ASK, don't guess or skim. KNOW before you build.

[mavallarino]

Hello all,

I am also starting the chipamp project. I have very limited electronics experience so this I think (hope) will be a good start.

I have ordered mine from www.chipamp.com. They seem to have a nice basic kit.

I find that doing things correctly the first time costs a little... I have already paid about €200 (USD $260) and I'm still without a chassis.

I would like to follow this thread since it is a good idea for the beginner.

Saluti,
MV

The scientific method is unduly constrictive, and the major discoveries have not been made as a result of following it.

- Feyerabend

[es44]

Originally posted by AndrewT
Hi Ski,
Try to avoid 6ohm and 4 to 8ohm speakers as well as 4ohm.

I think people might get a little confused about this sentence.
At least i am

Best regards
Ebbe

[drummer_Dave]

AndrewT means Just use 8 ohm and greater speakers ( 8 ohm, 16 ohm etc...) chip amps will run at 4 ohms but you need to have a better understanding of how it works (must run 2 amps in a parallel configuration) when ever AndrewT gives advice take it, it always seems to be good Read the data sheet on these things, there is a lot of technical stuff but there are some got things to notice. Check out the graphs, power supply voltage vs. power out. read the info it will help

data sheet

http://cache.national.com/ds/LM/LM3886.pdf

also check out nationals applications notes an-1192, good stuff in there

http://www.national.com/an/AN/AN-1192.pdf

hope you have fun with it

Dave

[jerishi]

I always remember using (an already dead) chassis/unit to pull parts from to build!- especially with chip amps. A bit of recycling doesn't hurt.... and I hate throwing things away... unless it's impractical....to keep it around.

[AndrewT]

Originally posted by es44
Try to avoid 6ohm and 4 to 8ohm speakers as well as 4ohm.


I think people might get a little confused about this sentence.

means all of the following:-
don't use 4ohm speakers
don't use 6ohm speakers
don't use 4 to 8ohm speakers

if at all possible.

If you feel you must use lower impedance speakers then I suggest you aim for much less than 60W into your nominal impedance. You should not be asking the chipamp to hit it's output current limit on any valid audio input signal.

[jackinnj]

Use this interactive design tool from National -- you can use 4 ohm speakers without problem if the rail voltage is sufficiently low -- the LM3886T can be used +/- 28VDC with a 4 ohm load for 72W out and PDMax of about 40W. You will need a heat sink with a thermal resistance of 2C/W.

For calculating the thermal resistance of the heatsink you can use the Aavid/Thermalloy thermal resistance tool:
http://www.aavidthermalloy.com/technical/thermal.shtml

use 32 lfm as flow rate for still air.

National Excel Spreadsheet:
http://www.national.com/appinfo/audi...gn_Guide15.xls

[AndrewT]

Hi,
National's guide is an excellent design tool.

However, do take account of peak currents into reactive loads.
The maximum output current quoted in the datasheet of 7 to 11.5A is a peak value that the protection will allow to pass when Tc is <=25degC.
The actual limiting current that the protection is likely to allow to pass when the chip is at elevated temperature is probably going to be much less.

If you assume 24Vpk into a load from +-28Vdc supplies then the peak curent into 4r0 is 7A. Guaranteed by National to pass the protection when the chip is cold.

But, decide whether the peak current into a 4ohm speaker is a little more or a lot more than the current into a 4r0 resistive load.
Then try to unravel National's data to determine the limiting currents (guaranteed and typical) when the chip is warm or hot.

What I am saying is that the design guide is looking only at continuous sinusoidal outputs and ignores completely the transient nature of music signals into reactive loads.

My advice is to de-rate the maximum power from a chipamp whenever the speaker load is significantly below 8ohms.