LM3886 speaker protection from Ebay?

gideon1990

Member
2009-09-15 4:08 pm
I ordered all the parts to build my LM3886 amplifier but as I am waiting for the parts I stumbled onto the various DC speaker protection boards that one can find on ebay.

examples are
AC 12 16V Audio Amplifier Speaker Protection Board DIY Components Kit for Stereo | eBay
15A Current relay Speaker protection board Kit for DIY
UPC1237 Dual Channel Speaker Protection Circuit Board DC 12V 24V Boot Mute Delay | eBay
Dual 2 Channel UPC1237 Speaker Protection Board DIY Kit Boot Delay DC Protection | eBay
UPC1237 Speaker Protection Board Compatible with The BTL Protection | eBay

Did anyone try these protection circuits? And is it recommended to use them or do these cheap kits pose a greater risk than a (real) LM3886 on its own?

honorable mention which even includes an RL circuit:
1pair Mono UPC1237 Speaker Protection Board DIY Kits Mirror Symmetry Circuit | eBay
 
Hi, those links do not work.

The only speaker protection you need is protection against DC on the output. This can happen if you fuse both DC rails and one fuse blows due to over current or a faulty chip or an assembling error. First, don't fuse it that way but use a proper fuse at the primary side of the power transformer. I did use loads of LM3886's for over 20 years now but never encountered a faulty or broken chip.

IMHO a separate DC protection is only good for your peace of mind.
 

tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
The LM3886 itself contains protection for over-current and over-temperature, but that's it.

You can't really protect agains clipping. You can implement a clipping indicator by monitoring the differential voltage across the amp inputs. Once that voltage starts to exceed a few 10s of mV, turn on an LED.

DC on the output can be monitored by a pair of BJTs. You can integrate this with a delayed turn-on if you want to get really fancy. Randy Slone has a pretty neat circuit in his High-Power Audio Amplifier Construction Manual.

The LM3886 is pretty rugged and reliable, though. I personally don't worry about protection circuits with my LM3886 amps. Should I ever design a protection circuit, I'd probably integrate it into the amplifier and take the feedback on the "outside" of the relay contacts to minimize the distortion caused by the relay.

Tom
 
The LM3886 itself contains protection for over-current and over-temperature, but that's it.

You can't really protect agains clipping. You can implement a clipping indicator by monitoring the differential voltage across the amp inputs. Once that voltage starts to exceed a few 10s of mV, turn on an LED.
The circuit that Tom describes above can be used to drive an LED+LDR (e.g. Vactrol) based voltage divider on the input signal. Use a long time constant (several seconds) for the release. When clipping happens, the circuit automatically turns down the volume.