LM3886 speaker protection from Ebay?

[gideon1990]

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

 

[Pjotr]

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.

 

[gideon1990]

I wasn't planning on fusing the rails for that exact reason, merely a 1 or maybe 1.5 A slow blow fuse on the primary side. but judging from what you say it sounds like the LM3886 is safe enough to run without dc protection

For me the links work by the way?

 

[AndrewT]

The 3886 sends out DC when in fault condition, or it loses one supply rail.

 

[Hogwild]

Gideon1990:

I just finished assembling four of these a couple of weeks ago.

Soft starting switch full kit for power amplifier !
from eBay seller "jims_audio"
Soft Starting Switch Full KIT FOR Power Amplifier | eBay

I haven't tested them yet, but I'll probably be doing so in the next couple of weeks. If you like, I can share whatever findings I have.

 

[nigelwright7557]

I have started adding DC protection to all my amplifiers.
It doesn't take too many components to do it.
I use an 8 pin PIC to monitor audio out and control a speaker relay.
The software is minimal.

DC protection wont save speakers from simple over driving but they will help if an output transistor fails.

 

[gideon1990]

@hogwild

Sure let me and everybody know about your findings. For a lot of amp kits there seems to be a lot of info on which kits are alright and which sucks so more info is welcome.


@nigelwright7557

Is the information about your solution available somewhere?

 

[nigelwright7557]

@hogwild


@nigelwright7557

Is the information about your solution available somewhere?

Its a home build I used. It involves programming a PIC.

I believe there is an IC that can do the job but I cant remember its number.

 

[gideon1990]

Its a home build I used. It involves programming a PIC.

I believe there is an IC that can do the job but I cant remember its number.

UCP1237

Its what most of those Ebay kits are based off

 

[AndrewT]

There are many mentions of that UCP1237 on this Forum.
Search for some implementations. You should find at least one you like.

 

[gideon1990]

There are many mentions of that UCP1237 on this Forum.
Search for some implementations. You should find at least one you like.

I was just hoping to use a kit off ebay so I was wondering whether anyone had experience with a specific one

 

[Luke]

DC protection wont save speakers from simple over driving but they will help if an output transistor fails.

Whats a good way to prevent over driving? Is it best to use clipping indicator?

 

[AndrewT]

Listen to your distortion.
That means no drunks at your 40th brithday party in charge of setting the volume.
The amplifier and the speaker both complain when the signals are being clipped.
Listen to what they are telling you.

 

[Luke]

That's good advice. I'm looking for a solution to a problem I don't have
I had a flatmate many years ago who blew mid-range drivers twice and couldn't hear something was wrong.

 

[tomchr]

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

 

[CharlieLaub]

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.

 

[tomchr]

That's a pretty neat idea, though, I do wonder about the THD of the LDRs. I'll eventually get around to measuring one of those LDR-based volume controls so I guess I'll find out.

Tom