LM3875 Voltage

[Leglandu]

am just concerned that any over voltage could mean that if the chip reacts, blows up etc, that it will take my speakers with it ?!
This is my main concern. No one has commented ?

I would say, every electronic part is destroyable, either by over-intensity or by overvoltage with different effects.

In the case of the LM3875, due to the internal complexity... perhaps the manufacturer has made some destructive tests and knows what happens, but not the DIY guys…

So, your LM3875 may burn or explode… or not. And can destroy your driver… or not, nobody knows, that's is just a bet !

And I agree you might just have to live dangerously, like Achilles with its heel 🙂

 

[Puffin]

Leglandu. I was coming to the realisation that perhaps I was asking a question that no-one could answer.

I have run the amps for many hours, but I suppose that is no guarantee that they might not self-destruct in time

 

[Leglandu]

Exactly, perfect summary of the situation !

 

[peranders]

I have run the amps for many hours, but I suppose that is no guarantee that they might not self-destruct in time

"Many" hours is not enough to determine if it's going to last. What happens if you have a short surge on your mains? The margin for this is almost zero. High voltage can come after 6 months, or one year or never, who knows?

 

[Puffin]

Peranders. In the words of "smashey and Nicey" "wise words mate"

 

[danielwritesbac]

Fuses?

 

[Puffin]

Yes, I have a mains-in fuse and fuses on the ac to bridge rec and from dc feed to chip.

 

[troystg]

Yes, I have a mains-in fuse and fuses on the ac to bridge rec and from dc feed to chip.

5 fuses, somebody was bored... 😀

 

[peranders]

Peranders. In the words of "smashey and Nicey" "wise words mate"

Sorry, to internal for me...

 

[danielwritesbac]

Actually, I was wondering if there were 1 fast-blo fuse per each speaker output. 4 amp fast-blo seems fine.

I do like the AC mains fuse.

The other areas seem to promote the possibility of disconnecting one rail while leaving the other connected, for a possible 5 metre xmax experience.

 

[Puffin]

Peranders. British Comedy series included a parody of radio DJ's

One of the "catch phrases" was "wise words mate"

http://www.youtube.com/watch?v=7mzPeHNT7zs

Daniel. I had considered fuses on the speaker outs, but thought this may affect the sound ?

 

[peranders]

This TV show has never been sent in Sweden It would have been better if you had taken Faulty Towers

 

[Puffin]

I was wondering whether these would be of any use ?

http://www.maplin.co.uk/Search.aspx?menuno=12435&FromMenu=y&doy=18m3&MenuName=Circuit Breakers

 

[ashok]

Why don't you use a speaker protection circuit using a relay ? It's simple and works well. You will find lots of circuit implementations on this forum.
That way no dc at the chip output can damage your speaker.

 

[Puffin]

I changed the trannys to 25v secondary's to see what difference this would make. The heatsinks are by no means large, but I could barely feel any warmth from them at all. This was after 3 hours running.

I think I will live dangerously and keep 30v trannys going.

 

[peranders]

What was the advantage with 30 V transformer?

 

[Puffin]

I think the 30v tranny gives it an "edge". Maybe living life on the edge is what I like ?!

I seem to remember that over the years there have been many manufacturers of various items that have preformed spectaluarly, cars etc but have ultimately been unreliable, Hi Fi amps included.

I do not think that running the amp with 45v per rail is neccessarily "dangerous" as someone else posted, NS must have built in some leeway with the specs to account for fluctuations in voltage.

 

[peranders]

What is edge really? Edge to the expense of blowing your speaker and getting 1-2 dB higher output IF you can manage the cooling issue and a hotter chip.

If I had a choice to use a more safe supply voltage I should choose so. Why? I'm an electronic designer as profession and I see reliability as a very important thing and I would never choose to do something that could jeopardize this.

 

[Puffin]

Peranders. I take your point and it is a very valid point.

I am currently using 25v secondary's, so about 37v dc. I will see how I like it !

Thanks for your input in this matter.

 

[BWRX]

I do not think that running the amp with 45v per rail is neccessarily "dangerous" as someone else posted, NS must have built in some leeway with the specs to account for fluctuations in voltage.

NS does not "build leeway" into the specifications of the device! You must account for voltage, temperature, etc. variation in your design. That is not their responsibility...