Sansui AU-999 Speaker Protection

[stonehome]

I have a Sansui AU-999 that I like but am unsure of the speaker protection circuit. I have read restoration posts elsewhere that suggest completely removing the board and relying on the fuses only. Since my speakers cost many times more than the amp I think I want more than fuses.
Does the existing speaker protection seem adequate? Safe for speakers and amp? or would it be better to install an available board with relays and separate power supply.

Evan

 

[rayma]

Since my speakers cost many times more than the amp I think I want more than fuses.
Does the existing speaker protection seem adequate?

It appears that this circuit shorts the amplifier output, blowing the supply fuse (crowbar circuit).
You could use a smaller size fuse, or a fast blow type. Size the fuse so it blows occasionally.
Which speakers?

 

[stonehome]

Thanks, The speakers are a DIY 2-way with Accuton 30-6-358 tweeter and 173-6-191E mid.

I listen at moderate volume and this amp isn't used 100% of the time so maybe this circuit will be ok with proper fuses.

 

[adason]

There is plenty speaker protection kits on ebay, they work.
External, no need to touch the amp.

 

[adason]

Speaker Protection Kit for under $5

 

[stonehome]

Thank you, The old speaker protection is coming out.

 

[dotneck335]

It appears that this circuit shorts the amplifier output, blowing the supply fuse (crowbar circuit).

Shorting the amplifier output to ground seems a VERY poor way to protect the speaker!

 

[rayma]

Shorting the amplifier output to ground seems a VERY poor way to protect the speaker!

It can be very effective if the circuit is designed well, and works properly.
But, those electrolytic capacitors in the trigger circuit are not going to last forever.

 

[dotneck335]

It can be very effective if the circuit is designed well, and works properly. But, those electrolytic capacitors in the trigger circuit are not going to last forever.

Yeah, great!! Blow up the amplifier to save the speakers!! SURELY there's a better way......

 

[rayma]

Yeah, great!! Blow up the amplifier to save the speakers!! SURELY there's a better way......

They intend for the rail fuse to blow instead of the output transistors.
Instead, current limiting circuits can be added to the output stage.
File:Cc limit.png - OpenCircuits

 

[tiefbassuebertr]

I am looking for a service manual (technical manual) for this integrated amp. I only find the schematic diagram.