This question is aimed to TRUE Elec Engineers, not fuse or wire directionality believers.

@atmasphere , yes I meant SSR = solid state relay, not SCR.
Thanks

Has anyone used one of these before:
https://holtonprecisionaudio.com/collections/diy-audio-products/products/audio-solid-state-relay-hpa...

Again, I mean SSR (Solid state relay, audio power quality) *NOT* SCR.

If these work as flawlessly as claimed, they could be employed also on the supply rails too.  Cut the speaker AND the supply rails within milliseconds upon a fault detection.  According to specs, they are rated at 10s of amps (but no voltage is specified).  I need to email & ask.

Thanx but one has to be very careful with other SSRs.  Most of them are made for motor control and are not suitable for audio freq range (20 - 20k) and some of them cannot stop DC and are only made for AC.  There are so many out there but only a VERY FEW are suitable for audio.

That is why I wanted to know if anyone had specifically used one and hence happy with the results.

Thanks

@ssg308, can u pls tell me the EXACT model/make of the device u used ?  Also, the KEY is, would it work/disengage in case of a DC fault ?
Thanks

@ssg308, since some SSRs internally use back to back SCRs or triacs, they may NOT turn off when the trigger is removed and DC is flowing, which would destroy the speaker in a second under fault conditions.

Thanks

Let me try & respond to some of the comments made recently.

- First, a fuse will NOT protect a speaker from a DC fault.
  If and when a fault occurs, the speaker wire, especially the tweeter wire
  will melt and catch fire WELL BEFORE a fuse has time to act.
  Therefore your speaker will be destroyed, saving the fuse.  The ONLY 
  sure way to ensure that the fuse will blow before the speaker is to use
  a crowbar circuit.  I dont like the idea of that.

- Secondly, normal relays, regardless of whether they can carry
  HUNDREDS of AC amps will NOT be able to break a DC circuit,
  In a fault condition, The DC will arc and continue destroying
  the speaker and the relay.  At most, if one is lucky, the relay may save
  the speaker but it itself will most definitely be destroyed.  Look at
  relay specs CAREFULLY and note that MOST are rated at no more
  than 30 Volts DC.  I have +/- 90 Volt rails.

- The amp I am building is high power BIPOLAR transistor based
  so in case of a fault, it is more likely to fail as a short than an open
  circuit and hence more likely to destroy speakers as compared
  to a MOSFET output stage one.  Hence the need for a reliable
  speaker protector.
  
- Most commercial amps use a relay in the output MOSTLY to avoid
  thumps when first powered on.  Altho they MAY protect the 
  speakers in DC fault cases, their intention is the former not the
  latter.

- Thirdly, SSRs made with back to back MOSFETS driven down
   to a few milliohms will make a PERFECT wire, nobody (except
   the superhumans on some of these threads on this site) will hear
   the existence.

- As for the NASA fuses/relays, I know about them, they are
  encapsulated in nitrogen under pressure so that they MAY be
  able to break DC but they cost in excess of $200 or so for a
  15 amp relay.

- The control circuit I intend to use is one by Rod Elliott and here it
  is:   http://sound.whsites.net/project33.htm 

Thanks

Unfortunately, these are about $220 -> $320 on average:

https://omronfs.omron.com/en_US/ecb/products/pdf/J144-E1-05.pdf

Hopefully an SSR will replace this.

This is more like it:

https://www.mouser.com/ProductDetail/Infineon-Technologies/IPB017N10N5LFATMA1?qs=sGAEpiMZZMshyDBzk1%...

100V, 180 amps, 1.5mohms (almost lower than the speaker wire itself), about 80 nanosecond turn off time (increase that becoz of inductive speaker load) and only about 8 bucks a piece.

In theory, it looks perfect, the only issue is with switching MOSFETS, they dont unfortunately specify the frequency response....

As long as the MOSFETS stay hard on between 20 - 20khz it will be fine :-)

@gibsonian. Thanx for sharing your experiences with phase linear.  I guess i am trying to err on the side of being excessively cautious and not take the risk of leaving the tweeter protection to its filter capacitor. 

I did not mean to say I wont use a fuse. This is an ADDİTİONAL protection. Fuses will of course be there. 

And yes I will need a mosfet for at least 150 Vdc since 100 v is too close for comfort. 

As for fuse directionality changing the quality of sound I am sorry to say that I have done tests on this and have not observed ANY sound changes whatsoever. My ears are normal human ears not superhuman :).  So as far as PERSONALLY I am concerned fuses and how they are inserted, do NOT AFFECT sound. 

ssg308,

Crydom relays are typically for motor control apps.  They will not have a low enuf switching resistance and linear frequency response for an audio signal.

Ok, I bought a pair of these from down under:

https://holtonprecisionaudio.com/collections/diy-audio-products/products/audio-solid-state-relay-hpa...

I will post on this thread later when I have time to add them to my circuits.

Thanks

For anyone who risk blowing their thousands of dollars costing speakers because they rely on tweeter caps, be my guest and good luck.

I still will be building my protection circuit :-)

@ramtubes, I am aware that MOStTSSRs use thyristors and are not suitable for audio applications.  They are designed for motor controls.  That is why I am getting ones made with back to back Mosfets.  Pls see my post above regarding the audio SSRs specifically made for this purpose that are being sold by Holton electronics in down under.