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



Has any of you ACTUALLY worked with and recommend a SSR which does not introduce any audible distortion on the speaker line and which can operate with a large range of trigger voltages (12 - 48 VDC, may need to have on board voltage regulator for this range).  I am building a speaker DC protector and do not want to use electro mechanical relays becoz of DC arcing and contact erosion issues.  It needs to be capable of switching up to 15 amps at about 100 volts.

Only TRUE engineers reply please.

Thanks

cakyol
SSR is unfamiliar to me, but from your post, did you mean 'SCR'? The latter were used in crowbar circuits for speaker protection...
This is a good question. I have an amplifier with a mechanical relay on the output. Replacing it with a solid-state relay might be a good move.
@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...



Aerospace engineers oft outperform EEs, for example directionality and fuses.
OOPS(never heard them referred to, with that acronym)!
Again, I mean SSR (Solid state relay, audio power quality) *NOT* SCR.

Has anyone used one of these before:
https://holtonprecisionaudio.com/collections/diy-audio-products/products/audio-solid-state-relay-hpa...
Not used it but I see no reason why it shouldn't work just fine.
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.


Please let us know what you find out. 
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






I did that with 25 amps ssr and it works great. No sound changes at all 
@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
Hi Cakyol

Darn, a legitimate question on this forum.  Ok, I'm a real EE.  I'm not aware of a high failure rate in amplifiers, but perhaps just that...unaware.  Are you concerned with a specific aspect of your system that you want to protect your speakers with something faster than a fast acting fuse?  I admit to not having used an SSR in your application, but like you, would be curious about any acoustic artifacts associated with putting even a low impedance semiconductor in series with the speaker wiring.  On the other hand, as infrequently as a mechanical relay would be switched hot, i.e., under heavy load, I wouldn't have any concerns about contact erosion or wear for one with contacts that are properly sized.  Also, I'm curious what you were going to use as a derived control signal for the relay of your choice.

Keep us posted on your progress and results!

Hi Cakyol

It might save some time and effort by going to (as suggested above) some engineering or diy audio sites to ask this question. Reason I say this is because finding someone here who is experienced at swapping out different solid state relays is more than likely to be over the engineering pay grade here.

Not saying there aren't some smart people here, just saying maybe not as specialized as what your hunting for.

good luck

Michael Green

Just on the surface analysis, an SSR would sound like crap, overall, in any audio application.

This is so obvious to me, that I’ve never made it past the idea of looking at the acronym of SSR, and then moved along and away from such an idea.

Ie, that the thought was discarded as thoroughly as possible, before it even began.

Like the idea of taking the tuna sandwich I might be holding and smearing it on my face, as a way of ingesting it. Silly beyond belief, not to be considered a thought whatsoever.

And that’s what I think of the idea of SSR’s in audio gear. That the thought was discarded long ago, by just about anyone in the world of audio that you can imagine.

A gentle but quick mental/internal ’no, that’s not going to work’, and then they moved on. Relay or circuit breakers is better, as the quality in sound, is better. Better than any SSR.

And all those audio designers and engineers you might want to get an opinion from, they invariably understand audio quality and that definitely includes the power cords, the fuses, and the cables -- all as being important. This is about audio quality, not some numbers squeezed out on the face of a meter and analyzed via spec sheet.

1000 kilos of raw dung will, displacement wise... fit inside my car, and the volumetric spec is there for it, but I’m not about to test that or do it.

My response is mildly over the top but honest in my analysis of SSR’s and my opinion on them in quality audio... I’m just reflecting the seeming mood of the OP itself....
I’ve never put a relay int he signal path. But Omron made nice, reliable relays electro-mechanical relays that I used in many commercial products for soft turn-in. triggered by DC - just what you need. The relay chatter issue typically comes when one uses AC to control AC with predictable, feedback-induced results. Ask me how I know.
I cant comment on SSRs.  I do believe that solid state switches are  superior to mechanical ones in low level signal paths, but they vary all over the lot.  Most power SSRs are intended for just that - power.

But where is the DC coming from? If unreliable equipment or prototypes/etc do what IO do and insert a fuse box during those periods.
Even NASA uses fuses, just like most everyone in high end audio does. Fuses have come a long way, baby. NASA started studying advanced fuse concepts twenty years ago which, ironically perhaps, is about the same time advanced audiophile fuses were introduced. Coincidence? Now, NASA might not give a hoot about sound quality but audiophiles certainly do.

- Ex NASA Range Rat
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

cakyol
- 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.

>>>>Nice that you know all about them but apparently what you don’t know is that advanced audiophile fuses can oft exceed $149 and sometimes even exceed $200. Maybe NASA needs to step up their game. Audiophiles have two or maybe three conflicting requirements, cost, sound quality and protection.

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....


The MOSFETs will be hard ON all the time- you don't have to worry about bandwidth, as the resulting circuit will be good from DC to well past 100KHz. They have some capacitance associated, but that will be negligible unless your amp is really high output impedance!
As long as the MOSFETS stay hard on between 20 - 20khz it will be fine :-)
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.

Even NASA uses fuses
That's how they got Apollo 8 to circle and come back, they just reversed the fuse as they went behind the dark side of the moon, the rest is history.
But there is no dark side of the moon; as a matter of fact it's all dark.
As long as the MOSFETS stay hard on between 20 - 20khz it will be fine :-)
Yup- if they are On, then the frequency is almost irrelevant.
I have +/- 90 Volt rails.
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.
I think you need higher voltage rating than 100V

http://www.geofex.com/Article_Folders/ampprot/dcprot.htm
failure with no fuse could burn your speakers and the amp pcb ...you flip the coin if it really makes a difference in what your ears tell you.
Most speakers have a capacitor in circuit before the tweeter which blocks all DC.   The tweeter won't be harmed in this case.

I used a Phase Linear 700 without output relay for years, (original design had no relay) and it had multiple issues and would go full DC (105V) on  occasion.   Fuses protected the speakers each time this happened.  

Mechanical relays work as well to protect speakers.   Two solutions out there already, that are time tested, and my empirical experience confirms it quite well.   
What is a fuse believer?
It’s an expression used by someone who still thinks there’s room for argument regarding aftermarket fuses and fuse directionality. A renegade. A refusenik.

It’s an expression used by someone who still thinks there’s room for argument regarding aftermarket fuses and fuse directionality. A renegade. A refusenik.


Ok, then that sounds a lot like me then.  Not a fancy fuser here.   Although wire directionality as in IC directionality is a thing, with a purpose. 

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. 


@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. 
Hi Gibbs
I was referring to the main drivers that will burn, I am well aware of the audio bypass cap on tweeters...which wont pass dc.ANDthere are speakers out there with a resistor to limit the tops, so they could be smoked.Many retro speaker systems used a resistor on the tops.
@cakyol

Please look at the link I posted. It should answer your questions regarding the use of solid state relays in audio amps. 

 
3:18am
Hi Gibbs
I was referring to the main drivers that will burn, I am well aware of the audio bypass cap on tweeters...which wont pass dc.ANDthere are speakers out there with a resistor to limit the tops, so they could be smoked.Many retro speaker systems used a resistor on the tops.

A simple in line fuse will protect your main drivers that have no blocking capacitor.    I have much experience with this as well.
I would recommend getting any older full sized soundcraftsman amp And take it apart.   if your goal is to kill the dc at the rails before it reaches the speakers they did this back in the 80s