DC Fault protection For Speakers (Amplifiers Without Protection)

Instead of taking the risk of burning an expensive pair of speakers due to some amplifiers that doesn't have  DC fault protection built in, here is an small retrofit that can be connected outside the device powered by an simple adapter and continuously watch for DC tension that may appear in the output of the fault amplifier.

The minimal tension for detection is +-2,5V and max voltage 200V pk-pk.
Speakers lines are total isolated from the circuit. Can be connected in any polarity ( just need to respect input output)

Images:



Further info: valente.olimpia@gmail.com

Ave_Rapina escreveu:

Instead of taking the risk of burning an expensive pair of speakers due to some amplifiers that doesn't have  DC fault protection built in, here is an small retrofit that can be connected outside the device powered by an simple adapter and continuously watch for DC tension that may appear in the output of the fault amplifier.

The minimal tension for detection is +-2,5V and max voltage 200V pk-pk.
Speakers lines are total isolated from the circuit. Can be connected in any polarity ( just need to respect input output)

Images:



Further info: valente.olimpia@gmail.com

Suponho que o circuito alterará as características do sinal produzido pelo amplificador (os componentes devem alterar  a curva de resposta !?!?!?)   

Além do mais a resistência oferecida por este gadjet deve ter efeito no damping   (estarei errado?).

Ave_Rapina escreveu:

Instead of taking the risk of burning an expensive pair of speakers due to some amplifiers that doesn't have  DC fault protection built in, here is an small retrofit that can be connected outside the device powered by an simple adapter and continuously watch for DC tension that may appear in the output of the fault amplifier.

The minimal tension for detection is +-2,5V and max voltage 200V pk-pk.
Speakers lines are total isolated from the circuit. Can be connected in any polarity ( just need to respect input output)

Images:



Further info: valente.olimpia@gmail.com

Isso é para vender??? ...

E por quanto?...
  

Suspeito que queimei qualquer coisa numa das minha colunas das minhas experiências O O P S ? ....
  

 

Mário Franco escreveu:

Ave_Rapina escreveu:

Instead of taking the risk of burning an expensive pair of speakers due to some amplifiers that doesn't have  DC fault protection built in, here is an small retrofit that can be connected outside the device powered by an simple adapter and continuously watch for DC tension that may appear in the output of the fault amplifier.

The minimal tension for detection is +-2,5V and max voltage 200V pk-pk.
Speakers lines are total isolated from the circuit. Can be connected in any polarity ( just need to respect input output)

Images:



Further info: valente.olimpia@gmail.com

Suponho que o circuito alterará as características do sinal produzido pelo amplificador (os componentes devem alterar  a curva de resposta !?!?!?)  
 



Além do mais a resistência oferecida por este gadjet deve ter efeito no damping   (estarei errado?).

In terms of the circuit, it behaves like an series R-C Zobel network to ground.
The purpose of the Zobel network is to ensure that the emitter follower output
stage sees at least some resistive loading out in very high frequencies. This is important if the amplifier has no load or if the loudspeaker load becomes highly inductive at high frequencies. In this gadget configuration the impedance is  2750 much higher than the normal R-C Zobel that is normally present at the output of the amplifier.

The minimal impedance that the circuit presents to the Amplifier is 22Kohm, The cutoff freq is 0.4Hz. It's only an R-C Zobel series circuit in parallel with lines to sample the output tension as normally used in amplifiers that contains DC protection inside.

reirato escreveu:

Ave_Rapina escreveu:

Instead of taking the risk of burning an expensive pair of speakers due to some amplifiers that doesn't have  DC fault protection built in, here is an small retrofit that can be connected outside the device powered by an simple adapter and continuously watch for DC tension that may appear in the output of the fault amplifier.

The minimal tension for detection is +-2,5V and max voltage 200V pk-pk.
Speakers lines are total isolated from the circuit. Can be connected in any polarity ( just need to respect input output)

Images:



Further info: valente.olimpia@gmail.com

Isso é para vender??? ...

E por quanto?...
  


Suspeito que queimei qualquer coisa numa das minha colunas das minhas experiências O O P S ? ....
  

 

Please contact the email presented. I don't do fabrication.

Sorry to ear about, simple circuits avoid easy large damages on speakers woofers due to amplifiers that don't have this protection built-in.

PCB ready to mount



Further info: valente.olimpia@gmail.com

On the final assembly:





Further info: valente.olimpia@gmail.com

Hi

Great!

Whenever i see the expressoin "DC output protection" i remember my QUAD 405 has no DC output protection module, because it's an earlier version. It was later issued by QUAD throughout the updated circuits for this model and the 405-2.

Nevertheless it does have the R-C series Zobel Network (has most of the amplifiers if not all, have) and very low DC offset output (less than 2mV at no load).
In the event of a DC failure, I believe the current dumping section should instantly choke the output, leading the amplifier to fry the internal fuse in the board, thus preventing DC output to the speakers (i find this hard to believe in the event of a sufficiently punchy transient)

Are you familiar with the 405?
What do you reckon? Should i worry about it? QUAD is an all time claimer of the "unconditionally stable amplifier" eversince the 303 model.

Now i have a 606 MK2 which doesn't have it as well, but for a different reason. It feeds back the output to an opamp whose only task is to maintain near 0mV DC at the output along with the floating ground. As you may know, both the 405 and the 606 don't rely on DC blocking capacitors at the output.

On the other hand i've came across the fact that : for relay dependant circuit designs, it is possible that the relay contacts fuse themselves together during a massive DC event, making it impossible to quickly disengage the Speakers from the Output stage of the amplifier, eventually leading those to irreversible damage.
What are your thoughts on this?


Once again, great Job!
I like your DIY's very much!

FBatista

Citação :

Hi

Great!

Whenever i see the expressoin "DC output protection" i remember my QUAD 405 has no DC output protection module, because it's an earlier version. It was later issued by QUAD throughout the updated circuits for this model and the 405-2.

Nevertheless it does have the R-C series Zobel Network (has most of the amplifiers if not all, have) and very low DC offset output (less than 2mV at no load).
In the event of a DC failure, I believe the current dumping section should instantly choke the output, leading the amplifier to fry the internal fuse in the board, thus preventing DC output to the speakers (i find this hard to believe in the event of a sufficiently punchy transient)

--- The main difference between both is the active protection device formed by an low pass RC filter combined with an DIAC to define the DC threshold value to trigger the TRIAC that will short-circuit the output and forcing to blow the line fuses.

Citação :

Are you familiar with the 405?
What do you reckon? Should i worry about it? QUAD is an all time claimer of the "unconditionally stable amplifier" eversince the 303 model.

Now i have a 606 MK2 which doesn't have it as well, but for a different reason. It feeds back the output to an opamp whose only task is to maintain near 0mV DC at the output along with the floating ground. As you may know, both the 405 and the 606 don't rely on DC blocking capacitors at the output.

--- DC output blocking using capacitors normally relies on very high values of capacitance that is most of the time only possible using electrolytic capacitors. That raises other genres of problems and most of the times is deprecated in systems that use symmetric tensions. Normally only used in single ended configurations.

Citação :

On the other hand i've came across the fact that : for relay dependant circuit designs, it is possible that the relay contacts fuse themselves together during a massive DC event, making it impossible to quickly disengage the Speakers from the Output stage of the amplifier, eventually leading those to irreversible damage.
What are your thoughts on this?

--- The circuit that is used on the QUAD is normal used in very high power amplifiers due to the fact that in such massive DC current it will destroy totally the relay contact. But most of the <200W use the relay genre due to the fact that is no so destructive in terms of making direct short-circuit to the output and most of the time destroying all the output transistors.

--- The short circuit device must be always combined with line fuses on the DC supplies, and many amplifiers don´t rely on line fuses what makes the solution infeasible.



--- Some protections use MOSFETS in series with the DC power lines to when the output presents DC fault the lines are disconnected.




--- One problem that ofter occurs is that some amplifiers develop some abnormal DC tension that is not equal to the total value of the DC lines ( +VCC or - VCC) due to transistor polarization problems in some stage. In this situation, the solution of the Low pass RC filter + DIAC and Triac is totally dependent on the DIAC reference tension value used and may pass unaware of this DC value.

--- The circuit can handle floating or non-floating outputs, it´s total indifferent.

--- Note that many amplifiers have A-B selectors and that is made with relays for example. Some accuphase use it.


 

Citação :

Once again, great Job!
I like your DIY's very much!

FBatista

Thanks.

Some more ones:




Further info: valente.olimpia@gmail.com

Hi Ave_Rapina, thanks a lot for your explanation.
That was very clear!

Though not worried about it, i'm intrigued why the 606 never had an output protection device. QUAD implemented it in the 405 and 405-2 but didn't in the 606 MK(whatever I or II)

The boards for your project turned out great!

Cheers
Fbatista

FBatista escreveu:

Hi Ave_Rapina, thanks a lot for your explanation.
That was very clear!

Though not worried about it, i'm intrigued why the 606 never had an output protection device. QUAD implemented it in the 405 and 405-2 but didn't in the 606 MK(whatever I or II)

The boards for your project turned out great!

Cheers
Fbatista

The QUAD 606 has an virtual ground instead of an active ground. In case of transistor problem what will happen is that you will short one capacitor to one rail and the virtual center is also dragged to that potential avoiding that any DC tension reaches the Speaker due to the fact that is connected to that virtual center.

That should be punchy on the rail caps

I knew the lack of a DC protection had something to do with the virtual ground. Now i know it exactly, great explanation!
I really like QUAD's simplicity.
Thank you!

Fbatista

On the Box:



Further info: valente.olimpia@gmail.com

Very good looking!

Any more photos?
Front plate?

Congratulations


(what's your next project?)