Speaker Turn On Delay and DC Protector Board Set (V2)

[JojoD818]

Looking at your schematic, the speaker line will pass through the thermal switch?

Shunting the base of T6 to ground would be best imho.

 

[pmchoong]

Thermal switch

Hi,

The thermal switches are normally closed.

 

[AndrewT]

I think you need to use a transistor to invert the switch signal.

 

[pmchoong]

Thermal switch

why is there a need for a transistor? The thermal switch will open and shut the connection once it sense more than 70 degrees.

Thanks.

 

[JojoD818]

The idea is to stop T6 from conducting, thereby cutting off the relays.

Your idea can also work if you are more comfortable doing it, granted that the speaker signal coming from your amp is not passed through that thermal switch. Problem is that your schematic shows it passes through the relay contacts and also the thermal switch.

 

[AndrewT]

why is there a need for a transistor? The thermal switch will open and shut the connection once it sense more than 70 degrees.

Thanks.

a normally closed switch will open on overtemp.
It cannot "shut the connection" if it has gone "open" on overtemp.

A normally closed switch if suitably rated could be used in the mains supply to your transformer primary.

A normally closed switch with a transistor to invert it's operation can be used to shut down the delay relays, by pulling base of q3 low.

 

[pmchoong]

I see, which means its' only gone 'open' but will not cut off the connection. Andrew, are you suggesting that the normally closed thermal switch to be put between the mains power supply and the transformer? I do not want to complicate the speaker protection circuit.

Thanks.

 

[AndrewT]

The Thermal switches that I have are all rated for 250Vac. A few are normally open, the majority are normally closed.
I use the normally closed as a mains cut-off if the heatsink gets too hot.

 

[pmchoong]

Thanks Andrew. So these thermal switch will go between the mains power supply and the transformer. Any specific brands that you recommend?

 

[goober5]

sc945 replacement

Hi

Would it be possible to replace the 2SC945 with 2SC3940A and combine with MPSA05 for T6.

Thanks

 

[JojoD818]

Hi

Would it be possible to replace the 2SC945 with 2SC3940A and combine with MPSA05 for T6.

Thanks

2SC3940 looks good but you'll need MPSA06 for T6, not MPSA05.

Cheers

 

[philbyx]

In this schematic if one channel has +V offset, and the second has -V offset, the summing point will remain 0V, then, the relays will not open.

I agree that it's very unlucky, but...

 

[JojoD818]

In this schematic if one channel has +V offset, and the second has -V offset, the summing point will remain 0V, then, the relays will not open.

I agree that it's very unlucky, but...

It is not entirely unlucky, but it is unlikely.

However worse case it may be, if it did happen, the differential voltage at the summing point will still shut the circuit down.

 

[toastedcrumpets]

Can someone confirm/deny if, for the DC protection to work, the GND of the Speaker Protect board needs to be connected to the GND of the amplifier power-supply?
Thanks!

 

[hughatava]

I sure could have used this circuit in my old Adcom GFA 555-II which failed and put 85 V DC on my speaker. I thought the amp was bullet proof but after 20 years all bets are off.

 

[coolnose]

What relais to choose ?

I am finished gathering parts but I am reluctant on using the GL5 relais (10A) on the outputs of a F5T.

The circuit is, accordingly to NP, able to deliver around 44 Amps max and I was wondering if the GL-5 relais with it's 10A rating would work in case of a failure.

I found some 70 Amps automotive relais, but having taken those apart once, I don't want to use them either.

Any thoughts on the GL-5 as according to the BOM with high output amps ?

Thanks in advance for you help!

Cheers,

Max

 

[BobEllis]

NP's arc welder currents can only be delivered into a very low impedance load. With an 4 ohm nominal load, let's assume it dips to 3 ohms at crossover. You'd be hard pressed to exceed the relay's operating current, even with a shorted output device and the usual 30V rails. If in doubt, parallel a couple of GL5s or use one board per channel.

 

[mattmcl]

I was wondering if I read 44 amps correctly... wow. You can weld submarines together with that kind of power.

 

[coolnose]

Bob,

thanks a lot for your insight.

The amp is actually running on 48V rails, but anyway I found 16A relais having the same footprint and will go for those (still GL5 series).

As I am building 2 mono-blocks and the PCB is providing space for 2 relais I might go the way of paralleling those....

Not very "esoteric" or "audiofool", but hey....

Cheers,

Max

 

[coolnose]

I was wondering if I read 44 amps correctly... wow. You can weld submarines together with that kind of power.

Well,

according to NP article of the F5 turbo, the V3 variation is given for 44 amps if I'm not mistaken, not that I need it, but I thought it was worth mentionning with regards to the choice of the protection relais.

Max