Speaker Turn On Delay and DC Protector Board Set (V3)

Thanks JSA1971 for letting me know I am not the only one with this issue. For a while I thought I did not assemble the board correctly but looking at it and checking to see if the DC blocker works, everything works the way it is supposed to.

Thanks taurro0221 and prasi, right now I am running the board off the DC side on the same positive rail that is going to the amp board (+24 dc). I will switch it over to the AC side. To get this correct, just connect to the leads that are going to the diode bridge from the transformer?

Thanks for all the help guys.
 
Thanks taurro0221 and prasi, right now I am running the board off the DC side on the same positive rail that is going to the amp board (+24 dc). I will switch it over to the AC side. To get this correct, just connect to the leads that are going to the diode bridge from the transformer?

Thanks for all the help guys.

any two secondaries that have 18-24VAC between them. I am guessing here that you are using 18vac transformer. For a Center tapped transformer, it will mean , any one secondary and the center tap. for a dual secondary transformer, two adjacent secondaries that go to the positive side of the PSU OR negative side of the PSU
 
So finally rewired this thing. Now I understand how this works and I should have been on the AC side the whole time. But for some reason the 18v transformer just does not have enough juice to activate the relays. I have 12v relays on the board so in series they need 24v. Even in the old manual I found online it says you can run them 18-24v but for some reason the relays will not activate on 18v AC. The LED just flashes. I found a wall mount transformer for a crossover I have that outputs 24V ac. I connected it to the board and it worked. The LED stopped flashing in a few seconds and I heard the relays click. So my next step is to get a separate transformer just for this board. I will get a 24V one but do you guys know what VA I should be looking at? I was hoping to keep it small because I am running out of room, so 25VA or 50VA or 100VA. Which one would work for this?
Thanks for the help.
 
So finally rewired this thing. Now I understand how this works and I should have been on the AC side the whole time. But for some reason the 18v transformer just does not have enough juice to activate the relays. I have 12v relays on the board so in series they need 24v. Even in the old manual I found online it says you can run them 18-24v but for some reason the relays will not activate on 18v AC. The LED just flashes. I found a wall mount transformer for a crossover I have that outputs 24V ac. I connected it to the board and it worked. The LED stopped flashing in a few seconds and I heard the relays click. So my next step is to get a separate transformer just for this board. I will get a 24V one but do you guys know what VA I should be looking at? I was hoping to keep it small because I am running out of room, so 25VA or 50VA or 100VA. Which one would work for this?
Thanks for the help.
I should have been more careful, as ckt uses single diode for rectification. you could measure the voltage after D6 with respect to ground. It will be less than 18VDC with 18VAC as supply . it will be approx 17VDC.
the series relays would need atleast 18VDC as this is the 'must operate voltage' for the 2 relays.
so with 24 vac transformer, you will be safe.

regards
Prasi
 
Last edited:
Received my Antek 24VAC(10VA) transformer yesterday. This one is tiny compared to the 600VA one for the main amp. I only hooked up one side of it, I hope that is OK. Power it up and it worked perfectly. LED flickered for a few seconds and then the relays locked in. When I turned the amp off it disengaged the relays before the main power supply turned off and there was no pop out of the speakers. Very happy about this.

#1. Get this kit, great boards, stops speaker noises and the soft start board gives you a connection for a second switch for the front.
#2 Just get a dedicated transformer for it. They are small and easy to place.
#3 Make sure you run the speaker board off of AC and not the DC side if you still want to use the main transformer. On the DC side it will not work because the board powers off the same time as the power supply and your speakers still pop.
 
Prasi
Thank you for your response.
P2n222a are cbe, 2n222a are ebc as per pcb, I had used 2n222a previously witn diy A d/c pcb in f5 mono's.

When I was experiencing led issues I had been using a veriac to slowly power up the d/c protect. I found that with a power lead the led's and relays operate in the correct sequence !. Anyone shed light on this.

Many Thanks
 
An RC timer reaches ~63% of the final voltage in one RC time constant.
Provided the voltage holds steady during the whole charging period.

eg. a 1k0 resistor charging a 1mF capacitor that has zero leakage current from a 10Vdc supply will initially start charging at a rate of 10V/1000ohm i.e. 10mA
The RC time constant is 1000ohms times 0.001Farads = 1second
That initial charging current of 10mA reduces as the capacitor voltage builds and has reached ~12*(100-63%) / 1000ohms = ~3.7mA after one RC.
Leaving the capacitor charging, it will have reached >95% in 5*RC

But if the capacitor leaks, then some of the current charges up the capacitor and some leaks back to source, i.e. the capacitor takes longer to charge up.
If the source voltage is lower than expected, then when the capacitor reaches it's expected time delay, less voltage has built up, so the event does not trigger. It takes longer for the charge to build up to reach triggering level.

Using a Variac, to lower the source voltage, to start the delay timer affects the RC timer so much that it never triggers because the capacitor never reaches trigger voltage.

That is what is wrong with all the simple RC timers that use a variable source voltage.
A 555 timer is arranged internally to ignore variations in source voltage, but the chip still requires the voltage at the pins to remain reasonably constant during the timing sequence.
 
Last edited:
Hi
Help my please!
The loudspeaker protection board is mounted on F5t, the board is powered by a 24V main transformer.
The board turns off the speakers all the time. The amplifier output is zero DC.
As I disconnect the amplifier output cable from the protection board "IN", the relays close and the red LED stops flashing.
Who can help you I will be very grateful.

Sincerely,
Antanas
 
the speaker isolation relay should isolate (open contacts) when power is OFF.
check you have used the normally open contacts.

When the relay receives the signal to trigger/switch over, the relay contacts close and the speaker becomes connected to the amplifier.

A normally closed relay is no good for speaker protection.
 
Hi Andrew T.
When power is off, relay contacts is open. I check with multimeter. But, when amplifier power on, relay contacts do not close, and red led does not stop blinking. Loudspeakers are disconnected from the amplifier.
Only after the speaker protection bord "IN" is disconnected. The relay closes and the LED stops flashing.
I checked again. The output of the amplifier is DC zero
 
Transistor replacements

I haven't tried BC549 in there but a quick peek and I don't see why it wouldn't work. 2N2222 is also ok in lieu of the 945. 2SC828 is also a pin for pin replacement.

Just please watch out for the pin configuration when you substitute transistors.

Cheers


I think 2N2222 is a pin to pin replacement for KSC945YTA with few changes in characteristics...I am using a 12V version for DC protector circuit, hopefully this should be sufficient


For MPSA06, can I replace it with 2N5551, stats read much more that MPSA


C-E Voltage 160V
C-B Voltage 160V
E-B Voltage 6V
C Curr Cont. 600mA


I have plenty at hand...hopefully they are good to be used for Q4
 
Hi All,

I just test my 2 builds. One is V2 , the other V3. I took care of the changed pinout of the transistors on the different version. Both builds act the same.

On power on led 2 turns on, led 1 flickers, the relay engages after a while and turns led 1 definitely on, the other stays on as well.

On turn-of led 2 dims slowly and led 1 flickers off....

The only change I made is 330uF in C6 instead of 220uF ...

Thanks

Max
 
Actually I think both boards are working fine, I'd just like to lower the flip flop frequency of LED1 as I expect the flickering to indicate a proper function, just to quickly ....

Just tested 4.7uF instead of 2.2uF for C1/C2 ... no change.... I suppose altering (increasing) R2/R3/R4 will slow down the blinking led ... any suggested value instead of 33K ?

EDIT: 2 x 10uF does the job for me, no resistor changes.


I understand that the speaker protection board cannot be used in a double mono configuration .... what PSU ground would the board be referenced to ...? So one board to order...

Cheers,

Max

Hi All,

I just test my 2 builds. One is V2 , the other V3. I took care of the changed pinout of the transistors on the different version. Both builds act the same.

On power on led 2 turns on, led 1 flickers, the relay engages after a while and turns led 1 definitely on, the other stays on as well.

On turn-of led 2 dims slowly and led 1 flickers off....

The only change I made is 330uF in C6 instead of 220uF ...

Thanks

Max
 
Last edited:
Engagement voltage and isolation from chassis ground

This might help you if you want to use the protection board and still maintain some ground isolation between the left and right channels on your power supply.

I built the speaker protection board for my Pass A6 project which is being built as independent mono blocks in a single case with one protection board. I wanted to preserve ground isolation between the left and right channels. The idea was to use a chassis ground as the single bonding point between channels but have some isolation between signal ground and chassis ground and isolation between left and right power supply grounds. The Pass schematics show a CL-60 thermistor for isolation between signal ground and chassis. The CL-60 has 10 Ohms of resistance when cold. I'm going to use a 10 Ohm resistor in parallel with two pairs of two series connected diodes paralleled in opposite directions in my amp. I'll have one of these isolation networks for each channel. Since the speaker sense circuit of the protection board shares a common ground for both channels, I did a test to prove that having the ground isolation network in series with the sense ground will not affect the performance of the protection board's sense circuit. To test I connected the speaker terminals on the protection board to a bench DC power supply and slowly increased the voltage. I found that it engaged the protection at 2.1 Volts DC. Then I placed the ground isolation network in between the sense ground and the power supply and I repeated the test and found the trip point was still 2.1 Volts DC.
 
To be clear, you hooked up one ground isolator for each channel at U1.1?

Yes but let me clarify. The U1 connector is the power supply input for the speaker protection board. My speaker protection board's power supply is it's own separate supply that floats. My U1.1 connects directly to chassis ground for the ground reference relative to the amp's speaker's ground. Each channel's power supply ground (shown as PG-1 on the amplifier boards) connects to their own ground isolator which connects to a single star point on the chassis ground. So each amp has only one connection to chassis ground via a ground isolator and the speaker protection board only to chassis ground.