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

OK. I'm confused now. When the amp is off my f4 measured higher than 200 ohms. The speakers are 4.7 nominal. However when I turned the amp on after reconnecting the speakers it now measures over 20 ohm. How is that possible. Surely it should read slightly to a lot lower than the speaker impedance.
 
You can't read the output resistance with the amp powered up.
You need to use a method to measure output impedance.

With the amp unpowered you cannot measure output impedance but you can measure it's resistance. It will probably be near infinity provided you don't blow up the semiconductors due to reverse voltages.

Adding the speaker just confuses any of those reading attempts.
 
I seem to have got that wrong. Sorry. Just put a meter across my f4 and the impedance is high.

Yes - the amp is biased and below 10 mV dc offset.
Everything looks nice.

When i meassure impedance/resistance from out to out it is 58 ohm with no power - and approx 22 ohm with power.
Turned off my continuity tester shows 58 ohm as well.

When the dc board turns on there are 5 seconds to steady led.

The continuity exist also when i disconnect the protection board.
It is a F5 matter.


And the above meassures are between left and right "out" - not between "out" an "ground" on one board.
I have common ps for the boards.
 
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Andrew, when you say reverse voltages do you mean connecting the power up in reverse (i known thatll beak it) or the voltage from a dmm checking resistance? I would have thought that would have too low a voltage to damage semiconductors. Although I think I'll stop probing around. I certainly don't want to break mine.
 
When on I measure 6.8 ohm between left positive and right positive. And just contact resistance between the gnd terminals.
Im curious as to why your measuring the positive to positive terminals. Are you using it in bridge mode?

I was just checking everything - and checking on / off relays on the speaker protection board. So no exact purpose - just checking, and my logic said, be aware of this ;-)

When looking at the schematic, I can see that there is connection from "out" via resistors/transistors to both V+ and V-. And V+/V+ on the PS board are connected to both right and left board, same goes for V-/V-.

That must be the explanation????
 
Yes, looking at the schematic, when the board is on, spk 1 and spk 2 out will be connected via r12 and r13.

This are 27k so you wouldnt get any noticeable crosstalk.

On the f5 board you have a 0.47ohm resistor between the mosfet and the rail which feeds both sides. Once on the mosfets are biased constantly on so i guess there wouldnt be much limiting current in that path. I think that measurement is a red herring and as andrew said, youre probably not measuring what you think you are measuring.

As your amp didnt go bang when you powered and connected the speaker board it sounds like its ok.

When i made mine i first powered the individual boards from my bench supply and ramped the rail voltage up gradually to make sure nothing was going wrong whilst I set up the bias to a safe level according to the build guide.

At this point i used a light bulb in series with the mains to limit current in to the psu whilst i tested that and made sure that that wasnt going to smoke and was providing the correct rail voltages.

Only at this point did i connect the output boards and still using the light bulbs i gradually put bigger bulbs in and as they were getting dimmer then i supposed the whole thing to be ok. If they are getting brighter then youve got a problem as the whole amp should only draw ~160w therefore in turn starting to limit the bulbs rather than the bulb limiting the amp.

If you've powered on both, connected the speaker board and nothings popped ( i really think that a short in the wrong place would cause fairly immediate damage) I would connect to some speakers and try something. But turn the volume up very gradually. If there is a problem you dont want to turn the amp up full whilst its either is shorting somewhere or has no load on it. I dont think it would particularly like either condition.

If youre still not sure, test the speaker board on its own. (which if you havent you should probably do) I think it uses a single rail supply so...

Connect your multimeter to the in and out on one side
There should be no continuity
Power the protection board
It should turn on, you reckoned 5 seconds or so.
The multimeter should now beep
Introduce a small voltage between ground (on the power input to the board) and the speaker in on the protection board, the relay should disconnect the in and the out within a volt or 2.

Repeat for the other side.

That should confirm correct operation.

Hook it all back up with the amp and off you go.

Hope this helps.
 
Using speaker protector board with Leach amp

I'm planning on using the speaker-turn-delay-dc-protector-boards with the multi channel Leach amp I'm building. In his documentation of his design, Mr. Leach he explains:

"R49, L1, R50, and C25 suppress parasitic oscillations that could be induced by shunt capacitance in the loudspeaker load. R50 and C25 mount on the loudspeaker output binding posts. On the first amplifier I built, I had these on the circuit board where they caused violent oscillations because the current through R50 and C25 generated positive feedback when it flowed through the circuit board signal ground lead. When the oscillations occurred, the heat sinks would get very hot. Moving R50 and C25 to the loudspeaker output binding posts solved this problem." R50 = 10 ohm, 2 W, C25 = 0.1 uF, 100 V film.

(The Leach Amp - Output Stage)

I'm concerned about the possibility of inducing oscillations with adding the speaker protector boards - is anyone here able to comment on their likely effect?
 
Hey everyone! I am sry, but also after reading through this whole thread I am still worried about the transformer for the speaker protection...

I understood that either i provide a 24V or 12V supply depending on the relais i buy. As everyone talks about a 24V transformer i think 24V refers to AC, right? But then, if not using a seperate transformer, a possibility would be to use the PSU of (for example) the F5 which leads to 24V DC??

When i look at the schematic there is a diode (D6) at the voltage input UI2 which would work as a AC to DC (loosing the second half of the sine wave...) so I think both, 24V AC and 24V DC would be a valid answer... But as the relais need for example 12V DC i think i should provide a 24V DC supply? (but why a 24V AC transformer then???)a

So please help me. What is the needed power supply for the speaker protection?

By the way. I would like to buy this relais:
http://www.mouser.at/Search/Product...V-Fvirtualkey66710000virtualkey769-JS1F-12V-F

is it ok?
 
Ah... do i need a 24V AC transformer because

24 * 1.41 ~ 34

minus 2 * Vf of the rectifier diodes minus Vf of D6 leading to (a little bit more than) 24V DC?

Although in the BOM it says 24V AC supply?

Hi,
I used 12VDC supply for 2numbers of 5V relays. I found that led blinks too rapidly, so i changed C1 /C2 to 10uF.
ofcourse i etched my own PCB and not using the DIYaudiostore PCB's.
 
Just a question on a small transformer to power the speaker protection board. I will use a series connection with my 24v - 25va transformer. Do I join the center tap to the star ground on my power supply ? and take the ground from the power supply to the board plus one feed from my small transformer? This way both the main transformer and the second smaller one are tied together on the center tap ?
 
The transformer centre tap gets twisted with the two AC feed wires.
This goes to the bridge rectifier, where the two AC wires connect to ~ & ~
The centre tap carries on past and the two outputs from + & - get twisted to form the next triplet.
This triplet feeds into the first pair of series connected smoothing capacitors. The + goes to cap +ve, The - goes to cap -ve and the centre tap goes to the zero volts link between these two capacitors.
For all of the preceding wiring the loop area at every termination must be minimised. Leaving excess loop area creates avoidable emi.
 
1% is pretty standard for metal film resistors.
Only high power or metal oxide or carbon now come in 5% or higher tolerance.
I would recommend you do not buy any small resistors specified as 5%. They are very likely to be fakes, or poor copies, or just plain bad production.

tempco for metal oxide is commonly around 300ppm/C
metal film comes in a wide variety from 100ppm/C down to as low as 5ppm/C but these are very expensive.
expect 50ppm/C to be similarly priced to 100ppm/C