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Old 12th March 2016, 06:43 AM   #1
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Default Soft start question

Pictured below is my Chinese soft start circuit, I purchased this assembled and I assumed plug and play but after wiring no juice, the plug/wires pictured when brushed together activate the unit and it works fine. I am not familiar with the symbol on the drawing and my Chinese is a little rusty so my question is how to wire this into the mix. I get the impression it requires a momentary switch in addition to mains on and that doesn't make a lot of sense to me. If you are familiar I would appreciate your help.
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Old 12th March 2016, 06:49 AM   #2
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This circuit has its own power supply which is on constantly. You should not use a power switch at the 115V/230V side unless you want a real 115/230V off function (Service/safety power off) for instance at the back of the device. Normally this device IS the switch to the transformer of the device you want to switch on. Please note that you MUST use a mains fuse to the 115/230V side of this device !!!!

You need a small switch to activate the relays and thus the output to the transformer. It serves like a standby/on power switch and gives the opportunity to keep 115V/230V at the back of the device and low voltage DC wiring to the front of your amplifier. That way you can buy a nice small esthetically pleasing power switch instead of a clunky 115/230V 10A rated one. No 115/230V AC wiring to the front means no possible mains hum straying in your audio electronics.

To be honest I don't see power resistors so I think this is not a soft switching device but merely a relay controlled power switch. But then again it has 2 x 30A relays so maybe there are power resistors at the bottom of the board ? It does have 2 thermal switch connectors that switch off the amplifier when either one of the channels overheats. Those are the 2 other inputs. Since it has a NE555 timer IC I think there is a delay involved too. Does not make much sense when it does not "soft switch" .....but gives a different "feel" when switching your device on. Maybe the 555 is for blinking of the LED ? Please confirm that.

*Normally soft switching means first switching the output via a resistor to lower the inrush current and then shorting that resistor to give the transformer full juice.
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Last edited by jean-paul; 12th March 2016 at 07:10 AM.
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Old 12th March 2016, 06:53 AM   #3
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I see a 555 timer on the sheet.

So you apply mains and nothing happens. You then short the contacts and the unit operates...

Then what ? Do have to remove the mains input to reset back to off or does the momentary switch (yes that's what that symbol seems to show) turn the unit off ?

I would also as a safety precaution make sure that the momentary contacts are isolated from the mains. Is that a mains transformer in the middle powering it all ?
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Old 12th March 2016, 07:12 AM   #4
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First experiment is to connect mains voltage and then try the on/off function by connecting the wires for a very brief time. If the device stays switched on you need a momentary switch. It it only switches on when you keep the wires connected you will need a normal on/off switch.

Keep in mind that there might be a delay involved so just wait 30 seconds after you have had the 2 wires connected together.

Work safely !

1. I see dangerous Faston connectors that are normally used in 12V car electronics. You need the ones with plastic covers for mains voltage !!!!

2. You will also need to use a plastic sheet glued to the bottom of the chassis in case one of the connectors comes off

3. You will need to mount the PCB with all 4 mounting holes and 4 stand offs with screws or nuts.

4. You do need a correctly rated mains fuse from the IEC connector to this circuit.

5. Nice to have: a plastic sheet between PCB and back cover
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Last edited by jean-paul; 12th March 2016 at 07:23 AM.
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Old 12th March 2016, 08:16 AM   #5
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Mooly, The only supply to the unit is mains voltage with a rectifier for the dc on the board. I think I have this now. When you short the leads to turn the unit on it has to remain on for 10 seconds or so before shorting the leads again will turn it off, if you don't wait the 10 seconds it will not have any effect on it. This is what had me baffled, On but no Off. If you concur, it sounds like the mains are not switched to the soft start and the low voltage (5V) is used with a momentary switch as the on off control. Your question does it turn on and off by shorting the leads caused me to go back and explore the possibilities and discovered the 10 second dilemma. P/S If you don't mind have a look at my "NAP-140 Clone kit test & failure" post in solid state and give me your thoughts. Ian Finch gave me great advice and I do greatly appreciate respected opinions but as always I have my uncertainties in myself.
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Old 12th March 2016, 08:17 AM   #6
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OK thanks for the reaction, it is appreciated.

BTW I think you don't have it now. Mains voltage goes to the transformer and is then rectified to DC. This PCB needs to be powered on continuously for the controls to work correctly. The small switch should be the only power on/off control. I think the chinese description says that it will switch on when the momentary switch is pushed 3 to 5 seconds.

It just occurred to me that thermal protection switches normally are "always closed" types. This could mean that you need to short the other 2 inputs when you don't use thermal protection. Just guessing....edit: I am right about this as these devices are NC devices. You will need to either connect them or short the contacts on the board.

Since you are the responsive type of guy I googled some more. The 4 devices next to the transformer are PTC resistors that limit the inrush current so it really is a soft switching device. There are insulated connectors delivered with the board.

Class A Soft Start Delay Temperature Protection Board with Switch Function | eBay

The description is as follows:

4: When the amplifier board heatsink temperature exceeds 75 degrees, the board can immediately turn the power off

Source, not to the amplifier overheating. Until the temperature dropped to 75 degrees below the radiator,

Amplifier can reboot or power amplifier can not drive
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Last edited by jean-paul; 12th March 2016 at 08:45 AM.
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Old 12th March 2016, 08:33 AM   #7
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So it seems this board is just an electronic on/off type of thing allowing a small momentary switch to be used. As J-P suggests, I to don't see any 'soft start' type of feature which would be a thermistor or power resistor.

Your NAP-140... something is seriously amiss for the 100 ohm to burn. Firstly the B-E junction of the output device should conduct and limit the voltage across the resistor to 0.8 (ish) as a maximum. If there were excess current available in that path then I would have thought the output device would fail short B-E anyway and save the resistor. A C-B short on TR12 would cause this as would a problem around TR10. Check if the 1N4148 has gone short. That would give a clue as to the failure mode.

You also need to check very carefully that all the devices are correct and fitted correctly. Use a bulb tester and short out the vbe multiplier from C to E (TR5) before switching on. That will force the bias current to zero.
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Old 12th March 2016, 08:34 AM   #8
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Default RE: soft start

Quote:
Originally Posted by jean-paul View Post
First experiment is to connect mains voltage and then try the on/off function by connecting the wires for a very brief time. If the device stays switched on you need a momentary switch. It it only switches on when you keep the wires connected you will need a normal on/off switch.

Keep in mind that there might be a delay involved so just wait 30 seconds after you have had the 2 wires connected together.

Work safely !

1. I see dangerous Faston connectors that are normally used in 12V car electronics. You need the ones with plastic covers for mains voltage !!!!

2. You will also need to use a plastic sheet glued to the bottom of the chassis in case one of the connectors comes off

3. You will need to mount the PCB with all 4 mounting holes and 4 stand offs with screws or nuts.

4. You do need a correctly rated mains fuse from the IEC connector to this circuit.

5. Nice to have: a plastic sheet between PCB and back cover
All good advice Jean-Paul and appreciated. The 30 sec. wait was the issue, I believe I have the switching issue in hand. I ran short of machine screws and misc hardware so I used enough for a mock up to form a usable layout and for testing which did not go as hoped but perseverance will prevail I hope. (see solid state)( Nap-140 test) for other rookie issues if interested.
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Old 12th March 2016, 08:52 AM   #9
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Are you sure you bought the 115V version ? I see there exist several versions of this board. Some are for both 115 and 230V some are explicitly not. Some use momentary switches and some newer ones need normal switches. Some have a bug that they don't start. They all look the same !

This one speaks about the need for a normal switch instead of a momentary switch.

Class A Power Amplifier Soft Start Delay Temperature Protection Board 220V New | eBay

This one speaks of a bug that is does not always start and they changed it.

Douk Class A Amplifier Power Soft Start Delay Temperature Protection Board 220V | eBay

It would be best to ask the seller for a connection diagram and an explanation what switch you need.
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Last edited by jean-paul; 12th March 2016 at 08:55 AM.
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Old 12th March 2016, 08:55 AM   #10
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Quote:
Originally Posted by Mooly View Post
As J-P suggests, I to don't see any 'soft start' type of feature which would be a thermistor or power resistor.
Hi Mooly, the 4 x 10D-11 devices right from the small 12V transformer are thermistors/PTCs.

Some useful info to change the delay time:
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Last edited by jean-paul; 12th March 2016 at 09:03 AM.
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