Power Supply Soft Start Board (V3)

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migkiller1971

Member
Joined 2010
Live from mains into Live/Sw1
From Live/Sw1 to power switch
Switched live from power switch back to Sw2
Transformer connected across XFMR1 and XFMR2






Maybe I'm doing something wrong but I have 120vAC on the board as soon as I turn on the switch on the main IEC. Now, it doesn't turn on the PSU board. I have to turn on the main switch for that. Not too comfortable knowing that I have a live 120vac even if I turn off the main switch.
 
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patoperro

Member
Joined 2013
I have a Naim amp that trips a breaker occasionally when I hit the front switch. An EE colleague told me that it was because of the inrush current and advised I solder in a thermistor (B59955C0120A070 | EPCOS PTC Thermistor, 800mΩ, O 13.5 x 3.5mm, Toleranz +-25% | RS Components). This would result in a loss of power (although minimal he assures) but would eliminate the issue.

I gather that I could use this to do the same, although I assume I would need to shield it somehow. But, what would be the advantage to using this over the $1.50 thermistor?
 
Mark Johnson

Mark Johnson

Member
Joined 2011
Paid Member
One reason might be that an influential textbook (Audio Power Amplifier Design, 6th edition, by Douglas Self) recommends this approach and NOT the Negative-Temperature-Coefficient-Thermistor inrush current limiter approach.

Another reason might be that an influential website (Elliott Sound Products) recommends this approach and NOT the NTC-Thermistor inrush current limiter approach.

A third reason might be all of the previous messages in this thread, which report success with this board. Dozens and dozens of people have used this board successfully in their audio equipment. On the other hand you only have the assurance of one person (your EE colleague) that the NTC-Thermistor Inrush Current Limiter will be successful.

A fourth reason might be power loss. The NTC-Thermistor Inrush Limiter will gobble up about 1% of the incoming mains voltage, leaving "only" 99% of the mains voltage applied to your audio gear. This PCB applies the full 100% of the mains voltage to your gear.

A fifth reason might be flickering mains. The NTC-Thermistor Inrush Current Limiter needs 60 to 180 seconds to reset itself. After you turn off your equipment, you should not turn it back on for 60 to 180 seconds, which gives the NTC-Thermistor ICL enough time to cool down and become ready for a new inrush. However if your AC mains experiences flickering or On-Off-On-Off failure in a brief period of time, or if your wife or child flicks the power switch on and off too quickly, then you will not get any inrush current protection. This PCB resets immediately and does not require any cooling time between on/off events.

A sixth reason might be heat within the equipment chassis. The NTC-Thermistor ICL will remain warm to hot to Very Hot while the equipment is turned on. This might be frightening, or possibly dangerous to other components and cables inside the chassis, or possibly dangerous to repair personnel. This PCB does not remain warm or hot while the equipment is turned on.

It may be worthwhile to mention that many of the amplifier PCBs sold in the diyAudio store (F4, F5, F6, M2X, ACA, AlephJ, etc), are circuits that were designed by Nelson Pass of Pass Labs and First Watt. Mr. Pass recommends a power supply circuit for these amplifiers, which includes NTC-Thermistor inrush current limiting and not this PCBoard.
 
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astromo

astromo

Member
Joined 2017
Mark Johnson said:
One reason might be that an influential textbook (Audio Power Amplifier Design, 6th edition, by Douglas Self) recommends this approach and NOT the Negative-Temperature-Coefficient-Thermistor inrush current limiter approach.

Another reason might be that an influential website (Elliott Sound Products) recommends this approach and NOT the NTC-Thermistor inrush current limiter approach.

A third reason might be all of the previous messages in this thread, which report success with this board. Dozens and dozens of people have used this board successfully in their audio equipment. On the other hand you only have the assurance of one person (your EE colleague) that the NTC-Thermistor Inrush Current Limiter will be successful.

A fourth reason might be power loss. The NTC-Thermistor Inrush Limiter will gobble up about 1% of the incoming mains voltage, leaving "only" 99% of the mains voltage applied to your audio gear. This PCB applies the full 100% of the mains voltage to your gear.

A fifth reason might be flickering mains. The NTC-Thermistor Inrush Current Limiter needs 60 to 180 seconds to reset itself. After you turn off your equipment, you should not turn it back on for 60 to 180 seconds, which gives the NTC-Thermistor ICL enough time to cool down and become ready for a new inrush. However if your AC mains experiences flickering or On-Off-On-Off failure in a brief period of time, or if your wife or child flicks the power switch on and off too quickly, then you will not get any inrush current protection. This PCB resets immediately and does not require any cooling time between on/off events.

A sixth reason might be heat within the equipment chassis. The NTC-Thermistor ICL will remain warm to hot to Very Hot while the equipment is turned on. This might be frightening, or possibly dangerous to other components and cables inside the chassis, or possibly dangerous to repair personnel. This PCB does not remain warm or hot while the equipment is turned on.

It may be worthwhile to mention that many of the amplifier PCBs sold in the diyAudio store (F4, F5, F6, M2X, ACA, AlephJ, etc), are circuits that were designed by Nelson Pass of Pass Labs and First Watt. Mr. Pass recommends a power supply circuit for these amplifiers, which includes NTC-Thermistor inrush current limiting and not this PCBoard.
Click to expand...

Thanks Mark, that's an excellent run down of the pro's/con's and considerations. Not having thought it through too hard, I've sourced componentry to go either or both ways. Your commentary gives me an excellent spring board to think matters through.
 
J

jphabc54

Member
Joined 2018
I recently integrated the soft start board into my F5 build. Multiple power ups went as expected and everything looked good until I started biasing the F5 channels. With one channel at full bias and the second channel at about 70 percent bias, the 180R / 5W resistors went nuclear — solder joints glowing and smoke coming off of them. Any thoughts on what might have gone wrong?
 
K

kevinr

Member
Joined 2009
Transformer

Does Mouser carry a transformer that is a good choice for this pcb in a stand-alone case ?
I printed out the BOM but didn't see a p/n listed for one
In reading through the threads for v2 and v3 posters are using various transformers in various configurations, so it is not clear

Thank you
 
astromo

astromo

Member
Joined 2017
kevinr said:
Does Mouser carry a transformer that is a good choice for this pcb in a stand-alone case ?
I printed out the BOM but didn't see a p/n listed for one
In reading through the threads for v2 and v3 posters are using various transformers in various configurations, so it is not clear

Thank you
Click to expand...

I don't know where I found it (it's not included at Post #1) and it's not linked on the relevant store page but check out the write up here:
diyaudio-softstart-build-guide-v1.0.pdf
Particularly, the detail provided on p. 13.
[EDIT: Although, you'd need to make some adjustments to account for the v3.0 PCB changes as offered at Post #40:
Power Supply Soft Start Board (V3)
... ]

I may be wrong and am happy to be educated but transformer selection doesn't feature in a big way. There is commentary on p.5 regarding transformer VA rating. Apparently, the PCB "works well even with high VA transformers".

What "high" means I can only guess but I'm working with a 400VA toroid to power an Aleph-J. That's more than the minimum but I'm not going crazy, so I'd expect I'll be right with a plain vanilla BoM. What appears to be important is to align your supply's AC mains voltage with resistor specification R15-R18 and the capacitance of C9.

EDIT:
Note that with the v3 board, the Reference Designators are different. By my interpretation, I get the following equivalence:
C9 (v1.0) = C2 (v3.0)
R15-R18 (v1.0) = R3-R6 (v3.0)

I'd appreciate a check on all the info that I've related. This board is fed directly from the mains, so it's a smart move to be sure of the detail.

Also, if you look at the comments from Post #17 on, there are some pretty sizable VA ratings mentioned:
Power Supply Soft Start Board (V3)
 
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K

kevinr

Member
Joined 2009
power supply for soft start

Thanks for your post astromo .
I did read through those posts and links; but hobby wise at this stage I'm pretty much just a "parts changer" as they say.
I was hoping to get referred by someone here on the forum to a part number from Mouser for a transformer to power the soft start pcb.
I just don't see anyone selling a speaker protector circuit ready to go anywhere online.
That online auction site has some assembled speaker protection circuits from Asia showing 12 Volts needed for power but I wanted to go with something here in the US first from the diyaudio store if possible.
Is a SMPS an option to power the Soft Start board ?
 
M

mrdave45

Member
Joined 2010
If its the same pcb Ive got, the soft start is powered by the mains, then the soft start part of the circuit goes in line with the primary of the main tx. Have a look at schematic and see what it's hooked up to. Can you see anywhere to connect to a second transformer?
 
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