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DIYAudio SoftStart Build
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Old 26th July 2012, 03:00 AM   #1
mattmcl is offline mattmcl  United States
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Default DIYAudio SoftStart Build

I'm putting a BOM together for the Soft Start in the DIY Store. I'm wondering about C11, it's specified as 0.001uf to 0.01 uf, 250 v Y-Class. Why the variable? Also I'm having trouble finding this leaded, all seem to be surface mount.
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Old 26th July 2012, 05:29 PM   #2
mattmcl is offline mattmcl  United States
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Anyone?
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Old 26th July 2012, 05:47 PM   #3
macboy is offline macboy  Canada
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This is not a variable capacitor, it is specified as any value between 0.001 uF and 0.01 uF, since the value is not critical. The safety rating of Y class is important. These are commonly available in through-hole, you should have no trouble there. Hint: search "safety capacitor" on digi-key, then filter any showing any "Y" under "Ratings". Also pick through-hole, in-stock (checkbox), bulk packaging, and select the range of values. That will narrow it down to a page or so of results.
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Old 26th July 2012, 05:53 PM   #4
CharlieLaub is offline CharlieLaub  United States
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C11 is across the switch to suppress arcing. Keep in mind that this will also leak some current and the circuit will never truly be "off", although that is not a serious problem IMHO.

The value of the cap is ballpark, because the "best" value depends on the inductance and other things in the rest of the circuit. There might be an optimum value, but this would be best found using an oscilloscope on the as-built circuit so don't worry about it. Just pick something in the recommended range and go with it. I have seen 0.01uF used in commercial amps on the switch, so I would go with that personally.

Make sure to get the Y-type, because it is rated for this kind of application. Do not just throw any 250V rated cap into this position as it will likely fail after awhile.

-Charlie
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Old 26th July 2012, 06:09 PM   #5
mattmcl is offline mattmcl  United States
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Great. Something like this?

CS17-F2GA103MYNS TDK | Mouser

The class is X1Y2. I'm not familiar with safety caps, there seem to be Y1, Y2 and Y3 classes.
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Old 19th August 2012, 11:32 PM   #6
mattmcl is offline mattmcl  United States
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Could someone confirm these parts?

D9, D10, D11, D12
1N4001 Fairchild Semiconductor | Mouser

D13
1N4749A Fairchild Semiconductor | Mouser

R13
CPF3220R00FKEE6 Vishay/Dale | Mouser

R14
PR03000201004FAC00 Vishay/BC Components | Mouser

R15, R16, R17, R18 (for 110v)
PW51350K IRC | Mouser

R19
271-2.2K-RC Xicon | Mouser

C9
RDED72E684K5E1C13A Murata | Mouser

C10
EEU-HD1H102 Panasonic Electronic Components | Mouser

C11
CS17-F2GA103MYNS TDK | Mouser

LED1
LTL1CHCBK Lite-On | Mouser

K1
Not sure about this, any suggestions?
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Old 20th August 2012, 06:50 PM   #7
mattmcl is offline mattmcl  United States
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Old 21st August 2012, 11:13 AM   #8
AndrewT is offline AndrewT  Scotland
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Do you know anything about what you are proposing to do?
Mains electricity can kill.
You have so many very basic questions that I fear you don't realise the risks involved.
__________________
regards Andrew T.
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Old 21st August 2012, 03:06 PM   #9
mattmcl is offline mattmcl  United States
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Yes... I have built several audio projects including a tube amp. I am simply looking for a Mouser part # for the relay as I can't seem to narrow it down.
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Old 27th February 2013, 08:35 PM   #10
HiFiNutNut is offline HiFiNutNut  Australia
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Thanks to Jojo to come up with this excellent softstart circuit. I have been using softstart for a long time, but the circuit I have been using is powered by a transformer. Jojo's version is powered by the mains and this not only reduces costs but also saves space. While I am rebuilding my amplifiers I think I will use Jojo's circuit.

The Build Guide suggests using 180R for R15-R18 but does not provide the formula for calculating the optimal value for the paralleled resistors. I think this resistor value can be customised to specific applications.

Here is my 2 cent contribution - Let me share with you the way I calculate the resistor value. If you find it wrong, please correct it.

It is rather simple. We only need 3 input parameters to determine the value : (1) I_limit - The desired inrush current limit; (2) Vp - The Primary voltage; and (3) Vs - The secondary voltage.

The paralleled resistors value should be: R = Vp ^ 2 / I_limit / Vs

For an example, if the primary voltage is 240VAC, the secondary voltage (before rectification) is 2 x 45VAC for two secondary windings (45-0-45, or 90VAC), and we want to limit the inrush current to 10A, then R = 240 x 240 / 10 / 90 = 64. Since we use 4 resistors in parallel, Each resistor R = 64 x 4 = 256R, and we can find the nearest value in E24 of 240R.

Note that the R has nothing to do with the size of your reservoir capacitors. The size of your reservoir capacitors does not determine the R value, rather, it determines how long it takes for the relay to click in.

The formula is based on the equation of turns ratio Vs / Vp = Ns / Np = Ip / Is. The primary current is derived from the desired current on the secondary transformed by the turns ratio then ohms law R = V / I. This assumes that the transformer is 100% efficient. In real life, the loss is very small and can be ignored.

Next, what value would I choose for C9? Actually, I would prefer to have the circuit to allow fixing C9 and replacing R13 with a trimpot for the initial setting. This would be far more convenient. Once a value of resistor is found, replace the trimpot with a resistor.

I understand that everyone recommends a couple of seconds or so before the relay clicks in. I personally don't mind a much longer time, say, 5 - 10 seconds. The reason is that, if the capacitors are not charged up yet, you want the current limit to stay on for protection. If the capacitors are already charged up, the current demand becomes so small it is completely harmless for the current to pass the resistors (unless you are already playing music at maximum volumes beyond clipping level). If not sure, model it with PSU2.

I hope this helps.


Regards,
Bill

Last edited by HiFiNutNut; 27th February 2013 at 08:38 PM.
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