hamfist Posted October 2, 2013 Share Posted October 2, 2013 I've just installed a mini SPDT switch in an active bass on the hot lead of the battery in an active bass. This allows me to keep the lead plugged in but disconnect the battery. Works great but there is, unsurprisingly, sometimes a small pop when I turn it on/off when amplified. not a huge issue but I'd like the switching to be silent if poss. Does my memory serve me rightly in that I just have to put a capacitor of some sort across the contacts on the switch to get rid of the pop ? Electronics gurus, your advice would be welcome. Thanks in advance. Quote Link to comment Share on other sites More sharing options...
Ou7shined Posted October 2, 2013 Share Posted October 2, 2013 A 1meg resistor aught to do it Quote Link to comment Share on other sites More sharing options...
hamfist Posted October 2, 2013 Author Share Posted October 2, 2013 [quote name='Ou7shined' timestamp='1380708530' post='2229183'] A 1meg resistor aught to do it [/quote] Ou7shined ...... Outstanding. Thankyou sir ! Quote Link to comment Share on other sites More sharing options...
rmorris Posted October 2, 2013 Share Posted October 2, 2013 [quote name='Ou7shined' timestamp='1380708530' post='2229183'] A 1meg resistor aught to do it [/quote] That will reduce 'switch noise' although it means some very small current might be constantly drawn from the battery. But isn't the issue here likely to be a pop caused by the electronics 'turning on' rather than switch noise or bounce ? Quote Link to comment Share on other sites More sharing options...
Ou7shined Posted October 2, 2013 Share Posted October 2, 2013 [quote name='rmorris' timestamp='1380714225' post='2229312'] That will reduce 'switch noise' although it means some very small current might be constantly drawn from the battery. But isn't the issue here likely to be a pop caused by the electronics 'turning on' rather than switch noise or bounce ? [/quote] It will do if you have it in the circuit all the time but if you bring in the resistor as you engage the switch it aught to kill the pop. Although I don't think a SPDT will cut the mustard. Quote Link to comment Share on other sites More sharing options...
Count Bassy Posted October 2, 2013 Share Posted October 2, 2013 Get a two pole "Make before Break" double throw switch Use one pole to short the output on the jack socket to earth, and use the other pair to open the battery connection. Then the output is shorted/Muted fractional before the battery is disconnected. and when turning on the battery is connected and the output un-muted a fraction later. However, if the power up time of the pre-amp is longer than the both on time of the switch you might still have a problem. Quote Link to comment Share on other sites More sharing options...
hamfist Posted October 3, 2013 Author Share Posted October 3, 2013 I tried the 1 meg resistor on the switch and it made no difference. To be honest I will not bother any more trying to change things as it's so easy for me to mute my signal with my tuner whilst I activate/de-activate the switch. It works well. In fact I can't imagine why any active bass wouldn't actually have a switch to isolate the battery. Quote Link to comment Share on other sites More sharing options...
Grangur Posted October 3, 2013 Share Posted October 3, 2013 Please can someone tell me where I'm wrong here? I would have thought the problem causing the pop is a spike in the circuit caused by the switching. So surely what we need is a smoothing capacitor going from the live of the battery to the earth, or maybe across the terminals of the battery. Just another thought, would the pop disappear if you only used switching of one cable - the live, maybe? Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted October 3, 2013 Share Posted October 3, 2013 (edited) [quote name='Grangur' timestamp='1380782960' post='2230381'] Please can someone tell me where I'm wrong here? I would have thought the problem causing the pop is a spike in the circuit caused by the switching. So surely what we need is a smoothing capacitor going from the live of the battery to the earth, or maybe across the terminals of the battery. Just another thought, would the pop disappear if you only used switching of one cable - the live, maybe? [/quote] I think you are right about the source of the noise, inserting the jack switches the power on just before making the connection and avoids this. The capacitor the OP refers to is a low value cap designed to reduce sparking in mains switch, or sometimes to remove radio frequency noise on the AC mains. Edited October 3, 2013 by Phil Starr Quote Link to comment Share on other sites More sharing options...
paul_5 Posted October 3, 2013 Share Posted October 3, 2013 Yup, smoothing cap'll do it. start with a 0.1uf / 100nf (capacitor code 104) and see where that gets you. Quote Link to comment Share on other sites More sharing options...
hamfist Posted October 3, 2013 Author Share Posted October 3, 2013 (edited) [quote name='paul_5' timestamp='1380804813' post='2230800'] Yup, smoothing cap'll do it. start with a 0.1uf / 100nf (capacitor code 104) and see where that gets you. [/quote] Where do I put the cap ? Across the contacts of the switch ? The switch I have installed is a SPDT switch on the hot lead coming out of the battery BTW. Edited October 3, 2013 by hamfist Quote Link to comment Share on other sites More sharing options...
paul_5 Posted October 3, 2013 Share Posted October 3, 2013 Yeah, that would make sense to put it on the +9v supply. Check that it's rated for 9v though (most of them are, but the last thing you want to do it blow up a cap - it stinks! Basically you're using it to build a bridge between the voltage output of the switch and the voltage input of the board. Once the power gets turned on there'll be a couple of milliseconds of silence, then the sound should come back in. The bigger the cap, the longer this delay (initial charge up time). Quote Link to comment Share on other sites More sharing options...
hamfist Posted October 3, 2013 Author Share Posted October 3, 2013 Admission ... I can be a bit dim sometimes. So ...... Do I put the cap across the contacts of the switch or across the hot and ground contacts of the battery circuit ? Maybe I'll try both and see what happens. It's only 18V. What can go wrong ? Lol. Quote Link to comment Share on other sites More sharing options...
paul_5 Posted October 3, 2013 Share Posted October 3, 2013 Chain would look like this: Battery >switch lug 1 > cap on lug 2> active EQ circuit board. If you put the cap on the "voltage input" side of the switch you'd still have the pop. Quote Link to comment Share on other sites More sharing options...
hamfist Posted October 3, 2013 Author Share Posted October 3, 2013 [quote name='paul_5' timestamp='1380827585' post='2231288'] Chain would look like this: Battery >switch lug 1 > cap on lug 2> active EQ circuit board. If you put the cap on the "voltage input" side of the switch you'd still have the pop. [/quote] OK, one contact of the cap on the switch contact away from the battery ... yes. What about the other end of the cap ? just to ground ? Quote Link to comment Share on other sites More sharing options...
paul_5 Posted October 3, 2013 Share Posted October 3, 2013 'tother cap leg goes to the +9v input on the circuit board instead of a wire. What should happen is that when the switch is flicked to the 'on' position the voltage will flow to the baord, but the cap will slow the rate at which it gets there, eliminating said 'pop'... Quote Link to comment Share on other sites More sharing options...
hamfist Posted October 3, 2013 Author Share Posted October 3, 2013 Well I've tried everything and the circuit still pops when switched on. No problem. I'm still pleased with having it there. I'll just have to mute whilst activating it. Quote Link to comment Share on other sites More sharing options...
Grangur Posted October 10, 2013 Share Posted October 10, 2013 This circuit should do it: Quote Link to comment Share on other sites More sharing options...
neepheid Posted October 10, 2013 Share Posted October 10, 2013 [quote name='hamfist' timestamp='1380781273' post='2230368'] In fact I can't imagine why any active bass wouldn't actually have a switch to isolate the battery. [/quote] We're all different. I can't imagine why people have this desire to leave their bass plugged in all the time, but that's just me Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted October 10, 2013 Share Posted October 10, 2013 [quote name='Grangur' timestamp='1381391583' post='2238280'] This circuit should do it: [/quote] there's a little confusion here I think. the capacitor on a mains switch is there to prevent arcing and to suppress rf interference, you use a very low value to short out high frequencies and to present an open circuit or very high resistance to the 50Hz mains. If you want to use this circuit the capacitor needs to be a very high value as in this case it is being used to store charge from the battery and smooth out the peak to the pre-amp on switch on. Basically on switch on the resistance of the capacitor is low and all the battery current flows into this, as it charges the resistance rises and so will the voltage to the pre amp which will then switch on gently. This could present a problem, the capacitor is effectively shorting the battery when you switch on, some batteries can't handle high current flows well and this may shorten their life. You could put a small resistor in line with the cap if this is a problem. I'd start with a much higher value cap, something like a 10uF electrolytic, make sure you connect it + to +. Quote Link to comment Share on other sites More sharing options...
Grangur Posted October 10, 2013 Share Posted October 10, 2013 Phil Starr - thanks I'm always happy to be corrected. If you can suggest a better position for the cap I'm sure the OP would like to know. (Me too) Cheers Rich Quote Link to comment Share on other sites More sharing options...
hamfist Posted October 10, 2013 Author Share Posted October 10, 2013 [quote name='Grangur' timestamp='1381419305' post='2238857'] If you can suggest a better position for the cap I'm sure the OP would like to know. (Me too) [/quote] I certainly would still be interested. I have currently paused in my quest for silence for this switch, but it would be nice to perfect it at some point. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted October 12, 2013 Share Posted October 12, 2013 [quote name='Grangur' timestamp='1381419305' post='2238857'] Phil Starr - thanks I'm always happy to be corrected. If you can suggest a better position for the cap I'm sure the OP would like to know. (Me too) Cheers Rich [/quote] Sorry I think I may have created more confusion. If you want to put in a high(ish) value cap to smooth out the power supply to the pre amp this circuit is spot on. This is exactly the place to put the cap. The confusion I was referring to was over the value, so far the only value suggested was a 0.1uF connected across the switch terminals which would suppress switch noise in an AC circuit but is too small to smooth the DC voltage. Quote Link to comment Share on other sites More sharing options...
Grangur Posted October 15, 2013 Share Posted October 15, 2013 If you're still interested in an answer to this, try mailing Kiogon of this parish. He's your top man on this subject Quote Link to comment Share on other sites More sharing options...
BanditSid Posted October 15, 2013 Share Posted October 15, 2013 (edited) [size=5][sup]The thump you are hearing is the pre-amp circuit powering up, in particular the capacitors on board reaching operating voltage. Adding a capacitor across a switch is a common fix for switch induced noise, but since that isn't the problem it will only add to the thump noise. There's not a simple fix for your problem, the only way to really fix it is to short the output for a fraction of a second, something a lot of power amplifiers do for the same reason.[/sup][/size] Edited October 15, 2013 by BanditSid Quote Link to comment Share on other sites More sharing options...
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