How to switch input caps

[spargo]

Hi, I have a circuit where I'm trying to install a SPDT (On/On) switch to switch between two different input capacitors.

I currently have the input signal going to the center lug, and the left and right lugs going to the respective capacitors and returning into the signal path.  One side of each capacitor is hooked to one side of the switch, and the other side of the caps are connected to each other back into the signal path.

When I have the switch one way, it works.  The other position of the switch does not work and just produced a very loud hum.  Any idea what the problem is?  Thanks!

[makaze808]

Try changing switch or cap.

[jkokura]

Either the switch is bad, or the cap is bad, or the soldering connection is bad. I believe it's usually the last, then the switch, then the cap.

Jacob

[spargo]

I tested the continuity of the switch, and it appeared to be faulty (one position worked but the other was dead), so I grabbed another SPDT switch and tested it before soldering leads to it.  It tested fine.  Then I soldered wires to it and it has the same problem as the others.

Do you think it's possible it's getting too hot and killing the switches?  They are very difficult to solder - I have to solder the wires parallel to the leads because the holes are really small, smaller than 26 guage.  I got them on ebay from Hong Kong.  Maybe cheap switches?  Are they normally easy to solder?

[petemoore]

  If/when the switch fails the circuit still defaults to a value of capacitor [ie it'll still work].
  put a *DC blocking cap in the PCB [the large, selected *uf value for 'fat' setting].
  Put another cap 'into' [cut/splice] the input cap wire from *PCB.
  Since two capacitors in series is a smaller uf value than *1 this added capacitor will be selected for 'thin' sound.
  With each side of the spliced in capacitor having a wire attached, mounting this to an SPST switch jumpers the capacitor for 'fat', opens the switch for 'thin'...whif the switch breaks 'thin' works.
  Alternatively:
  Same basic thing for paralleling 2 input caps to achieve two uf values, except parallel capacitors makes a larger sum Uf value. ie wire the input as shown with 1 capacitor, parallel a capacitor through an SPST switch for 'fat', switch breaks and 'thin' works.
   

[jkokura]

I tested the continuity of the switch, and it appeared to be faulty (one position worked but the other was dead), so I grabbed another SPDT switch and tested it before soldering leads to it.  It tested fine.  Then I soldered wires to it and it has the same problem as the others.

Do you think it's possible it's getting too hot and killing the switches?  They are very difficult to solder - I have to solder the wires parallel to the leads because the holes are really small, smaller than 26 guage.  I got them on ebay from Hong Kong.  Maybe cheap switches?  Are they normally easy to solder?

I've largely gotten my switches from smallbear. I've never had the problems you've having. I don't know if the ones you've got are less durable, but if you're using a normal amount of heat, and trying hard not to burn them out, I can't imagine that it would be easily done. Do you have a third?

Jacob

[petemoore]

  Shaped, tinned leads.
  Pretinned lug.
  Hot, Cleaned, medium-weight-tinned iron.
  Pre-prepared excellent positioning for steady, precisely controlled approach / contact / lead-hold>tip retreat.
  Position the wire lead and practice the touch and hold in position movements while dry and cool [alternatively..if lead is cleaned and lead is placed in lug-hole, somehow fixed in place], use of angle-needlenose pliers or other wire control device such as clampable tweezers may help here, positioned on a pivot point on the box or otherwise having x-axis fixed]. Practice pinning/not bending the wire.
1 touch iron to tinned lead that is in position over the lug
Within about 3 seconds:
2 touch the pre-heated, heavily tinned lead and iron tip to the switch lug.
  Because the solder is all fresh it flows' more easily, the internal portion of the switch is only exposed to low enough temperatures because the thermal conduction takes time. 
  I use XXBlack resistors all the time as 'leads' because:
  of no personal no cares about say 47ohm resistance here and there [such as where a 1k already is],
  I have nothing else to use 'em for.
  They make easy to handle leads for finer work.
  They can hold shape.
  I like installing cleanly a thermal resistor on my switch lug, 1 time, then I'd tire before the internal 'damage temperature' was reached.
  The make easy 'put a bit of insulator right there, making de-insulated wire bundles at switch...well...it's an art, think through...quick heat on the switch lug does it, may take a switch or two...and a cold solder too.
  Let the switch lug cool between heatings.
  By making everything 'freshened up' [solder/materials wise] the heat time becomes more predictable.
 

[CynicalMan]

I used to order my switches from Hong Kong on ebay, but I order them from small bear now. The Hong Kong switches are fragile and poorly built compared to the small bear taiway switches. I've had them fall apart just by tightening them onto an enclosure.
Also, it sounds like you have submini switches. Miniature switches are easier to solder too and they're probably more resistant to heat damage because they're bigger.