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Help! Negative Feeback Switch Popping!

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5/10/2003 7:30 PM

Help! Negative Feeback Switch Popping!

Hey there,

Darn, I thought I had this one figured out but I guess not! This is the second try for me on getting a three value negative feedback switch in my amp that does not pop when switched. Here's my latest failure schematic:

http://home.attbi.com/~frostamps/wsb/media/157771/site1013.jpg

I'm using one DPDT On-Off-On switch for it. Previously, I tried a parallel type arraingement which always had one resistor in the signal line. Here's its schematic:

http://home.attbi.com/~frostamps/wsb/media/157771/site1014.jpg

If anyone has any suggestions or input, I sure would appreciate it. Thanks,

-Heiko Frost

5/10/2003 11:06 PM

Heiko:

    Were you getting pop(s) with the first arrangement, too? Also, are you getting pops each time you flip the switch, or only between certain positions?

    I guess the 1M position is essentially no NFB- right? And that you put the resistor there to keep the switch from popping? Have you tried a 470k resistor there instead?

    One other thought is to try using a shorting-type 3 position rotary switch. You might try that temporarily just to see if it eliminates the popping.

--Good luck!

Steve Ahola

5/11/2003 12:46 AM

Hey there Steve,

I'm getting popping with both schematic setups. As my chassis is drilled for a miicro toggle switch, I'd rather not have to resort to a shorting rotary setup. I even just tried running 3.3M resistors to ground at each of the junctions between the negative feedback resistors like they do on tone control switch arangments (ala Dumble) but that popped too! What to do, what to do...

5/11/2003 12:38 AM
Chuck	Hi Steve stole my suggestion of using a shorting switch, thats a good place to start. My other idea would be to use a big ass capacitor prior to the switch bridged over a "standard value" resistor. I don't know how to do the impedance/capacitance math but I should think one of those big Solen poly caps rated in the 10s of microfarads should bypass all the audible frequencies. Good luck. Chuck

5/11/2003 3:45 AM
Heiko Frost	Hey guys, I just quickly rigged up a shortening rotary switch with the resistors in series but that pops just as much! Does no one else have this problem? Very, very confusing?! -Heiko

5/11/2003 5:22 PM
Chuck	You can still try the big cap in parallel with a standard value resistor. In fact, if you do it this way you can have a variable NFB pot instead of a switch. Finding the sweet spot will be cake after that. You can even locate it at the tail of the PI like a presence control. All you need is a big enough cap to bypass all frequencies. Chuck

5/11/2003 4:01 PM

heiko, i'm really surprised to hear about the shorting problem in your latest design. when you emailed it to me (thanks again, btw) i was convinced that it had to be the most clever wiring solution i've come across.

did you try that parallel method that i suggested earlier? i haven't gotten to it yet, but my thought was that it would avoid popping because the high value resistance would always remain in the circuit.

bob

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