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Threshold Coda Phono Stage Toggle DIP Switches

For Threshold Coda Phono Stage owners there are Toggle DIP Switches which turn out to be more complicated than meets the eye. I need some help with interpreting them. The manual does not go into detail.

Pico Farads I now understand that default is 50, and rather than toggle the 50, 100, 200 and 1000 for those particular values, it turns out that that is not how it is intended. Those 4 values are values you ADD to 50 pF to get the desired pico farads. so start with 50, add 50 switch yields 100 pico farads altogether.

but the 4 impedance switches have me stumped. how do we interpret 22 ohms, 47 ohms, 100 ohms and 1000 ohms toggle DIP switches with a default setting of 47 K (and notice it says 47 ohms on the switch, not 47K) :) HELP !!!
128x128bluelight988
almarg's avatar
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almarg
9,670 posts
 
The "very close approximation" statement reflects the fact that for resistances in parallel, if one resistance is MUCH higher than the other, then their parallel combination as calculated with the formulas I described will be approximately the same number as the lower of the two resistances.

For the example you cited, using the reciprocal of the sum of the reciprocals formula (which applies to the parallel combination of any number of resistors):

1/(1/22 + 1/47000) = 21.9897 ohms.

Using the other formula I described, which applies to the specific case of exactly 2 resistors in parallel, gives the same result:

(22 x 47000)/(22 + 47000) = 21.9897 ohms.

21.9897 ohms is "to a very close approximation" equal to 22 ohms.

It's not that the 22 ohms "overrides" the 47K, it's that (based on the formulas) 47K becomes an insignificant contributor to the overall resistance when paralleled with a MUCH lower value.

Best regards,
-- Al
bluelight988's avatar
bluelight988 OP
8 posts
 
Thanks Al,
Now I can re-calculate and you have helped me to be able to do that! Thanks loads,
Ted
taam
14 posts
 
I would email the company whose product it is. I have gotten fast responses and correct information on my 30 year old Threshold Amp. They are a great company and will be more than willing to help.
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