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 !!!
I'm not an owner, but I took a look at the manual for the 06X Phono Stage at their site. It is indeed very unclear, but I believe that your interpretation of the capacitance settings is correct, and that the interpretation of the resistance settings is similar if we take into account the differences between how resistances in parallel and capacitances in parallel combine.

Capacitors in parallel simply add together, but that is not the case for resistors. Resistances in parallel combine as the reciprocal (the number divided into 1) of the sum of their individual reciprocals.

So with all of the resistance switches in the off position, you would get 47K (47,000 ohms). With the 22 switch on, you would have 22 ohms in parallel with 47K, which is 22 ohms to a very close approximation. With the 47 switch on, you would have 47 ohms in parallel with 47K, which is 47 ohms to a very close approximation. Likewise, the 100 and 1000 switches would give you very close to 100 ohms and 1000 ohms.

If you have more than one resistance switch in the on position, as I said resistances in parallel combine as the reciprocal of the sum of their individual reciprocals. So if you have the 22, 47, and 100 ohm switches on, the overall resistance would be:

1/(1/22 + 1/47 + 1/100 + 1/47000) = 13 ohms.

An equivalent but sometimes simpler way of doing the calculation is based on the fact that if exactly two resistances are in parallel, the formula for their combined resistance corresponds to the product (multiplication) of the two numbers divided by their sum. If more than two resistances are in parallel, you can calculate the value of the overall combination by finding the combined resistance of any two of them using the product/sum formula, then taking the product/sum of that result with a third resistance, etc.

-- Al
Hi Al,
thanks for responding. I feel that the manual should go into detail for anyone who has not used these switches before. I do not really understand your explanation, so lets take your first example.

"With the 22 switch on, you would have 22 ohms in parallel with 47 K, which is 22 ohms to a very close approximation."

Could you please let us know what this statement means and also how it may relate to the math formula ? in other words, are you saying that with the 22 ohms switch on that it over rides the 47 k and just becomes 22 ohms (and not 22 K)? I am really confused. But I have confidence you can help us understand. and the "to a very close approximation" phrase is also confusing to me as to what this phrase really means.

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
Thanks Al,
Now I can re-calculate and you have helped me to be able to do that! Thanks loads,
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.