resistor loading question/RM5

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Photon46

resistor loading question/RM5
« on: 22 Jan 2008, 12:19 am »
Roger, I was reading the Stereophile review of the RM5 from April 1990, and I noticed that you installed some quick change mounting posts for the phono loading resistor in the example you sent RH. Is this something that is still posible to do and if so, does it compromise sonics over the usual solder installation? Is this something I can install myself (RM5III in my case) or is it something you'd need to do? Thanks.

Roger A. Modjeski

Re: resistor loading question/RM5
« Reply #1 on: 25 Jan 2008, 05:05 am »
We can do that here or you can install jacks yourself if you are good with a drill. We have nice gold jacks for $15 a pair plus shipping, 8 pair for $100 for those of you who want some nicely made jacks at a reasonable price.

The process is a simple one. Make sure the body of the jack makes good connection to the chassis by scraping away the the anodizing around the edge of the hole. The hot of the loading jack is tied to the hot of the existing phono jack. This can be done to any preamp, it's quite simple. As long as the jack is near the existing phono jack and of reasonable quality there is no degradation of sound and the possible improvement of a different load. If all loading is below 47K the existing 47K resistor can stay on the board. If you are working below several K ohms it will make little difference to the total load.

The formula for parallel resistors is: 1/R total= 1/R1 + 1/R2. If R1 = 47 K the parallel resistor, R2, will be 1/R2 = 1/47,000 - 1/R desired. If the desired load is 10,000 ohms the parallel resistor will be 12,702 ohms. Don't sweat the exact value, 12 K or 13 K will do just fine. Those of you who have a Hewlett Packard Reverse Polish calculator (yes, that's the official name) will find this can be done in about 5 strokes.

Roger