What phono stage?
7 responses Add your response
I use to own an ARC SP6B many years ago.It is factory set at 47k.What is the output of your cartridge in Millivolts?
If its 2.5Mv or lowere you may need to purchase a pre-preamp to get sufficient output.I used a Music Reference head amp to output my moving coil that needed the 100 ohm load.
If you have very specific questions that need addressed I would contact Lenord at ARC.He is very knowledgable of all the classic ARC pieces and he will gladly assist you over the phone.He has helped me several times and is a kind soul.
I don't think on this preamp you have provisions for changing resistor values internally.
The 6B will not run your Helikon, you need a step up. There is a switch on the back to change from 54 to 6_ gain. But it still is not enough and the higher gain setting is very noisy. It was designed for moving magnets. The 47k is part of the design and isnt meant to be changed like in a moving coil stage.
The phono stage of the ARC SP-6B was designed for MM, not MC. It is not a resistor loading problem. It just doesn't have enough gain to use with the Helikon. There are two ways to solve this. (A) You can connect a separate MC phono stage to the SP-6B AUX input. Or (B)front-end the SP-6B phono input with a step-up transformer. Since the phono stage of the SP-6B is really very good if you have good tubes, I would go with option B.
Hope it helps.
Thanks all for the feedback, here is an update: I spoke with Lenard at ARC-the preamp is factory set for 49.9k ohm, having resistors soldered onto the board. Adding resisters in parallel accross the rear of the RCA jacks is not a problem. Based on extreemly beneficial phone support from Ngarch (thanks Neil!), I experimented with various resisters ranging from 100 ohm to 225 ohm and settled on 163 ohm, providing fair deeper and tighter base and much much sound staging air and presence. As gain goes, the Helikon is doing a fine job without additional step up.