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Help with phono cartridge loading/ARC SP6B preamp

My new Lyra Helikon has a recommended load between 100 and 47k ohm, and as I'm running it directly into my phono stage (no step up needed) I have been listening during the break in period without load. I assume my preamp is factory set at 47k ohm, do I have to remove the factory load resistors prior to installing the new load resistors (100 ohm or more)? If so, can anyone tell me where these factory installed resistors are located? A quick search of the preamp indicates they are not soldered to the RCA terminals where I plan on installing the new load resistors so they must be soldered directly to the circuit board? Can anyone with Helikon ownership experience suggest the ideal load? Thanks!
badboss429
7 responses Add your response
dougdeacon
3,338 posts
 
What phono stage?
76doublebass's avatar
76doublebass
254 posts
 
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.
shasta
155 posts
 
Don't you have an owners' manual? If not, consider obtaining one from ARC to answer all your Q's.
linnlp12
79 posts
 
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.
sidssp
1,077 posts
 
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.
dougdeacon
3,338 posts
 
Badboss429,

Sorry for missing the info in your thread title, duh.

At any rate, I agree with the responses above. To run a Helikon you'll either need a stepup (which would also adjust the impedance) or a phono stage designed for LOMCs.
badboss429 OP
21 posts
 
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.
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