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Need help on changing loading on phono

I am using ARC SP8 (built-in MM phono) and also a tube headamp for my low output cartridge. I have just changed the loading from the standard 47K ohm to 150 ohm on the SP8 to get less forward sound. After the change, I noticed the the volume would go from minimum to a certain level and then remain at the same no matter how high I turn the volume knob. I then tried it with just the SP8 MM phono without the headamp, it works. But, when I used it with the headamp, it didn't work. This obviuosly works if I only use the SP8 MM phono and not together with the headamp for the extra gain. Is there any thing I could so it would work with the headamp? Or, should I have changed the loading on the headamp instead of the SP8? Many thanks in advance.
blptwp
albertporter's avatar
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albertporter
4,949 posts
 
Blptwp. Your phono cartridge should see the 150 Ohm load. This means moving the resistor into the head amp. The way you have it now the head amp is trying to drive a 150 Ohm load into the ARC, and the cartridge is still seeing the original factory setting.

Putting all this right should make the phono cartridge more linear in bandwidth, while lowing distortion. The volume should behave as before once the ARC is returned to normal.

Hopefully you checked to verify that 150 Ohms is the correct load for you particular cartridge. The requirement is different for almost every brand and model. Please let us know how this works out for you.
blptwp OP
40 posts
 
Albertporter. This is the second time you offered your expert opinion on my problems. I appreciate very much. I removed the resistors from the SP8 and I checked the loading on the headamp, guess what? It has already been changed to 150 ohm, I guess by the previous owner. So, everything back to normal. Thanks again.
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