Roberts 770 Mic Pre - Not Enough Gain?

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timjimbaker
audio school
Posts: 6
Joined: Sun Aug 29, 2010 6:24 pm

Roberts 770 Mic Pre - Not Enough Gain?

Post by timjimbaker » Wed Aug 29, 2012 9:36 am

Hello. I racked up a Roberts 770 as per Rod @ beyondsanityproductions.com instructions... Thanks Rod! Big ups!

The 12ax7 DI side is working great. Quiet and tons of gain. It is the ef86 mic pre that is giving me a bit of grief. It seems like I'm not getting as much gain out of the ef86 as I should be. I tried a few different input transformers. The current I am using is from a shure m68 mixer. None of the input iron I tried made much of a difference in increasing the gain of the ef86.

The mic pre section is also humming quite a bit. I've moved the wires around try to reduce the hum to no avail. I imagine both of these problems are pretty common, any suggestions on how to fix either problem would really be appreciated.

Best regards,

Tim

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