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  1. #1

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    Default Ground loop on Digital RIAA setup

    Hi all,

    I'm trying to isolate a ground loop. My setup is a little unorthodox, so please bear with me. I've been spending a lot of time on this project and I'm so close, I just need to figure out a course of action from here, and I really appreciate any guidance.

    Here's a lot of detail.

    The 60hz noise is barely audible at full gain, but there is a lot of energy in the LF right now.

    My friend used a high quality FFT analysis of our two different units "at rest"; his has a lot of noise in the upper ranges (he thinks due to Firewire and his preamp).

    Mine:



    His:



    I have explained the setup and signal chain above (other thread) but to recap: Grado (balanced wiring)>AEA TRP ribbon pre>Lavry AD-10>Toslink>EMU1212M

    All power for the AEA and all my DACs and PC are on transformer isolated power outlets of my Panamax conditioner and behind a Brickwall power unit.
    I covered the tonearm wiring (coax config: shield is - and inner covered wire is +) with some 89259 braided shield. This shield covers both wires (all tonearm wiring as it comes out of chassis) and terminates on the chassis of the tonearm on one side and to EACH Pin1 of the mic-pres two mic inputs. When I float the shield at the tonearm chassis more noise seeps in; I'm considering lifting on of the pin1 XLR connections to see if that is causing a problem. Maybe I should lose the shield altogether?

    I can make the ground loop "lessen" by almost 10db by touching the XLR barrel (any of them) and then touching the barels on the other unit or by touching a barrel and then with the other hand, the giant slab of marble atop my audio rack (but the above analysis includes this grounding).

    Should I run a wire out to my home's Earth ground outside and connect this to the pre of AD10? But why so much LF noise even after my faux grounding that drops the 60hz to inaudible levels even when my main audio preamp is maxed out to my speakers.

    thanks,
    Jonathan

  2. #2

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    Default

    Quote Originally Posted by doctorcilantro View Post
    ...My friend used a high quality FFT analysis of our two different units "at rest"; ...
    Very thorough--I'm assuming the analysis was done on a PC? How or what was used to get it there? A mic? Just curious as I've been interested in trying to record my setup before and after an XO cap upgrade-I wanted to see if I could see a difference.
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  3. #3

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    Default

    No mic. I know this post is a bit haphazard; sorry about that. This is direct from Grado Reference phono cartridge>AEA TRP ribbon preamp>LAvry AD-10 analog to digital converter, recorded by Samplitude at 32bit float/96kHz.

    Gotta make some food for the boy....

    DC

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    Lift every AC ground and see what happens-pre, amp,PC, DAC everything. Also I assume you double checked the connections at the cart and polarity is correct. If there is a DVD player connected to the pre and to a TV with cable or SAT disconnect it from the pre. Disconnect the network cable from the PC. Good luck.
    Last edited by awe-d-o-file; 09-18-2008 at 04:14 PM.


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