Finally getting around to reporting back...
0.01uF ceramic disc capacitors from the input RCA to ground lugs helped but didn't solve it.
Bundling the interconnects to/from the phono pre with some zip ties changes the antenna effect and reduces the FM intrusion. This is a relatively significant improvement.
Ferrite beads on the turntable>phono pre interconnects knocked out what remained.
0.01uF ceramic disc capacitors from the input RCA to ground lugs helped but didn't solve it.
Bundling the interconnects to/from the phono pre with some zip ties changes the antenna effect and reduces the FM intrusion. This is a relatively significant improvement.
Ferrite beads on the turntable>phono pre interconnects knocked out what remained.
"Ferrite beads on the turntable>phono pre interconnects knocked out what remained."
A photo please...
A photo please...
I had an issue with one specific tube amp (A Wilsenton R8) picking up a radio station when using my EAR834 clone and moving the turntable ground wire around would change the "reception". Turned out the grounding inside the amp was very poorly laid out and fixing the amp grounds to a good star ground system resolved the issue.
I still wonder if there is a fundamental grounding flaw. My turntable ground doesn't impact the issue though. I've looked at my ground a lot and can't spot a problem. It all grounds to a single point on the power supply and then to the mains socket. The chassis then also grounds to the mains. It's under control now but I still feel like something is not right.
Like I was saying, mine turned out to not be a problem in the preamp, but in the amplifier it was feeding. Did you try the pre-amp with a different amp to see if the problem was still there? Also some models of turntables don't really "Main ground" through the ground lead but ground through one of the RCA cables negative shield.
We usually can't do much about the detection (conversion to audio) of radio signals, so we have to work to make ourselves poorer antennas. As rayma mentioned early on, enclosing both signal conductors, hot and return, together in a separate non-signal-carrying shield is a great first step. We usually cheat and use the shield for signal return, but it can (has!) bite us on the posterior. Shield from phonograph to preamp should connect at the preamp end (only) to chassis ground. Microphone cable works great for this gig.
To minimize standing waves on the cable, add a Zobel of 75 or 100 Ohms in series with 100pF (COG/NPO disc) directly across the input jacks, or across the board's input terminals if proper internal wiring is used, to terminate the cable's characteristic impedance and thus reduce voltage peaks. Proper interior wiring to and from the board to jacks would be two conductors together in a shield (braid is fine). I'd start with these shields connected near the jacks (only). At FM frequencies these are not just wires; they're antennas, and grounds are not grounds; they're inductors and antennas. We often get away with a lot of sloppiness, but you don't have that luxury at your location.
Might help to exchange all line level interconnects with something besides simple coax - again, both conductors inside a shield which is only a shield. RF gets in everywhere. Folk are sometimes surprised by how much better things sound when properly shielded, even when nothing was obviously wrong before the change.
All good fortune,
Chris
To minimize standing waves on the cable, add a Zobel of 75 or 100 Ohms in series with 100pF (COG/NPO disc) directly across the input jacks, or across the board's input terminals if proper internal wiring is used, to terminate the cable's characteristic impedance and thus reduce voltage peaks. Proper interior wiring to and from the board to jacks would be two conductors together in a shield (braid is fine). I'd start with these shields connected near the jacks (only). At FM frequencies these are not just wires; they're antennas, and grounds are not grounds; they're inductors and antennas. We often get away with a lot of sloppiness, but you don't have that luxury at your location.
Might help to exchange all line level interconnects with something besides simple coax - again, both conductors inside a shield which is only a shield. RF gets in everywhere. Folk are sometimes surprised by how much better things sound when properly shielded, even when nothing was obviously wrong before the change.
All good fortune,
Chris
Morning properlydeafened.
If you completely bypass the phono preamp and plug your turntable directly into amplifier do you still have an rf antenna?
If you completely bypass the phono preamp and plug your turntable directly into amplifier do you still have an rf antenna?
Some notes on internal "grounding" schemes:
UL code requires protective Earth (PE) to have its own dedicated (no other connections) chassis connection (from the IEC input block in this case) with its own bolt, star washer and nut.
The best place (usually, and in this case) to chassis ground the signal "ground" is nearest the circuit board's (PCB's) inputs. Ideally, run a separate wire from PCB inputs' common signal ground to chassis right near the input jacks. Have no other connection between signal ground and chassis. Power supply B+ return should connect to PCB near the output end of the signal path (usually, and probably in this case). It and B+ hot can be a twisted open pair or both conductors together in a common shield, which would connect to chassis near the PCB end.
If we think about things in terms of current flow, and cancellation of fields by conductor pairs really near each other, a lot of Best Practices voodoo becomes obvious and easy to understand.
All good fortune,
Chris
UL code requires protective Earth (PE) to have its own dedicated (no other connections) chassis connection (from the IEC input block in this case) with its own bolt, star washer and nut.
The best place (usually, and in this case) to chassis ground the signal "ground" is nearest the circuit board's (PCB's) inputs. Ideally, run a separate wire from PCB inputs' common signal ground to chassis right near the input jacks. Have no other connection between signal ground and chassis. Power supply B+ return should connect to PCB near the output end of the signal path (usually, and probably in this case). It and B+ hot can be a twisted open pair or both conductors together in a common shield, which would connect to chassis near the PCB end.
If we think about things in terms of current flow, and cancellation of fields by conductor pairs really near each other, a lot of Best Practices voodoo becomes obvious and easy to understand.
All good fortune,
Chris
@Chris Hornbeck are you
I have a dedicated IEC>chassis ground connection. You can see it the second picture I posted (post #10)
From the beginning I've been a bit confused about how signal ground is setup on this board. For sure though...there is NOT a signal ground to chassis ground connection near the inputs. And saying that out loud...it stands to reason that this RFI problem is traversing the entire circuit as a result.
Hang on...so are you saying I should ground the RCA inputs for the turntable to chassis ground?
I have a dedicated IEC>chassis ground connection. You can see it the second picture I posted (post #10)
From the beginning I've been a bit confused about how signal ground is setup on this board. For sure though...there is NOT a signal ground to chassis ground connection near the inputs. And saying that out loud...it stands to reason that this RFI problem is traversing the entire circuit as a result.
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Why it has that metal foil on the inside ? If the case is not from metal the issue is clear ... we had discussions before about a wooden case picking hum .
Correctly build EAR834 clones don't have such issues.
Correctly build EAR834 clones don't have such issues.
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For the output long wires I would use shielded cable . I don't say that this is the cause but ...
I agree, I've ordered some. I don't think it's the primary cause either, but it wouldn't hurt. I think the signal>chassis ground mentioned by Chris above is probably the answer.
Chassis should be connected to star ground in the power supply , anyway such changes could be important for reducing hum a bit , nothing major , picking FM radio is very unusual . As was said maybe the power amplifier is prone to this issue .
And don't forget to use good quality cables for input to turntable , if everything is shielded as it supposed to be , I don't see how is possible to pick a radio station in the first place .
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It's not the power amp or the turntable. I have several power amps and a couple of phono preamps. It's definitely this EAR clone. The cable from the turntable to pre is Belden 1694A...so it's shielded. The RFI at my location is severe. For example the cable internet company came to my house several years ago b/c they thought a bad connection was leaking noise into their infrastructure. The tech that came out ultimately determined that it was all external noise and he said it was some of the worst he's seen.
Anyway.... I think the issue with the EAR is that I need check the signal to chassis ground.
Anyway.... I think the issue with the EAR is that I need check the signal to chassis ground.
What I'd really recommend is to have both signal conductors separate from shield, and shield be connected to phono preamp chassis (only) near input jacks. The important bit is to not have signal return on the shield. Yes, this is done all the time, and no, it's always wrong. Ordinary situations let us cheat, but your location is not ordinary.
I'm seeing another green wire traveling away at 10:00, but can't see where it's going. Wherever it's going it's likely causing a ground loop, and in any case is not UL code, which requires one connection from PE to chassis.
Star grounds are a fiction if examined too closely, and at RF are significant inductors and antennas between various signal "grounds". They trade a zero impedance common point for significant impedances getting to and from that point. Works at low frequencies but poor at RF. Not even really great at audio frequencies.
All good fortune,
Chris
The star ground and safety earth to the chassis are grounded at the IEC socket. The turntable ground lug goes to the star ground point. I now understand that's wrong and I need to move the star ground and TT ground both to the chassis. Here's a pic with labels.
And I understand what you're saying re: shield. I'm waiting on some wire to arrive and my plan was to replace the input/output wiring and ground the shield to the chassis near the input.
And I understand what you're saying re: shield. I'm waiting on some wire to arrive and my plan was to replace the input/output wiring and ground the shield to the chassis near the input.
Or maybe TT ground should stay at the star point but definitely the star ground needs to move off the IEC to the chassis near the safety ground point.