F5 - is normal ICs twist out the Hum? - Page 2 - diyAudio
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Old 29th November 2012, 10:47 AM   #11
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I've done everything, and I'm about to give up.

This hum is not a problem ground, turned off the ground while doing the experiments, the ground on or off is equal.

The problem is mass, with everything turned off and only the F5 on the speakers as makes no hum, just connect the ICs that starts right tinnitus.

I used many ICs, directional unshielded at the destination, the unshielded source, etc, etc.. and nothing, always that little hum.

I am forced to think that the problem lies in the components, or 400VA toroidal Sedlbauer of Conrad, or PCBs in the channels or the PSU pcb (Jim Audio).

The AC input wires are shielded by the toroidal.

I wonder why he only hum when I turn the ICs with the same pre Rotel off

I have exhausted my wisdom.
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Old 29th November 2012, 10:59 AM   #12
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If you´re sure the grounding is not the problem (i can see that left side signal ground goes through right side amp to ground).

Try shorting the signal in right at the cards (solder a wire across in and ground).
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Old 29th November 2012, 02:34 PM   #13
Zen Mod is offline Zen Mod  Serbia
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there is no other way than to post good pics of PSU board , both sides

now I remember that we already solved some problem with similar pcb , in some thread
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Old 29th November 2012, 02:41 PM   #14
AndrewT is offline AndrewT  Scotland
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From Blink's description it sounds like the ground loop is in the interconnects link to the amplifier/receiver.
If the Source has a common ground point for the two output phonos and the receiver also has a common link between the two input phonos, then there MUST BE a ground loop.
That loop requires that the route have a current reducing resistance inserted to minimise the voltage appearing along the interconnect return wires.
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Old 29th November 2012, 02:46 PM   #15
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Short the inputs right at the boards.

No hum = ground issue between amp and pre or hum pickup in signal cable.

Hum = grounding or PSU issues in amp.

That it should be component issues in both channel is not likely.
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Old 29th November 2012, 05:55 PM   #16
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Quote:
Originally Posted by AndrewT View Post
From Blink's description it sounds like the ground loop is in the interconnects link to the amplifier/receiver.
If the Source has a common ground point for the two output phonos and the receiver also has a common link between the two input phonos, then there MUST BE a ground loop.
That loop requires that the route have a current reducing resistance inserted to minimise the voltage appearing along the interconnect return wires.
That's exactly what happens.

With F5 only on the speakers as no hum (without interconects connected).

I have been to confirm and all the RCAs Rotel have common mass.

When I turn to only one pre interconnect (Rotel RA-1520) there is no hum, turning on the 2nd there appears hum.

If you turn off one interconnect the hum disappears. I listen to music in stereo, of course.

I'll put the pics of the PSU.

When solving this hum, I'll open a bottle of champagne.

Did the voltage on the output DC to AC multimeter scale and each channel has +- 0.012V, I think the PSU is okay...


Click the image to open in full size.


Click the image to open in full size.

Last edited by Blink_PT; 29th November 2012 at 06:02 PM.
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Old 29th November 2012, 06:04 PM   #17
Zen Mod is offline Zen Mod  Serbia
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did you tried that fat wire bridge ?
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Old 29th November 2012, 06:11 PM   #18
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Quote:
Originally Posted by Zen Mod View Post
did you tried that fat wire bridge ?
Yes, soldered a fat wire between the GND left channel and the GND right, has the same hum, it seems that even a little longer.

I had already made ​​this connection before, now everything is standard.
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Old 29th November 2012, 11:32 PM   #19
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>> When I turn to only one pre interconnect (Rotel RA-1520) there is no hum, turning on the 2nd there appears hum.

At risk of stating the obvious, given the issue is with this particular preamp, why dont you just disable the input ground on one of the interconnects either in the preamp OR in the f5 amp.

Example:
left channel : Hot and Ground,
right channel: Hot only no ground.

Not ideal but if it works ....
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Old 30th November 2012, 02:38 AM   #20
omishra is offline omishra  India
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Okay, I faced similar situation in another amp, not F5. It was connecting both input grounds used to start hum while disconnecting either one input ground - no hum. Yes I agree its ground loop in input return path.

The similarity here is, PS used here is too having single floating ground. Simple solution which worked for me was - separate both input RCA ground from each other and chassis. Run them to the amp PCB input ground pad. Connect PS ground separately to each amp board and speaker output. This you have done correctly. Only problem I see input ground need to run separately till amp board.

Just for curiosity , does your preamp has zero resistance between grounds of both RCA?
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