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F5 V3.0 Help with Hum Issue
F5 V3.0 Help with Hum Issue
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Old 22nd February 2019, 01:27 PM   #11
TheNuge is offline TheNuge  Germany
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Quote:
Originally Posted by mpmarino View Post
What is this wire? Probably better to ground it outside of the toroid regardless.

I'm not sure what the wire is exactly - my Polish is somewhat lacking - but I think it's a shield.
I did try disconnecting it, but that didn't help...


I'll open up the amps in the next couple of days and see what can be done!


Thanks for all the input guys!


Es
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Old 28th February 2019, 02:15 PM   #12
jphabc54 is offline jphabc54  United States
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I have an almost identical build with the exact same issue, though my hum is considerably louder coming out of the channel on the left side of the attached picture. I quickly tried adding a 10R resistor between the input RCA jack ground and input wire screen on that louder input. The result is that hum on the side with the resistor is louder, but the hum in the other channel is completely gone.

Since initially building the F5, I have replaced the transformer, soft start, and diodes; but havenít made any progress in eliminating the hum. I donít think anything was wrong with the originals.

That said, I now have everything I need to migrate to a dual mono PSU, which I am thinking of putting in a separate chassis.

Iíve inspected every angle of the louder humming channel (again, left in this picture) but I canít see any bad solder joints or anything suggesting itís not wired identically to the other channel.
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Old 2nd March 2019, 04:27 AM   #13
astromo is offline astromo  Australia
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Quote:
Originally Posted by TheNuge View Post
I'm not sure what the wire is exactly - my Polish is somewhat lacking - but I think it's a shield.
I did try disconnecting it, but that didn't help...


I'll open up the amps in the next couple of days and see what can be done!


Thanks for all the input guys!


Es

I'd expect that it's the transformer's electrostatic shield earth wire. Ensuring that you've got a "Star Ground" earthing arrangement reputedly helps to avoid hum.


Info like this could possibly help:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
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Old 2nd March 2019, 07:19 AM   #14
TheNuge is offline TheNuge  Germany
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Thanks for the input guys!
I haven't gotten around to looking into it yet, but possible this weekend...
Cheers
Es
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Old 5th March 2019, 04:32 AM   #15
TheNuge is offline TheNuge  Germany
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Hi again,
I'm going to try star-grounding the amp in the following way (unless you guys tell me otherwise):
Star Ground point will be a post isolated from the housing using a CL-60 thermistor. This post attached to:
1. PSU board ground
2. F5 board grounds
3. Speaker negative posts
4. Input terminal grounds.
All using equal length wire.

The inputs signal tabs will be connected to the boards with coax wire, with the shield only attached at the board end.

Will that work in theory?

Cheers
Es
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Old 11th March 2019, 04:45 PM   #16
cviller is offline cviller  Canada
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I would probably do a bit more testing before rewiring the whole thing - your wiring looks quite clean and it would be a shame to waste a lot of time if the issue is somewhere else.

Few questions:

Is you green/yellow wire going straight from the EIC to gnd on psu and chassis? You may have a ground wire loop with your preamp. Common solution is to use a bridge between psu gnd and chassis.

Have you tried different sources, preamps etc? I like to test with a phone/ipod (battery operated) straight into the amp with no preamp - might be a good idea to use test speakers. Also try with one channel at a time with the other shorted.

Twist your wires, especially output and input (separate twists).
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