F5 Ground Loop - Need Ideas..

Hello,
I believe I have a ground loop in my F5. It varies from day to day and ranges from almost totally inaudible to audible from 5-6 inches away from my hornspeaker (Cornscala). When only one RCA input cable is connected, the amp is dead silent (this is the same for both channels). When both are connected, I have a very slight hum/buzz. It just bothers me because I know how silent the amp is supposed to be.
I am about to do a couple of upgrades here in the next few days so I would like to fix the ground loop problem while I am at it. I connected a thick (15 ga) wire between the grounds of the two amp boards. This was advice given to me when I first built the amp.. This took care of about 50% of the hum..

Should my speaker ground wires be removed from the amp boards and soldered directly to star ground?

Also, should both the speaker binding posts and RCA input jacks be totally isolated from the chassis?

I am just trying to sort out what would be best for me, due to having dual-PSU with a single transformer.

Star Ground connections:


AMP GND=>PSU GND=>NTC Thermistor=>Star Ground<=NTC Thermistor<=PSU GND<=AMP GND
&
Earth Ground (From Mains)=>Star Ground<=Transformer Shield

I am biasing at .59VDC and have DC offset of extremely close to zero.

I drew out a diagram of my current wiring... I hope it is clear enough.

The F5 is the finest amplifier I have ever heard and if I get this ground loop fixed I will be extremely happy.

Please, any ideas will help. Thanks in advance!
 

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More Photos

Here are some more photos of the F5.. I also included a blank diagram if you would like to save it and draw wires the clearly illustrate a solution. I am hoping this will be an easy fix.

(I squeezed a couple photos of my Hot-Rodded DCB1 that is nearly completed)...
 

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Ok great, thanks for the advice. I will try using only one NTC, with both PSU boards connected. What do you think about moving the Speaker grounds from the amp boards and soldering directly to star ground (Speaker Ground=>Star Ground). Also, I have been looking at the various ways to connect the RCA input jacks. I am seeing some use a twisted series of 3 wires between RCA input and Amp board. Something about one of the wires is floating earth...?

The attached image shows a couple of ideas...? In bright green, I have traced the ground through the components and there seems to be what I would call a "loop". I remember reading about lifting one of the channels ground (from AMP GND=>PSU) and interconnecting the two amp boards ground. But by lifting that one channels ground, you have effectively removed the loop... In dark pink, I have connected speaker ground directly to Star Ground.. I don't see how this could hurt anything.. But, then again, I am far from a professional.

I don't have good DIY Audio vocabulary yet, sorry... I have been learning about electricity/circuits/diyaudio/speaker building/acoustics pretty much obsessively for the past 15 months and I have literally only scratched the surface.. I love it though..

I see there is some concern about my dual power supply with a single transformer and 4 bridge rectifiers.. Honestly, I was initially planning on going full dual mono with 2 toroids, etc. I went to order the second toroid from Antek and learned that their factory had burned down a few days earlier.

I got the idea for my configuration from the "Official" build guide for the diyAudio universal power supply. This configuration is used on a Honey-Badger amp.

From the build guide..
As you can see in the picture on the previous page, a couple of PSU Board PCBs were used to make a “dual mono” power supply. The advantage of this is better channel separation and independence, as well as an extra power reserve for those loud music passages that are completely separate for each channel. The “dual mono” configuration proved to be a better choice for me, using a single PSU Board will work of course, but the additional benefits of using a dual mono configuration were just too great for me to pass up!
This amplifier quite literally sounds better than any other audio component I have ever heard. Sometimes I wonder how it would even be possible for my ears and brain to hear something that is more satisfactory than the F5. Thanks Mr. Pass!

Anyway, thanks for the help up to this point. I have a good place to start now.

Be warned, I am going to keep this thread alive until my problem is solved. Hopefully one day I will be able to return the favor to a newcomer.
 

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What I would do is establish another star ground, isolated from chassis, that will be your "Main Audio Ground". Ground from each power supply board to this ground (fat wires). Ground from each amp board to this ground (fat wires). Ground from negative speaker posts to this ground (fat wires). All RCA's and binding post's definitely isolated from chassis. Twisted pair from each RCA to amp board (small wires). Single CL-60 from "Main Audio Ground" to your already established "Earth Ground". No other grounds. And I always do my earth ground the way it's shown at figure 3 with the star washers and everything: Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
 
in diagram post1 you have shown STAR ground.
It is not.
The mains PE wire should be bolted to the chassis where it enters the chassis.
The transformer screen should be bolted to the chassis at the transformer using the shortest possible screen leadout wire.
The Two NTCs can be bolted to any part of the chassis. They do not need to meet up with any of the other chassis connected wires.

The Star Ground is an Audio Ground that all parts of the Audio circuit can take a reference. Since you have a two channel amplifier running from ONE pair of secondaries, you MUST create a common Main Audio Ground for the two channels. This is the thick wire that Zen is referring to. For best performance this wire should have zero length. This is an impossible target. Make it as short as possible.
 
Last edited:
Hello,
Sorry for the delay on the response to your suggestions. I have ordered a few new parts and some wire. I have received everything and my amp is on the bench ready for a new grounding scheme. There are some conflicting suggestions written above..

This is what I would like to do:
What I would do is establish another star ground, isolated from chassis, that will be your "Main Audio Ground". Ground from each power supply board to this ground (fat wires). Ground from each amp board to this ground (fat wires). Ground from negative speaker posts to this ground (fat wires). All RCA's and binding post's definitely isolated from chassis. Twisted pair from each RCA to amp board (small wires). Single CL-60 from "Main Audio Ground" to your already established "Earth Ground". No other grounds. And I always do my earth ground the way it's shown at figure 3 with the star washers and everything: Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
I have read this article as well as a few others that are highly regarded. Here are my last remaining questions..
1. Does "Main Audio Ground" need to be fully isolated from chassis? How would you recommend doing this?
2. Is a single CL-60 between "Main Audio Ground" and Safety Earth a good replacement for a "ground loop breaker".
3. Should my transformer shield wire go to "Main Audio Ground" or to its own independent place on the chassis?

Here are my tentative connections:

MAIN AUDIO GROUND: PSU Boards, AMP Boards, NEG Speaker Posts (Six Wires).

Twisted Pair from RCA input to AMP board.

Main Audio Ground connected to Safety Earth via CL-60 Thermistor.

I would be forever grateful for clarification. I have the day off today so I would like to get started. Thanks so much in advance

-Madison
 
OK great, thanks so much.. This is almost exactly what I had in mind.

Is it necessary to have two wires from each AMP board to Main Audio Ground (GND and INgnd).

Should I leave the two CL-60's in place? Connect them both the Main Audio Ground?

Should main audio ground be isolated from chassis?

Thanks so so much
 

6L6

Moderator
Paid Member
2010-10-22 6:43 pm
Denver, Colorado
Main audio ground must be isolated through a ground loop breaker - in this case the CL-60.

Safety earth NEVER is connected through the CL-60, it must be on chassis metal (the PSU ground, and therefore the main audio ground) is what's isolated from the chassis, through the CL-60)

Transformer shield should connect to the chassis, as AndrewT explained.


Hopefully your efforts will make things quieter!
 
1. Main Audio Ground definitely isolated from chassis. I have attached a picture of what I used in my monoblocks. I have this mounted a short distance from the big filter caps.
2. CL-60 is OK as a ground loop breaker
3. I agree with 6L6, follow Andrew's suggestion

Safety Earth should really be very near your AC inlet, connected very securely to the chassis as shown in that article if possible.
 

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