removing AC Hum on Aikido????

[cbutterworth]

OK, so a few days ago, I reckoned that I had reduced the hum on my new Aikido. Well, it is greatly reduced, but still very audible.

I followed Sy's recommendations of chassis mounting the volume control. I also chassis mounted the jacks, and lifted them from the chassis using electrician's tape (a temporary measure). I also encouraged the signal wiring to avoid the AC wiring.

Anyway, the level of hum diminished significantly such that I could actually listed to a CD.

The hum is at around 60Hz (I don't have a scope, but just played a 60Hz tone on my Mac). So this means AC doesn't it?

My options are to:

1. Install proper jacks. I have good jacks with insulating color-coded washers.
2. Use signal cable with braided shield. I have Canare cable, which I could use and connect the braid to signal gnd or even chassis gnd?
3. Remove the tube delay / relay network and install a second switch for the HT voltage.
4. Install a sheet steel panel to comparmentalize my chassis. It could go between the PSU section and the PCB ground.
5. Float the PCB ground using a capacitor. It is currently connect to the chassis / IEC / Earth bolt.


Any thoughts, opinions on any of these????

Once I get the Christmas / New Year break over with, I'll be able to think about the Aikido once again. Although my first Saturday of the New Year will see me busy with "birthing classes" which I am sure my wife would prefer me at rather than tinkering at home with our sound system. But how can I bring a child into a world in which "Baby Got Bach" isn't played through an Aikido

Regards,
Charlie

[cbutterworth]

I forgot....

My amain amp is an Aksa 55N that I built. It could be that some hum is derived from the grounding system in the AKSA.

It has a star earth for PSU and PCB, but I chose not to connect it to chassis/IEC earth, as I got no hum. I have never connected it, so I don't know if this could be a fix. I know that one AKSA owner (Ginger / Gingertube) did experiment and found that connecting the star-earth to the chassis ata point a little distant from the chassis/IEC earth worked well.

Anyway, should I try connecting the star-earth to chassis earth in my main amp?


Charlie

[Sheldon]

A picture of the bottom side would help. This is a problem that probably has a fairly simple solution.

Sheldon

[SY]

If the hum is 60 Hz, figure that you've got pickup from the AC wiring running near the signal circuit or a ground loop with the power amp. As a fast experiment only, put the preamp power supply on a cheater plug to lift the safety ground and see if the hum goes away. If it does, then you've got a ground loop that can be broken up safely. Don't leave the preamp on the cheater plug! If the hum persists, your next steps will be to dress the AC wires well away from the circuit or use tight twisting for cancellation. Or, preferably, both.

[FastEddy]

SY: " “It would be an idyllic tropical paradise if not for the malaria, the insects, the constant diarrhea and resulting hemorrhoids, and the fact that the people are dirty and smell bad and eat each other and use human heads for decoration.”- Neal Stephenson "

One would hope that M. Stephenson will shortly release yet another complicated and whimsical yet scientificly factual, fun filled and timely yet historicly interesting tome ... I may have to reread his last 9000 pages just to keep the monkey alive. (Your impressions appreciated.) ...

[SY]

An English friend of mine, noting that quote in my sig, quipped, "I see you've been to France."

I greatly enjoy NS's writing.

[FastEddy]

NS' alter ego, Enic Root ... discoverer of the "new pearl of great price"?