Bose 901 Equalizer

[Guarddog32]

I have tried adding 3 different equalizers to my audio setup to work with my vintage Bose 901 speakers and all of them cause a loud humming noise which you can hear when the music is not playing or there is no talking when watching a movie. I was told by a vintage audio repairman that I need to stick with the Bose equalizer that came with the speakers, which has very basic adjustments on it. Can anyone tell me if this is true or what could be causing the humming noise? Thanks in advance for your help.

 

[americanaudiophile]

The problem is not caused by your not using the original Bose EQ.
Sounds like you have a ground loop which can cause that hum. You can try using one of these on the AC plugs
http/www.target.com/p/ge-grounding-adapter-polarized-2-pk/-/A-14442316?sid=1139S&ref=tgt_adv_XS000000&AFID=google_pla_df&CPNG=PLA_Home+Improvement+Shopping_Local&adgroup=SC_Home+Improvement&LID=700000001170770pgs&network=g&device=c&location=9004455&gclid=CLyvpLy-mtMCFYONswodLxYP6w&gclsrc=aw.ds
Some general guidelines on ground loops here
http/web.mit.edu/~jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

 

[Guarddog32]

I read in the article that you posted AmericanAudio and here is what I found in there:

NEVER, EVER use devices such as 3 to 2-prong ac plug
adapters, a.k.a. "ground lifters," to solve a noise problem!
Such an adapter is intended to provide a safety
ground (read the fine print) in cases where
3-prong plugs must be connected to 2-prong
receptacles. If a proper safety ground isn’t
available, always use a ground-fault circuit
interrupter or GFCI. A GFCI works by sensing the difference in current
between the line and neutral conductors. This difference represents current
in the hot conductor that is not returning in the neutral - the assumption is
that the missing current is flowing through a person. If the difference reaches
about 5 mA, an internal circuit breaker is tripped. The GFCI shown at left is
unusual because it has a retractable ground pin that allows it to be used with
a 2-prong outlet. [5]
Consider two devices connected by a signal cable, each device having a 3-prong ac plug. One
device has a ground “lifter” on its ac plug and the other doesn’t. If a fault occurs in the “lifted”
device, the fault current flows through the signal cable to get to the grounded device. It’s very
likely that the cable will melt and burn! Defeating safety grounding is both dangerous and
illegal - it also makes you legally liable!

 

[Guarddog32]

Also, if I do have a grounding loop somewhere, why doesn't the Bose EQ cause any hum in the system? The Bose EQ is totally quiet when hooked up;

 

[jsmithepa]

The 901 was made when home eq was not sophisticated as now, perhaps your modem receiver home EQ alone will do the job?

 

[americanaudiophile]

The Bose EQ may be old enough that is doesn't have a 3 prong AC plug,
And yes if you check with electrical code you don't want to lift AC grounds but a lot of equipment doesn't even have 3 prong AC plugs or have the 3rd prong attached inside the unit. Subwoofers often don't since they are plugged into a different outlet than the receiver and are prone to this kind of problem.
The only time I have had the damage you suggest was when an electrostatic speaker (which plugs into the wall) and a single ended amp were used in a room where the AC outlets were improperly grounded. The amount of current was not enough to damage any gear just the plug on the speaker wire.
You are supposed to use a audio transformer to lift the ground on the signal cable but those are a bit more money and are not good for bass performance.