"Buzzy" noise

[Karl5150]

I have been enjoying my Reduction for several years, first with a S.E.X.2.1, and now a Stereomour II. There has always been a faint "buzz", only audible with an ear next to the speaker, and not noticeable while listening. With a Rega phono stage swapped in the system is dead quiet. I know the troubleshooting notes say this points to a lifted ground, but I wonder if the fact that it is so faint and in both channels points to a likely area of the kit to focus on. As always, thanks in advance for any help.
Karl

 

[Paul Birkeland]

Do you have the integration installed on your Reduction?

A zero feedback RIAA preamp will tend to be a bit noisier than your typical opamp or feedback EQ type phono preamp. A faint buzz would tend to indicate a little 120 Hz noise coming from the Reduction, which is reduced with the Integration.  This can also occur from flaky solder joints in the Reduction, though it's hard to say how significant this might be in your system.

To further quantify your situation, approximately how efficient are your speakers?  Is this buzz present at a normal listening level, or only when you have the level control on the Stereomour turned up past a comfortable listening level?

-PB

 

[Karl5150]

Paul:
Yes I do have an integration installed, honestly I don't remember if the noise was there pre integration, driving the S.E.X at the time.
At normal listening levels, around 50%, the buzz is only audible in a relatively quiet room with an ear within an inch or so of the driver. At full volume I can detect it a couple feet away under the same room conditions.
My speakers are listed at 93-94dB efficient, but there is a simple 2nd order, 105Hz, 2-way speaker level crossover installed between the OBs and subs. (So maybe 90dB?)
The comparison with the Rega phono stage was done using all the same cabling and other equipment.
This in no way detracts from my enjoyment, and I wouldn't sweat it but the Reduction may find its way into a good friend's system. (Potentially allowing me to try out an Eros.) I would only want him to take possession knowing it was as close to perfect as possible.
If it would help I can provide some volume and frequency info from tablet/phone apps.
Thanks,
Karl

 

[Paul Birkeland]

You can add a small capacitor from IA to bB on each of the small front C4S boards.  Any old film cap between 0.1uF and 2.2uF at 250V will do.

This will bypass the zener stack, and IIRC takes out a dB or two of noise, so feel free to give it a shot!

-PB

 

[Karl5150]

Thanks, I'll give it a try.