Bee Pre hum on both channels

[fritzthecat]

Hi fellow bottleheads


got some hum issues with my Bee Pre...

Just thought if voltage and resistance checks went fine, everything should be okay, but I was wrong...;o)


When connecting to my system trying to listen to music, I heard a quite loud hum (not only 50 Hz - 100 Hz and higher as well) on both channels not changing when doing adjustments on selector switch, volume or balance controls.


Any tip for me where to look at first?


I already checked solder joints - everything seems okay but I will redo it tonite.


Looking forward to any advice.


Thanx and all the best wishes,


Chris

[Paul Birkeland]

Are you in the US, or abroad?

[fritzthecat]

Hi Paul


I'm in Switzerland... I guess you are asking because i wrote 50 and 100Hz... ;o) We have 230 V / 50Hz mains here in Switzerland. I measured several times what's coming out of my sockets and it is 233,1 to 235.3 V (dependant on daytime and if its weekend or workday) and yes it's 50Hz.




I'm learning a lot through kit building as I am going through any possible mistake a newbie can go through...;o)


Thank you and have a nice day.


Chris

[Paul Birkeland]

The 240V PT-7  in the BeePre is OK to run on 50Hz.  What DC voltage do you get at POS_IN on each of the PC boards sitting above each power transformer?

I know in some EU countries, we will see the "240V" mains sitting at more like 225V, and this can present some issues with noise since not enough DC voltage is available in the low voltage supplies.

-PB

[fritzthecat]

On PT-7 A it's 12.66 V/DC and on PT-7 B it's 12.71 V/DC - Mains input voltage is 231.2 V/AC.

What do you think? In Switzerland we have much more 230 than 240 V mains...;o)

Strange that the mains are different from day to day - last time I measured it was like 233 / 235. Today it's less.

Thank you for helping - I am looking forward to find out what it is.

[Paul Birkeland]

How sensitive are your speakers, and are you using the Kaiju with them currently?

[fritzthecat]

Hi Paul


I am running a high sensitive speaker system with 2 Silvercore Monoblocks for the corner horns and 3 stereo Kaijus für low mid, mid and high. The bass is @ 102dB, low mid @ 104dB, mids @ 108 and the tweeters @ 105 dB. The Kaijus all have the psu upgrade and are dead quiet. It is managed via a Mini DSP to which the BeePre connects at the moment.


Does it make sense to try other tubes? I have several sets of EH 300B, EH 300B Gold, PSvane 300B mesh plate / Hifi Series and a PSvane set of EL84.

[Paul Birkeland]

How do the trimmers on the Kaijus affect the noise floor you're experiencing?  Are the Kaijus set to 2 or 4 Ohms on the output transformers?

[fritzthecat]

The Kaijus are wired 8 Ohms and the trimmers do not seem to have any effect (got the dc filament update - should there be any effect then?)


Something else: I inserted other 300b (eh gold) and the hum is still there (on one side only - not swapping with tubes) but dissapears after lets say 90 seconds completely and then the bee pre is dead quiet beside a little hiss in the highest highs - with my Audio Note Kits I always had some 50 Hz hum (very low but audible) and it is completely gone with he BeePre.


 Yesterday I had the same effect with another set of 300b (EH norma) but the hum came back and dissapeared again (measures mains amd it seems if it goes down to 230.6 the hum is there, above 231 it seems to be gone. Strange but Imseem to have slightly alternating mains from 230.4 to 233.6.


Looks like this is just varying in the area where the BeePre is kind of hum sensitive? But maybe I am completely wrong.


Are there any 300b available that need less dc in the low voltage supply? Tried PSvane 300b mesh plate - hum on both channels.


Should I invest in an active power conditioner providing stable 240v?

[Paul Birkeland]

You could certainly try an isolation transformer.  Even a 1:1 transformer rated for 1000VA will give you a little nudge in voltage. 

-PB

[fritzthecat]

Hi Paul


Thank you - will try with my Variac first - there I can turn vorage up (somewhere around 265V)...


Strange thing yesterday night: as I wrote, hum disapeared after a minute plus - then I started Ironing (yes, I'm in the age where you start ironing your shirts on friday evenings rather than going out..😜) and the BeePre started humming each time when the iron heated up - that's actually what I expected. Later (no more large consumers on) while listening to music - and the BeePre sounds great - permanent hum on both channels again. I guess after some hours, when the device gets warm (actually quite hot but no wonder as there is a lot going on inside the chassis) some voltages settle to lower values? What do you think is this normal or should I be worried (as usual?)



Chris

[Paul Birkeland]

Oddly enough, some heat can actually be helpful for stabilizing voltages.

I have a couple of dimmers in my listening room that can elicit some strange noises from my system when set in certain ways.  With an isolation transformer between preamp and wall socket, slightly stepping up the voltage, I don't have any issues.