Hello fellow Bottleheads,
I would like to introduce myself on this forum with my BeePre. I finished the preamp today with installing the BeeQuiet attenuator. The BeePre played for some hours the last days with standard potentiometers for balance and volume i really liked it already.
My signal comes from a DIY DDDAC1794 DAC and runs from the BeePre into a LM3875 chipamp. My speakers are selfbuild Ellam-flex threeways designed by Troels Gravesen.
At first i attached the BeePre to my power amp without modifications. The sensitivty from the chipamp is very low and the 300b's where singing on there own, a really spooky sound. When i heard this i thought my speakers where going to explode so i turned of my poweramp. After some warming up the BeePre became 'stable' and the singing was gone. There was still some hum and lots of microphonics. Time for some music to see of the BeePre was working like it should.
The music played wonderfull (aside from the hum and microphonics) i could imediatly here why so many people are pleased with this amp.
Time to find out where the hum comes from. First i searched for the problem within the BeePre. I did some resoldering and measring to asure everything was solderd properly. After all joints are checked there is still a hum present. The weirdest is that it its always present in in form with low amplitude and by times it gets really loud. The frequency of the loud hum is exactly 50Hz and only present in the left channel. I checked all my joints again and again but this weird coming and going of hum stays present. It always stays in both speakers and gets loud and kinda different form only in the left channeld.
Yesterday i lowerd the sensitivty from my chipamp with some different resitor values. It helped a bit for volume control (with standard potentiometer) and did a good job on the 'always present' hum and microphonics. I could listen for a while to my collection and really enjoyed my new amp. Until a certain moment the loud hum sneaks back into my left channel. Not as loud as first but still noticable behind the music. I found something on this forum about the same kind of problem (only in both channels) with fellow BeePre owners also from the Netherlands and it had something to do with the voltage from the wall sockets. As the voltage drops the hum gets present.
I started measring and found out the the hum was gone by 233,6 (or something) volts ans gets louder when the voltage drops. 232v is very noticable and under 230v it's unbearable.
The readings from the other Dutch guys where lower but i guess this has something to do with my high sensitive poweramp. This morning i lowerd the gain and sensitivty even more and installed the BeeQuiet to get some precise control on volume. As i wanted to test my new modification i hooked everything up to hear that terrible buzzy hum again. After measruing the linepower again i noticed that the amplitude of the hum lowerd (compared to same voltages as yesterday), probably because i lowerd the sensitivity some more.
I owned a Crack and recognize the hum from the first few seconds after the crack is turned on. Something like the transformer is working to get the tubes on temprature. The sound is the same as the soft mechanical hum from the transformer working on 50Hz with your ear close to the amplifier.
I hope someone knows a solution. I searched already for voltage stabilizers, but this solution is way to expensive. One thing that might be noticed is that non of my wallsockets are grounded (only the ones in bathroom and kitchen.
