BeePre sound signature

[m17xr2b]

So I have installed the Jupiter caps with some difficulty and I'm now burning the preamp as from experience new gear does sound better with time.
I tried to bypass the integrated preamp of the 600i but there is too much noise and even at the lowest volume setting on the BeeQuiet the volume is quite high(sound not hum). I though I would add some lead rings on the 300B and maybe some inline attenuates to tame the hum but I found something interesting. Even with the BeePre switched off, the power cord, input cables and tubes removed I still get the same hum.Unpluging the output cable kills the hum so there is something related to the BeePre. My first though is that something is acting like an antenna and picking up the hum so I will try to desolder parts of it to try and find out. With the tubes installed if my hand gets close to them without touching the hum is being amplified again with the power cord removed. I switch off the WiFi to rule that out without success. Could I do anything to shield it like adding copper tape inside?
I have remeasured my voltages and C3,D3 were a little off. With the stock EL84 I got 4.29 and 3.59 and with different ones I got 4.9(a little high) and 4.5. I will have to switch tubes to see if the imbalance follows but my gut is telling me it's not the tubes.
Also terminals 1 and 16 were 5.14. Shouldn't it be 5V exactly? My voltage is between 230-240V.
As for the build I am quite please with the results. I have some better knobs incoming to finish it:
http://imgur.com/a/Oqyhc

[m17xr2b]

So I have resoldered everything and even added Dynamat to try and keep vibration to a minimum. Resistances and voltages are within range. I still have a bit of current about 50mV on some terminals that should be 0 like 37. The hum is still present with both EH and Elrog tubes where I cannot use it with the Moon 600i bypassing it's internal preamp. I have tried with a headphone amp and the hum is audible at max volume regardless of the volume on the BeePre. Still my question is why does it hum even when it's off?
I have replaced the Cat5 cables with my own and using a braided copper shield while keeping the drain wire. I also checked all the grounds against the plate to make sure there were no issues there.
To make it usable I built a pair of RCA cables and soldering 20k and 2.2k resistors to  give me about 20db of attenuation. This works well on reducing the hum and I now have a good volume range.
The sound is great but I'm a bit reluctant that I had to resort to that. In case I never find the cause is there any danger for premature failure on the tubes or components because of the hum?

[Doc B.]

Hum when the unit is off is due to a ground loop or a bad shield in a cable. You will need to experiment with how the AC plugs are configured (use the same outlet for source, preamp and amp - possibly with a ground lift on one piece of gear), cable shielding (make sure the shield is only connected to the outer, signal cold part of the RCA plug at one end of the cable) and possibly with connecting the chassis of your gear together with a wire jumper. Without the equipment in front of me it's difficult to say which approach might be best.

In general it sounds like your amp has a lot of gain, and that you have taken the right approach to improving the noise floor. I'm not sure why adding an attenuator bothers so many users. It's no different than a volume control anywhere else.

[m17xr2b]

I decided to take it one step at a time to try and identify the source of the hum. I have now resoldered everything twice. I tested with three different amplifiers, the BeePre, Quickie and another tube hybrid preamp.
Only the BeePre had about a 20db hum with all three amplifiers and using two different pairs of 300B and three of EL84.
I did further testing where I switched off the power in the house and used my 230V regenerator which has an internal battery to power my dac, beepre and amplifier and this had the same hum. My mains has about 235V so this shouldn't be the issue.
I used both store bought and DIY furutech cables with the shield only at the source end without any difference. There is little to no phone signal in the house and no interference interference as I live in a small village.
The changes I have from stock is: neotech occ 22AWG cable,different power switch, replaced the CAT5 cable with the neotech wire with a braided copper shield, dynamat for vibration dampening. I removed the XLR plugs replacing them with RCA plugs and removing the caps and solder tab. I considered this to be the problem so I put the CAT5 back without any change.
I do have a hum even when the beePre is off and I built something like a faraday cage inside the wood base from fine copper mesh which did fix the hum when it's off but had no effect when it's on.

The resistances all check fine. I do think there might be an error in the manual where A1/B1 and A4/B4 should be reversed. Terminal 1/16 have 4Ω and they are linked with A4/B1 which also has 4Ω but the manual says they should have 5-6Ω.
During my first voltage checks after I just built it I accidentally shorter the 220uF cap at terminals 22,23 for a split second which resulted in a large pop.
Here are my latest voltages:
Terminal   Expected     Actual
1         5V         5.18V
2          90-110V      99V
3          0V         0V
4          9.85V      9.8V
5          0V         7.2mV
6          146V +/0 1%   145V
7          0v         fluctuates between 0mV 40mV
8          0v         0V
9          0v         0V
10          186V      177V
11          146V +/- 1%   145V
12          0V         fluctuates between -10mV to 10mV
13          0V         0V
14          0V         0V
15          186V      177V
16          5V         5.09V
17          90-110V      95V
18          0V         0V
19          9.85V      9.82V
20          0V         7.2mV
21          0V         0V
22          213V      203V
23          0V         0V
24          0V         0V
25          213V      204V
26          0V         0V
27          0V         0V
28          0V         -47mV
29          6.8V      6.45V
30          6.8V      6.45V
31          13.6V      12.95V
32          0V         0V
33          0V         0V
34          13.6V      12.95V
35          6.8V      6.43V
36          6.8V      6.42V
37          0V         -53mv
38          0V         0V
39          0V         0V
40          213V      202V
41          0V         -9mV
42          0V         -9mV
43          213V      202V
44          0V         0V
45          0V         0V
46          213V      203V
47          N/A         N/A
48          0V         N/A
49          0V         N/A
50          N/A         N/A
51          0V         N/A
A1          Too riskey to probe   
A2          90-110V      98V
A3          0V   0V
A4          Too riskey to probe   
B1          Too riskey to probe   
B2          90-110V      95V
B3          0V         0V
B4          Too riskey to probe   
C1,D1       N/A         N/A
C2,D2       0V         -5.8mV,-8.9mV
C3,D3       3.5-4.5V   5.1V,4.93V
C4,D4       N/A         N/A
C5,D5       N/A         N/A
C6,D6       N/A         N/A
C7,D7       147V      145V,145V
C8,D8       N/A         N/A
C9,D9       147V      145V,144V

The thing that jumps out are all those terminals with a few mV on them. I would have assumed if the cap that I shorted was the problem it would have an effect on only once channel but my hum is equal on both sides.

Any advice?

[Paul Birkeland]

I do have a hum even when the beePre is off and I built something like a faraday cage inside the wood base from fine copper mesh which did fix the hum when it's off but had no effect when it's on.

The thing that jumps out are all those terminals with a few mV on them. I would have assumed if the cap that I shorted was the problem it would have an effect on only once channel but my hum is equal on both sides.

The terminals with a few mV on them are close enough to 0V not to worry about.

Having hum while the preamp is off is concerning, and it's very odd that a Faraday cage would do anything to solve this.  I would be focusing on how tight the hardware is, and looking at all those ground lugs and center lugs on the 5 lug strips that touch the chassis to be sure they are conducting. 

We have had a BeePre or two come in that were noisy because of loose hardware.

[m17xr2b]

Thanks for the suggestion. Yes it has the same 20+db hum while being off, less without the 300B installed.
I have tighten everything and the ground lugs are conducting as expected but the hum is still present. I noticed with it switched off I can still hear music in my speakers even if that specific input is not selected and I can even adjust the volume on the selected input. I though maybe it's something with the selector switch so I bypassed the switch going from the rca jack to the beeQuiet input directly with no result. Even stranger the inputs the are no longer physically connected still pass a low level sound to my speakers.
Furthermore I can hear music with the beePre off if I touch any part of the ground such as the chassis with the positive part of the cable connected to my source.

If all else fails I might have to rebuild it.

[Paul Birkeland]

Yeah, there's a funky ground issue at work here.  Is everything plugged into the regenerator? (amps, BeePre, and sources?)

[m17xr2b]

With or without the regenerator it makes no difference. I decided to start from scratch so I disassembled it, got new capacitors, diodes, rectifiers, resistors and wires. This time I will be extra careful on everything. Just as well as I wanted to repaint the base anyway.