View Full Version : Low output and lot's of hum from BSS 366T

05-05-2012, 12:34 AM

I just received my newly aquired used BSS and I can't seem to get it to work properly in my system. I get a lot of what I think is 50-60Hz hum and the out put is tremendously low. The noise floor is very high if you know what I mean. I tried to change gain level at both inputs and outputs but this doesn't seem to fix it.

My setup is as follows: ARC LS7 unbalanced tube preamp-->BSS 366T -->ARC VT60 tube power amp & NAD 218 poweramp, both run unbalanced.

I live in an old house (1892) and there is no grounded power outlets in any room except where the pellet boiler is. I did try to take the power from this outlet but there was no difference in the level of noise.

I have studied the BSS papers in regards to connectivity when using it together with unbalanced units, and I think I have all the connections wired in the right way.

I will run off and by som RCA-XLR adapters now to see if this solves the issue.

If this is a ground problem, where can I earth the unit/units since there is no ground pins in the AC outlets?

Thankfull for any input.

Kind regards,


05-05-2012, 01:37 AM
My first thought is cabling/conversion between balanced and unbalanced.

If you make the cables yourself the standard way is to connect unbalanced ground to pin 1 and 3, while you connect the unbalanced signal to pin 2.

In some cases you might want a variation of this when making the balanced to unbalanced cable: 10K between pin 1 and 3, pin 1 to unbalanced ground and pin 2 to unbalanced signal.

Since your output is very low I suspect the connection between preamp and filter.


05-05-2012, 05:03 AM
Thank you Johnny for your quick response.

You were right. The xlr-->rca adapters I bought solved the problem. Hum is gone and output level is good.

Now the fun can begin to dial in crossover frequencies and so on.



Titanium Dome
05-06-2012, 09:51 AM
When we started putting the BSS 366T units into the PT250 experiment, I used a Citation 5.0 as the pre, single end (RCA) to balanced (XLR) on the BSS 366T using a JBL Synthesis cable designed for such a purpose, and the hum was intolerable. He (grumpy) did something at the XLR end (removed a strap, perhaps?) that ended the hum and didn't burn up the BSS units or blow up the Hafler amps. That solved the problem here. Maybe he'll chime in with a clearer recollection since he did the work.

The BSS 366Ts are really nice units, though the fans are a bit noisy. Are you going to disconnect your fans? I was told by a couple of pros that this is a regular practice with in home use, but I'd like someone else to try it first. ;)

05-07-2012, 07:29 AM
I would guess it was effectively the same as what Jakob's new adapters did...
It's been too long, and I don't do audio for a living, so the details have gone fuzzy.

Not having such adapters on hand, but having a soldering iron, I think
it was as simple a shorting two pins after taking off the connector back shell
(connecting the source ground reference to a similar point at the differential
input on the BSS, rather then leaving it floating).

One would want to check the BSS manual for their recommendation
in any case (I'm sure that's what we did). Not all adapters or pin connection
modifications are appropriate for all equipment (as Johnny stated earlier
it this thread).

05-07-2012, 10:58 AM
Yes, the BSS manual clearly states what to do when running unbalanced signals into the BSS and on to other equipment.

I must have gotten worse with the soldering iron with the years, can't put the blame anywhere else :o:.

The fan in my unit squeals like h*ll when powering up and the 2-3 hours to come, the it gets better. Seems as if the bearings out.

I'm very tempted of disconnecting it but I won't risk it. I talked to some PC-techs at work and their solution would be to build a new top cover and install a much bigger fan. A bigger fan doesn't need the same high rpm to circulate the same amount of air and the lower speed of the air passing through the bigger outlet will be less audible.

There is also more fans to choose from if you move up in size. You get a better chance of finding a real quiet one.

All in all, i love the BSS. I get great sound out of it, and I have just begun getting to know it :).

Thanks for the input!

05-07-2012, 11:23 PM
Get new and more silent fans.

If you have some space around your unit, i.e. cold air available, you could add some series resistance to reduce fan speed. A little speed reduction is normally by quite a good noise reduction.


05-10-2012, 10:04 AM
Not all adapters or pin connection
modifications are appropriate for all equipment (as Johnny stated earlier
it this thread).+1 :) Depends upon whether Pin2 (+) or Pin3 (+) convention is being used. BSS is Pin2(+), so the "ordinary" adapter, described by Johnny is perfect.

I still run into a fair number of Pin3(+) situations - old consoles and such. Surprising number of house engineers, new to the biz, are unaware. Let's just say I carry a lot of adapters, and turnarounds... :o:

stephane RAME
05-10-2012, 10:51 AM


05-20-2012, 07:35 PM
my two cents
I resolved hum problems in my home in Indiana via a isolation transformer, but thats easily a 800 to 900 usd option. I did find an excellent product made by Behringer, their Hum Destroyer HD400, at 25.00 each it converts unbalanced to balanced through a small isolation transformer with 1/4 phono to rca cables. It also works great with balanced to balanced. It worked great for me prior to converting to the full on 15kV isolation transformer.