Stereo BusBar OK?

[Salas]

I am about to run a bus bar in a stereo valve amp. In the schematic is my plan and some notes. Please review it for obvious bad (buzzzz) ideas. Also tell me if I have to attach the shields of the input coaxes both ends or not, and if not, where.

[arnoldc]

Hi, personally I don't like the path it took.

If I were to do it, I would, in order of preference-

1) Use star ground. My preamplifier projects benefits from this, none of them are noisy done that way. It does not look pretty (but better than Sakuma's ) and it does the job well.

2) Use "T" style bus. If you'll look underneath the posted picture of my 300B amp, you'll notice (aside from the blue capacitors in the wrong direction ) how I employed the bus. My 300B runs on AC filaments, and you will not hear any hum with your ears within a foot from the speaker cone.

re: shield, I normally use salvaged two-conductor shield wire from old heaphone units. I find them easy to work with and good for the application. So, I have never used a coax. I think the method you mentioned is a practice for interconnects.

Cheers!

ps.

What amp is this?

[Salas]

Its my design. 12AY7parallel - 12AT7 cascode tail CCS LTP - KT88 PP triode. Unfortunately I use a chassis from an older amp, that has a nice to look at tube placement, but output tubes and inputs are located extreme left and right. I am afraid it has potential to buzzzz. I will sketch a T in a minute so you can tell me a new opinion.

[SY]

Assuming V1 and V2 are input tubes and V3 and V4 are drivers, I'd do it like this:

[Salas]

Here it is. Better? As for the coaxes, my concern is, that if input interconnects are going to be grounded at the input RCAs connected with the front portion of the busbar, they must not get to the first stage gnd also, it looks like a loop. So I think its better I attach the internal coax shields at the rca rings only.

PS. Thanks SY!

[Salas]

Originally posted by SY
Assuming V1 and V2 are input tubes and V3 and V4 are drivers, I'd do it like this:

SY, in your proposition, the solid copper portion can be safely restricted to the picture's bottom and right 90deg angle part, and the other contacts come with cables, short of sub stars?



In the attached pic is Arnoldc's T method proposition for reference.

[SY]

Better?

Yes, but still not optimum. I've highlighted the thick copper bus from my earlier drawing.

[SY]

I should add, you want some form of groundbreaker between the amplifier ground and the safety (earth) ground. I show a resistor (27 ohms is a safe value), but it's been pointed out that this could compromise safety. These days, I use a 27-33R resistor paralleled by 1nF and two diodes (in parallel, each "facing" the opposite direction).

Others have used groundbreaking switches or plug assemblies, but those will then rely on the ground integrity of other components in the chain and make me nervous.

[arnoldc]

Hi Salas, I'd favor the short bus by Sy. Won't look as neat, but might be better.

ps.

Sy, I always have my circuit ground floating. Am I violating any safety rules? Sorry for being lazy...

[Magura]

Originally posted by SY
I should add, you want some form of groundbreaker between the amplifier ground and the safety (earth) ground. I show a resistor (27 ohms is a safe value), but it's been pointed out that this could compromise safety. These days, I use a 27-33R resistor paralleled by 1nF and two diodes (in parallel, each "facing" the opposite direction).

Others have used groundbreaking switches or plug assemblies, but those will then rely on the ground integrity of other components in the chain and make me nervous.

A CL60 thermistor is known to do the job, and do it well.


Magura