It seemed like a good idea at the time

Bob-I · Post by **Bob-I** » Thu Mar 09, 2006 5:54 pm

It still does, but it didn't work out.

In my 3 channel build I decided to use a brass bar as a ground bus. I mounted it just below the controls and grounded everything signal related to that bar. The cathodes, the controls etc are all grounded there.

After days of troubleshooting the noise in the reverb, I decided to try another grounding scheme. I connected all the cathodes together and to a single ground point at the end of the bar.

Oh My God.... what a difference. The amp is more open and bright, the buzzing is reduced maybe 80% and the gain is increased maybe 30%.

Now I've got a new issue, audible oscillation in the OD ckt. I swapped to shielded for the drive lead from the pot to board, but it's still there. I suspect later in the ckt and I suspect that shielded leads will handle the problem.

Bob-I · Post by **Bob-I** » Thu Mar 09, 2006 7:50 pm

Shielded wire took care of the oscillation

dogears · Post by **dogears** » Thu Mar 09, 2006 9:30 pm

So now my suggestions may actually sound good!! LOL.......

Make sure your shielded cable is super low cap stuff......

MarkB · Post by **MarkB** » Fri Mar 10, 2006 4:17 am

Bob

That's very interesting. I was having trouble with noise in my Wreckman build, so I tore out the messy preamp grounds and put in a buss bar. when I tried it again, it squealed like a pig. I blamed it on the rewiring I also did in the power section, but now I'll have to look at redoing the grounding - again!

Bob-I · Post by **Bob-I** » Mon Mar 13, 2006 1:00 am

I just finished up the relay work. This amp is so much quieter I can't believe that it's the same amp.

I did create a new problem though, the bass control isn't working so I guess I broke something. I'll find it.

BobW · Post by **BobW** » Thu Mar 16, 2006 7:18 am

Bob-I, Glad you got your noise floor down and the relay ckt works well. The ground bus bar method works but you must connect common stage grounds in close proximity along the bar. If you think of each stage working independently and connect stages in groups along the bar, this insures the least resistance between the common stage grounds, and insures circulating currents stay within each stage and have a smaller chance of circulating within other stages (a source of noise).

Am curious to know what end of the bar did you connect the common cathodes? I assume it was the end closest to the input.

Bob-I · Post by **Bob-I** » Thu Mar 16, 2006 2:13 pm

BobW wrote:Am curious to know what end of the bar did you connect the common cathodes? I assume it was the end closest to the input.

No actually the end furtherst away from the inputs.

BobW · Post by **BobW** » Sun Mar 19, 2006 6:02 am

Rethinking what you said Bob-I, grounding at either end WOULD work as long as the Cathode ckts ARE in close proximity, ie lowest resistance, and less likely to circulate currents between stages. Again glad you got in workin'

thanks BobW

Bob-I · Post by **Bob-I** » Sun Mar 19, 2006 6:53 am

BobW wrote:Rethinking what you said Bob-I, grounding at either end WOULD work as long as the Cathode ckts ARE in close proximity, ie lowest resistance, and less likely to circulate currents between stages. Again glad you got in workin' thanks BobW

That was my thinking. I made sure that cathodes were close, some on the same turrets where possible.

The Amp Garage

It seemed like a good idea at the time

It seemed like a good idea at the time

Re: It seemed like a good idea at the time

Re: It seemed like a good idea at the time

Re: It seemed like a good idea at the time

Re: It seemed like a good idea at the time

Re: It seemed like a good idea at the time

Re: It seemed like a good idea at the time

Re: It seemed like a good idea at the time

Re: It seemed like a good idea at the time