Re: 60 Cycle Beast from Hell ...Please help!

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6/28/2000 10:33 AM

Ray Ivers

Re: 60 Cycle Beast from Hell ...Please help! Stan,     Since 60 cycles has been mentioned, and you have a 'scope, it's evidently not 120 Hz (oh, OK, cycle; I kind of like that better, anyway) hum/buzz - which pretty much rules out the B+ supply. When you disconnected the heater supply, did you disconnect both wires at once? Just one won't do it - the hum will stay as the tubes cool off.     I think it's a grounding problem related to the first gain stage. I recently had a chance to look inside two Two-Rock amps. The early one had pretty much a textbook double star ground; every signal ground starred to right next to the input jack, every power supply ground to the green wire of the power cord near the power entry point. This amp hummed (60 cycle). The later model used a 'ground buss'; a single, thick, solid copper wire running from the input jack ground to (I believe) the speaker jack ground, with individual stage/filter cap grounds connected in order from input to output. The main power supply grounds (PT C.T., first filter cap) were still starred to the power entry point. This amp was much quieter. I'm not saying this change in grounding technique was solely responsible for the hum reduction, but my 'project amp' chassis I've been using for years uses this buss system too, and it's always been quiet, even with four cascaded gain stages (ah, the metal years).     I would connect the FWB and first filter cap grounds to a different star point near the power cord first, and then start looking at each stage's grounds starting with stage 1. R.G.'s Tube Amp Debugging Page may also be invaluable to you for hunting this thing down.     Ray Ivers   R.A.G.E Electronics

 

6/28/2000 5:39 PM
Stan Bailey	Thanks guys,   I'll try seperating the power supply from the signal grounds.If that doesn't do it, I went and picked up some heavy buss wire from the hardware store, and will try the buss grounding scheme.Also, I'll rework the first and second stages and keep going until that sucker stops humming. Thank you very, very much!   Stan

 

6/28/2000 6:20 PM

Stan Bailey

The Beast is Slayed! I connected all the signal grounds to the input jack(except output jack) and all power supply grounds to a star point on the tranny side ...Hello, no more hum! Well, maybe a little from my noisy work bench area. Now, if I do a buss arrangement,I read that one should have the power supply returns of the stage they are supplying connected at that stages ground on the buss. Can someone confirm this? BTW, I am very grateful for all of the valuable info you guys give out for free.   Thanks, friends!   Stan

 

6/28/2000 6:46 PM
Carl Z	Stan;     You might maybe hear a slight difference but not much. As long as you're running a ground wire from those caps to the same star location you should be fine.     Here's a little tip, if you want to really get nit picky, you can use flourescent lighting on your bench. If you can get the amp quiet under those circumstances you're golden!     Carl Z

 

6/28/2000 8:24 PM
Stan Bailey	quote: "Here's a little tip, if you want to really get nit picky, you can use flourescent lighting on your bench. If you can get the amp quiet under those circumstances you're golden!"   Yeah,   I have florescent lighting over the bench. It is pretty damn quiet considering that. I can't wait to hear how quiet it is at the gig Friday!   Thanks Carl.   Stan

 

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