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I just completed a 18 Watt and everything is working fine except noise !! , it could best be described as low-frequency hum. It occurs without the guitar jack plugged in and increases with the volume knob.The hum goes away when I remove V1 (I was told this could indicate where the noise originates from).I used shielded input wire and have since shielded the wires to the volume knob........Any thoughts ??......Thanks

Is it a Trinity Kit? You can compare your layout to the sIII one in the Resources forum. That is a proven layout design.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

http://www.brownnote.net/forum/download ... &mode=view

Not a trinity layout, still an 18 watt design, thought someone might have an idea ??

Have you tried getting out a chopstick and moving around the wires on V1? Particularly the filament wires.
Stew

Tried chopsticking without result, the chassis is powdercoated, I removed about half the diameter of the ground washers which seemed like enough, maybe I'll redo the grounds

So you think it's 60hz hum? Filament Center Tap?... I'm a big fan of DC offset on filaments.

I would have to research the dc heater thing, never done it, worth a try I suppose.

Not DC heaters but a dc offset. Where you take the heater centertap to dc source. I just take a couple of 1 watters off a powersupply node and a little 10uf cap. Adjust values to get 40 or 50 Vdc (ie 100k + 470K) and connect the CT. Works great for me!
I've heard some 18 watter guys connect the CT to the o/p tube cathode to get the dc offset. never tried that.

That's the last thing you should need to do. It's almost 100% that you have a ground loop in the vicinity of V1. And DC-powered heaters can often introduce more noise into an amp.

Can you describe how you've done your amp's ground scheme? It may also be a good idea to post some good pictures of the inside of your amp. Any shielded wire you use should only be grounded at one one. Also your input jack must be insulated from the chassis.


I'm a believer in DC-biasing (or "elevating") the heaters, although it only gives a small incremental improvement in the background noise floor. Taking the DC offset voltage from the power tube cathodes works pretty well, although tapping 40 to 50V off a pair of resistors (which can also act as the bleeder) is a tad more effective. In basicbilly's case, however, he first needs to fix the main hum issue and then look at some incremental improvements such as this.

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Great tones come in small glass jars!

I suggest you look over the layout posted in the resource forum and compare it. I know it works every time. I seperate the pre amp ground from the power amp ground. If your leads are far away from the heaters, and the heaters are well twisted, then that should be OK. As Phil suggests, ground the shielded cables at only one end. In the case of the inputs, at the jack end has always worked for me.

Check to see if the ground lugs are in 100% contact with the chassis too, and yes, for sure, insulate the input jacks.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I used Moss's layout pretty much exact, having a hell of a time trying to download pics, lets see what happens !


Trying to download pics but its saying file is too large.........HELP!!

can you just view it on line?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

http://s1213.photobucket.com/albums/cc468/crunchman1/

Pardon the children ! There always hangin around.

Anyway, its built according to the layout.

basicbilly, I can see some areas for you to work on that will help or evebn solve your noise issues.

1) the wires to the tube heaters, right up to the tube pins are not twisted well enough. If you dont do this, and if you dont keep them seperated from the signal level lines from the board, there will be hum due to the 6.3 VAC current.

2) The shielded cable for the input needs to be shielded at the input jack. Neither end is shielded in yours. Cut a new cable, expose the shield and solder it to the ground connections at the jacks. (there is a tutorial in the resource secion on doing that). Don't cut the shield so close to the input jack terminals.

3) Clean off the paint to make a good ground contact.

4) shorten all the wires from the board to minimize hum and noise pick-up.

5) some of those solder joints look like they could be touched-up. Check them all.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

coco, I used 22 g wire for the heaters, this wire doesn't seem to want to hold a twist.Is there a better alternative ?

I tried to keep it against the back wall like I see it usually done.

If you used stranded wire, it doens not retain it's twist or shape very well. I prefer solid core wire in almost all ocassions in an amp (except mains wiring). You may need to twist it, then tape or tie it to keep it's shape. OR replace it with solid core.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Im gonna redo the heater wiring with solid core, I'll get back with you when I get some time to look everything over.

With the output jacks you are using you should not have a wire going from them back to the chassis ground.

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I guess I can try lifting it and see if it helps, I tried to follow the layout, mabe their different jacks they he intended.

Kurt, I tried lifting the chassis ground wire on the inputs and the noise went through the roof.
I'm gonna re-do the inputs based on the normal cliff jack wiring diagram in the resources section (Thanks Coco !)

My only question would be where to ground the sheilding, will any chassis ground be fine? My thought would be right where the ground was! I didn't notice where Moss was using any shielding on the original layout, Live and Learn !!

This is really my first REAL assembly, past two where pcb based, not to mention my iron is taking a poop to complicate matters !! Thanks again.