Same question, different year

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#25
Years ago I had a Sumo Athena pre-amp that used a toroid power transformer and it had way too much hum. If I stood the toriod on it's side the hum would disappear but since it was a 1 rack unit tall pre-amp standing the toroid was not a workable option, the xfmr ended up in stand alone box, the pre-amp was quiet after that. That was my first and last experience with a toroid, don't know why some people love them so much. My friend here in SoCal owns a well known xfmr company can't stand them either. EIs are so much better in my experience.

Craig
 
#27
Good idea Craig.

Craig,
You gave me a good idea. You are "thinking outside the box" -- as I should have been!

I could take that toroid out of the enclosure and extend the leads and see what develops.

Well, I gave a more critical listen after I did the IEC earth to chassis modification and I do have to say the noise is now greatly reduced. I shut off the computer and everything else in the room and the noise was not very noticeable. Maybe to the point I can forget about it and enjoy the music it makes.

I can't believe I've lived with this these past several years and it was just a simple thing like this! And I also can't believe I'm so dumb as to not notice this before! 😱

Well, it's just an amp I run occasionally (although I will more often now!) and I've only ever had it apart once before. So that could be why I didn't pick up on the fact there was no earth grounding.

I think the Chinese are slowly trying to just drive us crazy! :cheeky::cheeky::cheeky:

Thanks everyone. I guess we can consider this closed. This is a really good little amp. Better now!

Mark
 
#31
Replace those crap brand 3300uF capacitors with some decent Panasonics/Nichicons I'd say.

To me this looks like a very simple Lin topology amp, so nothing very exotic. I'd be concerned about the RCA inputs being too close to the speaker outs and the possibility of feedback from there. I'd move the posts so that the two ground posts are next to the inputs
 
#32
Well, ya know, I might be inclined to look into an R-Core. At first, I resisted the thought of scrapping the toroid, but I might consider it if I could figure out what was needed voltage-wise.

This darned Amp One came with no schematic (like so much stuff does these days) so I don't really know what I'll need.

And, I'm not really sure how to measure this one. If anyone knows, and can translate it into layman's terms, give me a lesson and tell me how to measure what I've got in there now please.

Mark
 
#33
Mark2727 said:
Did I address this when I soldered the earth lead of the IEC to the case?
Click to expand...

No - as you said earlier you've made it safer but have no apparent connection between earth and the circuit 0V. Which means the exposed metal of your RCA inputs is potentially a safety hazard.

As you say you still get hum when no inputs are connected then the transformer swap is unlikely to fix this. I could not glean enough info from your description of the hum to make progress in tracking it down. But as you say its much better with the earthing then maybe its no longer enough to worry about. Connecting the 0V to earth might improve it further - try different points for the 0V to earth connection. But be warned - when you've done this you may well find the hum comes back with a vengeance on connecting your source!
 
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#34
jaycee said:
...I'd be concerned about the RCA inputs being too close to the speaker outs and the possibility of feedback from there. I'd move the posts so that the two ground posts are next to the inputs
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Jaycee,

Should I use a higher value cap? If so, what value would you suggest?

I'm not sure what you mean in the last sentence. Do you mean by the "posts" the negatives of the speaker binding posts should be physically closer to the RCA inputs? Yeah, I could re-arrange those easily enough I suppose.

Mark
 
#35
abraxalito said:
No - as you said earlier you've made it safer but have no apparent connection between earth and the circuit 0V. Which means the exposed metal of your RCA inputs is potentially a safety hazard.

As you say you still get hum when no inputs are connected then the transformer swap is unlikely to fix this. I could not glean enough info from your description of the hum to make progress in tracking it down. But as you say its much better with the earthing then maybe its no longer enough to worry about. Connecting the 0V to earth might improve it further - try different points for the 0V to earth connection. But be warned - when you've done this you may well find the hum comes back with a vengeance on connecting your source!
Click to expand...


Hi,

Well, I don't know what you mean by circuit 0V. Could you explain please? How do we measure this?

As for the nature of the hum, I'm not really sure how to describe it other than a low volume 60 hz hum. It's not a high tizzy sound or anything such as that. On a tube amp with a hum pot you'd dial it out.

Mark
 
#37
The circuit 0V is the internal 'ground'. Normally that's also the outer connection of the RCA input connectors - you have a 3 wire cable running from those to your PCB. The screen of that cable is almost certainly the 0V circuit node. Try running a wire from that screen connection point to your IEC earth. Double check this by checking continuity between the black speaker output terminals and this point - normally they're connected together.

If your hum is pure low frequency with no hashiness (higher freqs) then it'll normally be magnetic pick up which might be fixable by moving the transformer or the nearby wiring.

Wood shielding might look cool but will have zero effect on the magnetic field 🙂
 
#38
Abraxalito:

OK, let me get this absolutely straight. On my post at #15 here, the IEC lug you see that's bare (that was marked "earth")...........that has now been grounded to the chassis. I attached a wire to that lug and then looped the other end of the wire and fixed it to the foot nearby after scraping off some of the anodizing on the aluminum chassis.

SO...........I should connect the screen of the RCA inputs to that point? I thought this was mixing earth ground and signal ground and was a big mistake? Interesting.

Question two: Would it be worth the effort to extend the length of the wires running to the speaker binding posts so they are closer to the RCA input wires, and further from the toroid?

Thanks,
Mark
 
#39
Its a mistake to mix them together yes, but not a mistake to connect them at a single point. For safety purposes, unless you adopt 'double insulated' construction practices then they should be connected so that you do not have exposed metal parts which have the potential to become live to mains voltage. How they are connected (via some kind of 'ground lifting' network, or directly) is for experiment. Begin with a direct wire connection and see how it sounds when your source is connected - this might introduce what's called a 'ground loop' and give you even worse hum.

As regards your speaker wires - try twisting them together first (black and red, in pairs) and see if that makes a difference.
 
#40
OK, Abrax..........will try both of those tomorrow. Late here. Both easy experiments to do.

Thank you.

I need to read up on grounding. I thought the IEC plug was to be grounded to the chassis. Then anything "signal" was grounded to a different star ground point on a different part of the chassis. That way a loop would not be created.

Grounding is complicated, and I know people way smarter than I make careers out of it!

Mark
 
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