Original 300BPP hum fixed

[Richard]

Originally Posted by Greg.

Hi Richard,

Hmm, that does seem to be quite different and very interesting. Personally I don't have any hum problems as you know from listening to mine at your place last year, albeit close adjustment of the humbuckers is still important. Surely this is about balancing the valves to reduce hum/incorporate balance rather than dealing with an earth issue?

Best wishes,

Greg

Hi Greg,

Yours is superb and I wish mine was as tidy inside. I didn't know you guys had sorted this before so hats off to you - just let us all know next time . There will be different ways that work well. Star grounding isn't the only way and yours is pretty close with similar paths to mine so if it works it works

The humbucker issue is strange. I just reported it as it happened and am only thinking about it now you mention it. Maybe it's just to do with a margin of hum, before it was never hum-free so the minimum point was a definite point I was adjusting to. Now it's hum free over a wider range of movement and I have to turn the pot to hear hum. Saved me swapping the pots to cermets anyway!

Rich

[Richard]

Originally Posted by NealG

Rich, yes, it's something I had sorted out on my PP ages ago, the original build had chassis earth connected via the 10R res and the input via the coax input shield. I actually drilled anew hole for an earth post and also fitted the same insulated phono's as you have done. Great minds think alike! LOL!

I also fitted DC heating to the 6072 and 5687, can't remember if I had done the the same to yours when you bought it.....

BTW Darren tells me my Slatedeck is ready so.......expect and email sometime

And here was I sitting humming along and you guys were in silence . Ah well, we all got there.

For the benefit of anyone else reading my amp is an original bought from Neal a year or two back. He didn't costruct it either so we both blame the original builder for any faults

I think mine must be Version 1.5 Neal. You'd put in DC heaters for the 2 small valves but not done the earthing on this one. Each time the bottom comes off I tidy it a bit more but it sounds fantastic and is pretty on the outside....

I've just checked and there's no email yet. I want to hear the SP10/Slatedeck against the Teutonic Tearaway with Mayware. WD3 is all done and sounding fabulous. I'm shaking down different valves at the mo but they are just icing on the cake. It has 2 inputs and I use MM with DL160 high op MC. That leaves MC free so we could switch instantly if you still use Kontrathing.

Rich

[John T]

Yes, the star earth is set 10R above mains earth at the earth post.

The main problem with hum on the Kit/Kat6550 is purely mechanical, emanating primarily from the choke and then the mains transformer. The steel chassis, transmitting eddy currents doesn't help either.

[Clive]

Originally Posted by Richard

The humbucker issue is strange. I just reported it as it happened and am only thinking about it now you mention it. Maybe it's just to do with a margin of hum, before it was never hum-free so the minimum point was a definite point I was adjusting to. Now it's hum free over a wider range of movement and I have to turn the pot to hear hum. Saved me swapping the pots to cermets anyway!

Rich

I think that sums up the situation. On an amp I have with AC heaters I find the hum very tricky to set. It seems that adding hum to a constant level of background hum does require very careful adjustment.

[Richard]

Originally Posted by Clive

I think that sums up the situation. On an amp I have with AC heaters I find the hum very tricky to set. It seems that adding hum to a constant level of background hum does require very careful adjustment.

Hi Clive,

Yes, I've also got the later WAD 300bpp monoblocs. Firing them up with the valves mixed in any old order, I was surprised by no hum. Twiddling the pots showed them to be very insensitive. Really quiet amps.

I also note Steve S comments in another thread that he can get away with fixed resistors instead of pots and can understand that on this hearing.

So perhaps AC heaters are one source of hum which are not particularly bad but may then be compounded by other circuit hum present.

Rich

[Mike G]

Originally Posted by John T

Yes, the star earth is set 10R above mains earth at the earth post.

The main problem with hum on the Kit/Kat6550 is purely mechanical, emanating primarily from the choke and then the mains transformer. The steel chassis, transmitting eddy currents doesn't help either.

Thanks guys, you have confirmed my thought's - ie the main problem is mechanical hum. I couldn't remember what the earth arrangement was exactly, so I won't now have to remove the amp to check.

Many thanks.

Mike

[Greg.]

Originally Posted by Richard

I didn't know you guys had sorted this before so hats off to you - just let us all know next time . Rich

Hi Richard,

Just want you to know that none of us were being secretive. In building a clone we spent time considering the original design and what we could do to improve it and consequently came up with a better earthing path. We completed our builds before you bought your amp. Meeting with you last year we compared amps and there was no obvious hum issues revealed at the time. I never gave any consideration to tweaks I had done to my amp because yours sounded good.

You know we all would share any improvement we achieve. This is simply a circumstantial oversight for which I am innocently sorry. You know I'd never knowingly hold back on a build benefit you could make good use of.

Ah well, we've all got there in the end which is what we want.

Best wishes,

Greg

[Richard]

No problem Greg, never thought it for a minute.

Only reason it got done at all was the niggling safety issue, the sound was a bonus. It was a nothing job and I thought there must be others out there it may help

Rich

[steve s]

Originally Posted by Richard

I also note Steve S comments in another thread that he can get away with fixed resistors instead of pots and can understand that on this hearing.

So perhaps AC heaters are one source of hum which are not particularly bad but may then be compounded by other circuit hum present.

Rich

I'm more than happy not using these pots now,

I have just removed them from my det25 amp,
It was reasonably quiet since i converted to dc heating last year, with the hum pots in place.

the hum levels did not change after removing the hum pots last week
but the quality of the sound has improved..
As you all know, i use old troides, but have heard some amps that sound as good using modern output valves, it has puzzled me..?
.. i have at times had doubts about using the oldies....
but not now....

by the way, the det25 amp had not being used for 4 or 5 months.. it took around 2 hours of use before it really started to sing again..

steve

[richardcooper2k]

Originally Posted by Mike G

Thanks guys, you have confirmed my thought's - ie the main problem is mechanical hum. I couldn't remember what the earth arrangement was exactly, so I won't now have to remove the amp to check.

Many thanks.

Mike

i have found "washers" made from layers of cut up bicycle inner tube between transformer and chassis surprisingly good at reducing mechanical hum. remember you may need to add an earth wire