After loads of research and tons of advice I finally got the hum worked out of my amp! I want to thank everybody here for pointing me in the right direction. Some of this stuff I did not to reduce the hum but because I was going to do it anyway. Here's the stuff I changed:
- Swapped out the N.O.S. ARS filter caps for new F&T cans
- Swapped out the top hat diodes for Ultra Fast UF5408
- Swapped all of the 22AWG wire on the board for 20AWG
- Swapped out the skinny shielded wire for Lava Mini ELC
- Added a 1000pf bright cap (mustard)
- Incorporated the "Larry" star ground scheme
The amp is super quiet now. I have to play it to see if it is on! It is the quietest amp I have ever built. I am very pleased. Not only does it go to 11 but it goes there by odd numbers instead of even.
Here is the grounding scheme I used (this is for a JTM45 but I followed the same node positions):
Looks very nice! I guess you have had it running previously, but I'm wondering how hot it will get inside, and the OT is likely to get very warm being directly above the output tubes, no?
martin manning wrote:Looks very nice! I guess you have had it running previously, but I'm wondering how hot it will get inside, and the OT is likely to get very warm being directly above the output tubes, no?
Marshall has used the very same configuration for years as seen in these pics of the Bluesbreaker and a 1979 JMP. The 1962 Bluesbreaker reissue still uses it. I previously had a JTM45 Chassis in the cabinet with no trouble whatsoever. But thanks for looking out for me!
ampgeek wrote:Congratulations on running that hum to ground (pun intended)!
Where did you end up landing that pesky presence pot ground?
I was wagering that was the primary issue based on past experiences.
Awesome looking build Joe!
Cheers,
Dave O.
Dave,
I actually moved that twice (didn't help in my previous schemes) before redoing all the grounding! I believe I came upon some of your posts? I am sure I had other issues but I ended up with the presence ground to node 3 as in the JTM drawing.
Guess that I would have lost that bet. It wouldn't be the first!!
I sometimes feel like I have forgotten more than I currently know as I am a simple hobbyist at all of this so I can't recall if I ever posted on that specific issue. However, I know that I have faced it in the past.
I have pretty much settled on Merlin's approach to grounding whenever possible as it has never, ever let me down.
Did you do a very comprehensive comparison between VVRs and attenuators in Marshall circuits some years ago? The article/soundclips were very informative and useful.
If it was you and you still have that up, please consider posting a link here as I am sure that many others would be very interested in seeing/hearing it.
That is one sick build! Fantastic!
Congrats on tracking down the hum.
LARRY for me all the way with Marshalls.
Otherwise Dumble style does it for me in Fender builds
Thanks for all of the complements guys. I couldn't have done it without help from so many people on these forums. Seeing other builds inspires me. I am humbled.
ampgeek wrote:Guess that I would have lost that bet. It wouldn't be the first!!
Did you do a very comprehensive comparison between VVRs and attenuators in Marshall circuits some years ago? The article/soundclips were very informative and useful.
If it was you and you still have that up, please consider posting a link here as I am sure that many others would be very interested in seeing/hearing it.
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