Tube Amp Archive

I recently knocked out my hum by going with the "Larry" grounding scheme. It took a while to so it but I have the quietest amp I've even built!

Congrats on your build!

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...

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.

Congratulations on running that hum to ground (pun intended)! :lol: 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 previ...

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 JM...

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. A...

[quote="xtian"]*rant* GROUNDING SCHEMES ARE A BIG FREAKING MYTH!!! *end rant*

Ha Ha!

Let me know how it goes.

OK, so I'm a goofball. After checking again my voltages are indeed in the ballpark of where they need to be. I found another voltage chart from a JCM 800 and mine seem to be in the right range for the transformers I am using. Here are my correct readings: [img:506:88]http://www.joepopp.net/JCM%20800...

Jana wrote:Okay.

Something is still weird. Pin 7 of V2 should read the same voltage as pin 1 of V2--they are (should be) connected with a wire.

Let me recheck Monday. The 100k resistor would have no effect?

Jana: Typo! 177.5 it should read. Updating now. DOH!

So logged all of the voltages on the amp and compared them to the voltages Mark Huss recorded. Mark Huss Voltages: [img:798:121]http://www.joepopp.net/JCM%20800%20Combo%20Project/JCM800%20Combo%20Pictures/hussvoltages.png[/img] My voltages all seem relatively ok (My PT puts out 425 volts while Mark'...

If disconnecting that cap stops the hum clip lead it to the preamp ground wire on the pots. I would bet the hum will still be gone. I currently have it to a lug on the filter cap itself. But that lug also shares the Preamp bus. It is currently like the below link. Jana mentioned moving it which I h...

I am not sure if it is 60hz or 120hz. Is there an easy test for that? Very simple. The A (5th) string is 110Hz. 120Hz is between A# and B. 60Hz is one octave lower between A# and B below the low E string. Just plug your guitar in and tune up the A string a little and see if you can match the tone f...

Yes, great looking build--it's drool central for me! It sounds like the hum is from a grounding issue. I took a look at the link you posted and I would not be comfortable with that grounding scheme. I really hate to tell you to start moving wires around--such a beautiful build. But, if it was me, I...

I am thinking it is the filter cap can under the board. When I disconnect the ground for that cap the noise is gone. I ordered some new F&T's that I will swap in for the ARS. I also did a ton of research and it seems that a filter cap is the problem with this kind of hum. I am not sure if it is 60hz...