Rocket Hum

[mickephoto]

Andy - Wow! I thought I had already tried all possible grounding combinations with no difference, including removing the pots from chassis to isolate. I did both of the above and in combination with a heavy aluminum cover placed under a large book it's a night and day difference. I am so thrilled!!!

Why do all Rocket layouts I've seen use both bus bar behind pots and wire/bar to chassis? In my case separating preamp filter grounds from mains (still going to the same point on chassis) may have been a bigger factor though.

Regarding the cover suggested before. I should have tried this right away because it did make a major difference! For some reason I have never experienced this in the past so I didn't bother.

Now I just need to figure out how to make a real aluminum cover. Any ideas for cutting:-)

Thank you so much all for the effort and good suggestions!!!

[Tillydog]

Why do all Rocket layouts I've seen use both bus bar behind pots and wire/bar to chassis? In my case separating preamp filter grounds from mains (still going to the same point on chassis) may have been a bigger factor though.

Short answer is "I don't know" - If you interpret that layout pedantically, there isn't a connection between the busbar and the back of the pots, so the wire to ground would be necessary. If you look at the pictures of the 'Francesca' TW Express which has the busbar soldered to the pots, then there isn't a separate ground connection to it.

Anyway.....

Glad to hear you're making progress

Andy

[mickephoto]

Interesting and it all makes sense for sure. Again, in my case the reduction in hum seemed to be mainly due to separating filter grounds and the shield/cover, but they all add up for sure.

Next I'll remove the 68k input resistor and mount on the tube socket with shielded wire. Yes, only one side to ground:)

Now it's fine tuning and that's where the fun begins. Not with major hum...

[cbass]

Glad to here you found the problem.I never understood the buss bar soldered to the back of the pots.I don't do it on any of my amps.Never had any hum problems.

[mickephoto]

This is a great thread about transformer vibration / hum: https://tubeamparchive.com/viewtopic.ph ... 15b9a7d786
The Heyboers I use are pretty loud when close to them, and to some degree it affected my overall hum perception. I can still hear some hum through the speaker when in Standby. This is most likely due to orientation and proximity, not the construction of the transformers as mentioned earlier.

Once installed in a cab and while Rockin' out at high volumes these transformer hum, not ground loop, issues may soon become a distant memory. When I've just finished a build I get overly sensitive to hum. Now I hear it everywhere in my house. Amps or not

[surfsup]

Andy - Wow! I thought I had already tried all possible grounding combinations with no difference, including removing the pots from chassis to isolate. I did both of the above and in combination with a heavy aluminum cover placed under a large book it's a night and day difference. I am so thrilled!!!

Man, that's awesome. I remember my first amp. I followed the layout (bussbar) and had tried to debug hum for months. Sooo frustrating. Then I went to a star gound, fired it up, and it was like winning the lottery!

[mickephoto]

Yes, debugging can be very frustrating indeed. I learned a lot in the process though. Here's a photo of the final amp.

One thing worth mentioning...someone recommended hot glue for the cap stack. After some serious heat from playing and then moving a few wires around, once it was cool, the whole thing almost came off from the chassis. I redid parts of it with a silicon glue "Liquid Nails" and hope this works better. The chassis connection is my main concern with all the heat buildup.

If I do another Rocket I would seriously consider mounting them on a board. Besides the possibility of coming off, excessive heat can't be good for longevity of the caps. 65 C Max...I think my chassis was close to that.

[mickephoto]

Here's an update a few weeks later for future troubleshooters...

Initially I thought the aluminum cover made a big difference, but it really only helped when the amp was upside down while working on it in a room with dimmers. Occasionally the aluminum foil (now switched to a plate)would also touch the speaker selector, shorting it out, which eliminated hum and made it very quiet. It also removed the signal

A cover is a worthwhile investment, but it is not a hum solution. It's main use is for RFI prevention.

I have since, once again, tried every possible grounding combination known to the internet and man, including several made by Gerald Weber in his weekly webinar where we discussed my amp. The amp still has some 60hz hum.

After going a bit nuts trying to solve this I compared the Rocket in detail to my other amps...Dumble clone, Victoria Double Deluxe, JTM 45, Plexi 50, Matchless, Tweed Deluxe and others. I found that while the Rocket was not the most quiet, it was certainly not the worst. E.g. the Double Deluxe had a lot more 60hz hum. For some reason I never reflected on this much since I didn't build it. I've gigged with this amp for years though.

Point is that to some extent we have to live with some noise and hum in our beloved guitar amps. Makes me wonder how they build the high end HiFi stuff that are dead quiet. Filtering galore perhaps. I need to open up my Audio Research HiFi pre next...

[Big Jim]

I do another Rocket I would seriously consider mounting them on a board. Besides the possibility of coming off, excessive heat can't be good for longevity of the caps. 65 C Max...I think my chassis was close to that.

I am getting ready to start a Rocket. My plan is to board mount the capstack. My chassis is 2 1//2" deep....this should hopefully allow me to do that easily.
Jim

[mickephoto]

Sounds like a good plan and the height should be enough depending on which caps you use. Perhaps with any cap choice.

The Liquid Nails I used to mount mine has proven to work well so far. Much better than the hot glue.

[rooster]

I would try three things.

#1) Lose the Cliff jack and use a typical shorted Switchcraft - add sheilded wire and a 22K grid stopper.
#2) lift the 100 ohm resistors to the vertical position
#3) Disconnect the half power cathode switch and wiring - just set it up for a straight 4/EL84 Rocket, then go back to the half power setup. Try the Hoffman half-power wiring, BTW, it's a little different than your layout I suspect.

The Rocket is the quietest TW amp there is, you should not have any 60 hertz hum. Sorry to join the party so late.