Developing the DIY "Champ" for first time builders

[xtian]

Finished and working! Just did some quiet testing (it's loud!) and checked voltages:

B = 298
B+1 = 261
B+2 = 226
power tube pin 8 (cath) = 15.7
pin 3 (plate) = 290

This is my fourth SE amp, and it has the typical, low level 120Hz hum. I followed RJ's star grounding, except for running the input jack's ground way over to the lug for the mains ground. Could that possibly help, given the fact that the input jack is making contact and is grounded to the chassis where it's attached?

Also, I notice that RJ grounded pin 9 of the preamp heater. I did not. Let me know if you think this might help the hum.

I have battled this damn hum in all of my SE amps, and have never had any success making it better. I've replaced CTs with artificial CTs, elevated voltages, rerouted ground wires, manipulated lead dress, etc. I just can't eliminate that hum.

FYI: Total build time was about 8 hours.

[xtian]

Finished amp glamour shots.

[RJ Guitars]

Finished and working! Just did some quiet testing (it's loud!) and checked voltages:

B = 298
B+1 = 261
B+2 = 226
power tube pin 8 (cath) = 15.7
pin 3 (plate) = 290

This is my fourth SE amp, and it has the typical, low level 120Hz hum. I followed RJ's star grounding, except for running the input jack's ground way over to the lug for the mains ground. Could that possibly help, given the fact that the input jack is making contact and is grounded to the chassis where it's attached?

Also, I notice that RJ grounded pin 9 of the preamp heater. I did not. Let me know if you think this might help the hum.

I have battled this damn hum in all of my SE amps, and have never had any success making it better. I've replaced CTs with artificial CTs, elevated voltages, rerouted ground wires, manipulated lead dress, etc. I just can't eliminate that hum.

FYI: Total build time was about 8 hours.

WOW - looking good! I've since removed that ground off of pin 9 and didn't notice a difference. I got kinda worried that somebody would pop in a 12AX7 and there would be a short to ground and before you know it a ruined PT...

Try grounding that pin 9 and see if you solve the issue, maybe it's needed.

I see you grounded the center tap on the heaters - That is good? I'll also assume you made sure the path to ground is good by scraping away some of that really cool paint job you did.

The Star grounding on this might be too minimal to be effective. Randall Aiken has a great tech note on star grounding - worth the read. From that article it basically states you need to isolate each section of the amp with a discreet path to ground. I didn't take things that far in this design, maybe we need it.

For starters, I think you want to get everything on a separate ground wire from the filter caps, especially the first one. It's handy to bring them all back to that corner post, but maybe more wire would work better.

keep us posted on how it's going.

rj

[telentubes]

Interesting observation... I fixed my reversed 10K and 22K resistors between the e-caps and maybe(?) made some improvement in tone (not sure), BUT... the hum is more noticeable, maybe even bothersome, where it wasn't an issue AT ALL when the resistors were in backwards. I assumed I heated some components way too much (resistors, diodes), as getting the winds off the turrets took some time, and damaged them, or possible left some flux residue that resulted in poor solder joints. Any could be the case. I'm going to replace the parts in question and report back. Interesting that the "hum" topic has come up. My amp was pretty quiet at first power up, with resistors in backwards..

[M Fowler]

I know my circuit is a little different but not much and I have attached a paint brush photo showing my grounding all to three grounding tabs I drilled a hole and bolted to the chassis. I did not use the PT bolt.

This amp is quiet. I forgot to take final build pictures and the amp is in the combo cabinet now.

Mark

[RJ Guitars]

I know my circuit is a little different but not much and I have attached a paint brush photo showing my grounding all to three grounding tabs I drilled a hole and bolted to the chassis. I did not use the PT bolt.

This amp is quiet. I forgot to take final build pictures and the amp is in the combo cabinet now.

Mark

That looks like the way I was thinking would be best for a grounding scheme... curious what differences it might make to if you have a hum issue.

rj

[surfsup]

What mark did was what solved my HO hum. A sectioned star ground scheme. Same except i have a ground at input jack and also grounded v1 there as well with a lead off the filter cap's neg side.

[surfsup]

I have battled this damn hum in all of my SE amps, and have never had any success making it better. I've replaced CTs with artificial CTs, elevated voltages, rerouted ground wires, manipulated lead dress, etc. I just can't eliminate that hum.

Dont get me started...!

One thing you might want to also do, on rj's layout, the pt r/c cathode ground is tied to the v1 ground...i would split that off.

To do that, I would put a turret between the last filter cap and the Ck (just above the right lug on the pot on rj's layout on previous forum page, smack dab above the pot in ur pic) and put the R/Ck ground there, tied to the 2 filter caps for the powertube, and run the last green gnd off the two resistors only. Those three gnd leads to a star ground by the chassis like mark.

[RJ Guitars]

I tend to agree with running more individual ground wires if you don't have success where you are, but that might not be the only place to look.

You guys had me wondering so I just cranked up mine again to see if I had any excess hum. I've got minimal hum and was pleasantly surprised how nice this amp sounded.

I'll give you a gut shot on what I did. Keep in mind that this is the prototype and yours will not be exactly like mine. My power supply layout is a reverse image of normal but in this case it helps you see how I grounded everything.

You can see I pulled that ground lead off of pin #9 and it makes no audible difference.

Also, I don't think anybody mentioned anything about hum until these first few premiums were built. The obvious difference there is the tranny set... and in theory they have better filter caps. Dr. Fowler doesn't have any hum in his so it's a good mystery so far.

Keep digging, I am anxious to shake the demons out of this thing and be able to right "final" on the drawings.

rj

[xtian]

Star grounding is not helping me! See photos. I ran independent wires from B+, B+1,2, power tube cath ground, volume pot, input jack, and v1a cath. I did these one at a time to see if any made a difference. (Incidentally, with tubes installed, this amp discharges almost immediately--did you notice?) I removed the top two screws holding the turret board down, thus removing the connection to the chassis at these points, and thus allowing my new star grounding wires to be true.

Next I detached the input and output jacks from the chassis. No help. The output jack, in fact, wants to be grounded to the chassis--this is the only time I noticed a change in the hum; it got worse when not attached to the chassis. Clue here?

[surfsup]

Hard to tell, but your v1a cathode, is that gnd tied to the corner of the board, where it goes to the inpuyt jack grnd (green short lead), AND a lead goes to the star gnd near the PT? (brown long lead)

Also i see your PT R/Ck is still connected to the sa,e turret as the components coming off preamp tube, did you try splitting that off?

Edit, also did you have the back of the pot grounded b4?

[telentubes]

RJ,
Looks like the 10K and 22K resistors may be backwards in the most recent layout drawing you posted on page 23..

[xtian]

Hard to tell, but your v1 cathode, is that gnd tied to the corner of the board, where it goes to the inpuyt jack grnd (green short lead), AND a lead goes to the star gnd near the PT? (brown long lead)

Also i see your PT R/Ck is still connected to the sa,e turret as the components coming off preamp tube, did you try splitting that off?

V1a and V1b cath r/c grounds both go directly to star ground.

My power tube's cathode (pin is connected via yellow wire to 470R (the green one) and 22uF cap. I have lifted the 220K resistor and run it directly to ground, and the cathode's r/c has it's own star ground. No difference in hum.

[surfsup]

Instead of running a lead from the Ptube cathode to star, maybe try connecting it to the middle railcap, not the one next to it and break the gnd connect btwn the two 8ufs? That puts the Ptube grounds on its respective cap.

Run the v1 cap lead to star, maybe, and the preamp gnds to the preamp railcap, the last 8uf. That puts all the v1 grounds on v1 cap.

Also, i edited my other post, did you have the back of tje pot grounded b4?

[surfsup]

Looking again at marks, he has all the v1 going to star except v1 rail cap. He has that feeding to the Ptube RCk (btwn the two 8ufs) and then to the Ptube railcap, to star. Which obeys the smaller-to-heavier flow rule i read about. But your all go to star now...

You could try to connect the Ptube RCk to the middle cap running a lead around the last v1 cap.

Is that resistor connected to anything?

When i laid out the x10 build i posted the layout with the RCk for the Ptube next to the Ptubes cap, i later put it on the end of the board, mental note ... Move it back where i had it!