Developing the DIY "Champ" for first time builders

[M Fowler]

Okay I am trying to help figure out the hum problem but first I notice this e-cap is in backwards right?

Mark

[surfsup]

I believe the cathode lead runs under the board then double backs up over the board under the horizontal resistor above that cap, so its right. But the flash on the photos makes it hard to know for sure.

[xtian]

I tried grounding the volume pot body, and separate star ground for each of the three power filter caps. Again, no change. I also tried lifting the negative feedback line. No change.

So I ripped out all the extra ground lines I had put in, and reverted to my original design. Absolutely no change in hum. Nothing I did made a tiny bit of difference, except when I lifted the output jack away from the chassis, and the hum got worse.

I feel defeated.

[xtian]

Okay I am trying to help figure out the hum problem but first I notice this e-cap is in backwards right

No, it's OK. The negative end goes to ground, the positive to the cathode.

[RJ Guitars]

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

Thank you - Updated and revved. rj

[RJ Guitars]

I tried grounding the volume pot body, and separate star ground for each of the three power filter caps. Again, no change. I also tried lifting the negative feedback line. No change.

So I ripped out all the extra ground lines I had put in, and reverted to my original design. Absolutely no change in hum. Nothing I did made a tiny bit of difference, except when I lifted the output jack away from the chassis, and the hum got worse.

I feel defeated.

Hmmm - it's puzzling, but failure is often critical to success, so you are clearly on the road to success... if that helps.

I cranked mine up again and wanted to see if maybe I was just being too hum tolerant. I considered that maybe we were using a different threshold for an acceptable amount of hum but mine is really very good, especially for a SE amp. Certainly nothing that is begging for attention.

So I started looking at the drawings to see if there was anything remarkably different from my own build and the drawings. A couple things seem worth a look. I updated all the drawings that I've currently posted with a better representation of the input and output jack wiring. It is possible that someone might have run the feedback lead from the ground side of the output jack rather than the business end. I'm not sure what would happen in this case, but it's worth a check.

I went ahead and upgraded everything on my Eagle 100 to be schematically the same as layout 1.4h. It sounds very good and has minimal hum. I'd say it's gig worthy at this point and the amp would not be the weak point in a live performance when I am the player. At the 2 & 4 positions on the Strat it is a little compressed and there is no real excess of headroom regardless of which pickup I use. Rolling back the volume becomes very useful and it's plenty loud... the neighbors already confirmed that for me.

Let us know if any of this helps.

rj

[rhinson]

I tried grounding the volume pot body, and separate star ground for each of the three power filter caps. Again, no change. I also tried lifting the negative feedback line. No change.

So I ripped out all the extra ground lines I had put in, and reverted to my original design. Absolutely no change in hum. Nothing I did made a tiny bit of difference, except when I lifted the output jack away from the chassis, and the hum got worse.

I feel defeated.

you probably need more and different filtering in the power supply (the advantages of this was mentioned a few pages back in this thread). i'd try 33uf, then a choke (a fender twin choke would do fine) or even a small value resistor--say 50ohms/5-10watts, then another 33uf after that------all as the first filter bank-----known as a "brute force" filter bank (used in lots of old amps). something like this should help get rid of the power section hum. and as always, ground the power section stuff on that side of the chassis and the preamp stuff on the preamp end of the chassis. and it doesn't hurt to float dc on the heaters (if you've got a cathode follower in the circuit esp.), which i believe you have already done. rh

[rhinson]

duplicate

[ToneMerc]

you probably need more and different filtering in the power supply (the advantages of this was mentioned a few pages back in this thread). i'd try 33uf, then a choke (a fender twin choke would do fine) or even a small value resistor--say 50ohms/5-10watts, then another 33uf after that------all as the first filter bank-----known as a "brute force" filter bank (used in lots of old amps). something like this should help get rid of the power section hum. and as always, ground the power section stuff on that side of the chassis and the preamp stuff on the preamp end of the chassis. and it doesn't hurt to float dc on the heaters (if you've got a cathode follower in the circuit esp.), which i believe you have already done. rh

I have mine setup in a similar way and my grounds segregated as well.

tube rect>39 ohm 5W>30(32)uf>4H>16(19)uf>resistor>16(18)uf

TM

[surfsup]

Xtian, RJ, has the schematic for your eagle premium ever been posted?

Could an updated schematic be reposted? I saw the supre svhemo, cant find this one in all the pages. Or maybe edit the first OP and put em all there.

[telentubes]

My hum is typical of most small old Fenders I've played. Still, I'm thinking of a little more filtering, as was suggested. Mark used a little more filtering (16uf to 22uf) for that first e-cap. And how bout the "headphone trick" to see if any hum is coming from the OTs proximity to the PT?

I like this amp and have been playing through it a bunch.

[surfsup]

Instead of adding a choke, etc, can't he add another C before the Ptube? per Merlin:

" Adding a second filter before the power valve is sometimes done in single-ended amps"

http://www.freewebs.com/valvewizard1/smoothing.html

He goes on to say the choke is essentially overkill because it is not a high-powered amp, though maybe I'm assuming here.

[rhinson]

Instead of adding a choke, etc, can't he add another C before the Ptube? per Merlin:

" Adding a second filter before the power valve is sometimes done in single-ended amps"

http://www.freewebs.com/valvewizard1/smoothing.html

He goes on to say the choke is essentially overkill because it is not a high-powered amp, though maybe I'm assuming here.

yes, 2 filter sections separated by either a choke or small value resistor (to increase ripple reduction)----ALL as the first filter section. this is much better than just a single section, unless you REALLY increase the first cap/single cap. you see this done quite frequently in se amps and older p/p amps as well-----the brute force front end really helps to reduce ghosting in bigger amps (but you need a big choke here) while helping to keep the vintage feel of lower filtering. rh

[M Fowler]

There is plenty of room next to the board to add another filter cap on turret strip or small board. Plenty of room on the top side or inside for a choke as well.

I would start with the larger main filter cap and resistor (in place of the choke) before having to buy a choke.

My little amp has a very low level of hum standard of this type of amp. I went with 22uf and I may add the 50R rhinson suggested just to see how that affects my amp beside I should post the final gut shot and cabinet shot. Need to go through the motions of pulling this apart. Ufta!

Mark

[surfsup]

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

Looks like B is 300ish, I am going to keep this in mind with the supre amp.

But I am still wondering how bad the hum is. If its bad, it could be a ground loop. I doubt (maybe I'm wrong) that RJs and teletubes builds would be fine without the extra cap. Why is xtian's behaving so strangely? I wonder if it has something to do with the paintjob.

Wonder what would happen if he disconnected the blue lead to the 2.7k resistor off the OT. Not sure if that would affect anything.

Didn't he also wire the heaters a different way than normal?