Power section hum?

[dehughes]

INPUT JACKS!!!

Okay, I'll try not to get too excited, but I think I've solved the hiss problem.

The low level hum is power tranny hum that isn't getting filtered out due to the low filtering in the amp. Raising the filtering reduces this noise...problem solved.

The hisssssss and crackles are coming from, I BELIEVE, the input jack grounds. Moving/adjusting the grounds made a difference anywhere from nearly quiet to full squealing psycho noise. SO, I'm inclined to think that the hiss issue is coming from a lack of a good input jack ground.

SO, being as I have normal Switchcraft jacks that are currently just held to the chassis via a lock washer (and grounded there) how would I go about connecting the sockets to the ground buss bar? Would this even be a good idea? That is, should I connect the ring and sleeve of the "high" input to the ground bar, or do I need to wire in the "low" input to the buss bar also...?

For some reason when it comes to input jacks my brain gets all wobbly and lame...

THANKS!!!

[rhinson]

in your pics you don't have any star washers on the jacks on the inside of the chassis---i would use some. also check and make sure the jack barrel isn't spinning and has loosened from the jack housing--if so you'll need to toss it in the garbage. you don't need to connect these to the buss if they're ok---it's a not needed ground loop if you do. i'd replace them with cliff/rean marshall/hiwatt style plastic jacks and then connect ground at the first of the buss and then you'll know for sure if it's your problem. btw, you'll get massive squeals with the vol up a little and if you slightly move the jack tip from being shorted to the switch lug. rh

[dehughes]

in your pics you don't have any star washers on the jacks on the inside of the chassis---i would use some. also check and make sure the jack barrel isn't spinning and has loosened from the jack housing--if so you'll need to toss it in the garbage. you don't need to connect these to the buss if they're ok---it's a not needed ground loop if you do. i'd replace them with cliff/rean marshall/hiwatt style plastic jacks and then connect ground at the first of the buss and then you'll know for sure if it's your problem. btw, you'll get massive squeals with the vol up a little and if you slightly move the jack tip from being shorted to the switch lug. rh

The jack barrel seems to be solid...

Then, there is the issue of space...I don't have space for the Marshall style jacks, so I'll have to use these Switchcraft ones...otherwise, I'd do just what you say.

I put some star washers on, but I had to put larger ones on which grab just on the outside of the jack shoulder....they are touching metal, just not the shoulder that is one piece with the threaded shaft of the jack. This was due to the fact that 1) the threaded shaft of these Switchcraft jacks is too short to allow the normal size lock washer, and 2) my faceplate is a plexi-type, so it is thicker than the normal metal faceplates. The combination of the faceplate thickness, the shorter threaded jack shaft, and the relative close proximity of the turret strips has provided a relatively cramped space. I don't have oscillation issues, but I also don't have much room to work.

SO, I'll have to hit up S2 and grab the Switchcraft L12A...they will be perfectly long enough to let me use a lock washer AND actually thread the nut on. Then, with the lock washers on, I wager I'd get a better ground connection, as the non-shoulder metal on the jack is only touching the shoulder, NOT part of it. Yes?

Alrighty, more parts to order!

It's funny, as drz400 said right at the beginning that it was a ground issue and/or heater hum.... He sure was right about the ground issue...I just didn't know exactly WHERE the issue was. Now, I believe I do. Thanks guys!

I'll post back when I've made more progress...

[dehughes]

Alrighty...here is what I've found:

Power section hum: Almost gone. I installed a 440k-ish 2w resistor from the 1st filter cap to ground, and this has basically removed all power section hum. There is a little bit, but the preamp hiss is significantly greater and essentially masks what little power section is left. Doubling the 1st filter cap value from 16uf to 32uf gets things relatively hummm free. So, I'm all but certain the heaters are not an issue regarding the low, 60hz power section hum. I wager this was just a byproduct of the stock AC30 schematic, as the filter values are pretty low anyway...and installing that resistor to ground along with re-flowing that 1st filter cap/resistor/choke turret AND adjusting the B+ wire runs in the preamp seems to have taken care of that low hummm. WHEW!

Preamp hiss: BY FAR the worst problem. Oddly enough, the EF86 channel is way quieter than the 12AX7 side! I'd have figured it would be the opposite, actually. I'll take that as a compliment that I did SOMETHING right. No. I won't. I'll just call that a measure of luck...

I thought it might be the jacks, and it still may be, but I re-wired them and re-ran the wire from the jack to the grid of the 1st 12AX7 and the hiss is still there... The preamp hiss on the 12AX7 side is still pretty bad when the amp is FULL OPEN. At high gain/low master levels it really isn't too bad...but worse than it should be, based upon my many years of listening to very high build quality boutique amps. I know it is somewhat foolish to expect that same level of quality in my first build, but I KNOW that this problem is something simple and something stupid, and I WILL figure it out. Seriously, once this hisss is under control, this amp will be one of the very best I've ever played....and yes, I'm biased, but it really turned out COOL.

So, I re-flowed all the solder joints on all three 12AX7 sockets and their corresponding connections to the turrets. I also re-flowed all the solder joints on the other side of the components, leading to the pots, etc.., and re-flowed all the joints on the pots themselves. I also re-flowed the ground connections from the pots and the 12AX7 components to the buss bar. I installed lockwashers on the pots and the jacks so they are now fully secure and have a good, solid chassis connection (isolating the jacks from the chassis did nothing to reduce the hiss...so I went back to Plan A).

Would heaters cause that typical preamp hissss? I seem to think of them as causing other types of noise, but not that "too much preamp gain" hiss... Please correct me if I'm wrong.

Again, killing the EQ network completely removes all traces of hiss...but that's not saying too much as that would also take down the good signal. What I do believe this to say is that the hiss is coming either FROM or BEFORE the EQ network, which, if I have things correct, eliminates the PI from the equation. Yes? Please correct me if I'm wrong...(and I'm wrong a lot, apparently... )

Thank you all SO MUCH for your help.