How Important is the physical OT Placement, hum question

[Structo]

I installed the new OT today.
Check my thread.

[frischmann]

I saw it. I'm glad it went well.

So,
I spent some time troubleshooting.
I checked all the voltages-good
I checked all the grounds-good
I moved the standby wire of the PT-still hums

Then,
I pulled out the new OT and put back the old OT-the hum persists.
I disconnected the Choke and put back the resistor-Still hums
I tried the headphone method-I cannot hear any hum with any of the OT locations I've selected.

So,
This level of hum is either normal and I'm being super critical (I do play loud) or it's a component or layout issue.

BTW,
I did notice a slight dull thump in the background. It's very slight and sounds like a heartbeat and has a regular pulse.

I pulled the preamp tubes one by one and the thump went away. I replaced the tubes and it came back.

Any thoughts on tracking this dowm

[Structo]

Does your amp hum without a guitar plugged in?

Yesterday after I installed the OT I turned both the volume and master all the way up and it was quiet other than the typical hiss or white noise.
No hum at all.
But this amp does get a bit of hum when guitars are plugged in, I just figure it's the guitars picking up stuff.

[mlp-mx6]

But this amp does get a bit of hum when guitars are plugged in, I just figure it's the guitars picking up stuff.

If the hum disappears when you turn your guitar down, you are correct. If not, there is another source.

[heisthl]

I I pulled out the new OT and put back the old OT-the hum persists.
Any thoughts on tracking this dowm

If the amp was quiet before it may be because of the shielding in the cabinet.
On the background thump, see if you can change it by turning knobs. It may be the washing machine next door

[frischmann]

It hums with nothing in the input.
I don't know if it hums with something plugged in and the guitar volume all the way down.

That's a great point to check.

The shielding and the knbs are good points too.

I WILL get this...

Thanks guys.

[Structo]

My head cab came with no shielding.

I put some Stew Mac copper foil tape on the top of the cab then sanded the powder coat off where the mounting screws thread in to make contact with the foil.

I didn't really notice any change from before after I did this.

[frischmann]

O.K.
I've tried it without anything in the input
With a guitar plugged in and the volume down
with the original OT
With the new OT
With the choke
Without the choke
...and any way you slice it, I have a hum.... Not a big one but it's there.

I tried the headphone trick and there was no discernable difference between where I have the OT and just about anywhere else I could put it....except for on top of or directly behind the PT. Big hum there.

To be sure I'm not just being silly.
If you put the input and EQ at 12:00 and everything else at 10:00...do you get a slight background hum?

Does it increase with the PAB on?


Oh,
I get a slight pop when I switch the overdrive on and of, It kind of sounds like a static discharge.

Does that mean anything?

Thanks,
Paul

[Structo]

No hum here.

Did you do the OD entrance mod?

If so, did you put a pad on the cap to ground? Some use 10M, others half that. That should cure the pop.

[frischmann]

Hi Structo,
Do you mean the 220K and .05 cap after the trimmer?
I did that. I have the 10M resistor on there as well.

[fullerplast]

One additional option, not explored in guitar amps to my knowledge, is to mount the OT at an angle (in the vertical plane) relative to the PT. This will reduce the field coupling where mounting space is at a premium. It certainly would look strange, but who cares if it reduces hum.

Also, PT's that are wrapped in copper will radiate less EMF.

[Structo]

Yes the Brown Note PT has the Copper flux bands on it.

My amp is quiet until I plug a strat or other single coil guitar in.

With humbuckers it's pretty quiet overall.

[frischmann]

LOL,
Well, I sort of did the OD entrance mod... I left the jumper under the board in place so I had it paralled with the 220K resistor.

Removing it seemed to quiet things down a bunch. I had a problem with the lead channel being like 3X louder than the clean side with an insane amount of gain.

This may solve some of the issues. I'm still not sure about the noise floor.
I'll have to wait until the family is out.

[Structo]

Yeah I installed the OD entrance mod yesterday.

I had a hell of a time getting that underboard jumper out of there where the 220K goes.

I didn't want to pull the board because of the way I have it mounted and wired it would have been a pain in the ass.

So I sucked the solder out of those eyelets and then made a hook type thing out of a paper clip and snagged the jumper and was able to pull it out.

Seems to be gainier with the OD mod and possibly brighter.

I had also changed the mid cap to .01uf and the mid pot to 250K.

I didn't like the overall tone after that, made it way too bright.
So I put the .05uf mid cap back in but left the 250K mid pot installed.

I think part of my problem is a small room and having the 2x12 on the floor.

When I was testing it yesterday I was squatted down in front of the cab and man, talk about getting beam blasted!

So possibly what I am experiencing is room acoustics along with not hearing the cab straight on. Or psycho-acoustics......
Also the Tonkerlites I have in the cab may not be the best speakers for this amp.