Steel String Singer #002 Build - Noise Problem

[timrobertson100]

Before replacing parts, I’d suggest chopsticking a little more unless you are sure you’ve done enough. Get it loud, move every single red wire (e.g. standby switch) and poke the solder joint it connects to (e.g the cap can b+ on the signal board) - I say this just because it still sounds incredibly like mine did when the b+ had noise. Keep us posted.

[Richard1001]

You said the hum gets louder when you turn up the first volume pot. On the picture, the hum seems to be around 100 - 120 Hz.

I can't realy see how the cap can is connected and how it is grounded. Can you make a drawing of the wiring?

And did you shield the top of the amp while testing?
If you didn't, the preamp of your amp can pick up stray electrical interference. Always shield the open side of the amp and see how much hum remains, or else you may be chasing ghosts.

[Galef]

I can't realy see how the cap can is connected and how it is grounded. Can you make a drawing of the wiring?

The cap can is grounded on the Lug Strip, the can has one negative pole, and there is a black wire that goes to the lug strip. Hard to see of course.
The rest is as on the plan of Ryan.

And did you shield the top of the amp while testing?

Yes i already tested it with shielding, different cables, different rooms and different power outlets.

I get my scope back tomorrow, but the next days im a little busy. I hope i can get back to the amp on the weekend.

Thanks @all

[Galef]

So yesterday i tried to find the noise with my scope but around V1 i see nothing, the B+ supply after the plate resistor also looks good. Of course my scope is an relatively cheap USB Scope (I can only measure up to 400v with a x10 probe) and little artifacts are always there but with a 1000hz 150mv test signal i only see a good wave around V1. The same on V2 and V3.
But i must say working with a scope on a tube amp is something new to me. I read/watch a few tutorials.
Maybe someone have an idea where to measure exactly in this particular amp?

All Ground Points measure 000,0Ohm also the Pot Cases; I chopsticked everything, every solder connection, every cap, every wire. The only wire that makes real noise is the wire from the middle lug of the Volume pot to the bright switch. I measured the Coax cables and they are good, of course in circuit i have to take the pots into account.
I cleaned all tube sockets and pots.

The noise is not very loud, a single coil hum is louder than the noise, and the guitarsignal itself is a lot louder. So in principle i can live with that but i can hear that this amp is on.

Are your amps completely silent with Master and Preamp at noon without any input?

[erwin_ve]

Hi Galef,

When measuring hum you dont have to inject a signal at the input.
The hum is the signal you want to scope.
Youre looking for a 60/120Hz signal. Set the scope at 0.005 s/div( horizontal) a 60Hz signal should take around 3.5 divisions for a cycle, a 120Hz around 1.5 division for a cycle. The volt division (vertical) start with 100mV, if it isnt clear, lower it to 50mV etc. And measure after the coupling cap, not the actual plate itself.

Just follow the signal path from the first volume pot upstream. You mentioned the hum became louder when opening that pot. So you should be able to measure hum at that point on your scope.
My SSS002 has hiss and it is absolutely deafening loud while playing with the settings you mentioned.

Erwin

[Galef]

Thank you Erwin for your help.

i think i found the problem, its on pin 8 of V2 i can measure 150hz on the 0,22uf LNFB cap and on CX02 0,01uf. And from there its in the signal chain. I will now check the tube and components.

[timrobertson100]

Can you still eliminate it using the high filter?

[Richard1001]

On the second picture in the opening post, i think i see a single ground wire going to a solder lug which is lose. The lug itself looks like it is not screwed down to the chassis, or so it seems in the picture. It is just above/next to the plastic mount you used for the primary OT wires.

[sergio]

Hi , congrat for the build.
If you have a good twist AC rail , I suggest to check all the PCB board solder ground joint. And re-adjust your lead dress

Sincerely. I don't like the pcb for this type of amp, but that's my personal taste.

[erwin_ve]

Hi , congrat for the build.
If you have a good twist AC rail , I suggest to check all the PCB board solder ground joint. And re-adjust your lead dress

Sincerely. I don't like the pcb for this type of amp, but that's my personal taste.

Original Sss002 is also pcb, and the pcb used on this build has through holes, soldering from top is possible. This pcb has all connections labeled which should minimize connection errors.
For this type of amp it is the way to go imo. What are your considerations?

Erwin

[erwin_ve]

Thank you Erwin for your help.

i think i found the problem, its on pin 8 of V2 i can measure 150hz on the 0,22uf LNFB cap and on CX02 0,01uf. And from there its in the signal chain. I will now check the tube and components.

Hi Christopher, you mentioned in your initial post that opening your first volume pot increased the hum meaning the hum is generated somewhere in v1 tube or was this a typo?

[Richard1001]

If all the above mentioned things don't work you could try to get rid of the hum by using a balance pot on your filaments. Just remove the two 100 ohm resistors and replace them by a single 250 ohm trimpot, center lug to ground. You should be able to adjust the hum by turning the trimmer. I think the 150 Hz hum could be caused by filament imbalance if you have a 50Hz mains frequency.

Before this, first check if you wired all the tube filament wires the same way.

[bepone]

My artificial heater-CT is near the PT and not at the same spot like on Ryans layout, maybe is this a Problem?

yes, put is at the preamp side, out of high currents

also i have seen transformer secondary wires on the air, highest currents in the amp, radiating everywhere, they should be pressed against the chassis and routed on the chassis (i put them outside ot not interfere with the preamp circuits)

[bepone]

Thank you Erwin for your help.

i think i found the problem, its on pin 8 of V2 i can measure 150hz on the 0,22uf LNFB cap and on CX02 0,01uf. And from there its in the signal chain. I will now check the tube and components.

those spikes are probably rectifier diodes switching on off, collected by some wire and inserted to the signal circuit. try to see if they are in the heater line? if yes, then.........

[Galef]

Thank you Erwin for your help.

i think i found the problem, its on pin 8 of V2 i can measure 150hz on the 0,22uf LNFB cap and on CX02 0,01uf. And from there its in the signal chain. I will now check the tube and components.

Hi Christopher, you mentioned in your initial post that opening your first volume pot increased the hum meaning the hum is generated somewhere in v1 tube or was this a typo?

I think they are two noise "issues" one is this 100/150hz hum and then this 3000hz noise. On my picture with all of the frequencies we can see that there are these two who are relatively loud. When i use the high filter i can reduce this 3000hz noise and then it seems way quieter.

The noisefloor is still the same as in my recording and react the same way with the filter.

Thank you Erwin for your help.

i think i found the problem, its on pin 8 of V2 i can measure 150hz on the 0,22uf LNFB cap and on CX02 0,01uf. And from there its in the signal chain. I will now check the tube and components.

Hi Christopher, you mentioned in your initial post that opening your first volume pot increased the hum meaning the hum is generated somewhere in v1 tube or was this a typo?

Yeah, that is correct, but around V1 i found nothing with my scope; I only found this 150hz hum on V2.
Maybe the 3000hz noise comes in at V1 and gets amplified; and the 100/150hz hum come in at V2.

On the second picture in the opening post, i think i see a single ground wire going to a solder lug which is lose. The lug itself looks like it is not screwed down to the chassis, or so it seems in the picture. It is just above/next to the plastic mount you used for the primary OT wires.

Yeah it looks like it is loose but that only this slightly bigger lockwasher. The connection is good, but good eye

Thank you Erwin for your help.

i think i found the problem, its on pin 8 of V2 i can measure 150hz on the 0,22uf LNFB cap and on CX02 0,01uf. And from there its in the signal chain. I will now check the tube and components.

those spikes are probably rectifier diodes switching on off, collected by some wire and inserted to the signal circuit. try to see if they are in the heater line? if yes, then.........

Good Idea i will measure this, thank you

If all the above mentioned things don't work you could try to get rid of the hum by using a balance pot on your filaments. Just remove the two 100 ohm resistors and replace them by a single 250 ohm trimpot, center lug to ground. You should be able to adjust the hum by turning the trimmer. I think the 150 Hz hum could be caused by filament imbalance if you have a 50Hz mains frequency.

Before this, first check if you wired all the tube filament wires the same way.

Thank you, i will look into my filament wiring and try this out with the balance pot, i think i have one from an Silverface Fender.