SOLVED M800 and Golden Folks Overdrive hum at 18v (no hum at 9v)

[sbn31]

Hi, i tried running my M800 then my Golden Folks Overdrive on a 18v-2A dc switching psu (brand Rockpower) and i get the same drone hum when the effect is on. These 2 pedals are based on 201 jfet (thru hole no smd).
- There is no hum when running these 2 pedals at 9v.
- The PSU is new and I get no hum when powering an Aion Titan (OCD).

Any advices ?
Many thanks !

 

[jwin615]

You'll probably have to rebias it to get it to work at 18V.
Are you playing an active bass with super hot output? why do you want to run it at 18v?
Fet circuits aren't like other circuits that rely on a simple voltage divider or inverter and can run at 9-18v without issue(TS style).
Also, I'd recommend against just running 9v pedals at 18v unless you know it's cool. I've seen plenty of production pedals with power smoothing/filter caps rated near or under 18v. Some rated for 10v(looking at you Peavey)

 

[jwin615]

It may also just be a crappy power supply. Not all equal. Far from it.
Try it on something designed to run on 18v.

 

[darwin999]

@jwin615 raises some good points - do check your capacitors' voltage ratings as well.
Also, are you sure it isn't a grounding issue? That can often cause hum.
When you ran them at 9V, was it with the same supply connected the same way - or did you use a different supply?

 

[Paul.Ruby]

Could be either lack of earth ground or a ground loop. Your rig MUST have exactly one connection from earth ground to signal ground on your pedal board. Not 0 and not 2 connections. If you only have one power supply for all your pedals, that power supply must have a 3-pring earth ground and the earth ground must be connected to the negative of it's output. If you have more than one power supply, only one should have earth ground or you make a ground loop.

 

[sbn31]

Hi, many thanks for your answers and advices. I was just curious to ear those jfet circuit in 18v but it's not a big deal. I did test one by one with 2 differents psu one 9v the other 18v.
I will do some tests.

 

[sbn31]

So I did some tests and I conclude that the drone hum in 18v is relative to biasing on the 2 pedals and disapear almost when rebias.
Then I went back to 9v settings because that sounds more fat to me.
The Golden Folk Overdrive sound Nice with nominal bias setting so I kept them for now.
For the M800 I discovered something. When biasing Q2 i was unable to go under 4,8v so I did research and I replaced the 100k trim pot with a 200k that fixed the issue. Then I rebiased all the j201 with settings found on the PAL M800 pedal (all pot were at mid o clock)
Q1=3,74
Q2=3,36
Q3=3,36
Q4=9v (tied direct to 9v)
Q5=4v
Q6=3,15v
(I use thruhole j201)
The result was MAGIC clearly not the same pedal. The gain range is larger, more progressive and the pedal sounds quite better on everything. So 4,5ish settings are only a starting point.

Cheers