Tuner and pedal in one enclosure problem

[Lino22]

Guys i put my Si Rangemaster and my old Fender pedal Tuner guts in one enclosure and i can hear buzzing from the tuner. They are fed from isolated 9V lines.

I know i can make a switch to turn the tuner off when not used, just asking - can shielding help in this case? The tuner uses 4MHz crystal which then probably (i don't understand tuners) becomes a reference signal in audible spectrum and that is what i hear right?

Can it be somehow suppressed?

[Lino22]

Yes, the way i put it down is confusing. I'll try again
- I have one enclosure for Rangemaster, Tubescreamer and Fender Tuner. I place this box on  my amp, as i use these effects continuously, and work only with the guitar volume.
- It has its own in-built power supply, with 3 independent, isolated power lines.
- The power for all 3 pedals is constantly on once the power supply mains is plugged in.
- One point star grounding, no ground loops.
- There is a 3 way selector switch i use to select Rangemaster, Tube screamer or Tuner.

I can hear a distorted signal/fizz/drone on background of the Rangemaster/Tubescreamer, most likely from the tuner, as i expect there is some sort of reference signal it generates.
I can make a kill switch for the tuner power, but i prefer not to, i like as few switches as possible, i tend to get nervous on stage when something is wrong and there is too many control elements.

I shielded the tuner inside the box, and the fizz is now barely audible, but still present. My OCD tells me to continue work on it till eliminated.

[Rob Strand]

When the Rangemaster clips the input impedance becomes non-linear and it distorts the signal going *into* the Rangemaster.  You don't notice it when the Rangemaster is active.

If your switching doesn't disconnect the Rangemaster input when the Rangemaster is switched out that form of distortion will leak through the entire signal chain. 

If you hear the fizz with Rangemaster active then it's something else.  (It's possible the tuner has a similar problem but most tuners have an input buffer and the Rangemaster issue is a known.)

[Lino22]

Rob, the selector switch does disconnect all then inputs and connect just the one selected. Only power is left on.
I think i put it confusingly again - even when the guitar is not plugged in, and thus the common guitar input socket is grounded, there is the drone sound on the background mixed with the hiss.

[Rob Strand]

Rob, the selector switch does disconnect all then inputs and connect just the one selected. Only power is left on.
I think i put it confusingly again - even when the guitar is not plugged in, and thus the common guitar input socket is grounded, there is the drone sound on the background mixed with the hiss.

OK got it.

What about if you just trying selecting Rangemaster and the TS-9 individually but disconnect the power to the tuner.

[Lino22]

That is definitely a good idea Rob, i just have to get 3x4 rotary switch. That is what i can do.

[Rob Strand]

That is definitely a good idea Rob, i just have to get 3x4 rotary switch. That is what i can do.

I only really meant it as debugging idea to see if the tuner was definitely the cause.

Generally you can't turn off the power to effects pedals because you get pops in the audio.  If you use the tuner as input only and are disconnecting the input you might be able turn off the power with getting any pops and that means you could use it as a solution.

[FiveseveN]

The interference is usually from the display multiplexing. A simple RC filter on the tuner's power input should sort it:



The resistor should be as high as possible but low enough so the tuner still works, probably in the 10—100 Ohm range. Cap should be proportionally large, probably in the thousands of uF.

[duck_arse]

is the rangemaster positive ground? via an internal chargepump? that might beat against the tuner clock sig.

[Lino22]

is the rangemaster positive ground? via an internal chargepump? that might beat against the tuner clock sig.

It is an Si Rangemaster. The ground is all negative.

[Lino22]

The interference is usually from the display multiplexing. A simple RC filter on the tuner's power input should sort it:



The resistor should be as high as possible but low enough so the tuner still works, probably in the 10—100 Ohm range. Cap should be proportionally large, probably in the thousands of uF.

Do you mean to add the resistor to the Rangemaster and Tubescreamer rail. Right? They both have 220u||100n filter caps already.

[FSFX]

is the rangemaster positive ground? via an internal chargepump? that might beat against the tuner clock sig.

It is an Si Rangemaster. The ground is all negative.

The Rangemaster is a notoriously noisy design to start with unless run from batteries like the original one.
The original DRM design has an exceptionally poor 'power supply rejection ratio' (PSRR) due to a couple of features of its design.

The first main problem regarding noise is that the output potentiometer is used as the collector load for the transistor.
This has two effects regarding noise.
1. The first is that whenever the output level control is turned to its minimum, the signal output of the DRM is connected directly to the power supply of the circuit and so any noise on the power supply is fed in full to the following pedal or amplifier.
2. The second is that DC is flowing through the output level potentiometer and so whenever the level is changed you get a 'scratching' type of noise superimposed on the output signal. 

The second problem is that the bias voltage to the transistor is derived directly from what could be a noisy power supply via a simple resistive voltage divider with no additional filtering. - The problem here is similar to that of the LM386 audio amplifier where providing additional filtering with a bypass capacitor on pin 7 improves the PSRR by about 40dB.

Using silicon transistors in a DRM adds an additional potential source of noise due to the far higher gain and much higher frequency performance of silicon transistors. This means that a silicon version can potentially pick up a lot of extraneous high frequency noise such as radio transmissions and in your case digital circuit clock oscillator signals. Although these are far higher than the audio frequency range, they can be rectified by the silicon transistor and create intermodulation products inside of the audio spectrum. The use of a suitable size 'Miller capacitor' or additional RF filtering on the input can usually reduce or eliminate this type of noise. 


   

[Rob Strand]

The interference is usually from the display multiplexing. A simple RC filter on the tuner's power input should sort it:

Yes, the way i put it down is confusing. I'll try again
- It has its own in-built power supply, with 3 independent, isolated power lines.
- The power for all 3 pedals is constantly on once the power supply mains is plugged in.
- One point star grounding, no ground loops.

Noise on the power from the tuner to the rangemaster doesn't hold up because of the isolated supplies.

I'm assuming clean supplies.   Maybe those isolated supplies aren't clean.  That's a whole different set of problems.  The RC filters on the power would help but only if it was placed on the effect not the tuner.

What I was thinking previously is there's some interference from the tuner, which would have to disappear if the tuner power was turned off.

[Lino22]

The Rangemaster is a notoriously noisy design to start with unless run from batteries like the original one.

Thank you, my Rangemaster doesn't have the volume knob, it is permanently set to the maximum volume so this is not the problem i guess. I use BD139 with Hfe about 90. But yes, this transistor is noisy, in straight comparison to the Tubescreamer, it hisses way louder which was a surprise to me. But power transistors are like that i guess.
It may definitely profit from a resistor before the 200u||100n filter i have there.

[Lino22]

[Noise on the power from the tuner to the rangemaster doesn't hold up because of the isolated supplies.
... The RC filters on the power would help but only if it was placed on the effect not the tuner ...
What I was thinking previously is there's some interference from the tuner, which would have to disappear if the tuner power was turned off.

Yes Rob, i will put it on the scope to see if i can find the source of the drone signal. The kill switch is a good idea.
I will report back.

EDIT: i checked the Rangemaster inside and it already has the 100R in series with 220u||100n.

[Lino22]

The kill switch on the tuner power revealed it is the tuner that generates the sound.
When i move the tuner body away from the rest and just keep moving its power cable and the input cable around the rangemaster circuit, there is no drone sound. When i bring the tuner body close, the drone sound is audible again. The tuner body is now shielded. I have no idea how to resolve this but with a permanent kill switch for the tuner.

[Lino22]

[Rob Strand]

The kill switch on the tuner power revealed it is the tuner that generates the sound.
When i move the tuner body away from the rest and just keep moving its power cable and the input cable around the rangemaster circuit, there is no drone sound. When i bring the tuner body close, the drone sound is audible again. The tuner body is now shielded. I have no idea how to resolve this but with a permanent kill switch for the tuner.

Good debugging.

I'm assuming the shield around the tuner is present and the noise is still present, as opposed to: you have worked out a solution by adding the shield around the tuner.

I have a feeling the problem is the tuner might be using unshielded inductors as part of some on-board switch-mode power supply.   The *magnetic* field easily penetrates the thin shield.

Like you found distancing the tuner from the audio circuits helps.  So you might be able to relocate your PCB to reduce the problem.  Another point is there might be a particular spot on the tuner which is the origin of the noise and you need to keep that spot away from everything.  This type of solution is *sometimes* possible without a adding anything but there's also a risk that it's never quite good enough.

It's often possible to workout the offending area of the (tuner) board by placing it close to the sensitive circuits.

A different solution is to use metal plate in place of the thin shield.  The plate would form a partition between the tuner board and the audio circuits.   You could try thick aluminium, say 1mm or more, to see if that works better. A steel plate is another option.   Mounting such shield might end-up being inconvenient.   You could even try a few layers of household aluminium foil to see if it does anything at all, that way you have an idea you are on the right track.  Good idea to ground the plate/foil like you have done to your shield.

If you were building a product and had control over the tuner design it would be wise to use a (magnetically) shielded inductor.

All what I've said here assume the problem is magnetic.   We don't really know that's true.


Forgot to say, when you consider all the messing about required to narrow down the true cause, switching the power starts to look appealing.

[Lino22]

Thank you Rob. I will try to feed the tuner from battery for testing and will try to find the hot part that makes the mess.
I will report back.

[Lino22]

I was moving the Tuner PCB around the RM PCB and yes there is a section that makes an incredible mess when i put it close to the RM input cap.
When i put the grounded shield case on and do the same experiment, the drone signal is barely audible (but still there). That means the shield is actually very effective but not perfect.
So next step will be a thicker shielding around the hot section on the Tuner PCB as Rob suggested.