How to reduce the noise with my Thor build ?

[Darkness, Darkness]

Hello,

A couple of months ago I build a ROG Thor pedal which sounds very great but I found this build a bit noisy (gain at 10:00, volume at 14:00) The noise is coming from the unit itself as the Gibson LP plugged on the Deluxe Reverb amp (volume at 4) don't produce the noise. (I also tried other power alim, check the cables, ..). The noise is just annoying when not playing... and I would not like to use some noise gate in the signal chain

When building it I took care of choosing good quality components (metal film 1% resistor, orange drops caps, etc...) The perfboard is housed in a metal box which I grounded.

I wander if the transistors (Fairchild J201 and 2N5457 ) and/or  and op amps (Texas instruments TL71CP) could be the cause and if I could get quiter ones without affecting the tone ? Any suggestion ? By the way, the TL071 failled a couple of days ago (strange ??) so I replace it with the same model but the nose is still present.

Or could it just be my personal perfboard layout that could be the cause of the problem ? Are there special points that I should have take care when building it ? (like don't put that cap near that resistor, or ...)

Anyway, Thor is a wonderfull device ! If you're looking for a great distorsion unit, just visit the ROG website 

Thanks !

[Scruffie]

I'm having noise issues aswell, the Noise is quiet when the pedal is on full gain but back off the gain and theres a part of the taper that is overly noisy.

With my build however, I originally had a jumper going to the wrong pin of the TL071 so it may be damaged... I know this doesn't particularly help your problem but still in a simmilar vein.

I would say are the trimmers properly set on yours... but I assume you already double checked that.

[Darkness, Darkness]

Thanks Scruffie. Yes the trimmers are OK, and the sound is very good except for that noise floor problem.

[ninjaaron]

what kind of fitlering do you have on your power source?

[Darkness, Darkness]

Hello Ninjaaron,

I test it with a warwick pedalboard power supply and also with a pcioks Big john one : both these power supply are quite with several other devices but my Thor build is equally noisy with both of them so I don't think the power supply is the cause of the noise

Concerning the filtering, I followed ROG design and put a 100uF cap on the power input. Should I try higher values ?

[MicFarlow77]

Hey Darkness,

Have you taken a probe and started from the head of the circuit to see where the noise is coming in from.... might only have to probe the output of the op-amp and then the end of each of the other stages... this should help you to narrow down the noise a good bit...

Also, the noise.... are you referring to the hiss that often accompanies high gain boxes or are you referring to the power supply hum?

As for your trimmers... I have found some of them to be quite noisy... especially the cheaper carbon ones... I just bought some cermet 19 turn trims and they are virtually silent and they have a ton of accuracy.... they are very easy to adjust.... they were almost $1.50 each, but for the quietness, still very cheap! (Heck, they are more expensive than the pots I bought... go figure...)

Thanks,

Mick

[Darkness, Darkness]

Hello,

Thanks Mick 

Have you taken a probe and started from the head of the circuit to see where the noise is coming in from.... might only have to probe the output of the op-amp and then the end of each of the other stages... this should help you to narrow down the noise a good bit...

Yes, I usually always proceed that way, even when building each stage of the unit. From previous test,  it looks like the noise is buidling with the gain, stage after stage. But I'll check again next saturday (indeed I build this unit for a friend of mine...)

Also, the noise.... are you referring to the hiss that often accompanies high gain boxes or are you referring to the power supply hum?

Well it is not supply hum. Just some noise, a bit like white noise

As for your trimmers... I have found some of them to be quite noisy... especially the cheaper carbon ones... I just bought some cermet 19 turn trims and they are virtually silent and they have a ton of accuracy.... they are very easy to adjust.... they were almost $1.50 each, but for the quietness, still very cheap! (Heck, they are more expensive than the pots I bought... go figure...)

That's a good thing to check. Here are the trimpots I've used : http://www.banzaieffects.com/PT10-vertical-5k-pr-17169.html Do you think there are crapy ones ?

Thanks again for your help. I'll check these points

[solderman]

Thanks Scruffie. Yes the trimmers are OK, and the sound is very good except for that noise floor problem.

I assume you have put the effect in a metal box. If not that might be a good solution. When I did my 1590A Thor I compared it to my normal box size Thor before boxing the small one. The un boxed small one was very noisy and I tried everything I could think of with no good result until I boxed it and then 80% of the noise disappeared. So shielding seems to be important to Thor. You can also try shielded and grounded cables for the IN part of the hook up wiring.

[Darkness, Darkness]

I assume you have put the effect in a metal box. If not that might be a good solution. When I did my 1590A Thor I compared it to my normal box size Thor before boxing the small one. The un boxed small one was very noisy and I tried everything I could think of with no good result until I boxed it and then 80% of the noise disappeared. So shielding seems to be important to Thor. You can also try shielded and grounded cables for the IN part of the hook up wiring.

Hello Solderman,

Yes, the enclosure is metal and it is grounded (but I'll double check the grounding next time I will open the box) I could also try shielded / grounded cables for the input. Good Idea ! 

One other idea that also came following Mick post about the trimmer pots : Maybe I should also check the Alpha pots I have used especially the one used for the gain control. I might try to shield/ground also these cables.

Thanks for the help ! 

[Darkness, Darkness]

Another interesting thing I read on the forum and I should also try :

http://www.diystompboxes.com/smfforum/index.php?topic=76684.msg627397#msg627397

2.) ALWAYS place small bypass caps across all IC powersupply pins to ground. This does wonders for reducing hissy noises and it helps to prevent unwanted oscillation.
I wish everyone would incorporate both the ideas listed above into every circuit and pcb they design. Almost every data sheet since the early 1970's have included references to both of these principles, but few are listening. Bad habits prevail.

[ninjaaron]

Concerning the filtering, I followed ROG design and put a 100uF cap on the power input. Should I try higher values ?

Well, sounds like you've been pretty thorough. I presume the 100uf cap is going to ground. Anyway, that should be more than sufficient. However some people also suggest placing a smaller cap to ground as well, like 100pf, along with a rectifier diode (like a 1N4001) with the anode to ground.

I'm not sure that this will make a huge difference, but that's what I got.

[MikeH]

Using shielded cable (with the shielding grounded at one end only) for your ins and outs, as well as any other long leads, will help too.

[Darkness, Darkness]

Thanks ! 

I should be able to look at my Thor build this week end So here is the summary list of things I have to check :

- Verify with an audio probe if a clear source for the noise
- Check the enclosure grounding
- Check the power supply input 100uF cap
- Add a small cap on the TL071 power supply pin
- Use shield cables for input, output and gain pots
- Try other Trimmer pots ?
- Try other gain pot ?

[head_spaz]

Does it still hiss if you use a battery?

Hissy noises are generally caused by oscillation. Opamps can oscillate in the megahertz region with ease. It's more common than uncommon actually, especially in new designs and hap-hazard layouts. Success with opamps demand good circuit design and GREAT layouts.

You mentioned that your chip recently fried. Oscillation could be a good reason for that!
Opamps are especially famous for oscillating when driving capacitive loads.
Looking at the THOR schematic, I see it's driving a capacitive load. Depending on your layout, R15 might be too far away, and it's of quite high value to be of much help in this regard. Therefore I HIGHLY recommend placing a 100 ohm resister directly between the output of U1... and C13 / C10. Cut the trace and insert this resistor right on the output of the chip, as close as possible. A 100 ohm resistor will not effect the sound quality what-so-ever... and it will help to prevent oscillation in the opamp. (we should incorporate this into all of our opamp designs)

Also be sure to use a .1uF ceramic BYPASS cap from the IC's positive-supply leg to ground. Place that cap right on the legs of the chip, or directly underneath it on the PCB. AS CLOSE TO THE CHIP AS POSSIBLE.

Please do both of these things before you do anything else and then report your findings.

[Darkness, Darkness]

Thanks head_spaz, I'll try this 

I suppose when you say C13/C10, you are refering to part number from the PCB layout @ ROG website ? (as there is no part number on their schematic) ? Just to be sure :
- C13 is the 100n output cap
- C10 is the 1n cap in the feedback loop of the IC
So I just have to put the 100 resistor between output of IC and junction of output cap, feedback loop cap and the resistors/capacitors network (filtering)

On my layout, R15/100K is very close to the chip as I place it actually over the IC, without touching anything from the IC !(not the nicest way to proceed, but I wanted coponents from each stage to be as close and direct as possible)


So the updated checklist ! oops I just found out I have missed an interesting remark from of MikeH in my previous list  .... corrected ! :

- Verify with an audio probe if a clear source for the noise
- Check the enclosure grounding
- Check the power supply input 100uF cap

- Add a small ceramic cap (.1uF) on the TL071 power supply pin
- Add a 100 ohm resistor directly right after the output of  the TL071 IC, as close as possible to the chip
- Add a second small cap to the power supply input, like 100pF, along with a rectifier diode (like a 1N4001) with the anode to ground
- Use shield cables for input, output and gain pots
- Try other Trimmer pots ?
- Try other gain pot ?

[Eb7+9]

- Add a small ceramic cap (.1uF) on the TL071 power supply pin
- Add a 100 ohm resistor directly right after the output of  the TL071 IC, as close as possible to the chip
- Add a second small cap to the power supply input, like 100pF, along with a rectifier diode (like a 1N4001) with the anode to ground
- Use shield cables for input, output and gain pots
- Try other Trimmer pots ?
- Try other gain pot ?

sorry to say but you'd be wasting your time tweaking bells and whistles
unfortunately these jFET "emulator" designs are inherently noisy

It's been said before why this is so ... do a search

[caspercody]

Did you ground the pot ground terminal to the pot itself? I take a file and rough up the pot, and bend the terminal back to touch the pot and solder it to the pot housing. This helps eliminate some noise.

[B Tremblay]

For what it's worth, the two Thor pedals I've personally built using the official PCB layout have not had any noise issues.

[Darkness, Darkness]

Did you ground the pot ground terminal to the pot itself? I take a file and rough up the pot, and bend the terminal back to touch the pot and solder it to the pot housing. This helps eliminate some noise.

Good idea to try too ! Thanks Caspercody

sorry to say but you'd be wasting your time tweaking bells and whistles
unfortunately these jFET "emulator" designs are inherently noisy

Yeah, I know that it won't be possible to have this high gain box dead quite, but there are here enough good ideas, that I have not put it place in my initial (and first) build, and which will surely help to improve a bit the situation ! At least it will help me to get better builds for other projects next time. Thanks everybody 

Verify with an audio probe if a clear source for the noise
- Check the enclosure grounding
- Check the power supply input 100uF cap

- Add a small ceramic cap (.1uF) on the TL071 power supply pin
- Add a 100 ohm resistor directly right after the output of  the TL071 IC, as close as possible to the chip
- Add a second small cap to the power supply input, like 100pF, along with a rectifier diode (like a 1N4001) with the anode to ground
- Rewire pots to ground them
- Use shield cables for input, output and gain pots
- Try other Trimmer pots ?
- Try other gain pot ?

[Darkness, Darkness]

For what it's worth, the two Thor pedals I've personally built using the official PCB layout have not had any noise issues.

Yes I am sure that a lot of the issue is due to what I've (not) done...I have used my own layout... and as you can read, there are lots of little things to fix  ! I will check this on sunday