Fulltone Robin Trower - Very Noisy build

[jaredcohen]

I almost like it more when a build is just totally dead.  When one mostly works, but has a flaw, it's harder for me to troubleshoot.  I built the RTO and it works, but it's super noisy.  

It's not boxed yet, and I'm used to any transistor build having a little noise until boxed - but this is a whole new level.  The hum here is way louder than the guitar signal.  Tried a few ICs and 2N5088's.  No solder bridges.  I checked over the schematic and the circuit is so simple - I'm out of ideas.  Just wondering if anyone might have any other thoughts as to where the noise could be coming from.

I uploaded an audio sample: http://jaredmcohen.com/storage/RTO_Noise_Demo.mp3 -- Thanks for any help.

[Frank_NH]

Hi Jared

I've seen this before in a build I did (I think it may have been the Dyna Red Distortion).  It seemed that my circuit was noisy no matter what I did.  

First, read this:

http://www.muzique.com/lab/hum.htm

Then, make sure you are away from sources of EMI like fluorescent lamps or noisy power outlets.

Here are some things I would try:

* First, audio probe the circuit.  Is the noise present at the input or does it gradually build and become a problem only after a gain stage or at the output?

* Are you using a battery or a wall wart?  Try a battery.

* Try putting a 100 ohm resistor in series with the 9V input.  Also, see if increasing power filter capacitor from 10 uF to 100 uF helps (you can put the 100 uF cap from 9V to ground using alligator clips, in parallel with you existing 10 uF).

* If all of the above do not work, then try something more radical.  Try connecting your input wire away from the ground in the layout.  (see below).  That is, run your input to a 22 nF cap connected in series to a 1K resistor and connect that to pin 3 of the IC.  Make a temporary probe to connect this arrangement to the IC.  Is the noise reduced?

* You can use shielded wire for the input and output but I wouldn't think that would be necessary for this kind of "low-verdrive" (i.e. it's not a Dr. Boogey!).

* It still may be a cold solder joint or minor solder bridge.  The only way to confirm that would be to build it again and see if the problem repeats itself (which would be a pain, but at least you would know ).

Good luck and let us know what you find.



 

[jaredcohen]

Frank,
 Thanks for the advice.  This is one of those that just makes you look skyward and laugh.  I finally had some free time today so I powered everything up to start troubleshooting.  Circuit was still connected to my guitar and amp the same way.  Noise was gone.  So who knows.  Nothing in the setup or my apartment changed, but it sounds great now.  Exactly as it should.  Thanks for taking the time with all your help though.

[Ed Nice]

I'm glad you are sorted and great advice from Frank anyway :)

I'm surprised how much background noise comes from the power grid. I spent about 2 hours slicing the stipboard (and my fingers), re soldering and prodding a deep blue delay I did a few weeks ago which had a horrible hum. I eventually got so pissed with it, I pushed the magnifying light out of the way and the damn thing just shut up. I'm a n00b. It's how we learn. By being stupid. :)

Is it possible that something like someone hoovering (vacuuming) or drilling or mowing the lawn, well basically anything that spins some magnets, on the same power supply could cause a temporary or random noise? I don't know anything about power stuff, but I think there is a 'quality' that is affected by load and other things like electromagnetic fields? This might explain your temporary noise?

 

 

[induction]

Ed Nice wrote

Is it possible that something like someone hoovering (vacuuming) or drilling or mowing the lawn, well basically anything that spins some magnets, on the same power supply could cause a temporary or random noise? I don't know anything about power stuff, but I think there is a 'quality' that is affected by load and other things like electromagnetic fields? This might explain your temporary noise?

Yes, that happens often. Anything especially power-hungry operated on the same circuit as your music equipment can cause noise on the power mains. Vacuums and microwaves are common offenders. In my experience, vacuum noise actually comes through the amplifier sounding very much like an amplified vacuum cleaner.

[Beaker]

I've read accounts on other forums by guys suffering hum issues, and finally finding that the culprit is a frigde or freezer, so add them to your list of suspects. In my case I know to turn off my soldering iron before doing any testing, as that comes through my amp.

It is true in many builds though, that inadequate seperation between your signal/ground/power wires will cause hum or squealing.

One of my first builds was a Zvex Fuzz Factory that tested fine out of the box, but squealed like crazy every time I tried to box it, until I realised what was happening. Once I sorted my wire runs out it started to behave itself.

Edit: If like me you live in a terraced house, don't discount the possibility of the noise source coming from next door!

[Frank_NH]

Good to hear that it fixed itself, but still hum can be a problem and it's often difficult to sort out the source.  The main thing to think about for a given build is what can be addressed at the circuit board level.

But first, if you test your builds like I do with a test rig, use a battery or a well filtered power source to rule that as a source of noise.  I need to upgrade my rig with shielded cable and a better grounding scheme, but I use a battery to test my effects before boxing.  

Outside of that, if we can rule out solder bridges and cold solder joints, then the remaining area of improvement is the circuit board layout.  I know Brian Wampler has stated that he uses professional PCB layout practices in his products because it can have a significant impact on noise level and the quality of the signal.  For vero board layouts, there may be some things we can do to prevent oscillation and noise, like keeping high gain signal paths away from the input and preventing ground loops.  I also believe that making track cuts to isolate unused parts of a given row may help to reduce noise (but I haven't done any experiments to prove that).

There are resources on the web about how to reduce noise in pedals, but most focus on the power noise part and not much about circuit board noise and layout practices.  I someone comes across any interesting resources, post them here.

 

 

[Beaker]

You are absolutely right Frank, and Brian Wampler knows what he is talking about on this one (can't say I agree with him often though!).

 My Electronics knowledge is very limited, so I only know in very broard terms, what some of the problems are, and how to minimise them.

I used to work with a guy who used to be an Electronics design engineer for audiovisual companies - he now works on secret military stuff for the MOD.

He told me that electronics is far from being a "join the dots" exercise, and that the "beauty" of a well designed circuit board lies in how well the designer has laid out the tracks and components, all in order to minimise power noise, ground issues, EMF and cross-talk between components and their associated tracks. An awful lot of time and effort is put into achieving this by the best companies. (Might also explain some of the cost differences too.)

Put simply, two identical builds, using identical components, can (and often does in the case of copies or clones), result in one circuit - the one with the well deisgned board, working superbly, with absolutely minimal noise, no cross-talk issues, and which sounds fantastic. The other, poorly designed board will sound terrible, and will be plagued with problems.

I know that will not be an issue with a simple little fuzz circuit, but I do believe that some of our monster vero builds will have been laid out with little consideration to these issues. If these issues were to be taken into account, then a lot of noise problems might be avoided. It might make the veros even bigger though.

As I said at the beginning, my knowledge is very limited, so please don't imply any criticism of anyone who has posted up layouts, as none is intended. I'm super grateful to everyone who has!