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Extreme RFI

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Extreme RFI

Postby pjchappy » Wed Sep 30, 2020 1:26 am

I recently purchased a Fulltone Ranger treble booster. I had also cut out the treble bleed circuit from my SSS Strat (with a blender pot) before I tried out the pedal (a pre-wired harness purchased several years ago).

Now, when I turn down the volume on my Strat, as soon as it's down to 9, I pickup extreme RFI (with the pedal on). A radio station comes through quite clearly. This is the only pedal this happens with (I have also tried with just guitar-->pedal-->amp). This is ONLY when the Fulltone Ranger is on. I'm trying to figure out what could possibly be going on — If it's an issue with the guitar wiring or the pedal. Just get very minimal single coil hum when pedal is bypassed.

I visually inspected the guitar's wiring (using online diagram) and didn't see any issues. I have also tried different guitar cables. I have also tried this with a J-style bass. I get a good amount of RFI with the same set up, but only when the tone pot is turned completely off (v. the volume pot on the Strat).

Any initial thoughts on what the problem could be? The pedal was a "cosmetic" blem directly from Fulltone. I didn't find any cosmetic issues, however.

Thanks,


p
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Re: Extreme RFI

Postby ef37a » Wed Sep 30, 2020 9:18 am

Cannot find a schematic but found an internal shot,
https://www.fulltone.com/products/custom-shop-cs-ranger

And that looks about as sparse a design (I use the term loosely!) as it is possible to get. I can see no RF stop components at all, I doubt it has even been submitted for tests*.

The problem seem pretty definitely to be the treble booster and so your next move is to contact the retailer, it is HIS responsibility to ensure the product he sells are of "merchantable quality". I do however have some sympathy with them in this case because the RFI probably does not manifest itself in his premises.

The pedal could almost certainly be fixed by any competent amp tech but obviously at some cost to you.

*A costly and sometimes protracted procedure which is why many small devices do not get tested. Makes me bloody angry when reputable firms DO spend the money on such 'hidden engineering'. There orta be a LAW...Oh, there is! (but still in 2021?)

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Re: Extreme RFI

Postby Hugh Robjohns » Wed Sep 30, 2020 10:18 am

There are always two elements to RF interference.

The first is whatever is acting as an aerial to collect RF from the aether -- the guitar itself in this case -- and the second is whatever circuitry is demodulating that RF to make it audible -- the pedal.

If you can stop the RF getting in to the system -- removing the aerial -- you'll appear to cure the problem, although other guitars could reintroduce it.

And if you stop the circuitry demodulating it you'll also appear to fix it, but a different pedal could suffer the same problem, of course.

So ideally, you need to do both: stop the guitar acting as an aerial, and stop the pedal from demodulating RF.

In your situation, the pedal is obviously demodulating the unwanted RF to make it audible. Dave is right in that the manufacturer should have addressed that in the pedal's design and/or build, so that would be the first port of call. It could be a faulty build like a dry joint in a sensitive part of the circuitry.

However, if you're DIY-minded it might also be possible to improve things with the addition of some ferrite beads on the wires connecting to the tip terminals of the input and output sockets.

And secondly, it would be worthwhile fully screening the wiring recess of the guitar and making sure the grounding arrangements are effective (and not creating small internal loops!). The wiring in there operates within a very high impedance environment and it's all unbalanced and unshielded... so a perfect aerial for RF!

From your description, there is enough capacitance in the system with the volume control fully open to damp out any RF, but increasing the impedance around the pickups by reducing the volume control obviously messes that up... so it may be that adding a small capacitor across the pot is sufficient to kill RF without affecting the tone -- or more ferrite beads could help.
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Re: Extreme RFI

Postby ef37a » Wed Sep 30, 2020 10:47 am

Morning Hugh, you are right of course, the electric guitar is a pretty good 'receiver' for RF!

That was not much of a problem in valve days as there was almost a grid stopper of around 68k in the first grid circuit followed by at least 100pf of Miller capacitance plus strays. Valve amps WILL demodulate RF if close/strong enough e.g. try leaving a moblie phone on top!

The rot set in with transistors but a simple RC filter is usually good enough in mild cases but the PROPER way to do it is a common mode toroidal ferrite choke and a couple of capacitors.

Amplifiers and pedals must be proofed against any an all guitars, screened or nay. I can say I never had a complaint regarding RFI on any product save one guy on the coast where some email exchanges revealed he live but a few 100mtrs from some sort of military navy transmitter. I built and sent him a filter but unfortunately never got a reply. This was sometime after I had left the company.

Yes, ferrites could help but in my experience you have to fit the filters in the electronics.

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Re: Extreme RFI

Postby forumuser931182 » Wed Sep 30, 2020 12:28 pm

Definitely contact Fulltone - if it was sold with a "cosmetic blemish" it may be a previously returned pedal ( perhaps because it worked as a radio ). They may also have some helpful advice regarding RFI fixes.
Probable circuit can be found here: https://www.electrosmash.com/dallas-rangemaster
They mention a number of noise problems that can occur and Fulltone are using a " Proprietary Power supply design allows this PNP (Positive to ground) Germanium pedal to be powered by any standard NPN (Negative to Ground) power supply! "
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Re: Extreme RFI

Postby ef37a » Wed Sep 30, 2020 12:42 pm

forumuser931182 wrote:Definitely contact Fulltone - if it was sold with a "cosmetic blemish" it may be a previously returned pedal ( perhaps because it worked as a radio ). They may also have some helpful advice regarding RFI fixes.
Probable circuit can be found here: https://www.electrosmash.com/dallas-rangemaster
They mention a number of noise problems that can occur and Fulltone are using a " Proprietary Power supply design allows this PNP (Positive to ground) Germanium pedal to be powered by any standard NPN (Negative to Ground) power supply! "

Yea Gods! What a primitive circuit! To add insult to injury it uses an OC44 an 'RF' Germanium transistor when the humble OC71 would have been a better choice.
If OP is up to some surgery, a 68K after the input capacitor and 220pf from base to emiter (not ground) would I am sure reduce the problem considerably.
If not a complete fix go for a choke wound on a ferrite bead at the front end and the same in the output circuit with 100pf each side to ground. Also make ABSOLUTELY certain all parts of the case are tied to the output jack screen.

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Re: Extreme RFI

Postby Folderol » Wed Sep 30, 2020 12:45 pm

If that's really an OC44 in there, then that's half the problem. It's an RF transistor!
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Re: Extreme RFI

Postby Trevor Johnson » Wed Sep 30, 2020 4:11 pm

Just found this: http://swartamps.com/oc44_transistor_da ... master.htm

I still have some unused OC44/45/71/81D/82Ds. I have no idea why you would use an OC44/45 in an AF circuit unless you happened upon it by chance, e.g. picked up the wrong part!
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Re: Extreme RFI

Postby ef37a » Wed Sep 30, 2020 4:47 pm

Trevor Johnson wrote:Just found this: http://swartamps.com/oc44_transistor_da ... master.htm

I still have some unused OC44/45/71/81D/82Ds. I have no idea why you would use an OC44/45 in an AF circuit unless you happened upon it by chance, e.g. picked up the wrong part!

I have a very dim recollection that in the VERY early days of transistors, selected OC44/45s were lower audio noise than the run-of -the mill OC71s but that could be wrong. More likely the originator of the pedal got a bucketload at one P each!

I might have a Miniflux tape pre amp design manual in the loft, might have seen it in there, will brave the spiders.

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Re: Extreme RFI

Postby Folderol » Wed Sep 30, 2020 6:21 pm

Unfortunately they also have an fT something like 10MHz, as opposed to the OC71 of under 1MHz, as far as I recall.

P.S. For many years I had a Mullard OC45 in it's original package with the printed price of 17/6d.
I don't know how I manged to lose it :(
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Re: Extreme RFI

Postby pjchappy » Wed Sep 30, 2020 10:43 pm

Thanks, everyone. I'm not inclined to try to repair this myself (or add ferrites, etc.). I will contact the seller and have it fixed under warranty. I'm quite irritated, regardless, as my inclination is to believe this was a returned itemed, due to the same issue.

Wish I saw their repair process before I bought the pedal. I will never buy another Fulltone product, just because of the below. This is quite ridiculous.

Quote from website:

"We require you to upload a video clearly demonstrating the issue you are experiencing with your Fulltone product before we accept item for repair. You can use your smartphone, a video-capable digital camera, or a video camera. If you do not have this capability, ask a friend. After we have viewed your video, you will be contacted for troubleshooting and eventually issued a Return Merchandise Authorization (RMA) if necessary.

Basic video instructions:

a) Take our pedal away from all other pedals, no tuner, no looper, no amp effects loop, powered only with a battery or Fulltone power supply.
b) Plug into the front of a CLEAN-SET amplifier, no hi-gain distortion channels.
c) Keep camera focused on the pedal’s settings as you demonstrate the problem"

Beyond the RFI issue, I now realize a treble booster is a must have pedal for me!

Thanks again,


p
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Re: Extreme RFI

Postby ef37a » Wed Sep 30, 2020 11:16 pm

If you purchased the pedal in UK that is contrary to consumer law. Within a 'reasonable period' you are not required to jump through such ridiculous hoops.

A company is of course perfectly entitled to ask for details of the fault and certain conditions that seem to provoke it in order to aid diagnosis but only REQUEST not demand.

There is of course a high probability that the RFI problem will not show on their premises (pretty much guaranteed!) but any service tech who has been in the job more than a year will know that RFI is almost always a localized problem. You just do the standard mods and send it back. 90% of the time, job's a godd'un, (I am talking many years ago when kit was all wide open, even some top quality hi fi)

If they still insist on that illegal bllx tell them you will have the pedal fixed by a local tech and send them the invoice for the work. (next step, Small Claims Court then The Sheriffs!)

(I have to say, this sort of crap design followed up by equally crap service really pisses me off when I think of the work I put in a few years ago because the company wanted as bomb proof products as it was possible to make. Getting it right first time really does pay off in terms of low returns and also means you can treat the few customers that DO have a problem with respect because you are not snowed with crap coming back!)

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Re: Extreme RFI

Postby pjchappy » Wed Sep 30, 2020 11:33 pm

I'm in the United States.

Yes, the requirement of a video at step 1 is outright insane. It's understandable for a video after email troubleshooting, etc. doesn't work. To make this immediate leap is silly.


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Re: Extreme RFI

Postby ef37a » Thu Oct 01, 2020 9:27 am

pjchappy wrote:I'm in the United States.

Yes, the requirement of a video at step 1 is outright insane. It's understandable for a video after email troubleshooting, etc. doesn't work. To make this immediate leap is silly.


p

Ok well I guess you have state by state consumer laws? Personally, if the company will not do the decent thing and fit the filters I would cut my losses, take it to a good technician* and get it fixed. It cannot hurt anything to have him give you a report of the work done and the cost then send that to Fulltone. I doubt they will pay but that would give ME some feeling of satisfaction!

*You might look up 'Ham' radio enthusiasts in your area? Many of them are top electronics technicians in their own right. We USED to have an excellent Interference Investigation Service here run by the then GPO but privatization swept all that away. The TV firm I worked for was owned by a very keen 'ham' and we used to co-operated a great deal in tracking offenders and modding domestic gear. LOT of work when the Rubber Duck brigade started up!

And...I would post your problem in www.homerecording.com forum, they have a guitars and gear section. That is predominately a US forum so you will get the bad news to many more people.

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