Colorsound Power Boost 18v... Annoying ticking noise.

[jonnyeye]

First thing I'd check: Remove the input and output jacks. If there is paint/powder coat on the inside of the enclosure surrounding the holes that the jacks go in, remove it with a file or sandpaper. Reinsert the jacks and try again... The enclosure must have good continuity with ground in order to shield effectively.

[Electric Warrior]

Easy enough to use a multimeter to check if enclosure and jack grounds connect.

[bettsaj]

Hi Gus,

I've been trying to address this issue via this forum and also via some of the electronic tech heads over at Element14, so i'll try all advice as it comes.

currently I have removed the board from the enclosure, the consensus being that the oscillation is likely a grounding issue. i have mounted the pots on the other side of the board to the original, therefore the treble pot is no longer grounded to the board where on the original it was grounded to the board. I need to at least ground the treble case to the board, and possible connect the other pots to ground as well.

I don't have an oscilloscope... I think i may well be investing in one in the future if I continue to make pedals.

i'm ready to conduct some "process of elimination" tests. i'll wire the board out of the enclosure, and ensure all grounds are correct. I've drilled a few extra holes in the board and will ground the jacks directly to the board, so the wiring is cleaner with less chances of ground loops. Then i'll post an update video.

[bettsaj]

Ok guys, here's the latest update.

I've removed the board from the enclosure, and the noise is still there. It's been wired as basically as possible. I've wired the treble pot to the ground on the board, as the original pedal had the treble pot grounded directly to the board via the body of the pot.

I've checked a triple checked all soldering on the board and there are no solder bridges that I can see.I'm beginning to think it's the board, and maybe during my design phase I did something wrong somewhere.

Anyway, here's the latest video, i think I need to get this sorted before I stuff it into an enclosure.

[slacker]

A quick thing to try would be increasing the capacitance across the 18 Volt and ground rails, no need to remove the existing 22uF cap just try soldering say 100uF in parallel with it or even just hold it in place temporarily and see if it makes any difference.

Probably a long shot but you haven't got powerline networking in the house have you? I have and for some reason it makes my Tube Screamer make similar noise, it's weird because I've got other much higher gain pedals and it doesn't affect them so I'm at a bit of a loss as to how and why it interferes with the TS.

[bettsaj]

Powerline networking.. Nope, and I haven't got a 100uf cap.. i'll have a look and see what I have got, maybe something close.

[bettsaj]

I've done a bit more tinkering, and have a few positive things to report.

Forum poster Gus suggested I wire up a jack plug shorting the tip to ground this shorts the input to ground. This should reduce RF pickup if that is the problem. i wired up the plug and tested the board again, no cigar, still the same.

There have been some changes, and I've done nothing!!

1. The noise has reduced significantly by itself, i don't know why.
2. I can turn the volume of the guitar, the amp and the pedal all the way up and the noise is just audible.
3. However, when I back of the volume of the guitar all the way off, the noise increases in volume.

Here's the latest video.

[bettsaj]

Ok guys, I have an update.

I have been trying to cure the noise issue I have with this power boost clone pedal, and have been in long troubleshooting discussions with the tech heads over at the element 14 forum. you can see the posts here:

https://www.element14.com/community/thread/60782/l/colorsound-power-boost-noise-issue

The ticking noise I'm getting has been identified as "motor boating", and it's coming from the 2 transistor pre-amp section of the power boost circuit, I proved this by disconnecting the 4.7uf capacitor that connects the pre amp to the tone section and wiring the negative side of the cap directly to the output jack, the noise is still there so I know it's originating from the pre-amp stage. This is driving me up the wall.

I have even now sent Stu Castledine an email, I don't expect a reply but it's worth a shot.

My next experiment will be to increase the value of the 22uf capacitor that connects Q2 emitter to ground. This was suggested by one of the guys over at the E14 forum, and by slacker on this forum (a few posts above)

Anyone here ever had motorboating with this circuit before?...... If so, what was your work around?

[PRR]

> motorboating with this circuit

It is just possible.

Put 4.7K-10K in series with the input.

There's the path from Q2 E to Q1 B, and two caps: one to ground and one to ground through whatever feeds this. That's 2/3 of the way to a phase-shift oscillator. There's also a cap at Q1 E. Too much for matchbook analysis. Some ancient experience says a significant resistor at the input damps the tendency to subsonic bump. There is a hiss penalty, but it is small for a phono preamp and should be insigificant for guitar.

[bettsaj]

Thanks PRR for your suggestions... I'll give them a go next.

I've just finished conducting 2 more experiments.

• I increased the capacitor between the emitter of Q2 to ground (currently 22uF), increased to around 100uf..... No joy
• I removed the volume pot at someones suggestion that it may be iffy, and replaced it with a 10k resistor... that was ok, I then replaced the resistor with wire so there was no resistance and the noise was still there

I may try bread boarding just the pre-amp section as that seems to be where the issue lies.... If the noise isn't there (which I suspect i won't be) it may lead me to believe it's the circuit layout, or more specifically the board that I etched.

PRR, when you say put a 4.7 to 10k resistor in series with the input...... do you mean before the 0.22uf cap into Q1 base?

[bettsaj]

Just had a response from Stu Castledine, he builds these for Macaris in London..... He knows this circuit better than  anybody:

"Hi Andy,

Thanks for the link.  Yes, that's definitely motor boating, but I've never had this problem and I've "thrown together" well over a hundred Power Boosts. 

I would have suggested the same mods posted in that thread: more capacitance across the supply rails, less capacitance on the volume control and ensuring a good mechanical connection between the enclosure and 0V.  That said, it is a proven design, so it should be possible to make it work with the standard parts values.   It's odd that both of your circuits exhibit the same instability.

Sorry I can't be more help, I think you just have to go back and double check everything - it must be something common to both of your builds.

Best regards,

Stu"

[Electric Warrior]

Really odd that it improves when you touch the switch, though. It sure points to a grounding issue. Have you confirmed that the enclosure, the circuit board ground and the jack grounds all connect with each other?

Did you use a random set of transistors or did you audition them before soldering them in?

And have you checked if the LED that you added could cause the problem?

[bettsaj]

Hi Mr E. Warrior 

I'll triple check all the grounds tonight, however at the moment it's not in the enclosure and it's motorboating.

Regarding the transistors, I didn't test them. I bought about 20 in one go, and used a random 3 from the batch sent to me.

The LED isn't part of the equation as I've now taken the board out of the enclosure. It's definitely emanating from the first pre-amp stage, and not the tone stage or the output stage, as i've disconnected both the tone and the output stages from the pre-amp stage and the motorboating is still there.

[duck_arse]

when you disconnected the back end from the front end, did you remove the back end from the supply? seeing as you are BB'ing it, you might try an R//C supply decoupling between Q1 and Q2 and the rest of the circuit. what if it doesn't MB on the BB?

[bettsaj]

Hi Duck Arse (Great forum name lol)

In answer to your question, and i see why you're asking this.. no, is the answer.

I assume you're asking this as the 18v power is connected to Q3 base and the 22uf cap at the output. I didn't isolate those connections.......... Any reason why this could be an issue

[duck_arse]

I was just thinking that there may be some bad interaction between the high-gain front end and the back end, fed thru the supply. the R//C would isolate, possibly disprove my theory.

the 22uF cap at the output - do you mean the one connected to Q3 collector?

[the 22uF is not so much "at the output" as across the supply. it is drawn near the output stage, but could be physically anywhere, and no, don't remove that.] and you'd want to lift the 180k and the 3k9 from supply to isolate the transistor.

[bettsaj]

I can do that.... I'll try it tonight.

That way the pre-amp stage will be totally isolated from the rest of the circuit.

[bettsaj]

I've ordered some new transistors, BC184L, they should be with me on Monday.

Short term, I'm going to change the transistors over tonight..... I have some BC184's I can try... Only difference is the pin outs are different. So there'll be a slight bit of leg twisting.

[bettsaj]

Ok guys. This is where I am, and what I'm planning.

I've had a slight set back.... I'm now getting nothing from the board at all.

i took the board to work with me today hoping that i may be able to get the guys in Mechatronics to put it on an Oscilloscope. I didn't manage to do that, and when I got it back home a couple of wires had come away from the board.. Nothing major, i just resoldered them to the board, However, now i'm getting absolutely nothing from the board. When I took it to work unfortunately I didn't think to protect it from being knocked in my bag, and i also packed the two 9v batteries in with the board but they were  not secured and I think maybe have shorted something on the board in transit. I will keep trying to get life into it, but at the moment I'm at a bit of a loss as to what's wrong with it.... I may change the electrolytics although I am running low on them now, and could probably do with buying more. Anyhow, onwards and upwards.
I've checked all wires for continuity, and there's no issue there. I've checked all ground connections from the ground on the jack sockets, and then checking for continuity on the board... no problems.

I'm building another board, and it will be made with all brand new components. It will be using the same exact components as the 1st build, standard 1/4w carbon film resistors, brand new Vishay capacitors, brand new polyester caps, brand new etched board, brand new pots, and also brand new Fairchild BC184L transistors.

This third build will be finished hopefully by Sunday. I had the board cut this morning, and I've just finished printing the trace onto photographic paper for heat transferring tonight. With this board, I'm going to pay extra attention to detail..... Just to mitigate any possible build %^&*-ups. I feel fairly confident where all the components go, I've been living and breathing this pedal for around a year now and the level of research I've conducted into it is stupid for such a simple pedal. However, I won't take anything for granted, and I'll check and double check the location and orientation of every component as I put it in the board. regarding the board, when I heat transfer the trace onto the board I'll ensure i leave it longer to ensure I don't get any broken tracks... I'll also ensure I touch up any tracks before I etch the board..... Although I check all the boards I make, it is possible I missed something.

One thing I will do as an experiment during the build, is I'll populate just the pre-amp section of the board first... Then I'll try it out to see if there's any motorboating. Might be easier if I do that as it will take out of the equation the rest of the circuit.

All my 1/4w resistors are brand new...... I've got 100's. However, I'll ensure that i check all the resistors before i solder them to ensure they are within tolerance.

I want to make sure that I have everything as perfect as I can possibly make it... If this works, and I don't get any motorboating it'll be good. It may also indicate to me that the fix may well be the transistors as they will be the only things that are different between the 1st board I built, and this new 3rd board.

[amz-fx]

The original unit probably used low gain transistors, and you know that the problem is in the pre-amp section.

So I would change the 220pF capacitor from base to collector on Q2 to a higher value. A 470pF should be adequate to see if that improves the sound.  If you don't have a 470pF, then just add another 220pF in parallel with the original to get 440pF. The leads on the capacitor should be short and close to the pins of the transistor.

Best regards, Jack