Colorsound Power Boost 18v  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...

Re: Colorsound Power Boost 18v

Postby bettsaj » 23 Jul 2017, 16:01

Ok, this is aimed primarily at Electric warrior however please, if anyone has any ideas chime in as I'm desperate for a solution to this issue.

I have at last stuffed the PCB into an enclosure and the ticking noise is still there, however i may have misled you by saying ticking noise. It's more a rapid ticking... Not like a clock, definitely electronic and not anything to do with my rack system as I tested it through my sons practice amp. Check this short video,


Link



It's annoying, and I have to fix this, any advice would be greatly appreciated.

To recap and to bring everyone else up to speed, I have checked voltages on the transistors which were

Electric Warriors voltages

Battery: 18.84V
Q1 C 6.43V B 3.92V E 3.54V
Q2 C 11.53V B 6.44V E 5.82V
Q3 C 10.19V B 2.77V E 2.23V

My voltages:

Battery: 18.80V
Q1 C 6.37V B 3.90V E 3.52V
Q2 C 11.36V B 6.37V E 5.74V
Q3 C 10.54V B 2.75V E 2.19V

This is a 121 copy of Electric Warriors power boost, using the same values on all components, and the same trannys which are BC184L's.

All electrolytics are new Vishay caps, the same as the ones used by Stu Castledine in the reissue power boosts, the resistors are NOS Iskra resistors the same as the originals in Electric warriors and also Mullard caps... Again, the same as the original.

The resistors were all checked before being soldered, and are within tolerance. I have no way of checking the capacitors.

The only differences are the board which was etched by me from a trace of an original, and the pots which are standard off the shelf pots from bitsbox. The volume is a 10k rev log, and the bass and treble are both 100k lin.

I've built 2 of these now, with the same issue... The other one was built using all new parts as opposed to NOS, and the resistors in the other pedal were all 1/4w carbon film resistors.

2 pedals with the same issue.. 1 with NOS and the other with brand new components.
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Re: Colorsound Power Boost 18v

Postby bettsaj » 03 Aug 2017, 11:42

Ok guys... Update on the issue with this power boost clone.

Following some various tests kicked off by the guys at Element14 Forum, I have done the following:

    1. Increasing the capacitor value from Q2 emitter to ground, from 22uf, to around 100uf. This didn't work.
    2. removed the volume pot and replaced it with a 10k resistor, this worked but then i replaced the resistor with wire and the noise came back.
    3. Lifted the negative side of the 4.7uf capacitor that connects the pre-amp section to the tone section and connected the output jack directly to the negative leg of the capacitor. This in effect removed all the tone stack and the output stage from the circuit..... The noise is still there, so we now know that it's root cause is in the pre-amp.

My next tests will be the following, as recommended by a poster at DIYStompboxes. Put 4.7K-10K in series with the input. the reasoning behind this is as follows:

"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."


I really am running out of ideas now. I'm aiming at connecting it to an oscilloscope so I can get a proper idea of where the noise is coming from. I can't understand how this is happening on a PCB layout that has been around since the late 60's.... Realistically you should be able to throw the components onto this board it should work fine....... Someone has suggested i try different transistors, I'll try that also.
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Re: Colorsound Power Boost 18v

Postby bettsaj » 07 Aug 2017, 13:04

Ok chaps, 2 things.

1. I've revised the PCB layout, improved it, and made all pads and traces black
2. A guy over at DIYStompboxes has asked me for a copy of the tracing file so he can make one too... The good thing is, he's an electronics engineer, sio will be able to properly troubleshoot the pedal and identify where the motor boating is coming from.

I honestly believe now, after reviewing my build, that the reason i am getting motor boating on the circuit is due to board intergrity and also iffy soldering in some places.

i'm therefore making another board tonight with my new rev 3 PCB trace, and hopefully that will be the answer. If not, hopefully Ian Dempsey, who's also building one can scrutinize the circuit to identify the root cause..... I'll lay money on that it's something silly.

I also, in a moment of madness emailed Stu Castledine and he was gracious enough to reply with his thought os the issue:

"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"



So, for all intents and purposes, it should go together with no issue... hence why i'm building another one and why I've revised the board layout.


For those that are interested, the revised Revision 3 board is attached. This supersedes the previous revision 1 and revision 2 boards posted earlier in this thread. As before, print it out at 100% and it will be the right size
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Re: Colorsound Power Boost 18v

Postby bettsaj » 09 Aug 2017, 08:55

Brief update....

Populated a new board etched with the new revised artwork... Worked a charm, perfect.

[youtube]https://www.youtube.com/watch?v=gQpPRjSwKp8&t=2s[/youtube]


I believe the issue was caused by either low quality etching of the board, iffy soldering or both. Anyhow, it's working now, exactly as the original, the only modification I may make to it is the addition of a master volume control as this thing is really loud when you try to drive it into distortion.
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Re: Colorsound Power Boost 18v

Postby snofla1900 » 13 Aug 2017, 10:51

Glad you finally got it right !


And reading about this motorboating problem taught me some things about the importance of a good layout.


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Re: Colorsound Power Boost 18v

Postby bettsaj » 21 Aug 2017, 10:28

I have a few updates, which is really making me think there's something untoward going on with my house. I thought I had it sorted.... But it looks like I have an issue not directly connected to the pedal.

First update is, I sent my "vintage correct" board to a guy over at the Element 14 forum, he lives in Scotland, and is an electronics engineer. He took my board connected it to an Oscilloscope and nothing was wrong. He then connected it up to an amp, and a guitar and the power boost pedal worked faultless, with no issues. The only noise he had was in his words "humming coming from the cheapo guitar". This has made me feel stupid, as there doesn't appear to be anything wrong with the pedal.

He's now going to send me some videos before he returns it to me. Once i receive them I'll share them here.

Secondly, Ian Dempsey in Australia has made a Power Boost from my PCB layout and it works faultless with no issues. The only difference is he used the photo resist method to make the board, where I use the transfer method.

Thirdly, I built another board using an upgraded artwork. The results are in the below video...... I'm now officially at a loss.


[youtube]https://www.youtube.com/watch?v=Fa7RjM3tb5A&t=189s[/youtube]
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Re: Colorsound Power Boost 18v

Postby bettsaj » 21 Aug 2017, 10:29

Sorry the you tube video is here


Link
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Re: Colorsound Power Boost 18v

Postby bettsaj » 25 Aug 2017, 08:29

I have a very good update...... I think I've discovered what's causing the issue.

I got home from work early, and while there was nobody in the house I started turning things off...... And this is what happened



Link
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