Colorsound Power boost noise issue

Hi Andy,

You are getting an oscillation that could come from a number of sources. Here is what I observed as differences between the original and the newer units. By mounting the controls on the opposite side you are loosing the shielding that would have been provided by the metal control housings. In the original the treble at least was grounded on the circuit board.  I would tie the metal control housings together and then to a good common ground. Notice how the original control has the input and output lines carefully run down the sides and away from each other. You might even try putting the input lines in coax to help minimizing the chance that they can couple with the output wires. It isn't obvious why the original switch and your switch are different. The difference may be bringing the input and output lines too close together and letting them couple by capacitance. Instead of tying the grounds together on the input and output jacks you might try tying them together on the ground of the circuit board. Hopefully this will give you some experiments to try out. If it doesn't lead to a solution come back and I will try to think of some more.

John

Hi John, thanks for your reply. I'm off to sunny Yorkshire today until Friday, but will check the groundings at the weekend and report back.... In a nutshell, you suspect it's a ground issue?

Hi Andy, I would start with the simple things like position of the signal wires. Next I would bring all the ground wires to a common point on the circuit board and eliminate loops and strings. Finally I would look at the proximity of things on the switch to see if that is where the problem comes from. Your noticing that the switch has some hum to it may be the unit trying to tell you something.

John

Hi John,

OK, this is what I'll try.

I'll solder some wire between the 3 pots, connecting them together in a string then finally connect the last one to the ground of the board. I'll do the same with each jack socket. This will mean simply drilling 2 or 3 extra holes in the board.

I'll try my best to separate the wiring, and channel it around the edge of the enclosure.

I'll take plenty of pictures so you can see exactly what I've done.

Andy

Hi Andy,

That sounds good. One other suggestion, lets have a 1000uF 25 volt capacitor that we can put on the board from the 18 V plus to the Ground. The length of the power wires up to the AC adapter jack and back to the board could be causing the power to pulse at higher volume.

John

I'm not 100% convinced that the DC power lines are an issue as this problem occurs using both DC power and batteries. Here is a gut shot of a reissue power boost with an LED, and a DC power socket. This also has a master volume installed

solasound 18v power boost

The difference between the 2 switches is because of the inclusion of the LED. You need the extra pole for the LED.

I think this is purely a  shielding/grounding issue as you pointed out initially.

When I get home I'll pull the board out of the enclosure, and connect all the pots together and ground them to the pcb, I'll then just connect a battery, and run the board out of the enclosure... I'm sure the issue wasn't there previously when I ran the board out of the enclosure, but process of elimination looks like the key to this issue.

I'm not 100% convinced that the DC power lines are an issue as this problem occurs using both DC power and batteries. Here is a gut shot of a reissue power boost with an LED, and a DC power socket. This also has a master volume installed

solasound 18v power boost

The difference between the 2 switches is because of the inclusion of the LED. You need the extra pole for the LED.

I think this is purely a  shielding/grounding issue as you pointed out initially.

When I get home I'll pull the board out of the enclosure, and connect all the pots together and ground them to the pcb, I'll then just connect a battery, and run the board out of the enclosure... I'm sure the issue wasn't there previously when I ran the board out of the enclosure, but process of elimination looks like the key to this issue.

Hi Andy,

I just noticed that the original case and the new case are made of metal and your replica is made of plastic. The metal could have a shielding effect that the plastic doesn't give you. I hope the extra ground wires and the separation of the signal in and out wires solves the problem. Keep in mind there are a few possibilities and I may have missed on my guesses.

John

Hi John,

My case isn't plastic, it's a Hammond enclosure made of aluminium.

You are correct the original cases were made of pressed steel.

UPDATE:

I have removed the board from the enclosure, and removed all the wires from the board. I'll now start a process of elimination.... first of all I'll tidy up all the wiring with new wires and ground the jack sockets to the board, and then test the board as it is, and post a video.... coming soon

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 and 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.

Hi Andy,

It is a high gain circuit, perhaps some component values were misread (e.g. red instead of brown) on the resistors? In the photos, some colours look brown on the original, but red on the replica. But it could be lighting conditions.

It would be worth confirming with a multimeter.

As I understand it is an amp with tone controls. According to the video, it is functioning fine when the volume control on it is set low. At that low setting, is the output comparable to the original amp, at the same setting, or at a higher setting? Due to the long wiring, perhaps there is some instability due to the very high gain as that control is turned.

Hi Shabaz,

I can understand your query regarding the resistors values, but the values were taken off the schematic, and confirmed by comparison with the following images. one of these images was taken from a boost pedal that is owned by a forum member over at www.freestompboxes.org. The other is a stock image from the internet.

The schematic was drawn by the forum member (Electric Warrior)

The values were confirmed via a thread on that forum last year. Here's a link to the thread on the forum,

freestompboxes.org • View topic - Colorsound Power Boost 18v

Hi Andy,

I see.. One other thing that could be worth doing (since your circuit appears to work when the gain is set to the lowest setting) is to swap out the 22uF capacitor at the bottom-left of the circuit diagram (i.e. the one connected to the volume pot) and change it to (say) 10uF, and if that doesn't help, also swap out the 4.7uF capacitor at the bottom-right side (the one in parallel with the 1k resistor) and replace that with 2.2uF.

The old capacitors may have not had the capacitance to match the value written on them, whereas modern capacitors are a bit more closer to the value printed on them. Half the capacitance could be a possibility.

Also it could be worth lifting up the variable resistors slightly off the PCB, to see if a few additional mm air gap makes a difference. There could be capacitive coupling if the back of the pots is metal, and that will be reduced if the gap is increased.

Hi Andy,

This is an excellent experiment that you have conducted to solve the problem. It eliminates several of the concerns that I expressed. I have gone back and examined the schematic that you posted. I am not enough of an expert to say anything specifically on this but I have never seen a volume control configured like the one in your schematic. Perhaps someone like michaelkellett can take a look at the schematic. I personally would like to understand how this configuration is controlling the volume. It obviously works fine up to the point where the oscillations start. If we can understand what is going on perhaps we can find a way to suppress the oscillation at high gain.

John

Prior to the latest experiment, the pots has plastic dust covers on them that prevented them from touching the board. i have since removed the plastic covers so that i can ground the metal covers to the board.

John, it's less of a volume and more of a gain potentiometer. Increasing the "volume" pushes the sound into distortion. It doesn't really happen on this little practice amp as the pedal is really intended to be used on powerful valve amps. When i plug it into my big guitar system and switch the pedal on even with the "volume" on it's lowest setting it adds around 20db boost. this is standard for this pedal.....

So, think of this control as less of a volume, and more of a gain.

Here is a YouTube video of a demo... it'll give you an idea of how it should perform.

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RE: Colorsound Power boost noise issue

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

In DIYStompboxes a forum poster 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.