Ideas to battle PSU noise?

[deeaa]

I have a 1-Spot and it works great, but the Biyang pedal needs it's own 5-volt supply...and that is noisy. Can't readily find a 5-voltter with similar specs, so, has anyone had any success in quieting down a noisy PSU with some trick?

It's not a horrible noise, but still clear enough, especially as I use the pedal as my lead sound OD, meaning it's LOUD when it's used, so the noise also can be clearly heard.

 

[Ch0jin]

Well that depends. Are we talking 5V AC or DC from that biyang supply, and does the noise sound like regular 50hz hum?

If the answer is yes to the hum then it's likely a case of insufficient filtering. Either inside the supply (if DC) or inside the pedal (AC).

If the supply is DC, the likely fix is to add a polarized electrolytic cap directly across the 5V supply.

If it's AC it's slightly more complex as you'll first need to figure out if the pedal has a rectifier and filtering circuit, and then upgrade it. Still only by adding a cap though.

All that assumes nothing is faulty too.

 

[deeaa]

Well that depends. Are we talking 5V AC or DC from that biyang supply, and does the noise sound like regular 50hz hum?

If the answer is yes to the hum then it's likely a case of insufficient filtering. Either inside the supply (if DC) or inside the pedal (AC).

If the supply is DC, the likely fix is to add a polarized electrolytic cap directly across the 5V supply.

If it's AC it's slightly more complex as you'll first need to figure out if the pedal has a rectifier and filtering circuit, and then upgrade it. Still only by adding a cap though.

All that assumes nothing is faulty too.

Thanks! Yes it does seem like it's more of a low rumble type noise, could well be caused by that. 60 Hz here though, but I assume it's the same thing.

The only problem is I have very little knowledge of electronics and even more lacking in the terminology in English. I know what a cap is though, and I know polarity...in my lingo that means I need a 'condenser' with + and - marked on it. Does the word electrolytic mean the type of cap that is like a small barrel in layman's terms? And by accross the supply, does that mean between the original + and - leads of the 5V side, and if so, does it matter which way the polarity goes - plus to plus? And what about the cap value - will any do? And finally - I do have a multimeter, but how do I verify which lead is the plus and which minus?

I guess you see it might be over my head right now to make the fix...or what do you think? I suppose I could also just ask the local amp builder if he knows how to fix it or suggest a better PSU for it maybe....could be safer and better.

 

[Ch0jin]

If you know someone who can build amps then they absolutely could sort you out. If it's what I think it is, it's a simple fix for someone who has a little electronics experience.

To answer you questions though.

Yes, a low rumble type noise is almost certainly hum from mains power whether it's 50Hz or 60Hz. Obviously the sound would be slightly higher in pitch for 60Hz, but the cause and cure are the same regardless.

You are right about pretty much everything else as well. A cap is indeed a condenser, I just thought "condenser" was a really old word, not a geographically variable term. You know, like "Wireless" Vs "Radio" rather than "valve" Vs "tube", but there you go, I learnt something new

Electrolytic caps are indeed the barrel shaped ones, and the type you would use would have a "-" and a "+" with the "+" going to the 5V and the "-" to ground. It matters a lot which way they are connected, just like a diode or a transistor. The wrong way and they fry. In fact its really easy to make them explode if you have enough voltage to play with, but with 5V nothing is going to go boom, it just wont work.

As to cap value, honestly I'd use whatever I found in my junk box that was over 10uF and rated at 16V or above. 100uF or even 470uF might be good to try actually, but there's likely a wide range of values that'd fix it up. Just FYI though, using a -very- high value cap you run the risk of killing the power supply as it tries to quickly charge the cap when it's turned on, a phenomenon called "surge current".

There is a complex formula (and by "complex" I mean, I cant think of it off the top of my head right now) to determine the exact amount of capacitance needed to squash ripple (hum) in a power supply, but that's only really worth bothering about if you are designing a power supply that cranks out many amps, not a little 5v brick. You'd also need to know if the power supply was bridge rectified or not, and to figure that out without pulling it apart you'd need a scope and bleh, too much hassle.

Lastly, all polarized caps are marked, so thats easy, no need for a meter there.

But as I said at the start, any amp tech knows how to fix this and it's not a big deal for them. A well filtered 5V brick as a replacement is not a bad idea, but I suspect they will be slightly rarer than 9V ones.

Oh and one last thing. All that assumes the power supply is 5VDC. If it's 5VAC then you'll need to hack the pedal itself. The power supply should have that written on it really 5VDC or 5VAC.

Oh and to satisfy my burning curiosity, what kind of pedal will run on 5V?


Oh and lastly.... I wrote a bit of a thing on caps for someone else over HERE if you want to read more..

 

[deeaa]

Ok! Excellent info, thank you! I'll check whether it's VDC or VAC and see what I can do about it. Good to learn something new!

It's the Biyang tube overdrive/distortion thingy...those run at 5V for some reason, I think it was 5V 2A...they claim the pedal uses full plate voltage to tube, not starved plate, I guess it requires different type of power from 9V standard. Whatever it does, it sounds bloody good for the price, only the rumbling hum noise bothers at higher levels.

 

[Ch0jin]

Ahh OK. I've just missed 2 of those on ebay actually. They looked like a nice little platform for mods (apart from the board with the surface mount stuff).

The bad news is, I'm almost certain they run from a 6VAC adapter. What they do is use a transformer inside the pedal to change the 6 volts AC to 100 volts AC or more, they then rectify this to around 250VDC (from what I've read) to feed the tube.

If I'm right then adding extra filtering is a little more complex as I mentioned earlier. I've seen some hand made schematics of the audio section of these, but nothing on the power section so I can't really advise much.

I have read that they run DC heaters (filaments) on the tube so at least you know it's not that causing the hum. (this is a common source of hum on tube amps)

I'd say take it to a tech for a look.

 

[deeaa]

Aw, bummer! Well, it does sound so good...live the hum doesn't really matter much at all..funny, at home I can't really distinguish it at lower levels.