Ruby guitar amp noisy when plugged with DC adapter

[bzblues]

Hello everyone!

I've been building a couple of ruby guitar amps. I'm a begginer but I've been practicing a lot and learning but still have doubts.

This is the problem: The amp works judt fine with the 9V battery obviously, but when I use the dc adapter (9V 1A or 2A) it gets noisy. I tried different adapters but the problem persist.

I don't quite know how to solve this. Any ideas?

Thank you!

[ChopSauce]

Seems to be a common problem. Maybe you can try one or two CRC filters in series between the adapter and the amp?

[garcho]

Welcome to the forum!

Ah yes, the Ruby, daughter of the Smokey, DIY staple. Noise has many flavors. Is it a low hum (60Hz)? Is it a high pitched squeal? Hiss? I'm guessing it's 60Hz hum.

If you haven't already, try putting an electrolytic capacitor, say 47uF or 100uF, between the power rails (V+ and 0, or V-). Report back, we'll take from there.


Take some pics, post the schematic, don't make people search for stuff in order to help you

[iainpunk]

yeah, most power supplies have poor noise characteristics, and deposit a bunch of noise in to high power loads.
i recommend an CLC PI filter, since the lower DC resistance of an inductor will produce less heat and drop less voltage, which keeps more headroom intact.

i think a 100uH 1A or 2A inductor and a pair of 10uF capacitors on either side would do the trick if the problem is hum (50Hz in the old world or 60Hz in the new world, parts of Saudi Arabia and parts of Japan IIRC)

cheers, Iain

[Vivek]

Besides cap across power rails,

Wasn't there a need to have a cap from some pin to ground, since that would remove ripple from some internal voltage divider ?

like 10 to 100uF or so from pin 7 to ground ?




Does Ruby have this cap ?

Please post your schematic. Thanks

[iainpunk]

Besides cap across power rails,

Wasn't there a need to have a cap from some pin to ground, since that would remove ripple from some internal voltage divider ?

like 10 to 100uF or so from pin 7 to ground ?




Does Ruby have this cap ?

Please post your schematic. Thanks

that should reject power supply noise indeed, but the Ruby already has this cap, but its only 100n not the 10u or 100u.
at 100n, the cutoff frequency is alt the way up just under 200Hz ( 2x15k in parallel is 7k5 with 100n that gives 212hz, this is an aproximation since there is an active load and the impedance would be a bit higher so about 150Hz LOW pass would be more realistic, but its still way to high for hum rejection.....)
i strongly recommend changing it to at least 1uF, but higher is better in this case.

cheers, Iain

[amptramp]

I have one wall wart DC multiple-voltage adapter at home that I took apart and found a surprise inside: there was a tapped transformer with a selector switch and diode bridge with the output shunted with a series R-C network that had a one ohm resistor in series with the electrolytic capacitor.  This was done to limit inrush current but it definitely left a lot of ripple on the output.  Do not trust DC adapters to be filtered effectively unless they are specifically stated to be regulated.

You need filtering in the amplifier to make up for the fact that not all wall warts are created equal.  The suggestions above on putting electrolytic across the power rails and from pin 7 to ground are good advice.

[bzblues]

Hello everyone!

Thanks for all the answers. Got a bit confused but I'll have to re-read it and try each one of the solutions. Let me see if I understood. Is it ok like in the drawing?

[GibsonGM]

You would put the electrolytic cap from pin 7 to ground, not 'take pin 7 to ground'....the other cap is ok across the power jack if that works better for you...in some cases, having it right on the board would work better/look better.   Sometimes there isn't space, though. 

Welcome to the forum, Bz! 

[garcho]

You definitely want to put a 47u or 100u, as in µF, microFarads, not n, or nF as in nanoFarad. The nano won't hurt, it might even help with a bit of higher frequency noise, but you want a BIG electrolytic cap.

[bzblues]

Sorry! it was a typo! I meant uF (microfarads)

I'll try it and I'll get back to you guys. Thank you!

[bzblues]

Hello!

Well... Didn't work out. No difference, nothing...still noisy. I put a 100uF capacitor from the pin 7 to ground and another 100uF cap into the power rails just like instructed, but there is no difference...and the dc adapter is a fairly quality one.

Do you guys have ay other idea that might work? I really don't know what to do here.

Thank you!

[iainpunk]

please describe the noise.

have you tried adding a ground wire? you can just use a long piece of wire connected from the circuit's ground to a radiator or the ground clips of your wall outlet.

cheers, Iain

[Vivek]

Could you post a video of your breadboard and the output sound

Thanks

[bzblues]

I tried with previous amps to isolate the pcb with a little aluminium box and solder a wire to the cirucit ground and still, nothing happens.

Here is the video: https://youtu.be/NDmaJYrWbfA

[FiveseveN]

Sounds like the noise is being picked up by the pickup(s) to me. Does it go away when you turn the guitar's volume to 0?

[bzblues]

Yes, it goes away when the volume pot is down, but the noise is there with or without the guitar plugged in.

[Sooner Boomer]

Stupid idea, but one worth trying; short the input. Now how much noise?

[FiveseveN]

That would have the same effect as turning the volume down.

the noise is there with or without the guitar plugged in.

Which is expected, assuming you don't have a switching jack that grounds the input when unplugged (most amps have this). A floating input will pick up EMI just like pickups or an unplugged cable at the guitar end.

The mystery is why it would go away on a battery. Maybe there's interference (not ripple) coming up the power cord?

[iainpunk]

That would have the same effect as turning the volume down.

the noise is there with or without the guitar plugged in.

Which is expected, assuming you don't have a switching jack that grounds the input when unplugged (most amps have this). A floating input will pick up EMI just like pickups or an unplugged cable at the guitar end.

The mystery is why it would go away on a battery. Maybe there's interference (not ripple) coming up the power cord?

the wall wart might give a bad pseudo ground, adding to the antenna effect, adding a real ground would probably stop the wart from acting like a antenna.

i believe its not logical to expect anything but noise when you have no ground connection on an amp. especially when there is a wall wart adding to the antenna effect. the fact that it had little noise when using a battery is more luck than logic.

cheers, Iain