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Looking for more help with my electronic ‘bagpipe’ project...

Explorer

Mar 28, 2014
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For whatever it’s worth, I finally found a second power supply that ‘sounds’ good in my new circuit. (See photo, the one on the left.) But, I feel like there should be a way to resolve the sound issues created by power supplies. I thought the new little switching supplies were supposed to be a huge improvement over the older, heavier, klunky ones, in terms of performance.

B7BCF89F-59CE-4A38-9715-EC12E34F2336.jpeg
 

Explorer

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Well, I take that back. It only ‘sounds’ good if the drones circuit is not connected. The ‘warbling‘ comes back, across the whole keyboard, when the drones circuit is also powered.
 

bertus

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Nov 8, 2019
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Hello,

A SPMS powersupply will generate high frequency noise.
Adding a filter on the output can reduce the noise:
smps output filter.gif

This was found on this site:

The warbling you hear might be an interference between the SMPS and the drone circuit.
This is caused by the "beating" of the different frequencies:

Bertus
 

Alec_t

Jul 7, 2015
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Try de-tuning the drones circuit slightly. Does that affect the warble frequency?
Are you feeding the mixer with the voltages across the timing capacitors of the drone/chanter (~triangle waveforms), or the voltages across the IC outputs (square waveforms)?
 

Explorer

Mar 28, 2014
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First off, I’d like to say that pointing me towards definitions of Vcc just proved my point about obfuscation. There are 2 modes of electrical power on this planet, AC & DC. To leave off mention of either one of them on a data sheet seems beyond stupid to me.

Bertus, I added a 100uf cap and a .1uF cap to my soldered board, on both the drones and chanter circuits—which I didn’t have on the breadboard. I had added a nice new, tiny ceramic .1 cap across the “Vcc” and ground pins of each IC, beneath the board, with leads as short as possible. Yesterday, I removed the 100uF cap from the drones circuit, as well as the .1 cap from the drones circuit flip-flop IC (because there was no way to have nice short leads on that one; the pins are at opposite ends of the IC). It didn’t seem to make any difference.

Then, I built a bandpass filter and added it before my amp. I used high-pass and low-pass calculators to figure out capacitor and resistor values for both sides of it and was targeting frequencies as close I could get to to 261 and 932Hz. I put 2 trim pots in the filter, to try to get the resistances spot-on. It did nothing. It didn’t even knock out or knock down my drones. I started playing with the 2 trim pots, and it struck me that they mostly worked like 2 extra volume controls.

With the filter that you‘ve shown above, Bertus, are there any guides for component values, or would I be experimenting with that vast range for 3 of the components, if I decide to try it?

I also spent quite a lot of the day yesterday researching SMPSs and audio problems and every page I hit upon seemed to be aimed at SMPS designers, not at audio circuit designers.

And Alec, your question is interesting and rather psychic. I haven’t tried detuning the drones. However, my new chanter circuit takes output from BOTH the timing cap and from the output pin, runs them through 1N4148 diodes and then to my mixing circuit. Actually, I’m figuring that the 2 diodes form another mixing circuit for the 2 outputs I’m taking from that 555 timer. (Feel free to disabuse me of that notion.) I think the addition of the output from pin 2 makes the chanter circuit a little bit more nasal sounding. (I have the circuit diagrams on my desktop computer. If someone wants to see them, I’d have to boot that up... They are also in the second PDF on my mediafire page: https://www.mediafire.com/folder/q4ave4tjk87ns/Bagpipe_Project )
 

Explorer

Mar 28, 2014
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Oh... I’ve got another low-current 100mA SMPS on order, that I found on eBay last night.

And BTW, the new drones circuit has a 555 timer feeding a dual flip-flop, instead of a crystal-controlled oscillator (on my first board, in my first device). So, there are two 555 timers on this new board. So yes, Alec, I could easily try detuning the new drones circuit and will do so later on today.
 

Explorer

Mar 28, 2014
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Bertus, the page you offered has this comment down farther below that schematic:

“As john12ax7 points out, SMPS actually may not like caps directly on the output. It's not like you're filtering rectified AC. You're trying to get HF hash. And since the inductor will effectively be isolating the SMPS from the cap that follows, I would use a large inductor and small cap instead of the other way around like you're schem shows. I would use the largest inductor you can find with the right current requirements and then just pick a cap that gets down below 20Khz. For example, you should be able to get at least 1mH which with a 10uF cap gets you down to 1.5kHz. You might also use a common mode choke but I have heard people say it doesn't matter. Personally I always liked the idea of using a common mode choke to completely isolate both outputs of the SMPS and then use the point right after the choke as 0V and star ground point. Same applies if you're stacking two to make bipolar. You'll just need two chokes. Of course SMPS must be isolated type.”

I know nothing about common-mode chokes. I think perhaps I‘ve removed some from things that I have taken apart. Nice cube-shaped things with neat coils on each side??? If they might be a solution and anyone wants to show me a schematic and tell me how to figure out “current requirements,” I’d be interested.
 

Alec_t

Jul 7, 2015
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However, my new chanter circuit takes output from BOTH the timing cap and from the output pin, runs them through 1N4148 diodes and then to my mixing circuit.
I think that may be the source of your tremolo effect. The drone circuit will, via the mixer, source or sink some current from the chanter timing cap and hence modulate the chanter signal. Try disconnecting the diode from the timing cap and see if the tremolo disappears.
 

Explorer

Mar 28, 2014
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Detuning the drones didn't help. I found this thread, where a guy talks about trying everything, finally giving up, and switching to a linear power supply:


Using a linear power supply for one of my circuits does help a lot. Trouble is, most of the ones I have on hand are 9V or higher. And the 6V, 300mA one that I dug out up of one of my boxes generates A LOT of heat! (I need less than 9V for the drones circuit, because of the flip-flop IC that I'm using. (Over the last couple of years, I've collected a lot of SMPSs, every time I saw one in a thrift store for a buck in an odd voltage output, thinking they were the greatest things since sliced bread. So, I have lots of 'em, but mostly with pretty decent current ratings.)

And Alec, just to clarify, you want me to try this? (Sorry about the artifact in the image from the "Grab" app):
Chanter-2.png
 

Alec_t

Jul 7, 2015
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you want me to try this?
No. Just remove/disconnect the diode, so that the chanter cap voltage isn't fed to the mixer. Don't bypass the diode. You don't want the drone circuit to affect the chanter cap voltage.
 

Explorer

Mar 28, 2014
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That didn’t help, Alec.

At this point, I’m going to just wait for the new power adapter that I ordered from eBay. Or keep on the lookout for some low-power linear supplies. Or make it portable and go back to batteries.

THANKS! Unless anyone has another brilliant idea. Something that they’ve tried, to reduce SMPS noise, that they know works.
 

Explorer

Mar 28, 2014
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So far, the 2 things that have helped the most are a linear power supply, and, if I power the circuits with 2 SMPSs, a wire from my ground rail to the ground connection in a wall outlet. The latter doesn’t get rid of the ‘warble,’ but it reduces it a lot.
 

73's de Edd

Aug 21, 2015
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This relates to your second paragraph in your post # 25


(because there was no way to have nice short leads on that one; the pins are at opposite ends of the IC).

HOWTODOITTOIT . . . . .


If that is the situation / case, then assign and make the LONG run lead of the capacitor as the one being connected to GROUND , that then leaves the other VERY SHORT clipped lead of the cap being connected to the bypassed power connection .
 

Explorer

Mar 28, 2014
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I’m not sure what I’ve just learned. But, if anyone wants to see what’s inside the power supply that solved all my problems with my first device, photos are below. And also below are all the markings I’ve been able to glean from the board and components, as well as some online information. (I’ve ordered another identical one from eBay and am about to tape this one up and see if it still works.)

Chip in middle of board, markings =
1503
SC1139DG
2A


Accurate CV Switcher
——-
BD1 markings =
— +
ABS10

Bridge Rectifier
——
T1 markings =
T001-00102-00
71001-00102-00
TP103-3 TenPao

——-
C1 = G-Luxon, 3.3uF, 250V
C2 = (same)
C3 = 4.7uF, 50V
C4 = 220uF, 10V
——
D5 markings...

I can only see “19R” and a “Y” below that.
I think there might be an “8” in front of the “1.”
——
PCB2869
REV0.3
20130712
FR-1(KB-3151C)
12MM OSP

0937303E-EED7-4FC7-B9DE-44EAE45AA439.jpeg



75277F45-68FB-4C1F-89FD-64A0C0D1A0E2.jpeg
31D44632-188E-406A-AB3F-AC8AF6B9F652.jpeg
 

Explorer

Mar 28, 2014
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The adventure continues... I finally found some useful info (below) on power supplies and have learned what an idiot I have been: I.e., not realizing that both of my little circuits could be powered with one supply—which nobody here bothered to tell me.



I also discovered something about my new chanter circuit over the last 2 days and have changed that. I’ve got a revised PDF on the second iteration of my ‘bagpipe’ project my mediafire page, where I’ve noticed a few downloads.

If anyone—especially an electronics newbie who would like to avoid all the stupid mistakes I’ve been making—would like the complete chronicle of them, revisit:

 

Alec_t

Jul 7, 2015
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not realizing that both of my little circuits could be powered with one supply—which nobody here bothered to tell me.
Well, we're not psychic so didn't know what other modules you intended to build and power with those supplies.
Perhaps you're thinking of adding further tone generators to simulate the massed pipe bands of the Royal Edinburgh Tattoo ? :) :)
 

Explorer

Mar 28, 2014
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The 7V, 300mA linear power supply from a salvage place powers both of my circuits fine and produces dead silence when I plug in my little amp. But, I was still getting some annoying noise at the low end of my keyboard.

Here’s my solution, with a small piece of brass tubing (that fits into the ground connection of an outlet) and a piece of copper—a wire running from the ground rail of my circuit, wrapped around the wire feeding the power supply, and connected to an Earth ground:

0FF83B1C-3A2E-4423-BAA7-DD3D87022264.jpeg


7BAEB8EB-14E2-46F0-BCE4-2D7C0CB7111A.jpeg
 

Explorer

Mar 28, 2014
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For anyone who is at all interested in this project, I’ve posted another PDF on my mediafire page with more build photos. The link to the mediafire page can be found above in the thread. It includes an image of my new contact devices, made from Montecristo aluminum cigar tubes. For newbies, looking for build help/ideas, as well as avoiding my mistakes, as I said above.
 
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