My son and I are newbies to amp and audio technology. Been doing Arduino based stuff for a while but I cannot find a clear answer to my question on other pages/forums etc...
He is 8 years old and assembled and soldered this thing by himself and it works perfect for devices with built in volume adjustment. We needed a decent little sound unit to test some of the amazing synth builds on here. Just completed the Mosquito I. Freaking amazing. Since I had a couple matching speakers in cute little boxes we decided to assemble this kit with the use of a small little pc power supply.
a cheap but effective build for a test amp.
My question is where would/should I put a pot, and what kind of pot would be best?
I tried a 10k linear pot but it just made it very distorted and garbled. I found a circuit using a mosfet transistor and tried that but some odd high pitch sounds come out of the speakers, like interference?! I am told there are other types of pots we could try, but thought I would ask before I started buying things.
Just a little about the "Mosquito I" synth. I believe that because the output signal is coming from digital pin 9 that the output is square wave and floats around 2.5-4 volts, while my phone and mp3 players(with volume adjustments) float closer to 6 volts. I am not sure if this would be a problem for the potential potentiometer.
Thank you all so much for a wonderful community, and so many amazing and wonderful resources.
First off you need a LOG law pot not a linear one. With a linear pot you don’t get equal changes of volume with equal changes in rotation angle.
Second you probably need a capacitor in series with the output from your Arduino output.
Use about 10uF with the positive end towards the Arduino. That will block any DC bias, what you call floating voltage. 10K to 100K should be fine for the pot.
I would have thought so but you still need that capacitor. Otherwise the 10k linear pot would have “worked” , with only the way the volume reacted to rotation being the only problem.
I am still having issues putting a pot in the mix for volume. I have 250 and 500k in the log types. When I incorporate it into the mix I get static and loud pops. Now I am not sure if that is interference. I did put all this into a wooden cabinet and there is a arduino, amp, mini light ballist, and speakers close together. I am curious if I need to shield and if so how...
The idea that I had was to make a box, add speakers and amp and a couple switches and indicator lights and a small fan for cooling. Then have enough room to add an arduino synth or two. I have all that, just can't get it to jive.
I see you've got a bit of screened twin-core there, but you've also got a great big lovely pick-up coil right next to the Arduino. Not good. Get some more screened wire, ground the screen at one end only, and get rid of unnecessary lengths trailing around. Keep the wiring away from the Arduino as much as you practically can. Might not fix it, but it's a step in the right direction.
I have 250 and 500k in the log types. When I incorporate it into the mix I get static and loud pops
Those values of pot are way too high. The higher the impedance the more “static” you pick up. The plops are caused by sudden changes in DC level. A capacitor in series with the audio line will often sort that especially if you reestablish the DC bias afterwards.
Using solderless bread board in a permanent instillation is just asking for trouble.
When using screened wire keep the screening right up to the board. Don’t stop a couple of inches the board.
As Mike says, you don't stand a chance until you build it all properly on a board. It is going to radiate all sorts of interference.
I would be building it properly with a Nano on some perfboard, then enclose that in a screened box, like a die cast project box. You might also be in for feed through capacitors etc to keep it properly quiet. Keep wire lengths to a minimum and never coil them, that as was said above is a very efficient inductive pick up / radiator.
I don't see a schematic of your amplifier anywhere. A volume control pot should be placed where the signal voltages are the lowest level possible. Near the input to the amplifier. Pots hate current through the resistive elements and will give you noise and smoke when they get tired of it.
My question is where would/should I put a pot, and what kind of pot would be best?
It sounds like you are talking about trying to attenuate the amplifier output with a pot.
This is not the right approach for a number of reasons.
The place for a pot is on the input to the amp.
I believe that because the output signal is coming from digital pin 9 that the output is square wave and floats around 2.5-4 volts, while my phone and mp3 players(with volume adjustments) float closer to 6 volts. I am not sure if this would be a problem for the potential potentiometer.
If on the other hand you are generating a signal from an arduino, you need the series cap (1 uF)Mike mentioned to block from your amp. Are you using a guitar amp to amplify the arduino digital signal ?
Wow. A lot of feedback. I will try to address each thing you folks mention.
My brother is a bit of a audio file and seen this and said he wanted to slap me...the coil of wires and too much wire. He suggested I plot it out draw a picture and refine it before trying to put it into practice...so yes I am going back to the drawing board literally.
I have placed an order to get the appropriate sized pots, I was going off of a google search for size of pot, because it fit what I had...realizing cheap may not be the best approach.
I also have ordered better buttons and actual boards to solder this build to to get rid of the breadboard.
I believe I will make either an aluminum enclosure for the various parts, or steel sheeting 1/32" or thinner...I have a lot of stock laying about I should be able to make something reasonably attractive.
I have ordered a dozen nanos and some various shields for them which will help cut down on the size as well...and I am going to upgrade to shielded copper wire instead of this cheap silver crap. I am fighting with it taking solder properly anyway.
AND I will include caps and blockers for implied reasons.
Here is the original prototype of the "mosquito I". This is a arpeggiating synth with arduino...my son loves it and wired the bread board himself...now we are upgrading to a cabinet. Mosquito I
I bought him a 3 watt stereo amp kit off some site and he assembled and soldered it himself. This is the kit. kit 90
First off C2 is in the wrong position. Where it is makes C1 and R6 just do nothing. C2 needs to be connected to the junction of C1 and R6.
So I would change that first before doing anything else. Then shorten the leads.
instead of this cheap silver crap. I am fighting with it taking solder properly anyway.
That is because the shielding is aluminium and you can’t solder to it with normal solder, those sorts of leads are designed to be clamped. So what is happening is that you are not soldering it at all but are getting a wire to stick to it with just the flux as it as it sets when it cools. So it is not making good contact. So replace those next.
Only if that fails then go to a screened box, but I am not convinced that a screened box is the answer it seldom is. A screened box keeps things in and increases the chance of anything in the way of interference generated inside the box seeps into all components in the box.
I am just giving you all kudos and my thanks for the patience you have showed me. I know you must think I am a newb. Funny thing. I have been recapping and reflowing PC components, and repairing electronics for more than a decade. I even had electronic classes in school...but I never created anything really other than simple lights...like simple stuff. Recently been asked to work on a lot of iot stuff at work using "libelium" products. Similar...but mostly it is just making cables and installing special LEDs...so I am a very experienced newb. Lol.
I will circle back around to this in a few days after I get all my new stuff and correct that rat nest in the box...hopefully with you guys' notes and the new stuff I can get this project working...what is funny. My son now wants to add an FX module to this, which I told him to put that on the list to do after we have a working thing.
Thanks again...Happy Holiday or at least Happy Tuesday!
I got all our stuff, but the pot for audio. Looks like I am going to have to re-order them. Seller marked it unavailable the day it was suppose to arrive, what a wash...sometimes you win and sometimes you bang head until morale improves.
Anyway, I am still working on making it neat, I replaced all the wire with a slightly heavier gauge and it is copper so much easier to solder. BUT About your comment Mike...
"First off C2 is in the wrong position. Where it is makes C1 and R6 just do nothing. C2 needs to be connected to the junction of C1 and R6. So I would change that first before doing anything else. Then shorten the leads."
I have looked real hard at that schematic and cannot see an R6, but I do see an R4 and I assume that is what you meant. I have not made that change just yet...but his "RC network" may be making the output too quiet...
As it is right now during testing the sound from synth sounds very weak but the speakers sound very very hot...almost like a really hot hummbucker on a guitar. In fact, if you bump the shielded cable at all it almost acts like a pick up. Moving the little bit of slack around causes all sorts of strange sounds...
I hooked up the synth to headphones and it sounds pretty good, then to my PC speakers, I have to turn them up a lot before it sounds good.
We got everything working...well just almost everything. I cabbaged a stereo volume pot from an old head unit instead of waiting on another china shipment...
It quieted the noise right down, and your suggestion did the trick for the "hot" sound. Tested it for about an hour with my phone and jived with the tunes...clear sound.
The OP's schematic has been followed exactly and everything is working but the buttons...Powered on and everything is working, press a button and it whistles, though it does technically function to change the rhythm or tones as implied. Once you press a button the sound quality degrades steadily until all you hear is that whistle. I suspect I need a bigger resistor on the neg. of those buttons.
Sorry yes it was R4, but it was very faint and blurred.
I have not made that change just yet...but his "RC network" may be making the output too quiet
At the moment those two components are doing nothing. They are supposed to be a restoration filter, that is one to get rid of the high frequency PWM signal coming from the Arduino. They will help reduce the overall interference in the environment.
jumper_d_1981:
... press a button and it whistles ...
What power supplies are you using, and what's the layout? (Or have you already described it and I missed it?).
A picture (schematic) is worth a thousand lot of words.
johndg:
What power supplies are you using, and what's the layout? (Or have you already described it and I missed it?).
A picture (schematic) is worth a thousand lot of words.
Hey there. Thank you for the response. I know a lot of folks that come onto a forum will read way more than they have to...suffice to say here is a summary.
My son and I are undertaking this "mosquito" build which is a "mozzi" like synth for arduino nano. We are adding it to a amp kit my son put together. We had some issues with getting the right parts, and a couple mistakes on the original posters schematic which you can see here. The man was nice enough to give us some guidance but we hit a wall with incorporation into a single box. I thought it was magnetic fields. Turns out that Mike pointed out it was a much too large pot. I also got rid of like 30 feet of cabling and replaced it with a much more user friendly copper wire.
So, suffice it to say. We have the amp working with a pot for volume and a cap and the amp itself works good. The synth itself works great too, but the sound degrades after a few minutes, like distortion eventually the distinct mozzi sound is gone and the only thing that is left is a whistle of sorts. Restarting or resetting the nano fixes it for about 2 more minutes. I am reaching out to the OP again in hopes he knows what is happening here. I am going to attempt reloading the virgin code tomorrow.
So we just need to get that sorted and put everything in the box neat like and we will be finished. Then onto our next planned projects. Shelves. Lots of shelves. We have all these projects and no place to put them...lol.
