LittleBits Mixer

[4pyros]

Hock up a audio source. (CD player) and listen.

I will try it when I can get off the couch.

 

[4pyros]

The littlebits website you posted the link to seems about as well designed as the circuit you posted, more a random series of unconnected pictures than anything else?.

I would have to agree its a mess, I hope they can do better!

 

[ronsimpson]

Ron, How would it look with a square or saw wave input? Thats what the oscillators that come with it make.

Square wave in.....square wave out.....works "OK"
Saw in....Saw out. "OK"

It is based off the idea that all "audio" starts out at 0 volts and some other positive level. Never a negative level.
example: the output of a 555 is 0 and 5V. If you change the volume it is now 0 and 3V or 0 and 2.39V.
example: A saw wave form from 0 to 3V. and with with a volume control it changes to 0 to 1.5V.
There is this common theme of "o volts". No negative.

Audio from a CD player is positive and negative. A volume control changes the amount of + and - the same amount.

I think it works with these noise makers just fine. As long as audio is defined as a signal that all wise returns to ground and never goes negative.
I don't think it should be advertised to work with normal audio.
My guess is that it does not work the way the inventor think it does. This splitting up the AC and DC then added them back together is not doing anything good, and can be achieved more simply.

With the audio you are getting there are many harmonics. So if the amplifier is clipping, who will know?

 

[Nigel Goodwin]

Wow I find it hard to believe its that poor of a design.
Can you point out an audio defect that I should be able to hear?

Unless it's biased externally, which isn't shown on the diagram posted, then it would be extremely distorted, as shown by the sims from Ron. But even if it's biased from the inputs, the bias (and distortion) will vary with the input, and with the settings of the volume controls.

Also the DC through the volume controls will make them crackle horribly when moved.

How hard would it be to improve it? and what advantages would the improvements provide?

Make it a proper mixer - there's no reason not to use actual virtual earth mixers, this doesn't (it uses opamps in non-inverting mode, NOT mixers).

 

[4pyros]

OK I get what you guys are getting at, I suspect that all the models are biased above 0 volts and that the input model that takes audio from MP3 players and the like does level shifting and/or converting to bring its output above 0 volts.
They have not posted the schematics for the input "Mic" model yet.
https://littlebits.cc/bits/microphone
Would it all make more sense if everything was above 0 volts?

 

[4pyros]

So Vref on the audio opamp sets the center voltage to 2.5 volts, so its all above 0 volts.

 

[Nigel Goodwin]

So Vref on the audio opamp sets the center voltage to 2.5 volts, so its all above 0 volts.

Only the AC coupled amp in the middle is biased correctly.

 

[4pyros]

Only the AC coupled amp in the middle is biased correctly.

What about the rest of my assumptions?

 

[ronsimpson]

Simple mixer: Supply is +6V and -6V
Note input and output is AC coupled to strip off any DC.
It could work with +6 volt supply, and with "gnd" connected to 1/2 supply. (vref)

 

[4pyros]

Simple mixer: Supply is +6V and -6V
Note input and output is AC coupled to strip off any DC.
It could work with +6 volt supply, and with "gnd" connected to 1/2 supply. (vref)
View attachment 85660

Yes but that would not work with the DC component as well.

 

[ronsimpson]

Yes but that would not work with the DC component as well.

Your speaker can not pass DC. Your ear can not hear DC. Don't bother with the DC.

 

[4pyros]

Ron; Sorry but all the modules in the kit pass DC as well as AC so they all work with the other modules this company makes.
This module works with other things you can and needs to mix DC to.
And yes the speaker will obviously not work with DC but a light or motor output module will.

 

[large_ghostman]

Ok now I am curious!! I only got up for a drink at 3:40am and now I have got to go and look at this!!! That will teach me to switch the laptop on instead of going back to bed!

 

[large_ghostman]

how old is your son? for me that seems a lot of money, but I am becoming the master of the freebie! From what I have seen you could make something better and cheaper yourself, but on the other hand it has bits that others can buy him. Tough call, yes the Canadian representative is going to shred this lol, however the one saving grace is no 741 Opamp (please tell me its not a 741). Depends on his age (the son, not you know who), I can see merit for some but the price is steep (to me anyway).
Can I ask why you didnt just take the idea and build something yourself? That surprised me a little bit as I had you down as a builder and tinkerer, then again this would save you time.
I am not bothered about the sound, as most of what I listen too dad calls noise anyway. Adding DC bits sounds good, so I think under 10 go for it, over 10 build with him something better and cheaper. Whatever you do if you see anything with 741 on, then scratch it out . Oh and expect a couple of , from certain regions of the globe with a police force known to ride a certain animal!
I do think you were brave posting it tho lol

 

[large_ghostman]

Ahh just seen the STEM/STEAM thing, that explains alot. Dont expect too much from anything designed for STEAM/STEM, they use this STEAM (whatever it is) at my School, there is some STEAM stuff we have that is for I.T it's really awful, but to be fair whoever came up with the whole STEAM thing for Schools was a box ticker and nothing else!
We also use the MATCH teaching system at my School, its for art design and textiles. Again none of the MATCH certified stuff is much good for actually teaching, but my School has spent a fortune on it.
Then there is the whole GROW SCHOOL nonsense! Pen pushers shouldnt try and dictate what gets taught and how!!!

 

[4pyros]

LG It took you some time to find this. LOL
My son Anakin is 12. As I said before he is not into making stuff as much as I would have hoped.
He is into playing with sound thoe.
I am laid up with a bad ankle right now and cant sit at my bench for to long.
I was manly interested in this stuff because KORG helped develop it.
It uses some of there chips.
And no there are not any 741 chips in it.
I am thinking of making some of my own stuff to go along with it and that should be fun.
Yes it is pricey but I did not have to try and sit at my bench for hours to make it so I am considering this kit a sample.

 

[Nigel Goodwin]

What about the rest of my assumptions?

As I said, it's going to all depend on exactly what's coming in, and where the controls are set - but it's no way to try and design something, it's completely bizarre and shows little understanding of electronics and opamps.

Notice Ron's post #29, that's how a simple mixer should look - and 'could' be made DC just as easily, but as it destroys the operating conditions for AC then it's not something which is ever done.

Would you buy a TV that only works on specific exact inputs and only if you very carefully adjust the controls to allow it to do so?.

I'm EXTREMELY dubious about claims that Korg helped develop it. I don't believe they would have anything to do with such a poor effort.

 

[4pyros]

I'm EXTREMELY dubious about claims that Korg helped develop it. I don't believe they would have anything to do with such a poor effort.

Nigel its true! it has been posted all of the internet , in the electro sound forums and such.
They even use some of there chips in the filters and modulators.
Just what other parts I don't know but maybe not the mixer.
As I said before some of KORGs designs were unconventional, but I don't think we should knock it without knowing the full picture.
I think if we knew all that went into the design we would see it in a new light.
But to outright say it can not work is wrong because it does we just have to understand how it works.

 

[4pyros]

Notice Ron's post #29, that's how a simple mixer should look - and 'could' be made DC just as easily, but as it destroys the operating conditions for AC then it's not something which is ever done.

And that was one of the challenges for this system that they overcame.

 

[tvtech]

Hi Guys

So nice to see people agreeing/disagreeing and no Neg Reps given
Pretty cool....now if only someone here could ask a little CRT advise from me

tvtech is pretty much redundant here

And feeling sorry for himself.

Regards,
tvtech