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The CMoy++ ==With 3D printed case==

post #1 of 6
Thread Starter 

I finally got all the parts I wanted for the base model of my CMoy++ so I started to prototype it out on a board from RadioShack. (I'll borrow a friends camera to show how it looks later) It's basically a CMoy with a real ground, buffered outputs, bass boost, and a DC jack for charging the batteries (2 NiMH 9V bats) I'm still waiting on a voltage regulator from LT but I have the rest of the circuit ready to go.

 

There is a question that I'd like to discuss though.

 

I wanted to make a real ground as it reduces the amount of components needed and also creates less noise and lower output resistance than a buffered ground. (according to this, this, this, this, this, this, this, this, this, and this (to admins: I like to add refrences to my things so I A: give credit where credit is due to people who actually know what they are talking about, and B: to give myself credibility so I am not just talking out of my a**))

 

The only issue is if one of the batteries were to come disconnected by accident. (I don't mention batteries draining unevenly because before there was an issue you would get distortion making this a non-issue) 

 

If I go with a real ground I think I'd like to implement a circuit somewhat like the O2 that would cut power if a battery came unplugged (or just cut at low voltage so that it retains quality)

 

I'd like thoughts on this. I don't know the circuit used by the O2 yet but I can easily go look at how its implemented and do something similar. A virtual ground would solve this issue, but would also introduce more problems itself.

 

So virtual ground or a real ground with low voltage protection?

 

PICTURES: bro was home from college so I borrowed his S III and took some pics. had cyanagen mod on it though so the camera isnt as high quality as it is with default :/ oh well, they work:

 

 

middle line is my ground on the pic below. At present moment its a real ground but can easily be converted.

 

 

 

Its obviously not finished (feedback loop isn't even built) but its a start. This is just a prototype (going to get into etching my own PCBs) but what do you guys think of my placement? Any criticism except incoherent fits of rage are accepted :)

 

P.S. will label some pics soon and upload them

 

 

 

NEW PICTURES WITH CASE AND FINISHED AMP:

 

 

Keep in mind the case is not final. As it says on the front, it is a prototype (and actually doesnt work ;) ) it was a fast print and simple design (the lines you see on the front are supports that used to extend across letters to support certain parts (again, fast print)) and I've already got a new design in the works (I design my cases in solidworks and then print them) tell me what you guys think :)

 

Side note: Amp's done. has a gain of 4.7 and a real ground (at present moment) i'm going to run it through some tests but measurements of DC offset are kind of high (probably due to one of the batteries being more drained than the other (right channel is 45mV and left is 30mV)) anyway, I think 4.7 might be a bit too high with the amount of bass boost I have implemented (then again in final design there will be a lot less bass boost, I just wanted to see how much it could take) so I'm going to have to play around with some things. Of course, again, this is a prototype. The official design will be on PCBs that I plan on etching soon. Going to try to use Eagle or similar to print out the designs....any recommendations for which is best for printing designs to etch?

 

Any comments, crtiques, help greatly appreciated.


Edited by backspace119 - 2/24/14 at 6:58pm
post #2 of 6

I won't club you over the head with my opinion. You already know it.

 

I will observe that you've hit on exactly the issue: TANSTAAFL. People talk about "real" ground in a portable as though it is entirely problem-free, and so that a virtual ground is simply a collection of costs, rather than a collection of tradeoff choices.

post #3 of 6
Thread Starter 
Quote:
Originally Posted by tangent View Post
 

I won't club you over the head with my opinion. You already know it.

 

I will observe that you've hit on exactly the issue: TANSTAAFL. People talk about "real" ground in a portable as though it is entirely problem-free, and so that a virtual ground is simply a collection of costs, rather than a collection of tradeoff choices.

Thank you. I'm trying to see if I could design a product I could sell locally and maybe eventually on the web. (always looking for ways to get a little more cash ;) ) so the issue of headphone killing DC offset from a real ground was rather scary. I know I could implement the protection circuit, but I just wasn't sure if the cost to benefit ratio of a real ground versus a vGnd was good enough to warrant it. Also board space is an issue as no one wants to buy a brick just to give them a bit more volume. (would also mean I could probably use only one battery) 

 

I'm really just considering the costs of both. I haven't had a chance to analyze the protection circuit yet but I would guess that it has close to the same cost as a vGnd. I've already cut costs at every corner (was recommended cutting on the case and I had to laugh at this, because I'm printing my cases with a 3D printer I have access to. It costs about 70c and 6 hours of my time (really cheap and slow printer (also makes mistakes a lot giving me only a %60 yield on average))) I've gotten my cost down to 20$ without buffers or bass boost, with the BUF634 that goes up dramatically (going to try the LT1010 to see if its as good (honestly having to pay extra shipping for it probably adds up to the amount of a BUF, probably going to just buy a high output set of opamps from mouser for the buffers in the end)

 

anyway enough of my ranting. I like to believe that I have a head on my shoulders every now and again, right now that being considering all the actual pros and cons of each option.

 

I value the opinions of those who have much experience in the subject.

post #4 of 6
Why not PM Fred_fred2004 who has sold many, many cmoys, often with dual-rail, true ground systems without flat battery protection, and ask him how many complaints he has had from people whose headphones were destroyed by them?

w
post #5 of 6
Thread Starter 
Quote:
Originally Posted by wakibaki View Post

Why not PM Fred_fred2004 who has sold many, many cmoys, often with dual-rail, true ground systems without flat battery protection, and ask him how many complaints he has had from people whose headphones were destroyed by them?

w

I sent him a message, thanks for the tip.

 

I do have to say that the people we sell to are a bit different though. I'm marketing to people who might want my product to "just werk" so having sound quality degrading and possiblity of idiots frying their phones might not be an option...I'll really have to get some friends of mine to beta test it and see what they think.

 

thanks for the comment. Always looking for more opinions :)

post #6 of 6
Thread Starter 
I'll post schematics and case design tommorow hopefully
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