[Techsmarty]

Here's the issue @ hand, I'm going to be doing my senior project (required for graduation @ my high school) and have been deciding what to do for my project, i know i want to do something related to music/audio/headphones/car mp3 project etc..
The Issue: I want something I can do in my spare time (which I have a lot of right now) and the total needs to be over 20 hours (easy for diy project). but I’m looking @ spending up to 80+ hours on this...

This is where the Head-Fi people come in handy :d
I want something that is going to require a lot of effort, not to much electronic background (except computer & basic electronics), have high quality, be useful, and have fun while doing it (don't think the last one will be an issue)

I want to build something for my headphones... the latest and the greatest

Cost: unlimited for the most part... although i would like to keep in under $250 is possible

Another thing I am suppose to have a mentor to help me with this (over the internet is fine) (the mentor wouldn't have to help to much, maybe donate an hour or so to this wonderful cause

so if you know of someone that would like to help...

Thanks

Techsmarty~

Note* this doesn't have to be done till Feb of 2004 so i have some time to do this, but i would like to do it ASAP

 

[Tim]

Build a headphone amp or two. That's what I'm doing for my senior project.

Although racking up 80 hours could be tough.

There are many DIY headphone related projects to be found at Headwize. Look under the library section then click on 'projects'.

 

[rickcr42]

Quote:

Although racking up 80 hours could be tough.

nah , that's the easy part

screw up .troubleshoot ,aw crap it hums ,troubleshoot some more

what's that buzzing sound ,more trouble shooting.......................................... ........................................

 

[rfbrw]

Digital domain crossfeed ?

 

[puppyslugg]

If you got $250 to spend, build a maxed-out Meta (amp) w/x-feed.

 

[tangent]

If you're looking to do something novel (as opposed to just building something that many others have built before) there's something someone asked me to build for them that I haven't had time to get under way: an active crossfeed filter with balanced inputs and outputs. I've done a bit of thinking on this, and I could guide an effort to finish the project; it's clear that without some interested outsiders, I'll probably never get around to finishing it.

By "active", I mean that you've basically got a crossfeed filter mated to a headphone amplifier with just enough gain to counteract any losses through the filter. The active components also act to present a better impedance profile to the components it goes in between. There is no volume control, and there is no worry about driving headphones directly. It is to be designed to go in between a source/preamp and a headphone amp. For various reasons, the amplifier section must be similar to the META42.

The simplest way to do this is to take the building-block approach: META42 + modified Linkwitz filter + balun circuits. A 'balun' is a balanced to unbalanced converter of some kind. This lets you take a signal from a balanced source and drive a balanced component down the line, allowing everything in between to work in unbalanced fashion, for simplicity.

Simple balun circuits are readily available. They're so straightforward that you can do this project without access to balanced equipment: just add a converter to one of your sources and convert back to unbalanced at the output of the active filter circuit. Probably a better idea is to design the circuit so that the baluns are readily bypassed so that you can test the core unbalanced active filter by using unbalanced components. Then later you'll have to add external baluns to your system to test the baluns in the circuit.

The above would work, but what would be really nice is if it were balanced clear through the system. Assuming that the core unbalanced circuit is laid out well and designed well, this won't matter except insofar as it is likely to have fewer components in the signal path in each channel. This is not likely to be a major advantage, but the user for this kind of circuit will likley have a rather high-end system, and they appreciate this kind of touch. The guy who asked for this has a balanced preamp currently feeding a balanced Stax electrostatic headphone system. He likes the sound of the META42 and the modified Linkwitz crossfeed in his other system and wants something similar for the balanced Stax system. There are probably other good uses for this kind of circuit. Imagine a studio engineer who wants to occasionally insert some crossfeed into the system -- balanced is the rule in studio work, unbalanced the exception.

To get your 20 hours in, all you'd have to do is basically take on all the work of bringing the first version to life. I could help with arguing out the initial schematic and such. Once you've got that, you'll spend several hours assembling the first version, hopefully very little troubleshooting it, and then several more hours testing and characterizing it. If you're skilled enough that you can do all of that in under 20 hours, you could supplement it by doing a printed circuit layout for the circuit.

To hit your 80 hour goal, you could then make some improvements to the initial circuit. This would involve trying out variations on the original idea, fixing problems turned up by testing of the prototype, and coming up with a second complete schematic and PCB layout. Repeat until you're sick of looking at the circuit or you run out of time, whichever happens first.

It's probably not going to be a terribly popular circuit, but I think it sounds like an interesting project anyway. Send me an email if you're interested and I'll dig up my notes on this and see if there are any useful hints in there that I can pass along to you.

If you decide to take this project on, it'll be handled in the same way as the other circuit projects I've been involved in, except that mass-produced boards aren't likely to be produced. I'll just host project pages and circuit design files for those few who do want to build one. Maybe I'll make a few boards, I dunno. I guess that depends on how interesting the final result is.

 

[aeberbach]

Why not grab a good textbook on tubes and design a tube amp? There is easily 80 hours in that, and if your teacher is older person it might strike a chord

Present curves, show how you chose the operating range, show the desired frequency response of the output transformer, how you arrived at the number of turns, why you chose those particular capacitors etc. Really showing an understanding of something simple should get you a better grade than a complete AV receiver that you built from someone else's plans.

 

[Techsmarty]

See Attached file for a little bit of what i'm thinking @ this point in time... If you don't know what i'm trying to show just ask...

Basically it's a META42 + modified Linkwitz filter + balun circuits that has two outputs (can select either, or both) (so 2 people can listen to the same music if I want...)
although now that i'm tying this i relize that i don't really need to select both with a switch instead have the switch have two options 1.) output to headphone one 2.) output to both.. this seems to make more sence to me as I probably don't need to have a switch to do all 3 funcions...

my next project is to figure out what the linkwitz filter does, if i need it, and what it's good for...

Giving a little bit more thinking i've thought about combining the portable mp3/harddrive player (I'll give the link when i get home and find it) and then have it hooked up to this amp in either the same or a different case

I really don't care if it goes over 80 hours, or even 180 hours for that matter... i've got the entire summer more or less. i just want the smallest/biggest (depending on the way you look @ it

) and the best. I don't care if I have to design the circuit although i must worn if i design the entire thing it may not work

so Tangent you may have volenteered yourself for something big

I would love to get more details on your proposal tangent, hope this all works out great

 

[Techsmarty]

http://www.pjrc.com/tech/mp3/ is the mp3 hard drive board link i said in the last post... tell me what you think, is it good quality?
This is going to be a HUGE undertaking for me, hard drive mp3 player w/amp and a few other goodies... hehe

I want to have this to be able to be powered by 1.) 12 v car outlet 2.) regular outlet and 3.) batteries (as long as it doesn't consume to much... which i think it is

but that's not as large of an issue as i will be playing it mainly in the car and @ home

BTW: Anyone how to make a fm transmitter (aka you plug it into the headphone jack it wirelessly transmits the data to a FM station... could be usefull until i get this project built....

 

[tangent]

Quote:

See Attached file for a little bit of what i'm thinking @ this point in time...

Putting the volume control after the amp circuit is not a good idea. If you want dual outputs with separate volume control for each, you really need two separate amp sections, especially for headphones. This isn't a univerally-held view, but I and many others believe that you're best off with a 0 ohm output impedance on the amp in order to get the best control over the headphones. Your idea puts a variable resistance between the amp's output and the headphones -- disaster!

Quote:

my next project is to figure out what the linkwitz filter does, if i need it, and what it's good for...

It's a crossfeed filter. Go to the Headwize library and read Chu Moy's article about it. You can also find that through the crossfeed page in the META42 docs.

Quote:

Tangent you may have volenteered yourself for something big

I mentioned it because I you gave the impression that you had a lot of time to throw at it and you needed to do a significant amount of it yourself to justify the project to your teacher. In other words, I'm hoping to get you to do most of the work.

Quote:

I would love to get more details on your proposal tangent, hope this all works out great

It sounds like you first need to look up all the circuits and terms I used in the previous post and figure out what I'm talking about to begin with. Then if that sounds like something you'd be interested in doing, I can dump some more info on you. If you want to go off and do this dual output amp thing or an MP3 player project, then nevermind. My project can go back on the shelf.

Quote:

12 v car outlet

Two big problems with that: 1) cigarette lighter voltage is very noisy in most cars; 2) 12V isn't much to begin with, and if you add regulation to fix problem #1, you're left with even less voltage to play with. These problems aren't insoluble, but they'll require a lot of work to solve if you want great sound. If you just want good sound, then you can compromise on the audio circuit so that it will run on 9V regulated.

Quote:

regular outlet

Once you've got the circuit working on 12V input, you just buy an off-the-shelf wall wart to convert wall voltage to 12V. You don't need a fancy power supply since you'll have lots of regulation built into the device already.

Quote:

batteries

Batteries are a different problem. You can either make the amp efficient so that it will run well on batteries, or you can add lots of regulation so that it will run on any old ugly power source but is inefficient, or you can try and have it both ways. The latter involves things like DC-DC converters and other switching regulation setups.

 

[Techsmarty]

Quote:

I mentioned it because I you gave the impression that you had a lot of time to throw at it and you needed to do a significant amount of it yourself to justify the project to your teacher. In other words, I'm hoping to get you to do most of the work.

Well the only problem with that is i'm not sure that i should "start" by doing that project... maybe a little something easier... then maybe that project, concidering when i look @ the schematics i don't really understand what each part does other than it makes sence (more or less) i can build it but i wouldn't be able to make the plan...

part of the problem i have about 6 dyi projects i want to do right now, and i don't know what is the best, the easiest most time consuming, the most educational, etc...

 

[Techsmarty]

oh ya... as for the dual output i was just showing an example i'd have to research it more to figure out the placement of it how it would tie in and blah blah....

Also concerning the 12 volt car outlet i was thinking that i have a 120 watt inverter that's not being used, would this work?

 

[Squalish]

Quote:

Originally posted by Techsmarty Well the only problem with that is i'm not sure that i should "start" by doing that project... maybe a little something easier... then maybe that project, concidering when i look @ the schematics i don't really understand what each part does other than it makes sence (more or less) i can build it but i wouldn't be able to make the plan... part of the problem i have about 6 dyi projects i want to do right now, and i don't know what is the best, the easiest most time consuming, the most educational, etc...

The standard answer for an intro project around here is to build a CMOY. There is ample documentation available to munch on, and it's one of the simplest amps you can build. Crossfeed circuits like the modified Linkwitz aren't really required to have, and just make listening a little more comfortable. Tangent only made his suggestion because it is something that's never been done before, and would require you to learn a bit in order to make it. Think of him more as a mentor than a tutor.

Try not to ask questions that are easily researchable with a google or a search of the forums, you'll find people here have a cold reception to people who want to be taught things they could otherwise find out easily.

You will want to read and reread tangent's excellent tutorials, in addition to Headwize's project pages. A quick search here or in Headwize's forums will solve 90% of your questions.

If I may ask, what are the 6 projects you are throwing around? We'd be glad to comment on which we think is most worthwhile. The mp3 HDD player sounds quite complicated for a newbie, and mp3 has a lot of detractors in the audiophile community, but I kind of like the idea.

In my opinion, if budget/time isn't a concern, you should try for a complete audio chain, from CD transport (try taking apart and remounting or otherwize modifying a NEC multispin, they are pretty cheap, or you could try for one of the expensive full DIY transports) to DAC, to headphone amp. You could also make the headamp have preamp functionality, and lead to a power amp, and DIY speakers. It seems to me that in addition to the standard posterboard/diagrams, pumping music through the display room and being able to say "I built all of that" would be more impressive than anything else.