[Adso]

Hi folks, I've been trolling for a bit, but I think I'm getting ready to jump in with both feet. I am considering building my own amp, and have read through, though not exhaustively, several of the tutorials and references that have been made available here. I have a pretty specific project in mind that entails a few questions I haven't been able to find the answer to. Here's what I would like to do.

I am looking to build a decent headphone amp that will be incorporated into my PC case. I haven't done a lot of research on different types of amps, but I seem to see a lot of consensus that CMOY style amps are good entry-level learning to DIY amps, and that a Meta42 style amp is a much higher quality step up that is feasible after one has acquired some skill. Any thoughts on this, or other possible options are most welcome.

First of all, I have run into references here and there about noise inside a computer affecting sound quality. Would this be something I would need to consider in this situation? If so, are there ways I can mitigate or eliminate this interference? Ideas or reference links most welcome again.

Secondly I would like to install it in one of the 5.25" drive bays with a modified front bezel for the headphone out, LED, and volume knob. After checking out many many pictures of all the fantastic amps y'all have built around here, I think there is more than enough room inside a 5.25" bay for even the Meta42. But, this brings up a couple issues.

How much heat does a CMOY amp generate? How about a Meta42? I play around with my computer a lot and most of it's parts are in various stages of overclocking, but I am pretty uptight about the noise it generates. It is a fine line to walk between performance and silence, so introducing an amplifier to the system may not be the best idea if it is a little furnace.

Power? Can an amplifier be powered by a computer power supply unit? These days, there are a lot of high quality, high output power supplies out there. They use 4-pin molex connectors to power PC components, can one of these be modified to power an amplifier or can the amplifier be modified to accept molex connectors?

(I included this link in case anyone would like some background info on PSU's. http://www6.tomshardware.com/howto/20030609/index.html )

I don't currently own the Audigy2 ZM SC, but I plan on buying it soon. Does anyone know if there is another way to get the sound output from the card to the amplifier without running a wire from outside the case and the SC's audio out port BACK inside the case and to the amplifier's audio in port?

And for extra credit, if I have enough space in the same 5.25" drive and on the bezel I'd like to also add a seperate microphone in port to the package. Anyone have any ideas or reference links to sources on how I would do this?

Yuck, well I didn't realize how long this would turn out, so many thanks to those of you who made it to the end, and thanks in advance to any and all input.


Adso


ps - I haven't decided on headphones yet, but I am leaning towards HD 590's. See my thread under the headphones forum if that information is pertinent to this thread.

http://www4.head-fi.org/forums/showt...threadid=48439

 

[tangent]

Quote:

a Meta42 style amp is a much higher quality step up that is feasible after one has acquired some skill. Any thoughts on this, or other possible options are most welcome.

Many succesfully build amps of the complexity of the META42 their first time, but others fail utterly when starting that way. Since the parts for a CMoy are cheap, it seems to me good insurance to start with one of those. It's much less painful to fail building a CMoy than a META42. If you succeed with the CMoy, you have a high likelihood of succeeding the first time with the META42.

Quote:

I have run into references here and there about noise inside a computer affecting sound quality.

Computers use switching power supplies. You can read my thoughts on that here: http://tangentsoft.net/audio/opamp-ps.html

You also have to contend with EMI and RFI inside the computer. The only way to cope with that is to put the amp inside a metal box within the computer. You could gut a CD-ROM drive and use that for your amp enclosure, for instance.

A further problem is that you only have +5V and +12V. This is limiting to say the least. Some op-amps favored here just barely get going on 12V.

You can solve a lot of these problems all at the same time by putting a high-quality DC-DC converter between the computer power and the amp. This will boost +12V or +5V to +24V or +30V for the amp, and a high quality unit will give cleaner power than the PC power supply. Your alternative is to put a lot of passive power filtration on the power inputs and use a low-voltage op-amp.

Quote:

How much heat does a CMOY amp generate? How about a Meta42?

Negligible in either case. Even a PPA runs cool enough that you wouldn't worry about it inside a PC case.

Quote:

Does anyone know if there is another way to get the sound output from the card to the amplifier without running a wire from outside the case

Look at your current sound card. It should have several 3- or 4-pin connectors. You can buy cables that fit these connectors and cut one end off, strip the wires on that end and run them to the amp.

Quote:

I'd like to also add a seperate microphone in port to the package.

How you handle the microphone depends on the type. You may have to provide power to the microphone, you may need varying levels of gain, etc. And building high-gain low-noise amplifiers is not trivial. Get the headphone amp working first, then make this a completely separate project.

 

[stereth]

Looks like Tangent answered most of your questions. On power considerations, I think you'd be fine if you took the 12V line, regulated it down to 8-10V (experiment some here) and used a stable, low-power opamp like the OPA2132 or 2134. At reasonable volume, the 2132 in my amp runs without distortion on as low as 3.5V.

And if your power supply is unusable, stick a 8xAA holder in there. It runs my Jung multiloop amp very well and should last 150 hours or so.

 

[A3rd.Zero]

be wary of using the opa2134 in the computer case, if you are an overclocker as you stated the inside of your computer case may run quite hot and dual opamps tend to have some noise issues between channels due to thermal problems.

The first amp I built was the cmoy pocket amp with the opa134. it is a neat little amp but I want a little more. Use a solderless breadboard first before you commit to anything, being able to build, test, tweek, and enjoy before you solder, cut, and commit is the best thing in the world for a newbie.

Milo

 

[Adso]

Thanks for the quick responses.

Well, it sounds like what I have in mind is doable then.

A3rd.Zero : That sounds like a good suggestion on the solderless breadboard. I had read about them at Tangent's site, and I'll try and find some more info about them.

stereth : I'm sure that is an excellent idea, I'll keep it in mind. I've read through all the Audiologica material at Tangent's site (though I will need to do it several more times I am sure), and while I think I could assemble one of the easier amps if I copied the directions and parts list exactly, I still need to do quite a bit of studying to actually understand what is going on with the circuit. What you said sounds simple enough, but I'd like to understand what kind of differences in performance I could expect using your suggestion vs. the DC-DC converter Tangent mentioned.

Tangent : Great site, I had already marked it in my favorites , and the plans there are what gave me the bug to build an amp myself.

I was about to post that I couldn't find any META42 boards for sale on your audio parts page last night... but today, I see why. I think I am careful enough and willing to take the risk to give the PIMETA a go when I am ready to build. If it's not too much trouble, could you or someone else answer a couple followup questions?

Will a gutted CD-ROM drive completely shield the amp from interference? Will any sealed metal container work for this purpose, or is there some way to insulate the inside of the container?

Could anyone suggest a DC-DC converter? I am not sure which brands or types would be considered high quality. Hehe, and actually I'm not really sure which specs I need either. I did search digikey, newark, and mouser for these, but I generally got a list of like 1400+ different converters and most seemed to convert the input voltage to an equal or lessor output voltage, not stepping up from +12V or +5V to +24V or +30V. Is there space on the PIMETA board to fit this?

Finally, I'd be interested to hear any opinions on whether this project would be worthwhile or sort of wasteful for the return I could expect from the computer source, the enclosure, or any other factors I may not have considered. I understand that this is a pretty subjective question, but there seem to be a lot of knowledgable folks on these forums and any information I can get is useful.

Thanks again,

Adso

 

[tangent]

Quote:

I'd like to understand what kind of differences in performance I could expect using your suggestion vs. the DC-DC converter Tangent mentioned.

A DC-DC converter is a type of switching power supply. Switchers can do all kinds of marvelous things like change voltage levels, cope with a wide variety of input voltages and still put out the same fixed voltage, etc. Ones that will take 5V or 12V in and put +/-12V or +/-15V out are common. The downside is that they all put out a certain amount of electrical noise and high-quality ones are expensive. Neither problem is fatal, just something to keep in mind.

Using a linear regulator instead will be a lot cheaper (on the order of a few $$ vs. $30) and the power is potentially cleaner with that option. The downside is that a linear regulator can only drop the voltage, it can't boost it. This limits your choice of op-amps and it limits the dynamic range of the resulting amplifier.

Quote:

Will a gutted CD-ROM drive completely shield the amp from interference?

To the extent that it is a seamless metal box, yes. But this does not happen. You must have holes in it for cabling and such, and there are gaps at the corners and edges, so some RFI or EMI can still get in, either radiated or conducted in. But even then, you don't really worry about this up front unless you're an electromagnetic compatibility engineer. What you do as a DIYer is just keep these things in mind, test for problems after you get it up and running, and decide how to cope if you detect problems. Or, you decide up front that it would be a whole lot simpler to just build an amp for your desk and use a mini-to-mini to hook it up to your sound card.

Quote:

Could anyone suggest a DC-DC converter?

Cosel makes good stuff for this purpose. Headroom uses their converters in their portable amps. You can get them from Allied and Digi-Key.

Quote:

I generally got a list of like 1400+ different converters

There's a very broad array of technologies under the DC-DC umbrella, and a lot of it is totally unsuitable for audio. Low end charge pumps, for instance, put out some of the nastiest power you'll find this side of Iraq.

Quote:

Is there space on the PIMETA board to fit this?

You'd mount it off-board, or design your own PCB to incorporate it. You've got more than enough space inside a 5.25" bay for this.

 

[Chipko]

ATX Powersupplies all deliver -12V and -5V with enough oomph to drive an amp.

Get a common mode choke on the cables supplying your amp to get rid of some of the noise.

 

[tangent]

Quote:

ATX Powersupplies all deliver -12V and -5V

Yes, but only to the motherboard power connector. I don't know about you, but splicing into that line doesn't seem like a good idea to me. Using a drive power connector is a lot safer.

 

[Adso]

I was wondering if someone had a ballpark figure for the total parts price for the PIMETA. I attempted looking them all up, but in some cases I'm not exactly sure I'm looking at the right parts etc.. I understand that there are different part options here both for the basic design and any 'tweaks' but I was just looking for a general price range for this amplifier if someone has it handy.

Thanks,

Adso

 

[A3rd.Zero]

Price is one of the most diffucult questions ever. I know you dont want to hear that but its true. I priced out every part for an amplifer that I wanted to build and got over $300. My second pass substituting things I had around the house and building the enclosure out of cherry that I had in the woodpile brought the price down to $54. One thing to remember is that if you are a fiddler and you have lots of misc parts lying around you should absolutely look through them for parts you need. Power supply parts are particularly easy to find, if you save old junk. You can also substitute many parts for parts in the diagram. For instance all capacitors can be switched out for higher voltage equivalances. You should be able to keep the price under $150 if you make sure to shop around and dont buy particularly expensive audiophile parts like stepped attenuators. Look at www.percyaudio.com for great prices on pots and caps.

Milo
I have no affiliation with percyauido, i just really like his prices and selections.

 

[tangent]

You can certainly make a PIMETA for way under $150. Set your own budget. If you can't afford Black Gate caps, don't feel that you're getting a weak amplifier if you settle for Panasonic FCs. If you can't afford three $15 op-amps and you settle for three $5 chips, you'll still have a good amp. True, you get what you pay for, but the level below which it makes little sense to go is more like $60.