[Myren]

I'm looking to build an amp to run inline between my mp3 player and Grado SR 80's to turn this:

into

Currently my volume levels are just too low, and the sound starts clipping like a mofo when the volume is all the way up.

I had some schematics I was looking at using, but a lot of the amps I saw had rediculous power supplies: 8 or 16 double a batteries which lasted the wearer about 14 hours. That seems a little psychotic to me. My mp3 player uses a single triple a once every 7 hours.

Anyways, I'm wondering why so many of the designs I saw drink so much power. Are they setup for really high gain? Is it simply a choice of inefficient chips? Exceptional fidelity through overkill power supply?

What are some of my best bets for a power-efficient amplifier? I'll likely be using a DC-DC convertor since I dont plan on having more than two double a's. I figure my 2300 mah Sanyo's should work just fine.

I'm hoping you guys can help me get the ball rolling again. I was working on the PCB design for my amp before I ran into this dilemna sometime June, and I havent been back to work on this much needed project since. Anything you all can do to help me would be much appreciated.

 

[null]

CMOY? MINT?

 

[einolu]

AA batteries arent too popular because you need so many for higher voltages, and since most opamps need around 5V+- to run smoothly. This is why most people use 1 or 2 9V batteries. Those usually last 20+ hours, depending on how you set it up and stuff. There is actually a nice cmoy design under the thread "cmoy pcb something" that people are designing. Good luck! Im really too new to this stuff to help you out.

 

[Pars]

Do a search here or on Headwize. Works fine off of one 9V battery; two would be better. It's easy to rework Tangent's CMoy layout into an A47. Replace the voltage divider with a TLE2426 rail splitter, or if you are going for two 9V, split them like the Grado RA-1 does (see Tangent's article on his site for info). You should be able to fit this into an Altoids tin with a pot, in and out jacks, switch and an LED. Basically a somewhat buffered CMoy with higher current capabilities than the CMoys... just what your Grados are looking for. This amp seems to get overlooked alot, but I rebuilt two of the CMoys I built into these, and like them alot better.

MINTs are good too, but are more complex, but easy to fit into a tin with 2x9V... kind of a toss-up. With an AD8620 in the MINT, the sound is more analytical and refined, but in mine, the A47 has more, ermm, balls. I haven't reworked an A47 to fit with 2x9V in a tin (yet).

Chris

 

[Myren]

I understand the power supply problem. I've been aiming to use double a's since I have 24 NIMH's I paid a mint for.

From the start, I have been planning on using a DC-DC convertor. The goods ones out can get ~96% efficiency, or so I'm told. I'm still not sure how exactly I'm going to get +/- rails. Maybe two convertors, one for each battery, but then I'd need to find 1.5v -> 5v convertors, which may or may not be problematic.

What precautions should I take to stabilize a dc-dc line?

How many mAh does a 9v pack usually?

thanks!
Myren

 

[Nisbeth]

You can find DC-DC converters which gives you a +/- voltage from a single voltage supply AFAIK. the problem with these converters are that they are very noisy so their suitability for audio is questionable. A 9V NiMH will usually have between 150 mAh and 200 mAh capacity where as AA's are typically around 2000 mAh.


/U.

 

[Myren]

will a decent pair of caps reasonably stabilize a dc-dc convertor?

someone on diyaudio suggested using an inductor to stabilize the line as well. i'll have to go dust off my old basic circuit theory text book to go remember what they do.

i'm leaning once more towards an A47.

thanks again everyone
myren

 

[bpribadi]

I have Grado, and after trying a few op-amps, I would say I fall in love with OPA2228. I have also tested the OPA2604 which have a higher slew rate, but I found that OPS2604 sounds heavily 'veiled' for me.

OPA2228 also can be driven by low voltage, ideal for single 9 volt battery, or you can even drive it with 4x AA batterys. With low quiscent current, it will last long enough.

But please note, that I tested this Op-Amp in 'ala Pimeta' amp, with class A biasing. It may sounds different in CMoy circuit.

Just my 2 cents

 

[Myren]

fyi, i'm going with OPA2228. looks like a really nice amp.

i'm researching whether to go with a simple a47'ish current doubling system, or whether to use a buffering setup ala pimeta. probably the former; looks a little simpler.

 

[Earwax]

Quote:

Originally Posted by Myren fyi, i'm going with OPA2228. looks like a really nice amp. i'm researching whether to go with a simple a47'ish current doubling system, or whether to use a buffering setup ala pimeta. probably the former; looks a little simpler.

If you end up building a A47, try a pair of NJM4556 opamps in it.