[tomgrossi]

I was thinking about Daniel Pumphrey's comments in another thread that for the Etymotics he recommends building the simplest possible amp... My CD player and mp3 player currently drive my etymotics loud enough, so I don't think I need more voltage gain. In addition, they each have their own volum controls so I shouldn't need that. Why not just have an Ultra simple buffer amp made with two Elantec 2001's and a power supply and nothing else. Would this work? What kind of power supply is needed to make them sound good? (Also, would I still need the input caps or are the Elantec's pretty good about stray DC... I assume there is not much of it coming out of my portable players.) Thanks. -Tom

 

[Tomo]

Hello,

Yes. That will work.

You can use battery supply or dual polarity PSU. Former is pretty easly. Latter may require some PSU understanding. You could pick anyone of the articles at HeadWize and you should find one schematics of this. Any of these will do fine considering the fact that EL2001 has PSRR of its own if you look at the specs.

You probably would not need input capacitor as long as your input does not have offset. (assuming your CDP MP3P do not have crappy output.)

If you are concerned so much about sound quality, you should just try out our success stories. Apheared's projects are fairly simple and many HeadWizers report its wonderful sound. He even has a design specific to Gradoes. Aos and Ppl were building and testing Gilmore amps with their super PSU last time I saw them here. They say good things about their projects. I think their project is harder to build if you are a newbie. (Gilmore amp is also designed for low impedance cans like Grado) Several people build SDS amp with great results though I have not heard people building it lately. Rick and I built and customized Szkeres' amp. I am pretty content with my customized amp though it eats electrocity like a hog. Lastly, you can always try out Mr J.Meier's headphone amp. He sells kits and completed amps commercially now.

Tomo

 

[tomgrossi]

Thanks. Yes, I am intending to build an (or several) all-out project as well: possibly a variation on the "No-compromise" amp from headwize or EL2008 buffered solid state... or maybe both in one -- a tube amp with a high-impedance OTL tap and a low-impedance solid state follower.

But I digress... for this amp, I'm just looking to build the smallest/most-convenient amp for use with my mp3 jukebox and etymotics when travelling. It seems that a simple buffer like this might be the perfect choice just to give the player a bit more drive capability (since I'm sure the designers were interested more in battery life than anything else). Two follow ups:

1) Can the EL2001 be driven by a single 9V split into +/-4.5 or do I need a full +/- 9?

2) Might the 634 be a better choice since it seems to be spec'd for low voltage operation? Does it sound decent at +/-4.5 (and +/- 2.5 since that's how low the supply will likely go as the battery runs out)?

Thanks.

 

[Tomo]

Hello,

1. Jee. Do I have to do everything here? Read the darn specs at www.elantec.com. If you browse thru the specs, you should see PSU voltage range.

2. BUF634 will operate as low as +-2.5V. Many prefers EL2001 lately on the other hand. ... Its quiescent current is about 1~2mA kinda large for battery use. But then some people use portable phones that you can only talk for only few hours ...

You should just go ahead and build yourself one. It's not much of expense compared to other amps. Use battery supply for CMoy amp with dual 9V. Sound like few hours work to me. It would be facinating to compare it to OPA132 or OPA604.

Personally, I use opa134 with gain 2 so my CDP will last longer. I am content with it. Cans don't need super high output like 250mA. And, BUF634 will last shorter with batteries than OPA134 because of higher quiescent current. So I chose OPA134 instead.

To digress, note many buffers are current feedback amplifier with gain 1. That could increase IMD which is very very bad. Voltage feedback amps like OPA134 or OPA604 tends to have lower IMD.

Tomo

 

[Joobu]

A quiescent current of 1~2mA is actually quite small. You'd be hard pressed to find an op-amp with similar drive characteristics with less current consumption.

If I were a purist, I'd avoid using the headphone jack of the CDP and use the line out. Then maybe a little gain and volume control would help. All in good time.

 

[Daniel Pumphrey]

I recommend building the simplest amp, but do not compromise with the component quality of resistors, caps and wire. It makes a difference. I do not know the Elantic buffer, but if building a buffer only amp I would not choose the Burr Brown because operating it with an OPA is recommended.
The Elantic might just do the trick if it has enough gain. I just finished a hot rod Hansen and the buffer OPA in it helps the sound too. It also drives the AKG K-501 quite well and a single opamp design would not do that. I am also operating this at a gain of 10 with no noise what-so-ever. It is just the fact that my little face amp is so easy to build.
Dan

 

[ppl]

If it were me go for the EL-2001 while it is spec at 1.3 MA most i have used are under 1 ma, Moreover the BUF-634 sounds dark and slow in comparrison to the EL2001. since you dont need any gain and are going to use the Buffer open loop the DC offset of the BUF-634 is about 30-65 MV and the EL-2001's about 2-10 MV. Any non Fet input Buffer will require a resistor in parralell with its input to drain off the Input Bias current so a resistor of about 1k from the Input to Gnd is Needed Regardless of weather or not you cap Couple the Input. As for power Supply You should use a virtual gnd driver as showen on the BUF-634 data sheet and other places on Headwize and this fourm.