low impedence buffer

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plexi0

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Joined 2014
#1
I've had a hard time finding a headphone section commercially available that has a 2 ohm or less Output impedence and a headphone buffer or slight amplification

I have 12 ohm IEM's that really don't need amping I don't believe.

I also need RCA in and out's to take the RCA out of my phono section.

So any ideas or suggestions of layouts or actual devices that meet my needs?
 
#3
yep, that's where i'm headed if I can't find a simpler solution.

I really don't need that gain of course but I do need it's .5 ohm output R.

There are few amps that have under 1 ohm for that spec. And it seems in order to get it that low, it seems to require some sort of circuit that involves amplivication of the signal. I wonder if it's not even possible with a buffer?
 
#5
<1R OP impedance is not uncommon. Parallel a few 5532s in unity gain. Use a 49600. A BUF654. Build a diamond buffer (google it). You don't need amplification in the strict sense, you just need output devices that allow more current, not a bigger voltage.
 
#8
so it is possible....wonder why it's been so hard for me to find. I guess not many kids are looking for no ampage as they are under the impression more power is better. I really want the signal to go through what is necessary and no more...to that end I see the amb a10 is quite a bit more involved as far as part count than the diamond buffer and yet they accomplish teh same simple task (buffer with more current no gain- low output R)


thaks for all the info, will have to study and learn how to read schems better. HAve a hard time correlating schems with physical part layout. I guess it's up to each builder to place things where he wants. I have built guitar amps but it was off of actual diagrams and point to point wiring, not schematics
 
#10
I guess i'll just buy a 02 and hope the extra 3 chips and un-needed parts do not anything to the sound. I like the idea of a passive buffer but.....why no one makes such a device is puzzling. not even the chinese make it. There's alot of people who use 16 ohm or less IEM's that just want a simple headphone jack to plug into. I guess the 02 is the only ready made device that will work
 
#11
From your initial post i got the impression you are looking for a buffer, and that's what A20 is. It has relatively low parts count, and pcb is available from that site.

A10 you mentioned is a complete preamp, which uses A20 as a line stage and adds other components like relay-based volume control. You probably don't need all that complexity.

As for A20 vs other topologies: you might want to check this testimonial (jisbos = unity gain A20):

http://www.diyaudio.com/forums/solid-state/121834-jisbos-great-headamp.html
 
#16
jerluwoo said:
As many around here say, there's no free lunch. To get that low output impedance you basically have 2 options. Make alot of gain and spend it on feedback or parallel a bunch of devices.
Click to expand...

No. This is not the case. Some devices have the low output impedance you are looking for. When I suggested paralleling 5532s, it's just because it's cheap and you'll get good fidelity with a little effort on layout without risk of instability. I'm pretty sure LME49600 or BUF654 have output impedances <1R.

You have a fundamental misunderstanding where Ohm's law and power are concerned. You need to read a chapter on the subject in a good textbook and successfully complete the questions at the end. I think there are some good US military teaching materials, perhaps somebody else would be good enough to point them out.

I get the impression that you are operating on some assumptions based on some audiophile mythology, such as an overweening concern for minimizing the number of devices in the signal path. This just really doesn't make much sense in an environment full of 'black-box' devices containing unknown numbers of discrete components all considered as one device because they're fabricated on the same substrate.
 
#20
counter culture said:
I'm pretty sure LME49600 or BUF654 have output impedances <1R.
Click to expand...

Looks to be a faith-based claim. Examination of the DSs reveals no explicit specification for Zout, however there is a line in both DSs where the voltage gain is given a figure, into a specific (100ohm) load. These datapoints suggest output impedances of 5ohms for the LME (gain 0.95) and 7ohms (gain 0.93) for the BUF.

@plexi0 - the output impedance of an emitter follower is a function of its emitter current. So the output impedance of a diamond buffer depends on its bias current. To get below 2R you'd need the ballast resistors (R11, R12 in rjm's schematic) to be say 1R5 and then run at around 15-20mA bias. Oh and I almost forgot - R13 would need to be a zero ohm.
 
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