I am intested in making a super high current output pocket amp to drive orthodynamic phoens. Here are my questions on output buffers:
1) other than BUF634 and LMH6321, what options do I have?
2) The power supply will be +/- 7.5v, which of the buffers will sound better with this power voltage?
3) I want 1000mA output capability per channel (just for reserve), I know I can stack BUF634, how about the other buffers?

Thanks for all your help

have you tried options like LT1020?

LT does have some pretty beefy output current, CFB opamps.

LME49600 also, if you require a buffer. Lots of opamps can handle large output currents, you probably have hundreds of choices.

Also literally 'stacking' these at high output currents probably isn't a good idea. If you're actually driving a difficult load and the chips are sourcing/sinking large currents, they're going to be dissipating a fair bit of heat as well, from a small package. Stacking them on top of each other is not good thermal design. Not sure you literally meant you were going to put them one on top of the other or not...

Any of these should be stackable with an output load sharing resistor for each device. Experiment, it may not be required.

What orthodinamic phones are you planing on using?

Thanks for the replys guys.

Heat issue will definitly be addressed. My plan is use 4x BUF634 for each channel, I will use TO-220 package so stacking will be very simple, just have them all standing up and parallel all the pins. But I don't know how well the 634 can do at lower voltages (I use them @ +/-14v in my little amp), so I wonder if other buffers do better in this situation.

The headphones will likely be Yamaha HP-2, will definitly be silver/copper recabled. After finishing the Stax SRM-001 Ultra mods, I think is there is probably no portable system under $500 (phones + amp) can rival the Ultra-001's clarity and speed, but the baby stax transducers can not respond low enough for my taste, and I still want the deep bass....

HP-1 and 100 will be way too heavy for portable, so HP-2 is probably the only option I got.

Don't think you need outrageous current capability for them just make sure you have good voltage swing.
My portable drives HP2's ok from a 8 cell nimh pack and around 200ma output capability from the buffs.[though it's a while since I listened or made any real drive comparisons]
Personally I would not use the 634 as I am not wild about the sound of them.
But if you do I would be surprised if you need to go for 4 per channel, then again it is alway nice to have the headroom!



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If the 634 is not that good sounding (that is the only buffer I have ever used), which one might be a better choice?

1000mA reserve is necessary. I need 2x (500mA) per channel just to drive the 150 ohm Senn555 well, and the 555 is usually considered as a easy driven phone. Spec # doesn't mean anything, do a hot unplug test (stack two buffers, and while listening to the music, take away the top one and see what happens) and you will know what I mean. The ortho's are very very current hungry, I actaully suspect 1000mA per channel might not be enough to bring out the full potential....We are talking about competing with the modded 001, so the HP-2 will need every bit of help it can get

Well I have not had experience with a huge amount of phones.
I am no expert but it was my understanding that planar phones were largely resistive loads.
Just looking at the hp-2 spec it says max input 10w!
it would be interesting to play a signal through them and ramp it up to see what sort of voltages needed to get this!
Got the feeling the poor things would not be too happy with a continuous 10w input though

Well out of curiosity I just hooked them up to an amp to re acquaint myself with them.
Warm full bloom of a sound , with some cup resonance , but pleasant sounding,just as I remember.
The amp had a 9.6v battery pack and uses stacked HA5002 buffers, so it has around 400ma per chanel current available.
they went way louder than I care to listen to without any obvious change in sound noticeable for my brief blast.
I also drove them from my single ended mosfet follower reserved for IEM driving.
Again listenable but soft, not bad considering voltage drive was the CDp output of 2vrms max.

In the past I have also made my own Planar/ribbon phones and some of those variant only had dc R 's of 4-5 Ohms.
That little amp could also drive them quite well when used with a 15v supply, but i was careful not to push the volume to far as 4 OHm could finitely push the HA 5002 beyond their limits and let out the magic smoke!!!
Other 'home mades' were more like 20=30 ohm DCR and could be driven very nicely from it on a 15v supply.

Do check out the the HA5002 buffer ,in my view it is a far nicer chip and better suited the the HP2 sound.
Only downside being lack of short circuit current limiting protection .
They can chuck out around 200ma max.

Anyhow it indeed seems that having 1A headroom is not such a bad idea !


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you, my good sir, is insane lol

the Yamaha HP-2 are 150 Ohm, 93 dB/mW, 101 dB/V (these sensitivities don't match; from: http://www.head-fi.org/forums/f4/ort...ml#post1328206 using the dB/mW # below)

low sensitivity by todays standards, but high impedance

these cans need Volts (high impedance), some current is needed for the high power (low sensitivity) but not amps

1 W into these cans requires ~ 17V pk @ 115 mA

1 W would give 123 dB peak SPL at amplifier clipping - probably the diaphram would bottom long before at low frequencies

used as open loop buffers, especially those with moderate output R could be expected to be audibly different when paralleled into low impedance cans

I doubt any number of buffers inside a feedback loop -Jung style could be heard as different from a single buffer at any output current less than 80-90% of its rating

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Exactly,makes you wonder what an earth that 10w spec means!

in my current amp the BUF634's are within the feedback loop. Like I have mentioned, "hot unpluging" one and you can definitly hear the difference.

At this point my only ortho's are some DIY phones utilizing 32 ohm SFI plannar tweeters (said to be very silimar to the Pro-30 driver, if not totally identical) in Sony housings. And the best way to drive them, I found, is connect directly to a speaker amp's output. (I do have 12 ohm resistors in series to the driver and use diode over voltage protection though.)

The 1000mA capability is all for more control on instantanenous output, calculating RMS ratings wouldn't mean much to the real life sound performence. As a matter of fact, there is no way the phones can allow 1A to go through, even if you hook the drivers directly to the power supply, there is only 15v/150R=100mA per channel.......

Thanks guys, will definitly look into the HA5002's

by the way, who in the states carry HA5002? I just checked Jamco, digikey, mouser, newark and none shows any....

Maybe its that stacking buf634's sounds better. Perhaps you need to stack 4 to get the sound quality you want and not the amount of current they can push.