[pmikka]

Hi
I have a question, which opamp should i use and which outputbuffers?
My Idea was to build an opamp based Amp with output buffers.
So what opamps would you recommend.
Opa 134,627,637,lm6171,lf356,ad823,ad812?
Buffers:
buf604 or diskrete outputstage.
Which transistor to use?
I think bout using senn hd600, system is for home use.
THX
p.s. do you have to pay for shipping whem oredering free samples at TI

 

[tomgrossi]

I think a lot of this will depend on the headphones you plan to use as well as the power supply. Some headphones (e.g., Grados) require quite a bit of current drive and therefore might be best driven with a buffer. Others may require less so you could get away without a buffer. If you are building a portable amp then op amps like the OPA134 seem to be preferred around here since they can be driven off of lower voltage supplies and draw less quiescent current. Others like the OPA627 seem to need a full +/-15 to sound their best which can be a pain to get from batteries. Do a search here... there is lots of info on this. I know some like the AD823 buffered very much.

 

[pmikka]

okay now
i thought bout using an opa134 and buf03.
What do you think bout this?
Is shipping for free samples free?
THX

 

[Daniel Pumphrey]

Pmikka,

The main problem DIYers are having at this point is deciding on which opamp and buffer to use in this day of so many great design with such incredible specs.
I would suggest using parts based on the type of layout you will be using. Some really great parts require very careful board design to avoid problems. There are some fine parts which don't have these problem such as the very nice old standby from Burr Browm the OPA 132 134 or 2132 2134 in dual and 4232 4134 in quad. The BB Buf 634 is a very nice buffer which has quite a lot of output and is not really hard to impliment.
Also If you build for these parts using a standard 8 pin socket then you can try other parts later.
Dan

 

[shinew]

I use a OPA132 & 3 BUF634 for each channel to drive my ER-4S phones. They sound great!

I think which opamp to use heavily depends on what headphones you want to drive. For my HD-580, I prefer OPA627 than OPA132 w/ the same setup above because 627/637's mids are just amazing! However, for Etymotics, OPA627s sound just too sharp & dead in the highs. So swap them around & try them out yourself to see which opamp you prefer.

 

[tomgrossi]

Quote:

Originally posted by shinew I use a OPA132 & 3 BUF604 for each channel to drive my ER-4S phones. They sound great!

Do you really need that many buffers to drive the 4S? I just got a pair of Etys and I'm still waiting for my parts to build a portable amp but if I did my calculations right from the Ety specs they only draw 10ma for 108db (which strikes me as pretty loud... isn't it?) Are the buffers just there so the amp can drive other phones, too, or should I make sure to design some into my design (which right now will probably be exclusively used with the etys? Thanks. -Tom

 

[Tomo]

Hello,

This is a fact. Etymotics ER-4S can be driven to earsplitting volume by OPA134/132. Note 4S is in-ear phone. So it can be very loud at even lower levels.

Tomo

 

[shinew]

nope, it can't!
I've tried driving the phones without buffer & w/ just one BUF634 as buffer per channel before. Yes, it did sound fine most of the time, but when I listened to recordings w/ great dynamic range such as Mahler symphony No. 5 or some solo piano music(no, Heavy Metal is not as dynamic as these), they didn't have enough juice to drive my ER-4S(distorts during peak passages). I think parallel two BUF634 will be plenty, but one is definitely not enough, for me. that's a fact too.

 

[Tomo]

Hey,

That is something else. Distorting at peak passages are not necessarily caused by juice running out. It is likely that BUF604 is clipping.

If BUF604 were running out of juice, it should show at extremities such as high freq end or low freq end.

Tomo

 

[shinew]

really? huh, never thought about that....

but how come after I paralleled the 634s, the distortion went away?

Edit: Tomo, I know the sort of clipping distortion you're talking about. I've had that problem too before. But I don't think that's the case here.

 

[topher]

I don't recognize BUF604. Who makes it?
Is that the right part number?

 

[pmikka]

Hi
I think the buf 03 was build by Analog Devices.

Has anyone ever ordered free samples @ TI?
BYE

 

[shinew]

oops! I mean BUF634, not 604. what was I thinking...?

 

[pmikka]

Buf 634 is build by Burr-Brown aka TI.

 

[topher]

shinew,

when you found you needed to parallel buf634's,
did you notice if the bandwidth control made a
difference?

For example, did 2 buffers set to high bandwidth
do as well as 3 on low bandwidth?