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borges 8th December 2003 09:03 AM

Best low-noise low-distortion buffer?
At the output of a CD player project I need to buffer (and possibly multiply by two) the output of a passive filter. There's plenty of power supply voltage (+-18V).

The buffer should be fit for driving both phono and XLR inputs of preamps.

I don't care too much if the buffer introduces an offset voltage as long as it doesn't change too much with temperature and across channels.

I have been thinking about opamps as unity-gain buffers and maybe in a gain of +2. Now I wonder if I can get better audio performance with a source follower. I have been reading Douglas Self's page on CPF source followers (

What I want to ask you is if this is my best option. Or will a good opamp like for instance the OPA2134 offer better sound quality?


PRR 8th December 2003 08:51 PM

The better chip-op-amps are very good. I don't see how the CPF is any better. It is more work, has substantial offset, can't give gain as shown, and is very prone to self-oscillation (which can be a royal pain to find and fix).

Jocko Homo 9th December 2003 02:41 AM

I do not like op-amps as unity gain buffers. JFET followers sound good, although they will not drive 600 ohms.

CFP are ok, but I have never needed one as a buffer for a CDP. They may sound a bit too constricted, when compared to a follower.

Diamond buffers would work fine, if you need current drive.

If your D/A chip is a R-2R type, just change the load resistor to get that 6 dB gain.


PAM 9th December 2003 08:51 AM

easy buffer
An easy way to make a good buffer is the BUF 634.
WADIA used them in there CD players.
I compared a Musical Fidality X10D (tubes) with an stand alone batterie powered BUF 634. The BUF 634 wins clearly at 1/10 th of the costs.
The BUF 634 is cheap, fast and powerfull.

sobazz 9th December 2003 09:01 AM

In the high-end headphone amp project PPA they chose Intersils HA3-5002 over BUF634.... And Intersils is cheaper.

m.parigi 9th December 2003 09:17 AM

Need good buffer schematic
I wonder if anybody can help me out with a buffer circuit design.

I'm currently building an APOX preamp and I would like to have a couple of tape outputs. Just tapping into the input selection bus doesn't seem to me a good idea, bacause I'd probably end up overloading the source.

Can anybody point me to a very good buffer schematic? Possibly I'd like a tested design, so that I don't have to experiment too much...
It seems to me that it should have a 1:1 gain. FYI, the signal bus is balanced.

borges 9th December 2003 09:19 AM

Thans folks

Jocko, what is a diamond buffer?

My dac is a current output type which I planned to filter passively and then buffer.

I saw a previous thread on the use of CPF followers( which seemed very interesting. Do you think this circuit with a constant current generator is capable of pulling 600Ohms?

Another issue is that the signal current those 600Ohms will be downscaled by beta and be seen at the base. However, I don't mind (small) constant base currents.

So the question remains: Do you have any experience with FET CPFs?

What I plan to do is to make a test board with an opamp socket and a couple followers that I can jump in and out. Now I'm just trying to figure out which followers are worthy of occupying FR4 real estate :cool:


johnferrier 9th December 2003 12:40 PM

Re: Need good buffer schematic

Originally posted by m.parigi
Can anybody point me to a very good buffer schematic? Possibly I'd like a tested design, so that I don't have to experiment too much...


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