Buffer Circuits

[Structo]

I have need for a couple buffers.
For me and a few other people.

Anybody have a favorite design or circuit?

Something to keep the impedance and high end intact for an amp?

I have found opamp buffers and discrete JFET buffers.
This opamp one can use one dual opamp in place of all the singles.

Like with a 5332 is supposed to give good results.

[selloutrr]

GO TUBE

[ChrisM]

Tube buffer circuits have no real advantage over SS.
SS is better I'd say, you don't have to worry about the limits of the heater to cathode voltage.

[Super_Reverb]

Attached is a pretty standard buffer circuit used in battery powered effects. Input resistance is about 1Meg (2*2.2Meg in parallel). TL071 is a pretty good opamp. Large output coupling cap is due to very low output impedance.

Cathode followers offer you some tone sweetness (2nd harmonic distortion) due to compression effects. See Merlin B's book on tube preamps - it's a good read.

I have seen amp designs that used a high voltage MOSFET as a source follower to drive a tonestack or effects loop out. If that's what you're driving, it would be easy to substitute a HV MOSFET for a 12AX7 stage (grid=gate//plate=drain//cathode=source) in a source follower buffer circuit.

cheers,

rob

[dave g]

Cathode followers offer you some tone sweetness (2nd harmonic distortion) due to compression effects.

Only in one very specific configuration in which it's used the completely "wrong" way from a proper design perspective.

Solid state is nothing to be afraid of. Especially not in this application.

The "Super Buffer" circuit is way overkill btw. A 741 connected as a voltage follower would be more than enough.

[Deric]

I've played with several different buffers including the AMZ Super Buffer. I like (and use) the simple IC buffer posted by SuperReverb the most. I've tried several different IC's and always go back to a TL071.

[Cliff Schecht]

Cathode followers offer you some tone sweetness (2nd harmonic distortion) due to compression effects.

Only in one very specific configuration in which it's used the completely "wrong" way from a proper design perspective.

Solid state is nothing to be afraid of. Especially not in this application.

The "Super Buffer" circuit is way overkill btw. A 741 connected as a voltage follower would be more than enough.

741's sound like shit and have a low input impedance. Not the best op amp for audio. TL07x/8x series are much better for general purpose audio applications. I know the whole JRC4558 argument WRT tube screamer circuits and how most people can't tell the difference, but in a clean buffer setting it's pretty easy to tell the difference different quality op amps.

[Ian444]

I tried a FQPF2N60 as a mosfet source follower in place of a cathode follower recently, worked great, driving a tone stack, did not require a heatsink (but got warm), retained the highs, more highs than the triode section it replaced in the amp. I also used same piece as a cathodyne and that worked too.

I recently did a bit of research on buffer ccts and basically came up with the general gadgets cct Tom, which I think is very close to/derived from the Electronics Australia magazine tremelo circuit buffer/booster. From what I read from users that cct would be #2 on my list to try. #1 on my list is same cct with 2 x 2SK170 jfets, one in the position of the 2N5457 and the other below it configured as a CCS, instead of the 10K resistor, with gate and source simply tied to ground, aka Nelson Pass Buffer B1 from hifi. The cct is published on the net. I actually use one of these in my simple DIY home stereo and it is transparent like air. #3 on my list is a simple IC buffer using OP275, the reason I would use OP275 is I tried about 8 different IC's to make a PI for a stereo tube amp, and the OP275 sounded the most natural and warm, much better than TL072. The RC4558 put up a good fight, the JRC4558 did not do so well. That does not necessarily mean the OP275 will be good for guitar but I can't see why not. The IC's do not all sound the same at all. But in my application there was gain, maybe with no gain (buffer, gain =1) then it does not matter what you use. Some IC's are not so comfortable with gain = 1.

[Structo]

Thanks guys!

[jjman]

My only experience with a buffer is the foxrox for wahs :

http://www.foxroxelectronics.com/Wah%20 ... t%202.html

Although it improved the situation caused by the loading of the wah by the fuzz's input, it did not completely resolve it. Using any Boss pedal before the fuzz fully resolves the loading issue for me.

I don't know which technologies each uses but the Boss's works for my situation. I guess the wah > fuzz situation is especially tuff.

[Structo]

Yeah, all Boss pedals have buffers in them as far as I know.

A buffer is a unity gain amplifier that has a high impedance input and a lower impedance output.

It can help recover some of the high frequency loss you sometimes can get with long cable runs.
Some guys put them at the beginning of the chain while others put it at the end or even middle.

Eventually I will have about 30 foot of cable into the front end so I am planning ahead for that.