Simple Input Buffer

[Adam M.]

Does anyone have thoughts on a SIMPLE input buffer, like one that involves an op amp, an input wire, a feedback wire and an output wire? (Well, not that simple, but you get the idea, I don't want a 10 component buffer). I posted this in the bottom of a thread below, but the more I think about it the more it belongs in its own thread.

the OPA627 was suggested, and the spec sheet looks like it can be used with no external parts, but that doesn't seem right in a practical application, but ok from a theoretical standpoint.

As a side note, I have read a few commercial products that rave about using Burr Brown amps, which I found out were TI products. Anyone use these as buffers, and if so does anyone have a suggestion to which chip?
Thanks,
Adam

[matjans]

buf634 ? nice buffer but it somewhat degrades sound quality when used outside of an opamp;s feedback loop (imho).

/matti

[macboy]

The OPA627 would work fine. So would the OPA132, OPA134, OPA604, or their dual versions (OPA2132, -2134, -2604), or any other high quality opamp that is stable at unity gain. All that you need to do is tie the output pin to the -input pin, and put the input signal onto the +input pin. This creates a "voltage follower" configuration, where the output voltage is equal to the input voltage. Now you can set the input impedance as high as you want (within reason; note that higher impedance will mean higher noise) and drive the chipamp with a low input impedance. Just make sure that the opamp you choose can drive the impedance you choose for your chipamp's input impedance (most will drive 600 ohms or higher). Make sure to decouple your opamps with a small capacitor connected very close to the opamp.

[GregGC]

I hope you don't want to connect the buffer in front of a NIGC.

/Greg

[carlmart]

Originally posted by macboy
The OPA627 would work fine. So would the OPA132, OPA134, OPA604, or their dual versions (OPA2132, -2134, -2604), or any other high quality opamp that is stable at unity gain. All that you need to do is tie the output pin to the -input pin, and put the input signal onto the +input pin. This creates a "voltage follower" configuration, where the output voltage is equal to the input voltage.

Just a question that nobody seems to have raised yet when using an inverting gainclone: what about the absolute phase the music was originally recorded at? With an IGC we are listening to inverted version of it.

There has been lots of discussions on whether keeping original phase is important or not for the music experience.

So why not trying a basic inverter here? We would have a buffer and also get phase back to normal.

Has anyone tried that? Pros and cons in that path?

One con I can think of is how would I use a BUF634 inside the feedback ring on a basic inverter.


Carlos

[GregGC]

Originally posted by carlmart


Just a question that nobody seems to have raised yet when using an inverting gainclone: what about the absolute phase the music was originally recorded at? With an IGC we are listening to inverted version of it.

There has been lots of discussions on whether keeping original phase is important or not for the music experience.

So why not trying a basic inverter here? We would have a buffer and also get phase back to normal.

Has anyone tried that? Pros and cons in that path?

One con I can think of is how would I use a BUF634 inside the feedback ring on a basic inverter.


Carlos

To solve the problem with the IGC you just have to connect the two speakers in revers (- of the speeker to the output of the amp and the + of the speaker to GND).

/Greg

[millwood]

wouldn't an emitter follower be a simple and effective solution here? I posted a simple (one transistor, 6 resistor and 2 caps) pre-amp circuit on the solid state forum and it can be easily set up as a follower and it works unmodified with a lot of transistors / rail voltages.

to me, that would beat out an IC buffer.

[Adam M.]

This is all thinking right now, but somewhere down the road, it'll be in front of a parallel lm3886 or a bridge/parallel config with the same chips. How are the buffers that National specs for the BPA200, the LF411?
Thanks,
Adam

[PMA]

Originally posted by carlmart


Just a question that nobody seems to have raised yet when using an inverting gainclone: what about the absolute phase the music was originally recorded at? With an IGC we are listening to inverted version of it.

There has been lots of discussions on whether keeping original phase is important or not for the music experience.

So why not trying a basic inverter here? We would have a buffer and also get phase back to normal.

Has anyone tried that? Pros and cons in that path?

One con I can think of is how would I use a BUF634 inside the feedback ring on a basic inverter.


Carlos

Carlos,

I have checked invereted polarity vs. correct polarity many times. There is a considerable audible difference. For example - bass is lazy and worse defined, when inverting the phase.

I would always recommend to keep the correct phase.

Pavel

[Hybrid fourdoor]

In regards to buffer to amp, which resistor method would be best here?