BUF634-based buffer

[g3rmanium]

Hello,

I was trying to build a BUF634-based buffer today. I've read that the BUF634 can be used with single-supply, but I wanted to use one of these DC-DC-converters because I might use one of these in the frequency doubler I plan to do.

Anyway, here is the first version. Can you tell me if this looks good? Apart from the DC coupling, would this work?



Thanks.

[g3rmanium]

Can you tell me if this looks good?

Here is a new version with a LP filter on the input:

[g3rmanium]

Could anyone look over these and tell me what he thinks?

Thanks.

[lovekraft0]

Do you have an application that requires you to drive a 600 ohm load at line level with pro-audio distortion and noise specs? If you're just buffering a chain of stomps, a simple parallel opamp buffer like Jack's Super Buffer is simpler, cheaper and probably better behaved. Don't get me wrong, that's a great device, but for any signal chain that ends up feeding a guitar amp, it's waaay overkill!

[g3rmanium]

Do you have an application that requires you to drive a 600 ohm load at line level with pro-audio distortion and noise specs?

For me, there are three things of interest here:

1. I want to decide where I want distortion. And if I don't want distortion in one place, why not buy "pro-audio" parts?
2. The simplicity of the design. Really, I'm just starting with this. And I'm using veroboard so the design shouldn't be too complicated.
3. I want to build one of the frequency doublers I have talked about. These are all using ICs so I figured I could need the experience.

If you're just buffering a chain of stomps, a simple parallel opamp buffer like Jack's Super Buffer is simpler, cheaper and probably better behaved.

Maybe, but it's also more complicated and uses more parts.

[lovekraft0]

OK, but replacing a $.75 standard dual opamp with an exotic $6.00 50MHz buffer chip to avoid a couple of $.03 resistors isn't my idea of really good judgement. Is there a schematic to check your layout against somewhere? Point me to it, and I'll take a look. You're going to at least need coupling caps and pulldown resistors on both input and output to make it useable, so those need to be added immediately.

You might also want to look into how complex those DC-DC converter circuits are - there's a good reason why that voltage divider bias gets used so often. Again, unless you need the extra headroom (extremely unlikely in a unity gain buffer), it's massive overkill.

[jrc4558]

Hey, what do you need 250mA of signal for? You cant run that off of batteries... Design is good though

[g3rmanium]

OK, but replacing a $.75 standard dual opamp with an exotic $6.00 50MHz buffer chip to avoid a couple of $.03 resistors isn't my idea of really good judgement.

It keeps the circuit simple, that was my point.

Is there a schematic to check your layout against somewhere? Point me to it, and I'll take a look.

Will do that in a minute (or so).

[The Tone God]

IMHO you are using the wrong tool for the job. Have you done any research on commonly used guitar/audio circuits ? If so what problems do you have with any of these circuits ? What is/was your design criteria ? You cannot tell me that nothing made with common and appropriate parts can be found to fit your needs. You can make a simple cheap buffer with an opamp and four to six parts. Have you read the datasheets to something like say the TL072 ?

Andrew

[slacker]

If you really need a high quality buffer that can drive loads down to 600ohms you could just use something like an NE5534 opamp. This would be no more complicated and a lot cheaper.

[g3rmanium]

Will do that in a minute (or so).

Ok, that was a long minute, but here you go:

[lovekraft0]

OK, first of all, using a DC-DC converter to go from 9 volts to +/-5 volts is a complete waste of time and money - refer to the SuperBuffer cited earlier for a simple, inexpensive and well-behaved voltage divider bias. And while a split supply will theoretically allow you to eliminate input and output coupling caps, you're gambling on the hope that whoever designed the unit placed at the input is using a coupling cap - any DC on its output is going to rebias the buffer, with unpredictable, possibly unpleasant results.

The buffer layout is apparently correct, except you'll need a track break between pin 1 and pin 8 (as drawn), and I can't decipher the power supply at all, so that's as may be. I still think you're swatting flies with an iron monger's hammer, but good luck!

[Ardric]

The buffer chip's job is move current from the power supply to the signal output, under control of the signal input.

• Instrument signals need very little current.
• The DC-DC power supply is complicated, noisy, and in the end makes little current.
• The BUF634 is a really high-current device.
• The BUF634 will never get a chance to do what it's good at.

So compared to the common NE5534 buffers tossed about here, it ends up more complicated, more expensive, noisier, and poorer performing than the normal approach.  It's because this is far from the kind of job the BUF634 is intended for.  I think that's where the criticism is coming from.  But still, it should be possible to get it to work.

Your schem above has errors in both the buffer and PS parts.  The BUF634 is just a big opamp, so consider building a commonly used circuit with the usual protection frills but with the BUF634 instead, changing pinout as appropriate.  If you want the BUF634 to ever stretch its legs, you'll have to give it a strong power supply to match.  Then don't kill anything with it.

[g3rmanium]

• Instrument signals need very little current.
• The DC-DC power supply is complicated, noisy, and in the end makes little current.
• The BUF634 is a really high-current device.
• The BUF634 will never get a chance to do what it's good at.

That's a point I will think about. Thanks.