Adding a (variable) gain boost to this non-inverting opamp buffer circuit?

[audiovisceral]

Thanks snake.

I was working on my own abysmal photoshop of your ideas as well (which is much worse looking than yours). Attached. Diagram wise, this is getting embarrassing. 😀

Anyway, is that what you're suggesting on the power supply, as close to the pins as possible? The three caps would be for + and - lines. I just couldn't make space for them on -. Duly noted on polarity for lytics.

Re: C1, I'm thinking it should be 5-10 nF or so to filter more up to around 16 hz or so. Unless this is going to reduce its DC blocking ability since I guess that's more it's purpose.

Also do I really need both R1 and R3? Seems silly somehow though I don't really know.

 

[bentsnake]

...do I really need both R1 and R3? Seems silly somehow though I don't really know...

Needing both depends on what you're plugging in.

Plugging in a guitar pickup directly? Then you need both. E=IR.

When the guitar is played the magnetic--or piezo--pickup develops (creates) a given voltage, with a given current (small) available. But without a resistance to complete Ohm's law, a grand total of nothing happens. Compelled by voltage, the current needs a resistance through which to flow, and that resistance is R1.

In any case having both does no harm. A can't hurt might help situation.

Good news, you're not being graded on your draftsmanship.
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[bentsnake]

...is that what you're suggesting on the power supply, as close to the pins as possible? The three caps would be for + and - lines. I just couldn't make space for them on -. Duly noted on polarity for lytics.

Nooo! Only as shown at the power pins of the OPA2134 (yours edited).
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[bentsnake]

Re: C1, I'm thinking it should be 5-10 nF or so to filter more up to around 16 hz or so. Unless this is going to reduce its DC blocking ability since I guess that's more it's purpose.

For all audio--and most other--purposes we consider that:

All capacitors block all DC all of the time, and:

All capacitors pass all AC all of the time.

(AC might be attenuated--as by a filter--to a very low level, but it still passes, you just can't measure it without lab instruments.)

Regarding component values, nothing is ever either-or with audio, or with electronics in general. You're always taking less of one thing to get more of another.

I suggest leaving C1 as is. There are benefits to having this filter set to a low frequency, the math of which is frightening.
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[AndrewT]

......................Also, would it be good principle to put any caps or anything on my V+ or V- rails just before they hit the opamp? The power will be travelling through a 10-15 foot 13-pin guitar cable before it gets to the buffer circuit.................

You must read and implement the datasheet advice on supply rail decoupling.

 

[bentsnake]

...would it be good principle to put any caps or anything on my V+ or V- rails just before they hit the opamp? The power will be travelling through a 10-15 foot 13-pin guitar cable before it gets to the buffer circuit...

...is that what you're suggesting on the power supply, as close to the pins as possible? The three caps would be for + and - lines. I just couldn't make space for them...

Clarifying the situation, I hope.

Regarding Ca and Cb, first I said they should be 10uF, then I said 470uF, now I'm back to 10uF because that's more of a decoupling value.

Well heck, I already said I don't know.

A 13-conductor cable. Lawsy. Again I don't know, but that sure is a lot of conductors packed in with the relatively enormous power supply voltages.

I greatly wish you'd run some sort of test with the cable you'll be using before getting into, for instance, housings. The transformer is the most expensive part of the electronics, but often the housing and trim dwarf that, both in money and effort.

Of course...you're always supposed to test in stages, verifying each step as you go along. I suppose somebody somewhere might actually do that.
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