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Postby jeghers » November 17th, 2008, 3:45 pm


I am designing a 3-way guitar selector switch with gain controls for all 3 guitar inputs. It will use op-amp buffering and is meant to NOT affect or "color" the tone of the guitars in any way.

Here is my problem: I have identified what I *think* is a good candidate for a very high quality op-amp (OPA132). But I am not completely certain it is the best pick, and I am also having trouble finding it in a DIP package.

Most web pages discussing good audio op-amps are geared towards headphone amplifiers, which is not quite the same application as what I am doing. An op-amp well suited for that use might not be best for mine. I just don't know.

I am also bothered by the fact that the dual and quad packages have some diminished performance numbers, so I might be pressed towards using more single-unit 8-pin DIPs.

So my question is this: what is the best op-amp for low-distortion, no tone coloration, good low-power & (maybe) low-voltage performance, and overall stability? And also very important: WHERE CAN I GET IT IN A DIP PACKAGE??? The OPA product line seems to be only sold in SOIC packages now...

Thanks for any and all help,

ps Here are my design goals:

- 3 guitars in, one low impedance output to a pedal/amp/whatever.

- Op amps allow high impedance guitar inputs so guitar tone is not adversely affected.

- The device is meant to NOT affect or "color" the tone of the guitars in any way.

- Each guitar input has a gain control (e.g. a volume knob) with a gain somewhere between 3 and 12 db (I've not decided how much yet).

- It will use non-popping (debounced) solid-state switching with CD4066 analog switches.

- Powered by either external or battery. I am willing to design for 2 9v batteries, but I'd prefer just one 9v battery if I can get away with it. So power consumption is important bt not paramount.

- Some digital logic (with capacitor-debounced Schmidt triggers will provide with exclusive (1-of-3) or multiple (more than one combined) guitar selection.
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Postby gnease » November 18th, 2008, 7:45 am

sorry not to reply to your other req for suggestions, but was too busy at the time. if you are going to limit yourself to DIPs, that will be a problem. SMT is where you need to be for the latest. if you are hand wiring/soldering, it's still possible to solder to SOIC packages -- or you may be able to buy a test board that accepts an SOIC and "cut and paste."

okay -- a quick look tells me the OPA134 is a better device for your application (than the OPA132, an instrumentation amp). note that the OPA134 is a high perf AUDIO opamp, and IM distortion is spec'ed at unity gain as an impressive -98 dB1Vp-p.
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