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Old 18th November 2008, 01:27 AM   #1
jeghers is offline jeghers  United States
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Default Need help selecting and LOCATING the best op-amp for guitar audio

All,

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,
/Mark

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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Old 24th November 2008, 04:59 PM   #2
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Default Guitar Opamps

The opamps Rod Elliot uses should work for your project. Google Elliot Sound Products and click on projects, then musical instruments. They are available in 8 pin dip.
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Old 24th November 2008, 10:32 PM   #3
Minion is offline Minion  Canada
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Any Fet input opamp is suitable....You don"t need a super low noise opamp as the Noise picked up by your Patch cord and Guitar electronics will totally swamp any Noise caused by the Opamp...Guitars are Noisy and so are guitar amps so I don"t think getting a super high quality opamp is going to make any Differance....

I use the OPA132/2132 in my Active guitar electroncs designs and they are great as they have a high input impedance and and low power consumption (I"ve been useing the same battery for 2 years)......

Cheers
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Old 18th December 2008, 11:52 PM   #4
teleman is offline teleman  Norway
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You could also try TL061 or NE5534.TL061 is a JFET device while
the NE5534 is an mono op-amp.But this needs an external bias offset cap.Both these chips are dirt cheap & readily available.Can also be used on single 9v supply or 2 x 9 v batteries with a little diminished performance.

Ideally you should look for an single supply,preferably a 5 volt dc driven chip & use two NiCd batteries to power it if you want to install in your guitar.Thare are plenty of these "chips"out there!

I don't think you would need a device with so high slew rate for audio!Anything up to 5uv/sec would be more than adequate.Besides,devices with very high slew rates & ultra low noise would just gobble up your batteries since they tend to demand a very high quiesent current to the chip!
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Old 2nd January 2009, 03:46 AM   #5
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as far as the "best sounding" opamp, or having low coloration, it's really up to your ears.

Plenty FET opamps will run from a single 9V for ages.

The TL071 may also work.

If you had your heart set on the OPA132, but can't find a DIP, you may try the OPA2132 (the dual opamp version of the OPA132) or a similar OPA134 (single) or OPA2134 (dual) that still come in DIP packages. (TI still offers samples of these via their website)

lots of standard CMOS parts will tolerate being powered directly from a 9V. Just check the datasheets.

For controlls, since you have a knob to attenuate each input, why not have an on / off button for each input (using Flip-Flops, like the 4013),

or if you only want a single button, you could use a johnson (decade) counter (like the 4017) cycle through with the switches on only one at a time,
or using a binary counter like the 4510, so all possible combinations would be cycled through.
-the decade counter or the binary counter could have the next pin connected to reset, so you don't have too many extra button presses to get back to the beginning.

check out Beastie Zone
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