[AudioI] high impedance guitar input with Octo RCA sound card

[hugh crawford]

Randy,
Thanks for such a prompt response!
Yes a schematic would be nice to have and very much appreciated. Thanks for
the warning about the power noise. For proof of concept purposes, a battery
would make a pretty clean power supply I suppose.

I am amazed that there isn't a commodity widget for guitar to line level.
Of course I may be overestimating the market since I need 6 x everything.

Thanks
Hugh

On Fri, Dec 25, 2020 at 8:23 PM Randy Reichenbach <randaji at gmail.com> wrote:

> I have experience with using the AudioInjector Zero for guitar
> processing.  It works great at long as you have a preamp or unity gain
> buffer feeding the input.  I created an open-source project around it:
> http://treefallsound.com
>
> I tried many different op-amps (5) and discrete transistor buffers (2).
> The biggest problem I had was noisy power since I needed it to be powered
> from the same supply as the Raspberry Pi.  The 5v rail is simply unusable
> without regulation.  The 3.3v pi rail is regulated and less noisy, but
> still not usable IMO.  If you could steal 3.3v from the AudioInjector, that
> would probably be your easiest option.  That would have required a hack to
> the Zero card, so I settled on regulating the 5v rail with a AMS1117-3.3
> low-dropout regulator (same regulator the AudioInjector Zero uses).
>
> For the buffer itself, I found the MCP6292-E/P opamp (
> https://www.mouser.com/ProductDetail/579-MCP6292-E-P) to be the best
> performing.  Best noise floor and output swing.  You'll want a rail-to-rail
> opamp cuz even 3 volts is not much headroom for a guitar signal.  If I
> could justify the extra cost and board footprint for my project, I'd go
> with their "isolated soundcard" which has almost double the headroom and
> I'm sure the noise and audio quality are much better too.
>
> If you'd like a schematic for the opamp buffer and supply regulation I use
> for pi-Stomp, let me know.
>
> Cheers,
> Rand
>
>
> On Fri, Dec 25, 2020 at 5:23 PM hugh crawford via People <
> people at lists.audioinjector.net> wrote:
>
>> The Octo RCA sound card supports six audio inputs and I would like to use
>> it and a Pi card for electric guitar signal processing preferably built
>> into the body of the guitar eventually but outboard is fine for now.
>>
>> I am using passive high impedance guitar pickups. A coil of wire
>> wrapped around a magnet for each string.
>>
>> It seems like an obvious application, and I would imagine that I am not
>> the first to try this. Does anyone have any experience with this? Some sort
>> of minimalist signal boosting / impedance matching / buffering perhaps?
>>
>> I could make a balanced connection on the pickup side if that helps
>>
>> Thanks
>> Hugh
>>
>>
>> --
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>> People at lists.audioinjector.net
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>
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