I want to use Axoloti for guitar effects, primarily delay and reverb and was wondering about either building or buying some sort of preamp/buffer that matches levels and impedance to accept guitar signal then output back into a guitar amp.
has anyone done this yet?
What level and impedance are the audio in and out?
Even though it is not designed for guitar input there is enough gain for it. I'd get a radial passive DI. I only have an active one - needs phantom power - so I've plugged my guitar and bass directly to it and it works.
I think in the next hardware revision it would be nice to have two jacks, one high impedance and for line/mic level.
If will work without preamp or buffer, but if concerned about pickup loading, you can use a EQ or boost stompbox before Axoloti, or maybe a passive DI, or use a fx send/return of an amplifier.
This is much less a concern in my opinion. Driving a high-impedance audio input with a lower-impedance source than expected does not matter.
Input impedance depends on the gain selected (with the audio/inconfig object)
-12 dB gain -> 84.5kΩ
0 dB gain -> 53kΩ
35.25 dB gain -> 2kΩ
Line out impedance is around 40Ω
I have not found impedance specs of the headphone out, but it is designed to deal with 16Ω loads.
Maximum in- and output levels are around 2Vpp.
You probably you already have a stompbox that will work as a pre-amp. If it's not true bypass then you can use it with the effect switched off.
Just plugging straight in would probably change your tone a bit compared to going into an amp...but if it sounds ok to you then it is ok.
Ax output into guitar amp should be ok ...try it though.
OK, thanks that's what I needed to know, running it in an effects loop sounds like the best way, though some of the amps I use don't have one,
Pickup loading is the main issue, which I can sort with a buffer before the Axoloti, when I'm not using it in effects loop.
One Strymon delay or reverb costs at least $600 AUD and I figured they must be built around some generic DSP board.
So I thought there might be an open source DSP board that could do it and be much cheaper, and much more flexible.
One google search and I found Axoloti, saved me building one myself , and the years of work developing the software.
The other thing I wanted to use Axoloti for was as a mastering EQ, compressor, exciter and stereo enhancer for live gigs, for that I'll need a preamp with XLR and balanced TRS jacks and some sort of converter from balanced to unbalanced and back again.
Does such a thing exist?
I could build it myself given schematics but my analog electronics design is not that sophisticated yet.
I'm very impressed and pleased that you guys are so helpful and quick to respond, thanks,
IMHO this sort of support and an active helpful community of users is as important as the hardware itself.
Awesome
Integrating a high quality mic pre-amp was once considered, but the requirements get very demanding. Say, a TI PGA2505 as front-end, but requires a bipolar 5V supply, and 400mW per channel, then for condenser mikes need to add a step-up supply for +48V phantom power - that can also demand significant power, ~300mW/channel, then maybe a relay to switch phantom power..... This 'd add significant cost, board space, and demand power, while not everyone would need this.
I have found the integrated programmable gain stage in the selected audio converter a reasonable compromise between flexibility and cost for a wide range of applications. It can't compete with a dedicated mic preamp of ~100 euro/channel but also avoids a similar cost... Its lower input impedance at higher gain is most often a benefit, as signal sources that require high gain also tend to have a low source impedance too.
It seems you do not need the gain associated with a mic preamp there, I'd suggest a passive DI-box.
I don't think adding a preamp is a good idea. You simply can't do it without changing the price bracket of the axoloti. And then people would still complain because it does not meet their expectations...
What I think would be nice is a 1M impedance parallel input path so you could plug a guitar or bass and don't get surprised by the tone due to impedance mismatch.
I believe the cost of additional electronics required would almost be negligible and would allow you to market it as guitar ready for people looking for a digital DSP stomp box.
Just a thought!
I'd be more than happy to pay more to have a good preamp onboard.
Phantom power would be nice but it's not necessary a preamp is.
My first experiments with using it for guitar effects have not been encouraging to be honest, it needs a preamp for both input and output stages to be able to use it as part of a live setup, it needs to be able to handle balanced lines in and out at much hotter levels.
for a mic preamp with phantom power you need very likely a bipolar power supply plus 48 phantom power, so you will need a completely new PSU. There are great diy solution you could pair with an axolotl expat audio for instance have nice preamp cards.