Matching guitar pedals average level?

#1

Anyone has tips about how to match the "average" level for a guitar pedal build ?
It's already been - partially - discussed here and there, but without any clear solution... Especially if you want to feed it with a standard 9V power supply (-) centered.
Not talking about an input buffer, as it's easier to implement. I'm talking about the output level. I did some simple attempts with a TL072 to gain some dB (thus, a bit stronger p-p voltage), but sharing the same 9V with the axoloti board made a fairly strong whine, too high to be filtered...
I did it with a voltage divider / virtual ground. Need to find another solution.
If someone has an idea.
thanks !

#2

Hello,

Is there a specific reason you need more hardware?

I've made the axoloti act as a pretty decent guitar pedal by modifying the configurations of the codec ADAU1961. That chip has internal input and output buffers so you should be able to gain up or down as needed.

audio/inconfig lets you configure the input gain, but to control the output gains you will have to modify an object to send IC2 commands to the codec.

Let me know if this helps, thanks
Ryan

#3

The reasons are multiple.
First, i like how pedals behave in general as they're kind of universal in terme of level (except in modular, but I avoid getting into modular) : I mean they work in most situations without caring too much (instrument/line input, insert etc).
I happen to build axoloti-based effects for people, and i'd like to fix the dB drop which has been much discussed in this forum. I can't presume the way they're gonna wire it (ie in series or parallel).

Another example would be to include a true bypass switch in the design without any strange surprise in volume...

You're right about the input gain object. It works fine by adding a basic audio buffer (like Klon for instance) before it with a +/- 1Mohm impedance and add some dB. And why not, an input gain control with a nice clipping led, or a pad switch.

Still it doesn't fix the output level, which, again, is talked many times here. I understand the software side is OK, but has to see with the limit in p-p voltage. The idea would be to boost it a little. Just some dB.

That's where i face my limits in circuit design, and especially on the power supply side. I'd like to make a simple post-amp, opamp based (why not transistor), which could be driven with the same 9v supply i'm using to power the axoloti. Put a trimmer, test it with a sine wave until happy, et voilà.

Until now i'm getting some noise / whine. There must be an easy way to do it....?

#4

I use axoloti extensively in a guitar context and I completetly abondened the idea of using the same 9v for any pedal before and after axoloti. It always introduces terrible noises in all imaginable colours.

In the end I ended up using something like this seperate the ground between axo and my pedals:https://www.thomann.de/de/harley_benton_powerplant_iso_2_pro.htm

But i understand that this is not exactly practical to build into a pedal.

So you could maybe investivate a bit in ground loop break circuits. But having a seperate ground for axo and the pre/postamp circuit seems problematic since you want to have everything grounded to the enclosure in the end...

#5

You're right to point this out. Though I didn't plan to make it on an industrial scale... I mean, it's easy to ask for people to take some care about how they power it.

Actually, last time I built a pedal, I didn't even ground the enclosure. All i did was make a bunch of tests with +/- shitty power supplies, including rechargeable 9v batteries. The worst I had was with a generator, but still it was acceptable considering i was using single coils and the hum was low, and equal using any other pedal...

I didn't mean to make it insensitive/ compatible with careless daisychain powering. I just will to cleanly gain some dBs, or extra voltage if you prefer... Sure, that's where I face my noobness in circuitry.

#6

Yeah no I don't think you have to make it work with careless daisy chain powering, that is the same with other digital pedals. You can't expect your fuzz and a dsp based reverb to work on the same daisy chain.

The problem is here you should be able to expect to have all of your axoloti pedal on one power supply + you should be able to achieve normal guitar levels/have input at same level as output.

Did you check this? https://sebiik.github.io/community.axoloti.com.backup/t/any-interest-in-this-line-levels-expander-board/5238/8
has a dual power supply unfortunately, but maybe you can still make it work with a virtual ground?

#7

Sure I did ! Yes, i'll make some breadboard tests as I see some OPA2134 lying around...

#8

I mean at this point this new akso hardware could be interesting. with its +-12v maybe you could have this extra audio circuits with less noise.