Analog pre and post axoloti addons

[Blindsmyth]

As we all know Axoloti has it's flaws considering signal level. This has been quite intensly discussed here:

Updated or Pro-grade version of Axoloti?

Until you clip your soundcard and then you will have to restart your computer.. In that moments is when I discovered [clip~] ...

Although I agree that clipping axolotis input and low output volume can be a problem I don't want to conclude that axoloti is unusable and would like to discuss practical solutions, like adding analog circuitry to the ins and outs.

I've noticed that there is a lot of these cheap preamp boards on ebay. It seems like this could be a convient way of raising the low output volume of axoloti. Does anyone here have experience with these?

NE5532 OP AMP HiFi Preamplifier Signal Amplification Board Für Bluetooth Pre-amp...

DC 5V-15V 12V AD828 Stereo Preamp Power Amplifier Board Preamplifier Module D

Further more I would love to have compression and eq/filtering at both input and output in a very small form factor. I'd prefer not to build this on breadboard but rather have a ready board like above or a soldering kit. Any suggestions welcome!

[strum]

My long term solution is to bypass the whole existing analog section and add on a new adc/dac and balanced analog audio side then get it to talk to axo with spi or some other protocol.

In the meantime i am running the Axo output into a limiter to boost it up a bit and just not using the input for fear of burning it out.

[Blindsmyth]

My long term solution is to bypass the whole existing analog section and add on a new adc/dac and balanced analog audio side then get it to talk to axo with spi or some other protocol.

That sounds not easy to achieve but like a super good plan!

n the meantime i am running the Axo output into a limiter to boost it up a bit and just not using the input for fear of burning it out.

Wich Limiter do you use for that? I'm just thinking if I want a compressor/limiter at the master stage anyway I could just skip using a preamp. But I would really something in a small form factor...

[strum]

I'm using an alesis micro limiter, it's a 1/3 of a rack unit size.

I picked it up cheap at a music shop clearance sale

[Ersatzplanet]

Sparkfun has a few boards that are under $10 that are amp boards.

[rbrt]

Hey-ho,
...same here,
I would like to use the axo as an all-purpose tool in a club/studio environment where you need 'pro-audio' input and output levels.
What I'm going to try is to simply scale down the input with a potentiometer,and add some cheap pre-amp at the output.
I already got myself a cheapo kit at 'conrad electronics.I can post the results once I got it up and running

[Blindsmyth]

I'm using an alesis micro limiter, it's a 1/3 of a rack unit size.

I picked it up cheap at a music shop clearance sale

ok thx. Since I'm building something ultra portable and light this is already too big for me.

Sparkfun has a few boards that are under $10 that are amp boards.

But these are power amps right?

What I'm going to try is to simply scale down the input with a potentiometer,and add some cheap pre-amp at the output.

That could work. Right now I'm using this cheap conrad mini mixer before the axolotis to hook up different inputs and turn them down with the pots.

I already got myself a cheapo kit at 'conrad electronics.I can post the results once I got it up and running

Cool, keep us updated!
I for myself have figured out that I want something compressing/limiting/saturation at the masterstage wich should be at the same time be able to raise the output volume.

At the moment I'm looking a bit in the guitar diy world like here for example:
https://www.musikding.de/

Only thing that might be a problem with guitar stuff is impedance...

[Ersatzplanet]

Sparkfun has a few boards that are under $10 that are amp boards.

But these are power amps right?
rbrt:

I was thinking ,more along the lines of this - https://www.sparkfun.com/products/9816

"This is a simple 5V Op Amp breakout board, set up as a 2-stage amplifier with a gain of 100 (gain of 10 for each stage). The on-board trim pot sets the signal level between the stages, not the feedback path. The bandwidth is set to 15.9kHz by a pair of feedback capacitors, or over 100kHz with the caps removed. The LMV358 opamp can source up to 160mA and works well as a low impedance driver/buffer."

[Blindsmyth]

"This is a simple 5V Op Amp breakout board, set up as a 2-stage amplifier with a gain of 100 (gain of 10 for each stage). The on-board trim pot sets the signal level between the stages, not the feedback path. The bandwidth is set to 15.9kHz by a pair of feedback capacitors, or over 100kHz with the caps removed. The LMV358 opamp can source up to 160mA and works well as a low impedance driver/buffer."

Ah doesn't sound too bad and looking at the demo might be able to do a bit of distortion as well...

[johannes]

The reason that Axoloti Core can only output around 2V peak-to-peak is that the +5V voltage from usb (or regulated to 5V from the DC input socket) is considered noisy, and is regulated down to a clean 3.3V for the analog circuitry.

An opamp like the NE5532 can be used to amplify the analog output, but this particular opamp requires a +5V/-5V symmetrical power supply minimum, and recommends a 2V margin between supply and output voltage, so the output swing with a +5V/-5V supply would be 6V peak-to-peak. That would work, but would need to get the +5V/-5V supply from somewhere. Alternatively an asymmetrical +10V supply (or even up to 30V) could work

The AD828 Stereo Preamp Power Amplifier Board Preamplifier Module D has a bit of a confusing name, first I thought it would be a class-D power amp, but it is really a preamp. The AD828 opamp is also a bit of a strange choice as it is designed for video signals. The output signal when using a +5V supply is 3.5V peak-peak, so the optimum maximum gain setting would be around x1.75.

The LMV358 opamp on https://www.sparkfun.com/products/9816 is a "rail-to-rail output" opamp, that means you can get close to 5V peak-peak output swing when powered from +5V. The two stages of x10 gain combined to x100 gain will be too much, it would be better if it was designed for two channels of x2 gain.

[Blindsmyth]

Thanks for bringing some clarity into this!

The reason that Axoloti Core can only output around 2V peak-to-peak is that the +5V voltage from usb (or regulated to 5V from the DC input socket) is considered noisy, and is regulated down to a clean 3.3V for the analog circuitry.

Ok but does that mean If you would feed it clean 5V you could get higher output level/voltage?

The AD828 Stereo Preamp Power Amplifier Board Preamplifier Module D has a bit of a confusing name, first I thought it would be a class-D power amp, but it is really a preamp. The AD828 opamp is also a bit of a strange choice as it is designed for video signals. The output signal when using a +5V supply is 3.5V peak-peak, so the optimum maximum gain setting would be around x1.75.

Ok, this also means higher supply voltage higher gain/output voltage?

The LMV358 opamp on https://www.sparkfun.com/products/9816 is a "rail-to-rail output" opamp, that means you can get close to 5V peak-peak output swing when powered from +5V. The two stages of x10 gain combined to x100 gain will be too much, it would be better if it was designed for two channels of x2 gain.

I think you could change the gain with the trimpot right? Sounds like the most convenient option so far.

Although I'm still intrigued by some analog compressor/drive combination that at the same time raises the output, so if anybody has suggestions, small form factor and either ready made board or kit with ready pcb preferred.