VLF MD with digital signal processing : Bee-Buzz 1

[Marchel]

Here are three pre-amps that I made and tested. The first (equinox) had some problems with oscillations and low bandwidth. It used some flea sized components, so I blamed it on pcb design and poor soldering. The second (vanq) worked well but the bandwidth rolled off in the 30khz range. I modified the third to to work up into the 40khz range. These operate at 3.3v and have a low impedance differential output which allows using simple twisted pair cable. Credit to Orbit on helping reverse the vanquish pcb. I am interested in how it would be received and fed to the ADC.

Hello

I would like to know what the output signal shape is from this amplifier at the RXN and RXP outputs. Do you have any photos of the output measurement on an oscilloscope ?.

[Carl-NC]

Any decent audiophile will design with vacuum tubes, not transistors. For that more realistic and "detailed" sound, whatever that means.

[moodz]

"IC op amps are dead. And we killed them. "

https://sparkoslabs.com/discrete-op-amps/

Been looking at discrete op-amps with rail-to-rail output.

Those discrete designs usually dont have good CMRR or PSRR because they only focus on noise preformance. Additionally your spec is barely making 16 bit performance ... its never going to be 24 bit compliant.
For 24 bits you will require fully differential amps which is going to be very messy implemented in discrete.
Besides that you are trying to fix asynchronous noise on a synchronous detector.
Great HIFI discussion though just wrong thread.

[Detectorist#1]

But, one my friend said 15 years before - if you want to haven't problems in analog design - use integral circuits - not discrete solutions! The future is here - let to use it.

[Aziz]

"IC op amps are dead. And we killed them. "

https://sparkoslabs.com/discrete-op-amps/

Been looking at discrete op-amps with rail-to-rail output.

[Detectorist#1]

Hi Aziz,
The high results in the MD area depends more from side factors than from our knowledge in hardware design of the very fast or very low noise solutions. But this is not capable to stop us!

[pito]

so you can say sensitivity is 1 microvolt and output will be 47 microvolt noise free ?
15 mV -> no distortion expected. Output voltage peak-to-peak would be approx. 1.5 V.
15x47 = 0.705 V not 1.5 V

[Aziz]

and minimum ? = sensitivity

Hi pito,

you have misunderstood me. Due to the low battery voltage of 3 V only, the input voltage is limitted at a specified gain of approx 50.
Input 0 - 15 mV -> no distortion expected. Output voltage peak-to-peak would be approx. 1.5 V.
Input above (> 15 mV) -> distortion to output happens.

[pito]

Hi all,

max. 15 mV input voltage

Aziz

and minimum ? = sensitivity

[Altra]

Thanks! That completes the basic hardware picture. The rest is code.

[JoyJo]

Here are three pre-amps that I made and tested. The first (equinox) had some problems with oscillations and low bandwidth. It used some flea sized components, so I blamed it on pcb design and poor soldering. The second (vanq) worked well but the bandwidth rolled off in the 30khz range. I modified the third to to work up into the 40khz range. These operate at 3.3v and have a low impedance differential output which allows using simple twisted pair cable. Credit to Orbit on helping reverse the vanquish pcb. I am interested in how it would be received and fed to the ADC.

Equinox has such an input part in the block. The second differential input is used to monitor the current in the coil Tx.

[Aziz]

Hi all,

well, ok. I have got rid of the op-amp and made the AC pre-amp fully discrete now (the good old days style ).
It operates now at 3 V battery voltage and allows max. 15 mV input voltage at gain of 47. Beyond the limit, it begins to disturb the output as there isn't enough voltage range due to the transistor voltage drops.
Power consumption: 25 mA at 3 V.
Noise-Specs? It's Ultra
See below:

Cheers,
Aziz

[JoyJo]

I guess that's what I was looking for! Thank you!

[Altra]

Here are three pre-amps that I made and tested. The first (equinox) had some problems with oscillations and low bandwidth. It used some flea sized components, so I blamed it on pcb design and poor soldering. The second (vanq) worked well but the bandwidth rolled off in the 30khz range. I modified the third to to work up into the 40khz range. These operate at 3.3v and have a low impedance differential output which allows using simple twisted pair cable. Credit to Orbit on helping reverse the vanquish pcb. I am interested in how it would be received and fed to the ADC.

[Aziz]

Again, you dont need special chips. Use discrete transistor preamp just designed to operate at 3 V.
I should look at them too. Could be very useful.
Cheers