Hello everyone
I´m Francisco from Argentina. I'm trying to make an analogue dj mixer. The main idea it is make fully modular (a schematic is attached). I Take the main circuits from an schematic from RANE MP2016. I’ve been working hard but the results are not the best.
The mains problems are:
1-The level potentiometer does not cut the entire signal. When I turn down the volume and close -the potentiometer, It´s keep coming signal, the attenuation achieved is about -62dB, which is quite poor for a an audio mixer. In the schematic I show how I measured with the oscilloscope. I think that is a ground issue or a bad pcb design, but I couldn´t solve it.
2-The LED VU meters introduce noise. I´m using a cheap VU meters that it´s use a KA2284 IC. The noise show´s up when the led s are blinking. The Vcc(+15V ) used by the meters is the same that is used for the audio op amps. I assume that using different Vcc with different regulators It´s going to help, but I appreciate any suggestion.
3-CUE button introduce clicks when it´s pushed off. I´m using a relay to switch on/off the cue, I think the same in the case of vumeters, maybe using different Vcc helps, but I really appreciate any suggestion.
I hope I was clear.
Thank you.
I´m Francisco from Argentina. I'm trying to make an analogue dj mixer. The main idea it is make fully modular (a schematic is attached). I Take the main circuits from an schematic from RANE MP2016. I’ve been working hard but the results are not the best.
The mains problems are:
1-The level potentiometer does not cut the entire signal. When I turn down the volume and close -the potentiometer, It´s keep coming signal, the attenuation achieved is about -62dB, which is quite poor for a an audio mixer. In the schematic I show how I measured with the oscilloscope. I think that is a ground issue or a bad pcb design, but I couldn´t solve it.
2-The LED VU meters introduce noise. I´m using a cheap VU meters that it´s use a KA2284 IC. The noise show´s up when the led s are blinking. The Vcc(+15V ) used by the meters is the same that is used for the audio op amps. I assume that using different Vcc with different regulators It´s going to help, but I appreciate any suggestion.
3-CUE button introduce clicks when it´s pushed off. I´m using a relay to switch on/off the cue, I think the same in the case of vumeters, maybe using different Vcc helps, but I really appreciate any suggestion.
I hope I was clear.
Thank you.
Attachments
-60dB at full cut is typical for affordable pots. Especially if you are using Linear pots with heavy loading to get semi-Log curve.
Layout and decoupling is EVERYTHING in radio network mixers. Not SO much for party-DJ mixers because there are no "foreign" sounds in the console. You do have queueing-up the next track, but this is usually behind another loud track.
Layout and decoupling is EVERYTHING in radio network mixers. Not SO much for party-DJ mixers because there are no "foreign" sounds in the console. You do have queueing-up the next track, but this is usually behind another loud track.
So do you think changing the potentiometers for better ones like ALPS will help?
Any advice on the layout ?
Thank you for your time.
Any advice on the layout ?
Thank you for your time.
Yes, you need to use a professional fader circuit with proper offness - cascading two linear pots is one approach, this gives a reasonable log-response and doubles the offness to 120dB (assuming decent grounding).
Separate power supply, good grounding (star grounding).
You will always have clicks if you hard switch an audio signal - a soft-switching circuit is needed to avoid this.
BTW your cue circuit in the channel section schematic makes no sense at all - you are switching a 300 ohm resistor to ground on the output of an opamp - the opamp is going to ignore this completely. If you directly shorted the opamp output to ground this would have effect (but is poor circuit design). You just need the switch in series with the signal to block it.
Also you have 9k09 resistors in series with opamp inputs in several places - this serves no purpose other than to raise the noise-floor somewhat as far as I can see.
Change the pots to a cascade of two 5k linear pots for better offness and lower noise - 50k is high enough to add audible noise.
In the mixer board schematic you buffer the output of the input opamps for no reason - buffering the output of an opamp with another opamp does absolutely nothing. There's a lot of unncessary DC-blocking going on too, but its good to see each potentiometer wiper has a DC blocking cap - those are needed with bipolar opamps.
Hello
Not to much progres. I decided to remake the pcb´s. I did some change´s in the PSU and put ground planes this time. So I´m waiting the new ones from jlcpbc. I hope this time works.
Thanks