problems with DIY audio mixer - Page 1
Forum section: electronics / projects

author: panchito
author_rank: Newbie
timestamp: April 12, 2021, 11:02:37 pm
content: Hello everyoneI´m Francisco from Argentina. This is the first time that I post something, so I hope do it in the best way.I'm trying to make an analogue dj mixer. The main idea it is make fully modular[ Specified attachment is not available ][ Specified attachment is not available ][ Specified attachment is not available ]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.

author: Renate
author_rank: Super Contributor
timestamp: April 15, 2021, 02:28:26 pm
content: Nothing pops to my eye.That a 50k pot still might measure 50 ohms at an end position doesn't surprise me all that much.Did you measure them?Maybe different pots work better?It's probably overkill, but you could use a dual pot.The 2nd one would be used as an off position detector and feed a mute.Figure out where all the click is coming from.Is it the relays themselves or the fact that you're switching a 300Ω load onto the the op amp?Pull the resistor and compare noise.You're using a bipolar supply which eliminates the rail splitter/power supply interaction question.Still, it might be good to do a reality check.Feed the +15 (or -15) through a diode for a drop.Bypass the diode with a switch.Does flipping the switch back and forth generate large noise?

author: tooki
author_rank: Super Contributor
timestamp: April 15, 2021, 09:04:32 pm
content: Please fix your images. Right now you essentially have very low-res schematics floating in a giant sea of white.

author: Bassman59
author_rank: Super Contributor
timestamp: April 16, 2021, 01:32:04 am
content: Pots and faders designed for pro audio will connect the wiper to the other pins at the extreme ends of the travel. This ensures that you have infinite attenuation when the level is turned all the way down, as in the usual circuit the CCW pin is grounded, so when turned all the way CCW the wiper is grounded too.So get some better pots!

author: panchito
author_rank: Newbie
timestamp: April 19, 2021, 02:48:27 am
content: Quote from: Bassman59 on April 16, 2021, 01:32:04 amThank you , I'll try with ALPS potentiometers, may be works better.

author: panchito
author_rank: Newbie
timestamp: April 19, 2021, 02:50:07 am
content: Quote from: tooki on April 15, 2021, 09:04:32 pmsorry I modified it

author: panchito
author_rank: Newbie
timestamp: April 19, 2021, 03:01:28 am
content: dQuote from: Renate on April 15, 2021, 02:28:26 pmI did not measure the resistance, it is a good point. I'm going to check it out.I am using dualpots since the channels are stereo, to think of double dual pot is very expensive. The potentiometers I use are not the best, some agree that this may be the problem.I think the clicks come from the relay since it always appears everywhere, not only on the channel used.

author: tooki
author_rank: Super Contributor
timestamp: April 19, 2021, 05:59:50 am
content: Quote from: panchito on April 19, 2021, 02:48:27 am👍Alps, Bourns, and Panasonic are always good choices.