scratch mixer???

[hank reynolds 3rd]

does anyone know of a schem/ a way to build a cheap (lo to mid fi?? :shock: ) scratch mixer??? am i right in thinking that its basically two single channels and a pot for blend (like switching twixt the two channels on turntables in a hiphop stylee??) and an eq cut/boost for each of the two channels???
if not, does anyone know of any schems for a simple opamp mixer and eq circuit (just splice em together!!)

thanks in advance

sam

[petemoore]

I believe there's one at AMZ.

[Nasse]

Old proverb "If it aint at Geofex, you dont need it". Eh, I mean check Geofex and "panning for fun" article. I think crossfade between two channels can easily be done with such circuit, in principle. And with opamps like tlo7x or Ne553x you can make it hi-fi instead of lo-fi.

Alps pots are concidered as good quality/price ratio. Or use VCAs to control volume

Last time I bought rice crispied for my kids at market there were a cd on package, and some PC program on it, that you could "mix your own hits".

My first homemade mixer is in somewhat unstable state as now, but I have had no DJ gigs so it does not worry mee for too much. I made a "disco mixer" from Elektor 303 circuits book, just nice pcb with onboard power supply and left and right summing amplifiers and didtn make preamp sections cause used CD player and that give enough oomph with just passive vol control. I used a mini-sized aluminium tool suitcaseas enclosure. I added active subwoofer filter for my 15" active self-made subwoofer and left/right difference circuit on separate pcb for some "surround sound" with old patented finnish "ortoperspekta" principle and two satellite side speakers, sounded gorgeous.

one link much info about stuff: www.dancetech.com

Lastly, I want to share a very good tip from one respected local DJ: All you being in this bisnes know that problem: Old records and popular songs sound dull and boring as they age and your audience has heard those too many times. Good  and working DJ trick is to put your CD´s in icebox before playing, so they sound fresh and like new.

[Nasse]

:oops: I continue this interesting topic. I too have been wondering what is the technology how DJ´s "lift" off bass lines and bass drum or hi-hats and cymbals from CD or vinyl.

I believe what you need is high or lowpass filter with suitable cutoff freq and steepness, and some noise gate after may help mask what the filters can´t remove.

Listen some modern music trough high pass filter tuned high enough and hats and crashes and rides and tambourines are whats left. Bass instruments can be extracted same way with lopass filter. When two pieces are mixed together, t.ex bass removed from another and extracted from another, music masks out not always so perfect removals.

Anyone with some info what kind of filters those fancy dj mixers have?

[Paul Perry (Frostwave)]

If you want to lift out bass, an MS20 style low pass is good, because you can push the resonance up, which gives you a peak that you can tune to the bass & emphasise it. I guess there are other LP filters that would do as well, but my experience is with the MS20 style.
Putting it at the edge of resonance, you can bump it into doof dof dof..

[Mark Hammer]

The MC3340 is an analog attenuator chip that, has some annoying properties when it comes to trying to use it for rapid modulation, but works fine when you use it for its original intent which is remote volume control.

You can find the datasheet here: http://www.ee.washington.edu/stores/DataSheets/linear/mc3340.pdf

And a 3rd party users circuit and user comments here:
http://www.idg.se/personal/bergfors/bergfotron/vca/mc3340%20vca.htm

I think you'll agree that as a remote attenuator it sure doesn't get much simpler than that.

Since you'd want a stereo cross-fade, the simplest way to do it is with a linear dual-ganged 100k pot, with the wipers tied to ground, and the outside lugs of each pot tied to the same side/channel of the other input.  When centred, you'd get equal levels from each input source, and as you pan in one direction one source would drop in level while the other would increase.  If you wanted to get really nuts, you'd build simple Bi-Fet op-amp input stages for each channel of each source, and wire up another dual-ganged pot to work the gain of each channel, so that you could turn up the gain for the left side vs right side (independent of overall source level) and adjust the source/pan level (independent of channel level/gain).  Figure out a way to work both knobs at once and you've got some wild and crazy panning and sound rotation.