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Old 1st July 2014, 07:47 PM   #1
bcmoore is offline bcmoore  Germany
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Default very very simple DJ mixer aka summing amp?

Hi there,

I was going through this DIY DJ mixer thread on the forum, and I noticed there was some talk about a very basic DJ mixer set up (mancuso inspired) where say for example: you have two turntables, then you connect the turntables to two phono amps, and then you run that to I guess what would be a summing amp (??) and then run the "resulting" signal to your amp and furthermore speakers.

I thought this was really interesting. The possibility of having a very simple mixer with two stereo channels in and one (maybe another for cueing) stereo channel out as a basic unit which you could then add an isolator or filters to in the output stage could be really great. Because, once you take a DJ mixer and remove all the eqing and effects, you're basically left with a summing amp with phono stages right?

my idea was to just get two really nice phono amps (possibly tube, and yes I'm aware tubes are **** in terms of fidelity, but pleasant coloration can be nice sometimes) and then hook them up to a summing amp and then maybe just get an isolator for the master output if I want to eq it...

So, I guess I'm looking for a simple/reliable summing amp schematic someone out there might recommend. And, also, would this be possible to do with a passive summing box type setup? I don't think so right? why?

Any input is greatly appreciated.

Cheers,
ben
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Old 1st July 2014, 08:19 PM   #2
adason is offline adason  United States
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simple JFET buffer with volume pot and resistors from each source into the gate...as simple as that
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Old 1st July 2014, 08:20 PM   #3
adason is offline adason  United States
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https://www.google.com/search?hl=en&...0audio%20mixer
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Old 1st July 2014, 09:09 PM   #4
bcmoore is offline bcmoore  Germany
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Thanks for the prompt reply! much appreciated. That sounds interesting...
On that note, I'd like to mention one of the main references that got me thinking about this. This is a DIY design by bozure, for what seems to be a very simple mixer, Bozure.com - Custom Made, Standard and DIY Professional Rotary DJ-Mixers However, that schematic is far from simple, when comparing to that JFET setup. What in your opinion would be the main difference between the two? Or do you figure Bozure's design just uses the same concept repeatedly to achieve further functionality with the cueing, master, send receive etc
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Old 1st July 2014, 09:45 PM   #5
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I designed and built a valve disco mixer a few years back.
It had 2 stereo channels, a line input and a high gain mic input.
Loved the sound of it, gave the music a bit of color and bite.
However it was mono out.

Recently I revisited the project and designed a proper stereo version with stereo out as well. I must have improved with circuitry and pcb layout as this time it had almost zero noise/hum.
Click the image to open in full size.
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Old 1st July 2014, 10:48 PM   #6
bcmoore is offline bcmoore  Germany
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Wow, nice! that looks really interesting!
so, are those valves amplifying a phono stage to line level?
What is the summing process like in this case?
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Old 3rd July 2014, 05:13 PM   #7
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Comparing the JFET mixer to the Bozure is apples and oranges. One is a basic building block, and the other a complete working mixer circuit with 2 channels, input gain and master volume, FX send/receive, and even a separate headphone out with cue bending and dedicated volume control.

The equivalent of the JFET mixer would be the very first stage in the Bozure - same principles, only that the opamp makes a far better inverting amplifier.
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Old 6th July 2014, 02:30 AM   #8
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For 2 channels you can do passive mixing like this one but with -6db and high output impedance.
A preamp with short cables with this mixer is needed.
The only dj mixer that uses fet at the summing amp is the vintage Bozak cma-10-2dl
You can study the schematics here. Very tube like sounding mixer.
A British company have cloned it but I don't know with what part have replaced the fet 2N3822
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Old 6th July 2014, 12:48 PM   #9
bcmoore is offline bcmoore  Germany
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Thanks for the input guys. Much appreciated. Thanks for the links bozakdla! really helpful...yeah, I guess ideally the best would be 3 channels, just in case you want to add a CDJ (with line level input, no pre amplification required). So you're saying 3 channels wouldn't be possible with a passive setup?
I think you're talking about these mixers ?
pretty nice, not sure about the given valve phono stages, I feel like mixers should give the user the option of not having to have a colored phono stage.
there's also the condesa mixers, which claim to be fully discrete signal path as is the bozak. The Bozak is always praised for its "warmth" yet it doesn't use valves. I've heard that technically speaking, this "warmth" is really the result of THD for 2nd and 3rd harmonics due to its discrete signal path. Is this something that would be easily achieved with a passive mixer in your opinion?
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Old 6th July 2014, 12:50 PM   #10
bcmoore is offline bcmoore  Germany
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I guess the phono stages on the cma 10 are highly repsonsible for that "warmth" people talk about...
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