JohnAudioTech stereo to mono magic mixdown box with difference mode

This passive device allows you to convert stereo to mono and features L or R channel only listening and a difference mode.
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Thank You!

[@isoguy.]

Praying for your Brother, family and friends. Those musicians/ big corporate copyright owners will lose out in the end because nobody will ever hear their music. Really interesting box of tricks, thank you for sharing. 👍👍👍👍👍

[@cassvirgillo3395]

Hey John, I hope your Brother, you and your family are all doing good. You're all in my thoughts and prayers. You can look at prayers as the power of positive thinking if you're not religiously inclined. Very cool. Wishing you and yours all the best, Cass.

[@davidjones9730]

Made one of these, really useful and simple to build! Wins on all counts. Thanks for the circuit John. Great videos, I’m learning so much from your channel.

[@raymondheath7668]

Thank you!............2 hours later mine is complete and it works. Thanks again!

[@sayantanmaiti2513]

john audio tech is the best channel for learning about audio stuffs. really your channel was a breakthrough in my life as an engineer

[@manFromPeterborough]

Most stereo amps mono switch simply shorted the channels together, the Shure M78S cart has the channels summed - to - and + to +

[@1pcfred]

I must say I was expecting something more than just switches and resistors in that box.

[@Spentelectrons]

Same here. I was expecting a summing and differential op amp circuit.

[@1pcfred]

@@Spentelectrons that's about what I had in mind. Just goes to show how simple things can be though. I do admire minimalist simplicity too. There's just something about it that really does it for me.

[@extoprak]

Hi John, thanks for the awesome videos. I am planning to make an amplifier, something simple and I will get a couple of LM2876TF for free from a friend. Have you tried that before? The datasheet shows less THD compare to LM1875. Thanks.

[@oldmaine4314]

John, your “DIF” setting is similar to my experience. Many (many) years ago I used to hook the L+ and R+ outputs of my stereo to one speaker to create what was called a “phantom” channel for my favorite albums. I played and listened to these albums maybe a hundred times or more so I felt I knew every note and every small subtlety by heart. I was amazed. I’d hear things on stereo albums like Sgt Pepper that I never heard before.

[@JohnAudioTech]

I discovered this effect back in the 80's (even though it was used in the 70's for rear channel sound) when I miswired a stereo phono cartridge into a mono amp. My brother would love to hear his records in "cut out" mode as we called it because it cut the singer's voice from the music.

[@amitghosh6966]

@@JohnAudioTech how can we make Rear Left and right channels out of the Front Left and Right ones ?

[@Musinformation96]

Awesome build here! I’ll be breadboarding this one :-) Would be cool to see the 25th anniversary active version of this box - filters and such as you mention. I may be missing a fundamental concept… but do you think there would be any way to fade from diff mode to sum mode? Could be a really cool effect to go from out of focus to in focus. Have you ever looked at Douglass Small’s stereo width control schematic? It’s in Small Signal Design… maybe another cool idea for a video for you to do. Thanks for all the great info John, greatly appreciated.

[@analoghardwaretops3976]

IMHO.. the out connection with the 4k7 resistance should have been split with 2 resistances of either 2k4 or 2k7 and the junction of the two connected to the unused / open contact to common / gnd when switch is in" DIFF. " mode .....that will balance the impedance ..

[@amitghosh6966]

I have two demands : 1 Please make a stereo amplifier with surround sound system 2 please make amplifier system with Microphone output and mobile phones audio output mixing together so we can sing along with the music from mobile phone

[@mpingo91]

Have you ever try building some kind of pseudo-stereo circuit?

[@mpingo91]

Why only the input cable has to be shielded? I see the output one is just a twisted pair...

[@SixChris]

Hi John Thank you for your many informative videos they are very useful. I would like to ask you a few questions (two of which relate to your mix down box) I convert old radios to add music players and internet radio, they include a good quality stereo DAC with line level output. In the larger units i can fit a stereo amp and speakers, but on the smaller units this becomes a problem, so my questions are.. 1. can i use a stripped down version of you mix down box to provide a mono line level signal i can the feed to a single speaker, the output of the DAC would be switchable before mix down to provide external stereo line output, which leads me to my second question. Oh yeah how are the resistors sized?? 2. Can i simply split line level signals with a switch? Should I switch both line & gnd for both L&R? Are there any other precautions I should take? 3. My third question actually relates to one of your other videos.. You obviously like the LM1875 IC kits out there, my final question is.. The board needs a Ve+ & Ve- psu, most of my projects use a brick type PSU that most are just +Ve & Gnd, what would you recommend for an external PSU for the LM1875 IC, or could you recommend a different kit. Many Many Thanks in advance Chris

[@jprevard]

Gotta have Snickers!! I love your electronics videos but they just wouldn't be the same without Snickers! haha

[@johnsampson1096]

Really thorough explanation, John. I want to duplicate an Am top forty chain in mono. I will try using the two thousand ohm resistors summing left right channels into a small tube preamp and add some audio compression and limiting as well. Not a lot of dynamic range, but certainly loud! Would love your thoughts on compression. Thanks for informative videos. Stay healthy, John BTW From afar the sum position on your magic box sounds best............

[@ipissed]

So reduce to mono, make in dif mode, split the output to simulate stereo, sneak on system and when Snickers is playing annoying rap music he can't has bass? He no gonna like this. -Dog next door 🐶

[@TononiaWorld]

can the resistor values be change, and what would happen if you leave it without the 4k7 ?

[@garygranato9164]

hi john please make the more advanced summing circuit that you referred to in the video.

[@jp040759]

Nice tool I was expecting a capacitor in series to block any possible DC coming from the source.

[@alphahr]

Good info. The addition of the diff switch is indeed interesting

[@trevortjes]

This reminds me that I have a passive subwoofer lying around that I want to connect to an amplifier but I am not sure how I can mix stereo to mono without losing too much signal (because of passive mixer resistor values) or causing the protection circuitry of the amplifier to kick in. Any ideas on that?

[@trevortjes]

@ Already stated that it's a passive subwoofer :)

[@JohnAudioTech]

There really is not a good way to do this. It is better to mix the signals up front in a preamp stage and then use a separate subwoofer. A dual voicecoil subwoofer is another option.

[@SianaGearz]

My urge to that end would be to convert the sub to active.

[@creepingmee]

Such a simple way to encode 4 channel audio. How facinating. Thanks for this John. Best wishes to your family.

[@Mandrag0ras]

John, the wires you use on your diy audio jacks, like the red mono seen in this video, are they stranded or solid? Are they made of copper? What use are they made for?

[@amitghosh6966]

I think it's single strand wire like the commonly used in tubelight fittings. It's also called hookup wire used in breadboard for prototyping

[@rajivdogra1250]

sir how work dpdt switch

[@HammyTechnoid]

Way back in the '80s, there was a company called APT, and their line of preamps became legend because they were designed by Thomlinson Holman, the engineer responsible for the THX audio that nearly all modern movie theaters use, On the preamps there was a knob labeled *image* and it enabled a stereo spread adjustment using a potentiometer. Center detent was *normal stereo* , full left position was *mono* and full right was *middle/side* .

[@amitghosh6966]

Can this circuit be used to mix Microphone and mobile phone audio signal for feeding the power amplifier or for mixing two Microphones signal and feeding into the power amplifier ?

[@qwertyasdf66]

If the diff function is essentially the side channel, does that mean you could add a mid function? I'm guessing you'd have to take the diffed signal and then diff it against a summed signal.

[@SianaGearz]

Is it possible to add bypass switch with a single additional DPDT and a stereo output socket? Can't come up with an elegant way.

[@ferrumignis]

Need to be very careful of ground loops with a simple switch box like this, ideally you'd have a transformer on the output. Edit: You mentioned this about 30 seconds after I typed it!

[@uK8cvPAq]

Difference mode sounds like someone is playing music outside on a windy day.

[@KissAnalog]

Fun to see what was in your magic box;)

[@kokodin5895]

can you make a video about how old mono to stereo decoder worked?

[@TononiaWorld]

In you schematic diagram it shows that if you are in DIF Right channels is basically off, so you can't have the rich channel alone

[@SianaGearz]

DIFF mode connects right to sleeve of the output and left to the tip of the output. The difference is computed on the differential input of whatever device you're connecting it to. Sleeves of input and output aren't allowed to be grounded together, or otherwise channel R in DIFF would die indeed. This has been said in the video. So the circuit is only permitted with floating or battery powered player on the input. It cannot be used betweeen grounded devices.

[@TononiaWorld]

@@SianaGearz my statement was not only obvious, but redundant, I just posted cause it helps boost the channel rating in KZbin :) just a way on helping John, I love his channel

[@eugenepohjola258]

Howdy. I have been thinking along those lines lately. Been thinking about mounting both channel woofers in one enclosure to save space in my small apartment. The question has been should I use active filters and just sum the bass and use one separate bass amplifier and one woofer ? It turns out that this will deliver a level unbalance anywhichway one tweaks the levels. Ok. What happenes if one mounts both channel woofers in the same enclosure ? Well, if there is a bass signal in one channel, but not in the other, one woofer will deliver and the other just works as an acoustic short circuit. The woofers would need acoustic separation resulting in the enclosure volume (space) beeing acousticly halved. So. I've been thinking about doing say a 20 % channel intermixing. In my mind that would deliver enough signal to the passive channel woofer to fight the acoustic short circuit. I don't think this level of intermixing will deteriorate the stereo imaging. Regards.

[@JohnAudioTech]

It is much better the first way to sum the channels into an active filter and power amp for a subwoofer. The acoustic short circuit you speak of would not be complete due to resistance in the coil and other mechanical limitations.

[@eugenepohjola258]

@@JohnAudioTech Howdy. I posted this comment on PS Audio some time ago. What do you think ? Let us assume a frequency of 80 Hz just to be sure there is no directionality. The same signal is fed to both channels. We feed a voltage of U Volts corresponding to a power of P Watts into a stereo woofer system. we get a total output power of 2P. Then we have a common woofer with a single woofer amplifier. It is a summing amplifier. The voltage is 2U Volts and the power is 4P. So we reduce the signal to a level of 0,7U Volts. The sum signal is 1,4U Volts and the power is 2P. We might think we got the balance issue covered. Now let us consider the signal is fed only to one channel. The stereo woofer system will yield 0P + 1P = P. A common woofer system will yield only 0,7 x 0,7 P = 0,5 P. No matter how one tweaks the attenuations. There will be some unbalance. So yeah. I advocate using stereo woofers. Regards.