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Old 16th February 2020, 02:32 PM   #11
sgrossklass is offline sgrossklass  Germany
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Going unbalanced into active studio speakers / studio amps from a computer is just asking for trouble with ground loops - BTDT. Had to crank the input level trim way down back then. (A Behringer HD400 eventually came to the rescue.)

While you can always convert unbalanced to (impedance) balanced without too much of a problem, this requires constant output impedance - and if you need a volume control as well, that won't be the case in an all-passive setup. Like ol'd Einstein said - as simple as possible, but no simpler. Your idea qualifies as "too simple", I'm afraid.

Even if you do decide to go active, it seems quite hard to justify going DIY for this. Decent compact mixers, especially used, are cheap. You literally can't make 'em for what they cost. I would look for a decent mid-level Mackie or Yamaha or whatever (the kind with an external power supply). I almost can't imagine that there isn't anything of the sort floating around in Melbourne of all places. (Maybe a broken one if you insist making it a DIY project, but fixing stuff usually works much better when you're not totally green any more.)

Then you could concentrate your DIY ambitions on making some cables as far as still needed - 1x stereo TRS to 2x whatever unbalanced inputs the mixer takes (coax or shielded twisted pair with TP tied together), 2x TRS to XLR male balanced. I would make the unbalanced cable only as long as absolutely required, the balanced side would be far less critical.

Sorry to say, but sometimes the obvious solution is in fact the best one. People in the DIY realm have a certain tendency of trying to shoot themselves in the foot as hard as possible at times - this is definitely not my preferred approach.
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Old 17th February 2020, 03:44 AM   #12
Polym0rphed is offline Polym0rphed  Australia
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Originally Posted by sgrossklass View Post
Going unbalanced into active studio speakers / studio amps from a computer is just asking for trouble with ground loops - BTDT. Had to crank the input level trim way down back then. (A Behringer HD400 eventually came to the rescue.)

While you can always convert unbalanced to (impedance) balanced without too much of a problem, this requires constant output impedance - and if you need a volume control as well, that won't be the case in an all-passive setup. Like ol'd Einstein said - as simple as possible, but no simpler. Your idea qualifies as "too simple", I'm afraid.

Even if you do decide to go active, it seems quite hard to justify going DIY for this. Decent compact mixers, especially used, are cheap. You literally can't make 'em for what they cost. I would look for a decent mid-level Mackie or Yamaha or whatever (the kind with an external power supply). I almost can't imagine that there isn't anything of the sort floating around in Melbourne of all places. (Maybe a broken one if you insist making it a DIY project, but fixing stuff usually works much better when you're not totally green any more.)

Then you could concentrate your DIY ambitions on making some cables as far as still needed - 1x stereo TRS to 2x whatever unbalanced inputs the mixer takes (coax or shielded twisted pair with TP tied together), 2x TRS to XLR male balanced. I would make the unbalanced cable only as long as absolutely required, the balanced side would be far less critical.

Sorry to say, but sometimes the obvious solution is in fact the best one. People in the DIY realm have a certain tendency of trying to shoot themselves in the foot as hard as possible at times - this is definitely not my preferred approach.

Oh, I agree with Einstein (and you). Any attempt at finding a solution to this problem that may look like an over-simplification or over-complication is just an extension of my general lack of understanding of things.


I have started studying up on the fundamentals of electronics, but having no prior scholastic experiences in the sciences (at all), it is a minefield of new concepts - nothing too complicated for me to understand on a conceptual level so far, but it takes me a long time to properly absorb each layer of information before I can move forwards with less likelihood of becoming confused immediately haha


Perhaps I picked the wrong problem to try to solve as a DIY project huh?


I had thought it would be a little more simple ... from the layman's perspective, connecting an output to speakers should be pretty straight forward - adding a box in between that allows volume control seems like it should be simple too.




Am I correct then in stating that unless I'm plugging in headphones, I shouldn't use the 75ohm output to interface with speakers? It just seems like it shouldn't be so hard to do something that many users would inevitably consider doing.
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Old 17th February 2020, 04:25 AM   #13
indianajo is offline indianajo  United States
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Originally Posted by Polym0rphed View Post
Am I correct then in stating that unless I'm plugging in headphones, I shouldn't use the 75ohm output to interface with speakers? It just seems like it shouldn't be so hard to do something that many users would inevitably consider doing.
You can do it, but it is likely to be noisy. A cheap experiment except for all the hole drilling & sawing. Instructive. Don't try to parallel the two channels for centered bass without 1k resistor in series with each hot. Use a recipe box from charity resale shop, shouldn't cost you more than $30 except for tools. I don't buy $$$ punches for big or square holes, I drill many 1/8" holes and connect the dots with a Stanley carbide hacksaw blade.
To sgskloss point, you'll get good music quicker with a new mixer, but repairing a used one may be above your training. PV6 & PV8 have TRS cable drive (ring is phantom but that works quietly into twisted pair) I don't know about the cheaper mixers out there are the same. I changed the volume pot on the PV8 in only 8 months, most of it staring at it and wondering what to do next. Finding the reason for a dead channel took another 3 months, probing with an analog VOM to follow the music flow. Bit subtle for a newbie. I'm experienced enough to not blow up IC's with the probe.
Read the analog devices tutorial on single op amp gain circuit, the inverting one is fewer parts. Or another electronics tutorial. It's $10 from turning a passive splitter box into an active drive. Plus $100 in test equipment, either a scope or a good analog VOM with 20 vac & 2 vac scales. DVM make up random numbers on music, are great for DC analysis.
BTW, I do experiments that fail. Trying to do CCS (constant current source) this month, JFET single part solution was a big failure. Actual Idss was 7 times the "typical" on the datasheet, WAAY too big, and current out was sensitive to the voltage it pumps into, also.
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Last edited by indianajo; 17th February 2020 at 04:32 AM.
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Old 18th February 2020, 06:56 PM   #14
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by Polym0rphed View Post
Am I correct then in stating that unless I'm plugging in headphones, I shouldn't use the 75ohm output to interface with speakers? It just seems like it shouldn't be so hard to do something that many users would inevitably consider doing.
Then you would need some speakers that are a bit more accommodating to the consumer audio realm though. (Home) Studio gear has a habit of being IEC Class I (mains earth referenced), just like your PC - not a good combination with unbalanced audio connections. You'd need something floating (IEC Class II appliance, double insulated), as common in consumer audio and traditional hi-fi.

Your headphone output ultimately is much the same as a consumer line/headphone output, just a bit louder. So you can expect to encounter the very same problems that people have faced trying to connect studio gear to those for years - and the same solutions.

If you didn't need an external volume control, it wouldn't be that bad. You could use an external line isolator like the aforementioned Behringer HD400 and enjoy your silence. But when you are looking at kludging together that plus a monitor controller, the (technically better) mixer starts looking like the more attractive solution, especially if you can also make some "ground lift" (shield disconnected) balanced cables for the run from mixer output to speaker amp input (otherwise ground loop currents could still take the route PC output ground --> unbalanced audio cable shield (the problematic part) --> mixer --> shield of balanced connection --> speaker amp ground).
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