m00dawg Posted January 9, 2011 Report Share Posted January 9, 2011 As part of my attempt at designing a rackmount control surface for my MB-6582, I was thinking of having a phono jack up front and in the back for the mixed output. That way, if I want to just listen in quickly, I can just connect some headphones and what not. I was also thinking of using a volume knob up front. I know Wilba says the output from the mixed out is attenuated but it's actually pretty loud to me when using headphones. So I was thinking of having a volume knob up front. I assume I just need to get some logarithmic dual input pot (for left and right)? Any ideas on values for that? Also, and perhaps more importantly, I'm not sure how to handle the switching between the two phono jacks? I don't want to pickup noise when one (or both) are not in use. I know some jacks have internal switches I could use for that? I read that Wilba did something similar with the discrete audio outs on the MB-6582 board (see ) so I was thinking of something similar. I was going to use panel mount jacks as well so any advice on where to find those would be great :) Stereo or mono does not matter to me as much (I assume with mono jacks I tie both into the common ground?). Thanks for the help! Quote Link to comment Share on other sites More sharing options...
julienvoirin Posted January 10, 2011 Report Share Posted January 10, 2011 have a llok My link Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 10, 2011 Author Report Share Posted January 10, 2011 Ah looks like I was mostly on the right track. Only part I didn't totally follow was the headphone part. I understand I typical pot is not the best choice there but was not clear why. I know it had something to do with voltage :) Google Translate didn't do a great job there and unfortunately I do not speak French. The rest of it was very good information, thank you very much! Quote Link to comment Share on other sites More sharing options...
Imp Posted January 10, 2011 Report Share Posted January 10, 2011 Have a look at this then ! Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 10, 2011 Author Report Share Posted January 10, 2011 Wow tons of awesome info here! Thanks guys! Quote Link to comment Share on other sites More sharing options...
Duggle Posted January 12, 2011 Report Share Posted January 12, 2011 If you are using the pot to attenuate a headphone load, then you will want a pot with a resistance value similar to the impedance of the 'phones. Something like 100R log dual gang should do the trick. (not 100k like the french site.this value would be good for driving a hi impedance line input) Quote Link to comment Share on other sites More sharing options...
nILS Posted January 12, 2011 Report Share Posted January 12, 2011 I can highly recommend the CMOY Headphone Amp. If you feed the output of the sids to various pieces of equipment an extra buffer can never hurt :) Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 12, 2011 Author Report Share Posted January 12, 2011 I haven't tried it on my new headphones yet, but I found the audio to be almost on the loud side when tapping off headphone out on the MB-6582. But yeah I really want a volume knob for the front :) Given what you say, is it wise then to use the same buffer for both the front input and back? I was reading on Wikipedia and it seems like I won't have to do as much with switches as I thought given that many jacks included internal switches? I'll have to play around with that. Funny you mention that amp, I almost built one for powering my DJ headphones while on a plane but ended up grabbing a Li-Ion powered tiny thing. It probably doesn't work as well but it avoids having to go through a cavity search at security :) Now I have an excuse to build one potentially so that will be fun! It looks like I may need a bipolar power supply though? Would 12V work instead since I would need that for the filtering stuff anyway? Quote Link to comment Share on other sites More sharing options...
Imp Posted January 12, 2011 Report Share Posted January 12, 2011 When i built my CMOY, I used a voltagedivider to get -4.5v, Ground and +4.5V from a 9v-cell. But i think you can't do that with the supply of MB-6582. +/- 12v will do fine, though. Quote Link to comment Share on other sites More sharing options...
nILS Posted January 12, 2011 Report Share Posted January 12, 2011 Yes, you can do that with the mb6582 supply (or any other power rail for that matter). Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 12, 2011 Author Report Share Posted January 12, 2011 Hmm I guess I don't understand then because the schematic on the side has a +, - and ground? Quote Link to comment Share on other sites More sharing options...
nILS Posted January 12, 2011 Report Share Posted January 12, 2011 That's why you'd use a virtual ground (the resistor version will do). +9V becomes your V+, Gnd becomes your V- and the "virtual ground" between the Rs is your new ground. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 12, 2011 Author Report Share Posted January 12, 2011 Aha ok. That makes sense. Since I'm planning on a bipolar supply anyway, would it make more sense to just use that, though? In other words, would there be any benefit to one over the other (other than drawing less current from my 9V rail but I can't imagine that would change that much)? Quote Link to comment Share on other sites More sharing options...
Imp Posted January 12, 2011 Report Share Posted January 12, 2011 I'd use the bipolar supply, because of it's higher voltage. +-4.5v could be enough, while +-12v surely is. Also: you save 2 resistors or 1 divider-ic Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 12, 2011 Author Report Share Posted January 12, 2011 Do I need to worry about any voltage bias that way? I recall reading that AOUT (well, and the headphone amp too it seems) likes to have balanced +/- voltage. Since I would be using two things that both use a bipolar design, that seems like it would not be much of an issue? Quote Link to comment Share on other sites More sharing options...
Imp Posted January 12, 2011 Report Share Posted January 12, 2011 The CMOY has caps between input and op-amp, so any DC present in your signal can't get through and therefore won't be amplified. If the op-amp gets e.g. +12v and -11v as supply it won't hurt either. Quote Link to comment Share on other sites More sharing options...
nILS Posted January 12, 2011 Report Share Posted January 12, 2011 I was under the impression you'd want to fit the headphone amp in the mb6582 itself, in which case a second PSU would be somwhere between suboptimal and stupid. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 12, 2011 Author Report Share Posted January 12, 2011 I do, but I am also planning on adding analog filters which require a bipolar design themselves. I am also wanting to offer two methods of output - one at the back (which I will likely not add an amp to since that would go into my mixer) and one at the front, specifically for headphones. Quote Link to comment Share on other sites More sharing options...
nILS Posted January 12, 2011 Report Share Posted January 12, 2011 You won't be adding the filters to the mb6582 but you'll have those in an external box. So it seems more reasonable to me to keep the mb6582 as a standalone device with headphone out ;) Quote Link to comment Share on other sites More sharing options...
m00dawg Posted January 12, 2011 Author Report Share Posted January 12, 2011 (edited) Actually I'm converting my MB-6582 into a 3U rack, with the hope being I'll have a lot more room for things like filters. Correct, in a standard MB-6582 enclosure, I can't imagine how anyone would be adding filters. Edited January 12, 2011 by m00dawg Quote Link to comment Share on other sites More sharing options...
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