MissionBrown Posted August 10, 2010 Report Share Posted August 10, 2010 For all intents and purposes, my MB-6582 is complete. I have used PSU option A. The PSU itself works properly, everything measures normal. But... I have this huge hum on the audio lines. It gets worse when I connect the fan and is really loud when I use the feedback pots. I've tried mix/matching the two c64 psu's I have. eg: breadboarded to use the AC and DC supply from each and the noise remains. Even used a separate regulated 5v supply. The only thing different in the PSU filter from the spec is that I'm using a Greencap on c2 instead of a Monolithic. Could this be the problem? Any help would be most welcome. I really want to close this thing up and get playing it. Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 10, 2010 Report Share Posted August 10, 2010 Is it a 50Hz hum type thing, or is it more of a buzz / roar type noise? The SID's are noisey F#@ers. I realise you are using the feedback pots, but disconnect these, and tie all the SID input pins to ground (with the small jumpers) Does the noise go away then? Regards Mike Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 10, 2010 Author Report Share Posted August 10, 2010 Is it a 50Hz hum type thing, or is it more of a buzz / roar type noise? The SID's are noisey F#@ers. I realise you are using the feedback pots, but disconnect these, and tie all the SID input pins to ground (with the small jumpers) Does the noise go away then? Regards Mike Hi Mike, The hum was there when the in was tied to ground (the pots took a while to arrive from OS). It's a lot worse with the feedback dialed up (lots of noises), but more like the 50hz hum on the lines. Though I haven't looked at it with a scope to nail down where the buzz is located. I could live with it if I have to, but I really don't want to. The machine is near perfect! :frantics: Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 10, 2010 Report Share Posted August 10, 2010 Hi Mike, The hum was there when the in was tied to ground (the pots took a while to arrive from OS). It's a lot worse with the feedback dialed up (lots of noises), but more like the 50hz hum on the lines. Though I haven't looked at it with a scope to nail down where the buzz is located. I could live with it if I have to, but I really don't want to. The machine is near perfect! :frantics: How much gain do you have to give the synth to get it up to a decent level? Is the hum on all the outputs? I recall some issue once with the switch jack sockets being incorrect.. But I doubt this is your issue, unless you have to gain the crap out of it to get a decent level. My 6582 is pretty damn quiet, so something is obviously wrong with yours. Maybe check all your components around the power section.. maybe an electrolytic cap with wrong orientation etc.. It could be that your analog power is too low before the regulator, causing it to sag. What measurements do you get before and after that section. It's not likely the 5v supply. (Could be, but I feel unlikely) Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 10, 2010 Author Report Share Posted August 10, 2010 Thanks Mike, The levels in my mixer are pretty good. I set the input trimmers to 0 and the faders to unity. The hum is there loud and clear. You can't really hear it when playing the lead, poly and bass engines, but is evident with the drum engine in the gaps between notes. The voltage I get on the psu is 9vac, after the rectifier is just shy of 12vdc on average. The 5v section drops to 4.7-4.9vdc and the 9v regulator outputs about 8.7vdc Would it be a problem to feed 12vdc to the 9v regulator without removing the rectifier? I'm at work for the next 8 hours so I can't check my cap orientation for a while, but I am pretty sure that they're oriented properly. While I have built loads of stuff over the years, nothing has been so arduous as building this machine. That said, if I could spare the cash, I'd happily build another :) Cheers A Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 11, 2010 Author Report Share Posted August 11, 2010 Checked my caps. All oriented properly. Should I try a beefier PSU and go for option c? Jaycar 2a AC psu. Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 11, 2010 Report Share Posted August 11, 2010 So, you are using a C64 power supply? I know they are a pain to get, but have you tried another? Maybe borrow someones? I had one 1/2 work, another work, then die, then finally, one that worked all the time. As my 6582 had a built in keyboard etc, I used this http://www.jaycar.com.au/productView.asp?ID=MP3108&keywords=switchmode&form=KEYWORD (expensive, yep, and now cheaper alternatives are available online) The 5v Rail sucks a fair bit of juice on the MB6582.. about 1Amp iirc. While the 9v / 12v a fair bit less.. You could try to feed in another supply to the rectifier & regulator (option C).. I'm a bit concerned about you measuring 8.7v instead of something more close to 9v. It could be your multimeter, but I thought a 7809 would be closer to 9v. Can you explain 'the 5v drops to 4.7v-4.9v' ? How about a small audio sample? Cheers Mike Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 11, 2010 Author Report Share Posted August 11, 2010 (edited) Good morning Mike I didn't think about my MM being off the mark. I'll have to dig up my spare and check. I did measure 9v from a 7809 on my breadboard fed by a 12vdc supply(no load). Same with the 7805 I tried(got 5.1v) but that sucker got really hot under load. While it did power the 5v rails of the mb-6582 it got really got and started to make that electronic death smell so I shut it down. In any case the Hum was still there, so I think the problem is indeed with the 9vac supply of the c64 psu. I actually have two of them(c64 supplies), one can only power the synth if I have 6 sids maximum on board. Any more than that and the supply from the 5v rail drops to 1v. I did as you suggested and mix n matched the different rails via my breadboard and the hum remains. As it happens I do have a similar switchmode in the house that I bought to use with my MusicFromOuterSpace modular(awaiting rebuild again). It's a +-15 and +5 supply made by Meanwell(I think 60w, it's in an enclosure). 15v should be ok on the 9v regulator shouldn't it? I noticed the 7809 on the MB6582 barely gets warm, but am concerned about how hot the 7805 got on my breadboard without a heatsink. Will need to get another heatsink and do further testing to make myself comfortable. Another thing I thought of after I read your post is that there is concern of the voltage being below the 9v mark after the regulator. This happened with two regulators, is there a possibility of a bad cap or a solder bridge causing this problem? Maybe a faulty chip? Cheers A Edited August 11, 2010 by MissionBrown Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 12, 2010 Report Share Posted August 12, 2010 Whoah.. too many variables.. Why are you using a 5v Regulator? The C64 outputs 5V.. if it's crapping out with too many SID's installed, the C64 power supply is not so good. (It happens, they are old) How about running your MB6582 Option A (C64 Power supply) with only a two SIDs in.. do you get hum? (I asked earler, is the noise / hum on all outputs, you never replied regarding that) I can't see how your 9v AC can be bad.. it's just AC from the C64 transformer.. then it gets rectified (turnt to choppy DC).. then smoothed by the caps.. (Bumpy DC) then rectified by the 9v regulator = Smooth 9v DC. (regulator c o u l d be faulty.. only a $2 part, maybe worth trying) If you used a 5v regulator to get 5v DC.. and you are say feeding it 9vDC, and a fully stuffed MB6582 pulls about 1amp on it's 5v Rails. The voltage drop across the regulator is gonna be say approx 4v x 1Amp = 4 Watts of heat. that little guy ain't gonna cope being a small heater for too long.. lol. If you use a switchmode PS as you mentioned, and feed that 9vAC input on your 6582 with 15v DC, that'll be fine.. the regulator may get warm / hot but should be ok to try. Regards Mike Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 12, 2010 Author Report Share Posted August 12, 2010 Whoah.. too many variables.. Why are you using a 5v Regulator? The C64 outputs 5V.. if it's crapping out with too many SID's installed, the C64 power supply is not so good. (It happens, they are old) How about running your MB6582 Option A (C64 Power supply) with only a two SIDs in.. do you get hum? (I asked earler, is the noise / hum on all outputs, you never replied regarding that) I can't see how your 9v AC can be bad.. it's just AC from the C64 transformer.. then it gets rectified (turnt to choppy DC).. then smoothed by the caps.. (Bumpy DC) then rectified by the 9v regulator = Smooth 9v DC. (regulator c o u l d be faulty.. only a $2 part, maybe worth trying) If you used a 5v regulator to get 5v DC.. and you are say feeding it 9vDC, and a fully stuffed MB6582 pulls about 1amp on it's 5v Rails. The voltage drop across the regulator is gonna be say approx 4v x 1Amp = 4 Watts of heat. that little guy ain't gonna cope being a small heater for too long.. lol. If you use a switchmode PS as you mentioned, and feed that 9vAC input on your 6582 with 15v DC, that'll be fine.. the regulator may get warm / hot but should be ok to try. Regards Mike Oops sorry. I thought I'd got to that point. Yep, noise is on all outs. I only started messing with a 5v regulator after both of my c64 psu's yielded unsatisfactory results. I have used two different 9v regulators and the noise is still there. The noise does get worse when i connect the fan, that's the #1 reason I suspect the regulator isn't getting enough input. Yesterday I read that regulators need 30% more input than they output to regulate smoothly. Will try the 15v PSU as well as remove some SIDS on the c64 PSU that at least powers the whole lot, even if it is noisy. Fingers crossed! Quote Link to comment Share on other sites More sharing options...
nILS Posted August 12, 2010 Report Share Posted August 12, 2010 A sample of the noise might help us to identify where it's coming from ;) Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 12, 2010 Author Report Share Posted August 12, 2010 A sample of the noise might help us to identify where it's coming from ;) As requested, the noisy noise. Starts with input tied to ground, ends with feedback all the way up.noisy noise.mp3 Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 12, 2010 Author Report Share Posted August 12, 2010 Just did some more measurements with my "working" c64 psu. The DC after the rectifier is only 10.5v the DC after the regulator is 8.7v 5v measures 5v. So I'm guessing the regulator aint getting enough juice. Furthermore I took Mike's suggestion and removed some SIDs from the board. 8 x 6582 = Lots of Hum 8.7v 6 x 6582 = less hum 8.8v 4 x 6582 = No Hum 8.9v Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 12, 2010 Author Report Share Posted August 12, 2010 (edited) More power was the cure. I ran my 15v switchmode PSU into the 9v reg and the hum went away. I used c64's 5v rail in the test and it was just fine. Thanks guys. Now I need to donate some beer money to 4 people :) If anyone is interested I used the Meanwell T-60c +-15v +5dc switchmode PSU. Nice and quiet. PDF Specs I think it cost me $60 Aussie clams. Edited August 12, 2010 by MissionBrown Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 12, 2010 Report Share Posted August 12, 2010 Good to hear.. Well done. Quote Link to comment Share on other sites More sharing options...
nILS Posted August 14, 2010 Report Share Posted August 14, 2010 Hehe, too late to respond, but anyways: Regulating 10.5V to 9V with a 7809 is too tight. The regulator needs some Volts to burn. Also the fact that the voltage drops with all 8 SIDs (= more current consumption) usually indicates that the PSU can't deliver enough current, which (following Ohm's law) causes a voltage drop. Now you get no noise from the switching supply? Switchers tend to be really noisy, if you found one that's quiet - woohoo! Can we have a sound sample with the new PSU, please? Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 14, 2010 Author Report Share Posted August 14, 2010 Hi nILS, I'll get you a sample as soon as I've re-housed the PSU and modified the MB-6582 to permanently accept the new power arrangement. This is the first time I've worked with Regulators. Actually the first time I worked with Pics too. The feedback pots do pickup noise irradiating from my PC. As for the switchmode PSU, several of the VicMod guys have the t-60c and have reported no problems with noise when powering their Eurorack modulars. Anyway, I hope to get it done today, but I do have a child and that does slow down building time considerably (not that I mind). Quote Link to comment Share on other sites More sharing options...
nILS Posted August 15, 2010 Report Share Posted August 15, 2010 Hey, no hurry :) This here is fun, not work! I just really like the idea of having a noiseless switchmode option - a lot of people have been looking for that! :thumbsup: Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 16, 2010 Report Share Posted August 16, 2010 When I built my MB6582, I A/B'd between a switchmode power supply and a C64 power supply.. And even with the gain right up, the change in background noise was negligible. Many people who are racking up Neve / Calrec / SSL / Ward-Beck etc channel strips are using switchmode power supplies, so I guess they can't be that bad. I guess YMMV. Cheers Mike Quote Link to comment Share on other sites More sharing options...
nILS Posted August 16, 2010 Report Share Posted August 16, 2010 Many people who are racking up Neve / Calrec / SSL / Ward-Beck etc channel strips are using switchmode power supplies Correct, but certainly not the $5-15 ones you get at pretty much any store, right? :yes: Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 16, 2010 Report Share Posted August 16, 2010 (edited) Correct, but certainly not the $5-15 ones you get at pretty much any store, right? :yes: True, but you didn't mention $5 - $15 being your budget. I guess if you fork out $60+ on a power supply, you'd hope it'd have better performance than a $5 special from a junk shop. Most of the geezers racking up channel strips are using 2x laptop power supplies to give them +/-24 v DC. those power supplies are not toooo expensive, say around $30 each. Regards Mike Edited August 16, 2010 by Futureman Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 16, 2010 Author Report Share Posted August 16, 2010 Seem to have a wee power hiccup. Psu don't seem right when plugged in and mb-6582 switched off.... Need to take pic of my mods and get some more advice. One thing though, should I remove the big psu filter caps now that I'm using option D? Quote Link to comment Share on other sites More sharing options...
nILS Posted August 16, 2010 Report Share Posted August 16, 2010 True, but you didn't mention $5 - $15 being your budget. It isn't. It seems to be what the average boxer is spending on a noisy switchmode PSU though ;) And you can pretty much pick any off the shelf $50+ puter PSU and get some really nice heavy noise. Quote Link to comment Share on other sites More sharing options...
MissionBrown Posted August 17, 2010 Author Report Share Posted August 17, 2010 So.... I'm a little paranoid because I've broken several things in the house today (blew up a humidifier while cleaning it and kicked over a glass in my work area, shards glass and water all over the floor). I don't want to kill my PSU or synth. Anyway, on the mb-6582 rev 2 board, where should I put the positive and negative leads from my PSU for the 9v lines(being fed by 15v)? That is, before the switch where its marked 9VAC. With the board facing me as if it were in the PT case. Do I put the + on the left or the right? I've removed the rectifier and left the caps in place before the regulator. Should I remove those caps? Nearly there....... :thumbsup: Quote Link to comment Share on other sites More sharing options...
Futureman Posted August 17, 2010 Report Share Posted August 17, 2010 (edited) No need for you to remove the rectifier or caps. Leave em in. (If you took em out, and you can, put em back in) The rectifier will rectify the already DC into DC & will drop the 15VDC down by 0.6V and then feed this new 14.4VDC past the caps (Will smooth out the already smooth DC) and then into the 9V regulator. No big deal. no harm done. Leaving the rectifier in will protect your caps and regulator incase you get the polarity of your switchmode wrong. Regards Mike Edited August 17, 2010 by Futureman Quote Link to comment Share on other sites More sharing options...
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