Per one of my earlier notes, I took out my BB opamp part U4 and replaced it with a rewired Tl074 where I lifted the ground pins 3, 5, 10, 12 and rewired them to a different ground. Bottom line: Using a different ground for U4 made very little improvement in noise. It did reduce it a bit, but the noise reduction is not worth the effort. I even tried 4 different new ground locations,including the main ground by the xmfr, but none of the grounds resulted in any meaningful noise reduction. Anyway, this hack is not worth doing. Back to the drawing board... --- In k5synth@yahoogroups.com, Antoine Deschênes <antdes45@n...> wrote: > Good opamps might not change the noise amout that much. But I know wiaht > 2 opamps in parallel are doing with noise is like what 2 resistors in > parallel are doing: reduce it(noise in the case of opamps if it's not > series, I've read this somewhere) > > antdes45@n... a écrit: > > > Well, in my case, the mixer is pretty niosy too(A Kawai MX8R mixer > > from the same year), and I've never found Multi louder than Single nor > > Singles louder than Multi, nor that Mix is more noisy than > > Singles(Tried with VU meter too, maybe it's the same for you since you > > changed your opamps, but maybe you haven't changed the 4 opamps as I > > did). I've already plugged the K5 directly in the SBLive line in(Which > > is -90dB), but obtained a -46dB at the volume I get a -90dB without > > source on the SoundForge VU Meter. > > > > It's pretty noisy I know it, idtheory.com has a 6MB MP3 made with 2 > > K5s in 1991. > > > > nelsonj_sce@y... a écrit: > > > >> > >> You wrote: "I only use MIX output and headphones" > >> I don't use the MIX now, rather, I stack everything in a Multi to a > >> single output , Out 1 usually. It makes the sound cleaner because you > >> skip one of the op-amps. You might want to try this trick to help > >> clean up the sound. > >> > >> --- In k5synth@yahoogroups.com, Antoine Deschênes <antdes45@n...> wrote: > >> > You told a couple of replies before "I suppose you now have socketed > >> > opamps, like me", well I don't have some, I forgot to ask them at > >> the shop. > >> > > >> > "U1 if you use MIX" > >> > I only use MIX output and headphones. I don't have time/want to build > >> > some 4 ½ m wires. And my mixer is 8 channels : 2 for the first Roland > >> > D110, 2 for the second one, and 1 for the K5, if I would do that, I > >> > would lose all the 3 other inputs, which I use sometimes. Also, I > >> don't > >> > use the K5 for recording or anything else, I modifiy it even if I'm > >> just > >> > playing it when I've got nothing to do. The K5 is just a kind of toy > >> for > >> > me(And my father owns it, and uses it rarely to use it as a controller > >> > in Finale). > >> > > >> > nelsonj_sce@y... a écrit: > >> > > >> > > > >> > > You wrote: "They connected the non-inverting(+) input(if I'm > >> right) to > >> > > the DG?!?" > >> > > Not directly. The schem show that the (+) is connected to the > >> AG, but > >> > > it appears from the wiring board layouts that the AG and DG have > >> > > ground planes that connect in several places. So basically, there is > >> > > no physical seperation of the AG and DG ground planes on board > >> MI-004. > >> > > As a result the (+) is connected to this single ground plane that has > >> > > both A and D parts on it. > >> > > > >> > > > >> > > You wrote: "What's the VCA's ground?" > >> > > The same dirty AG/DG ground as that of U4. The VCAs are parts > >> IC6 and > >> > > IC7. The ground is pin 3, there is also a ground through a cap on on > >> > > pin 5 but this look like protection rather than ground. I am not > >> sure > >> > > if pin 3 is the third pin from the top or from the bottom, but pin 4 > >> > > is -A6. It can't hurt to move the VCA's grounds to a clean ground > >> > > also. Note that it looks to me that the VCA's do not play the > >> role of > >> > > traditional synth VCAs, but rather the are connected directly to the > >> > > main volume slider via pin 5. They don't seem to have any other > >> > > control voltages so my guess is that all the VCAs do is control the > >> > > overall volume of the keyboard. If that is the case, I am note sure > >> > > that a dirty ground will inject noise. But again, it can't hurt to > >> > > make sure they have a clean ground. > >> > > > >> > > So here is my plan: Step 1 is change the ground on U4 (and U1 if you > >> > > want to use the Mix output). Step 2 is change the ground on the > >> VCAs. > >> > > Parts U8 and U9 are set up as non-inverting amps and do not have any > >> > > direct connections to ground so no grounding to change here, but they > >> > > have that shielding that we may be able to improve as Step 3. > >> > > > >> > > I may be able to do step 1 tonight - it all depends on how sleepy my > >> > > baby is! > >> > > > >> > > > >> > > --- In k5synth@yahoogroups.com, antdes45@n... wrote: > >> > > > Pulling the DG from the boards not PSU board(Impossible, without > >> > > removing a bridge rectifier), I've already used the PSU without the > >> > > big brown connector full of wires for power and ground of the boards. > >> > > > > >> > > > They connected the non-inverting(+) input(if I'm right) to the > >> DG?!? > >> > > > Well, sure it will make noise, if that ground is that much noisy, > >> > > that would be like to plug a phono playing in the input and wondering > >> > > why you hear it.(Well, that's what I think) > >> > > > > >> > > > What's the VCA's ground? > >> > > > > >> > > > Also, they put two mono DACs for 4 channels, so (My theory) the > >> > > analog sound is passing thru a kind of flip-flop that switches > >> rapidly > >> > > the input from 1 to 2 to 1 ... and the other with 3 and 4. As I only > >> > > have a part of the output board, the opamp section and the > >> PSU(Thanks, > >> > > > > >> > > > > >> > > > "nelsonj_sce" <nelsonj_sce@y...> wrote: > >> > > > > >> > > > > > >> > > > >Antdes, > >> > > > >Ok, I still have more work to do but I did look more at the schems > >> > > > >while on a plane today. Some thoughts... > >> > > > >1) DO NOT simply remove the DG ground on the power supply and > >> reroute > >> > > > >it to the AG (black transformer wire). If you do this the > >> inverter > >> > > > >for the backlight (as well as several caps and part D6 WILL NOT BE > >> > > > >GROUNDED. Basically the DG does not terminate on MI-010, rather > >> > > > >MI-010 needs the connection <CN1> in order to be grounded. I > >> am still > >> > > > >looking at things but it seems the main ground for the MI-003 > >> &MI-004 > >> > > > >comes from where they are screwed in to the K5 case. > >> > > > > > >> > > > >2) Although I am not 100% sure, it appears that for some > >> reason, on > >> > > > >board MI-004 the DG and AG are actually connected. Board > >> MI-003 is > >> > > > >all digital so the ground is pure digital. If I am correct, > >> and the > >> > > > >AG and DG grounds are not separated on MI-004, this may be the > >> source > >> > > > >of the noisy ground. The bad news is that there is no quick > >> way to > >> > > > >separate the grounds on MI-004. > >> > > > > > >> > > > >3) Part U4 (the op-amp right after the VCA that we have both > >> replaced) > >> > > > >has my attention. It has four inverting op-amps, where the "+" of > >> > > > >each amp is connected directly to the dirty ground. It is > >> possible > >> > > > >that the dirty ground is basically injection noise to these amp. > >> > > > > > >> > > > >I think we both have replaced this op-amp and it is now in a > >> socket. I > >> > > > >plan on taking out the amp(this is a total hack but if it works > >> I can > >> > > > >make it look nice later), and then bending connections 3, 5, > >> 10, 12 > >> > > > >(the grounds) out so that they do not connect to the socket/dirty > >> > > > >ground on board MI-004. Then, I will wire these connections > >> directly > >> > > > >to the K5's case to try and get a clean ground. > >> > > > > > >> > > > >4) If that does not help lower the noise, I am looking at lines > >> g0-g7 > >> > > > >that feed the op-amps U8 and U9. These are the only analog signal > >> > > > >lines that have Faraday shielding. These are low level lines > >> early in > >> > > > >the analog signal chain. If nosie gets in to these lines, the > >> nosie > >> > > > >will get amplified in each of the following amp stages. > >> Perhaps there > >> > > > >is a way to improve the shielding on these lines or to change the > >> > > > >grounds related to these singal paths...but I have to think > >> about how > >> > > > >to do it. > >> > > > > > >> > > > >Anyway, I will let you know what happens after I reground U4. > >> > > > > > >> > > > > > >> > > > > > >> > > > > > >> > > > >--- In k5synth@yahoogroups.com, antdes45@n... wrote: > >> > > > >> That's it, AG is analog ground, DG digital ground, +A6V dc > >> analog > >> > > > >6v. . . > >> > > > >> The kind of fork for the analog ground is an other sign for > >> ground, > >> > > > >maybe they mean different connection places, as the fork like > >> is used > >> > > > >for antenna too. But I think it's just a country/continent > >> difference. > >> > > > >> > >> > > > >> "nelsonj_sce" <nelsonj_sce@y...> wrote: > >> > > > >> > >> > > > . . . Cut the file, was 62k. > >> > > > > >> > > > -- > >> > > > Antoine Deschênes > >> > > > aka DragonMaster > >> > > > http://thehotcom.deep-ice.com/ > >> > > > Files:http://angelfire.com/ca7/hotcomcenter/ > >> > > > > >> > > > > >> > > > __________________________________________________________________ > >> > > > Switch to Netscape Internet Service. > >> > > > As low as $9.95 a month -- Sign up today at > >> > > http://isp.netscape.com/register > >> > > > > >> > > > Netscape. Just the Net You Need. > >> > > > > >> > > > New! Netscape Toolbar for Internet Explorer > >> > > > Search from anywhere on the Web and block those annoying pop-ups. > >> > > > Download now at http://channels.netscape.com/ns/search/install.jsp > >> > > > >> > > > >> > > > >> > > > >> > > Yahoo! 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Message
Re: Notes on Schems...update on grounding experiment
2004-10-17 by nelsonj_sce