I'm working on a cd player and have been getting some scope traces to see what noise levels exist at various points and have finally decoded (somewhat anyway) what I'm seeing. I'm using a 300mhz analog tek scope and get traces of the clock frequency (16.9344mhz) which occurs at probably what would be normal levels. Limiting the BW to 20mhz is what I use for this measurement and there does not seem to be much else on the trace. However, using the entire BW, I'm picking up all kinds of freaky stuff. I'm sure partly what I'm getting is just noise pickup by the probe, but I'm pretty sure there's a real signal in there after having messed around with it enough. Probably the most interesting reading came directly at the 5V regulator output in the form of a high frequency decaying toneburst waveform. Weird, huh? I counted the period and it measures about 250mhz. Other probe points showed a more steady frequency and resembled just noise until I played around with the probes enough to get a more clear reading of a steady frequency going on in there. I'm just curious if there is indeed some signal content in the digital portion of the circuit that warrants this measurement, or if there's some spurious resonance thing going on here, or just my measuring is introducing problems where none exist. Anyone else have similar experiences? I did some minor playing around like using a ferrite bead I had on hand in place of one of the jumpers being used on the power bus (I make no claims that I'm working on the best laid out circuit) but it actually seemed to make one test point a little worse which I thought was kind of odd. I'd really like to tame these power rails, at least for the sake of getting clean power to the clock pins.
I did some review over "how-to" measurements for digital circuits and this includes keeping the ground lead of the scope probe close to, or even partly wrapped around, the probe so as to minimize noise pickup. For example, taking a reading of a power pin could be done by connecting to the decoupling cap directly at it's + and - leads, instead of placing the 2 leads inches apart (which is otherwise more realistic but not good practice). I did notice differences in noise levels by using various methods. It is hard to get it the way you want to since layout doesn't always cooperate.
Anyone?
I did some review over "how-to" measurements for digital circuits and this includes keeping the ground lead of the scope probe close to, or even partly wrapped around, the probe so as to minimize noise pickup. For example, taking a reading of a power pin could be done by connecting to the decoupling cap directly at it's + and - leads, instead of placing the 2 leads inches apart (which is otherwise more realistic but not good practice). I did notice differences in noise levels by using various methods. It is hard to get it the way you want to since layout doesn't always cooperate.
Anyone?
Well, I have been busy tracing the circuit, finding out more, and installing new oscons (UCC PSA) and ceramic bypasses on the digital board trying to tame the rails and have succeeded to a degree. I was able to improve noise levels by a number of magnitudes. My #1 aim was to get clean power to the clock, but I felt it was important to get it anywhere I could once I got in and started testing. A separate clock p.s. that seems to be so popular isn't really possible in my cd player since it's traces are combined with others, namely the input serial data (w/clock) as read from the disk. Anyway, there does seem to exist a noise floor in circuit since even ground has a level. I'm kinda baffled by it so far and am still dealing with it I guess, even after having made some custom copper tape cabling for a makeshift ground plane.
I used this as a stopping point to listen and I thought I could detect a rather apparent change right off even before the system got warmed up. What I thought I heard was foremost a change in presence, or realism to the instruments. It seemed to become even more pronouced as the system warmed up. I'd have to listen more to make more of an evaluation, but the major change I think I have picked up on. I know that getting cleaner power to the clock can only help and perhaps this is mainly what I detected, but I also suspect that cleaning up the 1's and 0's might have made a difference, for example in altering the inherent hoise content. This may be an outrageous comment. I don't know cause I'm still learning what goes on inside a cd player. The only thing I do know is that p.s. rails have been improved by getting the noise levels down. I see no low frequency modulation of any sort or any additional high frequency funny business going on looking back and forth between idle and playing conditions just with the methods of using a wide BW scope, so perhaps all remains well. It certainly sounds like it anyway. And I havent even started with the analog board.
I used this as a stopping point to listen and I thought I could detect a rather apparent change right off even before the system got warmed up. What I thought I heard was foremost a change in presence, or realism to the instruments. It seemed to become even more pronouced as the system warmed up. I'd have to listen more to make more of an evaluation, but the major change I think I have picked up on. I know that getting cleaner power to the clock can only help and perhaps this is mainly what I detected, but I also suspect that cleaning up the 1's and 0's might have made a difference, for example in altering the inherent hoise content. This may be an outrageous comment. I don't know cause I'm still learning what goes on inside a cd player. The only thing I do know is that p.s. rails have been improved by getting the noise levels down. I see no low frequency modulation of any sort or any additional high frequency funny business going on looking back and forth between idle and playing conditions just with the methods of using a wide BW scope, so perhaps all remains well. It certainly sounds like it anyway. And I havent even started with the analog board.
Hi Retro,
It's probably not important but I just wanted to say that I am very interested in your results. I'm just starting to tackle power supply noise within my player but I don't yet have a proper 'scope. I guess I'm flying blind!!
I'm quite surprised that no-one else has chimed in yet. Keep up the good work and I'll be following your progress very closely.
Kind regards,
Martin.
It's probably not important but I just wanted to say that I am very interested in your results. I'm just starting to tackle power supply noise within my player but I don't yet have a proper 'scope. I guess I'm flying blind!!
I'm quite surprised that no-one else has chimed in yet. Keep up the good work and I'll be following your progress very closely.
Kind regards,
Martin.
Hi Sonus - Thanks for a reply. Doing the digital board has been interesting and a change from doing analog. It's a different world for sure and the wide BW scope has been a big help in seeing what I have. When I got it a few years back it was mainly for seeing oscillatory behavior in analog. I think it's a must have for any serious work in digital - just my opinion however. The caps I used turned out to be about the same in value as the stock caps, it's just that oscons are much better. The value must have something to do with operation too since I installed a number of different values to see what worked best. I thought that lesser value ones of better quality would be the best but that does not seem to be true, at least for this particular player. I guess one guide to be used is that we should remember that we're dealing with MHZ here and that 3-terminal regs do not really operate in this region effectively, so it's all about the cap taking over and doing the job. I haven't decided at this point if I'm going to pursue the digital board some more or go on to the analog. I did see something interesting during my last testing. Those decaying tonebursts I mentioned in the first post look like they might be a product of a clock (not the 16mhz one) I'm picking up from the data receive chip . It's a 5mhz clock, so the board label says, and it looks like it's been manipulated into a toneburst shaped waveform, or just the envelope rather, without the fill. I was expecting the usual sinewave shape for a clock signal. It's on it's own 5v reg. too, so perhaps I'm picking up ground bounce (or whatever) at the other 5v reg. output. I'm sure I'd uncover more if I went looking, but it's not easy taking it all apart to make access for something that is not meant to have access, only to turn around having to do it all over again. I'll wear out the connectors if not carefull. More later.
Oh yeah, something else I forgot to mention - I wondered about the XO (crystal oscillator) and how they are supposed to be so super sensitive to voltage supplies and vibration. Well, for a vibration test, I lightly thumped on the crystal itself while monitoring the 16mhz clock, and guess what - I didn't see any difference. I was expecting to see that fast of a signal change and become blurry, change levels, or something. I didn't and it stayed rock steady. As far as being a pure sign wave, it was not, but was a distorted one, although better looking than some clock signals I have seen published. This clock signal travels through a
wire to get get to the DAC clock input and is terminated with a 30pf NPO ceramic, sort of like traveling through an LC filter. I did not have access to see what the cleaned up clock looked like and will have to make access for that when I start working on the analog board. Just from this little test, I'm kind of wondering if vibration control isn't more for the disk drive than anything else. My unit does have an iron plate mounted below the drive bringing the weight up to about 15 lbs, a little heavier than your typical player weighing in at 10lbs, so the manufacturer must have thought it was good for something. Another test I thought of after the fact was to take a photo or something of the clock signal before the mods just for a simple comparison. Not sure if it's possible to detect a real difference like this or not.
wire to get get to the DAC clock input and is terminated with a 30pf NPO ceramic, sort of like traveling through an LC filter. I did not have access to see what the cleaned up clock looked like and will have to make access for that when I start working on the analog board. Just from this little test, I'm kind of wondering if vibration control isn't more for the disk drive than anything else. My unit does have an iron plate mounted below the drive bringing the weight up to about 15 lbs, a little heavier than your typical player weighing in at 10lbs, so the manufacturer must have thought it was good for something. Another test I thought of after the fact was to take a photo or something of the clock signal before the mods just for a simple comparison. Not sure if it's possible to detect a real difference like this or not.
It's not - the variation that matters is in the cycle-to-cycle timing, which is several orders of magnitude below the jitter in the o'scope display timebase. But don't let that stop you trying!
I usually limit the scope to 20Mhz or rather less when looking at PSU noise, to be sure I'm really seeing what is going on rather than just my sloppy technique. I also like using a simple x10 opamp-based preamp between the probe and scope, with an input filter limiting bandwidth to 50-100Khz. An OP37 and 9v battery is a cheap and effective start. It helps on two counts - with a suitable inamp you can see well below 100uV/div, and - esp. for the analogue stages - the bandwidth filtering gives very clean traces, which helps pin-down which rails need better regulation.
Martin - Thanks for speaking up. I remember reading something on jitter and that some specialized gear is needed to evaluate. And yes, this 300mhz BW has been interesting to play with, not knowing if it was a curse or benefit at times.....
. I think it has revealed some things, but I am forced to insert a "fudge" factor here concerning readings. Collectively, they have made for some interesting comparisons that can perhaps serve as a guide at least. I like the idea of adding on a boost preamp to read lower levels when the time comes. I was able to get noise levels down to the order of 10-20mv on the clock noise, several times lower than what it was stock. As for the high freq. noise, I was getting 50mv - 100mv levels, also much improvement over stock. However, I'm not sure about absolute levels given the noise I pick up just on ground itself and probe pickup. Doing something like you suggest looks good to me, just have never had the need to go this far before.
One more thing about voltage regulators: I got into noise figures when I chose new ones to install (what the heck, I was just having fun and concerned about stability with the new caps, not being sure the stock regs could handle it). Anyway, at the levels here, the micro-volt noise level ratings appear to be swamped out by the p.s. noise levels. But another way of thinking is that perhaps it could still make a difference as to the total noise it does inject into the signal. I mean, why add more if you don't have to? Every bit counts and after all, the purpose of this exercise is to decrease noise any way possible. The new regs are staying in. I'll probably do some more thinking on this and come back to the digital board again. I just wish access and making measurements was easier on some of the signals.
But, overall I'm just trying to have fun and not get my knickers riding too high. I'm pleased with the results so far.
. I think it has revealed some things, but I am forced to insert a "fudge" factor here concerning readings. Collectively, they have made for some interesting comparisons that can perhaps serve as a guide at least. I like the idea of adding on a boost preamp to read lower levels when the time comes. I was able to get noise levels down to the order of 10-20mv on the clock noise, several times lower than what it was stock. As for the high freq. noise, I was getting 50mv - 100mv levels, also much improvement over stock. However, I'm not sure about absolute levels given the noise I pick up just on ground itself and probe pickup. Doing something like you suggest looks good to me, just have never had the need to go this far before. One more thing about voltage regulators: I got into noise figures when I chose new ones to install (what the heck, I was just having fun and concerned about stability with the new caps, not being sure the stock regs could handle it). Anyway, at the levels here, the micro-volt noise level ratings appear to be swamped out by the p.s. noise levels. But another way of thinking is that perhaps it could still make a difference as to the total noise it does inject into the signal. I mean, why add more if you don't have to? Every bit counts and after all, the purpose of this exercise is to decrease noise any way possible. The new regs are staying in. I'll probably do some more thinking on this and come back to the digital board again. I just wish access and making measurements was easier on some of the signals.
But, overall I'm just trying to have fun and not get my knickers riding too high. I'm pleased with the results so far.
Completely agree, with the caveat that I'd take a reg with lower output impedance but more noise over a very quiet, higher-Z reg every time. If the noise is random (ie not correlated with the load) it doesn't seem to matter much...
Remember that the reg's noise rating is the 'self noise' measured on the output of the reg with NO LOAD. That's where the difference comes from - the far-greater noise on the rails is mostly due to the noise contributed by the load(s) and the ways in which this noise is NOT absorbed by the regs (limited) bandwidth, output impedance, the decoupling caps, poor PS routing/layout (long traces) and so on and so on...
In fact, even if you had a perfect regulator with zero output impedance over an infinite bandwidth (!) I think you'd still see some noise due to the last two items in particular...
It is very refreshing to see some people still tackle the real problem in digital audio (well, in any audio) – noise.
I did the similar thing long, long time ago and together with reading various info on this topic, learned a fair bit about mods and how to get the most out of the spent dough. I experimented a lot in the exact same way as you are doing now. I found, for example, that uPC generate most noise and that noise had to be prevented from entering the common ground plane at all costs.
The real question is: what’s the point in spending a lot of money on expensive decoupling capacitors when all they do is couple the power supply rail noise to already very noisy ground plane? There are some good ground-plane designs out there, but only a few – MF does very good job in this regards.
As you mentioned already, reducing the noise by the order of magnitude (especially around digital receivers, decoders, upsemplers, DAC’s, clock signal generators…) brings tighter, better focused and extended sound, which is also better positioned in space around speakers. Re-designing the ground plane (I use very wide pure silver ribbons for this purpose) and careful observation of noise around digital IC’s (and proper selection / positioning of decoupling caps) can lead to fantastic results. After a while, you’ll know exactly which capacitors to use, and how. But before that, the real trick is reducing the ground plane noise. You’ll hear different opinions and read different solutions, and this is all good. However, your measurement (and your ears) will be in contradiction with vast (common?) thinking of many so-called (self-proclaimed) experts. Try as many options and apply as many approaches, but stick to what your measurements are saying to be the best, and follow by the listening test. Another tip: if you are tired, the low jitter, low noise results could sound too clinical; if you are well rested – they’ll sound amassing. A lot depends on the rest of the equipment. You can fine tune and merge the components of the system together by properly selecting the power, interconnects and speaker cables.
All sad, I decided long time ago to use the least amount of digital circuitry possible to obtain digital to analog conversion – receiver and DAC.
Boky
I did the similar thing long, long time ago and together with reading various info on this topic, learned a fair bit about mods and how to get the most out of the spent dough. I experimented a lot in the exact same way as you are doing now. I found, for example, that uPC generate most noise and that noise had to be prevented from entering the common ground plane at all costs.
The real question is: what’s the point in spending a lot of money on expensive decoupling capacitors when all they do is couple the power supply rail noise to already very noisy ground plane? There are some good ground-plane designs out there, but only a few – MF does very good job in this regards.
As you mentioned already, reducing the noise by the order of magnitude (especially around digital receivers, decoders, upsemplers, DAC’s, clock signal generators…) brings tighter, better focused and extended sound, which is also better positioned in space around speakers. Re-designing the ground plane (I use very wide pure silver ribbons for this purpose) and careful observation of noise around digital IC’s (and proper selection / positioning of decoupling caps) can lead to fantastic results. After a while, you’ll know exactly which capacitors to use, and how. But before that, the real trick is reducing the ground plane noise. You’ll hear different opinions and read different solutions, and this is all good. However, your measurement (and your ears) will be in contradiction with vast (common?) thinking of many so-called (self-proclaimed) experts. Try as many options and apply as many approaches, but stick to what your measurements are saying to be the best, and follow by the listening test. Another tip: if you are tired, the low jitter, low noise results could sound too clinical; if you are well rested – they’ll sound amassing. A lot depends on the rest of the equipment. You can fine tune and merge the components of the system together by properly selecting the power, interconnects and speaker cables.
All sad, I decided long time ago to use the least amount of digital circuitry possible to obtain digital to analog conversion – receiver and DAC.
Boky
Crowbar - I looked into using shunt regulators and zeners starting out but put them on hold since there was enough going on. I also didn't want to deal with the extra current needed to operate them. And you're right about shunts and the mhz dealt with, so caps are the issue here (for now).
Extreme - nice to hear from someone with similiar experience. The approach I'm taking as an EE is that of what one would read in one of the trade publications like EDN and app notes which are full of great info. But I'm probably less hardcore than most as I do favor a fun approach at all times, so I take the freedom to play and mull things over. I'd also like to think I'm in tune with the caps and other things that are suitable for audio. So far I've just been using oscon-like caps and NPO/COG ceramics. I have done some more testing and listening since my last post from the work I've been doing on this "data receive" chip with a 5MHZ clock. This chip is responsible for getting the data from the drive and clocking it to the 16MHZ main chip. I upgraded the caps on this 5v bus and put in some bypasses. One thing I noticed is that a 330pf ceramic was on this p.s. rail already and I wondered why. I thought it was a rather odd value to have at first for a clock of only 5MHZ, but I also knew more was going on and I'd have to pursue to find out instead of leaving it at just a guess. After more probing I found out the chip was processing this 5mhz into what appears to be a gated toneburst, and using only the first complete cycle (as spikey as it is) as the clock to the 16MHZ chip. Power rail measurements on this 5MHZ chip show a noise with spikes at intervals. With the new caps, seeing a reduction in noise measurements using the entire BW was inconclusive that I could see, but using a 20MHZ BW showed a 25% reduction from 40mv to 30mv. It was here that it occured to me that bypassing with the PROPER value of cap was paramount and that what it is I'm dealing with is, put simply, a tuned circuit. I have been using an approach in bypassing so far that consists of a .1uf and .01uf NPO cap soldered onto the oscons. I'm sure this has been helping to a degree since my measurements seem to indicate it, but knowing the frequencies involved at every juncture and bypassing with the corresponding cap is what is really needed, and that my method is not fully correct but only a rough approach. The 330pf cap as noted on the p.s. rail would seem to be a bypass meant for the outgoing clock signal, which is an intermittant but rather high frequency indeed. For keeping things cheap, I think the manufacturer knew full well what they were doing and I have been trying to pay attention to their intent all along, but it has been difficult at times. Sometimes I don't know if they're just being cheap or using their smarts.
Now, one more observation is that my previous finding of a toneburst at the 5v reg's output for the 16MHZ chip doesn't look so nuts afterall. It looks to be feeding the power requirements for it's input data and clocking setup. Big surprise, huh? Well, it was confusing at first but since I know more now, it makes a bit more sense. Less muddy at any rate. I'm also of an idea that perhaps a smallish picofarad cap at strategic points of this power rail may help. I might start at the 5v reg's output and give it a check to see how the trace is effected. I'll also have another look at the data stream and clocks to get more precise measurements and values and go from there. Ideally, a spectrum analysis of the p.s. noise is what's needed which would give way to proper bypassing, but I don't have that luxury. I can makes some guesses though and go from there. It looks like I might be covering the same territory as what Extreme has been through, but it's common fare for digital circuit work, so nothing really new. One other thing I noticed is that the value of caps at one location do indeed effect noise measurements at other locations. Case in point: On the 16MHZ chip, I decreased the value of capacitance on the analog power pins that occupied on side of the chip only because larger ones that emulated the stock values would not fit. Well, I moved some of the interfering parts on the other side of the board and installed stock-valued caps and noticed a decrease in noise on the adjacent and opposite side of the chip, namely the clock p.s. and various outputs. That was a good move since reducing the clock p.s. noise was the object here. Point is, on a daisy chained p.s. rail, caps feed the next one in line and interact with one another.
So, how did this additional "upgrading" sound? Well, on the first try my sinuses had been playing havoc and I was on some meds. The whole sound was absolutely horrible but it was me not doing so well. I listened the next day and things were much improved, but by how much is difficult for me to say. I didn't hear as dramatic an improvement as I did the first go 'round, but I do believe there was a little bit. If I had to describe, it'd be just more of the same as what I first heard, if anything. Certainly not worse. Nuances are standing out as much as ever.
I'll try to be back later with more if I can find anything noteworthy to do and see further improvement. Some of the traces are starting to pull up from desoldering, so my time is probably limited with this part. I do wish I could tune this to perfection though. I'd like to hear what one would sound like. Seems to me that could be the next step in player design and marketing, even if they did use cheaper parts. Nah, too logical.......gotta leave freaks like us wanting more....
Extreme - nice to hear from someone with similiar experience. The approach I'm taking as an EE is that of what one would read in one of the trade publications like EDN and app notes which are full of great info. But I'm probably less hardcore than most as I do favor a fun approach at all times, so I take the freedom to play and mull things over. I'd also like to think I'm in tune with the caps and other things that are suitable for audio. So far I've just been using oscon-like caps and NPO/COG ceramics. I have done some more testing and listening since my last post from the work I've been doing on this "data receive" chip with a 5MHZ clock. This chip is responsible for getting the data from the drive and clocking it to the 16MHZ main chip. I upgraded the caps on this 5v bus and put in some bypasses. One thing I noticed is that a 330pf ceramic was on this p.s. rail already and I wondered why. I thought it was a rather odd value to have at first for a clock of only 5MHZ, but I also knew more was going on and I'd have to pursue to find out instead of leaving it at just a guess. After more probing I found out the chip was processing this 5mhz into what appears to be a gated toneburst, and using only the first complete cycle (as spikey as it is) as the clock to the 16MHZ chip. Power rail measurements on this 5MHZ chip show a noise with spikes at intervals. With the new caps, seeing a reduction in noise measurements using the entire BW was inconclusive that I could see, but using a 20MHZ BW showed a 25% reduction from 40mv to 30mv. It was here that it occured to me that bypassing with the PROPER value of cap was paramount and that what it is I'm dealing with is, put simply, a tuned circuit. I have been using an approach in bypassing so far that consists of a .1uf and .01uf NPO cap soldered onto the oscons. I'm sure this has been helping to a degree since my measurements seem to indicate it, but knowing the frequencies involved at every juncture and bypassing with the corresponding cap is what is really needed, and that my method is not fully correct but only a rough approach. The 330pf cap as noted on the p.s. rail would seem to be a bypass meant for the outgoing clock signal, which is an intermittant but rather high frequency indeed. For keeping things cheap, I think the manufacturer knew full well what they were doing and I have been trying to pay attention to their intent all along, but it has been difficult at times. Sometimes I don't know if they're just being cheap or using their smarts.
Now, one more observation is that my previous finding of a toneburst at the 5v reg's output for the 16MHZ chip doesn't look so nuts afterall. It looks to be feeding the power requirements for it's input data and clocking setup. Big surprise, huh? Well, it was confusing at first but since I know more now, it makes a bit more sense. Less muddy at any rate. I'm also of an idea that perhaps a smallish picofarad cap at strategic points of this power rail may help. I might start at the 5v reg's output and give it a check to see how the trace is effected. I'll also have another look at the data stream and clocks to get more precise measurements and values and go from there. Ideally, a spectrum analysis of the p.s. noise is what's needed which would give way to proper bypassing, but I don't have that luxury. I can makes some guesses though and go from there. It looks like I might be covering the same territory as what Extreme has been through, but it's common fare for digital circuit work, so nothing really new. One other thing I noticed is that the value of caps at one location do indeed effect noise measurements at other locations. Case in point: On the 16MHZ chip, I decreased the value of capacitance on the analog power pins that occupied on side of the chip only because larger ones that emulated the stock values would not fit. Well, I moved some of the interfering parts on the other side of the board and installed stock-valued caps and noticed a decrease in noise on the adjacent and opposite side of the chip, namely the clock p.s. and various outputs. That was a good move since reducing the clock p.s. noise was the object here. Point is, on a daisy chained p.s. rail, caps feed the next one in line and interact with one another.
So, how did this additional "upgrading" sound? Well, on the first try my sinuses had been playing havoc and I was on some meds. The whole sound was absolutely horrible but it was me not doing so well. I listened the next day and things were much improved, but by how much is difficult for me to say. I didn't hear as dramatic an improvement as I did the first go 'round, but I do believe there was a little bit. If I had to describe, it'd be just more of the same as what I first heard, if anything. Certainly not worse. Nuances are standing out as much as ever.
I'll try to be back later with more if I can find anything noteworthy to do and see further improvement. Some of the traces are starting to pull up from desoldering, so my time is probably limited with this part. I do wish I could tune this to perfection though. I'd like to hear what one would sound like. Seems to me that could be the next step in player design and marketing, even if they did use cheaper parts. Nah, too logical.......gotta leave freaks like us wanting more....
Haha, you'll have to elaborate since you put in this parenthesized "for now".RetroAudio said:
Why not have star-type distribution, with L and/or R on the lines to help AC-isolate each branch?
Also, does anyone use shielding to prevent capacitive and inductive coupling of noise from one part of the circuit to another? I see a number of small shields covering various parts of PCBs in my radio.
Well, I have made another round of progress of cutting down on noise levels it appears. My setup includes both the digital and analog boards whose ground circuit is coupled to the chassis through .1uf ceramics. Apparently each board is leaking it's noise into the other, which is something I sort of saw all along but just didn't address. Perhaps I should have done this first. It is in this way the manufacturer thought it best to bring the chassis to "0 volts" potential, a figurative ground of sorts. The earth ground in the power mains is not used and I suspect probably is not in a lot of cd players. I don't know if this setup is typical or just peculiar to mine. I can see where addressing these noise problems all the way back to the transformer can be an issue since it's case is grounded to chassis and noise is most likely leaking in somehow. Even the xformer itself could probably aid in reduction if properly selected. I have used dual concentric bobbin types for this kind of problem before but would have to do further investigation for this application.
I was about to start on a series of bypassing trials, but think it's probably pointless here until I can take care of the external noise issues, whatever might be found. Doing the DAC board at this point might not be a bad idea either and may aid further digital work. Preliminary noise measurements with this digital board now "isolated" showed further wide BW noise reduction levels
of up to 50% (now 50mv), with intermittant spikes that reached higher levels (~ 100mv). Using the 20MHZ BW showed even smaller levels, down to 10-12mv instead of the 16-20mv levels. Holy cow, this has come a long way and the work is not even close to being done. And no wonder ground was driving me nuts from the start. Sheesh! I was right, it was messed up!
I was about to start on a series of bypassing trials, but think it's probably pointless here until I can take care of the external noise issues, whatever might be found. Doing the DAC board at this point might not be a bad idea either and may aid further digital work. Preliminary noise measurements with this digital board now "isolated" showed further wide BW noise reduction levels
of up to 50% (now 50mv), with intermittant spikes that reached higher levels (~ 100mv). Using the 20MHZ BW showed even smaller levels, down to 10-12mv instead of the 16-20mv levels. Holy cow, this has come a long way and the work is not even close to being done. And no wonder ground was driving me nuts from the start. Sheesh! I was right, it was messed up!
one more step:
Ok, here's an update. And yeah, this is wearing on but it needs to be logged, so here it is. I had to take the whole player apart to achieve 2 things - one was to see if there was any other places that were cap coupled to the chassis and the other was to upgrade/recap the display panel. This circuit is for control and display and partly runs off of the 5v circuit coming from the 5MHZ chip on the digital board. Past experience says that this will improve performance over the entire power rail. After reassembling the player with all boards now isolated from the chassis and an earth ground from the power mains installed, I tried a couple of spot measurements. What I saw was an increased stability in the scope's display with not nearly as much trigger level difficulty. Levels remained roughly the same as before (but remember, this digital board was previously isolated), and I can't say for sure what implications all this has, but hi-freq waveforms from past observations changed somewhat and were much easier to bring into focus instead of remaining fuzzy a fair part of the time. Those were just my initial impressions anyway and I then chose not to take any further readings. Instead, I thought it might be a great time to take a listen. I still think I will complete the DAC board and improve the entire grounding scheme before I attempt to come back for any accurate digital board p.s. measurements and bypassing trials. Oh yeah, I also disconnected the digital output circuitry, thus removing that as a noise source.
Listening proved somewhat interesting. At first I was too pumped to hear correctly and really tried to get out of the frame of mind of just doing work and listening for a respective change, since I wanted to just sit back and enjoy. Once I did I did hear a change and it wasn't trivial. At first I couldn't quite put my finger on it but the more I listened the more I realized that all that was happening was that a little more life was being pumped into the music. This was the second level of this happening and apparently a continuation of round one. It wasn't a matter of highs, lows, imaging, coloration, soundstage, what have you. It began to resemble my phono system, which I have not listened to for quite some time now. I guess I have almost forgotten what it can sound like. But yeah, a warmth was there not before and perhaps just a little less digitalitis. That's about the only way I know to describe and think what I heard. I do wish there could be more of an A/B comparison setup here since a number of days go by while the player is up on the bench to be forever changed. Memory doesn't always serve but it's the best I can do, but on the flip side knowing your system does help.
Ok, here's an update. And yeah, this is wearing on but it needs to be logged, so here it is. I had to take the whole player apart to achieve 2 things - one was to see if there was any other places that were cap coupled to the chassis and the other was to upgrade/recap the display panel. This circuit is for control and display and partly runs off of the 5v circuit coming from the 5MHZ chip on the digital board. Past experience says that this will improve performance over the entire power rail. After reassembling the player with all boards now isolated from the chassis and an earth ground from the power mains installed, I tried a couple of spot measurements. What I saw was an increased stability in the scope's display with not nearly as much trigger level difficulty. Levels remained roughly the same as before (but remember, this digital board was previously isolated), and I can't say for sure what implications all this has, but hi-freq waveforms from past observations changed somewhat and were much easier to bring into focus instead of remaining fuzzy a fair part of the time. Those were just my initial impressions anyway and I then chose not to take any further readings. Instead, I thought it might be a great time to take a listen. I still think I will complete the DAC board and improve the entire grounding scheme before I attempt to come back for any accurate digital board p.s. measurements and bypassing trials. Oh yeah, I also disconnected the digital output circuitry, thus removing that as a noise source.
Listening proved somewhat interesting. At first I was too pumped to hear correctly and really tried to get out of the frame of mind of just doing work and listening for a respective change, since I wanted to just sit back and enjoy. Once I did I did hear a change and it wasn't trivial. At first I couldn't quite put my finger on it but the more I listened the more I realized that all that was happening was that a little more life was being pumped into the music. This was the second level of this happening and apparently a continuation of round one. It wasn't a matter of highs, lows, imaging, coloration, soundstage, what have you. It began to resemble my phono system, which I have not listened to for quite some time now. I guess I have almost forgotten what it can sound like. But yeah, a warmth was there not before and perhaps just a little less digitalitis. That's about the only way I know to describe and think what I heard. I do wish there could be more of an A/B comparison setup here since a number of days go by while the player is up on the bench to be forever changed. Memory doesn't always serve but it's the best I can do, but on the flip side knowing your system does help.
conclusion, maybe
I finally got the DAC done, and in short, it made a difference. Power bus noise was reduced in about the same way as the digital board, only I had to install some caps where none previously existed. Sad in my opinon that none were even on the analog side, and the digital side had one pretty far away from the power pin. I was not able to take a reading at the pin either, so I just did the best I could and put in an oscon that would fit and did a sort of bypassing and let it go that that. On the bright side, even this move reduced noise considerably at the measure point. As discussion prone as the analog side is to the type of cap better suited for decoupling, my noise measurements indicated that an oscon still would be the desired one needed as there was plenty of noise in the wide BW mode. I did not use any other however so I have no comparison data and cannot say if the Blackgate (or any other) would have performed better. Listening tests at this point seemed to indicate that the sound had only improved further, and it was, you guessed it, more life still. I think this so-called life improvement is maxing out though and it seems like it's being restained by other system limitations, such as an unmodified amp (dual mono) that I happen to be using now and an unmodded interface in my martin logan CLS's. So, needed improvement does remain and the fight continues. I need to get my reference amp fixed here soon as this whole project started as a much needed break from dealing with it.
Anyway, outside of the tweaking of the bypassing, I don't think I have much more to say about p.s. rail noise and it's reduction. In short, it does do a system good and I could recommend it without reservation to anyone interested. The bypassing approach might be best served by using caps that span the whole range if limitless testing was to be avoided. I think what I'll do is add a 300-500pf cap (since that one 330pf one was on that 5mhz chip rail, it might give some indication to frequency content anyway) to the ones already in place, see if that might help, then just let it rest. I feel like moving on and frying other fish. I've also read where others have had luck in similiar approaches.
I did do some more work that does not entail p.s. rail noise, but has to do with p.s. stuff anyway. I reworked the post DAC circuitry p.s. and it did improve the sound. Some might get their hackles upset by this but I used oscons for bypassing and it seemed to only improve the performance and enforce the sound. Actually, the guitar I listen to only sounded more like a guitar, from top to bottom. Gone was the bass womp and it tightened up, not nearly as exaggerated as what I was accustomed to. I always thought those bass strings put out a little more than what they should have. I did use to play guitar so I do have a bit of knowledge about this, but also realize the whole thing is pretty subjective, so I won't come to any conclusions. And, I also did no comparisons with any other caps at this point either, so there's the other side laid out for everyone to see. I will say that not all oscon or like caps are created equal, at least from an ESR point of view. Some do not measure all that well in the audio range, and some do. If I was forced to make a contention, I'd start with knowing the particular cap you were intent on using, then go from there. The oscons I used all measured well in the audio spectrum, and I don't really see any problems in using them as such. But, again, I admit I have done no comparison testing and just might be surprised if I did.
In wrapping up this work, I do have a couple of thoughts about what might do a player good. First of all, I have come to the realization that all a cd player is is a noisemaker, and a rather blatant one, producing hash that is next to impossible to kill. That being said, one must realize that this is part of the entire system like it or not. If you have a preamp that connects to the player's ground, then you have a problem. This is not insignificant it looks to me and really should be addressed in some manner. It probably has been somewhere by someone, but it's kinda new to me. I have made no measurements but I'm sure hash is getting back into the power mains and there's certainly the issue of the ground itself. About the only way I can think of right now to reduce the ground bounce issue is to make for as much ground as possible, separate transformers where warranted, and pay as much attention to noise reduction technique as possible. One book that is a good read is "Noise Reduction Techniques in Electronic Systems" by Henry Ott. One method I can think of here that applies is a thing called loop reduction, i.e., make the entire circuit take up as least space as possible, including the power distribution lines (power and ground). This arose as an issue thinking about ground plains and such and I had an idea that perhaps such an approach is not really the best, although it certainly sounds great. What got me to thinking about it was the scope trace characteristics I encountered during my trials and the cabling used between boards for power, signal, ground, etc. At first I thought how horrid it all is but then as I made my own grounding cable from copper tape, I realized that it was making the loop area bigger as compared to the wire cabling wrapped together. My next approach to enforcing the ground would be to cable the grounding around the cabling itself, thus reducin power delivery loop area by a wide margin, kind of like it was doing in stock form. Now, a ground plain would have an increased area compared to the cabling technique. Comparison testing would just have to be done under controlled conditions for anything meaningfull to be measured, something I have not done and not sure I will. It's just a thought with a solid principal backing it up, so valid I think. Not sure how practical however. A second idea I had was in isolating the output from ground altogether, but how? Well, my player has balanced outputs and I was thinking that maybe these could drive an output transformer, like a jensen mic xfmr and perhaps avoid player ground that way. Just an idea.
That's just about it for me on this subject. I hope it's been entertaining and useful to some. I'll probably continue the work since more needs doing, but may not be back for awhile or at all if nothing is worth logging outside of what is already known. If anything interesting happens I'll be back. Right now the player is sounding pretty respectable and I'm actually enjoying what is coming out. I would not want to go back!
I finally got the DAC done, and in short, it made a difference. Power bus noise was reduced in about the same way as the digital board, only I had to install some caps where none previously existed. Sad in my opinon that none were even on the analog side, and the digital side had one pretty far away from the power pin. I was not able to take a reading at the pin either, so I just did the best I could and put in an oscon that would fit and did a sort of bypassing and let it go that that. On the bright side, even this move reduced noise considerably at the measure point. As discussion prone as the analog side is to the type of cap better suited for decoupling, my noise measurements indicated that an oscon still would be the desired one needed as there was plenty of noise in the wide BW mode. I did not use any other however so I have no comparison data and cannot say if the Blackgate (or any other) would have performed better. Listening tests at this point seemed to indicate that the sound had only improved further, and it was, you guessed it, more life still. I think this so-called life improvement is maxing out though and it seems like it's being restained by other system limitations, such as an unmodified amp (dual mono) that I happen to be using now and an unmodded interface in my martin logan CLS's. So, needed improvement does remain and the fight continues. I need to get my reference amp fixed here soon as this whole project started as a much needed break from dealing with it.
Anyway, outside of the tweaking of the bypassing, I don't think I have much more to say about p.s. rail noise and it's reduction. In short, it does do a system good and I could recommend it without reservation to anyone interested. The bypassing approach might be best served by using caps that span the whole range if limitless testing was to be avoided. I think what I'll do is add a 300-500pf cap (since that one 330pf one was on that 5mhz chip rail, it might give some indication to frequency content anyway) to the ones already in place, see if that might help, then just let it rest. I feel like moving on and frying other fish. I've also read where others have had luck in similiar approaches.
I did do some more work that does not entail p.s. rail noise, but has to do with p.s. stuff anyway. I reworked the post DAC circuitry p.s. and it did improve the sound. Some might get their hackles upset by this but I used oscons for bypassing and it seemed to only improve the performance and enforce the sound. Actually, the guitar I listen to only sounded more like a guitar, from top to bottom. Gone was the bass womp and it tightened up, not nearly as exaggerated as what I was accustomed to. I always thought those bass strings put out a little more than what they should have. I did use to play guitar so I do have a bit of knowledge about this, but also realize the whole thing is pretty subjective, so I won't come to any conclusions. And, I also did no comparisons with any other caps at this point either, so there's the other side laid out for everyone to see. I will say that not all oscon or like caps are created equal, at least from an ESR point of view. Some do not measure all that well in the audio range, and some do. If I was forced to make a contention, I'd start with knowing the particular cap you were intent on using, then go from there. The oscons I used all measured well in the audio spectrum, and I don't really see any problems in using them as such. But, again, I admit I have done no comparison testing and just might be surprised if I did.
In wrapping up this work, I do have a couple of thoughts about what might do a player good. First of all, I have come to the realization that all a cd player is is a noisemaker, and a rather blatant one, producing hash that is next to impossible to kill. That being said, one must realize that this is part of the entire system like it or not. If you have a preamp that connects to the player's ground, then you have a problem. This is not insignificant it looks to me and really should be addressed in some manner. It probably has been somewhere by someone, but it's kinda new to me. I have made no measurements but I'm sure hash is getting back into the power mains and there's certainly the issue of the ground itself. About the only way I can think of right now to reduce the ground bounce issue is to make for as much ground as possible, separate transformers where warranted, and pay as much attention to noise reduction technique as possible. One book that is a good read is "Noise Reduction Techniques in Electronic Systems" by Henry Ott. One method I can think of here that applies is a thing called loop reduction, i.e., make the entire circuit take up as least space as possible, including the power distribution lines (power and ground). This arose as an issue thinking about ground plains and such and I had an idea that perhaps such an approach is not really the best, although it certainly sounds great. What got me to thinking about it was the scope trace characteristics I encountered during my trials and the cabling used between boards for power, signal, ground, etc. At first I thought how horrid it all is but then as I made my own grounding cable from copper tape, I realized that it was making the loop area bigger as compared to the wire cabling wrapped together. My next approach to enforcing the ground would be to cable the grounding around the cabling itself, thus reducin power delivery loop area by a wide margin, kind of like it was doing in stock form. Now, a ground plain would have an increased area compared to the cabling technique. Comparison testing would just have to be done under controlled conditions for anything meaningfull to be measured, something I have not done and not sure I will. It's just a thought with a solid principal backing it up, so valid I think. Not sure how practical however. A second idea I had was in isolating the output from ground altogether, but how? Well, my player has balanced outputs and I was thinking that maybe these could drive an output transformer, like a jensen mic xfmr and perhaps avoid player ground that way. Just an idea.
That's just about it for me on this subject. I hope it's been entertaining and useful to some. I'll probably continue the work since more needs doing, but may not be back for awhile or at all if nothing is worth logging outside of what is already known. If anything interesting happens I'll be back. Right now the player is sounding pretty respectable and I'm actually enjoying what is coming out. I would not want to go back!
very nostalgic
I remember a few years back then doing basically the same thing as u did, and yes it was fun
along the way you will discover that many myth in audio is not true,and more prepared to tackle problems in other electronic area other than power supply
for signal decoupling avoid ANY electrolytic if possible, for beginner good cost compromise is to use run-of-the-mill metallized polypropylene. If u must use electrolytic, stick with non-polarized ones.
hint about jitter : no amount of jitter-less clock will do any good if the ground is not clean,the DAC/ or other digital switching element change state at a treshold, and treshold is referenced to ground, the treshold within the device itself also may vary dynamically in the operation.
Complete removal of ground and supply noise is practically impossible, meaning in most cd player low jitter clock will have very limited effect on the final output. Mostly it will just change the sound, not really improving it.
better grade DAC chips definitely bring significant improvement. But all other problem also need to be resolved to bring the full potential of the DAC.
zero ground bounce in digital circuit is almost impossible so one have to resort to various trick to maintain signal/timing integrity and this is bordering to extreme method,optical isolation, transformer isolation, feedthrough capacitor,extremely clean PCB,good transmission line termination, unusual cabling, thorough shielding, new and extreme construction technique is required !!
keep up the good work and most importantly have fun !
I remember a few years back then doing basically the same thing as u did, and yes it was fun
along the way you will discover that many myth in audio is not true,and more prepared to tackle problems in other electronic area other than power supply
for signal decoupling avoid ANY electrolytic if possible, for beginner good cost compromise is to use run-of-the-mill metallized polypropylene. If u must use electrolytic, stick with non-polarized ones.
hint about jitter : no amount of jitter-less clock will do any good if the ground is not clean,the DAC/ or other digital switching element change state at a treshold, and treshold is referenced to ground, the treshold within the device itself also may vary dynamically in the operation.
Complete removal of ground and supply noise is practically impossible, meaning in most cd player low jitter clock will have very limited effect on the final output. Mostly it will just change the sound, not really improving it.
better grade DAC chips definitely bring significant improvement. But all other problem also need to be resolved to bring the full potential of the DAC.
zero ground bounce in digital circuit is almost impossible so one have to resort to various trick to maintain signal/timing integrity and this is bordering to extreme method,optical isolation, transformer isolation, feedthrough capacitor,extremely clean PCB,good transmission line termination, unusual cabling, thorough shielding, new and extreme construction technique is required !!
keep up the good work and most importantly have fun !
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