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In Reply to: RE: Ow, I now see the mis-understanding. :-) posted by hfavandepas on August 25, 2011 at 07:56:02
I am using the i3 core 540 processor for my cMp. Linear psu for Julia & P4. Last evening I bought a few ferrite beads to start with & used just one where the P4 plugs into the motherboard. Same with a p4 extension cable so that I can test with & without it. Sounds slightly better with the ferrite though. You were saying something about adding caps along with the ferrite ???
When I made both the linears, I had kept the one powering the Julia inside the cMp & the one for the P4 outside. Two days ago, I wanted to manage both of them inside the cMp for aesthetic reasons. So I kept both inside the cMp side by side. To my surprise, the sound changed quite a bit for the worse. The liquidity in music deteriorated & the bass became less tight & uncontrolled. I'm still wondering what caused this to happen. Any ideas??
Follow Ups:
Hi Jolida,
I’m not an expert in this matter.
I would guess you have your home made linears not boxed.
So they are not magnetically shielded
So the (powerfull) magnetic fields of these transformer coils will induce currents (distortions) in there immediate surroundings.
Other than that I have no idea.
Mark
fully optimized cMP2 PC -> ESI Juli@ -> Van den Hul Optocoupler MkII-> Lavry Black DA10 -> XLR Mogami Gold -> Klein & Hummel O300
The linears are kept side by side next to each other inside the cMp cabinet which houses the motherboard as well. The cabinet is grounded though. Does each linear psu need to be individually boxed & grounded ??
fully optimized cMP2 PC -> ESI Juli@ -> Van den Hul Optocoupler MkII-> Lavry Black DA10 -> XLR Mogami Gold -> Klein & Hummel O300
Does each linear psu need to be individually boxed & grounded ??It's a bit of a myth that linear PSUs are necessarily a noise-free panacea for the ills of the switcher. Quite the opposite. Way back in 1989, an article in Hi-Fi News on power supply design for pre-amplifiers put it well and, as I happened to build part of the design (I've still got it), I kept a copy. The author has a weakness for purple prose but this extract might be useful:
. . . the standard PSU circuit is a devil. It pollutes the supply by drawing current in swift packets as the voltage peaks. A sideways look reveals a multi-resonant network, snapped on and off by switches (disguised as rectifier diodes) and damped by a load which happens to be an audio circuit in series with a pair of regulators. Each diode commutates (switches) current at least twice in every cycle, producing a pattern of back-EMF spikes with a PRF of (say) 200Hz. Sags and surges in the mains voltage only add to the poly-rhythm. If the spike’s own (oscillatory) frequency is high enough, there’s no guarantee it’ll be spotted with anything short of a VHF lab’s sampling oscilloscope. Still, it won’t have any trouble making itself manifest once it’s inter-modulated with another signal containing components harmonically related to 200Hz - such as music. If this is so, the most likely symptom is modulation noise, noise which follows legitimate audio signals.For a local but equally helpful discussion, see link. It doesn’t give you a recipe but it does explain things really rather well.The bi-phase capacitor ‘smoothed’ supply’s output ripple has high harmonic content. Thanks to brute-force filtering, AC filtration is typically zero at 100Hz, becomes slightly effective (eg -5 to - lOdB) in the audio midband, only to return to nil above the reservoir capacitor’s resonant frequency, between 1 and 10kHz.
Small wonder dedicated audiophiles have taken to the hills, powering their pre-amplifiers and CD players from batteries. . . .
The mundane approach to building audio supplies crumbles further once we acknowledge that all conventional voltage regulators (whether discrete or IC) rely on NFB. It makes them rugged, predictable workers at low frequencies but their ability to ‘filter out’ incoming garbage is progressively impaired with ascending frequency and decreasing periodicity. Conventional regulators (whether IC or custom) are especially hapless in the face of VHF voltage spikes. They need protection as much as the op-amps they serve. Summing up, it seems likely that, if universal AC/DC power conversion techniques influence sonic quality, then they do so by offering cross-rhythms of their own making, as well as introducing others from down the line. Up to now, most ‘good sounding’ PSU’s have relied on empirical turning. That small changes to values, to component makes or mere layout has led to dramatic sonic differences is neatly explained by the exaggerated sensitivity of multi-resonant networks. It’s small wonder high resolution sound systems often sound radically different from day to day.
In short, I wonder if you’re not asking more of your kit than it is able at this point to give you. That’s not a very helpful answer of course.
Why not start by putting the units back where they were and making sure that that restores your earlier ‘inner peace’? Then take it from there. I have little experience in this area but I'm not convinced that just playing about with the grounds is going to be a fruitful approach. On the bright side, there's plenty folk round here who should be able to help.
Edits: 08/26/11
Awesome. I shall try to implement one soon. If the psu for the P4 & the Julia need to be kept outside the cMp cabinet, is it ok to run a twisted wire with a length of about 12 to 16 inches from the psu to the P4 and/or Julia ?? Does this cause any harm in any way? Or is it mandatory to keep the psu close to the load using short lengths of wire. The problem with the latter is that the transformers (AC power) will radiate inside the cabinet. Which of the two would be a wise choice??
Jolida,
Provide or point us to more details on and post some pictures of your linear supplies & how they fit into your cMP case... That will help a lot in understanding what happened when you located your linears inside of the case.
But before I go into a few ideas, let me amplify something Dave suggested... If you want to learn a lot about practical power supply design, read up on what John Swenson has written. In addition to the thread Dave referenced, I suggest the following one on DIYHIFI.ORG: http://www.diyhifi.org/forums/viewtopic.php?f=15&t=1957 and also doing a search for posts by John on low-Z power supplies, mostly in the Tube DIY forum a few years back.
To reduce noise induced in your linear supplies, I can think of several things to try:
1. Use 'transformer-ringing snubbers' as John mentioned in the computer PS article Dave cited or the one I listed above from DIYHIFI.ORG.
2. If you aren't using good soft-recovery diodes (like MSR860's), change to them.
And of course, John Swenson's supply is a great solution. BTW, I believe it is his raw DC supply section (transformer -> snubber -> small cap -> choke -> larger cap) that does the supply noise reduction trick. I suspect that any good regulator will work well after this portion.
Then, I can think of a number of other causes for the sound differnces you hear with your linears inside of your cMP case:
1. How your wires are configured and dressed. For the least amount of radiated field, all wires should be twisted or braided with their opposite... Positive against related ground wire, the three wires coming out of a center-tapped transformer braided, etc. Also, route the wires so they are suspended in free-air as far away from other wires, surfaces, and components as possible. If they must come near other wires, try to cross them at 90-degrees. If they have to touch a surface, use a small block of wood to hold them away from the metal. And take your AC inputs to the transformers out of the case as quickly as possible and especially minimize what they touch and come near.
2. If you haven't sexed your transformers (or don't even know what that is), let me know & I'll post references. But if you haven't and if your transformer's cores are electrically connected to the case of the cMP, circulation currents from your transformer's cores may be polluting your grounds.
3. If your cMP case is steel, then it is a good idea to leave the linear supplies outside... And eventually move all of your cMP out of the case. Magnetic steel cases and hardware (non-magnetic is a little better) tends to add a thinness & harshness to the sound.
4. How you have your linear's parts, especially the transformers mounted, will impact the sound. See the pictures of a couple of my supplies... Note that I've removed the steel cap around the laminations and mount the transformers to a wooden (in this case, bamboo) base using brass hardware & nylon standoffs. The brass screws/bolts go all the way through the wood base & are fastened with brass acorn nuts which act as small 'tiptoes' to better control vibration from the transformers. When I have some noticable vibration on a transformer I use compliant footers (typically from Herbie's Audio Products) to isolate them and their bases from the case.
5. Vibration damping of the case, bases, transformers, and supply components like the diodes, capacitors, and heatsinks will make a difference. I use a combination of Dynamat Xtreme (very good for resonant surfaces, but tends to emphasize & muddy bass a bit) and EAR SD40AL (more neutral than Dynamat).
While I do agree that the radiated field from your transformers can cause a problem too, IMHO these factors will generally make a larger difference in the SQ.
All of this does not detract from Dave's post or the information imparted there. But these are all pretty simple things you can easily do and try.
As for how to run wires from your supply into your P4 or Juli@, of course shortest is the best. You are better to have the regulator as close to the power consumer as you can manage. And if you do need to run wires, use a good conductor and insulation and twist/braid them as suggested above. 12-16 inches is not too bad.
Greg in Mississippi
P.S. Also read John Swenson's comments in these threads to better understand some of the complexities of the mechanisms that impact the sound quality of our cMPs and also help explain why things that seem like they shouldn't make a difference in SQ do:
http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=90268
http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=87759
http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=89544
Everything matters!
Great Work. I have made my linears following your instructions. The parts i used are the MUR 860 diodes ( only two diodes doing a full-wave rectification, as the transformer i used has a center-tap),ELNA Silmic II Caps,& a Dexa Regulator. It looks quite different from the pictures u posted above though. I will post some pictures once i go home this evening. I have no complaints with the linear supplies. They have improved the cMP a lot. The only issue i faced was when i kept them side by side inside the cMP cabinet ( Alumimium), which is grounded. Before i put them inside, i had just the linear for the Julia inside the cabinet & the one for the P4 outside. This was very fluid & clean. The moment i brought the one for the P4 inside, it messed up the whole spectrum to a very great degree. Last evening i wanted to do another trial so i moved both the linears about 3 inches apart (inside the cMP itself)& surprisingly it performed a lot better. Im not able to figure out what is going on technically. But by now its quite evident that both the fellows dont like to share the same place. I intend to revert them back to where they were originally, one in & the other out of the cabinet to see if it solves the problem...
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