| ewildgoose |
Since there seems to be a lot of opinions on the best design for a UCD or Zappulse power supply, and the advice is rather scattered over a number of threads, I think it would be useful to document a decent basic design here. Hopefully others will also post tweaks as well.
In any design we need some parameters to optimise to, so I am going to loosely propose the following (which might hopefully be applicable to most builders)
- Need a good basic design. There is little point trying to add exotic parts for a 1% improvement if a better design exists that gives a much better improvement
- Stereo amps. Two modules in a box
- Modules placed physically apart (to reduce interference, and give more options to control heat)
- Case sizes need to be reasonable 80mm to 120mm maximum. For most purposes, this probably means that dual large torroids are not feasible, hence dual mono supplies are going to be difficult to implement. Note that LCAudio do have some very slim 200va torroids where you can pack 2 in a 1U case, and 4 in a 2U case!
- These digital modules appear not to need quite such high end supplies as a more traditional design. Therefore the design should be simplified appropriately.
Now, from reading here:
http://www.tnt-audio.com/clinica/ssps1_e.html
..and also from the notes on the UCD180/400 threads, and from comments from Lars and Jan-Peter, I believe the following design is suitable for a decent digital amp power supply:
[IMG]htp://www.wildgooses.com/downloads/ps.jpg[/IMG]
However, there are still some unknowns that I don't quite understand:
Firstly, the small caps across each diode were suggested in the UCD180 thread.. Are they still appropriate to this design and have I drawn them in the correct place? In the UCD 180 thread it was suggested that they only be place on the AC to DC negative diodes, is that advice good, and how would it relate to the design above? The LC Audio design does not include these
Secondly, LCAudio, and the link above recommend a small cap placed (100-330nF) between the two ac inputs to each rectifier. Should we add this to the design here?
Thirdly, does the use of double rectifiers make much useful difference? Would, say, two torroids and single rectifiers per channel be more useful for these modules in practice?
Finally, I drew in the two pairs of caps to be physically closer to the modules. Is this sensible/necessary?
Does anyone have any comments on this design? Can we improve it (usefully)? Any suggestions on minimum sizes for the various components (given a certain application)
In my case, I have a choice of a single large 1000Va torroid + 2 rectifiers to feed two UCD400s. Or I have a pair of slimline 200Va torroids that I could use with one rectifier per channel (dual mono though). Any thoughts on how these two options would stack up?
Thanks
P.S. Anyone know why my images aren't appearing inline? |
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| indoubt |
Interesting topic.
I consider buying the ultrafast diode bridges from the group buy elsewere in this forum for my zappulses (2.2 SE) or alike
Probably one toroid per zap, so I'll need four single bridges.
Whether the capacity will be a singe big one per rail or a configuration as per TNT suggestion I do not no yet.
The 200VA seem to small. It has been regularly stated that the Zap modules benefit from sufficiently sized transformers to really make them sing.
What is unclear to me is whether that only relates to VA rating or also to the secundary voltage. |
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| ewildgoose |
| quote: | Originally posted by indoubt
Whether the capacity will be a singe big one per rail or a configuration as per TNT suggestion I do not no yet.
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Thanks for the thoughts.
Bruno (UCD designer) has stated in the UCD180 thread that quality of caps is more important than size. His own reference amp uses (I think?) 4,800uF caps (somewhere about post 258 in the UCD180 thread I think?) |
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| indoubt |
I am aware of that, I'm still indoubt as I have 8* 68.000Uf in stock. Unfortunate they are 50V. I'm still considering to go to a 33V tranny as I do not need the full power of the zapp but would like to have the current (2*800Va tranny or alike)
I have some time before building starts. Tomorrow I'll get the key of a new house so I will be building :) although the amp will have to wait. The zapps are on stock waiting to be used. |
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| ackcheng |
| I remember I read somewhere that ultrafast diode bridges is not as good as Fast Slow recovery bridges..... |
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| tiki |
Hi,
In the last days I experimented with a softstart circuit. The result is to be seen here. May be, this circuit was done before anywhere, but I did not find this version. The sum of all elements of the PSU's softstart part cost below 10 Euro. It is very simple too.
The SCR's gate is very sensitive, so high resistor values work well. It's extra supply with the two 1N4004 is not tested yet, I connected the circuit to the 10000µF caps directly until now. This version's disadvantage was the long switch-off time (appr. 10 seconds, dependend on the on-state duration). With the extra supply this will be shortened to below a second, hopefully.
The diac is necessary to turn on the SCR safely (another pulse generator may do that too). The two resistors at the relays' contact hold the inrush current below 2A. It takes around 0,7 seconds to load the main caps up to appr. 5V below the nominal supply voltage. After that the relays switches on and the caps will be charged fully. The circuit works fine.
Any suggestions for advancements?
Best regards, Timo |
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| tiki |
Good Evening,
Some modifications of the circuit above:
C4: 100µF -> 22µF,
added diode (small signal) between C1+ (anode) and C4+ (cathode),
Resistor 15k between C4+ and GND.
And the diodes D5 and D6 were added, of course, while C4+ was disconnected from the positive rail.
This modification shortens the relay switch-off time to below 0.5s (after mains switch). This time is independent from the rail voltage now. That means, if the mains switch is off for a period longer than 0.5 seconds, the softstart is functioning, otherwise (well below 0.5s), the relay switches immediately on. That's not too bad, because the rail voltages are still near to their nominal value. So there cannot be an exceptional inrush current in this case.
The supply voltage of the relay has a ripple of about 3Vpp due to the small filter cap of 22µF. This is ok, because there is no connection to the rest of the amplifier circuit except ground and secondary transformer AC. And the currents are very low, therefore I do not expect any disturbances.
The delay is in the range between 0.5 and 1 second with the given values (on my bench).
The relay is a 16A-type for 48V nominal supply, consuming less than 10mA.
I would be happy about some criticism. Maybe, this circuit could get better.
Best regards, Timo |
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| micheat |
| What I am curious to know is, how important is the use of the ferrite beads? Also would using 2 10000uf capacitors per modules have any negative effect on the sound, over just using 1. Or how about 1 15000uf cap per module. If cost was absolutely no object, what would be the very best way to go for the absolute highest sound quality? Considering the efficency of the modules, and ability for them to operate with such a small power supply, compared to class a, or class a\b designs, cost wise a person can put alot better quality parts into the power supply, and still keep the project cost low. Hopefully achieving better over all sound quality then class a or a\b designs, costing the same price. At least thats what I'm hoping. |
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| chrisb03 |
| How do you calculate the correct size for resisitors across the power supply caps? These will be for discharging the capacitors on power off. Will these affect the sonics of the UcD400's? |
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| classd4sure |
"Bleeder" resistors, easy, use RC time constant to come up with a value that will discharge them in a reasonable amount of time, 5 to 10 seconds perhaps, make sure of the wattage rating as well.
Sound? Try it and found out, I doubt it though. |
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| ericpeters |
I've built several versions with zappulse 2.2SE modules.
Started with one stereo version with a kit power supply built 12 pcs 100v deawoo caps. 550VA 55V torroid. one bridge built of 4 fast skotchky diodes with polycap bypass.
This sounded terrible, especially the treble was very bad. sounded more like a first generation (well maybe second) soundblaster card.
the second step I did was shortening the cables between capacitors and modules form about 15cm to 8 cm. This gave a modest but good audible improvement.
I only swapped the torroid for with a 1000VA 42 volt version and the sound quality dramaticlly improved especially the treble.
After that I built my own power supply according this scheme: http://www.zero-distortion.com/tech.../powersi_05.htm
I basically used 2 1000VA 42 volt torroids, 4 BC components 33000uF capacitors per channel, 2 skotchky based bridges per channel including all bypass capacitors on the bridges and the capacitors before the bridge (this should filter HF rubbish from the mains) I've also installed 10 watt bleeder resitors
This lead in to a very good sounding amplifier with sweet treble, like a tube amp and very deep bass like an old Krell. (I actually was not aware that my speakers could go so deep and found that my REL subwoofer became obsolete when listening to music.
I also built 2 monoblocks and have NOT encountered any problems with unsynched switching frequencies so i had no background noise (until one module broke down and started humming and whistling a lot)
I used to have cabling between the poles of the capcitors but I've changed that to solid 5mm copper plate, this was more for mechanical reasons. I also added a lot of bitumen damping to the aluminium housing of my amps.
Apart for the defect (that is being repaired) I'm very happy with my current result but I wonder if it is not just a lot of overkill.
- LC audio suggested smaller and better quality capacitors: because I have low impedance and current hungry speakers I decided to go for the larger bank.
- According LC audio a 500va torroid should be sufficient: without any doubt I do not agree with that statement. The change of the transformer was by far the biggest improvement.
I believe (but can not explain why) that a current capability of the power supply is by far the most important part when designing a power supply for a zapp amplifier. This might be less important when speakers are used with good sensitivity.
BTW: I also have added a softstart circuit from ESP in each monoblock, it was impossible to start the amps without blowing the mains fuses and I had to change the timing because I need a few seconds to slow-charge the capacitors, instead of the suggested 1/2 second for these softstart units. |
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| bambadoo |
What Ericpeters did, is almost identical to my psu with my Zappulse monoblock. I have not filtercaps over the diodebridges, and no bleeders. Otherwise, this is the best result I have made with the zappulse modules.
I use 2 pcs Elna Cerafine 18000uf/module (monoblock), and 1pcs 800VA trannie 42 v/channel (monoblock).
Internal cabling is pure silver, except the power cabling.
Best Regards |
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| Paul Ebert |
Given the efficiencies of these amps, is it at all feasible to use a bank of SLA batteries and a charger as a power supply? That is, if one was willing to ignore size and weight. What would it take in terms of amps-hours to run, say, a UcD180? I'm not very knowlegeable about this stuff. But, the idea intrigues me when I consider trying to find and afford good capacitors.
Are there other potential problems besides current capacity and/or recharge time, to using batteries?
I seldom listen to my system for more than a few hours, giving the rest of the day for the batteries to recharge.
Is this a ridiculous notion?
Thanks.
Paul Ebert |
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| ewildgoose |
| quote: | Originally posted by ericpeters
This lead in to a very good sounding amplifier with sweet treble, like a tube amp and very deep bass like an old Krell. (I actually was not aware that my speakers could go so deep and found that my REL subwoofer became obsolete when listening to music.
I also built 2 monoblocks and have NOT encountered any problems with unsynched switching frequencies so i had no background noise (until one module broke down and started humming and whistling a lot) |
Hi, this is a really interesting comment, because it pretty much confirms something that I am seeing here. My second amp with single 1,000va 45V torroid is heaps better than the dual 200va amp. However, there are other differences as well like spacing out the two modules, and removing the Y caps on the power inlet, also triple the size in main caps. However, I suspect that the Y caps in the main filter might be a big part of the problem...?
I have that whistling going on one of my modules. It hadn't really occured to me that the module might simply be broken though..
Just a quick question though. How big a difference did you find your final design was from the original version with the 1,000va torroid and shorter wires? Just curious as to the benefits of all that extra work (was it a big change or just a little better..?) |
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| ericpeters |
| quote: | Originally posted by ewildgoose
Just a quick question though. How big a difference did you find your final design was from the original version with the 1,000va torroid and shorter wires? Just curious as to the benefits of all that extra work (was it a big change or just a little better..?) |
Very difficult to say because I had about 2 days without listening between dismantling the first design and starting to listen with the new ones. My feeling is that bass improved and also imaging and treble.
I would probably built the same monoblocks again but use a normal heavy duty rectifier bridge if I would built them again.
Because one module is being repaired I'm now looking to change the layout to make the wires as short as possible. I will also change the low-level signal wires to single strand pure silver. (I currently use teflon isolated twisted pair copper (CAT 5) which is quite good but I do have plenty of silver wire laying around and can't use the amps anyway until my module get's returned.
My Zapp module PROBABLY broke down after feeding source into the input of a module without power supply, with disconnected speakers (but no short circuit, open circuit) and then while this was the case it was switched on. The result was a high pitch whistle and humming and other background noise. This noise is also there when the other monoblock is switched off. I tried several scenarios but the noises were alwas related to that one single zap module.
Before that problem both amps were absolutely silent.
My next project will be using the old power supply from the first design to drive 2 Ice modules, I want to test how small the power supply for a class-d amp can be built without loosing quality but when using power hungry speakers. I already tried this with the stock evaluation kit (400VA transformer) but this was unsatisfying. I will first put another transformer on the kit and after that I will move to a bigger capcitor bank and test both transformers. |
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| mattjk |
So you guys are saying a larger transformer would be more of an improvement than a large bank of caps? My amp case is pretty limited in size, so I could only go really big on one area.
I am currently using a 500va toroid, and the stock predator PS.
would it be better to swap out the 500va with a 1000va. or just add another 500va? If I do that, I think I have enough room to add 4 more 10k caps.
And, what kind of speakers are you guys running?
I had a chance to try my amp on a pair of B&W 703's, and the sound was absolutely stunning. It beat all the other amps they had there. On a pair of Sonus Faber's, it sounded downright horrible. |
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| ericpeters |
| quote: | Originally posted by mattjk
And, what kind of speakers are you guys running?
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I running on Apogees; my main speakers ar Duetta signatures but I also got Calipers. They do require a lot of current and the D-sigs got an almost flat impedance of 3 ohm, the calipers smaller but even less efficient. That's one of the things I don't know: is the size of the transformer directly related to sound quality or is there also a strong relationship with the efficiency of the loudspeaker?
I would start with the transformer. (Try Farnell i found their prices for Torroids are 1/2 the price I paid for mine.) |
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| mattjk |
I hooked up a 100V 82,000uF capacitor to only one channel tonight. I set my preamp to mono and I listened to one channel at a time. It definately made an improvement in the high frequency. Cymbals sound a bit more detailed and forward. Before it was rolled off and too laid back sounding.
Still too soft sounding though. |
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| mattjk |
Now, I hooked up 3 additional 10,000uf caps to the other channel, for a total of 40,000uf.
I can't tell the difference between the two, but the amp certainly sounds more lively. There is a certain song that is all acoustical guitar. It was unlistenable before, but now it sounds very very good, but not perfect. Time to try a larger tranny now.
The overall sound seems more effortless as well.
I am running acoustat 2+2 speakers, BTW.
still too rolled off though. :bawling: |
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| ewildgoose |
If you read the UCD thread and look for comments from Bruno he suggests a formula for calculating required size of the main caps bank. Basically he points out that "power" factors out and it depends entirely on the output resistance of the speakers.
I think the punchline was around 12,000uF per channel was good for 8 ohms? Bruno states though that he uses only small caps on his reference amp..? |
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| Cobra2 |
I tried a few, and found that the amps (Zap & Tripath) responded extremely on psu size & caps.
And bigger is better. A good start (minimum) would be a 500va trafo + 30 000uF x 2
-So much for efficciency...
Arne K |
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| ewildgoose |
| Into what speakers? (This seems extremely relevant you see) |
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| stef1777 |
PSU for ONE UcD180.
4 x 10000UF 63V BHC slit foil
2 x MCap 2.2UF
4 x IR hfa25pb60
4 x Wima MKP2 22nf 100V
1 x toroid 160VA 2 x 33V |
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| tiki |
Hi,
here is the final schematic of "my" softstart circuit and here the "PCB" of the softstart circuit.
Delay is about one second, recovery time (minimum time between switch off and switch on for "retriggering" the delay) below half a second.
I realised, that it is better to let all the circuit on the primary side of the supply, to avoid mixing primary and secondary voltages. The actual board is 120mmx50mm. All necessary connections to mains, two-pole mains switch and transformer are included in the connector.
Unfortunately I did not find the time to complete the amp. And I still miss the right loudspeakers for comparison of the amps too. :bawling:
Regards, Timo |
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| janneman |
Read all output the intricacies of class D and especially the psu at http://www.edn.com/article/CA476906...1&rid=243880419
Like this:
"No matter what type of supply you use, Class D amplifiers are much more sensitive to the quality of the power supply than their linear counterparts. So, although Class D technology will almost certainly reduce power requirements by 50% or more, the actual design of the supply tends to be rather more intricate. The reason is simple: With nothing but switches (power MOSFETs turned fully on or fully off) between the supply and the output, any mains or audio-band ripple on the supply rails will modulate the output signal. In other words, all-digital Class D amplifiers have a PSRR (power-supply-rejection ratio) of 0 dB; they essentially use the supply as a voltage reference."
Jan Didden |
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| classd4sure |
Hi,
Not posting this to start a war!~
Howsoever:
| quote: | | all-digital Class D amplifiers have a PSRR (power-supply-rejection ratio) of 0 dB |
That's brutal, but the key here is "all digital", so it doesn't really apply to the topic of this thread at all. I don't think there's very many all digital solutions out there either.
I would still agree with that, until feedback is applied in one form or another.
I guess an amplifier can no longer rightfully be considered "all digital" if it employs feedback? You would need a conversion in there someplace, which then classifies it as an analog amplifier.
ZapPulse and UcD both are not "all-digital" and do employ feedback, therefore the PSRR is not 0dB.
I have read that article, I haven't analysed it thoroughly, but it seems out of touch with what the cutting edge seems to be today (all analog, self oscillating), and perhaps, more geared towards selling their own products.
"Julian Hayes is the vice president of marketing at Wolfson Microelectronics plc "
I hope this wasn't the same article recently referenced to in our "sticky" thread here.
My views on the power supplies, I don't like the OEM way of calculating a transformer, OEM typically lacks, this is what brings us all here in the first place. I don't think DIY'rs here want to pinch pennies in areas it really makes a difference, or throw away tonnes of money in other areas where it doesn't make a difference. If we pool together we can avoid such things occuring for everyone, lessen the learning curve, and cost of it.
So I don't think 70% of calculated requirement is a good way, for whatever that's worth, I also dont' think 130% of calculated value would get you much of anything. Why not go for 100% of what the calculated requirement is, maybe 110% or 120% for good measure (usual losses etc).
Overkill here will only hurt the pocketbook.
Caps, Bruno's requirement, calculated ripple requirement, seems the smart method. He also warns about power factor .. as ewildgoose reminded us:) Bruno has even provided, if I recall correctly, a very general rule of thumb for sizing them according to the load. This is engineering so there should be no black magic voodoo solution here.
Perhaps there are other factors to the supply capacitors which could be discussed here that might have more of an impact in quality than mere size alone. ESR.. ESL.. Ripple capability, etc.
It would be nice if we could work out what works and what is BS so we dont' all go running for split foil gimmicks that cost a fortune, and just stick to the basics that do actually work.
Kind of like, we all know what's best for rectifier diodes, right? Thanks to the dozens and dozens of previous posts on the same subject here =HexFred, or any ultra fast/soft recovery. And voila, our work is done.
Has anyone ever compared a standard set of properly selected computer grade caps to "possible" gimmicks like split foil/virtual 4 pole etc? Or do we just buy them because the marketing got to us?
Thanks,
Chris |
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| ericpeters |
I found the link interesting because it basically said that it is very important to have low ESR in your capcitorbank. Also the bank should be big enough but if ESR wasn't low this was not enough.
All ESR curves I've seen show that ESR drops with rising temperature..... Would it make sense to heat up the capacitors? |
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| classd4sure |
Hi,
So far I've really seen nothing to turn me away from good computer grade caps. They seem to have the best "package" spec wise.
Nice observation you had about ESR dropping with temp, perhaps we should look at the ESR value at operating temp.
Alot of cap manufacturers give rather sparse information on their product though, enough that you can't really compare one brand to the other alot of the time.
Well, I'll be the first to say I don't think intentionally trying to run the caps hot is a great idea, as it will drastically reduce their life span. Do you think it would be worth it? What's the rule of thumb (correct me if I'm wrong) every 10 degree C increase in temp halves the life span, over a certain range before you reach a point on either end where it of course doesn't matter (meltdown).
They aren't cheap I'd want em to last a very long time personally.
A good question to ask might be, what's a good ESR to aim for anyway? At what point does ESR no longer play a roll? No point having a cap with a lower ESR than the wires/traces themselves, at least I'd imagine anyway.
It would be great if we could just narrow the list of possibilities down to just a few brands/models that cut the mustard and leave the voodoo out of it?
For example, can anyone really say gold plated leads are worth it? We don't use gold plated wires.. I think it's pretty easy for manufacturers to stamp "audio" just so they can jack the price up, as they push their gold plated leads or split foil whatevers, and ignore the specs of it that actually do make it a decent cap for audio. Let's get some light on the subject yes?
Thanks
Chris |
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| ericpeters |
I know we don't want to run caps hot for the obvious reasons, but it might be a posibility to use the idea to test the effects of esr on the sound quality, while keeping the rest exactly the same.
Putting more caps in parallel operation is a much easier way to lower esr.
I also made me thinking about several famous class-A designs that use to run very hot (Old Krell's, old Musical fidelity) and had good sound. Was there a relation? Probably not but still an interesting idea.
One other thing I notice is that all theory suggest that this has most impact on lower frequency's.
My practical experience with Zap 2.2SE was that with too smal power supply the HF was much more affected. I assume that the current draw in the bass does affect the voltage on the supply rails and this generats IM distortion in treble. |
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| stef1777 |
| quote: | | Originally posted by ericpeters I also made me thinking about several famous class-A designs that use to run very hot (Old Krell's, old Musical fidelity) and had good sound. Was there a relation? Probably not but still an interesting idea. |
I personally have a 50W Class A power amp (French design with bipolar transistors). The sound is very good only when it's (very) hot (15 mm).
But not sure it is the caps. |
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| classd4sure |
Yeah that's an idea, for testing /experimentation purposes.
Sure, this all makes alot of sense.
I wonder if ESL would play a roll on affecting the highs as well, I would think so between a certain range.
edit:
We could all really speculate until we're green in the face but someone is going to have do some serious experimentation before we get any answers, maybe they could be sent sample caps to keep costs low and help make the results meaningful, just an idea. |
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| tiki |
Hi,
I did not read the texts behind the last link, maybe there's something described better.
Thanks, Chris, for your statements to stay tuned to engineering, not to vodoo.
My opinion concerning ESR drop with temp. The disadvantage of ESR is twofold at least:
- ESR will produce heat due to the I^2*R power loss, induced by ripple current, 2A at 20mOhm will result in 0.16W. The according temp rise has to be added to the operating temp.
- ESR produces steps on the capacitor voltage (= rail voltage) due to I*ESR. This is important, because the charging current of the main caps is much higher than the average discharging current.
I did not measure it, a rough estimation instead (assuming 2A average, resulting in about 160W at 40V rails, from 10mF caps): delta(V)=I*delta(t)/C will result in 2V(!, pos and neg individually) rail drop per 10ms.
To get the charging time, I go the loop way calculating sin(x)=2V/40V; delta(t)=(90°-x)/90°*5ms (90° and 5ms are the equivalents for the raising part of the charging sine voltage).
This will result in approximately delta(t)=1ms, which ends in a charging current, ten times of the discharging one: Icharge = 20A (I(charge)/I(discharge)=t(discharge)/t(charge)). Multiplied by the ESR, this will add 0.4V steps (within 1ms) to the rails.
Hopefully I'm not completely wrong.
Regards, Timo |
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| chriscam |
| quote: | | P.S. Anyone know why my images aren't appearing inline? |
change htp in [IMG]htp://www.wildgooses.com/downloads/ps.jpg[/IMG] to http. |
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| classd4sure |
Hi chriscam,
Don't know myself, maybe they have that feature turned off again to save bandwidth? Your link works though.
Excerpt from http://capacitors.com/picking_capacitors/consider.htm
(C). ESR is determined by:
ESR = (Xc/Q = Xc (tan ð), with Q = 1/DF.
From this, we can see that "lossy" capacitors and those that present large amounts of Xc will be highly resistive to the signal power.
Circuit designs employing low Q capacitors usually produce large quantities of unwanted heat because tan ð and DF (or 1/Q) typically increase in a non-linear fashion with rising frequency and temperature. With some capacitors, this effect is enhanced by the naturally occurring decreased capacitance at high frequencies. High currents also produce increase heat, which in turn again increases the ESR and DF.
Even with substantial changes in current flow, high Q (low DF) capacitors will not exhibit the value shifts common to equivalent components exhibiting high DF, ESR, and other parasitics. Low ESR reduces the unwanted heating effects that degrade capacitors. This is an important goal in designing these components for high -current, high-performance applications, such as power supplies and high-current filter networks.
End of Excerpt.
Something of interest, according to this site, the affects of high frequency bypass capacitors are nullified by the wiring inductance should you put them close to the PSU's main caps. Remember Bruno saying high frequency bypass caps weren't needed, they were already on the amp? It seems this is the ideal place for them to be, since their main function is to combat the ESL.
Oh yeah, great work on the slow start circuit Timo :)
Regards |
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| Golgoth |
| quote: | Originally posted by Bruno Putzeys
The amount of stored energy is a certain factor T times the amount of power (=energy per second) the amp is supposed to put out.
If the caps are recharged 100 times per second, and we want to lose (and recharge) no more than 10% of total stored energy every mains cycle (translates to 5% voltage droop), the rule of thumb becomes to store T=0.1 joules per watt (=seconds!) of rated power.
This figure in seconds also works out to be the product of load impedance and storage capacitance.
T=C*R
or
C=T/R
This is for a single rail. For dual rail systems like UcD you get two caps of half that value.
Example: For T=0.1s (rather conservative in CE terms), a half-bridge class D amplifier designed to operate into a 4ohm load requires two capacitors of
C=0.5*T/R=0.5*0.1/4=12500uF
If the fact that output power factors out is counterintuitive, consider the fact that an amp of 4 times the power will have twice the supply voltage so the same capacitance will hold 4 times the energy. Naturally, at twice the rated voltage the caps will be a bit bigger too.
Do not forget to multiply the capacitance by the number of channels connected to the power supply...
Another part of your question concerned the use of transformers.
Normally you will use one transformer per power supply. If one 2x50V supply is used to power two amps, there is only one transformer. If you have two transformers you should have two independent power supplies too (dual mono).
The only exception would be if you were to attempt making a "super-screened pair" where two transformers are stacked on top of eachother into a single steel pot and placed in parallel (but with the magnetic fields going opposite ways) with the aim of getting super-low stray field. Such an excercise is most probably overkill, given the already low stray field of good toroids.
Hope this sheds light on your question. |
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| Golgoth |
So that's, per rail and per channel,
12500 µF for 4 ohm speakers
6250 µF for 8 ohm speakers
Timo, to pick up from your last post (#320) in the UcD400 thread, apart from overkill and inrush current, oversizing the capacitors increases the peak recharging current, which may not be totally innocuous even if it doesn't increase the corresponding voltage pulse due to ESR (if you double the capacitor you double the peak current but you halve the ESR so R*I doesn't change) |
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| stef1777 |
Hi Folks!
I tested my UcD180 mono block with and without the filtered IEC plug. No difference.
What is the common symptom with this when problems with the filtered IEC plug?
Stef... |
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| Golgoth |
| quote: | Originally posted by stef1777
Hi Folks!
I tested my UcD180 mono block with and without the filtered IEC plug. No difference.
What is the common symptom with this when problems with the filtered IEC plug?
Stef... |
So that we have a copy in this thread for future reference, here is Bruno's opinion (post #345 in UcD180 thread):
-------------------------
Do not use mains filters with Y capacitors installed. An Y capacitor makes a capacitive connection (several nf) from the mains lines to your chassis and hence audio ground.
So there is the audiophile designer, using transformers with a shield to remove the slightest chance of the mains polluting his system ground, then installing a schaffner inlet that puts 2.2nF straight from the mains into the chassis, simply because he heard somewhere that mains disturbances are audible. They are, more precisely when such a filter is used.
All commercially available "combined mains filters" have Y capacitors. Don't use them. If all your audio devices are connected to one wall outlet (likely), you can use such a filter there, but by no means on individual boxes.
In principle you could make a filter with only chokes (cm/dm) and an X capacitor. Fine with me, but unless you have a problem with heavily polluted mains you don't need them. The UcD will not be a source of mains pollution. If your mains are polluted by an external cause (like you have a car factory next door), a centralised filter on the outlet is more effective.
Fyi, none of my audio devices have mains filters on them.
----------------------------------
Stef, Bruno's arguments do seem to make sense. To actually hear the difference you could try testing again while deliberately creating mains disturbances eg by having somebody action a power drill somewhere in the house. Do keep us updated :) |
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| stef1777 |
| quote: | | Originally posted by Golgoth Stef, Bruno's arguments do seem to make sense. To actually hear the difference you could try testing again while deliberately creating mains disturbances eg by having somebody action a power drill somewhere in the house. Do keep us updated :) |
:dead:
I can try to connect a large drilling machine directly on the same power supply plug! :bawling:
;)
I prefer to have no problem. :) |
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| chrisb03 |
| quote: | Originally posted by OA51
Is there a "maximum'" limit of PSU capacitor size, i.e 100000µF/rail or whatever, where the sound quality of the UcD400 will start to degrade?
Given that you use a suitable transformer...
-like with the chip-amps...
/Stefan |
| quote: | Originally posted by chrisb03
I'm also interested in the answer to this question. I have made a couple pcbs with 27200uF on each rail. I'm a bit worried that this may have a "bad" sonic difference. The capacitor banks are my last bits to go into the enclosure installation. I'm just holding off incase there is a problem with capacitor quantity.
I've also changed the layout. I have attached new pics if anyone interested.
Chris |
| quote: | Originally posted by wytco0
Chrisb03, I think Bruno said something about this on the UCD180 thread and someone else referred to it recently, so if you go to the end of that thread and work backwards you should find it.
I notice you have a load of what I think are called snubber caps in your power supply, why have you included them? |
| quote: | Originally posted by tiki
Hi,
I know, it's not my competence, in my humble opinion it would be better to avoid mixing the themes between the threads. I would kindly ask you to discuss these supply problems in the appropriate thread. It will be easier to find any special information later, not only for me.
Thank you very much indeed!
For minimum capacitor requirements see Bruno's post. I for myself do not see any disadvantage for too big rail capacitors, except overkill and inrush current without a softstart circuit. :redhot:
Best regards, Timo |
| quote: | Originally posted by Golgoth
Hi,
Timo is referring to this thread:
http://www.diyaudio.com/forums/show...&threadid=44515
Indeed it is a good idea to summarize supply discussions in that low volume thread, as the main UcD threads have become near-impossible to browse (about 95 pages for the UcD180 thread!), and the "search this thread" function is not very powerful.
I will quote Bruno's post on capacitor sizing on that thread. |
Just moving this topic to appropiate thread.
The snubber caps are base on existing designs. Link to one is already mentioned in this thread by ericpeters.
http://www.zero-distortion.com/tech.../powersi_05.htm
Chris |
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| rha61 |
indeed there is sonic differences when you increase the PSU capacitors of a classD amp
Give it a try
start with 1000uF , and then 10000uF , and then 20000uF of same brand
it's the same effect than with chip amps ! (big damped bass and dull midrange )
alain |
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| chrisb03 |
| quote: | Originally posted by rha61
indeed there is sonic differences when you increase the PSU capacitors of a classD amp
Give it a try
start with 1000uF , and then 10000uF , and then 20000uF of same brand
it's the same effect than with chip amps ! (big damped bass and dull midrange )
alain |
I don't understand why this would happen. What's the difference between using large amount of capacitance and a battery? |
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| rha61 |
| quote: | Originally posted by chrisb03
I don't understand why this would happen. What's the difference between using large amount of capacitance and a battery? |
one of the problems is probably the capacitor impedance vs frequency curve
only some batteries give good results ( a thread talked about alkaline )
optima batteries are renowned ( high current peak , very low ESR )
www.optimabatteries.com
alain |
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| chrisb03 |
| quote: | Originally posted by rha61
one of the problems is probably the capacitor impedance vs frequency curve
only some batteries give good results ( a thread talked about alkaline )
optima batteries are renowned ( high current peak , very low ESR )
www.optimabatteries.com
alain |
In other words, if you had low esr it's ok to have large capacitor bank? |
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| FransDHT |
Okay,
I have read this stuff. I have 5 UcD400's. If I am correct I need the following (minimum) supply (my main speakers are rated 8 Ohm):
-> 5*400/2=1000VA toroid, or should I take the 210W/8Ohm?-> 5*210/2=525VA toroid)
-> 0.5*0.1/8=6250uF, 10 times for 5 channels (or 6 10,000uF caps)
Correct?
Frans |
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| Golgoth |
| quote: | Originally posted by FransDHT
Okay,
I have read this stuff. I have 5 UcD400's. If I am correct I need the following (minimum) supply (my main speakers are rated 8 Ohm):
-> 5*400/2=1000VA toroid, or should I take the 210W/8Ohm?-> 5*210/2=525VA toroid)
-> 0.5*0.1/8=6250uF, 10 times for 5 channels (or 6 10,000uF caps)
Correct?
Frans |
Cap sizing is correct, but transformer should be sized as follows:
- Power factor (W/VA) for this type of supply can be as low as 0.5, in other words you need 1/0.5=2 VA/W
- Watts needed: 5*210=1050
=> VAs needed = 1050W * 2VA/W = 2100VA
Note these computations leave zero margin for impedance dips: if you want to allow for impedance dips at half the nominal i.e. 4 ohms you should double the above values, both caps and toroid (BTW there is no point in oversizing further than a factor 2 as the UcD400 will never draw more than 450W anyway, thanks to its OV and OC detections) |
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| rha61 |
| quote: | Originally posted by chrisb03
In other words, if you had low esr it's ok to have large capacitor bank? |
the best way is to test different caps of different brands ( the result depends on your speakers )
unfortunately , big ( and good ) caps are expensive
Elna , i think , is a good standard
alain |
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| tiki |
Hi,
Michel, apart from my possibly insufficient calculation (e.g. missing transformer impedance) I cannot fully agree to your statement about the higher recharging current. This current is, in my opinion, primarily dependent on the discharging one. The discharging current takes a tangible amount of charge from the caps while the approx. 10ms discharging time, independent of the cap value. So the recharging current should be determined by: the recharging time, the voltage drop (which is indirectly proportional to the capacitance), the capacitors combined impedance (ESR, ESL) and the source (transformer) impedance. The frequency dependent influence of the capacitance on capacitors impedance is constant due to the more or less constant recharging voltage rise. In fact, if the source voltage follows a sine function, the recharging current will vary over recharging time, so there is a dependance of the current waveform on the capacitance, but this is not valid for the averaged recharge current.
Again, That's only my opinion.
Regards,
Timo |
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| rha61 |
| quote: | Originally posted by tiki
Hi,
Michel, apart from my possibly insufficient calculation (e.g. missing transformer impedance) I cannot fully agree to your statement about the higher recharging current. This current is, in my opinion, primarily dependent on the discharging one. The discharging current takes a tangible amount of charge from the caps while the approx. 10ms discharging time, independent of the cap value. So the recharging current should be determined by: the recharging time, the voltage drop (which is indirectly proportional to the capacitance), the capacitors combined impedance (ESR, ESL) and the source (transformer) impedance. The frequency dependent influence of the capacitance on capacitors impedance is constant due to the more or less constant recharging voltage rise. In fact, if the source voltage follows a sine function, the recharging current will vary over recharging time, so there is a dependance of the current waveform on the capacitance, but this is not valid for the averaged recharge current.
Again, That's only my opinion.
Regards,
Timo |
Hi Tiki
when i was speaking about impedance vs frequency curve , it was that large can capacitors have often a better curve than small one
alain |
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| chrisb03 |
| quote: | Originally posted by rha61
the best way is to test different caps of different brands ( the result depends on your speakers )
unfortunately , big ( and good ) caps are expensive
Elna , i think , is a good standard
alain |
I have four 6800uF caps in parrallel per rail, therefore esr should be lower. As I'm new at this, I'm trying to make sense of statments made in many posts. To recap, large capacitance is ok as long as you have low esr.
Chris |
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| Golgoth |
| quote: | Originally posted by tiki
Hi,
...current waveform on the capacitance, but this is not valid for the averaged recharge current.
Again, That's only my opinion.
Regards,
Timo |
Sure, I did say the "peak recharging current". Average doesn't increase of course. |
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| rha61 |
| quote: | Originally posted by chrisb03
I have four 6800uF caps in parrallel per rail, therefore esr should be lower. As I'm new at this, I'm trying to make sense of statments made in many posts. To recap, large capacitance is ok as long as you have low esr.
Chris |
what i mean is that for the same value say 6800uF , large can capacitor is often better than smaller one
in your case , i would try 1x6800uF at first , and then 4x6800uF to define the impact on the sound
For example , if your speakers have already very damped bass , 4x6800uF will degrade the presentation
I think there is no rule for power supply caps , except a minimal and maximal value , but for normal listening levels at home , reasonable values often give better results
alain |
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| chrisb03 |
Found Bruno's post in Ucd180 thread, post 294
"Yes you can overdo on caps, at least when the power supply is hard-rectified (normal supply without chokes). The current through the rectifiers becomes more and more spiky and the magnetic fields coming off the hookup wires and even mains cords can potentially start degrading the performance of the rest of the kit. Even if you can't hear the buzz directly, you do hear increased "veiling" of the sound stage. This is one of the reasons "audiophile" mains cables sometimes have an audible effect. I don't like it when mains cables start to make a difference.
The 20000uF per rail that I have on my "esoteric amps" is really as far as I dare take it. I'm planning on a PFC supply to address this." |
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| Golgoth |
| quote: | Originally posted by chrisb03
Found Bruno's post in Ucd180 thread, post 294
"Yes you can overdo on caps, at least when the power supply is hard-rectified (normal supply without chokes). The current through the rectifiers becomes more and more spiky and the magnetic fields coming off the hookup wires and even mains cords can potentially start degrading the performance of the rest of the kit. Even if you can't hear the buzz directly, you do hear increased "veiling" of the sound stage. This is one of the reasons "audiophile" mains cables sometimes have an audible effect. I don't like it when mains cables start to make a difference.
The 20000uF per rail that I have on my "esoteric amps" is really as far as I dare take it. I'm planning on a PFC supply to address this." |
Good digging Chris, it confirms what I suspected: increased peak cap recharging current (i.e. rectifier current), which follows from increased rail capacitance, can be harmful. So until Bruno comes up with his PFC supply (PFC = Power Factor Correction) we should not exceed 20000µF per rail.
So the definitive supply capacitor sizing rule for a two-rail class D amp is:
(Number_of_channels * 50000µF / R) < Caps_per_rail < 20000µF
where R is the speaker impedance in ohms |
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| ericpeters |
| quote: | Originally posted by Golgoth
So the definitive supply capacitor sizing rule for a two-rail class D amp is:
(Number_of_channels * 50000µF / R) < Caps_per_rail < 20000µF
where R is the speaker impedance in ohms |
This would mean you can't size Class D for a 1 ohm Apogee scintilla. And this is exactly the speaker where the owners are the most happy with class-d amplifiers. |
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| Golgoth |
Oops the forum doesn't like "mu" symbols obviously, I meant:
The definitive supply capacitor sizing rule for a two-rail class D amp is:
(Number_of_channels * 50000uF / R) < Caps_per_rail < 20000uF
where R is the speaker impedance in ohms
Which means, BTW, that a single power supply of this kind should not power more than 20000/50000*R = 0.4*R channels! That's a maximum of 0.4*8 = 3.2 channels -> 3 channels per supply for 8 ohm speakers, and 0.4*4 = 1.6 channels -> 1 channel per supply for 4 ohm speakers :D |
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| Golgoth |
| quote: | Originally posted by ericpeters
This would mean you can't size Class D for a 1 ohm Apogee scintilla. And this is exactly the speaker where the owners are the most happy with class-d amplifiers. |
(very strange, my "mu" symbols display correctly now :confused: )
Hi Eric,
No, it just means they would be even happier if they had a PFC supply, or if they shielded their modules from the spiky rectifier current disturbances (faraday cage around each module). |
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| Golgoth |
| quote: | Originally posted by Golgoth
(very strange, my "mu" symbols display correctly now :confused: )
Hi Eric,
No, it just means they would be even happier if they had a PFC supply, or if they shielded their modules from the spiky rectifier current disturbances (faraday cage around each module). |
Note that, as Bruno hinted at in his post quoted by Chris, the rectifier current spikes could be smoothed out by inserting suitable chokes upstream of the capacitors. This would double up as a nice mains filter BTW.
Correct me someone if I am wrong, I find that a 2mH choke inserted between the rectifier and the hot end of the 50000uF rail capacitor would yield a low pas filter with a cutoff frequency 1/(2*pi*SQRT(L*C) of 16Hz, i.e. well below the 100 or 120Hz full wave rectifier current frequency.
Mmmm... it does look like a nice and simple way to achieve both passive PFC and mains filtering with oversized storage capacitors, but we would have to make sure that we don't run into nasty overvoltages when consumption changes suddenly, eg when a silence follows a loud thump. In other words we would need to make sure there is enough damping resistance in the RLC circuit: this may be a case where excessively low capacitor ESR could harm :D |
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| FransDHT |
| quote: | Originally posted by Golgoth
Cap sizing is correct, but transformer should be sized as follows:
- Power factor (W/VA) for this type of supply can be as low as 0.5, in other words you need 1/0.5=2 VA/W
- Watts needed: 5*210=1050
=> VAs needed = 1050W * 2VA/W = 2100VA
Note these computations leave zero margin for impedance dips: if you want to allow for impedance dips at half the nominal i.e. 4 ohms you should double the above values, both caps and toroid (BTW there is no point in oversizing further than a factor 2 as the UcD400 will never draw more than 450W anyway, thanks to its OV and OC detections) |
Why is the power factor that low for this type of supply? What is the effect of less VA and cap sizing?
Frans |
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| Golgoth |
| quote: | Originally posted by FransDHT
Why is the power factor that low for this type of supply? What is the effect of less VA and cap sizing?
Frans |
PF is low because current is very far from a sine wave proportional to voltage: it's in the shape of short current bursts at the peaks of the mains sine waveform.
Less VA and caps: you can't expect full power to be Hi Fi, but you probably don't need full power, especially if some of your speakers are high efficiency ones! You can actually work out your actual power needs from the max SPL in dB you want from each speaker at listening distance (no more than pain level 120dB in any case :) and its efficiency in dB/W@1m (allow for -6dB per doubling of the distance). For a typical home installation you'll be surprised at how little power you actually need! |
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| FransDHT |
| quote: | Originally posted by Golgoth
its efficiency in dB/W@1m (allow for -6dB per doubling of the distance). |
Thanks Golgoth,
My front speakers hav a sensitivity of 88 dB/2,83V@1m. How do I get from there to Watts?
Frans |
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| ericpeters |
| quote: | Originally posted by Golgoth
Less VA and caps: you can't expect full power to be Hi Fi, ...........
.....For a typical home installation you'll be surprised at how little power you actually need! |
I got the idea the requirements rise very fast when you got speakers with low efficiency.
So in my case I found that 550VA simply was not enough for Hifi with my Apogee speakers and Zap mopdules. Especially treble was horrible ( 2* 1000 VA was sufficient and everything very good)
However: I'm also running a test with B&O ice modules,. They are actually running fine with the same 550VA transformer and even smaller capacitor banks. Does anyone have an idea why?? |
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| classd4sure |
Hi,
You said smaller cap banks... =better power factor, maybe that's why?
__________________________________________________
I'd like to know how to calculate that as well Golgoth sensitivity on mine are 102dB @1W/1m, I'd like to see the equations, though, I doubt I'd actually use that method to design the supply, some sources just require turning up more before they come to life even with speakers like mine.
This is turning out to be a killer thread. |
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| Golgoth |
| quote: | Originally posted by FransDHT
Thanks Golgoth,
My front speakers hav a sensitivity of 88 dB/2,83V@1m. How do I get from there to Watts?
Frans |
Easy:
2.83V => 1W on 8 ohms (P=Vrms^2/R=2.83^2/8=1)
Suppose you want to be able to generate a maximum of 118 dB SPL (ouch) at 4m distance. 4m is two doublings of distance wrt 1m (1*2*2=4) so you need your speaker to produce 118+6*2=130dB SPL at 1m.
Now 130 - 88 = 42dB = 7 * 6dB -> 7 doublings of the 1W power necessary to produce 88dB (twice the watts = +6dB). So you need a maximum of 2^7=128 * 1 Watt = 128W from your amplifier, correct me someone if I am wrong. |
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| catapult |
| quote: | | Now 130 - 88 = 42dB = 7 * 6dB -> 7 doublings of the 1W power necessary to produce 88dB (twice the watts = +6dB). So you need a maximum of 2^7=128 * 1 Watt = 128W from your amplifier |
Doubling the voltage is (approximately) 6dB. Doubling the power is (approximately) 3dB.
dB = 10*log(P1/P2)
dB = 20*log(V1/V2)
Power rating for a 42dB boost (130-88) = 1 * 10^(42/10) = 15849 watts. Time for a more efficient speaker if you want to play it that loud. ;) |
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| Golgoth |
| quote: | Originally posted by catapult
Doubling the voltage is (approximately) 6dB. Doubling the power is (approximately) 3dB.
dB = 10*log(P1/P2)
dB = 20*log(V1/V2)
Power rating for a 42dB boost (130-88) = 1 * 10^(42/10) = 15849 watts. Time for a more efficient speaker if you want to play it that loud. ;) |
Oops thanks catapult for correcting, silly me yes it's only +3dB SPL per doubling of the power, quite another game! You have it all here Frans:
http://dju.prodj.com/courses/soundr...cement/c4a.html :
"EFFICIENCY
The ratio, usually expressed as a percentage, of the useful power output to the power input of a device. EFFICIENCY RATING OF A TRANSDUCER/ENCLOSURE...is the SPL the unit produces at a 1 W RMS input power level measured 1 meter from the unit. Doubling the input power raises the SPL 3 dB. Doubling the number of enclosures raises the SPL 3 dB. Doubling the input power and the number of enclosures raises the SPL 6 dB. Doubling the distance (near field) lowers the SPL 6 dB. " |
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| OA51 |
Does anybody have experiance from, or info on these caps....
I'm planning to use 1 or 2 / rail in a UcD180 stereo amp.
Regards Stefan |
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| OA51 |
Thanks a lot!!!
Are they any good?
/Stefan |
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| OA51 |
They seem to be manufactured 1997...
But they are not used and have been stored i original box etc.
This is not a problem, right?
/Stefan |
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| FransDHT |
| quote: | Originally posted by Golgoth
Oops thanks catapult for correcting, silly me yes it's only +3dB SPL per doubling of the power, quite another game! You have it all here Frans:
http://dju.prodj.com/courses/soundr...cement/c4a.html :
"EFFICIENCY
The ratio, usually expressed as a percentage, of the useful power output to the power input of a device. EFFICIENCY RATING OF A TRANSDUCER/ENCLOSURE...is the SPL the unit produces at a 1 W RMS input power level measured 1 meter from the unit. Doubling the input power raises the SPL 3 dB. Doubling the number of enclosures raises the SPL 3 dB. Doubling the input power and the number of enclosures raises the SPL 6 dB. Doubling the distance (near field) lowers the SPL 6 dB. " |
Well, that means that there is no way I (or anyone else) will get 118dB at 4 meters (in hifi) with the class D's there are right now, I guess.
What would be a 'normal' loud sound level we would be able to achieve?? With UcD400, that is?
Frans |
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| FransDHT |
| Doubling the enclosures and power, that is two frontspeakers driven by two UcD400's at 1 W will get me 94dB at 1m? |
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| classd4sure |
I noticed on page 5 of the first link
"For technical data covering
case size, ESR, impedance
and ripple current rating, on
any of the above designs,
contact BHC Components
technical sales."
That's... just stupid. It's hard enough to buy the suckers, they should at least provide the basics one requires, bad business :smash:
My view: If the specs can't speak for themselves, I sure don't want to talk to a salesman.
All I could find was one or two sights claiming they were low ESR, and had good high frequency characteristics..... but that's it, guess you have to take their word on it.
| quote: | Originally posted by OA51
They seem to be manufactured 1997...
But they are not used and have been stored i original box etc.
This is not a problem, right?
/Stefan |
Ummmmmm...... they've been sitting for seven years.. It could be a problem.
These kind of caps have a "shelf life".
Have a read:
http://www.acomstock.com/uploads/eccat2003.pdf
and I quote:
"Storage times in ambient temperatures of 40¡ÆC
or less can be four years or more before
leakage current should be checked for
conformance to the specified limit.
Longer storage times may require reforming of
the capacitor to reduce leakage current below
the specified limit. This can be accomplished by
applying rated voltage in series with a 1000§Ù
resistor for a time period of 30 ~ 60 minutes.
Under normal conditions, shelf life can exceed
10 years, providing that leakage current is
checked before use.
Long term storage in high humidity conditions
could cause oxidation of the terminal plating
which could adversely affect solderability."
I've seen some recommend 125% of rated voltage for the reforming process, and others recommending other methods, like sloowwwwwwwly bringing up the voltage to 125%, over a period of a day even, and leaving it over night. They all had one thing in common, limit the current! It's possibly best to go with the method the manufacturer in question recommends.
Looks like you have to call them to find out what the ESR is anyway.
If they were stored at room temp and not the trunk of a car the shelf life will be longer, these are long life caps, my guess is you'd be fine, but that's just a guess.
Know what I'd do? Put a 100W light bulb in series with each secondary to limit the current, turn it on and leave it for an hour or two, that'll reform them at the working voltage. |
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| Golgoth |
| quote: | Originally posted by FransDHT
Well, that means that there is no way I (or anyone else) will get 118dB at 4 meters (in hifi) with the class D's there are right now, I guess.
What would be a 'normal' loud sound level we would be able to achieve?? With UcD400, that is?
Frans |
| quote: | Originally posted by FransDHT
Doubling the enclosures and power, that is two frontspeakers driven by two UcD400's at 1 W will get me 94dB at 1m? |
I'll try to do it right this time :)
Better to compute for one enclosure first (besides you can't be at 1m from both enclosures ;)
- UcD400 can output 210W into 8 ohms, let's round this to 256W so it's an integer number of doublings (we'll be wrong by less than 3dB anyway), namely 8 doublings wrt 1W (256=2^8):
-> 8 times +3dB = +24dB -> 88+24=112 dB SPL @1m
- two doublings of distance for 4m (1*2*2=4):
-> 2 times -6dB -> -12dB -> 112dB -12dB = 100dB SPL @4m
-two enclosures:
-> +3dB -> 100dB +3dB = 103dB SPL @4m for 2 enclosures
Now if your 8 ohms speaker is n dB more efficient at 1m (88+n) you'll get 103+n dB SPL at 4m.
(again correct me someone if I am wrong)
Now of course you must also take into account the max power that your particular speaker can take before blowing up! |
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| FransDHT |
| quote: | Originally posted by Golgoth
-two enclosures:
-> +3dB -> 100dB +3dB = 103dB SPL @4m for 2 enclosures
|
But doesn't that mean you drive the two with one UcD400? And if you would drive each of them with one UcD ttaht you would have a 6dB+?
Frans |
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| ewildgoose |
...and hence we can also see the argument for high efficiency speakers...
1) There was some quip from Jan-Peter that distortion on the UCD is somewhat lower at lower output levels (which is intuitive)
2) Power compression on the speakers rises rapidly with input power
3) Sticking 300W+ through a long piece of wire is never going to be ideal
The pro crowd are all into compression drivers with 100dB/watt sensitivity. Makes it quite easy to play something with 110dB peak levels (and lower average levels) without breaking a sweat. One enthusiast suggested to me that I benchmark any fancy "hifi" driver that I was thinking of building against a JPL pro driver first. These sorts of things do indeed set a high baseline standard... |
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| Golgoth |
| quote: | Originally posted by FransDHT
But doesn't that mean you drive the two with one UcD400? And if you would drive each of them with one UcD ttaht you would have a 6dB+?
Frans |
No, 103dB is for 2 enclosures, each driven by its own UcD400, sorry :) |
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| FransDHT |
| quote: | Originally posted by Golgoth
- UcD400 can output 210W into 8 ohms, let's round this to 256W so it's an integer number of doublings (we'll be wrong by less than 3dB anyway), namely 8 doublings wrt 1W (256=2^8):
-> 8 times +3dB = +24dB -> 88+24=112 dB SPL @1m
- two doublings of distance for 4m (1*2*2=4):
-> 2 times -6dB -> -12dB -> 112dB -12dB = 100dB SPL @4m
-two enclosures:
-> +3dB -> 100dB +3dB = 103dB SPL @4m for 2 enclosures
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OK, back to the power supply. That means that the power of the UcD is 256Watt maximum (8Ohm), which means 512 VA toroid per channel, right? Since it is only 210Watt 500VA should suffice.
And the caps don't change, still 2*6250uF per channel. And that gives 103dB with to channels at 4 meter in hifi. |
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| FransDHT |
I want to take it form the other side:
I now have a 500VA toroid in my amplifier. Wth this it can delver 250W to the UcD's. That is 125W per UcD.
125W are 7 doublings, that's 21dB plus, makes 88+21=109dB @1m. At 4m that is 109-12=97dB. Two speakers makes 97+3=100dB. That should suffice for a living room?!
In this amplifier there are 5 Ucd's to drive 5 speakers in case of a 5-channel DVD. Assuming that the speakers are the same, we get 50W (250/5) per channel. That are 5 to 6 doublings, so about 16dB+, makes 104dB. at 4m that is 104-12=92dB. But there are 5 speakers, so 92+(4*3)=104dB. Should be enough for my living room.
What I do not understand is what does the capacity. Why do youn need how much (for this situation).
Frans |
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| mattjk |
I have some PSU parts for sale if anyone is interested:
LC Audio Predator psu $45
2 - Avel Toroidal transformers with mounting hardware.
they are 500va 40+40 Avel's. $60 each. both are like new. |
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| Golgoth |
| quote: | Originally posted by FransDHT
I want to take it form the other side:
I now have a 500VA toroid in my amplifier. Wth this it can delver 250W to the UcD's. That is 125W per UcD.
125W are 7 doublings, that's 21dB plus, makes 88+21=109dB @1m. At 4m that is 109-12=97dB. Two speakers makes 97+3=100dB. That should suffice for a living room?!
In this amplifier there are 5 Ucd's to drive 5 speakers in case of a 5-channel DVD. Assuming that the speakers are the same, we get 50W (250/5) per channel. That are 5 to 6 doublings, so about 16dB+, makes 104dB. at 4m that is 104-12=92dB. But there are 5 speakers, so 92+(4*3)=104dB. Should be enough for my living room.
What I do not understand is what does the capacity. Why do youn need how much (for this situation).
Frans |
Your maths look ok, except 5 speakers is a bit more than 2 doublings, not 4 !
For capacitance, since you will be using your modules at 50/400 = 1 /8 of the power, you can divide what was computed previously by 8 obviously, cf Bruno's original rule what matters is actual power drawn from the supply. |
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| FransDHT |
Thanks Golgoth,
That means that the 500VA and the 2x10.000uF should be enough. Jan Peter, you are right after all! I shouldn't worry so much.
Frans |
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| tiki |
Hi,
after all discussions I'm still not sure, what's best, lowest or moderate ESR. I'm pretty sure, that a high allowable ripple current cannot be bad, but this is possible only by achieving lowest ESR. Which may introduce high recharging current spikes.
If I'd go for lowest ESR in conjunction with high ripple current without any price restrictions, I would use Epcos Sikorel or Vishay PED-ST series. The Sikorel caps exhibit outstanding reliability data additionally.
Unfortunately I do not find the source, where to be read, that Aerovox caps exhibit a modest ESR only, around 30mOhms (in the interesting cap/voltage range), the ripple current was accordingly low.
The ESL question should be answered already by the higher wiring inductance (two parallel wires, approximately):
L{nH}=2*l*[ln(2*a/d)+µr/4],
where l = length of the wire, a = distance between the wires, d = their diameter (all in cm), µr = their relative permeability,
that gives in my setup for the two rail wires "in parallel":
L{nH}=2*20cm*[ln(2*1cm/0.18cm)+1/4]
L=106nH for each wire.
That is 10 times the cap ESL, minimum. And the wiring inductance may be of a high Q, possibly causing some ringing, if stimulated by current spikes.
Somebody stated this in earlier discussions already: so called Audio grade components do not need to have exceptional performance necessarily, marketing experts sell them by using "euphonious" brands and looking a million dollars.
Timo
God and RF are cutting their own path. |
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| Golgoth |
| quote: | Originally posted by Golgoth
For capacitance, since you will be using your modules at 50/400 = 1 /8 of the power, you can divide what was computed previously by 8 obviously, cf Bruno's original rule what matters is actual power drawn from the supply. |
| quote: | Originally posted by FransDHT
That means that the 500VA and the 2x10.000uF should be enough. Jan Peter, you are right after all! I shouldn't worry so much.
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Ah yes my mistake: previous computation was 50000/8= 6250µF, times 5 channels around 30000uF per rail corresponding to 210W per channel (full power on 8 ohms). You'll be using about 1/4 of that (50W/channel) so 30000/4 = 7000uF would be enough, so 10000uF, and not 10.000 uF :clown: seems just fine. |
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| hansen |
Hi.
Have any of you tried Rifa caps? I have real trouble finding large powersupply caps for my UcD400 monoblock project, but the Rifas I can buy online from Sweden:
http://www.elfa.se/elfa-bin/dyndok....dok=2012735.htm
Are they any good? Also, I wonder if I should get the 15000uF/100V ones or the 22000uF/100V. Is 15000 uF enough, is 22000 uF better or maybe even worse?
Thanks
(I'll take some pictures of my project when it's done and post them somewhere of course) |
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| Zvon |
Hi All,
I have received my second Zappulse 2.2SE (with BG capacitors to match the first module) and would like to build a dual mono amplifiers in one or two 2U rack enclosure(s). The amplifiers would be used to drive my home made ESL's. The electrostatics present rather difficult load to drive with impedance that drops below 1ohm above 16kHz.
I did try a quick setup with 2 x 40V (AC) 300VA toroid, standard 35A bridge and 4 x 8000mf /75V Lelon (?) electrolytics and it worked nicely. It actually outperformed a couple of reputable amplifiers quite easily.
To ensure I don't make silly errors and to exploit the full module potential I would appreciate your comments in regard to the following:
1. Should I put both modules in one 2U rack case or have each module in its own case?
2. If both modules are in one case, should I have two or one transformer?
3. What should be the transformer(s) VA rating (within reason)?
4. Are the two Rifa PEH200 electrolytics 22000uf/63v per rail/module sufficient and acceptable for 2x40V (AC) secondary windings? These capacitors are bulky, have reasonable low ESR and most importantly are localy available from RS Compononents.
5. Should I use standard 35A bridges with snubbers or go for something like MUR3020WT bridge?
At the moment I have one LC Audio soft start module.
Thank You,
Zvon |
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| hansen |
One more question (probably a real clueless one...):
I have a transformer with a center-tapped secondary, ie. there are three output wires, 40-0-40 VAC. I have enough rectifier diodes to do separate rectification of the positive and negative rails.
Is that possible to do with a center tapped transformer only with one that | | | |
