Alan I would believe too that bridging wouldn´t be a necessity for most well designed speakers driven with NCORE.
That said, and I suspect that we have been over this before, but bridging should not half the current capabilities of an amp, unless you run into other problems such as stability issues... We probably agree that with bridging each amp only sees one half of the load. But at the same time each amp also only needs to do half the work voltage-wise which means that they have to deliver exactly the same amount of current for the same total output to the speaker.
Effectively this means that where one amp would limit due to current capabilities it still will when bridging (same output potential) and where it would limit due to voltage swing you´ll get twice the potential swing of voltage.
Remember that both amps contributes hence their increased current output only occurs when you also have increased output power. The impedance of the speaker still follows Ohm´s law...
I understand that you don´t like what bridging does in the cases that you have tried it, but have you tried it with NOCRE´s?
That would still be interesting to try as the increased potential voltage swing possible could materialize into audible gains...
cheers,
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Alan I would believe too that bridging wouldn´t be a necessity for most well designed speakers driven with NCORE.
That said, and I suspect that we have been over this before, but bridging should not half the current capabilities of an amp, unless you run into other problems such as stability issues... We probably agree that with bridging each amp only sees one half of the load. But at the same time each amp also only needs to do half the work voltage-wise which means that they have to deliver exactly the same amount of current for the same total output to the speaker.
Effectively this means that where one amp would limit due to current capabilities it still will when bridging (same output potential) and where it would limit due to voltage swing you´ll get twice the potential swing of voltage.
Remember that both amps contributes hence their increased current output only occurs when you also have increased output power. The impedance of the speaker still follows Ohm´s law...
I understand that you don´t like what bridging does in the cases that you have tried it, but have you tried it with NOCRE´s?
That would still be interesting to try as the increased potential voltage swing possible could materialize into audible gains...
cheers,
AH! And the plot thickens. I guess I (we at AC) need to investigate this further. If I buy larger chassis for them and put in single mods and have room to bridge at a later date if I find out it would be worth it might be a way to go.
It's working, my 5 channel nCore. But it's getting pretty hot. Next step is fully vented cover and bottom. Sound? No! It doesn't sound. The music is just there!
I must say, that build looks absolutely fantastic. Congratulations!
Maybe I'm missing something here, but we can't have it both ways.
If the amp sees half the load, say 1.7 ohms instead of 3.4 ohms, it will potentially become current starved before the single amp configuration at the same volume level. Its not that the amp is any less capable when bridged, its that it sees half the load value. I'm not concerned with the voltage limiting, until someone measures and says they have peaks exceeding +/- 65V longer than 2 sec, I don't think voltage clipping is an issue.
Current is what I am referring to. The Ncore is rated into 2 ohms, how much below that I do not know. But we already see it sagging at 2 ohms. Current limiting is irrespective of voltage level (until we get to SOA concerns, which are negligible in class D amps)
Hence my comment that a single amp is better at delivering the power to the speaker within its voltage range. Yes, this is less than peak power with bridged amps, but I don't care about peak power, I care about current delivery in the area of concern, during the time it is below the voltage limitations of the single amp.
Does that make my view point clear?
Cheers,
Alan
Just tested to connect the NCore into a current feedback loop as described earlier in this thread, didn't work so well though.
With 0.6 ohm Rf resitor the output impedance became 11, which according to equation (1+20(Ncore gain))*Rf seems to be about right.
The problem however was that there was a constant noise, so I will probably just go with a series resistor instead until someone more knowledgeable presents a howto guide. Since I plan to use it for 500 hz and upwards with fairly efficient drivers the power waste of a large series resistor is negligible.
An interesting test though would be to test on a good driver is how high resistance must the resistor be in proportion to the driver to get say 90% of the possible distortion reduction.
With 0.6 ohm Rf resitor the output impedance became 11, which according to equation (1+20(Ncore gain))*Rf seems to be about right.
The problem however was that there was a constant noise, so I will probably just go with a series resistor instead until someone more knowledgeable presents a howto guide. Since I plan to use it for 500 hz and upwards with fairly efficient drivers the power waste of a large series resistor is negligible.
An interesting test though would be to test on a good driver is how high resistance must the resistor be in proportion to the driver to get say 90% of the possible distortion reduction.
Yes, you do seem to only look at one amp (one half of the bridge) and not the bridge as a whole (being one amp on the "hot side" and one on the "cold side" of the speaker).
One amp (one side) sees only 1,7R of 3,4R total but also only delivers half the voltage swing (for the same output power and current as a non-bridged amp would).
That means that a bridged amp can deliver as much power and current, but at only half of the voltage swing seen from each "amp" in the bridge.
Together they deliver the same total voltage swing and the same total current as a non-bridged amp would. The bridged config can´t deliver more current, but then it doesn´t have to either.
Lets take a quick n´dirty math example to make my point more clear:
non-bridged:
3.4R x 24A = 81.6V peak (this would in practice result in clipping due to the max 65 to 72V supply limitations, but if we overlook this we would end up with-> 81,6*24 = 1958.4 W peak and 979,2 W RMS both at 3,4R)
Bridged:
only one module:
1.7R x 24A = 40.8 V peak
both modules in the bridge will then deliver: 2 x 40,8V = 81,6 V peak
One module delivers +40.8V and the other -40.8V = total voltage potential on the terminals being the 81,6V
This then provides the 1958,4 W peak and 979,2 W RMS well within the voltage limits of 65 to 72 V per module
In comparison one module with one smps600 should according to the +/-65V "only" be able to deliver 65/3.4R = 19.12A which gives 19,12 x 65 = 1242,6 W peak and 621,3 W RMS @ 3.4R
The bridge is according to the math more powerful in a 3.4R load.
The point at which the bridge is only equally powerful to the non-bridge is in a 65V/24A = 2.7R load.
Hope that helped
cheers,
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Olle,
Respect for that you try to tweak even more out of your fine Ncore amp.
I am just not really sure what you are trying to achieve sound-wise as what you have described so far would seem like a downgrade from what I heard at your place back then?
If you are not happy with what the ncore "brings" to your system unmodified, I would humbly suggest to look for other causes hereof before than at the ncore´s themselves.
If you haven´t changed the XO´s in your omnipolar speakers and these are the ones that you primarily use still, then I would suggest you to look at them and calculate new values as a necessary consequence from when you adjusted the impedance of the HF slope. Believe me when I say that such a detail isn´t an insignificant one... If you precisely adjusted from a 4R to a 8R slope then simply half the cap value and double the coil value in the second order slope on the tweeters
Definitely worth trying if you feel that something isn´t quite there...
cheers,
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Olle,
Respect for that you try to tweak even more out of your fine Ncore amp.
I am just not really sure what you are trying to achieve sound-wise as what you have described so far would seem like a downgrade from what I heard at your place back then?
If you are not happy with what the ncore "brings" to your system unmodified, I would humbly suggest to look for other causes hereof before than at the ncore´s themselves.
If you haven´t changed the XO´s in your omnipolar speakers and these are the ones that you primarily use still, then I would suggest you to look at them and calculate new values as a necessary consequence from when you adjusted the impedance of the HF slope. Believe me when I say that such a detail isn´t an insignificant one... If you precisely adjusted from a 4R to a 8R slope then simply half the cap value and double the coil value in the second order slope on the tweeters
Definitely worth trying if you feel that something isn´t quite there...
cheers,
I've thought about just putting back the old resistors since the NCore has no problem with 4 Ohm. Or since I now have a measurement microphone tailor and improve the crossover from scratch. I have been too lazy lately though =)
And ofc it isn't the NCores fault and the current set up works fine, this this tinkering and testing is mainly for a future speaker project meant to replace my current omnis.
I'm planning to build myself a dipole where the n1 goal is get the best midrange possible, and when it seems that simply increasing output impedance increases driver performance there then it's something I want to research. Especially to research how easy it is for me to get a good enough result with as few disadvantages as possible. Series resistor seems to be the leader so far
+1
Someone used 1 smps on two Ncores and heard the difference(less quality) in comparing 1:1.
I aspect a lot of bridging ncore with hungry speakers like these B&W and Maggies.
The people designed the Ncore 400 make these Mola Mola (Ncore 1200) not for the show.
Jerry
Alan, I feel the same way, I always feel there is an uncertainty in behavior with bridging...not instability, but perhaps a worsening of distortion that just feels a bit impure. It's my emotional response, not rational. You asked earlier about a minimum Zload rating for ncore, and there is a spec of 1 Ohm minimum on the datasheet.
I notice almost everybody is using sealed cases for their Class-D amps. Aluminum does make a great heatsink material, but even a little ventilation goes a very long way. I would rather accept some holes or slots to enable my electrolytic caps to live longer. If I felt the need for an even quieter power supply, I would rather add some filter capacitance to the smps than even consider a big, uncool and ungreen linear supply. EDIT: extra filter capacitance firmly rejected in datasheet by Hypex, perhaps causes instability--never mind.
I think the 802Ds are fabulous speakers, and if I owned them I would prefer to have the amps never get close to a current shutdown. I really wish B&W offered them in a crossover-less mode (perhaps they do for important people), or at least a tri-amp option. Those bass drivers have amazing power-handling, so fast and honest; I think they are the best I've ever heard.
While we're at it, somebody should be making preamps with 3 output jacks for each audio channel, although the DLCP is getting closer and that might have different needs. Bruno and the boys have kept multi-amping in mind with the Mola-Mola preamp, as its Zout is under an Ohm!
I'm going ahead with plans for mounting my passive ATC20s on stands which also will rest the Velodyne DD12 Plus subs on the bases. The amps will move to a platform just below the ATCs. Sound Anchors is building me hybrid stands for the purpose
. I'll take great care to minimize modulation of the ATCs by the subs, and the arrangement will be absolutely time-coherent at the central listening position when I've finished. I do plan to put in ncores after my front end is (finally) redone. Thank you also for several excellent and very helpful replies, I neglected to mention them earlier.
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Chassi/Case current RCA
@bruno
I just finish my build in a metal rack case with 2 SMPS600 and 2 NC400. I’m using RCAs connected as explained in the datasheet of the nc400. Everything works and it seems to sound great.
I didn’t connect the Safety Earth. Using a simple “one-contact” test light and touching the case it show a current. It’s a little current not dangerous (one cannot feel it) but I wonder if this is normal. This happens only when none of the two RCA is connected. When I connect my Arcam rDAC (this also does not have the main Earth) there is no more current in the chassis.
Should I be worried about it?
Thanks
@bruno
I just finish my build in a metal rack case with 2 SMPS600 and 2 NC400. I’m using RCAs connected as explained in the datasheet of the nc400. Everything works and it seems to sound great.
I didn’t connect the Safety Earth. Using a simple “one-contact” test light and touching the case it show a current. It’s a little current not dangerous (one cannot feel it) but I wonder if this is normal. This happens only when none of the two RCA is connected. When I connect my Arcam rDAC (this also does not have the main Earth) there is no more current in the chassis.
Should I be worried about it?
Thanks
Very nice!
I think i have the same cases (still have to arrive from china
). How did you connect the power button on the front to the nc400/smsp? It looks like a LED illuminated Momentary push button/switch, correct (like this one )?
Have you added some softstart ciruit for it?
Very nice!
I think i have the same cases (still have to arrive from china
How did you connect the power button on the front to the nc400/smsp? It looks like a LED illuminated Momentary push button/switch, correct (like this one )?
Have you added some softstart ciruit for it?
It's a latching button, no softstart, I just connected it's led to the SMPS aux power.
Nice! But I still think you should twist your inner cables ( as mentioned in the datasheet)
most if not all SMPS's have some small ceramic capacitor connected from mains to chassis.
I have a generic SMPS in front of me and the caps (Y filter) are shown on the silk screen but not soldered. I guess it has to do with country-specific regulations.
the Hypex SMPS's does not use Y filters at the input AFAIK, Bruno explained a few times why he doesn't use them.
don't be too sure that you can't feel that current, I wouldn't try touching the chassis and anything that's earthed simultaneously.
thanks push_pull for your interest in my question.
In fact, I touched the chassis very carefully and I hopefully didn’t feel that current.
I’m not really familiar with electronic so my knowledge about it end just after the Ohm’s law.
When the RCA line input are connected to the Arcam rDAC the current disappear . I thought that, maybe, the current go through the USB cable to the PC that finally has the connection to the safety earth so it disappears.
Most of the nc400 builds have safety earth and uses balanced connections. But since I don’t have a balanced source and the amp will be installed in a computer rack full of other devices I thought it would be better to try without safety earth. So I carefully respected the prescriptions of Bruno here in the attached pdf (see “Choice A” at the end).
What I should do? Try to connect the safe earth as precautions? Making the assumption the sound quality is not compromised by it, is this a valid solution or just a bad workaround?
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