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Lex View Drop Down
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    Posted: 14 December 2011 at 12:37am
Hi,

Anyone had any experience with the Nexo NX amps?

I've got a ps10 r2 setup running off powersoft amps and TD controller, but can you get more out of the NX amps i.e. using the presets in the setup to get optimal performace? Thinking of repacing my powersofts with a 4x1 or 4x4. Like to hear peoples experiences rather than marketing hype.

Just FYI:
K8 running a PS10 per side
D4002 running an LS600 (going to get another sub soon hopefully)

I do mobile DJ'ing and private parties, looking for max efficiency and sound quality.

Thanks in advance! Smile

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Post Options Post Options   Thanks (0) Thanks(0)   Quote DjLeco Quote  Post ReplyReply Direct Link To This Post Posted: 14 December 2011 at 11:00am
Inside are YAMAHA amps autooscilant TD class.
 
Very small smps trafo, very weak storage capacitors (too less uFarads, just 1640uF per rail)
 
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonminns Quote  Post ReplyReply Direct Link To This Post Posted: 14 December 2011 at 12:02pm
K8 on PS10s?? That's totally excessive!!
4 ohms is for wimps
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 14 December 2011 at 12:14pm
I've mixed in a venue a few times which uses a single NX amp to drive two twin 18's and four PS15 R2's. No complaints about the amp at all, no headroom issues etc.  Wasn't a small room either.

Talking about secondary capacitors.  The Chevin A series amps only have about 15uF of Polyester caps per rail on the secondary side and no-one complains about them.  In fact having tested them on the bench, I couldn't detect any evidence that a lack of capacitance there was a problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DjLeco Quote  Post ReplyReply Direct Link To This Post Posted: 14 December 2011 at 1:25pm
Originally posted by ceharden ceharden wrote:

I've mixed in a venue a few times which uses a single NX amp to drive two twin 18's and four PS15 R2's. No complaints about the amp at all, no headroom issues etc.  Wasn't a small room either.

Talking about secondary capacitors.  The Chevin A series amps only have about 15uF of Polyester caps per rail on the secondary side and no-one complains about them.  In fact having tested them on the bench, I couldn't detect any evidence that a lack of capacitance there was a problem.
 
So, why Crown, Labgruppen, Powersoft, uses alot of 1000uF/200 Volts capacitors parralel per rail (between 10000 and 20000uF total capacitance per rail, 20000-40000uF total capacitance)?
 
 
They are stupid?
 
Uf , mondial crysis, amplifier will become, empty inside...
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dunc Quote  Post ReplyReply Direct Link To This Post Posted: 14 December 2011 at 1:28pm
Running a big gig at the minute at Doncaster Racecourse with 3 NX4x4 Amps (Totally Overkill)

Amp 1 runs 2 RS18 Subs and 6 boxes og GEOS12
Amp 2 runs 4 PS15s
Amp 3 runs 4 PS10s.

Im running out of speaker power, rather than amp headroom, however they are all intelligent enough to limit to the appropriate levels (and with my FOH engineer, we need it)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote teslaman Quote  Post ReplyReply Direct Link To This Post Posted: 14 December 2011 at 2:16pm
Whether you put your bulk reservoir storage on the primary side or secondary side (or both) of your PSU design is entirely up to you, one is not necessarily better than the other. In terms of getting small ripple voltage on the output DC rails VERY small capacitors can be used on an SMPS but only if the bulk storage is on the primary side. Vice versa is also possible and allows clever techniques like PFC to be included without needing additional stages in the primary circuitry...

Big secondary side caps do not in themselves say if an amplifier will have good performance or not. I'm not familiar with the Chevin amps but I can absolutely believe ceharden's comments if the PSU switching frequency is high enough. Also amplifiers whose secondary side voltages track the audio signal will have to have small caps otherwise they could not have the required slew rate...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DjLeco Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2011 at 12:48am
What's the association between secondary, or primary capacitor(s) and slew rate? Ha ha ha...
 
So, let's put just 1uF capacitor per rail, is enough, huh?
 
For increasing slew rate...
 
Bullshit.
 
Slew rate is alot dependant of internal compensation of that amp and Ft of output devices, at every amplifier based on AB Class, Class H, H2 , H3, or H4 step, G class amplifier, TD class is Tracking Class D amplifier, wich after downconverter is a classical AB class amplifier.
 
Bigger capacitor(s) storage, is better for heavier transient responses, and longer term sustained power, instead burst power, also lower ESR ,very important for noise ripple on SMPS output, especially on non regulated ones (like all Yamaha SMPS amps) we don;t talk about PFC here, Yamaha maybe never heard about active PFC....
 
Watch here Crown SMPS of Macrotech I series power supply, output storage is almost 12000uF per rail (24000uF total storage capacitors), loaded on dummy load 4 ohms each channel, how many volts dropping between IDLE, and MAX load on 4 ohms each ch:
 
 
Official is +/- 162,5 Vcc in idle, and drops till around 2x 161Vcc on max load, till limiting.
 
That means a very good SMPS , in mine opinion.
 
Proof:
 
 
 
 
 


Edited by DjLeco - 15 December 2011 at 1:15am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Muckerbarnes1 Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2011 at 1:03am
Originally posted by teslaman teslaman wrote:

Big secondary side caps do not in themselves say if an amplifier will have good performance or not. I'm not familiar with the Chevin amps but I can absolutely believe ceharden's comments if the PSU switching frequency is high enough. Also amplifiers whose secondary side voltages track the audio signal will have to have small caps otherwise they could not have the required slew rate...
 
Totally agree on switching frequency and storage, but not that small. I'm with Claudiu there. Big enough is OK, but bigger is better to a point.
 
I just don't see the slew rate relationship as above. Can you explain.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote teslaman Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2011 at 10:08am
Originally posted by Muckerbarnes1 Muckerbarnes1 wrote:

Originally posted by teslaman teslaman wrote:

Big secondary side caps do not in themselves say if an amplifier will have good performance or not. I'm not familiar with the Chevin amps but I can absolutely believe ceharden's comments if the PSU switching frequency is high enough. Also amplifiers whose secondary side voltages track the audio signal will have to have small caps otherwise they could not have the required slew rate...
 
Totally agree on switching frequency and storage, but not that small. I'm with Claudiu there. Big enough is OK, but bigger is better to a point.
 
I just don't see the slew rate relationship as above. Can you explain.

Yes I probably didn't explain that too well, happens when your brain goes off on a tangent! Thanks for asking nicely tho rather than unleashing the dogs!, I wish DjLeco could do the same!

I was referring to a very specific type system where the output of the power supply tracks the instantaneous voltage of the audio signal (with some DC superimposed) and is then followed by a BTL class-AB output stage, a.k.a. BASH amplifiers. The slew rate I was referring to was that of the modulated DC rail NOT the output signal. 
The principle is the same with tracking down-converter amplifiers like Lab Gruppen except they have standard DC rails followed by a non-isolating step-down converter (I believe). In either case the capacitor on the output of the power supply or down-converter needs to follow the audio signal whilst minimising ripple from the PSU switching frequency. It is thus a compromise on value as if it's too big it will not be possible for it to track the audio signal quick enough, hence limiting the slew rate of the DC rails and affecting efficiency and/or performance.

Regarding small caps on SMPSU outputs, what value do you think is an acceptable minimum? If we take the example of a non-regulated supply with the bulk capacitance on the primary side. The power supply would typically use a 95% duty cycle or thereabouts. After full-wave rectification at the transformer output we have a signal that is spending 95% of its time at the required DC voltage anyway, the 5% dead time it will not be supplying current hence the output cap will be supplying the load. So lets assume 100kHz switching frequency (low by modern standards) and work out the duration of the dead time, answer = 0.25us. Lets assume the load on the DC rail is 20A peak for this particular amplifier (fair estimate for 500W-1kW amplifier) and now work out the ripple for a 15uF capacitor:

dv/dt = i/C = 1.33V/us and hence approximate ripple with 0.25us dead time is 0.33V peak-peak!

I know there are various assumptions in this calculation but it's in the ball-park and 0.33V ripple at 200kHz (it's double because of full-wave rectification) is pretty good. You likely just as much due the ESR of electrolytics if you used a few parallel 'big' caps?

The situation can be worse if the supply is PWM regulated as the "dead-time" is increased but at the same time an inductor would be included between the rectifiers and the cap in this case which gets you back to the same ball-park. Same goes for the step-down converter used in Lab Gruppen etc. which will have an inductor by necessity.

Hence, assuming my maths and assumptions are OK then I return to my previous comment that I can perfectly beleive that nice quality low-ESR 15uF cap is OK for a power supply output Smile




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Post Options Post Options   Thanks (0) Thanks(0)   Quote DjLeco Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2011 at 12:51pm
I will make a test, soon, with a  capacitor Polypropylene of 25 uF/250 Vdc per rail, and after with a multiple capacitors parraleled (electrolytics) , and I will put scope probe on output DC of SMPS to observe the noise ripple, in 2 examples.
 
Freq will be exactly 100Khz, unregulated SMPS.
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tapeworm Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2011 at 1:55pm

Heres a nexo amp rack (3x 4x4s and 2x 4x1s) we are using at work for a theatre show we are doing in the colston hall bristol. running 4x rs15 subs, 2 hangs of geo s12, 2 hangs of geo s8, 4 ps8 front fills, and a load of ps10 monitors. this will be used in conjunction with their in house centeral hang of s12s also ran of nexo 4x4. the nx amps sound noticably better than our qsc powerlights with tds!

 
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