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And some tests…

Recently I bought a couple of second hand Yamaha P7000S in order to driver a total of 4 bass units, built on the RCF L15P200AK-II woofer; like i did for other amplifiers in the past I took a look on on the Italian Mercatino Musicale site and found them in very good condition and for a reasonable price, little more than 700€ both. I was looking for a couple of amplifiers over a single unit of more power in order to have better flexibility in the configuration; I can use them all in stereo @8Ohm or bridged @4Ohm on two bass unit each. Moreover, considering that I currently use a CC4000 to drive the 12” mid basses in both 8 and 4 Ohm setup I can also try different configurations and for example use the CC4000 to drive the 4 bass units in 4Ohm stereo and the Yamahas for the 12”.

Also for this model, like my CC4000, I read several different comments both positive and negative on some forums; as usual in the choice I used my head and decided to give it a chance. Looking and the schematics on the net once again I found and amplifier with:

  • a good number of output devices, you can see a total of 12 per channel; better damping factor, less power per device, and so on …
  • a full transistor schema from the input to the output of the power module, while as usual input, filters and other “accessory” units are IC based. On most amplifiers the input stage of the power module is IC based; the P series is just like the Crest CA all transistor based, and with 1 capacitor through the whole signal path
  • an interesting power supply technology (EEEngine) which seems to be promising in terms of total power consumption and dissipated (= wasted); this translates into less heat generated.

Here is a shot of the internals

P7000S Internal

I haven’t had yet the chance to do a listening test and compare it to both the CA6 and the CC4000,but found some time to put it under a small bench; as usual I used my 8 2Ohm 50W resistors to build up a stereo 8Ohm load of 200W, which is capable of handling up to 1000W with a duty cycle of 5 (1s on 5 off). I then connected a small power distributor to the wall plug with 5m of 3×2.5mm2 cable and powered the unit, which has a 2m supply cable, quite small in my opinion; it’s a 3×0.75mm2 unit and maybe could “eat” some watts (read my CC4000 review for details). Maybe I’ll come back later on this.

With the usual 3s on and 15s off @100Hz the P7000S clipped @675W/8Ohm, with the meter reading 73.5V RMS, the clip leds starting to light up and the wave figure like below

100Hz full power

The amplifier well met it’s specifications, which state 650W RMS for the EU version; yes the EU version (230V) seems to loose almost 50W compared to the other, and looking at the schematic this is due to a couple of inductors put in series on the main supply, which role sincerely is not so clear to me, even if on a forum i read that it should act like a PFC circuit, but PFC is something that is a little more complicated than a simple pair of inductors.

Supported by a video I saw on the net of a modded P7000S, and by a check on the schematic which confirmed me that their removal would produce only gains, I decided to disconnect the terminals of the coils and to put in place a jumper built with some cm of cable and a couple of faston; the non EU version have a jumper built on the board but it is the same.

I tested it again and got back around 740W 8Ohm, with the meter reading 77V RMS and the clip leds flashing lightly

100Hz full power no coils

As You can see the wave is still clean and this is very good; it seems that the removal of the coils not only give more power (65W) but also seems to present a better supply line to the switching modules and finally to the amps.

I then repeated the test @50Hz and the results were the same, if not slightly better (few mV more).

50Hz full power no coils

I currently do not have enough resistors to build  a proper 4Ohm load, so I cannot test such a high power unit without the risk of destroying the resistors, but I can test a 4Ohm bridge configuration with some safety margin; for this amplifier the sheet only report the bridge power for 4Ohm loads (2Ohm stereo) for 20ms peaks, and my objective was to have a unit which, when  bridged @4Ohm, just meet the RMS specs of my CA6 (currently 1650W) with some margin; so when used together they will deliver around 3200/3300W, and most important without pushing hard the amps to the limits; currently with the CA6 driving 2 bass units and with 2 satellites there is a very good sound balance, so with the whole 4+4 configuration the same balance will guaranteed, and also with a reasonable little margin to play a little harder when needed.

Given this I tried some tests with the bridged configuration @4Ohm and finally decided to stop at around 2350W RMS, that is 97V RMS; the two coils are still disconnected.

4Ohm bridged

This is more than enough form me, and the good thing is  that no breaker or other form of protection/limiting was kicking in; just remember that the CC4000 was triggering it’s circuit braker at around 2100W when bridged @4Ohm, so that I had to reduce the cycle to 1s on in order to be able to reach higher power levels.

As usual I also do some tests at higher frequencies to check for the absence of wave artifacts due to missconfigured idle current (higher distortion) or power supply residual; this time I was also curious about the behavior of the EEEngine.

This is the 10KHz wave at 2.83V RMS

2.83V @10K

And this is the same 10KHz wave at 80VPP (28.2RMS, 100W/8Ohm).

They are both clean; I then repeated the tests at 15Khz and the figures didn’t change, very clean the same.

I will order in the next days an additional resistors set in order to build a reliable 4Ohm load and will come back with the results under that load; moreover i think I will play around with the power chord.

Update on 08/12/2015

Today I replaced the power chord with a piece pf 3×2.5mmq cable, like You can see in this photo compared to the original.

20151125_090105

The results were almost the same, with the amplifier delivering 77.7V RMS @8Ohm (755W/8Ohm) at the onset of the clipping, confirming that the P7000S ,and also the P5000S I think, has a minimal sort of “regulation” for small undervoltage; the voltage at the board connectors was around 227V while with the original power chord it was around 222/223V.

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Here are some additional readings of this amplifier taken from the power box I use, just to get an idea of its power consumption

This is the at idle with no other equipment connected to the power box: 60VA

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This is at100W RMS @8Ohm both channels, with a total of additional 200VA used by a lamp, scope, pc and mixer; so around 470VA absorbed

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This is at 200W RMS @8Ohm both channels; around 800VA used

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And this is at full power @8Omh both channels: a total of around 1900VA for 1500W on the load

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a small review but at the moment without bench data…

Some months ago I decided to take an amplifier with higher specifications than the “wonderful” CA6, in order to fully kick my bass units, because when used outside, in bridge mode @4Ohm (~1600 Watts), the “small” CA6 appears to be a little undersized, even if it drives 4Ohm bridged without problems. Furthermore I’d like to not “overuse” a power amplifier, so that I carefully look at all the clip leds in order to have them light for few times during the events; I know, and already described, that the limiter circuits do a good job in keeping distortion at low levels when they’re on, but on the other hand there isn’t much more to obtain from an amplifier when it is already telling you that it reached its limit, that’s my point of view… I bought a second hand CC5500 in very good conditions so that it seems just came out of the box.

I read some very negative comments on the various forum .. “it’s crap”, “economical” and so on, but my impression was that many of them were driven by “fanaticism” for other brands, non technical/on the road opinions and assumptions: on the other hand the Crest Pro series is considered to be one of the best sounding line, so why not the CC5500 which has the same schematic as the Pro serie, and the Peavey CS series, with the CC and the CS having a traditional power supply instead of switching? You can also read very good opinions regarding the CS4080 which is CC5500 with higher supply rails and minimum 4Ohm load and, most important “The things I learned while designing the Crest 9200 carried over to your Peavey CS4080Hz. It’s mostly a Crest 9200 output stage with a linear transformer limited to 4 ohm/ch capability. That in turn morphed into the Crest CC5500 with a two ohm rating. Hence the similarity you noted. We would like to keep the two brands uniquely separated, but I’m not going to burn Hartley dollars reinventing technology. When the price point allows, the Crest gets more stuff inside”, forum words of an ex-Crest engineer… point…

In addition to the above I based my choice also on this review and this one  

Currently in this page You will not find bench data like for other units I own, basically for 3 reasons:

  1. my load resistors ( 4 x 2Ohm in series) are rated at 50W each for continuous drive, so 200W total, and a 5x overdrive capability for a duty cycle of 5s ( 5on and 5off). I already use a longer OFF cycle (10s)  and 2 fans blowing on the heat sink, however their life will be at risk with the CC5500, because they already “cried” with the CC4000.
  2. I always use  “real” home plugs in my tests, currently cabled with 1.5mm2 wires from the general switch having a 10A wall outlet, to which I attach a 3m extension (3×2.5mm2) going to the power distributor on the rack. This is far away from regulated bench supplies and almost reflect real usage scenario.
  3. The results of the CC4000 presented on this pages (for the point above) were misunderstood and interpreted on some forums (or from some people) as the amplifier not meeting its specs, and not as the result of the whole power supply line performance. As You can read here the CC4000 fully reached its 8Ohm specs on a bench supply but started suffering mains voltage drops on lower loads.

Dopo diversi anni di glorioso servizio alcuni mesi fa è giunta l’ora di “rottamare” le vecchie casse, destinando alla discarica la parte in legno, che dopo 20 anni iniziava a evidenziare problemi di vecchiaia, soprattutto quelle in truciolare per i bassi, che se non fosse stata per una struttura interna simil-matrix nell’ultimo periodo avrebbe avuto sicuramente problemi; per quanto riguarda gli altoparlanti, il CIARE HW380 è stato “ceduto” al miglior offerente mentre sono stati messi a riposo (momentaneamente) un vecchio PW322, che riporta ancora la scritta  M320-75… ed una tromba a direttività costante (T4439) con un profilo che si appoggia alla perfezione su un woofer da 12”.

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Con SQL Server 2014 ed il Cumulative Update 2 della Service Pack 1 di SQL Server 2012 è stata introdotta l’opzione “TO URL” del comando BACKUP, che permette di memorizzare direttamente un file di backup sul blob storage di Azure. L’operazione è possibile anche con le versioni precedenti (2005, 2008, 2008R2) tramite il tool “SQL Server Backup to Windows Azure”, reso disponibile nei primi mesi del 2014.

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A partire da SQL Server 2005 la Plan Cache di SQL Server si rende visibile tramite la Dynamic Management View (DMV) sys.dm_exec_cached_plans, che ritorna una riga per ogni Execution Plan memorizzato e che nella sua forma più semplice (SELECT * FROM…) ci dice sostanzialmente poco, a parte permetterci di fare delle aggregazioni su alcuni campi come ad esempio size_in_bytes per avere un’idea della distribuzione degli oggetti all’interno della Plan Cache stessa

 select sum(size_in_bytes)/1024 AS 'SizeInKB', objtype
from sys.dm_exec_cached_plans group by objtype order by 1 desc

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Che poi non si discosta molto dall’accordatura di uno strumento reale …

Dopo avere condiviso l’ultima versione di soundfont in questa cartella, mi è balenata l’idea di fare una verifica sull’intonazione dei vari strumenti, per verificare che non vi fossero grosse discrepanze di tono nelle varie note, anche se in realtà l’ascolto aveva già confermato una buona omogeneità; alla fine poi si è trattato di un’operazione di rifinitura, gli strumenti accordati erano tutti ben intonati.

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My Crest Audio CA6 amp

Pubblicato: 25 giugno 2013 in Elettronica, Musica
Tag:, , ,

A review with some measured data and some modifications to further better this amazing mid-power Pro Amp

I’ve been always fascinated by this line of Pro power amplifiers of the famous brand of Meridian, Mississippi, for several reasons, among which I count

  • Modular construction, there is almost one board for each section: input & and gain, pre/driver & protection, output stage, power supply.
  • “All Transistor” construction, excluding the input like in many Hi-Fi amps, which gives this series a superior sound quality; this is almost an Hi-Fi like amp, and the version with the output binding posts is considered such this way. Moreover there is only 1 ( I say 1) polypropylene capacitor in series with the signal… (I’ll show You later)
  • It uses and advanced (= well engineered ) Modulated Class H output stage, which exhibits no glitches at high frequency during rail switching, also without using RC networks across the switching diode; I simulated the whole circuit with LTSpice and there is always a clean wave and a perfect switch also at 20Khz.
  • Triple Emitter Follower output configuration with a total of 12 output transistors for each channel; this translates into better behavior on lower loads and less distortion, and more reliable operating conditions due to a great number of devices compared to other brands for the same rating, which use typically 8.

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