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Old 13th July 2010, 08:11 PM   #11
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Hey you guys,

thank you all VERY MUCH for your advices and suggestions!


@ lineup
Since this board I purchased from Rod actually is a revision of an earlier version, I guess Rod had a reason to make these values 100pF. He might have checked all this with a scope and considered it as right and stable. I do not own a scope, so changing any component values to others than the originals might lead to completely unpredictable results. That's why I hesitate to do that.
R15 and C7 are installed correctly.

@ sakis
Well, I know you don't like ceramics that much... ;-)
But it's Rod himself who suggests ceramics in these positions, and while we can always discuss the sound of ceramics, I'm pretty sure he suggests these caps because he knows that they work for the intended purpose. I'm thinking about changing these to silver micas or Wima FKP's, but I doubt that these ceramics do cause oscillation, only because of the fact that they are ceramics...
The method I used for biasing the quiescent current is exactly the method Rod describes in his article, the voltage drop across the two resistors R13 & R14.
Concerning the B1 Buffer: I thought about that, too. But the problem here is not only the slightly recessed dynamics, but also a noticeably lower output level with the P3A in comparison to the nxV200 with my dac as source. So I think a little bit of gain might be helpful here to increase dynamic headroom.
Rail voltage is +/-35V (2x25V transformer secondaries). Collector resistors are 0R33, voltage across them was 50mV (for around 75mA quiescent current) and is now 40mV (for around 60mA). All parts are purchased from Conrad Elektronik, Germany. A very good shop, not cheap, but all the parts are really good. No comparison to other german suppliers like Reichelt, fo example......... cheap, but really many fakes and bad parts!

@ richie00boy
Actually, in this revision the 100nF caps in the supply rails is paralleled to 100uF caps. 100nF is Wima MKS2 63V, 100uF is Vishay/BC 63V (non low esr).
The nxV200 and the P3A are two projects I started simultaneously. I purchased the board for the P3A months ago and parallel decided to build the nxV200, simply out of curiosity, and to have something to compare against each other. In fact, these two amps do have quite a different sound signature. They do things different, but I like both for the way they deliver music. In the end I will have to make a decision between those two, mainly because of monetary reasons :-(
This is going to be difficult...

@ jaycee
He already did! But I hesitate to attach the current schematic because of copyright reasons. You can always have a look at his web page.

@ Andrew.Thompson
Yes, you're right! But on page 147 of the solid state picture thread I explained why this is supposed to work as well. But beside this, even without the top plate of the case the heatsink temperature rises to a quite high level, even with no music playing. I mean, it is not THAT hot, but I have the idea that it is just a bit too hot for an amplifier that is just turned on with no signal on the input and no speakers connected (but anyway, there is no difference with speakers connected and without).

@ wahab & sakis
I can't say anything about the need of a LR filter instead of a CR filter because this is above my level of knowledge. The CR filter from output to ground in this revision is C=100nF, R=10R.


Well, I will send Rod a message, perhaps he is willing to have a look at this thread. We'll see!

Thank you all!
Martin

Last edited by martinbls; 13th July 2010 at 08:16 PM.
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Old 13th July 2010, 08:58 PM   #12
wahab is offline wahab  Algeria
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Hi , sakis

Well, if there s an output filter, all is good then.
Must aknowledge that it would be difficult to have less
parts for such a design, so no doubt that the cost/complexity/perfs
ratio is of first order...
Thank you for your kinds words, i hope that all
is well for you as well in these strange times we are
all currently living in since a few years...
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Old 13th July 2010, 09:16 PM   #13
wahab is offline wahab  Algeria
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Quote:
Originally Posted by martinbls View Post
Hey you guys,

Concerning the B1 Buffer: I thought about that, too. But the problem here is not only the slightly recessed dynamics, but also a noticeably lower output level with the P3A in comparison to the nxV200 with my dac as source.


Martin
You can slightly increase the gain of the amp to
match your DAC output level.
Just increase R5 to 27K.
R2 should also be increased in that case to 24.8K
in theory, but a 27K should do it perfectly.
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Old 13th July 2010, 09:27 PM   #14
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martin, ESP has it's own forum so why don't you ask the question there?
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Old 14th July 2010, 02:29 AM   #15
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Quote:
Originally Posted by richie00boy View Post
martin, ESP has it's own forum so why don't you ask the question there?
You're right, I should do that also!
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Old 10th January 2013, 12:02 PM   #16
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With 60mA bias, and both stereo channels mounted on the same heatsink, during hot summer days, it is not unusual for heatsink to get warm or even hot.
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Old 10th January 2013, 12:17 PM   #17
AndrewT is offline AndrewT  Scotland
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2channels of 60mA output bias on +-40Vdc is ~9W of total heatsink dissipation. A bit less than 2.4W per output device.
That should never be hot, if properly assembled.
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Old 10th January 2013, 12:25 PM   #18
dadod is offline dadod  Croatia
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Quote:
Originally Posted by AndrewT View Post
2channels of 60mA output bias on +-40Vdc is ~9W of total heatsink dissipation. A bit less than 2.4W per output device.
That should never be hot, if properly assembled.
If don't play a music with it!!
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Old 11th January 2013, 10:25 AM   #19
AndrewT is offline AndrewT  Scotland
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Playing a 50W amplifier with an average music level output of less than half a watt will run at just about the same temperature as at quiescent.
The leaves the usual overhead for fast transients of ~+20dB when and if they come along.
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Old 11th January 2013, 07:46 PM   #20
effebi is offline effebi  Italy
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I had the same problem with one of my P3A.
It was defenetely self-oscillating, due probably to the fast transistors I used.
Fixed raising the CB capacitor on the low side driver to 220pF. Did not touch Cdom. No audible difference, highs still crystal clear, 100Khz square wave still satisfactory.
But then heat sink (0.5 C/W x 2 channels) pretty cool at idle, after 10'. After a doublle live LP of AC/DC played at the onset of clipping (from CD, not the ugly compressed stuff) just warm, but defenetely not very hot, something like 60 C.

BTW bias at 45 mA, just a little bit over the crossover disappearing from my scope, I liked the sound more that way.
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