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Old 24th April 2006, 02:20 PM   #11
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C9 and C10 seem to be polypropylene caps. It looks like they were heated up too much.
These caps tend to melt instantly when the foil is touched with the soldering iron. The result is a dead short capacitor. If my assumption is correct, replace them.
Also, check your soldering work. On some pictures I see cold joints, especially on the bigger wires.
As Cheff said, connect something like a 20ohm/50W between + and ground and another one between – and ground. See if the PSU can supply that power. At 24.5V a 20 ohm R will pull a current of 1.2A.

/Hugo
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Old 24th April 2006, 09:55 PM   #12
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Cheffdegarr

I have measured Voltage across 0.1 ohm Resistor of my PSU during first seconds of normal amp. work :

Voltage drop is 0.61V on V+ side resistor and 0.56V on V- resistor side.

That mean a current draws on V+ side is 6.1 A and 5.6A V- side.

Is it normal ?

I notice also that one of my BYW99 rectifier diode is getting hoter than the others. May i check this diode when PSU has dropped to 8V?

I have checked my NTC values : it is an EPCOS rated for 220 V (265 Vcc) The C830 model in datasheet .http://www.farnell.com/datasheets/62080.pdf

Nevertheless, I will do a try without NTC


Netlist, C9 and C10 a styroflex capacitors (polystyrene) one. I have replaced them by new one and removed all unnecessary capacitors (including wima ones) and kept only C1 C3 C5 C6 C9 C10.

With no more success.


Next step to try without NTC and try with 20ohm 50 W resistors

thx Loic
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Old 27th April 2006, 06:45 PM   #13
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Loic, any progress?
The power test is crucial. The value of the power resistors isn't.
anything between 15 and 25ohm or so will do as a basic test, as long as their power rating is high enough.
The diode warming up is not good. Check every one of them and see if the polarity and wiring is correct.

/Hugo
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Old 29th April 2006, 06:06 PM   #14
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Gentlemen

Good news

The Problem is on my NTC. With NTC by passed , all is doing well.
My NTC is on primary side on my transfo.

The NTC i have is rated 120°c and 1.2A for 250 V.

My Amp is biased at 6A under 20V.

Is my NTC current rating sufficient? What can i use as a good alternative? a soft start circuit ? Is there a schematic or a ready to make product available?

Loic

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Old 29th April 2006, 06:15 PM   #15
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Good news.

I recall Nelson uses CL60 but I'm not sure where to buy them over here.
I'll have a look at what I used and report.

/Hugo
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Old 29th April 2006, 06:18 PM   #16
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Here you go:

http://be.farnell.com/jsp/endecaSear...SKU=606789&N=0

/Hugo
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Old 30th April 2006, 06:45 AM   #17
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Loic,

Glad you found it
Have you listened to the amps ?

Two more links to help you calculate your NTC ratings :

This one and this other one

Hope this helps
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/Cheff - Falling feels like flying, until you hit the ground
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Old 8th May 2006, 09:20 PM   #18
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gentlemen

i have listened to my amp in stereo :WOWWWWWWWWW.

A real surprise to me !!! great sound , wide and deep scene.

Happy man i am..

A question now : i have seen some guys use input caps for input signal.

I saw Neslon said that we shall avoid the use of the input cap as much as^possible but what the use of having it. What is its effect ?

For the moment i'm connected unbalanced.

Loic
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Old 8th May 2006, 09:31 PM   #19
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That is great news.

The input cap is there to prevent any DC component present at the input from appearing amplified at the output.
Your speakers don't like DC as you probably will know.
I your preamp has a very low DC offset, you can do without the input cap. Since you can adjust the AlephX to your needs, it's easy to connect your preamp and trim for the lowest DC value at the output. No need for a cap then.

/Hugo
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Old 8th May 2006, 10:27 PM   #20
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Netlist

For the moment my CD player is connected directly to the amp. Volume can be modified within the cd palyer with remote control.

What are max values of Offset between Outputs terminals?

I measured 0.022v on one side and 0.018V on the other.


Second point, i tried seting up the variable constant current source, (r12/r34 pots) following the WIKI.

The problem is i measure ZERO Vac through R2/R3 resistors and even R5 on both sides of the amp.

CD player connected to input and speaker connected to output. I tried to turn R12 or R34 with no visible effect.?

R2/R3/R5 are all 0.47 Ohm.

loic
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