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Old 22nd April 2007, 12:15 AM   #971
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Default I was remembering you those last days because of that Hugh.


And i could understand better why you jumped out from Kits production, into already builded units.

Doubts are unlimited, as each one has different experiences..and this takes time, to stay over the builder's shoulders controling everything.

regards,

Carlos
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Old 22nd April 2007, 07:42 AM   #972
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heheh Nordic - sometimes we do cook our heatsinks......look what i have done for a friend of mine....30kg unit and only 15W of power...hheeheheh
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Old 22nd April 2007, 07:43 AM   #973
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the transformer is 250VA unit and the box is huge.....
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Old 22nd April 2007, 07:45 AM   #974
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another view without the box - only heatsinks and two channels with psu....

hehehehe
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Old 22nd April 2007, 10:02 AM   #975
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Default He did that "for a friend".... there is the insigth to evaluate Sparkle as a person


How many guys do that?

regards,

Carlos
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Old 22nd April 2007, 11:42 AM   #976
kvholio is offline kvholio  Netherlands
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Yesterday i finally had some time to investigate the vbe-multiplier Carlos proposed.
The second 1k resistor is shorted, used transistor is bd139 .
I couldn't get it to work with 2k resistor, after changing to 1k it seems to work fine.
Click the image to open in full size.

Biased high at ~120mA , left is temperature of heatsink, right is voltage across rail-resistor (0.22 ohms).
The dynatek shows low-battery signal from monitoring too long , don't worry, the voltage shown is accurate.
Heatsink used is the small one i used before, 0.87 c/w.
Drivers used heatsinks too.
Measurement taken after > 1 hour , ambient-temp is 22 degrees celsius.
Click the image to open in full size.

To test something, you have to throw bricks at it.
The brick i used was a 800 watt hairdryer, i heated up the main heatsink:
Click the image to open in full size.
There is a little overshoot in bias, because i mounted the vbe-multiplier at the mounting-bar for the outputs.
When i heated up the heatsink the mounting-bar took a little more time to heat up.
Under normal circumstances the heat will come from the outputs,
this will cause the mounting-bar to heat up quicker than the main heatsink,
providing fast thermal tracking.

Cooling down:
Click the image to open in full size.

........
Click the image to open in full size.


Back to normal:
Click the image to open in full size.

The vbe-multiplier seems to provide excellent bias-control,
the channel under testing is now running at ~120mA bias continuously for more than a day.
This is not a bias-level i would recommend to others,
i just use it to see if the vbe-multiplier performs under these circumstances.

The DX-amplifier is, literally, still cooking

Best regards,

Klaas
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Old 22nd April 2007, 12:17 PM   #977
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Default Oh!...this made a relief in my heart...i was sick inside myself because your problem


Those things are strange, as i had mine one stable.

I see that things are running perfectly now.

I have a small suggestion to you....install a 220n or 100N capacitor into the points shown in the schematic.

Also, if you wanna treble boost, having not this adjustment
in your pré amplifier or sound source, install 33n to 150n capacitor as shown.

The TIP41 as driver use to loose treble.... very sligtly... this
is the main difference you may have using low speed transistors....the problem is not quality, but level only...compensating, dinamically, you will perceive everything
flat.

I am not telling you about graphics,... the amplifier is flat when testing...but listening, real world audition, some small losses in the high end can be perceived because of the low speed transistors used to make the amplifier simple and cheap...just try that if your transistors are not high speed.

The other 100n, installed at the differential long tail is for stability purposes.

regards,

Carlos
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Old 22nd April 2007, 01:31 PM   #978
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Default Juan, from Galícia, Spain, have asked me how to reduce his supply

....voltage from 63 to 36 volts to use into Dx amplifier.

Here is the schematic Juan.

The transistors are Darlingtons, TIP142 and TIP147...use two in parallell.

The NPN transistor is TIP41
The PNP transistor is TIP42

Condensers, all them, with 75 volts or more of maximum workable voltage.

The trimpot will be able to adjust voltage.... supplies from 45 to 63 can use this schematic without modifications.

The Output Darlingtons will need a very big heatsink..as they will dissipate enormous power if your supply keep this 63 Volts without too much losses.

Well...at least you will have a variable output voltage supply.....reasonably stabilized (5 percent).

regards,

Carlos
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Old 22nd April 2007, 01:34 PM   #979
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Default Juan, from Galícia, Spain, have asked me how to reduce his supply

....voltage from 63 to 36 volts to use into Dx amplifier.

Here is the schematic Juan.

The transistors are Darlingtons, TIP142 and TIP147...use three in parallell to each rail.

The NPN transistor is TIP41
The PNP transistor is TIP42

Condensers, all them, with 75 volts or more of maximum workable voltage.

The trimpot will be able to adjust voltage.... supplies from 45 to 63 can use this schematic without modifications.

The Output Darlingtons will need a very big heatsink..as they will dissipate enormous power if your supply keep this 63 Volts without too much losses.

Well...at least you will have a variable output voltage supply.....reasonably stabilized (5 percent).

Zener diodes can be 1 watt units to run cold.

Supply dimensioned to hold two channels operating 4 ohms

regards,

Carlos
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File Type: gif from 63 to 36.gif (92.1 KB, 343 views)
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Old 22nd April 2007, 02:38 PM   #980
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Hi Carlos,

The capacitor across R10 in post#977 could maybe have a small resistor in series with it; possibly of a value = R10 divided by between 5 and 10.

If R10 was a poteniometer, with the additional C connected between the slider and one end, the adjustment could be made pre-settable or variable.


Cheers .......... Graham.
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