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Old 4th October 2011, 10:00 PM   #191
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Default A friend from other forum told me these two heatsinks are reaching 52 degrées celsius

these units are too much hot... 52 degrées Celsius (Centigrades)... this is too very good.... better if you can keep these ones at 45 to 47 degrées.

A taller, or bigger heatsink will be needed for him to cool down these two transistors mounted in separated heatsinks.... they are lovely but small, not that tall as i was dreaming for.

The guys is using 68 volts supplies...... and the higher the supply voltage the bigger will be the problem related these heatsinks.

In my construction, home prototypes using standard supply voltage, i have not noticed heat there because these transistors where mounted into the main heatsink...but seems you may face some trouble because heat there.

Be aware you may have to replace these heatsinks for larger ones.

regards,

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 5th October 2011, 02:42 AM   #192
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Quote:
Originally Posted by Francois G View Post
Dear Vargasmongo,
Explain! what is different?
thanks,
Francois
No, is about the MKIII green board and the red one the 220pF cap is oriented, in a different way that is all, mister Junie show me, that is way I say that, nothing to worry about I'm sorry I'm Puertorrican I get exited for everything

regards
vargasmongo
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Old 5th October 2011, 03:46 AM   #193
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Quote:
Originally Posted by vargasmongo3435 View Post
No, is about the MKIII green board and the red one the 220pF cap is oriented, in a different way that is all, mister Junie show me, that is way I say that, nothing to worry about
Yes, the board is very crowded. I recall moving some things around to increase the space between tracks and between pads a bit. the schematics are the same. I apologize for any panic I may have caused.
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Old 5th October 2011, 05:12 AM   #194
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Default Canonnica, i have checked and the stand by adjustment

changes a lot when we use other voltage than the standard.

So, adjusting with 9 volts or 15 volts will not be final adjustment...in the real world this adjustment will not be good to 64 volts.

regards,

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 5th October 2011, 05:30 AM   #195
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Post Understanding the trimmer resistor

I'm getting to that point, so I'm re-reading Carlos' old posts - carefully this time. I want to make sure I understand Post #3 in this thread. Of course I could just blindly follow Carlos' instructions, but I want to understand why.

His instructions say that with a 64V supply, we should adjust our trimmer resistor so that the temporary 100ohm resistor in series with the rail voltage should have a ~4.4V difference across it, and result in 0.044A flowing from positive rail to ground. (Presumably -0.044A flowing from negative rail to ground.)
Using Ohm's law, I calculate that 64V=0.044A*(100R+XR), where X is the resistance from supply voltage to ground in the absence of the 100ohm safety resistor. Some high-school algebra tells me that X=1355ohms. Is this correct? Though I can't figure out where this 1355 ohms comes from, it seems that much of it comes from our trimmer resistor. We are setting the resistance of the trimmer to set the resistance from supply-to-ground to be ~1455ohms in the presence of, and ~1355ohms in the absence of, the temporary 100ohm resistor. If the voltage across the 100ohm safety resistor is 4.4V, then the resistance of the rest of the circuit must be ~1355ohms. Is this correct? And if we can't find any setting of our trimmer resistor which sets the voltage across the 100ohm temporary resistor to = 4.4V, there must be something wrong with our amp.

the problem is that when I check my math by calculating voltage drop from known resistances, I come up with different numbers.
In the absence of the 100ohm resistor: I=64V/1355ohms=0.0472A
In the presence of the 100ohm resistor: I=64V/1455ohms=0.0440A
Voltage difference due to the 100ohm resistor: V=(0.0440A-0.0472A)*100ohms=-0.323V. This value should be -4.4V

Well, it's too late at night for me to concentrate on this anymore

-Byron
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Old 5th October 2011, 05:44 AM   #196
Junie is offline Junie  Philippines
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Wooot!!!

I think i got a working DX Blame MkIII...Thanks Uncle Charlie.
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Old 5th October 2011, 05:51 AM   #197
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Default Yes, more or less your calculations Byron...too late to my old brain too

People that feel these 2 small vertical heatsinks too much hot can reduce VAS current in order to reduce heat there.... i have simulated and i found the original schematic fine... with the modification you will have changes in performance, but not that huge.

The 22 ohms resistor that sets the CCS current can be increased to 47ohms in order to reduce current...then you will have these transistors mounted into vertical heatsinks (CCS to VAS and VAS transistor) less hot.

I found power there not that big...the left one is the CCS transistor, CCS to feed VAS (Voltage Amplifier Stage) and it is dissipating 1.65 watt.... the rigth side one is the VAS transistor, the second stage, the most active unit, following the buffer and the power there, dinamic power, will be around 1 watt....not that huge power and the small heatsinks should fit in most of the cases... exception is when people is using higher supply voltage... say... really higher voltage.

You can replace the 22 ohms resistor by a 27 ohms, 33 ohms, 39 ohms or 47 ohms.... i suggest you to go to 47 ohms because will really cool down in order to work fine with tiny vertical heatsinks... with this resistor replaced, the performance when using low impedance output loads will clip earlier.... some loss in power...not that huge, not that important.

Some high current. high voltage and high speed diodes installed into the output, in the power transistors, from colector to emitter, can be used too as we gonna face some back EMF there.... so, if you intend to push the amplifier hard, then search for high speed, high current diodes used to fly back purposes there...what model to use i cannot suggest you as i do not use them, so they are not familiar to me... search for high power amplifiers and copy the diode model to apply to yours....this is to play heavy metal, full power, distorted sound and connected to 2 ohms loads... an extra protection if you intend to operate your amplifier above the limits, entering distortion and draining huge ammounts of current and generating enormous output having a lot of back EMF in your output line.... normal civilized use will not need these diodes.

If you decide to use alike dB competition of bass, operating in clipping mode..for sure you will need these protective diodes.

Enjoy your amplifier boys...sound is awesome and you will perceive that instantaneously.

regards,

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg

Last edited by destroyer X; 5th October 2011 at 06:10 AM.
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Old 5th October 2011, 05:58 AM   #198
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Default Good Junnie....enjoy.... this is what i want

That you feel good, feel happy.

regards,

Carlos
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Old 5th October 2011, 10:53 AM   #199
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Default Muchos gracias senior carlos

Quote:
Originally Posted by destroyer X View Post
That you feel good, feel happy.

regards,

Carlos
The amps sound pretty good, it's fantastic!
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Old 5th October 2011, 12:08 PM   #200
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Quote:
Originally Posted by ByronInLawrence View Post
I'm getting to that point,.......................

Well, it's too late at night for me to concentrate on this anymore
what you have calculated is basically correct.
The big difference between your assumptions and the real circuit is that the 1355r is not a resistor, but a complex combination of resistors and semiconductors.
The other assumption that does not hold, is that the +ve and -ve currents do not need to be equal. If they were then the ground would not pass any quiescent (no signal) current.

If you apply the correct supply voltage to the amplifier when the output bias is turned down to minimum then you can start setting up your amplifier.
Using Carlos' method.
Power down and insert a 100r in place of the +ve rail fuse. This 100r could be soldered permanently across the fuse holder terminals so that all you need to do to set up the amp is remove the fuse.
Power up using the bulb tester to prevent damage if something has been changed by accident.
Check the bulb is off or has a VERY DIM GLOW.
Measure the voltage across the power supply terminals.
Measure the voltage drop across that test/set-up resistor.
Now slowly increase the bias voltage across the Vbe multiplier. Use small increments and measure the bias voltage, measure the test resistor voltage.
Continue increasing the bias voltage. You will probably find that the bulb will become increasingly bright. Do not change the bias setting. Change the bulb to a higher wattage, or if you are really sure you won't make a mistake power up directly from the mains.
Recheck the bias voltage and the test resistor voltages. They will have changed since moving from the low value bulb wattage.
Why have the test voltage changed, I only removed the bulb tester. They change usually increase because the Power supply voltage will have risen.
Now start increasing the bias voltage checking both those test points. Keep increasing until you reach the final setting given by Carlos. Check device temperatures check for burning or overheating smells. Check device temperatures. Wait a while and recheck device temperatures.
When the amp reaches it's final operating temperature, 30 to 60 minutes say, recheck the test voltages. Readjust the setting is necessary. replace the fuse. You have now changed the PSU voltage. The test voltages will have changed, but you can't measure them, because you have bypassed the 100r resistor with a fuse.
Job done.

BUT DO NOT connect your speaker yet.

Short the input signal hot to signal ground. measure the output offset at the speaker terminals. Measure the output noise at the speaker terminals. Power off. Let the amp cool a bit.
Power up and recheck the output AC and DC voltages. Leave the amp running with shorted input for many hours with the occasional OFF/ON to stress the components. When you are sure that the amplifier is behaving itself, then it is time to connect a cheap speaker.
Listen for any hum.
Power OFF. remove short from input. Power ON. Is the speaker still working? Can you hear any noise? Is the cone still at it's centre travel position? Measure the AC & DC voltages at the speaker terminals. Are they similar to those from before.
Power OFF, connect an audio source. Power ON. Recheck your voltages. Is the speaker still OK?
Now listen to some quiet music. Does it sound "clean".

Job really done.
OFF, connect your real speakers, ON, enjoy.

Do you want to hear about the correct way to adjust the bias of DX amplifiers?
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Last edited by AndrewT; 5th October 2011 at 12:14 PM.
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