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Old 21st February 2013, 02:46 PM   #571
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The reason I want to reduce the supply voltage is because i like to use only 1 pair of output transistor (less parts), i just thought that it will be safer to do that with lower voltage say for 4ohms load, or perhaps what i think is wrong?

Thanks,
wattodo
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Old 22nd February 2013, 12:35 PM   #572
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Hello guys!

Here is the update silkscreen of Dx Super A, C30 = 220uF and C13 = 150pF to keep track of it, as Carlos did the updates already here are the images.

Regards
Juan
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File Type: jpg Dx Super A updated.jpg (820.3 KB, 404 views)
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File Type: pdf Dx Super A updated.pdf (82.3 KB, 126 views)
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Old 22nd February 2013, 01:16 PM   #573
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Default It is all right Wattodo

One pair to 36 volts...but cannot use 2 ohms loads.

Carlos
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Old 22nd February 2013, 03:39 PM   #574
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Thanks Mr. Carlos,

Now i know that i can proceed.

Regards/wattodo
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Old 22nd February 2013, 09:35 PM   #575
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Default I have made text instructing Brazilians about the Dx Supply and Dx Super A

Details about fuses rating, transformers VA rating to several levels of power, needs of electrolitic condensers and things alike.

I do think it is very usefull and may answer a lot of questions.

Now a days language can be translated using Google translator...you just copy and paste there... write portuguese in the left side and in the rigth side select your own language...not perfect but helps a lot.

I will be posting two word docs, not opened if possible, because not the forum main language, and i would like to say this was posted before in several threads, it is just infomation i put together.

We have several countries that uses portuguese..also Italians are able to understand and several spanish language countries can also understand.... others, if interested, then go to google and i hope it will make a good version of your own mother language.

Sadly forum system have not accepted doc.... if you want, please write to uncle charlie and i will upload to you.

nanabrother@hotmail.com
carlos.eugenio1951@yahoo.com

regards,

Carlos
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File Type: jpg Sem título.jpg (190.5 KB, 319 views)
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Last edited by destroyer X; 22nd February 2013 at 09:38 PM.
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Old 23rd February 2013, 02:50 PM   #576
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Thank you Carlos (uncle Charlie ) for sending me the two files doc!

Best 73's!
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Old 23rd February 2013, 03:01 PM   #577
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Default You are welcome!

If you need something more..just call me and i will be there to answer you.

regards,

Carlos
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Old 23rd February 2013, 06:46 PM   #578
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Default Here you see the Safety Operational Area related the transistor we are using.

To operate full undistorted power (aprox. 300 Watts RMS - 2 ohms) we gonna have 6 amperes to each rail..... 3 amperes to each transistor.... and 3 amperes multiplied by 42 volts result in 126 Watts of power in each one of them... datasheet says it can handle 230 Watts...so... we are not operating into the limits.

But the heat generated will be huge...you must keep transistors cool using huge heatsink, also good thermal compound and fan cooling..if inside an enclosure you should have openings in the up cover (holes) and below the circuit board too...air must circulate from down to up that is convection cooling without obstructions...and fan must take this into account..the correct cooling direction to the blow air.

Was tested with huge heatsinks and cooling fan...i had not troubles while using sinusoidal steady tones 3 db below the maximum because this is the average power when playing music.

Current will be 3 amperes to each one of our power transistors.... observe the S.O.A. that shows it can handle 5A.... and this is IF your supply voltage will really stand still in 42 volts...if you do not use a voltage stabilizer then the voltage will drop and then the transistor will work even more confortable.

Despite of all that technicall stuff, i would like to say that you should not trust on specifications, because this was made by manufacturers at 25 degrées celsius and this is not reality...so...better not to force your amplifier..better to use 4 ohms loads to be in the safe side..you will have minimum of 150 Watts RMS and will have peaks much higher than that...the amplifier will work in a very safe way, not so hot, not so dangerous and the best part of it is that you will be rid of the big trouble related speaker impedance.

If you find a speaker, a 2 ohms nominal speaker for instance.... a dual 4 ohms coiled speaker...you may believe you have 2 ohms.....NOT REAL....this will happens at 1 kilohertz, but you will have some frequencies where the impedance will drop down...this is dangerous..because 2 ohms is not 2 ohms anymore and this gonna force the amplifier.

Not only the speaker is the problem..also the crossover that introduces valleys of impedance.... if you see the real thing..the curve...the graphic, you gotta feel panic!..... because of this stuff...better not to force the unit, because it is very good, but cannot hold a panzer tank passing over it, also cannot survive to dinamite, also cannot operate under water, or exposed to direct sunlight or inside an oven.

regards,

Carlos
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File Type: jpg S.O.A. - MJL4281a.jpg (347.0 KB, 231 views)
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Old 23rd February 2013, 07:52 PM   #579
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Default Despite i have made pcboards having room to use " L" shape adapters

I do suggest you not to use them and to assemble the transistors directly into the heatsink.

" L" shape adaptors, depending on the kind of material used, may be a huge problem to heat transference.

Using them you gonna be limited related the power you will be able to use due to the heat transference problems... even using good grease, even using tight screws and several screws, flat surface, big contact surface and good kind of aluminum (duraluminum or aviation aluminum is not good due to be an alloy that is bad to thermal conduction)... even having a lot of care about you may face troubles while operating 4 ohms and 2 ohms.

Do use " L " adaptors only if you intend to operate 8 ohms.... this is what i found here.

regards,

Carlos
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Old 23rd February 2013, 09:16 PM   #580
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Default We have a problem.... a RECALL to the Dx Super A amplifier

A design problem.... error...mistake...be attention.... watch the video:

Dx Super A recall - a problem! - YouTube

I am sorry....my mistake!

regards,

Carlos
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Last edited by destroyer X; 23rd February 2013 at 09:23 PM.
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