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Old 25th April 2007, 02:50 AM   #1011
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Hi

I think I will try to do the Dx amplifier, what is the input sensitivity ? (I would use it with a passive preamp.)

Any TIP power output transistor that I can use to replace the 2SC5200 and 2SA1943 ?

I have some darlington TIP 142 and 147 power output transistors , I presume those will not work in the DX amp ?

And I did made power amps with TDA7294 and LM3886 , what are sonic differences betwen the Dx amplifier and those one chip amps ?


Thank

Gaetan
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Old 25th April 2007, 06:07 AM   #1012
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Default Make a good visit into this thread my friend, you will find all your answers already

posted...in the Greg's home page you will have other transistor options, there are one circuit posted using TIP142/147 too.

Give us the honor or your visit...than you will have no questions anymore.

Forum is very rich...has all informs someone may need, but we need time and patience to read it all.

I have readed all Solid State forum...all threads, including the ones i do not like the subject discussed....also the theorical threads that i dislike...i have made this twice and already started the third time, as i could find answers to all questions i had, and reading once more i am turning myself better in knowledge.

I use to suggest friends to read the entire thread....not too much to ask when i have readed the entire Solid State forum more than once..all threads, all posts, i could colect informs of all gênius, all bad educated folks, the most talking parrots, the provocators, the clever ones and almost everything forum could give me.

Incredible place this one...but we need, in advance, to listen a lot..to read a lot.

No University can provide all that knowledge..also you cannot listen, and receive personal answers from Gênius, famous designers and hardly experienced folks.

The only thing forum cannot provide is experience....for that we have to burn our hands, to let computer simulator rest in peace and to put our hands on the job.... forum is so clever that it's title is "Do it by Yourself"....as this is the most important thing, as no one can be experienced only reading theories...he will be a mobile enciclopedia only.

Dx amplifier is here, in the Greg's pages... transistor options are there...the amplifier with TIP is in this same thread...about those LM chips i can tell you that Dx amplifier sound very good..will not buy a figth against zillions of LM constructors...find the real thing by yourself...try it!

http://users.tpg.com.au/users/gerskine/dxamp/

regards,

Carlos
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Old 25th April 2007, 11:04 AM   #1013
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Default TIP141 and cousines are able to dissipate 100 to 125 watts.

This way...amplifiers that can produce more than 80 watts will be turn the use of those transistors very dangerous.

Dx amplifier, modified to work with those transistors, will be able to work only producing 50 watts, as it can produce much more power (distorted) and this will make the output transistors work near the maximum...if square, continuous, fully distorted clipping output signal was produced.

Also it is published as 125 watts, but when you put it to dissipate 80 watts you will perceive that 125 watts was something not precise as dissipation..hehe.

Dx amplifier, using 35 to 37 volts supplies....simetrical ones, will produce power enougth to melt those TIPs in a metter of seconds if you install a 4 ohms (nominal) impedance into the output...not able to work with 4 ohms using a single pair of darlingtons.

The internal arrangement of resistance you have inside darlington transistors, at least this one, is not very good to audio purposes, more adequated to fast switching purposes...because of that you cannot "adjust" the first transistors emitter resistance
to optmize VBE for both of them... result is a little distorted audio using very high and very low volume levels..working fine during average power work.

Of course you can use them in pairs...many pairs, and the gain is absolutelly the same, so, emitter resistances are not needed for them...if you wanna remove them, do it without fear, as you will not have tears.

Using them into DX, a better idea is to use smaller supply voltage... 30 Volts for instance...and do not worry about losses in power.... you have to double your power to perceive, and very hard to perceive increasings in power....clear will be if you multiply your power by 4...... this happens because of human perception...we cannot perceive....so....35 watts amplifier and 100 watts amplifier sounds almost the same...you perceive a little more punch into the bass area only....inverting the logics, or, reducing power, the effect will be be same.

Different than us, humans, the speaker can perceive any increase in power, that will be transformed in speaker diafragm movement (limited in the extremes, turning sinusoidal waves into square waves very easy) and also transformed by heat.

So...some increasings in power.... more 50 percent, more 80 percent... will be nothing to your ears...may kill your speaker of burn your output transistors.

regards,

Carlos
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Old 25th April 2007, 11:37 AM   #1014
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Default Here is the thread short cut to the TIP142 version.


http://www.diyaudio.com/forums/showt...23#post1168423

regards,

Carlos
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Old 25th April 2007, 01:23 PM   #1015
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Default Sorry, i have forgot to inform sensitivity.


750 milivolts to full undistorted power.... and easy to adjust tweaking single resistance.

More sensitivity, reduce R10.

Less sensitivity, increase R10

regards,

Carlos
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Old 25th April 2007, 01:41 PM   #1016
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Default Here you have the off set and stand by current


Off set in the middle.

Positive rail current is in the top
Negative rail current in lower position.

Differences of stand by current are the result of positive rail zener diode that is receiving something around 10 miliamps of bias... this appears in the positive rail as the stabilizing circuit is using positive rail and ground only...of course could be made different...but was made this way...next amplifier(if this really happens) will have the same bias for both rails...and them everybody will feel more happy.

regards,

Carlos
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File Type: jpg off set and std by current.jpg (87.2 KB, 526 views)
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Old 25th April 2007, 02:02 PM   #1017
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Default Here is an example, using darlingtons


Supply is 25 plus 25 volts.

Output power is 55 watts rms over 4 ohms

Condensers from Darlington bases to colectors are extremelly important..without them you will have oscilations and burns.

Simplified..extra small components count...zener suppressed...power on thump will be perceived clearly this way.

Bias will be small....5 to 10 miliamps each rail...off set smaller than 5 milivolts..audio quality is worst than normal Dx amplifier.

regards,

Carlos
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File Type: jpg 55w - 4 ohms.jpg (80.9 KB, 514 views)
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Old 25th April 2007, 02:09 PM   #1018
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Default Here is the Dx grandson schematic..sorry, not pretty.


But also no one is constructing this one.

If someone appear as interested, i will provide him a better schematic, more clear, and less confused.

But this one....even confused, is working in the simulator...for sure this one will work real world, as i have made some of them in 2000.

Attention!...no way to work without darlington condensers...those ones form base to colector..do not even try..boooom! will be the result.

regards,

Carlos
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File Type: gif here is the dx grandson.gif (73.2 KB, 574 views)
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Old 25th April 2007, 03:59 PM   #1019
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Hi

Using darlington may have a sonic difference, I did save your messages and darlington version schematic but I will try to find the non-darlington power transistors to use your original version
of schematic.

Tank you

Gaetan
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Old 25th April 2007, 06:17 PM   #1020
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Default Be free to decide the one to construct, and also, your choice can be other amplifier.

Never mind, and be happy.

Merci beaucoup pour la votre presence. C'est mon plaisir pour faire quelque chose pour vous.

C'a marche.

au revoir

Charles
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