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10th October 2009, 12:51 PM  #41 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

The back side, the transistor's back metal plate used not to be flat
this results the parts you see as copper colour are the parts are alike mountains and they would touch the heatsink..the lower parts, the valleys, the deep parts are the ones not touched by the waterproof, grain 500, sandpaper
The sandpaper was placed over a flat surface, a glass plate..and then i move the transistor to erode till turn it flat..you see material was removed into the parts you see copper...now it is flat. If you do not do that, then the parts are higher, the projections, to the metal bubbles, the peaks, the hills, the mountains into the metal surface, will be the ones will touch the heatsink..this will reduce (a lot) the heat transference. Check your transistors..you gonna be very surprised. regards, Carlos 
10th October 2009, 03:20 PM  #42 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Now, some circuit details
Dx Amplifier – bass unit – to work with 62 plus and 62 volts minus
Was made (adjusted, tuned, tweaked) to work from 1 hertz to 300 hertz (3dB) Sensitivity – 1 volts rms to full rated unclipped output. (39.75 Volts rms) Input impedance – 39K Output impedance – 8, 6, 4, 2 and 1 ohm.. depending the quantity of power transistors used into the output Power amplifier details with sinusoidal input signal, and delivering 39.75 volts to the load: 197 watts rms at 8 ohms, 200 Hz input with 1 volts rms of level, rail current 2.26A, and supply voltage at 62 volts to each one of the rails. 263 watts rms at 6 ohms, 200 Hz input with 1 volt rms of level, rail current 2.98A, and supply voltage at 62 volts to each one of the rails. 395 watts rms at 4 ohms, 200 Hz input with 1 volts rms of level, rail current 4.48A, and supply voltage at 62 volts to each one of the rails. 790 watts rms at 2 ohms, 200 Hz input with 1 volts rms of level, rail current 8.90A, and supply voltage at 62 volts to each one of the rails. 1135 watts rms, 1 ohm, 200 Hz input with 1 volts rms of level, rail current 14.9A, and supply voltage at 62 volts to each one of the rails. regards, Carlos 
10th October 2009, 03:30 PM  #43 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

About fuses and electrolitic condensers to the supply
About rail fuses and supply fuses… do not use fast blow
Operating with 8 ohms speakers, then use 2.5A fuse to each rail and 5 ampere fuse in series with the output (speaker) Operating with 6 ohms speakers, then use 3.0A fuse to each rail and 6 ampere fuse in series with the output (speaker) Operating with 4 ohms speakers, then use 5.0A fuse to each rail and 10 ampere fuse in series with the output (speaker) Operating with 2 ohms speakers, then use 10 A fuse o each rail and 20 ampere fuse in series with the output (speaker) Operating with 1 ohm speaker, then use 15A fuse to each rail and 30 ampere fuse in series with the output (speaker) About filter electrolitic condensers to the power supply Operating with 8 ohms speakers, then use 12.500uf each rail Operating with 6 ohms speakers, then use 15.000uf each rail Operating with 4 ohms speakers, then use 20.000uf each rail Operating with 2 ohms speakers, then use 50.000uf each rail Operating with 1 ohm speaker, then use 100.000uf each rail regards, Carlos 
10th October 2009, 03:43 PM  #44 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Continuing describing the power amplifier
Continuing with the specifications and details
The off set (Dc milivolts present into the output terminals due to unmatching of transistor devices) is adjustable tweaking the 4k7 trimpot, pré adjusted to 3900 ohms (R23)..of set will be around 1.2 milivolts Current crossing each power transistor is measured monitoring voltage Dc, milivolts range, directly picking the voltage into the emitter resistances extreme leads (0.33 ohm)… the voltage to be measure may be 656 microvolts..and this results into 1.98 miliampere of current crossing each one of the power transistors colector to emitter junction into stand by mode, with the input shorted, so, no signal entering the amplifier circuit…. maximum tollerable current to each transistor is 5 miliamperes each one. Positive rail stand by current..having base shorted to ground, so, no signal driving the amplifier…iddle mode, will be 37mA..and this is measured using supply series protective resistance, that resistance value is 10 ohms (10 watts minimum) and the voltage measured directly into the extreme terminals will be 370 milivolts… and this happens, only, when the power transistor emitter currents are fine..or … measuring less than 2 miliampere to each power transistors..and when they are 5 units…having more transistors, then the current into stand by mode will increase depending the number of transistors used. Negative rail stand by current, having base shorted to ground, so, no signal driving the amplifier… iddle mode, will be 29.4 mA…and this must obbey all conditions written above….. this means 294 milivolts measured over 10 ohms protective resistance. regards, Carlos 
10th October 2009, 04:01 PM  #45 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Some currents and more details
Long tail current is 1.42 mA, so, half of that to each transistor into the differential pair
Bootstrapp/VAS current is 9.68mA Driver current is 4.86mA External VBE multiplier has 1800 ohms resistance from base to colector and a series of resistances from base to emitter....the first resistance is a fixed resistance of 750 ohms (or other you choice) and the variable one (trimpot) is adjusted into 150 ohms (can be a 220 ohms trimpot)...so..total resistance from base to emitter is 900 ohms... set this way during start up. regards, Carlos 
10th October 2009, 05:47 PM  #46 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Post 44 had errors, reason why i am posting once again with corrections
Continuing with the specifications and details
The off set (Dc milivolts present into the output terminals due to unmatching of transistor devices) is adjustable tweaking the 10k trimpot, pré adjusted to 7200 ohms (R23)..of set will be around 1.0 milivolts Current crossing each power transistor is measured monitoring voltage Dc, milivolts range, directly picking the voltage into the emitter resistances extreme leads (0.33 ohm)… the voltage to be measure may be 750 microvolts..and this results into 2.2 miliampere of current crossing each one of the power transistors colector to emitter junction into stand by mode, with the input shorted, so, no signal entering the amplifier circuit…. maximum tollerable current to each transistor is 5 miliamperes each one. Positive rail stand by current..having base shorted to ground, so, no signal driving the amplifier…iddle mode, will be 37mA..and this is measured using supply series protective resistance, that resistance value is 10 ohms (10 watts minimum) and the voltage measured directly into the extreme terminals will be 370 milivolts… and this happens, only, when the power transistor emitter currents are fine..or … measuring less than 2 miliampere to each power transistors..and when they are 5 units…having more transistors, then the current into stand by mode will increase depending the number of transistors used. Negative rail stand by current, having base shorted to ground, so, no signal driving the amplifier… iddle mode, will be 29.4 mA…and this must obbey all conditions written above….. this means 294 milivolts measured over 10 ohms protective resistance. Differences in measurement around 20 percent plus and 20 percent Minus are considered normal..do not worry with that. 
10th October 2009, 05:48 PM  #47 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Post 45 had errors too... reason why i am posting it once again with some different
numbers..sorry folks..my mistake.
Some currents and more details ________________________________________ Long tail current is 1.42 mA, so, half of that to each transistor into the differential pair Bootstrapp/VAS current is 9.68mA Driver current is 4.86mA External VBE multiplier has 1800 ohms resistance from base to colector and a series of resistances from base to emitter....the first resistance is a fixed resistance of 1000 ohms (or other you choice) and the variable one (trimpot) is adjusted into 260 ohms (can be a 500 ohms trimpot)...so..total resistance from base to emitter is 1260 ohms... set this way during start up. regards, Carlos 
10th October 2009, 05:50 PM  #48 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Schematic, revision number one.
attached,
regards, Carlos 
10th October 2009, 05:52 PM  #49 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Parts that does not exist into the Dx Amplifier standard pcboard
The one you can find at Greg Erskine home pages:
http://users.tpg.com.au/users/gerskine/dxamp/ image attached. regards, Carlos 
10th October 2009, 05:54 PM  #50 
diyAudio Member
Join Date: Feb 2004
Location: Recife  Brasil Northeast

Components that had their values changed
image attached,
regards, Carlos 
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