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File name P400Tips.txt

Huh, beleive or not I received more than 200 letters with questions for this amp. I have no spare time and I'm working as a software engineer so I decided to remove project from site very soon. I answered only a few letters and this document is actually part of one mail I sent as reply. First of all excuse me for my bad English. It's not my native language. A little bit of history ___________________________ I built different kinds of amps (tubes, fet, integrated stk and so). Huh I designed a lot of different audio, microprocessor, ... circuits, but during 1999 NATO bombed us.They hit my house and all of this projects which I intend to put on net were burned. I designed this schematic and I built first in 1994 during my studies, and I built more than 20 amps of this kind, two of them (and one Quad 405) I still use as Dolbby 5.1 sistem connected to my comp. My idea was to build cheap but High Fidelity, highpower,high performance sistem. I can freely say that it has very good sound, better than most sistems I heard, and I heard a lot of amps. Only Quad 405 (very old clasic but still one of the best) is better in midrange. Schematic you saw is the last variant of this kind of amps. The last one I built in 1996, so I'll try to help you as much as I can because it was a long time ago. ( I used Textronix TDA220 2x200MHz digital osciloscope during tests.) Answers to most common questions ___________________________ Well... I designed circuit board for several diferrent amps. With small component modification you can make pnp-npn or pnp-pnp or npn-npn output stage amp, using the same board. There are no R10,R11,R14,R15 resistors, in this application, you should use shortwire (1mm copper wire=0 ohms). Q1-Q2 and Q3-Q4 are dif amps with common emmitors as you probbably noticed. I used this double dif circuit because it is fast, it has low harmonic distorsion but it has enough power for next amp stage. RSTAB and R10 in protection circuit are also shortwire. Schematic and circuit board for protection are different. There is transistor voltage stabilisator on schematic but I actualy used integrated positive 24V/1A on circuit board. I didnt' designed this schematic, I only designed circuit board. I find schematic somewhere, but it's great. It has 2sec timer during powering up to supress BUMMMM in speakers when you turn on amp, and it turns off speakers if there is any DC voltage on output of amp (if anything is wrong). I like it. I used two colors, three pin led for indication, connected on reley and it looks cool. Part two ___________________________ There are a lot of tip&tricks for amps making. First of all : input stage. Please use 2k2 resistors instead of 100 ohms for R4,R5, because you can hardly find so qualitet transistors with same hfe for output stage and rest. R6-R4-R5-R7 resistors and R3 trimer are used for tuning output offset with no input signal which should b