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Old 25th February 2010, 11:21 AM   #1
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Default DC Servo MOSFET Amplifier

Amplifier with no adjust (offset, bias) +/-60V. Simple to build, no oscilation, hum and noise. Praktik, usuful and good sound.
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File Type: jpg Miniharisonsch.jpg (298.1 KB, 7866 views)
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Old 25th February 2010, 09:32 PM   #2
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Clasic 120W RMS 8E amplifier. If anyone interesting, I will sent part list.
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Old 25th February 2010, 09:56 PM   #3
soekris is offline soekris  Denmark
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Basic 20 years old simple design, but:

Can't do without BIAS adjustment.... Unless you want pure class B :-)

Q5 should be PNP.
Drop Q7 & Q8, need just zener and diode in series.

And either:

A) drop the DC servo (just ensure Q1/Q2 get matched bias current) or
B) drop all the electrolytic capacitors in the signal chain


Soren
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Old 25th February 2010, 10:24 PM   #4
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Q5 is PNP, wrong drawing. Q7 and Q8 using HH and Harisson in similar design, give beter protection. Amplifier work in class B but there is 3V on gate and no crossover distorzion. DC servo just subsitute trimpot for manuel offset adjust.
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Old 26th February 2010, 12:59 AM   #5
soekris is offline soekris  Denmark
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Quote:
Q7 and Q8 using HH and Harisson in similar design, give beter protection.
No, their function would be minimal, if you want better protection put in a proper VI current limiter.

Quote:
Amplifier work in class B but there is 3V on gate and no crossover distorzion.
Incorrect. YOU might not be able to measure it, or YOU might not be able to hear it if just driving the bass speakers.... But I would never want to listen to it.

Quote:
DC servo just subsitute trimpot for manuel offset adjust.
A correct designed transistor input stage with no DC gain (as when having those capacitors in the signal chain) will have very low offset voltage needing no trim, so the DC servo would basically be waste of parts....

You only really need a DC serve if the amplifier is DC coupled.

Soren
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Old 26th February 2010, 01:50 AM   #6
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This amp is for beginer and for hobby. Experts like you can easy make much sofistic amp and adjust them properly, but thanks for your coment aniway.
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Old 18th March 2010, 11:17 AM   #7
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Schematics with correction.
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Old 18th March 2010, 09:44 PM   #8
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Just one question
Why do you bother posting amplifier design with wrong schematic? Just to complicate normal diy-ers life?
There is nothing I hate more than a published design with intentionally WRONG schematic or PCB. You know how they say "you want it you buy it".
If you dont want people to recreate the design just keep it private.
I have a friend that designs amplifiers and he does the same thing....puts mistakes on the schematics....often he accidentally send me the WRONG schematic....what a pain in the "head".
Now every time I try something new I have to ask experts "is it ok?"
I've seen you posted a lot of designs and I appreciate your effort but please try to post correct schematic and pcb from beginning. It would help all new guys that want to build an amplifier after your design.
I was thinking to make your mosfet(the one with 4 pairs) design but seeing so many "mistakes" on your postings made me reconsider.

Last edited by butch_vlad; 18th March 2010 at 09:50 PM.
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Old 18th March 2010, 10:01 PM   #9
stoc005 is offline stoc005  United States
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Default Why a DC servo??

When you have a capacitor (C6) that shouldn't be there if the servo works at all?? The point of a servo is to eliminate the dreaded bipolar (usually) 'lytic cap in the feedback path, IMHO.
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Old 18th March 2010, 10:39 PM   #10
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This schematics is for example, give ideas and information for experts, this are not DIY project or KIT-s. If you want to use something for your own project I give you all information and help, and no mistake. This old schematics was change at the time to time, and redraw mistake are accidentaly.
Sorry if this schematics are confuse you, just ask me I explain to you.
Regards
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