DC Servo MOSFET Amplifier

apexaudio · 25th February 2010, 10:21 AM

Amplifier with no adjust (offset, bias) +/-60V. Simple to build, no oscilation, hum and noise. Praktik, usuful and good sound.

apexaudio · 25th February 2010, 08:32 PM

Clasic 120W RMS 8E amplifier. If anyone interesting, I will sent part list.

soekris · 25th February 2010, 08:56 PM

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

apexaudio · 25th February 2010, 09:24 PM

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.

soekris · 25th February 2010, 11:59 PM

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

apexaudio · 26th February 2010, 12:50 AM

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.

apexaudio · 18th March 2010, 10:17 AM

Schematics with correction.

butch_vlad · 08:50 PM

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.

stoc005 · 18th March 2010, 09:01 PM

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.

apexaudio · 18th March 2010, 09:39 PM

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

18th March 2010, 08:44 PM	#8
butch_vlad diyAudio Member Join Date: Feb 2008	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 08:50 PM.

18th March 2010, 09:01 PM	#9
stoc005 diyAudio Member Join Date: Feb 2007 Location: Midwest in the USA	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.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
DC blocking cap in feedback path or DC servo?	roender	Solid State	27	19th September 2007 09:40 AM
To use DC servo or not?	jaycee	Solid State	40	17th September 2007 02:04 PM
DC servo	uli	Chip Amps	20	3rd December 2004 11:40 AM
N-Channel mosfet amplifier with servo bias	f4bok	Solid State	14	22nd September 2004 06:32 PM
DC servo	Bensen	Solid State	0	23rd May 2003 11:34 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

25th February 2010, 08:32 PM	#2
apexaudio diyAudio Member Join Date: Feb 2010 Location: Serbia	Clasic 120W RMS 8E amplifier. If anyone interesting, I will sent part list.

25th February 2010, 08:56 PM	#3
soekris diyAudio Member Join Date: Jun 2009	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

25th February 2010, 09:24 PM	#4
apexaudio diyAudio Member Join Date: Feb 2010 Location: Serbia	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.

26th February 2010, 12:50 AM	#6
apexaudio diyAudio Member Join Date: Feb 2010 Location: Serbia	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.

18th March 2010, 09:39 PM	#10
apexaudio diyAudio Member Join Date: Feb 2010 Location: Serbia	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

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)