Speaker output with offset..

unknow81 · 24th October 2007, 11:38 AM

Hi All,

this is my 1st time i build transistor amplifier...

when i measure the output of the speaker, i found it have offset -1Volt. may i know which component is defect or can i turning the VR. because when i try to turning the VR from 1k to 3xxOhm, the offset voltage is near to zero. but the Q2 is getting hot compare with Q1... :-s

VR1 = 1K
Q1 = Tip42
Q2 = Tip41
IC = MC1458

C7 = 22pF

Thanks all

unknow81 · 25th October 2007, 12:54 AM

attachment below is my resistor value...

hope can anyone help me...

thanks u all very much..

Leolabs · 25th October 2007, 02:17 AM

Ning Hao!

The output of the OPAMP should go to the center point of the bias diodes,not the upper half of the VR.

AndrewT · 25th October 2007, 08:15 AM

Hi,
will his CFP output work without emitter resistors?
There are no collector resistors on the drivers. They will switch off with the outputs, instead of retaining some bias current.
Will the circuit work? or work well?

Donk · 25th October 2007, 11:31 AM

Hi,

This circuit is from an old Texas application note form the 70's.
I clearly remember that emmiter resistors were needed (0.22...0.47 Ohm will be fine) and a Zobel (10 Ohm + 100nF poly) on the output is needed to.

See this page for a working "Texas"-amp:
http://skory.gylcomp.hu/25wamp/25wamp.html

Regards,

unknow81 · 25th October 2007, 11:31 AM

just now i try connect 1Khz sinewave to the input, but i can't get any output...

i think this circuit is not a complete circuit.. :-s

what value of resistor should i add in to the collector? can anyone help me? .. thanks AndrewT

tonight i will cut off the track that from OPAMP connect to VR and see the result. Thanks Leolabs

djk · 25th October 2007, 11:34 AM

You are best to drive the top side and use a pull-down to the negative 15V rail.

unknow81 · 26th October 2007, 03:05 PM

I try connect the output opamp direct to the center point, the o/p offset get more higher.. :-s (-2V++) and also cannot function.

later i will try put 100 ohm resistor to Q3 and Q4. take R3 and R7 out.

my q3 and q4 is using C1815 abd A1015. hope the 100 ohm resistor not destroy it..

25th October 2007, 08:15 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, will his CFP output work without emitter resistors? There are no collector resistors on the drivers. They will switch off with the outputs, instead of retaining some bias current. Will the circuit work? or work well? __________________ regards Andrew T.

25th October 2007, 11:34 AM	#7
djk diyAudio Member Join Date: Feb 2001 Location: USA	You are best to drive the top side and use a pull-down to the negative 15V rail. __________________ Candidates for the Darwin Award should not read this author.

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
Output DC offset.	nigelwright7557	Solid State	3	20th April 2009 01:14 PM
Doubt about output offset	suresh	Solid State	5	29th December 2008 04:50 PM
DC offset at analog output	LuisMCP	Digital Source	0	23rd September 2007 07:56 PM
How much output offset voltage is too much?	tubetvr	Solid State	14	1st July 2004 10:47 PM

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 October 2007, 02:17 AM	#3
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Ning Hao! The output of the OPAMP should go to the center point of the bias diodes,not the upper half of the VR.

25th October 2007, 11:31 AM	#5
Donk diyAudio Member Join Date: Sep 2007	Hi, This circuit is from an old Texas application note form the 70's. I clearly remember that emmiter resistors were needed (0.22...0.47 Ohm will be fine) and a Zobel (10 Ohm + 100nF poly) on the output is needed to. See this page for a working "Texas"-amp: http://skory.gylcomp.hu/25wamp/25wamp.html Regards,

25th October 2007, 11:31 AM	#6
unknow81 diyAudio Member Join Date: Oct 2007	just now i try connect 1Khz sinewave to the input, but i can't get any output... i think this circuit is not a complete circuit.. :-s what value of resistor should i add in to the collector? can anyone help me? .. thanks AndrewT tonight i will cut off the track that from OPAMP connect to VR and see the result. Thanks Leolabs

26th October 2007, 03:05 PM	#8
unknow81 diyAudio Member Join Date: Oct 2007	I try connect the output opamp direct to the center point, the o/p offset get more higher.. :-s (-2V++) and also cannot function. later i will try put 100 ohm resistor to Q3 and Q4. take R3 and R7 out. my q3 and q4 is using C1815 abd A1015. hope the 100 ohm resistor not destroy it..

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