musical fidelity p170

robskel · 14th March 2006, 01:50 AM

I am about to replce my op amps from 318's to 637's.
Have noticed that their is a capacitor (i think, it's marked 0.22 k 100 XkT ) soldered across pins 4 & 7 on the 318. Should i replace this on the new 637? I am new to all of this but think that it might be a filter/smoothing component across the op amp power supply
Thanks Rob

infinia · 14th March 2006, 06:24 AM

Hi
You are correct, it is a PS decoupling for the op amp.
I think the OPA should drop in, if you have already removed the 3 freq compensation parts for the 318 (5pF and the series RC).

robskel · 14th March 2006, 11:08 AM

Yes I am going to remove pin no'1 ,5 & 8. but still not sure if you mean i should solder back in the cap across pins 7 & 4.
cheers Rob

infinia · 14th March 2006, 12:41 PM

Hi,
Normal op amp practice is to use a bypass cap from each supply pin to ground. I see from the hand drawn scheme you provided, there is only one cap across both supplies. Is this correct? Not too sure about this technigue (low CMR), but if that the way it was designed, I would stick with that for now. (better than nothing).

AndrewT · 14th March 2006, 04:07 PM

Hi,
some designers specify caps from both pins to ground and from pin to pin.

The pin to pin leads should, as closely as possible, follow the route that the IC uses to transport current through the chip.

This practice is confirmed in a few papers I have found on the web usually written by in house chip designers.

robskel · 14th March 2006, 04:50 PM

hi Thanks for the response. Looking at circuit boards of this amp on the net there are no caps across pins 4 & 7 it just seems to be mine. if i replace it with a 627 it might not need it, or does it? what effect would it have if i leave it out. sound quality or amplifier damage , or none. have no idea myself. As i am not an electronics expert. I am a eletrician , trying to learn electronics. Must say ive been bitten by the bug.
Any help in this direction would help both causes
Rob

infinia · 14th March 2006, 07:44 PM

Add 2 caps 0,1uF from each supply pin at the IC pins to a wide ground trace. This is mainly for op amp stabilty. Also provides better Common Mode Rejection Ratio performance at HF (CMRR).

robskel · 14th March 2006, 10:35 PM

thanks for your help. but i'm not quite sure what you mean. are you saying put two 0.1 uf caps in parrallel to the positive rail from pins 4. Or put a 0.1 uf cap between pin 4 to Negative and a 0.1uf cap between pin 7 positive.

sorry to sound so dim but i am new to this.

trying hard Rob

infinia · 14th March 2006, 10:54 PM

Sorry chap my fault.
2 caps total, one for each supply pin at the op-amp.
hope this clears up the confusion.
regards

14th March 2006, 01:50 AM	#1
robskel diyAudio Member Join Date: Mar 2006 Location: Canterbury kent england	musical fidelity p170 I am about to replce my op amps from 318's to 637's. Have noticed that their is a capacitor (i think, it's marked 0.22 k 100 XkT ) soldered across pins 4 & 7 on the 318. Should i replace this on the new 637? I am new to all of this but think that it might be a filter/smoothing component across the op amp power supply Thanks Rob

14th March 2006, 06:24 AM	#2
infinia diyAudio Member Join Date: May 2005 Location: Californication	Hi You are correct, it is a PS decoupling for the op amp. I think the OPA should drop in, if you have already removed the 3 freq compensation parts for the 318 (5pF and the series RC). __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

14th March 2006, 12:41 PM	#4
infinia diyAudio Member Join Date: May 2005 Location: Californication	Hi, Normal op amp practice is to use a bypass cap from each supply pin to ground. I see from the hand drawn scheme you provided, there is only one cap across both supplies. Is this correct? Not too sure about this technigue (low CMR), but if that the way it was designed, I would stick with that for now. (better than nothing). __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

14th March 2006, 07:44 PM	#7
infinia diyAudio Member Join Date: May 2005 Location: Californication	Add 2 caps 0,1uF from each supply pin at the IC pins to a wide ground trace. This is mainly for op amp stabilty. Also provides better Common Mode Rejection Ratio performance at HF (CMRR). __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

14th March 2006, 10:54 PM	#9
infinia diyAudio Member Join Date: May 2005 Location: Californication	Sorry chap my fault. 2 caps total, one for each supply pin at the op-amp. hope this clears up the confusion. regards __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust


	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

14th March 2006, 11:08 AM	#3
robskel diyAudio Member Join Date: Mar 2006 Location: Canterbury kent england	Yes I am going to remove pin no'1 ,5 & 8. but still not sure if you mean i should solder back in the cap across pins 7 & 4. cheers Rob

14th March 2006, 04:07 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, some designers specify caps from both pins to ground and from pin to pin. The pin to pin leads should, as closely as possible, follow the route that the IC uses to transport current through the chip. This practice is confirmed in a few papers I have found on the web usually written by in house chip designers.

14th March 2006, 04:50 PM	#6
robskel diyAudio Member Join Date: Mar 2006 Location: Canterbury kent england	hi Thanks for the response. Looking at circuit boards of this amp on the net there are no caps across pins 4 & 7 it just seems to be mine. if i replace it with a 627 it might not need it, or does it? what effect would it have if i leave it out. sound quality or amplifier damage , or none. have no idea myself. As i am not an electronics expert. I am a eletrician , trying to learn electronics. Must say ive been bitten by the bug. Any help in this direction would help both causes Rob

14th March 2006, 10:35 PM	#8
robskel diyAudio Member Join Date: Mar 2006 Location: Canterbury kent england	thanks for your help. but i'm not quite sure what you mean. are you saying put two 0.1 uf caps in parrallel to the positive rail from pins 4. Or put a 0.1 uf cap between pin 4 to Negative and a 0.1uf cap between pin 7 positive. sorry to sound so dim but i am new to this. trying hard Rob

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
Musical Fidelity P170 Blown Transistors	rigel9999	Solid State	35	4th January 2013 11:03 PM
Musical Fidelity P170 Power Amp	maf_au	Solid State	67	1st January 2013 04:11 PM
DIY Musical Fidelity P170	MassiAudio	Solid State	4	13th February 2007 07:01 PM
Musical Fidelity B1	NamWong	Solid State	1	29th April 2004 01:46 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