opamp replacement & dc offset trouble

Raj1 · 23rd November 2003, 09:29 AM

Hi,

I had a couple of spare opa 627's, and also a spare pioneer pd-s 801, I haven't really used this machine cause I already have a modified pd-s model. In any case I thought I'd just replace the opamps in the 801 with the op627's. Trouble is I'm getting a massive dc offset of 1200-1400 mv per channel. Either the opamps are blown or perhaps something else is amiss (checked orientation of opamps, 'dot' is to pin one). The player worked fine with the 5532's in place. Normally the 627's have a low dc offset, which means that the problem lies elsewhere. Whilst I was working on the machine, I did not spot any dc coupling caps, I think it may have a dc servo instead, it must have had some kind of dc protection for the 5532's. Any ideas?

Thanks
Raja

PMA · 23rd November 2003, 09:41 AM

1) NE5532 have high input bias current, this results in DC voltage offset across input resistors, was not there a dc compensation for NE5532, this would make troubles with OPA627.

2) Do you have a chance to measure oscillations, if not, try to approach an AM/FM radio near to the circuit and listen if there are any whistles.

tbla · 23rd November 2003, 10:05 AM

isn't 5532 a dual opamp....?

PMA · 23rd November 2003, 10:17 AM

Of course, tbla, you got it

Raj1 · 23rd November 2003, 11:51 AM

hi,

It would sppear that you are correct, I wrongly assumed these were single opamps, as there is one per channel in the player........

don't have schematics, but do know it uses dual diff. dacs....

oh well!!

Thanks
Raja

PMA · 23rd November 2003, 12:27 PM

So try OPA2134.

tbla · 23rd November 2003, 12:51 PM

.......or OPA2604..............

blank527 · 4th December 2003, 10:44 PM

Hi,

I'm also in the state of changing my opamp to something different.
There seems to be two choices.
- Go with the opamps (mine is now an lm318)
-Go Discrete like this

What is the best option te choose?
Dicrete is more work-effort so it seems.

Regards,
Remco Blankesteijn.

Raj1 · 5th December 2003, 05:09 PM

Hi,

replacing opamps is easier, and will give some kind of results. I've built the cd enhancer II, believe me, Remco is very talented, even though he sings the praise of each circuit, they are far better than he mentions, if he says they're better than opamps then they are!!

Thanks
Raja

georgehifi · 5th December 2003, 07:37 PM

I got great results from that machine using OP275`s one of the sweetest sounding opamps, very valve like.
Cheers George

23rd November 2003, 09:29 AM	#1
Raj1 diyAudio Member Join Date: Jan 2003 Location: UK	opamp replacement & dc offset trouble Hi, I had a couple of spare opa 627's, and also a spare pioneer pd-s 801, I haven't really used this machine cause I already have a modified pd-s model. In any case I thought I'd just replace the opamps in the 801 with the op627's. Trouble is I'm getting a massive dc offset of 1200-1400 mv per channel. Either the opamps are blown or perhaps something else is amiss (checked orientation of opamps, 'dot' is to pin one). The player worked fine with the 5532's in place. Normally the 627's have a low dc offset, which means that the problem lies elsewhere. Whilst I was working on the machine, I did not spot any dc coupling caps, I think it may have a dc servo instead, it must have had some kind of dc protection for the 5532's. Any ideas? Thanks Raja

5th December 2003, 07:37 PM	#10
georgehifi diyAudio Member Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific)	I got great results from that machine using OP275`s one of the sweetest sounding opamps, very valve like. Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com

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
Cancelling DC Offset in a bipolar Opamp	ygg-it	Chip Amps	16	5th May 2008 04:47 PM
Zapfilter DC offset trouble, help needed	Sarman	Digital Source	35	12th February 2007 08:15 PM
Two Questions, Reading leads on Opamp and Offset Trim	pjpoes	Parts	10	28th December 2006 09:06 PM
Opamp/DC-Offset Problem (Help!)	MWP	Chip Amps	9	9th September 2004 04:13 AM
Opamp DC offset	jnxw2	Solid State	22	22nd May 2003 01:18 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

23rd November 2003, 09:41 AM	#2
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	1) NE5532 have high input bias current, this results in DC voltage offset across input resistors, was not there a dc compensation for NE5532, this would make troubles with OPA627. 2) Do you have a chance to measure oscillations, if not, try to approach an AM/FM radio near to the circuit and listen if there are any whistles.

23rd November 2003, 10:05 AM	#3
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	isn't 5532 a dual opamp....?

23rd November 2003, 10:17 AM	#4
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Of course, tbla, you got it

23rd November 2003, 11:51 AM	#5
Raj1 diyAudio Member Join Date: Jan 2003 Location: UK	hi, It would sppear that you are correct, I wrongly assumed these were single opamps, as there is one per channel in the player........ don't have schematics, but do know it uses dual diff. dacs.... oh well!! Thanks Raja

23rd November 2003, 12:27 PM	#6
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	So try OPA2134.

23rd November 2003, 12:51 PM	#7
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	.......or OPA2604..............

4th December 2003, 10:44 PM	#8
blank527 diyAudio Member Join Date: Nov 2001 Location: Haarlem	Hi, I'm also in the state of changing my opamp to something different. There seems to be two choices. - Go with the opamps (mine is now an lm318) -Go Discrete like this What is the best option te choose? Dicrete is more work-effort so it seems. Regards, Remco Blankesteijn.

5th December 2003, 05:09 PM	#9
Raj1 diyAudio Member Join Date: Jan 2003 Location: UK	Hi, replacing opamps is easier, and will give some kind of results. I've built the cd enhancer II, believe me, Remco is very talented, even though he sings the praise of each circuit, they are far better than he mentions, if he says they're better than opamps then they are!! Thanks Raja