Have anyone use non-matched 1% resistors for BPA??

Leolabs · 13th April 2007, 01:41 AM

It may sounds crazy,but have anyone try it before???

tiltedhalo · 13th April 2007, 04:18 AM

I have actually built a few useing 1% and even a very succesfull design useing 5% tolerance carbon comps in a BPA200

sangram · 13th April 2007, 05:03 AM

:Hands raised:

Audiosector LM4780 kits, connected as BPA, using the resistors that came with the kit. I don't think those are matched...

OzMikeH · 13th April 2007, 05:13 AM

Resistors are cheap. buy 20 or so and and measure them. pick the closest ones.

Dxvideo · 13th April 2007, 11:30 AM

Exactly true.
I done that methode for my LM4780 GainClone and have only 0.2mV offsets in each channel while inputz shorted (but I have very balanced SMPS for PSU)..
I bought 40 pcs for 20K feedback and input load and 40 pcs for 1K and matched them with my 4000 count multimeter. I also matched the capacitors with the same technic. It takes only 10 minutes! Thats all. No need for %0.1s..

Fenris · 13th April 2007, 02:20 PM

Most 1% are actually within about 0.3%. Should be good enough.

kscharf · 13th April 2007, 04:46 PM

Actually in the bridge circuits I've seen one side (the non-inverting side)
has 1k and 20.5k resistors and the other side (inverting side) has 21.5k resistors. I'm not sure why the difference or how critical this is. I suppose given enough resistors and an acurate ohmmeter one could hand pick 1k and 22k 5% resistors to work, or parallel high value resistors with the 22k to get the desired values.

kscharf · 13th April 2007, 04:48 PM

In the bridge ciruits I've seen one side (non invertng) uses 1k and 20.5k resisters and the other (inverting) uses 1k and 21.5k resisters.
I'm not sure why and how critical this is.

I suppose one could hand pick from 22k 5% resistors with a good ohmmeter or parallel high value resistors with the 22k to trim to the desired value.

Fenris · 13th April 2007, 05:45 PM

Quote:

Originally posted by kscharf
Actually in the bridge circuits I've seen one side (the non-inverting side)
has 1k and 20.5k resistors and the other side (inverting side) has 21.5k resistors. I'm not sure why the difference or how critical this is. I suppose given enough resistors and an acurate ohmmeter one could hand pick 1k and 22k 5% resistors to work, or parallel high value resistors with the 22k to get the desired values.

Because one side is inverting and one is non-inverting. The formula for calculating the gain is slightly different for the different types. See http://en.wikipedia.org/wiki/Operati...r_applications for the difference. If you plug the numbers in, you'll find they end up with the same gain using different resistors.

FastEddy · 13th April 2007, 06:07 PM

You might consider making your own Wheatstone Bridge ( http://en.wikipedia.org/wiki/Wheatstone_bridge ) ... I have one I picked up from a trade school inventory close out made in a nice wooden box = works great and can measure and match resistors to 0.01% with a 9 Volt battery as source and an el cheapo voltmeter.

13th April 2007, 01:41 AM	#1
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Have anyone use non-matched 1% resistors for BPA?? It may sounds crazy,but have anyone try it before???

13th April 2007, 04:18 AM	#2
tiltedhalo diyAudio Member Join Date: Sep 2005 Location: Melbourne Florida	1% not matched I have actually built a few useing 1% and even a very succesfull design useing 5% tolerance carbon comps in a BPA200

13th April 2007, 11:30 AM	#5
Dxvideo diyAudio Member Join Date: Nov 2003 Location: Turkey	Exactly true. I done that methode for my LM4780 GainClone and have only 0.2mV offsets in each channel while inputz shorted (but I have very balanced SMPS for PSU).. I bought 40 pcs for 20K feedback and input load and 40 pcs for 1K and matched them with my 4000 count multimeter. I also matched the capacitors with the same technic. It takes only 10 minutes! Thats all. No need for %0.1s.. __________________ Best regards, Ozgur

13th April 2007, 02:20 PM	#6
Fenris diyAudio Member Join Date: Jun 2004 Location: The last frontier	Most 1% are actually within about 0.3%. Should be good enough. __________________ Listen to the music through the stereo, not the stereo through the music.

13th April 2007, 06:07 PM	#10
FastEddy diyAudio Member Join Date: Jun 2006 Location: North Californie	You might consider making your own Wheatstone Bridge ( http://en.wikipedia.org/wiki/Wheatstone_bridge ) ... I have one I picked up from a trade school inventory close out made in a nice wooden box = works great and can measure and match resistors to 0.01% with a 9 Volt battery as source and an el cheapo voltmeter. __________________ Over compression is a problem with modern CD recordings


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13th April 2007, 05:03 AM	#3
sangram diyAudio Member Join Date: Sep 2002 Location: India	:Hands raised: Audiosector LM4780 kits, connected as BPA, using the resistors that came with the kit. I don't think those are matched...

13th April 2007, 05:13 AM	#4
OzMikeH diyAudio Member Join Date: Mar 2007	Resistors are cheap. buy 20 or so and and measure them. pick the closest ones.

13th April 2007, 04:46 PM	#7
kscharf diyAudio Member Join Date: Apr 2007	Actually in the bridge circuits I've seen one side (the non-inverting side) has 1k and 20.5k resistors and the other side (inverting side) has 21.5k resistors. I'm not sure why the difference or how critical this is. I suppose given enough resistors and an acurate ohmmeter one could hand pick 1k and 22k 5% resistors to work, or parallel high value resistors with the 22k to get the desired values.

13th April 2007, 04:48 PM	#8
kscharf diyAudio Member Join Date: Apr 2007	In the bridge ciruits I've seen one side (non invertng) uses 1k and 20.5k resisters and the other (inverting) uses 1k and 21.5k resisters. I'm not sure why and how critical this is. I suppose one could hand pick from 22k 5% resistors with a good ohmmeter or parallel high value resistors with the 22k to trim to the desired value.

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