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kjackman
Joined: Sep 05, 2010 Posts: 69 Location: Utah, USA
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Posted: Thu Nov 11, 2010 11:11 pm Post subject:
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I just breadboarded the awesomely easy +/-15v circuit provided by Bill & Will at Dragonfly Alley. Thanks, guys!
So, does -0.689 volts sound about right for a 2N3904 NPN transistor? I think I must have made a mistake somewhere, because without the test transistor, the test points show -14.49 volts or thereabouts, with a current of zero mA.
Bill and Will said,
Quote: | "The Voltage across the test points is 7.5V and without a test transistor in the socket, there's .100 milliamps (that's 100 micro amps or 100µA) across them - perfect!" |
...and that's not what I'm seeing
I'm using half of a TL072 in place of the 741 I don't have, with the pins appropriately rearranged. Would the choice of op amp make a difference?
Here's a closeup:
EDIT: The layout above is incorrect. Building it this way will not work. Scroll down to see the corrected version.
It's a little hard to see, but there's a green wire hiding under that resistor in the middle of the three at top. It connects TL072 pin 4 to -15v. And the end of the 10k at left that's hiding under a white wire, is connected to the collector of the transistor on the right. And there's a teeny jumper wire hiding under that resistor, that ties the white +15 wire to the collector of the transistor under test.
Ehhh, screw it, my breadboard layout is a disaster waiting to happen. I'll re-do the connections tomorrow with the right size wires and trimmed resistor leads, and go over it again. No wonder it takes me so long to troubleshoot these circuits. Neatness counts! Last edited by kjackman on Sun Nov 14, 2010 5:27 pm; edited 1 time in total |
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adambee7
Joined: Apr 04, 2009 Posts: 420 Location: united kingdom
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Posted: Fri Nov 12, 2010 12:14 am Post subject:
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yeah thats a bit high. they are usually around 600 mV. TL072 is ok but as your only using one of the opamps the unused one needs to have its + pin grounded and the output connected to - to stop unwanted interference with the other op amp. |
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Fri Nov 12, 2010 3:11 am Post subject:
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kjackman wrote: | Here's a closeup: ... |
I can't tell, is the second resistor from the right connected to pin 3 or to pin 4?
Ian |
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andrewF
Joined: Dec 29, 2006 Posts: 1176 Location: australia
Audio files: 4
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Posted: Fri Nov 12, 2010 3:20 am Post subject:
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thanks Ian
very succinct and easy to follow
I'll never buy another LM394/ssm2210 again! |
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kjackman
Joined: Sep 05, 2010 Posts: 69 Location: Utah, USA
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Posted: Fri Nov 12, 2010 6:40 am Post subject:
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frijitz wrote: |
I can't tell, is the second resistor from the right connected to pin 3 or to pin 4?
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Pin 3. Yeah, that's why I was saying I need to do this over. Way too hard to troubleshoot this mess.
I'll try your alternative method first though! |
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mark_olson
Joined: Oct 26, 2006 Posts: 177 Location: Lawrence, Kansas
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Posted: Fri Nov 12, 2010 7:24 am Post subject:
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frijitz wrote: | Here's a little doc on the simpler, easier and more accurate... |
Really nice!
Thanks so much for posting this.
Now, do know of a circuit that will help me recover the hours and hours of my life that were lost searching for affordable/available matched pairs?
Mark |
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Fri Nov 12, 2010 10:24 am Post subject:
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mark_olson wrote: | Now, do know of a circuit that will help me recover the hours and hours of my life that were lost searching for affordable/available matched pairs? |
Unfortunately not, but if you find one, please let me know. |
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kjackman
Joined: Sep 05, 2010 Posts: 69 Location: Utah, USA
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Posted: Sun Nov 14, 2010 5:24 pm Post subject:
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OK folks, I discovered my error. Here's the corrected the breadboard layout:
The transistor on the left is the one under test. The white wires leading away from it to the left, go to the voltmeter: Top wire goes to (-), bottom wire goes to (+). IC is a TL072 dual op amp; transistors are both NPN (2N3904). Note the power supply labels on the right side: +, -, and ground reference. The 2K trimmer helps to calibrate to exactly 100 microAmps.
I haven't tried frijitz's method yet, but it looks much simpler. Normally I would have scrapped the Moog method and jumped right on this simpler one, but: a) I didn't want future generations of DIYers to copy my faulty breadboard layout above, and b) I really need the troubleshooting practice. |
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adambee7
Joined: Apr 04, 2009 Posts: 420 Location: united kingdom
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Posted: Sun Nov 14, 2010 5:50 pm Post subject:
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its worth doing it both ways as a way of learning. i've done three different types of matching circuits on stripboard and bring them out when i need them. |
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adambee7
Joined: Apr 04, 2009 Posts: 420 Location: united kingdom
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emdot_ambient
Joined: Nov 22, 2009 Posts: 667 Location: Frederick, MD
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Posted: Mon Nov 15, 2010 1:31 pm Post subject:
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frijitz wrote: | Here's a little doc on the simpler, easier and more accurate method I have been using. |
Would there need to be any adjustment to that circuit when using +/-15V power supplies? |
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LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
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Posted: Mon Nov 15, 2010 9:20 pm Post subject:
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kjackman wrote: | OK folks, I discovered my error. Here's the corrected the breadboard layout:
The transistor on the left is the one under test. The white wires leading away from it to the left, go to the voltmeter: Top wire goes to (-), bottom wire goes to (+). IC is a TL072 dual op amp; transistors are both NPN (2N3904). Note the power supply labels on the right side: +, -, and ground reference. The 2K trimmer helps to calibrate to exactly 100 microAmps.
I haven't tried frijitz's method yet, but it looks much simpler. Normally I would have scrapped the Moog method and jumped right on this simpler one, but: a) I didn't want future generations of DIYers to copy my faulty breadboard layout above, and b) I really need the troubleshooting practice. |
Hi, and thanks for the layout, Confused about the 100mA though. I seem to be getting the 14V and 0mA too, that's with the new design (as I quoted)
Nothing I do seems to make the meter display even 0.0001mA _________________ LektroiD |
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kjackman
Joined: Sep 05, 2010 Posts: 69 Location: Utah, USA
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Posted: Mon Nov 15, 2010 11:41 pm Post subject:
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LektroiD wrote: | Hi, and thanks for the layout, Confused about the 100mA though. I seem to be getting the 14V and 0mA too, that's with the new design (as I quoted). Nothing I do seems to make the meter display even 0.0001mA |
I'm measuring current with both transistors in place. I break the connection at J20 on the board up there, and touch one meter probe to the resistor and the other to the transistor terminal at F20.
I first measured the current at zero, even after constructing the correct circuit above. It turned out my new meter has a different terminal post for measuring current than for measuring voltage. I just had to swap terminal posts!
If you've made any mistakes in the layout already, double-check all the connections and then try swapping out the TL072 and transistors. I'm pretty sure I fried the IC, or one or both transistors, somewhere along the way. I swapped all three out and things started working.
Which reminds me: How do I test a TL072? |
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JRock
Joined: Mar 05, 2010 Posts: 87 Location: Bucks County, PA
Audio files: 1
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Posted: Mon Nov 15, 2010 11:49 pm Post subject:
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This is a good coincidence cause I was just wondering where to ask this and I saw this Matching Transistors thread. Is there any reason this wouldn't work as a matched PNP pair? I know it's a quad and it probably won't fit on PCBs, But I'm building some stuff on Veroboard..
https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_260734_-1 |
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JRock
Joined: Mar 05, 2010 Posts: 87 Location: Bucks County, PA
Audio files: 1
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Posted: Tue Nov 16, 2010 12:02 am Post subject:
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Screw it. Frijitz! You rock! That's so simple even I can match my own transistors!
Awesome. |
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reve
Joined: Feb 23, 2008 Posts: 149 Location: USA
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Posted: Tue Jan 10, 2012 12:04 am Post subject:
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Sorry to resurrect a dead thread here... I'm curious if anyone could provide some guidance as to why constitutes an acceptable deviation from ground using Ian's method? I got this batch of 547c's from Mouser and I can't find a deviation beyond about 0.7mv. I'm not sure if I got a magic batch or if I should be looking for like... 0.01mv deviation.
Thanks! _________________ - r. mosquito
SynthDIY Synthpop -> http://www.reverbnation.com/photovoltaik |
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prgdeltablues
Joined: Sep 25, 2006 Posts: 222 Location: UK
Audio files: 12
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Posted: Wed Jan 11, 2012 4:55 am Post subject:
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You may have struck lucky. I went through about 20 or so BC547's to find a pair that matched to within 1mV (actually I found two or three such pairs, but only two trannies in each bin as it were.) Ian's note says the CA3083 is specced at a 1mV match, though in practice some pairs are much better - but it seems as if for the usual expo converter usage, matching to 1mV is fine.
One thing did puzzle me a bit - you say 'deviation from ground' - these measurements are of the potential difference between two points, neither of which is ground (0V). Sorry if that's a misunderstanding of your post on my part, but it did look as if you might have been measuring the wrong thing?
Peter |
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LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
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Posted: Wed Jan 11, 2012 5:19 am Post subject:
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frijitz wrote: |
I've never been able to understand why such a complicated circuit is used. Here's a little doc on the simpler, easier and more accurate method I have been using. It's similar to Jim Patchell's method, except he grounds the collectors. Either way is fine. If you are going through a pile of devices, use the procedure under "multiple devices". Note that you do not need to swap the devices when you use this method.
Ian |
I can't seem to download this PDF.. I had it on breadboard a while back, but after moving house, a few things have become unplugged. |
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arnoid
Joined: Aug 23, 2009 Posts: 57 Location: Belgium
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Posted: Thu Jan 12, 2012 8:07 am Post subject:
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frijitz wrote: |
I've never been able to understand why such a complicated circuit is used. Here's a little doc on the simpler, easier and more accurate method I have been using. It's similar to Jim Patchell's method, except he grounds the collectors. Either way is fine. If you are going through a pile of devices, use the procedure under "multiple devices". Note that you do not need to swap the devices when you use this method.
Ian |
Hi
I build this little circuit and tryed to match two 2N3906 PNP transistors but I have problems with step 3:
(3) Plug in your transistors, power up, and write down the DVM voltage. (Make sure you wait until the voltage is stable.)
The voltage get's never stable it keeps moving from 0.062V to 0.074V.
I checked with 2 different DVM's.
Any suggestions ?
thx _________________ http://www.soundcloud.com/arnoid
http://www.facebook.com/arnoid |
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prgdeltablues
Joined: Sep 25, 2006 Posts: 222 Location: UK
Audio files: 12
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Posted: Fri Jan 13, 2012 2:35 am Post subject:
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Does the rate at which the reading changes not slow down? It's to be expected that the dV changes as the transistors warm up as current flows through them, but it ought to level off after say 10-15 seconds. Maybe you're working in a slight draft? (If you blow on the transistors you'll see the reading change a fair bit, demonstrating this thermal sensitivity.)
Peter |
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arnoid
Joined: Aug 23, 2009 Posts: 57 Location: Belgium
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Posted: Fri Jan 13, 2012 3:34 am Post subject:
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Hi there thx for your answer.
Yes the rate slows down but the value keeps changing.
I know transistors are temperature sensitve but its hard to decide wich value you should take/write down.. _________________ http://www.soundcloud.com/arnoid
http://www.facebook.com/arnoid |
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funtykigs
Joined: Feb 09, 2010 Posts: 17 Location: UK
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Posted: Sun May 06, 2012 7:52 am Post subject:
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Hey frijitz,
I know it's a while since you posted your transistor matching document.. but I wondered if a 1N4004 diode is suitable?
That's what I'm using anyway... it's the only thing I'm unsure about, I just stuck a pair of 2n3906's in your PNP testing rig and the mV reading is still fluctuating after a couple of minutes.. slowly floating between -0.2 mV to -0.7 mv and not staying still.
The transistors are very close... do they need to touch?
Thanks - I was very pleased to find this document! |
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roborobert
Joined: Jan 15, 2013 Posts: 24 Location: austria
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Posted: Thu Jun 06, 2013 5:01 pm Post subject:
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Hey there,
thanks to frijitz 's very nice pdf i was able to build a transistor matcher within an hour
i wrote because i didn't understand part of the calculation.
after i finished writing this post i understood it... so i edited/deleted the question and leave this post as a big thank you
best, rob |
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fonik
Joined: Jun 07, 2006 Posts: 3950 Location: Germany
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Posted: Fri Nov 15, 2013 2:18 am Post subject:
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arnoid wrote: | Hi there thx for your answer.
Yes the rate slows down but the value keeps changing.
I know transistors are temperature sensitve but its hard to decide wich value you should take/write down.. |
is there any solution to this? _________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source |
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