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Matched transistors in Dynahi - Page 2

post #16 of 158
11/14/04 at 11:34pm
Cool, chillysalsa. Now you should measure the 2SA1358s and see if they fall within the same range, and pick the best matches you could. The datasheet of the 2SA1358 says that the hfe range @ 100mA collector current is between 80-160 for the "O" devices, and 120-240 for the "Y" devices. It would appear that you have the "Y" devices, and your measured values do fall between those extremes. Did you test with a collector current of around 85mA?
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post #17 of 158
11/14/04 at 11:57pm
Yes, I was measuring them at 85mA. And it looks like they are labelled Y on the package for both parts.

For 2SA1358 I got:

hFE
188.1
192.0
192.2
196.1
200.2
203.4
204.5
204.5
205.1
205.2
205.7
209.5
211.3
213.4
213.6
219.0
244.5

Pretty far off... but within spec. I guess I will just make the closest matches, lowest 4 with lowest 4, etc.

I was going to measure the 705's at 2mA, but my 16V supply and 500K pot don't let it go below 4.5mA for the collector current. Will pick up a 1M pot tomorrow and try to make the low current measurement so I get those in the CCS circuit matched very closely at 2mA.
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post #18 of 158
11/15/04 at 12:54am
Quote:
Originally Posted by chillysalsa
I was going to measure the 705's at 2mA, but my 16V supply and 500K pot don't let it go below 4.5mA for the collector current. Will pick up a 1M pot tomorrow and try to make the low current measurement so I get those in the CCS circuit matched very closely at 2mA.
You can also insert another resistor in series with the pot to get into the range that you'd like to measure. Maybe a 470K ohm will do the trick.
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post #19 of 158
11/15/04 at 1:00am
Yea, don't have any values above 100K right now. I think I'll just get a couple resistors, it's a lot cheaper than a pot I may never use!
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post #20 of 158
11/17/04 at 11:02pm
@ 2 mA:

2SA1145:
hFE
127.2
157.8
158.2
160.0
160.8
161.0
169.6
170.6
172.0
191.3
192.6
193.1
760.2

matching to 2SC2705:
163.7
170.9
177.0
180.3
189.3
193.0

Ok, at least two pairs there that would be spot-on.

Same parts @ 15mA:
2SA1145
78.5
80.9
82.5
85.7
86.0
88.0
90.6
70.0
121.0
164.6
581.7
615600.0
hmm... a few seem out to lunch here...

matching to 2SC2705:
95.0
94.0
91.5
97.8
95.6
86.8

Pretty much within spec. I'll figure out which go best together later. And yes, I had the same # of 705's, but a brain fart caused me to reverse the polarity, and then I shorted a couple by accident so they fried. Oh well, at least these are the cheap ones!
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post #21 of 158
11/18/04 at 1:22am
amb (or anyone?)

Per your suggestions regarding measuring hFE on the BJTs (and this refers to the 2SA1015s and 2SC1815s on a dynalo), I constructed a circuit similar to what was posted. Since I did not have any suitable pots (nor did ratshack), I decided to use a fixed resistor of 220K, giving an Ic value of 10-11mA on the PNPs (2SA1015). Since I know the resistance up front from measuring it, and powering it with 9V from a bench supply, I can more or less assume that when testing in one batch (i.e., one sitting without powering the supply down) that the base current (Ib) will be constant. I will still measure Vb and compute the base current each time unless I see that Vb is holding steady (it seems to be). I will obviously measure Ic for each device and compute the hFE from the measurements.

Also, since I had already characterized all of these based on Dr. Gilmore's circuit, and have them marked and separated, I should be able to see what correlation they have to those measurements. I picked around 10 mA because the outputs run at 15mA while the second stage runs at 1-2mA (I think)... seemed like a good compromise.

This seem rational?

Chris

[edit: meant Vrb across Rb, not Vb to ground)
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post #22 of 158
11/18/04 at 3:51am
Quote:
Originally Posted by Pars
This seems rational?
Yeah, it's fine. Certainly better than shooting in the dark and not matching them at all.
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post #23 of 158
11/18/04 at 5:09pm
Quote:
Originally Posted by amb
If the transistors are not matched closely enough, the DC servo will fail to correct the offset. In that case, you will need to do some surgery.
So from that I gather, if after the DC-adjustments with the trimpots on my Dynahi boards (non-matched transistors) I get a DC offset at the outputs below 10 mv (btw, Kevin indicated it should be within +/- 1mv in post #259 here), then I can assume they were sufficiently matched, and won't have to worry about doing surgery to replace them with carefully matched transistors?
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post #24 of 158
11/18/04 at 5:17pm
Quote:
Originally Posted by rsaavedra
So from that I gather, if after the DC-adjustments with the trimpots on my Dynahi boards (non-matched transistors) I get a DC offset at the outputs below 10 mv (btw, Kevin indicated it should be within +/- 1mv in post #259 here), then I can assume they were sufficiently matched, and won't have to worry about doing surgery to replace them with carefully matched transistors?
That's what I'm wondering too. It will be much cheaper then getting another $50 in transistors for matching
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post #25 of 158
11/18/04 at 10:45pm
Quote:
Originally Posted by rsaavedra
So from that I gather, if after the DC-adjustments with the trimpots on my Dynahi boards (non-matched transistors) I get a DC offset at the outputs below 10 mv (btw, Kevin indicated it should be within +/- 1mv in post #259 here), then I can assume they were sufficiently matched, and won't have to worry about doing surgery to replace them with carefully matched transistors?
The trimpot is used to force the offset back into submission. If the offset is too high without the servo and trimpots, then some transistors (and perhaps the LEDs) are not well matched. Of course by doing the trimpot thing and then adding the servo will bring the offset back in line (and the amp will work ok), it would be more ideal if the devices were better matched in the first place.
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post #26 of 158
11/18/04 at 11:08pm
Quote:
Originally Posted by amb
The trimpot is used to force the offset back into submission. If the offset is too high without the servo and trimpots, then some transistors (and perhaps the LEDs) are not well matched. Of course by doing the trimpot thing and then adding the servo will bring the offset back in line (and the amp will work ok), it would be more ideal if the devices were better matched in the first place.
Thanks Amb. Speaking of which, how do you match LEDs? Since those are just a couple per board, I would just need to desolder and replace one if need be. Well, that is, if I can measure their differences while they are still soldered on the board.

Btw, last DC offsets I measured from my boards were -14.4 and 35.1 mvolts respectively.
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post #27 of 158
11/18/04 at 11:48pm
Quote:
Originally Posted by rsaavedra
Thanks Amb. Speaking of which, how do you match LEDs?
Just measure the voltage drop across the LED and find the closest matches.
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post #28 of 158
11/19/04 at 2:12am
Thread Starter 
So I finally got around to measuring my 3421. Built up a little circuit, used a lab supply, 1 megohm multi turn pot, and a connector, which I used for a "socket". Then, I figured out my meter can measure it too, so I did it both ways. On the left, are the numbers from my circuit, where the collector current was between 60 and 70.

155.613826157
158.6586826160
138.4615385141
154.2446043157
143.0769231146
145.3846154147
154.4297719156
152.4909747154
156.7346939163

One other think, for the circuit measurements, I turned the power on, and measured right away. If I leave on power, the transistor will slowly heat up, and the collector current and hfe slowly rises. I was not sure if I should measure a room temp part, or a part that had heated up in the circuit.

My 1358 measurements, just from the meter
177
194
160
173
189
179
182
128
171

As you can see, these vary more. The 128 guy is trash, but even then the range is kind of big. I am not sure if this is OK, or if I should buy some more transistors. The transistors themshelves are pretty cheap, but I would have to pay shipping again.

Randy
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post #29 of 158
11/19/04 at 6:49pm
Quote:
Originally Posted by randytsuch
One other think, for the circuit measurements, I turned the power on, and measured right away. If I leave on power, the transistor will slowly heat up, and the collector current and hfe slowly rises. I was not sure if I should measure a room temp part, or a part that had heated up in the circuit.
You will get more repeatable and stable measurements if you let the devices warm up. However, the hfe variation due to temperature change should be fairly constant for any given transistor type. So, as long as you measure them using consistent methods then it should be ok.

Quote:
My 1358 measurements, just from the meter
...
As you can see, these vary more. The 128 guy is trash, but even then the range is kind of big. I am not sure if this is OK, or if I should buy some more transistors. The transistors themshelves are pretty cheap, but I would have to pay shipping again.
It depends on how a*al retentive you are with wanting as close a match as possible. I say go ahead and build the amp and test it before plunking down $$ for more transistors.
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post #30 of 158
11/19/04 at 10:45pm
Thread Starter 
Quote:
Originally Posted by amb
It depends on how a*al retentive you are with wanting as close a match as possible. I say go ahead and build the amp and test it before plunking down $$ for more transistors.
Thanks for the response.
Think is, I am a*al when it comes to this stuff, and once I finish a project, and it is making music, I tend not to want to touch it. So, I ordered some more transistors, will have them by next week.
I figured the output transistors, since they must act in concert with each other, would have a bigger effect if they are not matched, so I would like to match them as close as possible.
I bought more than I need, and may sell off the excess in matched sets when I am done.

Randy
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