Shawn,
I just got some of these this week from B&D Enterprise (PA, US, www.bdent.com). I hate to tell you this, but in your pic you have two different gain classes (from datasheet: Note: hFE classification GR: 200~400, BL: 350~700 ). B&D is pretty good about not mixing, but to be sure, if you ever do order from them, call them and request what you want. You might get lucky and have some high BLs and low GRs
From one of the previous posters: I would agree on the Vbe tracking hFe pretty closely, at least in the matching that I have done.
Chris
I just got some of these this week from B&D Enterprise (PA, US, www.bdent.com). I hate to tell you this, but in your pic you have two different gain classes (from datasheet: Note: hFE classification GR: 200~400, BL: 350~700 ). B&D is pretty good about not mixing, but to be sure, if you ever do order from them, call them and request what you want. You might get lucky and have some high BLs and low GRs
From one of the previous posters: I would agree on the Vbe tracking hFe pretty closely, at least in the matching that I have done.
Chris
anatech said:
I'm not much of a gambler but purchasing from non-franchised outfits comes with an automatic risk. Under the circumstances I do feel lucky Chris.
So what do you think so far? Can I get a couple of suitable sets from this batch of devices? I'll set up the "lineup" circuit and give it a whirl on the weekend for further scrutiny.
Thanks all,
Shawn.
I just bought (a couple weeks ago) Qty 100 ea. of 2sa970 and 2sc2240 from Futurlec.com. Do these folks have any reputation I should be concerned about? Any concerns about these being fakes?
Ordering/shipping/receiving was no problem at all.
My 2sc2240's are GR, and with my DMM's hFE checker, they all measure thus:
hFE: QTY
175-185: 50
190-195: 25
198-205: 25
The 2sa970's aren't nearly as consistent, spread out in a bell curve between 100 and 250 hFE, peaking at about 190, with plenty of matched pairs.
These measurements are much lower than Shawn's. Is that just because of the lower powered measurements, or something more sinister?
..Todd
Ordering/shipping/receiving was no problem at all.
My 2sc2240's are GR, and with my DMM's hFE checker, they all measure thus:
hFE: QTY
175-185: 50
190-195: 25
198-205: 25
The 2sa970's aren't nearly as consistent, spread out in a bell curve between 100 and 250 hFE, peaking at about 190, with plenty of matched pairs.
These measurements are much lower than Shawn's. Is that just because of the lower powered measurements, or something more sinister?
..Todd
taj said:
Very interesting. That is one heck of a set on the SC2240!! I can't say what the exact test system is in my situation as I am using a built in hfe measurement function on a Mastech DMM. From lineup's circuit I will re-calculate the hfe and compare.
Todd, what circuit are you using to measure your devices?
Cheers,
Shawn.
Hi,
I am not sure, but I think a DMM hFE test uses a constant current feeding the b-e junction and measures the resulting collector current.
This is very much different from setting constant collector current (Ic) and measuring Vbe and base current (Ib).
The constant Ic test set up is very easy to do on the bench IF you use a constant voltage supply.
This will give far more consistent results than the presumed DMM hFE method assumed above.
Tom,
copy the PASS method shown on his web site.
From the few tests I have carried out I consistently find a much bigger spread with PNP & Pchannel than the tight groupings I find for NPN and Nchannel. I think this points to the production difficulties in achieving good and reproduceable PNP and Pchannel characteristics.
I am not sure, but I think a DMM hFE test uses a constant current feeding the b-e junction and measures the resulting collector current.
This is very much different from setting constant collector current (Ic) and measuring Vbe and base current (Ib).
The constant Ic test set up is very easy to do on the bench IF you use a constant voltage supply.
This will give far more consistent results than the presumed DMM hFE method assumed above.
Tom,
copy the PASS method shown on his web site.
From the few tests I have carried out I consistently find a much bigger spread with PNP & Pchannel than the tight groupings I find for NPN and Nchannel. I think this points to the production difficulties in achieving good and reproduceable PNP and Pchannel characteristics.
Hi,
I am not able to test/measure the tiny errors (distortions) that occur when the diff amp (LTP) runs with unbalanced collector currents.
The current injected from the VAS can be very significant and if using the collector loads for measuring and balancing the LTP then the VAS current introduces an error.
According to D.Self, the required balance accuracy is quite critical to minimising this first stage distortion and when the currents are as little as +-1% there is a very significant increase in distortion (he shows his graphs with the current difference and +-1%=2% difference).
If you want to better that and I think Self implies you should aim better than +-1% then the currents should be measured at the emitter resistors and I suggest matching to 0.5% if you think LTP balance is important to your design.
I am not able to test/measure the tiny errors (distortions) that occur when the diff amp (LTP) runs with unbalanced collector currents.
The current injected from the VAS can be very significant and if using the collector loads for measuring and balancing the LTP then the VAS current introduces an error.
According to D.Self, the required balance accuracy is quite critical to minimising this first stage distortion and when the currents are as little as +-1% there is a very significant increase in distortion (he shows his graphs with the current difference and +-1%=2% difference).
If you want to better that and I think Self implies you should aim better than +-1% then the currents should be measured at the emitter resistors and I suggest matching to 0.5% if you think LTP balance is important to your design.
Hi Anatech,
I was trying to offer a reasonable viewpoint that would be acceptable to most. Personally, since it costs nothing but time, I try to match (not absolute acurracy) to +-0.1% if I can see a benefit.
There is nothing worse than seeing/finding a voltage error and not knowing if the error is in the resistor used for measuring or in the semiconductor upstream.
Have I interpreted the VAS base current contribution correctly and do you agree that Re is better than Rc for LTP balance measurements?
I suspect we do see eye to eye on many topics, matching of emitter resistors for future balancing measurements is important to me.
I was trying to offer a reasonable viewpoint that would be acceptable to most. Personally, since it costs nothing but time, I try to match (not absolute acurracy) to +-0.1% if I can see a benefit.
There is nothing worse than seeing/finding a voltage error and not knowing if the error is in the resistor used for measuring or in the semiconductor upstream.
Have I interpreted the VAS base current contribution correctly and do you agree that Re is better than Rc for LTP balance measurements?
Hi Andrew,
I agree that the effect of Vas base current must be compensated for. If emitter resistors are used, they will be very effective if matched. You may also unbalance these to compensate for the tendancies of the rest of the amp.
I try to make everything happy sitting near ground with minimal diff amp action first. Then your front end is more concerned with correcting errors than keeping the entire project from going DC.
I think we are in full agreement then. I just wanted to point out that there are other factors which may force the LTP from a balanced condition even though everything is matched in that location.
-Chris
I agree that the effect of Vas base current must be compensated for. If emitter resistors are used, they will be very effective if matched. You may also unbalance these to compensate for the tendancies of the rest of the amp.
I try to make everything happy sitting near ground with minimal diff amp action first. Then your front end is more concerned with correcting errors than keeping the entire project from going DC.
I think we are in full agreement then. I just wanted to point out that there are other factors which may force the LTP from a balanced condition even though everything is matched in that location.
-Chris
I'm new here, and I looked through the rules and didnt see anything explicitly against necro-posting, annoying as it may be......but I wanted to say that this was a very interesting and informative conversation be able to study. I'm also very new to electronics and alot of what was said here helped make some things click that werent before, as well as turning me on to some affordable toys I now have to have asap. Another cool thing is I've been having a hard time quantifying design of transistors, when very easy to understand that being based on organic material which is uncontrollable, the package and processes are designed, but the characteristics of the substrate will ultimately decide the stats of the transistor which determine the series/model number. Much like binning ddr IC's I suppose. Thanks for sharing everyone, you know, like 11 years ago.....
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