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Rykhaard
Joined: Sep 02, 2007
Posts: 1290
Location: Canada
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 Posted: Fri Jul 18, 2008 9:22 pm Post subject:
 Transistor matching and symmetry questions. Anyone?
Subject description: Matching 2N3904 and 2N3906's? |
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Hey all. I hope this is an appropriate area for my 2 questions.
I'm still working on add-on ideas for my KAOS Voltage Controlled LFO that I announced in the Factory thread.
Tonight I had yet another idea for the module. Looking at Thomas Henry's current control for the CA3080 reminded me that it's controlled by a glued together 2N3904 and 2N3906 with a tempco resistor.
Matching the trannies though. I remember recently reading something about the troubles with that.
My question HERE though - what exactly am I matching, for the transistors? The Base / Emitter voltage drop? (Only thing that I remember measuring, for matching 2N3904's for earlier VCAs for mine.)
(Also note - I'm still fairly clued out on trannies - just recently learning HOW they work and why, in general.)
Next question:
Can anyone tell me if, changing the symmetry of the waveform coming from the VCO, will change the frequency of the triangle waveform VCO itself?
I thought that - if only 1 pot is used to go from ramp through triangle to sawtooth, the total resistance of the rise and fall portions is still equal.
No??
Thanks for any possible help on these 2 questions.  |
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Uncle Krunkus
Moderator
Joined: Jul 11, 2005
Posts: 4761
Location: Sydney, Australia
Audio files: 52
G2 patch files: 1
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Rykhaard
Joined: Sep 02, 2007
Posts: 1290
Location: Canada
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| Posted: Fri Jul 18, 2008 10:14 pm Post subject:
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O-tay! Thanks muchlee Uncle Krunkus! I don't remember whether Thomas had said anything specific about such in the book or not and will be checking. I thought I'd ask for advice just in case, though.
I'd like to get the 1V/octave tracking as close as possible, as widely as possible as I thought today at work, that if this module could ALSO function as a usable VCO, that would really widen it's appeal!
And there - if I could give it VC Symmetry, that could widen it further still.
Here's to hoping my coming breadboarding test for both, will be successful. |
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bubblechamber
Joined: Nov 04, 2006
Posts: 280
Location: NYC
Audio files: 1
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| Posted: Sat Jul 26, 2008 8:34 pm Post subject:
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i've been building a lot of different expo converters lately. i'm growing quite fond of the 2sa798. they're a bit more than 3906s but i really hate hand matching them. the 2sa798 was a lot more stable than matched 3906s. i was using a 1k tempco with all the versions i've been testing.
david
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You can check your anatomy all you want, and even though there may be normal variation, when it comes right down to it, this far inside the head it all looks the same. |
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Rykhaard
Joined: Sep 02, 2007
Posts: 1290
Location: Canada
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| Posted: Sat Jul 26, 2008 9:08 pm Post subject:
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| bubblechamber wrote: | i've been building a lot of different expo converters lately. i'm growing quite fond of the 2sa798. they're a bit more than 3906s but i really hate hand matching them. the 2sa798 was a lot more stable than matched 3906s. i was using a 1k tempco with all the versions i've been testing.
david |
Thanks for mentioning that one David! Alas, on Thursday I just grabbed 100 x 2N3906's.  Ah well. They'll still be used anyways.
Now the 2SA798 - without checking yet - is it commonly available in North America, would you know?
(Side note: failed, in my attempt at doing VC Symmetry with the CA3080. I don't know that chips family well enough yet, to confidently know how to use it - without checking reference materials. Just going to go for the 1V/oct. setup for the KAOS VCLFO/VCO. Development is on hold though, whilst I finish my G.I.M.P.-S.E. panel. Few more weeks there yet.) |
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bubblechamber
Joined: Nov 04, 2006
Posts: 280
Location: NYC
Audio files: 1
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| Posted: Sun Jul 27, 2008 11:20 am Post subject:
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hi Rykhaard-i get mine from here.
http://www.electronicsurplus.com/commerce/catalog/product.jsp?product_id=76173
i've got plenty if you'd like a couple to experiment with.
d
_________________
You can check your anatomy all you want, and even though there may be normal variation, when it comes right down to it, this far inside the head it all looks the same. |
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Rykhaard
Joined: Sep 02, 2007
Posts: 1290
Location: Canada
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| Posted: Sun Jul 27, 2008 2:52 pm Post subject:
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Thanks for that link, David.
It's a dual PNP. Are they just thrown together or is it a matched pair? Tied together at the ..... (trying to remember tranny mirrors in VCOs and I'm lost) - tied together at the collector? (head scratching)
Though here now - I'd be using only a single portion of it for the NPN / PNP pair in the expo. converter, no?
Could it be used in other places like where the SSM2210 are used? Curious there as I'm running low on the 2210's and will have be ordering more very, very soon. (4 VCOs are currently on the soon to be done list.)
Now finally - if they are usable as I've asked above - how many would you have to spare?
Or - with my very very recent DUTY ripoff from my Canadian Government, (see * below) would it be possible to have you order a bunch and them shipped to your place, then you shipped them to me? They're definately cheap, price wise.
I would graciously prepay parts and dual shipping costs.
* - Outside of Small Bear Electronics, I wont be ordering ANYthing else from the States again. On my first (and now only) order placed with Mouser, not only was shipping (that took 7 days to hit this city) $16 but the amount of duty for the parts, is more than the original part's total cost. ) |
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bubblechamber
Joined: Nov 04, 2006
Posts: 280
Location: NYC
Audio files: 1
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| Posted: Sun Jul 27, 2008 9:34 pm Post subject:
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I'm not a fan of Canadian customs, either. i tried to move to Vancouver 8 years ago from San Francisco. it was going ok until the customs guys saw the amount of gear my partner and I had. they wanted $10kUS in cash to let us in as a "deposit" on the taxes for our gear in case we sold anything while in Canada. As the afternoon progressed Canadian Customs decided we would be happier in Seattle and we got to make the U Turn of shame in at the boarder.
d
_________________
You can check your anatomy all you want, and even though there may be normal variation, when it comes right down to it, this far inside the head it all looks the same. |
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neandrewthal
Joined: May 11, 2007
Posts: 672
Location: Canada
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| Posted: Sun Jul 27, 2008 11:54 pm Post subject:
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| Rykhaard wrote: | | * - Outside of Small Bear Electronics, I wont be ordering ANYthing else from the States again. |
Me neither. I do Digikey, Small bear and Futurlec. If I absolutely need something from mouser I'm better off paying small bear 25% commission to order it for me and shipping from Texas to New York, then New York to Canada.
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" I went through quite a few trannies til I found one I liked" - Wild Zebra |
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paults
Joined: May 08, 2006
Posts: 21
Location: Fort Worth, TX
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| Posted: Wed Aug 06, 2008 12:18 pm Post subject:
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a) just use SSM2210 or SSM2220s. If you need both NPN and PNP use a THAT 340P (at Digikey.com)
b) matching transistors in individual TO-92 packages is not going to 'solve' the problem of temperature drifting. The 2 parts have to be on the same *die*, the termal insulation of the 2 packages stuck flat-to-flat side negates most of the "matching". Remember, what is the issue is the 2mv/C Vbe drop coefficient for each transistor. |
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