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 Forum index » DIY Hardware and Software
Matched Pairs (ad infinitum)
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phdinfunk



Joined: Jun 04, 2008
Posts: 115
Location: Taiwan

PostPosted: Tue Oct 30, 2012 7:17 pm    Post subject: Matched Pairs (ad infinitum) Reply with quote  Mark this post and the followings unread

It seems there are fewer and fewer good matched pairs available. I used to really like the 2SC798s and 2SC1583s. They are discontinued as are their replacement!

I noticed that there are now DMMT3906

http://www.diodes.com/datasheets/ds30312.pdf

and DMMT3904

http://www.diodes.com/datasheets/ds30311.pdf

They say they're matched to 2%..... Maybe for a 48 stage phazer?

Good enough for an osc?

No? What else is out there these days?
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L-1



Joined: Dec 11, 2010
Posts: 39
Location: Belarus
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PostPosted: Fri Nov 16, 2012 3:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

I used BCM847BS. Work well in oscillators instead of matched BC547 or 550. And BCM857BS where pnp.
But don't confuse, third letter 'M' means 'matched', there are BC847BS they are didn't matched but have closely matched current gain, and are usable in many applications.
For example BC work well in Buchla 258 but in Yusynth osc they didn't work properly but BCM work well.

I've bought DMMT3904 and 06 but didn't used yet. Going to use them where 2N3904 and 06 are preferable matched.

This is my 6 Yusynth oscillators with BCM847BS on board.
Samples here http://www.muffwiggler.com/forum/topic-49531-840.html

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Sat Nov 17, 2012 9:18 am    Post subject: Reply with quote  Mark this post and the followings unread

New here - Hello! Just started doing some research for my first DIY oscillator and am attracted to the yusynth VCO for its simplicity and low part count.

My understanding thus far is that the the yusynth VCO design can use SSM2210 (or the newest SSM2212) or hand matched BC847Bs, but now there is the option of using the BCM847BS matched pair. The SSM2212 is $7 from Digikey and the BCM847BS is $0.55.

What's the downside here? I'd ideally like 6-8 octaves of 1v/octave tracking. Is that reasonable to expect from either matched pair?
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frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
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PostPosted: Sat Nov 17, 2012 12:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

minisystem wrote:
I'd ideally like 6-8 octaves of 1v/octave tracking. Is that reasonable to expect from either matched pair?

Matching is for temperature compensation. It has nothing to do with tracking. It looks like the SSM2212 is speced at the same level of log conformance as the SSM2210, so it should track well.

Ian
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Sat Nov 17, 2012 12:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Got it, so to be more specific, what's the downside to using a $0.55 BCM847BS matched pair versus a $7 SSM2212?

From my naive perusing of the two datasheets I see that the SSM2212 has higher gain (~600 vs the 847's ~250) and a much lower Vbe offset (0.2mV vs the 847's 2mV).

This is assuming I'm interpreting 'offset voltage' as being the same as ∆Vbe. Is that correct?

From the BCM847BS datasheet, Vbe is matched to within 2mV. Whereas the SSM212 has a maximum offset voltage of 0.2mV.
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LFLab



Joined: Dec 17, 2009
Posts: 191
Location: Rosmalen, Netherlands

PostPosted: Sun Nov 18, 2012 3:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Well the bcm's are smt parts so pretty small, you'll have to solder them directly. the ssm2210 is a dip part, so plugs right into a socket. less scary, depending on your soldering proficiency.
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Sun Nov 18, 2012 8:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Right, I should've mentioned that I'm going to try to implement the whole oscillator in a surface mount design, so no problems soldering surface mount components. Got a microscope and a steady hand (previous career dissecting fruit fly brains...). Wink
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fluxmonkey



Joined: Jun 24, 2005
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PostPosted: Mon Nov 19, 2012 6:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

or, the MAT12, only $27
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L-1



Joined: Dec 11, 2010
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PostPosted: Mon Nov 19, 2012 8:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Look closer to the photo. I made adaptors for DIP8 socket where placed BCM847BS and 0805 1K tempco.
BCM847BS has gain close to BC547B which has 200.
And Yves specified R15 = 10K for matched BC547B but 100K for SSM2210. Maybe for that reason.

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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Tue Nov 20, 2012 8:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

L-1 wrote:
Look closer to the photo. I made adaptors for DIP8 socket where placed BCM847BS and 0805 1K tempco.
BCM847BS has gain close to BC547B which has 200.
And Yves specified R15 = 10K for matched BC547B but 100K for SSM2210. Maybe for that reason.


Great. So I'll go for the $0.55 BCM847BS. Thanks for the info!

You used an 0805 tempco? I'm thinking about doing the same. Being SMT, the tempco resistor can't make direct physical contact with the BCM847BS. Presumably they are close enough together than temp differential isn't a problem?
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L-1



Joined: Dec 11, 2010
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PostPosted: Wed Nov 21, 2012 12:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

I made a stripe at center of layout for better thermal contact.
At last page of this file. http://electro-music.com/forum/phpbb-files/l_1_258_729.pdf

You must change a bit Yusynth layout because of different pinout of 847.

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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Thu Nov 22, 2012 3:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

L-1 wrote:
I made a stripe at center of layout for better thermal contact.
At last page of this file. http://electro-music.com/forum/phpbb-files/l_1_258_729.pdf

You must change a bit Yusynth layout because of different pinout of 847.


Ah, good idea. I wonder if a glop of thermal compound would also help.
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phdinfunk



Joined: Jun 04, 2008
Posts: 115
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PostPosted: Fri Nov 30, 2012 7:33 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm running into the Same thing. Panasonic makes those SMT tempcos and you can get a lot of SMT matched pairs. I went with THAT series tempcos, though I'm thinking of testing a build with 3096s (for Buchla 259 Osc Cores).....

I put the tempcos on the side with the NPNs. . . pretty effing close. Can most likely slide them up to touching and add a glob of heat-sink compound....

--Jonathan
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