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Dual matched transistor with tempco and more
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oldcrow



Joined: Sep 24, 2008
Posts: 25
Location: Chicago, IL USA

PostPosted: Mon Dec 19, 2011 5:49 pm    Post subject: Dual matched transistor with tempco and more Reply with quote  Mark this post and the followings unread

Santa arrived early, delivering my board order from BatchPCB. I got twice the charged quantity.

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

Left to right, they are:

1) My drop-in VCO153: drops into a Yamaha IG00153 DIP socket
2) My LM13600-to-CA3280 adapter: part of my research trying to revise my MOTM-480 to survive without the late and lamented CA3280.
3) My drop-in JH00151, a circuit the late JH and I discussed over the years: it replaces a Yamaha IG00151 VCA in various Yamaha gear...212 of them in a CS-80.
4) The dual SOT-363 transistor plus 0805 pads pinned to a DIL8.

Time to solder!

--Crow
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inlifeindeath



Joined: Apr 02, 2010
Posts: 316
Location: Albuquerque, NM

PostPosted: Mon Dec 19, 2011 8:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

very cool! is the 13700 adapter just to reroute pins or did you find you needed to modify to get the same response? i've been wondering if the statement that the 3280 has the best ota characteristics of the bunch, is in anyway based on fact or relevant in synth circuits.
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oldcrow



Joined: Sep 24, 2008
Posts: 25
Location: Chicago, IL USA

PostPosted: Mon Dec 19, 2011 11:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

inlifeindeath wrote:
very cool! is the 13700 adapter just to reroute pins or did you find you needed to modify to get the same response? i've been wondering if the statement that the 3280 has the best ota characteristics of the bunch, is in anyway based on fact or relevant in synth circuits.


It remaps the pinout so as to be able to plug a LM13x00/NE5517 into a CA3280 position.

CA3280 was the best because it had extra transistors in the amplifier bias current control, allowing 2mA Iabc (vs. the usual 1mA for a 13600). See
http://www.soiseek.com/INTERSIL/CA3280/2.htm and note the "totems" of transistors for the Id and Iabc (pins 1 and 3). 2mA of amplifier bias current means a 2:1 improvement in SNR vs. a 1mA Iabc part. The voltage input to an OTA is usually tiny, something like 3% of full scale voltage, so 5vpp becomes 150mV and the resulting output current of ~300uA at full Iabc needs less recovery gain in the summing amp/integrator the OTA is feeding, which means less amplified noise.

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inlifeindeath



Joined: Apr 02, 2010
Posts: 316
Location: Albuquerque, NM

PostPosted: Wed Dec 21, 2011 6:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

awesome, thank you. so does that mean running the two sides of a 13700 in parallel would result in the same S/N ratio?
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oldcrow



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PostPosted: Wed Dec 21, 2011 9:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

inlifeindeath wrote:
awesome, thank you. so does that mean running the two sides of a 13700 in parallel would result in the same S/N ratio?


This is what I am exploring. The question is can I achieve a better SNR with parallel cells, given that each cell will exhibit a similar SNR individually.

Crow
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