Exponential current source blues

[Bob Zimmer]

At 12:20 AM 3/26/97 -0800, you wrote:
>Speaking of EN PCC VCO option 2...
>
>1. Why do VCO's (and VCF's), that at heart are made up of simple 
>op amp oscillators (like LFO's), need the exponential current 
>source as given in most common circuits?  Is it mainly for scaling 
>of CV's? (1V/oct to 18mV/oct).  Can another structure do this 
>besides tempcos and transitors (either matched OR arrays)?

I'm not qualified to answer this.

>2. What are some of the latest sources of tempcos? Vishay 
>Electronics is still apparently carrying them (See my next post 
>for info).  Can someone check out the following web page and see 
>if these parts might work too:
>Koa Speer
>http://koaspeer.com/surface/lt73_1.htm

Chris List seems to be the resident expert on buying tempco's.  I bought
mine from one of his earlier posts.

>3. I called several of the distributors of Analog Devices products 
>and asked about MAT03's (and 02's).  After being transfered a lot 
>because I wasn't a company, I would finally get a price.  
>What is the difference in quality between the various versions 
>(MAT03AH, MAT03EH, MAT03FH)?  If they are matched and the 
>transitors have the same substrate should it matter much in a VCO 
>circuit?  The prices range from about US$5.15 to US$16.00 
>(although Wyle had them for $28.35!).  The FH's seem the cheapest.  
>The 5.15 price was from the First Stop division of Pioneer 
>Standard (1-216-349-9310, I talked to Mike Boyer).
>
>Steve Varner

Allied Electronics used to carry them, but only lists the 02 in their latest
catalog.

Newark still carries them (02, 03, 04)at decent prices.  I believe the 02FH
& 03FH are about $8.00 each or so.  I can check in their catalog tonight.  I
think (but am not sure) the difference between the EH & FH are temperature
range. I'm using the FH ones and believe that they should be fine for my
needs (non steel foundry temperatures!).

Also, can't you order in quantities < 10 from AD themselves???  I realize
that they would charge list price, but if the other sources dry up...

  >=== Bob Zimmer -- Philadelphia PA ===<
  >=== bzimmer at voicenet.com          ===<