[sdiy] uA726, heated pairs...

[Peter Grenader]

I have noticed lately that both Analogue Systems' VCO and Filter -as well as
Serge's NTO/PCO uses a 3046 configured in this way (using sections of the
array as an internal heater).  While I have no experience with the MAT04,
although considered trying it for a Buchla 258 clone I was considering, I
can tell you that in regards to FM, the 3046 does not yield the same result
as the 726 sonically.   Whether this is due to the 726 alone I don't know,
but they sound different, although both linear.

So basically, I don't know much about this (ha!), but I DO know that others
have incorporated heaters into other monolithic devices for VCOs along with
those mentioned in this string.

In my own experience with 3046s, which I've used to drive a vactrol LED, I
found that leaving the substrate floating (not connected to the lowest
voltage) kept the vac from bleeding when then light was off.  While
undoubtedly this was due to something else I screwed up,  simply
disconnecting the substrate was the most expedient solution to the problem.

Peter


Grant Richter wrote:

> Do you remember what you did with the substrate pin?
> 
> open, ground or -15V?
> 
>> From: Tim Ressel <madhun2001 at yahoo.com>
>> Date: Fri, 8 Aug 2003 09:23:59 -0700 (PDT)
>> To: Grant Richter <grichter at asapnet.net>, Keith Daniel <ensign7 at e-scape.net>,
>> synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] uA726, heated pairs...
>> 
>> Yo,
>> 
>> I use the heater circuit from AN299 on my VCOs. One
>> uses a 3046, the other uses a MAT04. It works as
>> advertised. I checked the circuit in an environmental
>> chamber so I could verify operation up to +40C.
>> 
>> --tr
>> 
>> 
>> --- Grant Richter <grichter at asapnet.net> wrote:
>>>> There is the little known National Semiconductor
>>> app note AN-299 (1986?),
>>>> where an LM3046 transistor array is used to
>>> provide a heated pair for a VCO.
>>>> 
>>>> I've tried it, but it seems to me that there was a
>>> change in chip manufacture,
>>>> and it doesn't work as advertised. The substrate
>>> pin is the problem.
>>>> 
>>> 
>>> Just a couple stray thoughts...
>>> 
>>> The ap note doesn't specify the pin out on the
>>> CA3046. You could probably
>>> get it to work by trying different combinations of
>>> heater and sensor
>>> transistor.
>>> 
>>> Also, the substrate connects to the most negative
>>> voltage used, in this
>>> case, it looks like ground and not -15V.
>>> 
>>> For a working example, see the Moog "Source" service
>>> manual which used a
>>> thermostated CA3046 for the expo-converter. The
>>> Serge NTO and PCO also use a
>>> heated CA3046.
>>> 
>> 
>> 
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>