[sdiy] [AH] Re: UA726 clone possible?

[Stewart Pye]

Hi Tom,

The THAT300 is a 4 NPN transistor array. I think there is also a MAT 4 
tranny array that Rick mentioned earlier.

I've designed (on paper) a VCO that uses the THAT300 for expo converter 
with sensor and heater. I'm planning on laying out the PCB this weekend. 
I probably should breadboard it first, but I like living on the edge! I 
asked THAT some questions about the maximum dissipation and they were 
quite helpful. If you're interested I can email the reply to you. Since 
the max Vce and Vcb voltages are 36V (compared to 15V for the LM3046) 
you can set it up so you have a higher Vce when the heater is on, so you 
can dissipate more power with the same current.


Regards,
Stewart.




On 9/11/2015 8:26 AM, Tom Bugs wrote:
> Well, yes, it is a learning project driven by curiousity rather than 
> particular need & hopefully I can get some learnings along the way..
> My understanding is that the CA/LM3046 has lower specs for the matched 
> pair than the LS318 (or similar AD NPN pairs) - though of course it 
> has been used in a heater arrangement in quite a few commercial synths 
> over the years.
> I would think that the heater element needs to produce a stable 
> temperature (somewhere above ambient) and this temperature needs to be 
> efficectively coupled to the matched pair - I would hope that as long 
> as the device is potted (or using the heat transfer epoxy compound I 
> have) this will be sufficient.
> It could equally be possible to have all components on one side and 
> have the PCB overhang the ua726 footprint (the current design already 
> does a little).
> Cheers, Tom
>
>
> On 10/09/2015 22:54, Richie Burnett wrote:
>>> Anyways, have managed to do a pretty compact test circuit - roughly 
>>> 0.5" sqr(ish) with pins in a rough circle - matched pair on top and 
>>> other components on the base.
>>
>> Isn't the whole idea of the uA726 that all of the components are 
>> fabricated on the same silicon die so that they're always at the same 
>> temperature? You're not going to get all the transistors at the same 
>> temperature if they're plastic packaged devices soldered onto 
>> different sides of an FR4 board.  Maybe I'm missing something here, 
>> but it seems to me that you'd be better off starting with something 
>> like a CA3046 transistor array where all devices are fabricated at 
>> the same time on a common substrate.
>>
>> -Richie,
>>
>