portabellabz ua726 replacement

portabellabz ua726 pcb

The pA726 is a CA3046-based analog exponential converter with thermal oven compensation as featured in various analog oscillator circuits with great stability and accurate tracking.
Thanks to the connections layout matching the (in)famous µA726 (UA726) pinout, it can be used as a direct drop-in replacement for this rare and expensive part.

The pA726 can work on +/-12V or +/-15V and replace the µA726 in any other circuit, for a new build or for repair. 
It can be mounted with component legs directly to the µA726's place or to standoffs, chassis, case etc... thanks to the mounting holes and wired to the µA726's place.

The pA726 needs a ground connection. The N/C pin 7 of the µA726 emplacement can be used, there's a connection to this pin on the pA726 PCB but an extra connection between the former µA726 pin 7's pad and ground must be added on the board which will receive the pA726, otherwise the circuit won't work as it should.
If for any reason this pin 7 can't be used as a ground connection, don't solder it and rather connect the pA726's 0V pad to ground.
On the 208 PCBs pin 2 is connected to ground and a bridge can be done between pins 2 and 7 to achieve the ground connection (pin 2 is not permanently wired to 0V in case the pA726 in used in a circuit with different layout).

The pA726 is available in 2 formats to match the TO-100 pinout or the Buchla 208 PCBs (original or clone).

FAQ

Does the pA726 sound as good as the original µA726 ?
The exponential conversion is about pitch only and has nothing to do with the timbre. Unlike some assertions one can read on the interweb, having a µA726 or another exponential converter doesn't affect the sound in any way, being NOS or new.

Does the pA726 installation need other modifications to the circuit ?
Some adjustment of the CV scaling resistor might be needed, same as if a µA726 is replaced with another µA726.

Does the pA726 need to warm up ?
The circuit needs some time to warm up and stabilize, evolving pitch during 5-10 minutes after power up is normal behavior.

Does the pA726 ensure stable pitch ?
When the circuit is warm no drift occurs.

Does the pA726 track as good as the original µA726 ?
In a 208r rev2, I can get perfect tracking on more than 5 octaves with the pA726, which is a little higher than the µA726.

Does the pA726 work with equivalent ICs ?
The pA726 works with TL071, TL081 or CA3146, CA3086, UL1111 etc... as well