CA3094 ---> LM13700

[Barcode80]

I can't believe I can't find anything on the internet about how to convert schematics using the 3094 or 3080 for use with an LM13700/LM13600 instead. Most of us know that the LM13x00 is two OTAs (the 3080, i believe) in one package. There simply HAS to be a way to create a daughter board that can be swapped into the olds designs by running wires to pin holes. Any input?

[Thomeeque]

There simply HAS to be a way to create a daughter board that can be swapped into the olds designs by running wires to pin holes.

Did you try to compare datasheets?

Since CA.. and LM13700 slightly differ internally (and LM lacks "sink" output, R1 and R2 of CA3094), one daughter board for all CA.. based circuits would be either impossible or complicated.

Do you have some specific CA.. based circuit on your mind?

T.

[StephenGiles]

Far less hassle and cheaper on your brain cells to buy CA3094s from Smallbear! I have only ever been successful in getting the EH Space Drum CA3094 env gen to work using an LM13600.

[Thomeeque]

Far less hassle and cheaper on your brain cells to buy CA3094s from Smallbear!

If you don't mind the price, e.g. 5x $7.50 + international shipping compared to 3x $2 in street shop if you would like to build Small Stone clone here in Prague..

Plus it's challenge and fun, isn't it?

T.

[Barcode80]

Well, for me, given that most other ICs run in the $1 range (less for most), I think our grudging acceptance of this cost is just laziness!

I'm specifically looking at the EHX Micro Bass Synth, which uses an alramingly large number of CA3094's in it.

Is there not some fixed circuit that would work as a drop in for all, even if actual values have to be changed? Like, say theoretically we came up with the addon for the project I'm working on. It seems logical to me that the same circuit could be used by changing the values of the resistors/caps/etc. for any other project. Or am I way off abse.

My knowledge of OTAs is quite limited, so excuse my ignorance. I just see this conversion done for other circuits, but I can't even find documentation on how THOSE were done. Even without a fixed circuit or drop in board, there simply has to be a fixed method/calculation/etc. to do come up with the drop in that can be reapplied case by case.

[StephenGiles]

One important thing I remember being told is to look at how pins 6-8 of the CA3094 are connected, which I believe determines on how the 13600 might be configured. The data sheet which shows the darlington transistor buffer in application circuits is easier to compare with those in the 13600 data sheet.

3094 observations

If pins 7/8 are linked, they are connected high - pin 6 is output
If pins 3/8 are linked, they are connected low - pin 6 is output

So you need to figure out what the 3094 is doing in each case and connect up the 13600 accordingly

If no links between those pins, pin 1 is output - probably used as a VCA

Page 2 of the mk 1 EH Microsynth shows all these configurations.

[Barcode80]

Hmm. So theoretically, we could come up with a drop-in board that accounts for both situations, and work up a logic for when to use which based on the schematic, no?

[Thomeeque]

If pins 3/8 are linked, they are connected low - pin 6 is output

What do you mean by this? Are you talking about A13? It's not connected "low" (to V-), it's connected to 1k/680k divider between V+ and ground and it forms some sort of feedback.. Since there is no "pin 8" (sink output) on LM13600/LM13700, you would probably have to form CA3094's output buffer externally by two transistors for A13..

[Thomeeque]

 Way I see it:

• CA3094 = OTA + BUFFER
  LM13700 = OTA + BUFFER (x2)
• Both OTA and BUFFER parts topologically slightly differ between CA3094 and LM13700, so it will never work absolutely same (despite any external adjustments).
• LM13700's OTA has additional "diode bias" input - it can be ignored when using LM13700 as an CA3094 (left N/C)
• CA3094's BUFFER has additional "sink" out at pin 8 (same wire is hardwired to V+ in LM13700)
  
  
  
  • it can be ignored in cases where CA3094's BUFFER is not used (pins 6 and 8 are N/C) or where it is connected to pin 7 (V+)
  • in other cases it cannot be ignored and BUFFER would probably have to be formed externally

Summing all this universal drop-in board would have to use only OTA's from LM13700, buffers would be formed externally (by two transistors and two resistors for each LM13700's half) to support "sink" outs and it may or may not work in given application depending on how much would internal differences matter. As I said, impossible or complicated..

T.

[StephenGiles]

I found this for those so inclined!!

http://forums.peavey.com/viewtopic.php?f=19&t=4300

[StephenGiles]

Way I see it:

• CA3094 = OTA + BUFFER
  LM13700 = OTA + BUFFER (x2)
• Both OTA and BUFFER parts topologically slightly differ between CA3094 and LM13700, so it will never work absolutely same (despite any external adjustments).
• LM13700's OTA has additional "diode bias" input - it can be ignored when using LM13700 as an CA3094 (left N/C)
• CA3094's BUFFER has additional "sink" out at pin 8 (same wire is hardwired to V+ in LM13700)
  
  
  
  • it can be ignored in cases where CA3094's BUFFER is not used (pins 6 and 8 are N/C) or where it is connected to pin 7 (V+)
  • in other cases it cannot be ignored and BUFFER would probably have to be formed externally

Summing all this universal drop-in board would have to use only OTA's from LM13700, buffers would be formed externally (by two transistors and two resistors for each LM13700's half) to support "sink" outs and it may or may not work in given application depending on how much would internal differences matter. As I said, impossible or complicated..

T.

I agree, but there may be a compromise out there.

[StephenGiles]

If pins 3/8 are linked, they are connected low - pin 6 is output

What do you mean by this? Are you talking about A13? It's not connected "low" (to V-), it's connected to 1k/680k divider between V+ and ground and it forms some sort of feedback.. Since there is no "pin 8" (sink output) on LM13600/LM13700, you would probably have to form CA3094's output buffer externally by two transistors for A13..

No, I'm wrong about a link between pins 3 & 8 of a 3094 - see IC 11 of the Mk 1 Microsynth dated 10/78. It would be good to have design notes for this unit, as it uses the 3094 in so many configurations.

I think there are so many variables relating to these 3094 configurations that a "drop in" replacement is as likely as Gaddafi inviting the Queen to tea - possibly with the exception of a basic VCA configuration, but even then the pinout changes would still need to be carefully considered – all, as I have said before, to save the cost of a gallon of petrol/packet of cigarettes/pint of beer for a 3094 from Smallbear!!!

[StephenGiles]

It may be useful to start a database for schematics of items using CA3094. Of course the Holy Grail of these would be (unethically) the EH Microsynth reissue, providing many clues to replacing 3094s with 13600s.

[StephenGiles]

http://www.freepatentsonline.com/4207468.html

This patent describes an item which uses 4 x CA3094!!!

[JDoyle]

In my humble opinion - use a 3080/LM13600/13700 for the 3094 OTA, and build your own buffer.

It is the OTA that matters (it is the same as a 3080).

This is a lot easier to say when I don't have an unpopulated PCB made for 3094s sitting in front of me...

[Barcode80]

I found this for those so inclined!!

http://forums.peavey.com/viewtopic.php?f=19&t=4300

See, when buying i bulk the parts for that can be pennies, and with a little forethought, it would take just a few minutes to populate and wire in. Good alternative for those like me who insist on cheaper parts!

[StephenGiles]

I found this for those so inclined!!

http://forums.peavey.com/viewtopic.php?f=19&t=4300

See, when buying i bulk the parts for that can be pennies, and with a little forethought, it would take just a few minutes to populate and wire in. Good alternative for those like me who insist on cheaper parts!

Possibly!

[StephenGiles]

Hmm. So theoretically, we could come up with a drop-in board that accounts for both situations, and work up a logic for when to use which based on the schematic, no?

I'm not so sure.

[StephenGiles]

We could all argue about this until the cows come home without any useful progress ever being made. There was an EH paper I once saw at EH UK which described various tricks using the CA3094. I don't think I ever had a copy, but if this ever turns up, it may go some way to solving the problem of convertion from 3094 to 13600.

[TELEFUNKON]

CA3080--->CA3094