[sdiy] BA662 and other OTAs

Adam (synthDIY) synthdiy at adambaby.com
Tue Jun 20 12:07:34 CEST 2023



> On 20 Jun 2023, at 4:00 pm, Roman <modular at go2.pl> wrote:
> 
> Looks very much like LM13700 to me, so why bother?


Only a non-member of the 303 cult would ask that !!  ;-)

Most of us would've seen this but fun to re-visit... (thanks Rene)

https://www.schmitzbits.de/ota3080.html







and this, although I couldn't find the original online, I found this text (by the inventor) in my archives...

------------------LM13600_13700---------------


The LM13600/13700 was the result of a trip made to
to an Electronic Organ manufacture. In those days
Electronic Organ were primary analog. RCA had
put out the 3080 transconductance and National 
Semiconductor was known for it ability to bomb
the price on anything. 

         ^
        /_\    LM3080
       __|_______________________   ___
      |           |  |           | |   | Output
       ->       <-    ->       <-  |___|
      PNP\|___|/PNP  PNP\|___|/PNP   |
        _'| | |`_      _'| | |`_     |
       |    |____|    |    |____|    |
       |         |    |         |    |
       |        <-    |        <-    |
       |______|/PNP   |______|/PNP   |
Control|      |`_     |      |`______|
Current|         |    |              |
   ^   |         |____\ ________     |
  /_\  |_______       /         |    |
  _|_          |      |         |    |
 / _ \         |      |         |    |
 \/ \/   _    _|      |__    _  |    |
 /\_/\  | |_|'  NPN NPN  `|_| | |    |
 \___/  |_| |`->       <-'| |_| |    |
   |    -IN    |_______|    +IN |    |
   |             |              |    |
  _|_           _|              |   _|
 |   |________|'  NPN      _____|_|'  NPN
 |___| |      |`->         |      |`->
 IABI  |     ____|         |     ____|
       |_   |   _|         |_   |   _|
    NPN  `|_|_|'             `|_|_|'  NPN
       <-'|   |`->         <-'|   |`->
       |_________|         |_________|
          _|_                  _|_
          ///                  ///
          Gnd                  Gnd


The design of RCA's 3080 did not need much 
improvement in that the control current had
at least a 80dB dynamic range. 
It did make sense at the time to maybe do a 
stereo version since all audio signal processing
was of course stereo.

The design really started out as a just a practice
layout for new mask designer. Bill Gross and myself
spent about 5 minutes on the whole design. 
         ^
        /_\    LM13600
       __|_______________________   ___
      |           |  |           | |   | Output       
       ->       <-    ->       <-  |___| 
      PNP\|___|/PNP  PNP\|___|/PNP   |
        _'| | |`_      _'| | |`_     |
       |    |____|    |    |____|    |  Buffer Input
       |         |    |         |    |  ___      ^
       |        <-    |        <-    | |   |    /_\
       |______|/PNP   |______|/PNP   | |___|   __|_
Control|      |`_     |      |`______|   |   _|    |
Current|         |    |              |   |_|'  NPN_|
   ^   |         |____\ ________     |     |`->_|'  50X
  /_\  |_______       /         |    |        | |`->
  _|_          |      |         |    |      __|    |
 / _ \         |      |         |    |     |       |
 \/ \/   _    _|      |__    _  |    |     |       |
 /\_/\  | |_|'  NPN NPN  `|_| | |    |     |       |
 \___/  |_| |`->       <-'| |_| |    |     |       |
   |    -IN    |_______|    +IN |    |     |      _|_
   |             |              |    |     |     |   |
  _|_           _|              |   _|     |     |___|
 |   |________|'  NPN      _____|_|'  NPN  |    Buffer
 |___| |      |`->         |      |`->     |    Output
 IABI  |     ____|         |     ____|     |   
       |_   |   _|   ___   |_   |   _|     |
    NPN  `|_|_|'___|'   |    `|_|_|'  NPN  |
       <-'|   |`-> |`-> |  <-'|   |`->     | 
       |_________|____| |  |_________|     |  
          _|_           |      _|_         |
          ///           |      ///         |    
          Gnd           |      Gnd         |
                        |__________________|

First, the design was to be stereo. At that time we
had a package where we could include a Darlington
as an output buffer to save the customer money. 
Since the dynamic range of bias current was at least
80dB, the bias method shown above was chosen for the 
LM13600. At the time, the dynamic range was more like
100dB. The speed of the amplifier is greatly limited
to 2MHz because of the lateral pnps. But this meant
one could built a VCO or filter that could go from
10Hz to 1MHz. Today that range may be from 1Hz
to MHz.  


         ^
        /_\    LM13700
       __|_______________________   ___
      |           |  |           | |   | Output       
       ->       <-    ->       <-  |___| 
      PNP\|___|/PNP  PNP\|___|/PNP   |
        _'| | |`_      _'| | |`_     |
       |    |____|    |    |____|    |  Buffer Input
       |         |    |         |    |  ___      ^
       |        <-    |        <-    | |   |    /_\
       |______|/PNP   |______|/PNP   | |___|   __|_
Control|      |`_     |      |`______|   |   _|    |
Current|         |    |              |   |_|'  NPN_|
   ^   |         |____\ ________     |     |`->_|'  50X
  /_\  |_______       /         |    |        | |`->
  _|_          |      |         |    |      __|_   |
 / _ \         |      |         |    |     |_   |  |
 \/ \/   _    _|      |__    _  |    |  1X   `|_|  |
 /\_/\  | |_|'  NPN NPN  `|_| | |    |     <-'|    |
 \___/  |_| |`->       <-'| |_| |    |     |_______|
   |    -IN    |_______|    +IN |    |            _|_
   |             |              |    |           |   |
  _|_           _|              |   _|           |___|
 |   |________|'  NPN      _____|_|'  NPN       Buffer
 |___| |      |`->         |      |`->          Output
 IABI  |     ____|         |     ____|     
       |_   |   _|         |_   |   _| 
    NPN  `|_|_|'  NPN   NPN  `|_|_|'  NPN
       <-'|   |`->         <-'|   |`->   
       |_________|         |_________|    
          _|_                  _|_ 
          ///                  ///          
          Gnd                  Gnd 

The main problem with the LM13600 method is the fact that the input
transistor of the darlington moves with the control current. Not a
very good thing for the audio application. Hence the LM13700 method
shown above. 
          ^
         /_\    LM13600
        __|_______________________   ___
       |           |  |           | |   | Output
        ->       <-    ->       <-  |___|
       PNP\|___|/PNP  PNP\|___|/PNP   |
         _'| | |`_      _'| | |`_     |
        |    |____|    |    |____|    |  Buffer Input
        |         |    |         |    |  ___      ^
        |        <-    |        <-    | |   |    /_\
 Linear |______|/PNP   |______|/PNP   | |___|   __|_
 Diodes |      |`_     |      |`______|   |   _|    |
  ___   |         |    |              |   |_|'  NPN_|
 |   |  |         |____\ ________     |     |`->_|'  50X
 |___|  |________      /         |    |        | |`->
   |             |     |         |    |      __|    |
   |______       |     |         |    |     |       |
          |      |     |         |    |     |       |
 Control  |_______\_  __\____    |    |     |      _|_
 Current  |       /     /    |   |    |     |     |   |
    ^     |      |      |    |   |    |     |     |___|
   /_\   _|_     |    __|   _|_  |    |     |    Buffer
   _|_   \ /     |   |      \ /  |    |     |    Output
  / _ \  _v_  NPN|   | NPN  _v_  |    |     |
  \/ \/  _|_    _|   |__    _|_  |    |     |
  /\_/\ |   |_|'        `|_|   | |    |     |
  \___/ |___| |`->    <-'| |___| |    |     |
    |    -IN     |____|    +  IN |    |     |
    |             |              |    |     |
   _|_           _|              |   _|     |
  |   |________|'  NPN      _____|_|'  NPN  |
  |___| |      |`->         |      |`->     |
  IABI  |     ____|         |     ____|     |
        |_   |   _|   ___   |_   |   _|     |
          `|_|_|'___|'   |    `|_|_|'  NPN  |
        <-'|   |`-> |`-> |  <-'|   |`->     |
        |_________|____| |  |_________|     |
           _|_           |      _|_         |
           ///           |      ///         |
           Gnd           |      Gnd         |
                         |__________________|


Well, there was one more pin left over on each side of 
the stereo transconductance amplifier. That could
not go to waste. So it was easy to simply add two 
linearizing diodes to each amplifier to predistort 
the input signal. Design done. No bread boards.
Remember, this was just meant to give a new mask designer
something to practice on.

But after the layout, the design manager (Tim Isbell) 
say why not make it into a product? So we did, it
came out working perfectly in that no changes where
needed. Test system was easy DC. This product was
trying to show us just how fast and cheaply it could
be brought into production. 

This was the days when you could sample a product 
without a data sheet. It was already generating enough 
interest to spend some time on a datasheet. The 
Electronic Organ Companies where already giving us
quite a few circuits. A few more circuits where developed 
to exploit the limits of the dynamic range. All
application circuits were fired up. No problem. 

If every there was a IC that appeared to have a life of
its own, the LM13600 did. It further when on to inspire
the development of Delco's DNR project. I find it quite
warming when I see magazines like "Popular Electronic"
copy all my LM13600 data sheet work into a dedicated 
couple of transconductance articles. They seem to 
do this every couple of years. That says there are people
out their who still love this kind of analog electronics. 


                                     Don Sauer
                                     DSauerSanJose at aol.com




>  
> Roman
> 
> 
> ---- Użytkownik Tom Wiltshire napisał ----
> 
> Interestingly, thre are a few minor differences between the reverse-engineered Open Music Labs schematic (which the Re-303 uses) and the Alfa clone. Some of the differences are obvious stuff, like diode-connected transistors being shown as diodes, for example, but not everything.
> 
> Here's the Open Music Labs version:
> 
> http://wiki.openmusiclabs.com/wiki/x0xb0x
> 
> And here's Alfa's:
> 
> https://www.alfarzpp.lv/eng/sc/AS662D.pdf
> 
> 
> 
>> On 19 Jun 2023, at 13:10, Todd Sines <sines_list at scale.la <mailto:sines_list at scale.la>> wrote:
>> 
>> Din Sync make them for their RE-X0X series
>> That link would be here 
>> https://shop.re-303.com/product/ba662-clone/
>> 
>> Todd
>> 
>>> On Jun 19, 2023, at 4:39 AM, Tom Wiltshire <tom at electricdruid.net <mailto:tom at electricdruid.net>> wrote:
>>> 
>>> Yes, Alfa make a clone - or at least a chip with that number:
>>> 
>>> https://www.alfarzpp.lv/eng/sc/AS662D.pdf
>>> 
>>> 
>>> 
>>>> On 19 Jun 2023, at 04:41, Adam (synthDIY) <synthdiy at adambaby.com <mailto:synthdiy at adambaby.com>> wrote:
>>>> 
>>>> Actually, yes you're right, the Roland BA662 OTA that they used a lot around this time, both for VCAs and VCFs. I've sent you the schematic.
>>>> 
>>>> I think they've been cloned successfully in recent years
> 
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