Double circle in schematics. How to build?

[matopotato]

The pictures are from Meridian schematic by Aion FX.
I like to breadboard before soldering to try out a few ideas.
How to handle the double rings at LM13700N?
Pin 1 to R8 and pin 5 to R9 and onward?
Should pins 1 and 5 be connected or is that happening inside the IC "automagically"?
Symbol should mean current source, but not sure if I should/could provide that...


Here 12 and 16 don't  go anywhere?
And 7 8 9 and 10 pins don't go anywhere either. So not sure why it is in there in the first place..

[duck_arse]

those darlington pairs can be left unconnected, won't harm anybody. they are an added bonus from the bad old CA3080, which had no output buffer provided. now they are provided, and even more usefully doubled, they are ignored in many/most translated circuits. the unused opamp, I think, still qualifies as an opamp, and should not be abused in the manner shown, shorting the inputs to ground.

as for the current source pins, just treat them as shown, connect your resistor to pin 1 so's the gain can be controlled, and pin 5 to whatever it's outputting into. look at the datasheet itself, it'll show you how it looks inside and what comes outside.

[ElectricDruid]

On the eternal question of "What's the right thing to do with an unused half of a LM13700?" I'd like to repost the following:

reporting from EEVblog:
—
I contacted a TI application engineer with this question a while back:

"I need to properly terminate an unused OTA section of an LM13700.
I'm thinking that connecting the amp bias input (pin 1 or 16) to V- (pin 6)
should disable the input. I also plan to leave the buffer inputs open.

Is this a good approach or is there a better way to do this?

Thank you."

This was the response.

Lee,
That will work well. Pin 1 or 16 can be open, but connection to pin 6 ensures no bias current.
Regards,
Ronald Michallick
Linear Applications

This doesn't mention the inputs or OTA output pin, but presumably the usual op-amp rules apply there - ground the +ve input, and connect up -ve input and output as a unity gain buffer.

[matopotato]

Thanks both of you!
Since I have the pcb, in the end it will be sorted as Aion FX intended. And I will not worry so much about the second pi ture on the breadboard.
No pics though as I wouldn't want to be responsible for upsetting @duck_arse... (I  am using bare copper bridges to ground though.)

[PRR]

....the unused opamp, I think, still qualifies as an opamp, and should not be abused in the manner shown, shorting the inputs to ground....

It is not a normal opamp.


Grounding the inputs takes ALL out of Q4 Q5, and thus out of the rest of the section. All dead. No harm done.

To be very sure, tie Amp Bias Input (AKA Iabc) to V- (usually ground). This also takes all the current out of everything. And this is wise because the Iabc pin can easily be blown-out by careless probing or static charge. In a permanent build you may not care; in 20 years we may be salvaging '13700s out of old pedals from the 2020s and we'd like to find both halves good.

[duck_arse]

No pics though as I wouldn't want to be responsible for upsetting @duck_arse... (I  am using bare copper bridges to ground though.)

no pics upsets me. is there pics?

[matopotato]

No pics though as I wouldn't want to be responsible for upsetting @duck_arse... (I  am using bare copper bridges to ground though.)

no pics upsets me. is there pics?

IBTT (.....The Taunting)

The upper board is for 6 places where you could choose between PS-021 and PS-020. If I can make it play (troubleshooting ongoing. No tone leaving LM13700 atm) I'd like to see if both are nice and if so set 2 3pdt switches on the outside. Else go with the version that sounds best.

[duck_arse]

you've got a wild style going there. circuit? problem? voltages? etc?

[matopotato]

you've got a wild style going there. circuit? problem? voltages? etc?

Yes, might redo it. Meridian compressor by Aion FX.
About half V+ on pin 3 and 4 and bias seem to work, but 0.05 on pin1. But need to verify that first.
I try to stay true to breadboarding even pcb kits, but some are a bit more demanding for me than others.
Overall goal is to figure out if I should mod for PS-0  21/20 or not.
Might start a new thread if I stay stuck.
Connectivity was OK last night though, but no signal on pin1

[duck_arse]

....  because the Iabc pin can easily be blown-out by careless probing or static charge. .....

pins 1 and 16 are the Iabc pins. be very careful as PRR sez. if yours are reading 0V05, your part may already be tot.

mod for PS-0  21/20

I have no idea what this means.

[matopotato]

mod for PS-0  21/20

I have no idea what this means.

Sorru, my bad. The Meridian Compressor is based on Guyatone PS-021 (guitar) and PS-020 (bass) providing alternative components to build either one.

[matopotato]

....  because the Iabc pin can easily be blown-out by careless probing or static charge. .....

pins 1 and 16 are the Iabc pins. be very careful as PRR sez. if yours are reading 0V05, your part may already be tot.

I had a spare LM13700N around. Swapped, same thing, no sound. However both read 1.1V on pin 1 so must have mismeasured yesterday. But neither makes it play. I will rebuild next step.
Good news I think is the LM is ok.

"tot" as in German?

[duck_arse]

I learnt all the german I know, maybe 4 words, from watching Inspector Rex [and Stocki] and Three Ladies and a Hot-dog Stand. tot, yes, kaput.

yours however, measures the magik number for the LM13700. it has to show two diode drops to ground, always.


I yust had a squint at that circuit. I can see why it might go wrong on the breader. break it down into sections, starting with the output. do IC4B to output, audio probe it, then do the section from R16 towards output, and audio probe that. [R15 or R16 - pick one only of correct value.] the section all the way up to C9 is a fairly standard compressor, Ross, Dyna, et al, so just bread that part seperate, get it to work, then join it all up for excitements. easy. it'll turn out neater if you do it in blocks, too.