Hey guys-

I'm relatively new to electronics and teaching myself. I am currently working on building a guitar effect, the Mutron III Envelope Filter (see attached image). The circuit utilizes a proprietary optocoupler that is unavailable. One of the given options is to substitute (2) H11F3 MOSFET optocouplers (see other attached image). The problem I have is that I am unclear how these devices fit in to the circuit structure. The circuit doesn't work as I have it laid out, and I'm guessing that the optocoupler setup is incorrect.

As I have it : IC1/1 ---> OC1/4
IC2/6 ---> OC1/6
IC2/7 ---> OC2/4
IC2/2 ---> OC2/6
IC3/1 ---> OC1/1 and OC2/1
R17 ---> OC1/2 and OC2/2

This is probably incorrect, so I'm seeking advice as to how to do this the right way and get a better understanding of the OC.

Also, I'm unsure of what to do with RX, as I am unable to observe the internal LED.
Thanks in advance for your assistance.

 

Your reasoning doesn't make sense, the circuit uses a led and two ldr's to detect the light, i assume the ldrs are in a tube with the led at one end??

Or are they inside the obselete opto? Rx sets the current in the led, based on the voltage set on pin 3 of IC3a, which is 3.6V, so that voltage will appear across Rx, if your led say needs 10mA, then Rx needs to be 360 ohms.

 

Your reasoning doesn't make sense, the circuit uses a led and two ldr's to detect the light, i assume the ldrs are in a tube with the led at one end??

Or are they inside the obselete opto? Rx sets the current in the led, based on the voltage set on pin 3 of IC3a, which is 3.6V, so that voltage will appear across Rx, if your led say needs 10mA, then Rx needs to be 360 ohms.

DD-

Thanks for the reply.

Can you be more specific? What part of my reasoning are you referring to?

I don’t know anything about the obsolete OC, as I can’t get one. I’m trying to find out how to set up the H11F3 as a substitute.

I don’t know what the requirements of the LED are, as it is buried in the IC, so determining RX is difficult. Normally, I would just throw in a few hundred ohms and adjust visually.

 

The inputs to the two optos (pins 1 and 2) should be in series at the output of IC3a, not in parallel.
Connected in parallel, one will tend to hog the current.

IC1/1 ---> OC1/4
IC2/6 ---> OC1/6
IC2/7 ---> OC2/4
IC2/2 ---> OC2/6
IC3/1 ---> OC1/1
OC1/2---> OC2/1
OC2/2---> R17

You may have to adjust the value of Rx and/or R8 and R9 to get the response you want.

 

According to the datasheet, the led takes upto 16mA @ 1.75V drop, so you could put two optos in series with Rx at 300 ohms, (you could put a 470 ohms preset insted and adjust) this will give you a led current of 12mA.

Then use the opto-coupler outputs to replace the ldrs,

 

Looking at the datasheet, the LED needs 60 mA, so RX should be 60 ohms.

 

Looking at the datasheet, the LED needs 60 mA, so RX should be 60 ohms.

That's the absolute maximum current, not the normal operating current.

Since the opto output should operate in a high resistance state (as the 220k ohm resistors in parallel would suggest) I suspect the normal opto operating current would be in the sub mA or microamp range.

 

That's the absolute maximum current, not the normal operating current.

Since the opto output should operate in a high resistance state (as the 220k ohm resistors in parallel would suggest) I suspect the normal opto operating current would be in the sub mA range.

OK, I see what you’re saying. I will reconfigure and see how it goes. Thanks for your help.

 

I would start with Rx in the 100k ohm range and go up or down from there to get the desired response.

 

You can simulate everything using LTspice and my collection of models. I have a model H11F1M. As far as I understand, this optocoupler differs from your optocoupler by the transmission factor. If you enter the circuit and start the simulation, then for the final fit I will make the model of your optocoupler. In my collection there are all the necessary elements. The opamp symbol is OpAmp_TI (TL072) or OpAmp_ST (TL07x).
http://bordodynov.ltwiki.org/
The necessary instructions how to use my collection is on the site.

 

I find it hard to believe that it's a useful replacement.

H11F3 is a current controlled current generator, and the schematic use a current controlled resistor.

 

See

 

H11F3 is a current controlled current generator

No.
It is a current controlled MOSFET that can be used as a current controlled resistor also.
See graph below from the data sheet.

 

.subckt H11F1M A C R1 R2
dled1 A 6 LED1
VT 6 C 0
dled2 A C LED2
B 0 T i=(165+(0.07229* ((2*i(Vt))**(-1.5)))) Rpar=1 Cpar=2.u
BRES R1 R2 R= V(T) Cpar=15p Rpar=300Meg
.model Led1 d(is=0.5e-20 )
.model Led2 d(is=0.5e-20 cjo=18p)
.ends