I’m fixing a McIntosh Mac 4100 that I have and on of the faults was that the power guard/clipping LED on one of the channels is very intermittent and the clipping of the waveform on the scope isn’t great either.
After a bit of diagnostic work I found the fault was due to a failing optocoupler.
Here it is in the 4100 circuit.
Does anyone know of a replacement I could pick up from somewhere like Digikey or Mouser? I wouldn’t trust any of the ones coming out of China that are littered all over eBay to meet the spec of the originals.
I’m not sure what to do if I can’t buy some replacement that will work in the circuit. If someone comes up with a replacement I’ll make sure to buy multiples for future encounters if needed.
Thank you,
Dan
After a bit of diagnostic work I found the fault was due to a failing optocoupler.
Here it is in the 4100 circuit.
Does anyone know of a replacement I could pick up from somewhere like Digikey or Mouser? I wouldn’t trust any of the ones coming out of China that are littered all over eBay to meet the spec of the originals.
I’m not sure what to do if I can’t buy some replacement that will work in the circuit. If someone comes up with a replacement I’ll make sure to buy multiples for future encounters if needed.
Thank you,
Dan
That part has been out of production for years and any cheap part claiming to be it is going to be a part from China with questionable specs. I did find that Audio Classics which is an authorized McIntosh parts dealer has equivalent parts, but they want $55 per optocoupler which seems ridiculous. I saw that Small Bear Electronics was the place to get them last at $10.25, but they no longer have them. So I’m hoping that maybe nowadays there might be an equivalent being made.
Dan
Your call. Who cares where they come from if they work? Why not just buy one of whatever questionable source and just try it?
Frankly I wouldn’t care where they were coming from, but the fact that a vast, vast majority, almost all really, fake parts come out of China doesn’t bode well. If someone came to me and said that there was a shop in China that was selling authentic parts with 100% certainty then I’d have no problem grabbing some from there. I could grab a couple and compare them to the originals, but from what I’ve read the originals are pretty special with their on/off resistances and the rise/decay time. Someone PMd me and told me of a vendor here in the US that has the authentic part for $10.75 each. I was just hoping that someone knew of another part number with similar specs at a fraction of the cost. Looks like I’ll grab a few of these here in the US and pay a premium, better than spending $55 each from the Mac parts dealer.
The last time I bought parts from China I got 16 TO3 output transistors, needed 8 for a receiver. The first 8 blew within 10 minutes of being powered up, I was barely able to get bias set. Second set of 8 lasted not much longer. I paid the extra money for a set from Mouser as I should have done in the first place, they’re still running to this day and that was over 8 years ago. Exact same part number, real vs fake. So I tend to stay away from parts if they’re questionable.
Dan
The brand name of that was Vactrol, but people called any CDS/LED combo device a vactrol, so it became a genericized term. The same European Union ROHS law that banned lead in solder also banned cadmium, an essential part of the CDS cell, so the company (originally Vactec, but was bought out, as shown by a different company name on that datasheet) that made "authentic" Vactrols finally quit making them.
Surplus dealer Electronic Goldmine used to sell these (generic LED-CDS optocouplers), but I no longer see them on the website. They still have CDS cells, and it's easy enough to make one of these with an LED and heat shrink tubing. You'll at least know it's an operational device, though you won't know the specs.
Whether something that "doesn't meet the specs" is going to work depends on just how the circuitry uses the part. I can't tell offhand from that schematic.
Surplus dealer Electronic Goldmine used to sell these (generic LED-CDS optocouplers), but I no longer see them on the website. They still have CDS cells, and it's easy enough to make one of these with an LED and heat shrink tubing. You'll at least know it's an operational device, though you won't know the specs.
Whether something that "doesn't meet the specs" is going to work depends on just how the circuitry uses the part. I can't tell offhand from that schematic.
817 / 1017, utterly common in PC SMPS, TV and LED drivers.
This is from a site I am not connected to:
An alternative PC817 ICs are 6N136 IC, MOC3041 IC, MOC3021 IC, 6N137 IC & 4N25IC. Equivalent PC817 ICs are PC817A, PC817C, PC817B & PC817D.
1.25 to 80V, so it will work.
Costs less than 10 cents, here, good quality Taiwan make.
Or strip it from an old PC supply / TV supply, it is usually in the feedback loop from HV to LV side, which controls the switching transistors.
This is from a site I am not connected to:
An alternative PC817 ICs are 6N136 IC, MOC3041 IC, MOC3021 IC, 6N137 IC & 4N25IC. Equivalent PC817 ICs are PC817A, PC817C, PC817B & PC817D.
1.25 to 80V, so it will work.
Costs less than 10 cents, here, good quality Taiwan make.
Or strip it from an old PC supply / TV supply, it is usually in the feedback loop from HV to LV side, which controls the switching transistors.
Build your own.
I do, for the Opto Compressor/Limiter in my Bass Guitar power amps.
A high efficiency 5mm Red Led (bag is labelled "something" 53 if that helps you) and a 5 mm CDS cell.
EDIT: I use this Led: https://uk.farnell.com/kingbright/l-53lid/led-low-current-5mm-red/dp/1142563
EDIT 2: and you can use these CDS cells, still availble: https://www.adafruit.com/product/161
But many similar spec ones availble.
I buy lots of 200 each which last me a couple years so haven´t bought any recently (lots of unused stock in my parts bin) but should be commercially available.
I grind Led "lens" flat and glue/epoxy it to CDS cell, then pack it in some heat shrink tubing.
It works fine, besides I know I am using a high quality LED and a good quality CDS cell, while "oriental substitutes" can have anything inside. 😱
So if you dare .....
I must make a few for a Keyboard amplifier I have to ship this week, if you need it I might take a couple pictures and upload them here.
I do, for the Opto Compressor/Limiter in my Bass Guitar power amps.
A high efficiency 5mm Red Led (bag is labelled "something" 53 if that helps you) and a 5 mm CDS cell.
EDIT: I use this Led: https://uk.farnell.com/kingbright/l-53lid/led-low-current-5mm-red/dp/1142563
EDIT 2: and you can use these CDS cells, still availble: https://www.adafruit.com/product/161
But many similar spec ones availble.
I buy lots of 200 each which last me a couple years so haven´t bought any recently (lots of unused stock in my parts bin) but should be commercially available.
I grind Led "lens" flat and glue/epoxy it to CDS cell, then pack it in some heat shrink tubing.
It works fine, besides I know I am using a high quality LED and a good quality CDS cell, while "oriental substitutes" can have anything inside. 😱
So if you dare .....
I must make a few for a Keyboard amplifier I have to ship this week, if you need it I might take a couple pictures and upload them here.
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Those are NOT equivalent by any means, you are suggesting Led-Diode or Led-Transistor Optocouplers, completely unsuitable for (linear) Audio use.
Please read (straight from datasheet):
They are still available in the UK from Farnell https://uk.farnell.com/advanced-pho...ler-2kv-resistive-o-p/dp/3692218?st=photocell
And Tortuga Audio in the USA use them in their LDR passive preamps https://tortugaaudio.com/ and sell them mounted on a little circuit board
And Cadmium Suphide photoresistors (similar to the ORP12) are still very much available in the UK too https://cpc.farnell.com/c/electroni...-displays/photo-light-dependant-resistors-ldr
So whatever the EU is alleged to ban, both CDS photoresistors and CDS photocells are easily available in the UK from major suppliers, and have been both before and after Brexit.
The company that make them is Advanced Photonix https://www.advancedphotonix.com/product/optocouplers/ and that is where Farnell get them, and the CDS photocells.
I was avoiding up to this point pointing the routes to the OP solving his problem, because all these options are easily available, in the USA from the usual suppliers (Mouser, Digikey etc) and can be found by using google. But he seems determined to let others do the work for him.
Sorry to be blunt.
There are two kinds of "Vactrol" devices. The original LED // CDS cell which is designed to work in the linear region as a current controlled resistor. Most were enclosed in a small hollow plastic case like seen in the photo.
There is also a LED / phototransistor version, most of which are used as an isolated current controlled high speed switch. These usually come in a typical DIP or SMD package. They were generally not used in the linear region. Some devices brought the base pin out to allow for bias, or used a mosfet as the controlled device for linear operation, but these are rare.
The included schematic just shows a variable resistor so the device is likely a CDS based cell. Attempts to use a transistor based coupler will likely be futile.
I bought lots of the surplus optocouplers from Electronic Goldmine whenever they were on clearance prices for my music synthesizer projects. They come either unmarked, or with a seemingly random 3 digit number on the side. Most of them worked, but I had to test them all to find ones that matched and worked in my circuit. My guess it that they were factory rejects. Their old stock number was G15396, but it doesn't work now.
Cabintech Global sells the Xvive optocouplers. I purchased 3 X VTL 5C3/2 dual optocouplers from them about 2 years ago for a eurorack synthesizer filter module kit. They worked fine. I have been buying their synthesizer chips for a few years and never had a problem. They don't list the number you are looking for, but an email wouldn't hurt.
https://cabintechglobal.com/semi
Stomp Box Parts (guitar pedals) has the VTL5C9 in stock but wants $10+ for them. I have never bought parts from them.
There is also a LED / phototransistor version, most of which are used as an isolated current controlled high speed switch. These usually come in a typical DIP or SMD package. They were generally not used in the linear region. Some devices brought the base pin out to allow for bias, or used a mosfet as the controlled device for linear operation, but these are rare.
The included schematic just shows a variable resistor so the device is likely a CDS based cell. Attempts to use a transistor based coupler will likely be futile.
I bought lots of the surplus optocouplers from Electronic Goldmine whenever they were on clearance prices for my music synthesizer projects. They come either unmarked, or with a seemingly random 3 digit number on the side. Most of them worked, but I had to test them all to find ones that matched and worked in my circuit. My guess it that they were factory rejects. Their old stock number was G15396, but it doesn't work now.
Cabintech Global sells the Xvive optocouplers. I purchased 3 X VTL 5C3/2 dual optocouplers from them about 2 years ago for a eurorack synthesizer filter module kit. They worked fine. I have been buying their synthesizer chips for a few years and never had a problem. They don't list the number you are looking for, but an email wouldn't hurt.
https://cabintechglobal.com/semi
Stomp Box Parts (guitar pedals) has the VTL5C9 in stock but wants $10+ for them. I have never bought parts from them.
Yeah, let the others do the work for me. You don’t think I saw those options, even Digikey sells a similar option, but all of those you pointed out have vastly different specs. Doesn’t even have close to the same on/off resistance nor rise and fall time. I talked with a McIntosh certified tech and he emphasized how important it was to get the right optocoupler. You come in with an insulting tone yet can’t even link to the correct devices. In my first post i specified i was looking for these specifically or something with similar specs. What you posted isn’t what i asked for. I saw the SNL devices at Digikey before coming here, do you think i would have come here if they fit the bill? Sorry to be blunt.
Dan
Sweet suggestion, I’d love to build my own! I’ll have to take a look at cells. As I mentioned earlier, I was told that the specs of the optocoupler were pretty important. Being that the cells you linked have an on resistance of 1k and off of 10kohm, I wonder how that would affect the circuit with the originals having an on of 1k and off of 2 megohms. I’m guessing rise and fall time would be dependent on the LED?
I’d love to see some pics. Looking at the schematic above, what’s your opinion of the changes made? I was told by two separate individuals that the optocoupler used was a pretty special device. Maybe not???
Dan
I did a similar thing.
The amp powered on ok but when I unplugged my soldering iron the glitch down the mains got into the amp and put outputs into breakdown region.
I bought in some parts from RS Components and 2 years on the amp is still working fine despite lots of mains noise.
Some stuff from China is ok. I bought some ad9220's for £1.50 each, they were £15 + vat in the uk.
Worked fine.
I really appreciate the input. I’ve run into the photo transistors in some tape players. I’ll probably go with the ones at the stomp box parts unless I can find the parts to make my own with similar specs. I’m always down to go the diy route.
Dan
If you intend rolling your own, there are several parameters that need to match. The first is the material type. The VTL5C9 is material type 1. That apparently defines the basic characteristics. But the VTL5C9 and VTL5C10 are both type 1, but have different characteristics (resistance vs diode current).
From my 1997 data book on phtotcells and Vactrols, photoconductive cells are type 0 and type 3. That may have changed now, but rolling your own needs to be done with care.
Presumably the type numbers refer to doping levels in the photocell.
Beyond that I can't help further. You seem to have as much data as I - so over to you.
From my 1997 data book on phtotcells and Vactrols, photoconductive cells are type 0 and type 3. That may have changed now, but rolling your own needs to be done with care.
Presumably the type numbers refer to doping levels in the photocell.
Beyond that I can't help further. You seem to have as much data as I - so over to you.
LEDs are fast in both the on and off times, MHz kind of fast. It's the CDS cell that's slow. Their resistance drops reasonably quickly when light is applied, but may take tens of milliseconds to decay when the light is removed. The decay time is not linear either, so time to return to the original "complete darkness" value from being in a bright light can be minutes.
I got a bunch of CDS cells from the Electronic Goldmine to play with several years ago. I was looking at using ambient light for a unusual pedal type device to control musical things like the VCF in a music synthesizer for a "ghost operated" Wah-Wah pedal, or the VCO for theremin sounds. In most uses the repeatability was just too random, but I did experiment with putting them in the guitar body for changing parameters with guitar movement. The attack / recovery time differences are quite apparent when playing with these cells. Two or three of the same cells can be quite different but again, they might be factory rejects. Many of the cheap surplus cells are slow enough that 60 Hz modulation of the light is not much of a problem, but much of my basement lighting is Walmart grade shop lights that use SMPS.
VTL5C8,9 and 10 have higher voltage drop LEDs, probably with higher light light output at same current yielding lower resistance in photocell
What I understand is that the coupler is used in a tube amp to modulate sound between stages?
Building an equivalent circuit will be tough.
And it does look like a selected in quality type part, so look around and get one for a reasonable price, $10 is 6 minutes of tech time at $100 per hour.......
Building an equivalent circuit will be tough.
And it does look like a selected in quality type part, so look around and get one for a reasonable price, $10 is 6 minutes of tech time at $100 per hour.......