RUNNING AN APPLE

So let me address all the issues and questions raised !

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In post #3, macintosh_nik wrote:

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"The topic of alternative power sources is very interesting to me. Our mains voltage is 220v, I, like many people in Europe, use Hammond 186D10 and 186D28 transformers. "

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聽"Very cool "pigtail" connecting the board and power supply, I like it."

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Uncle Bernie answers:

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I know ! It has been a huge problem for me. This is why my lab runs from a huge isolation transformer sourcing聽 110Vac and 220Vac on its secondary side. So I can use equipment from all over the world, and I can touch line voltage powered items on the lab bench without getting an electrical shock - it's only safe however if the old rule is followed to only use one hand/arm at a time, never two.聽Every professional learns this rule (and others).聽 For typical hobbyist types, it is not advised to do these things that way, but for professionals it's not always inevitable to work on "live" high voltage powered items.

As for the transformer conundrum, in my "Tips & Tricks" I recommend TRIAD "World Series" transformers which have a split primary winding with four pins. You can put these primary windings in parallel for 110Vac operation and in series for 220Vac operation. This is a very flexible solution because you can configure the line voltage input with four pins and then plug in the聽different line cords, which then select the series or parallel configuration.

Modern switchmode power supplies however can be fed with a wide range of line voltages, i.e. from 90Vac to 260Vac (or even DC). Which makes them "universal" they work anywhere in the world and they are ideal for places with a third-world standard power grid (such as the People's Republic of California). They have a big filter capacitor in their input circuit which has the benefit not only being able to kill you if you touch it, but it also allows the switchmode power supply to "ride" through brownouts.

So use of switchmode power supplies has merits !

About the braided cable between the PSU and the Apple-1: not only does it look nice, but it is also robust, still flexible, and it stays put. It is also cheaper in terms of materials (no heat shrink tubing which is expensive). So I recommend braiding such wires !

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In post #4, brouhaha wrote:

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"Some linear regulators (78xx, etc.) can be damaged by having the output powered but not the input. This varies by manufacturer, so cannot be determined solely by the part number".

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Oh, I know. I worked as an IC designer聽for that famous semiconductor company which is known as "the switchmode power supply IC company with an attached luxury shop for precision analog ICs at boutique prices".聽 I know regulator ICs inside out, literally, at the transistor and layout level. Guess what the two weeks of daily work in my lab were for ? I characterized every aspect of every suitable regulator I found in my lab, but with emphasis on the regulators I furnish with my IC kits. They are all from the same manufacturer and the same production lot. They were found fit for this type of application. Some regulators from other manufacturers failed my criteria. Unless you are willing to repeat my tedious lab work,

DO NOT ATTEMPT TO USE ANY REGULATORS NOT FOUND IN MY RECENT KITS FOR THIS DIRECT FEED METHOD !聽 BE WARNED !

However, these operating conditions do also exist in any normal application when the power is turned off and there is a sufficiently large bypass capacitance on the output of the regulator. This is what happens: the power is turned off, the voltage on the input of the regulator drops, depending on the size of the input filter capacitor and the load current, and when the input/output voltage difference drops below the "dropout" voltage of the regulator, it enters the dropout region of operation where it can't keep the output voltage constant anymore, and despite the error amplifier tries to turn the series transistor up, it won't source enough current anymore to the load. At this point, the output voltage of the regulator starts to collapse. Where it gets interesting is when the output side has a large enough capacitance such that the input voltage of the regulator collapses faster than its聽output voltage.聽 This is reverse mode operation which is abnormal. As it can only happen under specific and rare conditions, which almost never is the case unless the input voltage is suddenly shorted to ground,聽聽and聽there is a huge capacitor on the output side, early three pin linear regulators could get damaged and destroyed by this "reverse mode". It was simply a design oversight.聽 This problem was mitigated by adding the聽"reverse" diode you mentioned in the application notes. It protects the regulator from the "reverse mode" condition. Now, if you draw the circuit of the Apple-1 power supply and add a connection聽from the J1 pins 1 and 2 to the output side of the LM323K, you can see that the rectifier diodes will turn into these protection diode configuration, and all is good.

I agree with your statement that the inner circuit of the regulator IC may vary from manufacturer to manufacturer, even for the same type number. But once an IC is put on the "Released Product List", no manufacturer will ever change the inner circuit without notifying the customer(s) and without mentioning the change in the datasheet. These changes are extremly nasty and have huge repercussions as the ICs typically will need to be re-qualified in the customer's application(s). This process聽involves a lot of expensive lab work at the customer. To avoid, customers would prefer to just blacklist this IC from this manufacturer and use second source parts instead. So IC manufacturers avoid such running changes of a RPL'd product like the plague. They rather make an "improved" version with a slightly different type number instead, to address issues, but they won't change the original part unless absolutely necessary.

So I'm confident "my" regulators will not cause nasty surprises. I have overstock and would sell them as sets (no other ICs/parts) if need be.

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In post #5, Ronin47 wrote:

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"That looks suspiciously like the Meanwell PT-65-B"

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Uncle Bernie answers:

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It is a "Mean Well" PT-65B which is available from distributors all over the world.聽Thanks for providing the link to your 3D printable case !

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In post #6, Corey986 wrote:

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"I think running that聽switching supply would make the ACI not work very well if you had -12V. "

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Uncle Bernie answers:

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I tested all my ACIs with this configuration (the LM311 based original circuit and the 741 based circuit copied from the Apple-II) and all worked well, despite running from -12V coming from the switcher. No increase of volume was necessary. The performance / reliability of the ACI was as before, no noticable difference, perfect with AIFF files from a sound card / notebook (both recording, playback, and synthetic AIFF files were tried), and the usual mediocre performance with a real cassette recorder. You mileage may vary, though.

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Despite I have spent a lot of time in my lab testing and investigating the ACI, I never really got to the bottom of its lousy performance and its sensitivity to the negative supply voltage, which definitely is there and can be observed both in the Apple-1 and on the lab bench. The irony is that neither the LM311 nor the 741 should have any influence of the negative supply voltage per se, as long as it within the bounds where the comparator / opamp can do its job. If you don't believe me, just study the transistor level circuit of at least the LM311. There may be, however, influences of the power supply once the input differential pair is unbalanced. I have some ideas on what could be going on, especially when considering that the unregulated V- supply on the 44-pin bus has a lot of ripple coming from the rectified AC. If you reduce the AC voltage using a variac, the ratio of the DC content and the ripple changes. This may be the reason why we see an influence of the magnitude of the negative supply voltage and why some people believe聽聽the more voltage, the better. But this is speculation. I never had the time to really get to the root cause. And since my ACIs work fine with a sound card, and my cassette recorder has poor quality replacement drive belts made out of Chinesium, so I hate to use it anyways, any further investigation of the ACI topic has no priority for me. I have more important things to do. But if I ever get bored (maybe this Winter ?) I might look into the ACI again.

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Hope now all the concerns have been properly addressed !

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Nobody so fas has commented on the electrical hazards less experienced hobbyists might be bitten by if they try to do this. One 3D printed isolation case was contributed by Ronin47. But would them fools - which certainly exist even among the elite group of Apple-1 builders - use such a insulation case all the time or would they fool around and get killed (or fry their Apple-1) ?聽 This is my biggest concern. Technically, my proposed "direct feed" method is sound and it works. I now run two Apple-1 with it 24/7.

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Comments invited !