Why did Philips Use These in 1977? The GA-312

[00:00:00]This vintage Philips turntable uses touch controls like an iPhone, but it does it in a uniquely 1970s way. This thing is fascinating. The engineers made a lot of interesting interconnected decisions when they designed it, which I am genuinely excited to show you because I think it's really interesting to know why they did what they did. So, stick around. I think you guys are going to really enjoy this one.

[00:00:21]>> [music] [music] >> This is the Philips GA 312 [music] or 312. It's about as 70s as you can get down to the real wood veneer and this beautiful smoked acrylic dust cover. And I really like all the nice machined aluminum pieces that they use for the tone arm and the adjustment controls.

[00:00:44]It's really quite a handsomely designed piece of equipment, but that's not why I want to talk to you guys about it. It's full of a lot of unusual, let's call it, design choices.

[00:00:55]By far the most interesting part of this turntable is the touch control for the start and stop. For a couple of reasons.

[00:01:01]Number one, they are touch controls in the 1970s, which is something you don't find on most stereo equipment from this era, especially turntables. But, also how they work is really kind of a time capsule. I see these referred to as capacitive touch controls in a lot of online discussions. And while it doesn't really matter what they are since ultimately the point is that there's no button to press, calling them capacitive is not technically correct. These are in fact resistive sensors, not capacitive.

[00:01:28]And you can tell that from the way that they operate. The concept is simple enough. You touch your finger to the sensor and the platter starts and stops.

[00:01:35]But, if you notice, there are two concentric silver rings. That's not just a design choice. Each ring is an electrode. So, when your finger touches both of them, it's actually completing the circuit and triggering the internal logic just like a regular switch. And you can also do it with anything else that's conductive, like a screwdriver or a pen. I realize that may sound a little bit scary if you've never heard or seen one of these before, but you don't feel it because it's an absolutely tiny amount of current. But, it does conduct through your finger. I can show you with my multimeter. When I touch the probes, it actually registers a few megaohms instead of nothing, meaning it's able to detect a little bit of electricity passing directly from one probe to the other via my skin. And that is enough to trigger the sensors on the turntable.

[00:02:18]Capacitive sensors do not need to complete a circuit through your skin in the same way and can operate with a single electrode whose total charge changes when your finger touches it.

[00:02:27]That's important because if we touch the sensor carefully, you can see that it doesn't actually do anything when you only touch one of the rings. You have to touch both. A capacitive sensor would register if you only touched one of them. That begs a few questions. Number one, why does it matter, right? Number two, why choose resistive over capacitive touch sensors? And number three, why do any of this at all when most consumer turntables were using normal buttons at the time, which were perfectly functional?

[00:02:57]Well, let's start with number three because it's kind of an overarching theme for this entire unit. The goal, theoretically, when you're designing and engineering something like this is to make it sound the best it can within a given budget. And ideally, in a way that's better than your competitors, obviously.

[00:03:13]In service of that goal, the engineers that designed this turntable leaned into something called high compliance cartridges.

[00:03:20]Trust me, this will eventually circle back to the sensor question, but just go with me on this for a minute.

[00:03:25]High compliance is, in a very simplified nutshell, an approach to building a tonearm assembly where the cartridge, the stylus, and the arm itself are very lightweight and very responsive.

[00:03:36]The idea was the reduction in moving mass would allow the stylus to respond more accurately to the changes in motion associated with the audio signal physically etched into the record groove, thereby more faithfully reproducing the original recording.

[00:03:50]But, that comes at a cost. These types of setups are much more sensitive to vibrations, footsteps, the environment, the neighbors, the cat, and pretty much everything else. So, to effectively implement everything, they saw fit to try to eliminate as many sources of bumping and vibration as possible, including the pressing of buttons on the turntable itself. Hence, the touch sensors. So, we understand why they added them, but why did they use resistive sensors rather than the capacitive sensors which are so ubiquitous today if both exist existed at the time? Well, it comes back to that same design philosophy, performance versus cost. Touch sensors were a very cool feature to have, but the implementation complexity varied about as much as my relatives' political ideologies. To put it plainly, resistive sensors were just simpler. Simple was good at the time because electronics had not been miniaturized and refined into the tiny efficient devices that they are nowadays, and adding a capacitive touch sensor would have required more circuit board, wires, discrete components, labor, and manufacturing time, and therefore more cost. Now, I don't mean that as a criticism. I just find it interesting to know why they made the decisions that they did. Like this, for example.

[00:05:00]It jiggles.

[00:05:02]That's because the entire tone arm and platter assembly is suspended on a few springs, and they actually hang down from the top plate rather than sitting on top of them. And they did that because without a suspension, every little bump and vibration would affect playback. At best, that would manifest in hearing those sounds through the speakers, and at worst, knocking the stylus out of the groove entirely, resulting in a Just for reference, this is my Technics SL-D2. It has a heavier tone arm and lower compliance cartridge, which relied on a little more tracking force and the inertia of the heavier tone arm to resist bumps and noise. The feet themselves have a little give, but the tone arm, platter, and plinth are all coupled together. This setup was simpler to manufacture, less costly usually, and more often than not more robust. But the trade-off was that the stiffer stylus wasn't considered quite as responsive.

[00:05:52]Now, is that actually true? I couldn't tell you.

[00:05:56]Because I spent most of my teens and 20s at concerts twice a week with no ear protection, like an idiot. That's just one box of many full of old band shirts.

[00:06:04]They also did something else I found interesting to that same end. Like most turntables of this era, it's got an automatic stop feature when the tone arm gets to the end of the record. However, it doesn't actually return the arm back to its rest. It just shuts off, leaving the tone arm where it is.

[00:06:19]Again, why did they do that? An automatic return mechanism is exactly that. A mechanism with gears, linkages, springs, sliding surfaces, and bearings, all of which move and interact as the tone arm pivots across the surface of the record. Eliminating those parts eliminates the potential to introduce noise and distortion from all those moving parts that could manifest in those high compliance cartridges. Or at least, that was the intention.

[00:06:45]And of course, it does arguably save cost, too.

[00:06:50]The auto stop sensor is also interesting for 1977. It's optical, which means there isn't a mechanical switch or lever being engaged that lifts the tone arm.

[00:07:00]There's a light sensor that detects the end of the travel of the tone arm without physically touching it to prevent any thumping.

[00:07:07]They used one of these little red LEDs and placed it in front of a cadmium sulfide photoelectric sensor, then used a little tab that blocks the light to detect the tone arm reaching the end.

[00:07:17]That's pretty straightforward. It's the same idea as grocery store conveyor belts or the sensors on your garage door. But, this is what I thought was interesting. The previous generation GA212 used incandescent bulbs similar to these, but they were hot, power hungry, and prone to burning out, which would render the stop function inoperable.

[00:07:36]When they switched to red LEDs, they used the same kind for the optical sensor bulb. I don't know this for a fact, but I would assume that they did that because it makes more sense to use a fourth lamp that they already have in bulk than to have to source a totally different bulb just to operate the sensor when one of the same red ones would work just as well. So, why did they use touch sensors in 1977?

[00:07:59]It was to effectively eliminate as many forms of bumping and vibration as possible to allow for the use of the very sensitive high-compliance cartridges so they could get the best sound they thought possible.

[00:08:10]Whether they achieved that stated goal, I will leave up to you to decide. Let me know in the comments if you've ever used one of these, and if so, what was your personal experience with them? According to a 1977 magazine ad in Hi-Fi Stereo Review, these sold for just under $180, which is about a grand in today's money.

[00:08:27]So, they were seen as a pretty decent piece of equipment back then.

[00:08:30]Also, I want to point out as a companion to this video, I'm going to put up a couple of high-resolution photos of the internal components onto the Patreon so that you can get a closer look at everything that's inside it. If you haven't already signed up for the Patreon, I encourage you to do so.

[00:08:43]There's a lot of cool stuff on there, and there's going to be a lot more to come. So, I put a link in the description for that. Go check it out.

[00:08:50]Let's take a look at what these controls do, though. On the left is your power button. It's got an ironically satisfying click. The touch controls we've been rambling about are your start, speed control, and stop function.

[00:09:02]To start the platter spinning, you touch the speed you want. To stop it, obviously, you touch stop. If you want to change the speed, however, you have to touch stop, or it won't react.

[00:09:11]Touching stop also raises the tone arm if it's down. This toggle is the control for raising and lowering the tone arm.

[00:09:18]It's actually connected to a miniature cable within a stiff sleeve just like a bicycle cable, which is itself connected to a large damper and a solenoid that clicks loudly as well when it operates.

[00:09:27]Something I find a little amusing considering they went to great lengths to eliminate so many other clicking and mechanical sounds. You have separate speed controls for the 33 and 45 RPM functions, which are calibrated by viewing this ring of marks under a regular incandescent light tied to mains voltage. You would just adjust the speed so the little marks appear to stand still instead of shifting to the side.

[00:09:50]To hold that speed steady, the motor has a built-in generator that outputs voltage proportional to its RPM that the internal electronics can use to monitor and maintain a constant speed by increasing or decreasing power going to the motor to keep it outputting as close to a constant reference voltage as possible, thereby maintaining a constant speed.

[00:10:12]Theoretically. This is the anti-skate control. Like most turntables, it's set proportional to the tracking force of the cartridge installed on the headshell. In this case, they have an Audio-Technica AT96E, which is not the original cartridge.

[00:10:27]With a recommended tracking force of between 1 and 1.8 g, it is, however, still correctly paired with a low-mass tonearm. So, whoever upgraded it was at least doing their due diligence, I think. The anti-skate knob allows calibration for round-tip styluses and elliptical ones. This Audio-Technica one is elliptical, which I know simply by Googling it.

[00:10:48]As you can see, they've correctly set the anti-skate to match the tracking force at about 1.5 g in the elliptical setting. In other words, at least they set it up properly. Though, I'll admit I went in and recalibrated everything myself before writing this just to be sure. There's a little curiosity I discovered on the dust cover as well.

[00:11:06]This little rectangle I assumed was missing a badge, that it had fallen off at some point. But, from what I can tell, it never had one. All the dust covers I see on these turntables online have the same little black rectangle.

[00:11:18]So, my next thought was that they used the same plastic mold for other OEM products for other companies, and they would have added their own badges. But, I also can't find any direct evidence of that, either. I did, however, see a bunch of other examples of Philips dust covers with little black shiny rectangles right in the middle. So, it's possible that it's just a simple design choice. Another thing I'd like to mention is this label up here, High Fidelity International. That refers to the family of premium home audio components that Philips was producing which this turntable was a member of.

[00:11:50]Here in the US, that line was also marketed under the moniker High Fidelity Laboratories. Oddly, I wasn't able to find any examples of this particular unit being marketed under that name, which I thought a little bit odd. I'm not going to go through the whole process of how to calibrate and align the tone arm. If you would like to see how to do that on this particular turntable, let me know and I'll make a Patreon video that goes over the whole process step-by-step. I also just briefly want to point out that the RCA plugs and ground connection are hardwired to the body of the record player. I find that to be pretty typical of turntables from this era. In this case, they're about 3 ft long. Though, I'll be honest, I'm not thrilled with the RCA plugs. They feel a little chintzy and I thought for a moment they weren't labeled at all since there were no color indicators, but they do have a little L and R molded directly into the plastic. It's just really small. But, that's all I can think of to say about this thing. I hope you guys enjoyed that. I'm trying to put new content on the Patreon as often as I can, so I encourage everyone to go check that out.

[00:12:48]It's only $6 and you get full access to the repair videos, thrifting vlogs, and DIY projects. I may also include access to a Discord if anybody wants that.

[00:12:57]But, until next time, have fun, keep thrifting, and I'll see you soon.

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