Classic Hifi Care

Remember that in the old days a lot of LPs were equalized with reduced bass so they would track on cheap players. It may not be fair to compare old LPs with modern signal sources.

The color code is here:

https://service.shure.com/s/article/col ... dge-wiring

Hard to tell from the photo, but it looks like your wires are soldered to the cartridge?

Chris Campbell

Well, after taking those pix, I tried another record, sounded better, but no left channel, fiddling some more, must have had dirty contacts on the cartridge! Sounds great now!

Still have the ac cord question....

I don't see any advantage in using a three-wire power cord. The chassis has a power transformer that isolates the chassis from the line. I used a larger power cord on my Concert Grand than it had originally, since I felt the small-gauge cord it had originally might be being overworked. Some guys get caught up in the "thick blade, thin blade" nonsense of having polarity on the power cord just so, but my thinking is the power transformer doesn't care.

Thanks for the link, Chris. That white thing is a plug into the end of the cartridge, so it'll come out. I'm probably going to coax it off, and put some deoxit on the pins so this issue doesn't crop up again!

Sonotone 9-T type on the left of photo.

Thanks for the diagram, Mogul! Deoxed cartridge contacts, sounds great now. Funny how dirty contacts caused poor fidelity, instead of something more intermittent.

I decided to put the Bluetooth adapter inside the cabinet, under the changer; my experience with it so far is that it's pretty hands-off, it just connects automatically to my phone whenever its power is on. I am using the switched ac outlet for the 5v adapter, makes for a very convenient setup! Regarding the power cord, I measured about 5 microamps AC leakage when shorting between floating chassis ground and AC power ground, so I guess that means there is some slight leakage in the power transformer, but that may be normal. I've never felt any "tingles" while working on it, so that's a good sign! However, I suspect the PT has overheated at some point in the past. So to be on the safe side, I'm going to use a grounded power cord, green ground to chassis, not worried about the hot/neutral issue at this point, as Electra225 says.

stbasil wrote: ↑Thu Jan 16, 2025 9:14 pm Thanks for the diagram, Mogul! Deoxed cartridge contacts, sounds great now. Funny how dirty contacts caused poor fidelity, instead of something more intermittent.

My living room amp is an older Denon with pushbutton source selection. The button contacts are dirty and need a lot of fiddling sometime. But t get it out to clean up, I will have to unplug one turntable, one cassette deck (inputs & outputs), one CD-R deck (same), one CD playback deck, and a tuner. Too many cables to get back in order, and it all has to be done from the front with the amp pulled almost all the way out. It is daunting so the project always bumps down to the bottom of the list.

Chris Campbell

Sometimes there are hum issues with AC polarity. Polarized or 3-prong plugs won't let you reverse the plug, but you can lift the ground and reverse the plug by using a 3-prong to 2-prong adapter with prongs ground to the same size.

Chris Campbell

When I removed the woofer a few weeks ago to begin working on the cabinet finish, I noticed that its "phasing dot" was connected to the ground wire, which is the opposite of the other speakers, and also the schematic. Since somebody miswired one of the tweeters at some point in the past (see above), I figured that might be the case with the woofer. So last week after I had put all the electronics back in the cabinet, I decided to check this out. I have seen woofer phasing discussed on this and other forums, so I expected that it could actually be wired correctly--however, it disagreed with the schematic so that was questionable. To test, I rigged up a wiring jig between the OT and the speaker using a DPDT switch to allow me to instantly do an "in-out" phase test while listening to some various types music from the front of the console. I used stereo sources from both phono and Bluetooth, mono sources were a little harder to detect differences. I am defining "in phase" as the phasing dot connected to the high side of the OT as shown on my schematic (Vibrasonic setting was zero while testing).

The sound effect switching between phasing was subtle to me, and did not appear make a noticeable difference in the bass, but when in the "in phase" switch position, sometimes, depending on the type of instruments, some of the the mid-range content almost disappeared, and I could also detect a slight "inside your head" effect which I have experienced in the past when stereo speakers are out of phase. So, for whatever reason, the woofer is apparently supposed to be "out of phase" as far as the phasing dot is concerned, and not as shown on the schematic.

Perhaps it's the harmonics of the bass that are above the 200hz crossover that are impacted, since they would originate from the other speakers and maybe they tend to get cancelled out if the woofer is connected "in phase".

I wish my hearing was that good, I have inherited hearing loss on both sides of my family so I doubt I could tell the difference even with my hearing aids which are a blessing and a curse. It kind of makes sense with the woofer being out of phase and I am sure there are others here on the forum that will be able to provide some reasoning why. I am not that smart to understand the why.

Bill

The midrange is where the woofer and the mid or high freq. speakers overlap some. Of the two or three speakers are out of phase they will tend to cancel each other in that overlap range.

Chris Campbell

My Fisher Regent blew a 5" midrange a few years ago , when I replaced it I saw that the woofer was wired out of phase... I too thought it was a mistake , then I removed the cover on the other channel and that woofer was out of phase as well, I read on the Fisher forum on audio karma , that this was done at the factory as Chris noted to prevent cancellation , I guess you would need special equipment to see it one way or the other

Your ears are best guide.

Chris Campbell

Moved this baby into the living area, in a temporary location for now. As I'm writing this, the console is on the opposite side of the room, facing away from me, behind a couch. Loaded up with some big band records, it sounds fantastic, really fills the room with sound! My wife loves it, we just have to figure out how to arrange things. It's really cool how much real metal parts there are in this thing--cast, chrome-plated trim and plaques, metal levers on the turntable, metal knobs on the electronics, etc. Hardly any plastic! I plan to move the 1948 Olympic to the garage to work on it some more, maybe add a Bluetooth adapter, and sell it.

So, here are a few pictures:
Top, before restoration, so you can see how damaged it was: Some other views: Notice the little orange pilot light! Of course, after all this, the FM stereo light is now not lighting up, and FM sound is clearly mono when in the stereo position. It has worked flawlessly for weeks, but something in the MPX chassis must have gone south, gotta figure that out. The lid is still a little warped, I have weighted it in the opposite direction with a heating pad underneath and that made a significant improvement over the last few weeks, but looks like it will need a little more coaxing!

It looks beautiful and if looks say anything and from what you just said the sound must be fantastic. I think stereo lights not working is a Motorola thing. My Motorola B1000 stereo table radio goes off and on when it feels like it, and yes, off is mono and on is stereo, sometimes.

Bill

I have a Technics receiver, an alley find, that lives in the garage shop. Its FM stereo gradually failed. Somebody suggested fiddling with the stereo switching threshold adjustment pot, as the contact point may have oxidized. Mark the position before fiddling, of course, unless you have signal generators and such to do alignment work. I have never got around to it because the receiver lives in a high cabinet and there are a cassette deck and CD player on top of it.

But my plan, if the opportunity presents itself, would be to try to slip some thin paper under the pot wiper (a lot of those board-mounted adjustment pots are open) as a very fine abrasive. Maybe dot some DeOxit on the paper.

Chris Campbell

Unfortunately, Chris, there is no adjustment pot on this version of Motorola's MPX, even though it is shown on the sticker! It's an HK-54-1, There's a Sam's for this thing, but I don't have it--I've got three different MPX schematics, but not that one. Well, the light now comes on, but it also lights between stations, so I suspect a flakey component in the MPX. At least it's readily accessible! I'll look into that in a little while, my schematics are close enough to be somewhat useful.

What is the HS-xxx number on that MPX unit? I have the same one and probably the factory version. I need to scan this for a download.

HS-996 is same chassis in my SK112, which I just confirmed behaves the same way. On the one mono station I could find, it goes out, FM stereo is indeed stereo.

Off station with just static, the neon indicator is flickering due to random noise triggering a pilot indicator?

I call mine a "mono indicator" light - LOL

Mine is HS-996 also, but that's not sufficient to describe the circuitry apparently. I just uploaded a description and schematic for reference. Unlike the upload, mine doesn't have a pot, uses diodes instead of a 6AL5 for the detector, doesn't have the extra inverted output, has a different stereo indicator circuit, etc, etc. Other schematics are similarly different from my unit, I know because I have traced wiring and found disagreement all over the place! There is a Sam's listed on UK eBay for the 54-1 version, and the picture looks like mine, but who knows what the schematic looks like!

The operation of the indicator light seems random. Sometimes it works perfectly as expected, sometimes it won't light on a good stereo station, sometimes it lights with just noise outside of stations. Doesn't respond to tapping and jiggling various stuff, so maybe it's a drifted or intermittent component.

Here's the back of my MPX chassis