Hello Folks. I'm trying to get some new ideas on how to replace that felt/fiber friction washer that places a drag on the take-up reel. I do not favor this type of clutch vs. the magnetic ones on some of the other Sony's. I had purchased a WM-150 that I started working on. I'm waiting on a replacement gear from China at the moment (no one else sells them) and trying to figure out how to remedy the slipping clutch. I initially cleaned the felt washer with 99% isopropyl alcohol and then took a tiny pick to sort of lift the nap. I did replace a cracked clutch gear and slightly stretched the metal spring. All this did absolutely nothing, the clutch still slips too easily, that felt washer is pretty much shot. How are you folks making this repair? Seems no one is selling this need material, essentially a 0.5mm non-woven compressed felt sheet. Cheers. -Norm
What's the symptom, very low takeup torque ? Note the reel gears are also failing in WM-150-type mechanisms and need to be glued or replaced. How have you figured out the clutch felt pad is the problem ? It's not something I've seen on this mechanism and restored many of them. An alternative solution is to remove the felt entirely (assuming it is indeed the problem) and put very high viscosity grease there instead. However this is a compromise solutiuon because the takeup torque will become highly dependent on temperature. Quantity of grease also has to be fine tuned to obtain the correct torque. You say extending the spring did absolutely nothing and clutch slips too easily. When rotating the 2 parts by hand, is there any resistance at all ?
Hi Valentin. Thank you for your reply. The symptom is very low take-up torque, not enough to pull the tape causing it to wrap around the capstan. The forward reel gear was indeed cracked, a replacement is on the way. The reverse reel gear is in tact and the tape did try to play in REV play mode but at some point the take-up reel begins to slip too much causing the tape to wind around the capstan. I'm guessing at this point, the felt pad and perhaps the plastic clutch disc has compressed and/or glazed too much? I will try to take a 3000 grit sponge to ever-so-lightly rough the plastic disc. I've read that someone tried applying rosin [the kind that you put on violin strings] to increase the friction but an AI search recommended against it. When rotating the two parts by hand, there is little friction. One small caveat, and I should have mentioned it earlier, the clutch spring was from a Panasonic RQ-SX70F. The WM-150 was bought as a parts unit and didn't have a spring. The Panasonic spring was the same size and fit right in. I just don't know if the gauge of the springs are the same. I may also try to make a new spring from a guitar B-string to increase the friction. Cheers!
The clue with the spring is important. I wouldn't focus on the felt pad or plastic disc surface, don't think the problem is there. The stiffness of the actual spring is by far the biggest factor determining friction in the clutch assembly. The friction coefficient of that surafce cannot be modified significantly by sanding it to make the surface rough or by adding rosin. The headroom is little, you can't increase it 5x by doing this. Rather what I think happens is the spring is simply too light and even elongated it just doesn't apply enough pressure. RQ-SX spring is much lighter, as the clutch itself spins much faster. This is another variable: stiffness of the clutch and clutch speed are inverse proportional. To increase the takeup torque one can either add more clamping force (stiffer spring) or make the assembly rotate faster by changing gear ratios. I think only fix is to either find the correct spring or make one with correct wire diameter (which is thicker than the RQ-SX one).
Thank you, Valentin, for pointing me in the correct direction. I will focus on the spring. I will attempt to remanufacture from a guitar high E or B string. I have successfully made one in the past for another parts unit that was missing one. I got lazy this time and grabbed an available RQ-SX spring that I had laying around, clearly not a good choice. Cheers. -Norm
Let us know how it goes. This clutch should have some resistance when rotated by hand, that should be the target. Like not hard to turn, but a fair amount of resistance.
Here’s an update to my WM-150 repair. I did fashion a clutch spring from a guitar B string. It worked well enough. Having said that, I did end up buying a compatible donor unit and used that clutch spring. The WM-150 is fully functional now. The azimuth is slightly off. Unfortunately, this unit does not allow for azimuth adjustment. But, it does sound pretty good. Overall, I’m pleased with the results. Cheers! Norm
As a side note, it does not sound so good with my Koss Porta Pro. It does sound fantastic with my Grado SR60 with the DBB in the mid position.
Azimuth is slightly off on one side or both ? Suggest reading this thread: https://stereo2go.com/forums/threads/the-key-to-perfect-azimuth-in-both-directions.10735/#post-88753
Thanks, Valentin, interesting article. The azimuth is slightly off in both directions. If listening to a cassette, you really wouldn’t detect it as the higher frequencies are not muffled, there is good detail and separation. But, the oscilloscope reveals all. Cheers. Norm
If it sounds good by ear I would leave it alone. Fact the L and R are not perfectly in phase on the scope doesn't necessarily mean there's a problem, especially on such units. Even SONY manuals allow 3 Lissajous patterns regarding this. In my opinion a more conclusive measurement is to measure the frequency response using a white noise tape. If that is flat with the rolloff corresponding to specification (18kHz @ -3dB, allow some margin here) everything is fine.
Thank you, Valentin, that is great advice. The more restore projects I do on these Walkman's, the more I use the 'listening' test. While there is great satisfaction in doing a restore project achieving factory numbers, sometimes it becomes an exercise in futility. As you aptly say, if it sounds good by ear let that be the final factor. Cheers!
Yes, I would add even more so if it sounds good with Dolby (on a known-good Dolby-encoded tape) that's the definitive test. Such walkmans won't have the azimuth stability of a dual-capstan deck, but nor is that needed to sound good.
I’ve very recently changed my opinion about Dolby. Maybe all my equipment is in need of Dolby calibration? I’ve found there is less compression, better dynamic range and more clarity when recording with Dolby off. A bit surprising to me as I’ve been a big Dolby fan all through the years.
Hard to say as I don't know what equipment you have. But generally speaking the tapes need to be recorded on a deck that's capable to calibrate on the individual formulation used. Also azimuth matching between the recorder and player is critical, even mismatches that would sound ok without Dolby can become obvious with Dolby. Hence my previous remark. Dynamic range should not be affected with proper encoding/decoding. Dolby B should render the same dynamic range as without it, while Dolby C will actually increase the dynamic range. It's to be kept in mind cassette itself tends to have some rolloff on both ends and having that extra hiss can give the (false) impression it has more high end and more clarity. The only potential artifact Dolby can create is the known breathing effect (noise modulation), but this shouldn't be audible with good encoding/decoding.
My recording deck is a Yamaha KX-630 that I partially serviced - new belts/pinch roller, clean/lube, demagnetized, speed and azimuth calibrated with test tape and oscilloscope. I did not touch the Dolby calibration. The Dolby capable Walkman's that I've tested with [WM-DD33, WM-DDII, and WM-150] were all serviced [clean/lube, electrolytic caps replaced, belts/pinch roller replaced, adjusted speed/azimuth, demagnetized] with the same test tapes and oscilloscope. Also, did not touch the Dolby calibrations on them as I don't have a Dolby test tape. So, perhaps, my Dolby calibrations are indeed off on all my devices? The ever-so-slight hiss that I do hear in between songs, doesn't bother me at all, especially since I am getting noticeably more engaging sound with the Dolby off. At some point, I suppose I'll get a Dolby test tape and pursue the Dolby adjustments. Thank you for sharing your insight. Norm
The Yamaha KX-630 only has a coarse bias adjustment, not a full calibration (level + bias). So right from the start this deck will only render good resullts with Dolby encoding on the specific tape you internally calibrate it on. It's no wonder the tapes recorded without Dolby sound better. The external bias adjustment can help to a degree, but you need a test tone in order to properly adjust it. And even so the levels will still be off on any other tape than the one used for internal calibration. You really need a deck with full external calibration (record sensitivity + bias and prefferably integrated test tone generator) or with auto calibration. In regard to players' level adjustments, DD33 doesn't have any so that one can be taken as a known-good reference. These have perfect levels, I checked that myself on a few samples. DDII needs to be cheked and adjusted if necessary (usually some adjusment is needed). Same with WM-150. While it is worth buying a Dolby level tape, in your case the main problem is the recording itself. When you have a properly encoded tape you may be surprised how good Dolby-encoded tapes can actually sound.
Thanks, Valentin. I have a Nakamichi CR-2a in the queue for restoration, I know it is an entry level unit. What is your opinion of that tape deck?
The CR-2a has the same limitation as the Yamaha, only an external bias adjustment. You have 2 options if you want properly recorded Dolby tapes: 1. Either stick to one forumulation and calibrate your decks to that. 2. Get a deck that has autocalibration or full manual calibration so you can calibrate on the individual formulation you're using every time. Do keep in mind for a deck to have these adjuments doesn't have to be high-end or expensive.
