Hi, I have a WM-DD30 that has a background noice I haven't been able to solve. It seems like it's related to the motor as it changes frequency when restricting the motor movement. It is independent of volume level and disconnecting the cable to the head makes no difference. I have replaced all electrolytic caps. Apart from the background noice the walkman works and sounds good. WF is great. Here is a sample of the noice: https://soundcloud.com/rune-lindman...d&utm_medium=text&utm_campaign=social_sharing Anyone have any idea where to look? Could it be the motor that is faulty? Is it the same motor as in the 1st gen DD?
I have seen this before in DDs, it's motor hum: it is caused by some unevenness in the motor rotation, which in turn is caused by intermittent friction inside the motor. This unevenness will create some back EMF, which will be conductued through the power supply line and get into the supply line of head preamp/headphone amp. This is why disconnecting the head makes no difference at all, because the interference is not radiated (the motor is shielded), but conducted. Now, older generation motors can be disassembled and repaired sometimes, while newer generation ones cannot. You can try increasing C316 from 1μF to 10μF to improve the power supply decoupling and see if it makes a difference. Motors are the same in almost all DD range: WM-DD, WM-DDII, WM-DDIII, WM-DC2, WM-D3, WM-DD100, WM-DD30, WM-D33. The ones that are different are the DD1/DD10/DD11/D22 and the DD9. In regard to wow&flutter, what do you mean by "WF is great" ? It's great by ear or have you actually measured it and it's within the 0.08% WRMS specification ? Motors which have this symptom will have the w&f increased a bit, but usually not by much. Something like 0.1% instead of 0.08% which will still be inaudbile. For reference it is to be noted that there are DDs where the symptom is just an increased wow&flutter without any hum. It's also to be noted this symptom can be dependent on volume (interference happens in the head preamp) or independent of volume (interference happens in the headphone amp). However the root cause is the same regardless. At the end of day, it depends how bad it really is. Does music cover it or not ? My opinion is if it's not loud and the music covers it, just leave it as it is. If it's a serious issue and w&f is also increased, then replace the motor. If w&f is within specification, then try replacing C316.
@Valentin many thanks for your reply. I measured W&F to 0.07%. using WFGUI. I also tried to swap the motor as I had one laying around but that didn't make any difference though I cannot say for sure the other motor is ok. I haven't tried to swap the capacitor as I don't have a suitable at hand. Wouldn't the effect of the EMF vary when flipping the PCB out of the way of the motor? The noice is very consistent no matter what I do. I would say it's not bad, mostly got hung up on finding the cause of this more out of curiosity than necessity. Using my calibrated DC2 with Dolby C recordings on good Chrome tapes have spoilt me with silence. I will leave it for now, maybe try the capacitor change later on.
The back EMF is conducted, meaning it's a singal that goes through the motor wires, not an RF singal (radiated). So flipping the PCB won't make any difference, since this back EMF travels through the motor wires back into the circuit. Given the wow&flutter is at 0.07% WRMS try to replace that capacitor with the larger value. Also check that the grounds are fimrly connected: motor mount to mechanism chassis and chassis to PCB. A high impedance path through the ground can also cause such a problem, so it's something to be double checked. By the way, what current draw do you have with unit in PLAY and no cassette inserted ? If you find a cause different than the 2 I already mentioned, please share it with us. But the hum is related to the motor and the unevennes heard in the hum does indicate uneven friction, otherwise there will be a cosntant hum. It is to be mentioned I did replace the motor on some units with this problem and it did fix the issue.
Current draw is 80mA@3V. Good point regarding ground, I will check it. The noice is lower after last assembly time which could point to screws not making good enough contact.
Current draw should be 70mA (at 3V, although it won't change much with a lower voltage). A higher current does indicate the motor has increased friction. With a perfect motor, the walkman will have a current draw almost exactly equal to the spec or even lower. The increase of 10mA might not seem like much at all, but even a 5mA higher current draw does indicate higher friction than perfect and can cause a bit of hum. So assuming you have tested both motors with PCB connected to chassis ground, I have to assume both motors have increased friction (which is definetely possible). Only things that remain to be done are to clean the PCB ground connections, tighten the screws well and eventually replace C316. The motor, if it's the newer one (branded NAMIKI) cannot be opened. However you can lubricate the front bearing if you have not done so already. Even the older type is quite tricky to open without any damage and even trickier to put back together (it also requires an adjustment when putting it back), so it's something I can't recommend unless you are very confident in your skills. However as said previously, if the hum is not loud enough to be audible with music, you can use the walkman as it is without any concern.
Btw how can I find out what the current draw should be for specific models? The dd_repair_guide states: "Normal consumption is 80 – 130 mA, depending on model of walkman used"
You can find the current draw for specific models in their respective service manuals, it's written on the schematic near the DC in jack symbol. The specification is without a cassette inserted or headphones inserted. I attach a screenshot of the DD30 manual section with current draw. The DD repair guide is giving a general guideline, not precise values.
I did read about what all did wrote back to you Rune L. I do agree in what all write but one thing that i did think was importen to also check is the tape head in your walkman for magnetisme (magnetic sound) this sound will come if the tape head have magnetisme. You can demagnetise it with a demagnetise tool or tape that is made for this. Mobile phones or other magnetic device that is close to the walkman can do this. A cassette walkman is sensitive to friction and magnetisme. I have not listen to your walkman when it play so I cant be sure exact the problem but I dont want to rule this out as well. A tip is allso to clean the tape head to make sure it is clean of dust and dirt. I have experience magnetic static sound on walkman and fixed this but so far i have not service any DD with this yet.
@RetroTech I will give it a try but I’m not very hopeful that this is the cause. @Emiel That is a great table!
