Denon DP-2000

[stratokaster83]

My new turntable project - Denon DP-2000 that I got almost for free because it is, uh, a bit problematic.

Damage assessment: it basically works but is very finicky. When I first got it, it appeared to work perfectly, but apparently it was just a fluke. Yesterday it didn't want to lock speed at all, but when I turned it on to take this photo, it locked instantly. The electromagnetic brake doesn't always engage when stopping the platter. What's a bit surprising is that the motor doesn't really fight you when you try to stop it by hand. My SP10 mk2 is seemingly capable of tearing my finger off if I try to stop it, this thing just stops when I apply pressure to the rim of the platter.

The armboard is missing, but the plinth is surprisingly substantial (3 layers of thick ply glued together). Alas, it's covered in nasty vinyl wrap that is bubbling up in places.

The rubber feet are in various stages of disintegration, two of them literally fell off when I lifted the plinth.

The mat is excellent, it's 6mm thick and the rubber is very soft. It's heavier and feels better than the Technics mat on my SP10.

There is a lot of corrosion on all metal surfaces which means that I will probably have to clean the switches and replace the adjustment pots on the PCBs.

I downloaded the service manual and there are a lot of very small electrolytic capacitors (like 0.47uF) which are probably gone by now. Most manufacturers don't even make electrolytic caps less than 4.7uF anymore, I guess I will replace them with film caps.

Also: no proprietary ICs inside! It uses a PLL speed control chip from Siemens (TCA955), I found a NOS one on eBay and ordered it to have a spare just in case.

[stratokaster83]

Interesting tidbits from the service manual.

1. This turntable uses an induction AC motor which is powered by a separate winding on the power transformer. Speed control is absolutely ingenious: there is a large power transistor in series with the motor windings which throttles the motor voltage supply and controls slip between the rotor and the rotating magnetic field of the stator.



The motor is nominally fed with 75V AC (I assume this is an RMS value), but the supply voltage drops to 50V peak-to-peak when there is no load and climbs up to 200V peak-to-peak at full torque. Since the motor is located directly under the platter, I guess this is not a good turntable for Grados and other unshielded cartridges. I will have to check if the black cover under the platter is ferromagnetic to shield cartridges from the motor's magnetic field.

[stratokaster83]

Opened the turntable today to take further assessment. This motor is no joke! 9cm in diameter, 7cm high. The case of the motor is made of die cast aluminium, no cheap stamped metal here.

The power transformer (fully encapsulated) is even more impressive.



Unfortunately, the rubber grommets supporting the transformer have perished 



Another piece of bad news: every other transistor in this unit is of the worst possible type - Hitachi 2SC458 from an early batch (in the S-8 package that looks like a brick outhouse) showing heavy oxidation on the leads (this oxidation gets inside the plastic package and ruins the hermetic seal, eventually the moisture gets inside the transistor and corrodes the connections).

[stratokaster83]

Also: can confirm that the black cover under the platter is made of some ferromagnetic material, possibly to shield the sensitive cartridges from the electromagnetic field created by the (very impressive) motor.

The speed control IC is indeed TCA955 made by Siemens und Halske.

[Willholmania]

Hi. I too have just bought one of these. It works, but it's very sensitive to the positioning of the tape head to the magnetic strip on the edge of the platter. Unless the clearance is very small it goes haywire. I'm planning on replacing the electrolytics in it, in case they're failing as I don't want the TCA955 to get fried if one goes down. I wondered whether you'd managed to get yours working reliably and if so, what you did to it.

[Willholmania]

[stratokaster83]

I have ordered the parts but haven't replaced anything yet. You will need to replace transistors as well, at least 2SC458 (replace with KSC1845) and 2SA844 (replace with KSA1015). The magnetic head amplifier consists of two 2SC458 transistors, if they go noisy... the turntable goes crazy.

[Willholmania]

Thanks - that's really helpful. Do you have any idea what kind of clearance there should be between the tape head and the platter?

[stratokaster83]

There is no information about magnetic head adjustment in the service manual for DP2000, but I found this tidbit in the service manual for DP-70M:

[Willholmania]

[/quote]

Thanks again. That’s exactly what I ended up doing, although I used a folded piece of paper. It’s fine, but if the bearing develops any play the head would likely destroy the magnetic strip. I better lubricate it before I use it.

[stratokaster83]

Mine has a plastic magnetic head so it won't even scratch the magnetic surface.

[Willholmania]

Mine is also plastic, but I’m paranoid about the strip getting damaged.

Please update us on your progress.

[stratokaster83]

I definitely will, but I'm a pretty slow DIYer 

[Willholmania]

My caps are on the way so I’ll let you know how I get on.

[Willholmania]

I've replaced all the electrolytics and oiled the motor (what a motor!). Waiting for the transistors for the tape head amp to arrived from China, but in the meantime it's running well now.