MHZS CD33F Modified Tube CD-player (recap/remod)

Recently I’ve bought myself a Chinese MHZS CD33F tube CD-player which was in working condition, except for the remote. The remote was already taken apart and the CD-player itself had already been modified by the previous owner. This modification was based on several articles found on the internet.

What he intended to do was the following (if I can recall it all):

• Replaced the output electrolytic capacitors with 10uF ClarityCap film capacitors
• Remove the opamp and bypassed it
• Removed the electrolytic capacitors in the audio path between DAC and opamp/tubes.
• Removed blue LEDs underneath the tubes
• Changed a few resistors to compensate for the absense of the opamp

Despite his pretty low level of knowledge and skills he actually did manage to modify the CD-player and it was working! Unfortunately it was not the best attempt of modifying a CD-player, that I will show you further on this page.

Remote

I started to take a look at the remote. A heavy and very well build remote with a metal casing. Very well crafted and a nice finish from the outside. Although, the inside was not that great.

Bad quality and obviously lead free solder made it look very bad, but that is what happens when soldering with lead free solder. All solder joints will dry up dull, no shine what so ever.

The problem was the way the battery was held into place and made contact or not with the circuitry.

I choose to order a bunch of battery clips that can be soldered onto a PCB. Although there was very little space left, I managed to fit the holder in and also get the lid back on.

Installed the new battery holder and give the PCB a good clean. Also replaced the electrolytic capacitor which was pretty bad already.

The CD Player

Now that the remote was fixed, I had the chance to listen to the CD player for a longer time. Sounded pretty nice, but I suddenly heard static noise comming from the right speaker. It was there when the relay in the output stage switched on, so it had to come from the CD-player.

I decided to take the complete CD-player apart and redo the modifications, also replace all large electrolytic capacitors in the power rails. The capacitors in the audio path were already bypassed or replace with film capacitors.

Let’s take a closer look at the PCB’s and the modifications.

Power supply board

I replaced the large electrolytic capacitor in the power supply as a precaution. It got very hot because of the large power resistors next to it. I replaced it with a 105°C which last longer.

Modifications and other work

The standard 10uF electrolytic capacitors were replace by much larger “ClarityCap” type film capacitors. Not the nicest way of putting them in there if you’d ask me. Not to mention the burnmarks on the capacitors inflicted by a soldering iron. Luckily the capacitors measured perfectly fine on my LCR meter, so no need to ditch them and get something new.

More damage by the soldering iron

Soldering works

Although the end result was a working CD-player, the soldering could have some improvements. Another thing the previous owner and ‘modifier’ did, was to remove the blue LEDs that lid the tubes from underneath. That’s certainly something I would have done!

The improvement

First I removed everything from the board that shouldn’t be there, was badly soldered, defect or will be replaced by something else.

The relay

I found a used but good relay of exactly the same type, so that one could go in.

New electrolytic capacitors

New film capacitors and the old ones reinstalled

Fix the output wires

The output wires were non-isolated. I thought that this short piece of wire also deserved an upgrade.

Reassembly of the CD33F

This was a really fun thing to do. Working on an already great CD-Player and improve it further.

I don’t think this CD-player will leave my audio setup any time soon!