Marantz CD50 modifications

[nigel]

I decided to do a bit of work on my most neglected piece of equipment - my CD player  

I feel a bit sorry for it, really. I was delighted when I got it - it was another car boot bargain - I paid £2 for it. One of a large number I bought in search of .... the elusive TDA1541A DAC !!

I had big plans for this machine, I had got as far as converting it to non-oversampling/no digital filter, schottky diodes in the power supply, all power supply & decoupling caps replaced, op-amps replaced with AD8542, all muting transistors removed, new output caps, etc, etc
My plan was to make a nice PCB to go inside the case, with separate supplies for the DAC, switchable oversampling/non-oversampling mode (so I could remind myself how much of a difference it makes!) and a switchable op-amp or passive I/V valve/tube output stage.

Then, I got a Lenco, so that was the end of that!  

So, the plans have shrunk a bit, but I decided to go ahead with the valve output stage, as I already had all the required bits. I abandoned the PCB idea, hardwiring is fine for the valve stuff.
Following photo is an overview of the top of the player. The area to the right usually houses the variable output board and headphone amplifier, so these were unceremoniously removed to make some space.



Looking closer, to the left is a small toroidal transformer which runs the valve circuitry. This only has a 6.3V and a 100V winding. The 100V is not really enough, so I used a voltage doubler to bring this up to what was required. There's a potential for a lot of hum as a result, but that isn't actually a problem, as the current drawn from it is very small. There's actually a much bigger gap between the toroidal and the front panel PCB, then it looks in the photo!



Next is the choke & capacitors for the power supply, next the regulator for the valve heaters and finally the audio bits. The hand-grenade sized capacitors in the middle are 10uF polyprops, which are the final decoupling on the valve anodes.

A view of the underside -



I can't claim any originality for the circuit, this is just a slightly modified version of a Thorsten Loetsch circuit. Likewise, I can't claim any originality for the method of sticking the valves out the back of the case like that - somebody on LL had modified a player in a similar way (can't remember who it was now).
Looks nice, though ...



As for the sound .... well I've only tried a few tracks so far, but it sounds very nice. Much smoother than the op-amp output. Cymbals, especially still have that kind of "false" digital sound (i.e. they don't really sound like cymbals ), but smooth as silk and entirely inoffensive. So, I'm glad I took the time to finish the job (sort of!). Anyway, at least it has some VALVES in it now  

Added noise from the valve stage is minimal - just a very slight buzz, with the amplifier turned up to full volume. Nothing at all at normal listening volume.

Does it rival a Lenco, though? NAHHHHH !!!  

If anybody wants the schematics, I'll post them.

[daiwok]

Your  a sick man Nigel !!!  for GBP 2 !!  Love to learn more of the Lampizator mod - schematics would be nice 

Lampizator is something I have followed but never done 

[nigel]

Your  a sick man Nigel !!!  for GBP 2 !!  Love to learn more of the Lampizator mod - schematics would be nice 

Oh yes, a sick man indeed 

"seek ye and the car boot sale shall provide!"

It's completely insane what people get rid of, for virtually no money. However, I have been going to car boot sales at least once a week, for about 10 years, so it does take a bit of patience. Sometimes I just come back with one scabby LP, sometimes with nothing at all (except sore feet).

I'll sort out the schematics tomorrow

[Nic]

i am so envious of you and all these wonderful car boot sales. All just on the isle of wight?

Anyways, I too am a fan of the TDA1541 chip. Nicest sounding ie most analogue like. I'm using a Naim CD3 with said chip.
There may be others which are more "resolving" but they're probably either too digital in sound or too expensive for me.

[rfgumby]

Nice mod Nigel-

   And now you can tube roll to tailor the sound if you want.  And the player still works.  Yeah!

[Lapi]

You're  a sick man Nigel !!!  for GBP 2 !!  Love to learn more of the Lampizator mod - schematics would be nice 

all thinks audio at car boob sayle in UK just 2 quids, Simples. 

[willbewill]

However, I have been going to car boot sales at least once a week, for about 10 years, so it does take a bit of patience. Sometimes I just come back with one scabby LP, sometimes with nothing at all (except sore feet).

Exactly the same here now, but going back about 8 years or so there was plenty of good stuff to find - pre ebay!

[nigel]

i am so envious of you and all these wonderful car boot sales. All just on the isle of wight?

Yep!

all thinks audio at car boob sayle in UK just 2 quids, Simples. 

Simples indeed! 

I won't tell you what I got at today's car boot, because -

(a) you're going to start thinking I'm making it all up and
(b) you will start to dislike me intensely and
(c) they only cost me 2 quids again (each!) 

And now you can tube roll to tailor the sound if you want.  And the player still works.  Yeah!

Yes - at the moment I have one Mullard ECC88 and another unmarked - or rather the markings have worn off. It clearly isn't a Mullard, but I don't know what it is.
I have some others to try, so I'll give these a go later.

Exactly the same here now, but going back about 8 years or so there was plenty of good stuff to find - pre ebay!

True enough. I followed my wife around car boot sales, just carrying stuff and looking bored, for years. Then I got back into audio and started looking for myself. I daren't think what I must have missed

Sorry, didn't get around to sorting out the schematics today (due to developments on other fronts), but will do shortly.

[joe]

Nigel, thanks for posting your work.  That player lends itself to fairly easy modification given all that space on the right side.  I did the lampizator mod (non-oversampling, SMD cap replacement around the 1541A, key Oscon 'lytic replacements, SRPP 6N1P out) to a CD40 player.  Lukasz states electically it's the same as the CD50 except your's has a nicer enclosure.   I really thought the CD40 sounded horrible before I modified it - very muddy, poor dynamics, basically unlistenable - quite startling after I completed the work - very enjoyable - I like it a lot more than my modded Toshiba 3960 player.  Anyway, I have another player (Rotel 855) that I'd like to mod and I'd greatly appreciate the schematic!
Thank You, Joe

[nigel]

Hi Joe,

sorry - I still haven't done it, have I 

I'll post them asap - I just need to draw out the PSU first.

[nigel]

Ahem ... sorry for the delay 

Right - like I said, nothing I've done to the Marantz is original. The valve output stage (but not the power supply) came from here -

http://www.fortunecity.com/rivendell/xentar/1179/theory/vasfda/vasfda.html

It's the second schematic down, after the power supply circuit. I haven't looked at the Lampizator site for some time, but from what I remember, it's fairly similar. I used a value of 47 ohms for the I/V conversion resistor, which is a little lower than suggested. Helps improve linearity/reduce distortion, at the expense of reduced output. Sounds good, so I haven't bothered to play around with the value.
My power supply was based on what I had available, or could easily get. Excuse the scabby hand-drawn effort -



The small toroidal transformer I used fits nicely in the space available, but has only a single 100V HT winding, so I used a voltage doubler to get the required voltage. The LT1085 regulator used for the heater voltage is a low-dropout type, so there is sufficient voltage on the input side (just!) to keep it in regulation under load. Obviously the use of schottkies in the bridge helps here.

So, there you have it!

Sounds wonderful!

Still don't use it much, though 

[joe]

Thanks Nigel.  I was certainly not going to rush you   I had heard about Thorsten Loesch's circuit but never found it - it was around after all.  Anyway, it's all stored away and will come out when I'm ready for the Rotel.  The 855 has much more room than the Marantz - piece of cake.
Again, Huge Thanks, Joe