Modifications to Mission PCM4000

I recently picked up a Mission PCM4000 dirt cheap (£20) off ebay. It works well, I like the styling and ergonomics of the player and as is it sounds pretty good through my Crimson pre/monoblocks and Rogers LS5s.

It has a sticker inside - "Modified G. Bevan 19/12/86" so has obviously been subjected to some tweaking already. Any idea what?

The player is based around a Philips CDM2/10 mech.

On the main board: DAC is a TDA1541. Filter (?) SAA7220P/A. The large IC in the photo is a M4804A (no idea what this is). Most of the caps are Michicon SE (M). Opamps 2x NE5532N.

The removed piggyback board contains a large Philips IC marked MAB 8441P T012 and two identical 74LS74AN ICs.

Presumably Mission provided the analogue circuitry for a stock Philips design in these players. I'm assuming that the output circuitry should be pretty good compared to budget Philips players of the day.

My question is - is this player a good basis for further tweaking? I was considering fitting the budget (£50) Trichord clock 2, but any other suggestions re opamps/diodes/caps etc... would be greatly appreciated. I have a basic understanding of electronics and am competent with a soldering iron. I can also get the help of a more experienced work colleague where my skills run out...

I like the sound of the old philips multibit dacs and appreciate the build of these early mechs. Where does this player lose out to newer models - and where can I help it catch up?

Thanks in advance!
 

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ash_dac

Member
2005-01-27 8:22 pm
UK
The usual... Op amps, I like OPA2604 and diodes, something with a soft recovery... I use BYT53
Separate regulated 5 V feed to SAA7220 if you are able....

I own a PCM 7000 fitted with better diodes ann OPA2604 for dual ops, 637 and 627 for singles and the 7220 supply mod. (thx to Jean Paul for that one.)

Does not stand far behind my Theta DAC and drive (and those are modded too!!!).

Zero O/S is also trivial to do on these machines and if you like it and can live with the bit of grit and confusion in the highs it is a great sound!!!
 
The diodes feeding analogue are most important but it is a trivial job so while you are there you may as well do all of them.
I got improvement on doing the diodes in my transport....

I took the crude supply feeding the main five volt regulator of the cdp from the cap and added a second 7805 to feed just the 7220 5v supply. Typically there is just a safety resistor of 0 or 5 or 10 ohms on this supply pin. Remove it and feed the 7805 output there.
I have no data sheet so can not tell you which pin :(( but a search for 7220 on this forum should result in a pin out list for it.
Obviously the ground of your new regulated supply remains atttached to the CDP ground.
 

BAKEHOVEN

Member
2014-12-18 11:25 pm
MISSION PCM 4000

I'M SORRY THIS IS NOT A REPLY - I HAVEN'T FIGURED OUT HOW TO USE THIS SITE; I AM NOT FAMILIAR WITH SUCH SITES.

Can anybody help me? I have this tape deck since 1987 and it's always worked perfectly. Now it doesn't work: I plug in and turn on at the socket and switch on the deck and nothing happens. I've tried different leads and it makes no difference, so the fault lies inside the deck.

IF YOU CAN HELP, THANKS IN ADVANCE.

BAKEHOVEN