non - OS vs OS, for amusement and entertainment only

[andrew_whitham]

first point, this is NOT a rant about the relative merits of one topology vs another, more an encouragemnent to find out yourself which suits YOU better. I'm putting this up because I've never seen it anywhere so I hope its not a re-post.

I recently managed to get a working Marantz CD40 off EBay for the pribcely sum of £9.99 result! first step was to remove all the op-amps, the TDA1541A and the SAA7220G/P and bung in some sockets (tip - solder wick is great)

I replaced the op-amps with OPA2134's, just because I could rather than to further the course of my grand experiment.

Next - 1 daughter board taking the pins of the SAA7220 up amd through a tristate buffer (74LS244) so that in one condition the data passed through the circuits as Marantz intended, in the other the data went straight across the O/S filter and into the DAC.

Muting was acomplished with a transistor on the 74LS244 so that if mute is low into the defeated SAA7220 (non o/s mode) then the 'LS244 is turned off and you dont get the chirps and clicks during the skipping to or forwarding of tracks.

bung a switch on the front to change between modes and you have a player that can do it both ways. With all other things being equal.

BTW I was concerned for a while about the 'filterless' non-OS doing damage to the rest of my system. Ultimately I figured that the rest of the player's output stage would chop out much of the ultrasonics anyway. it not being designed to effectively amplify 100Khz signals. (Doesnt mean I'd want to try this with a MOSFET amp though, Personally I'd be worrying about ultrasonic oscillation but that may be unfounded)

And the difference? well not to spoil it for you, it was more subtle than I expected. But consistent across the small number of CD's / amplifiers I tried it with,

Andy

[andrew_whitham]

Breadboard layout (I think)

Cant remember the value of the pull-down resistors - I think 10K

Andy

[poynton]

Hi.

An interesting project for a rainy day !!

Can you post the circuit as well, please?
I cannot see where the switch is to be connected or the resistor values.

Andy

[andrew_whitham]

This should be it.

Transistor used was a 2N3906, but only so I could put it in backwards and it wasnt automatically dead...

theres also a chuky 10uF cap across the power lines on the second board, which isnt shown.

Andy

[poynton]

hi.

What are the functions of S1 and S2?

Andy

[rfbrw]

Originally posted by poynton
hi.

What are the functions of S1 and S2?

Andy

You cannot be serious!

[andrew_whitham]

s1 open, s2 closed = non-os mode
s1 closed, s2 open = oversampled
s1 closed, s2 closed = silence
s1 open , s2 open = noise, lots of noise...


closing s1 makes the 1 output enable high when connected i.e. disables the data through the 1 channel, meaning if S2 is open then its over sampled data that's sent back to the mainboard.

Andy

[kevinkr]

Use a dpdt switch in place of S1 and S2 and you won't have to worry about selecting either of the two illegal combinations.

[andrew_whitham]

Break before make too, or you get a "click / pop" when switching.

which might not be good for anything.

[kevinkr]

dpdt by definition are break before make not make before break.. Rotary types can be either of course.