Playstation as CD-player

[JLPAS]

Hi, everybody, I've just gotten a 1002, has someone changed the output parts to get a better voltage , with a passive preamp I must set it nearly at maximum to get a decent sound level . Nonetheless it is a fantastic machine !

[Mick_F]

You probably have low-efficiency speakers - that may lead to the volume problems you are describing.

Well, a couple of pages back in this thread, people have described JFET and tube output stages that you may consider. I also have another idea, which has not been discussed before:


If you want to have more output voltage with not too much effort, you can replace the NJM2100 opamp (now operated as a buffer) by a better unit, for example the OPA2134. You have to fumble a bit with the signals and traces (we can discuss this in more detail if you are interested) but it should be possible to use the present opamp position on the board to install a pin compatible unit in non-inverting mode.
In combination with replacing some parts by better equivalents (e.g. the capacitors) and complete removal of some others (e.g. the muting transistors) this should lead to a higher output-voltage level at a better quality than in the stock unit.


Mick

[JLPAS]

Hi, are you Mick from the Dogbreath web site ? If I 've understood what you wrote , there are two MJM 2100, on the RCA outpout signal path and your idea is to replace one by another AOP ?

[Mick_F]

Yes, Dogbreath is my site.

In the RCA signal path there is one NJM2100 which is a dual opamp. My idea is to exchange that opamp by an opa2134, which is also dual. Some connections have to be changed to use it as an amplifying stage but that should be possible.

Mick

[JLPAS]

OK, but I'll need your help but don'tworry , I'm not in a hurry . I already have some OAP because I've made some tests on a Philips 723 :
OAP 2277P , 2132PA, 2664AP .

[pozo1992]

Dear gentlemen,


I have already replaced the NJM2100 by an OPA2134 and it works fine. Please be aware that your supply is +5V only, so the maximum output you will get is +/-2,5V peak or 1,76V RMS. Practically it is a bit lower. Regarding the opamp you have to make shure it will allow operating at +5V or +/-2,5V which is very low; anyhow, the OPA2134 will do.
If you desire higher output than above you will have to rise the supply voltage of the opamp. I have plans to realize this idea with a modified PSX powersupply either single +16V or bipolar +/-16V .
The modification on the powersupply is done on the secondary side only. The raw 24V is followed by a linear regulator preferably located close to the opamp. Attached you`ll find a schematic of the bipolar version, for unipolar you have to skip the negative votage generation.
You will have to cut the supply lines of the opamp and connect to the new voltage.
With symmetrical supply you get rid of the output caps, input caps are still required to block the DACs 2,5VDC.
Up to now I only have finished the modification of the power supply, it is working fine.
My final configuration will be opa2134 followed by a push-pull J-FET stage (2SK170, 2SJ74).

Regards,
Jürgen

[pozo1992]

Hi again,


attached the buffer circuit itself, not yet realized and tested.

Jürgen

[JLPAS]

Maybe one can make a power supply only for the OPA ? That's what I have inside my Philips 723 .

[Mick_F]

Hi Juergen,

nice to see that this idea can be realized. Some questions, however:
- If you use the second half of the Opa2134 as a servo, you need four of them for both channels. You cannot use the footprint of the present opamp then, right? This was one central point of my idea, though.
- If you make an extra supply line for the output stage, then you can use it to give the opa a higher voltage, and hence you dont need the extra jfet stage anymore. Or, argued the other way round, if you build a JFET stage, you dont need the Opa stage....

Cheers,
Mick

[pozo1992]

Hi Mick,

I agree fully to your comments. Yes you would need 2 dual opamps to do the whole thing on a seperate board.
If you like the minimal versions you could use the footprints of the components.
Personally I prefer the combination of both, the opamp and the JFET buffer stage. To my ears it sounds better than the opamp alone.
To use the buffer alone with an amplification of 1 has already been done in one of my PSXs and I like what I hear. (I even prefer it to the version with OPA2134 alone). This solution is very pure but does not give additional gain, maybe 2 or 3.
So in the end it depends on your personal taste and the equipment you are connecting your PSX to.

Regards,
Jürgen