NMS-1205 R41 resistor value

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By giuseve

Paladin (755)

giuseve's picture

17-06-2015, 14:25

Hallo,

does someone know how is the value of the original R41 resistor on the Philips NMS-1205 Music Module ?

I replaced it with a 27K resistor to increase the output volume to the same level as MSX-MUSIC, but results is very noisy.
So I want to reset it to the original one.

Thanks in advance

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By Daemos

Paragon (2044)

Daemos's picture

17-06-2015, 19:13

I gues you tried to increase volume on a very noisy component. You do not have schematics?? If you do have schematics I can help you out in deducing the correct value and techniques for volume increase

By Grauw

Ascended (10699)

Grauw's picture

17-06-2015, 19:54

By roadfighter

Champion (451)

roadfighter's picture

17-06-2015, 20:20

Schematics:

Music module NMS 1205

Page 9, original value is 10 K ohm.

By giuseve

Paladin (755)

giuseve's picture

17-06-2015, 23:20

Thanks to all of you guys.
So my music module works fine with 10k but with l8w volume when in combo with fmpac, and works noisy with the 27k resistor suggedted by wiki.
Daemos, hsve you a solution for me, also this time?
Once upon a time your suggestions were precious fof my msx2plus.
Roadfightervprovidesvthe schemstics and Graw the layout of the board.

Thsnks in advance.

Giuseve

By Daemos

Paragon (2044)

Daemos's picture

17-06-2015, 23:50

Your resistor increase shouldn't pose too much trouble in this case. I am afraid the noise is being picked up from the electronics behind the opamp. If there is space try creating a non inverter with a super low noise opamp to amplify the allready available signal. Perhaps you could check the output of the cartridge and see if there is natural noise present. In that case amplifying simply isn't going to cut it alone.

EDIT: R22 and R39 are the problem makers for your case, try lowering R39 to 4K7 or 2K2 if you start hearing noise again the noise is from the cart itself.

By Grauw

Ascended (10699)

Grauw's picture

18-06-2015, 01:25

guiseve: when you say noisy, do you mean hiss or hum, or do you mean loudness and distortion?

By sd_snatcher

Prophet (3642)

sd_snatcher's picture

18-06-2015, 01:51

@giuseve

What MSX computer are you connecting your NMS-1205 to?

By l_oliveira

Hero (534)

l_oliveira's picture

18-06-2015, 02:41

Just a comment, look how crappy the design for that board is. The choice of logic ports is "poor" and they even split the ground rail in two. MSX does not have "AGND" so splitting the rail (which will be joined again at the slot connector is silly.
The separated ground rail goes *only* to the ADC ground pin on the Y8950 chip.

My Music module has blown the ADC because of that design stupidity. I inserted it on a computer with dirty slot and the ADC ground pin did not make proper electrical contact. The cartridge operated properly (for playback) so I did not notice the problem until it was already damaged.

Because of that, my Music Module cannot record samples. Now, the only remedy is replace the Y8950 chip. -_-;

By giuseve

Paladin (755)

giuseve's picture

18-06-2015, 06:56

@graw
now it sounds loudness and distorsion.
@sdsnatcher
my msx is nms8245 upgraded to plus
@daemos
so i have to try with a 4k7 or 2k2 resistor on r39 with 27k on r41. Uhm, first time i see a strange for me resistor value. What are the number after the K?
I must go to the shop to buy some resistors, just to don't go up and down many times, what could be avresistor shopping list thinking to the possible next steps of the nms1205 fixing?

bye

By l_oliveira

Hero (534)

l_oliveira's picture

18-06-2015, 07:20

2K2 (2,2kilo Ohm aka 2200 Ohm) 4K7 (4,7kilo Ohm aka 4700 Ohm)

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