Where Mod Squad Prism CD player op amps? - diyAudio
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Old 14th December 2012, 04:31 PM   #1
bleget is offline bleget  United States
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Default Where Mod Squad Prism CD player op amps?

I removed the player cover and there appear to be no op amps in this player unless they're under the CD transport which I'm hesitant to remove. Theere are two 8 pin ICs near the back of one of the boards but they're not marked--they look too small to be op amps regardless. Anyone know if this player has op amps or uses discrete components instead? Thanks.
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Old 14th December 2012, 04:35 PM   #2
Mooly is online now Mooly  United Kingdom
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Most opamps are 8 pin

Check the DC voltages and that will help identify them. Supply voltage on pins 4 and 7 or 8 will confirm single or dual opamp.
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Old 15th December 2012, 12:57 AM   #3
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I measured the following DC voltages with the player on and when playing a CD:

Pins 4 and 7 = 16.39V
Pins 4 and 8 = 32.81V

I don't know what this means except that these ICs don't appear to be op amps, at least none that would be replaced with OPA-627s.
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Old 15th December 2012, 08:03 AM   #4
Mooly is online now Mooly  United Kingdom
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Just to be clear.

Are those the voltages across the pins or measured from ground to each pin ?

If across the pins they could well be opamps. Otherwise no.

(32 volts across pin 4 and 8 would indicate a -/+ 16volt supply and 16 volts from pin 4 to pin 7 would indicate the "opamp" outout is at zero volts as would be expected)
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Old 15th December 2012, 02:15 PM   #5
bleget is offline bleget  United States
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The voltages I measured are across the pins, not each pin to ground. The CD transport is a Phillips CD 650 which I've discovered via internet was used in this version of the Mod Squad Prism. My original manual does not have a schematic and I can't find one on the internet. Also, via internet, NE5532's were normally used in similar players. I've sent an email to McCormack Audio asking if Steve remembers what op amps were used but probably won't receive a reply since that was 20+ years ago. Still puzzling that they weren't marked. Any ideas why? Regardless, thanks for the info; it appears they ARE op amps.
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Old 15th December 2012, 02:30 PM   #6
Mooly is online now Mooly  United Kingdom
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The 5532 is a common choice but it could be something different. I've found the OPA2604 a very good alternative sonically (very very good sonically in the right set up) and also the OPA2134 which is probably the more neutral sounding of the two.

Rubbing numbers off is a trick (deception ?) by manufacturers to leave you guessing. They could be 4558's
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Old 15th December 2012, 02:39 PM   #7
Mooly is online now Mooly  United Kingdom
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Also its worth checking stability of any replacements. 9 times out of 10 there isn't a problem but then along comes something different. The NE5534 (single opamp) used here was a typical case in point,


Swapping Op-Amps... you have checked to see it's stable haven't you ?
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Old 15th December 2012, 09:58 PM   #8
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I read the posts in the link concerning swapping op amps. Is it possible to compare spec sheets for the different op amps to determine if a possible swap is acceptable? I don't have an o'scope or access to one.
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Old 16th December 2012, 07:55 AM   #9
Mooly is online now Mooly  United Kingdom
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No, the data sheet gives no clue in may cases.

From what I can turn up these players are based on old Philips technology (TDA1541 DAC's ?) and so will probably follow a fairly similar pattern to the original players.

I would fit sockets and try the OPA2604 and 2134 as mentioned and also the LM4562 (the successor to the 5532) which many rate highly.

Use solder braid to remove the old IC's neatly.
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Old 17th December 2012, 12:11 AM   #10
bleget is offline bleget  United States
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You are correct-the DACs are TDA1541. The main PC board is labeled Phillips and the board with the op amps is Mod Squad. I assume the mods applicable to the TDA1541 will work for this also although I don't want to tackle those yet. Thanks so much for your help/advice.
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