Technics ST-S7 tuners - best caps to use? is AN6552 an opamp output

Discussion in 'Tuners' started by Synchro-bias, Jan 1, 2018.

  1. Synchro-bias

    Synchro-bias New ClassA

    Messages:
    671
    Location:
    Australia
    I have matching ST-S7 tuners in black and silver for my 2 V8 amps. The displays were dim on purchase and i assumed it was due to failing and aging display.

    I decided to take a look and in both tuners exactly the same capacitors had green on their legs, so maybe the caps in question affected the display

    I was thinking of FM caps, to replace just the faulty ones? and with luck there wont have to be any alignment ? i thought silmicII maybe not suit for PSU, or maybe recap the PSU only , fix the other problem caps?

    AN6552 looks like an opamp for output? OPA2604 in place? 2.2uf to silmicII output caps

    green dots failed caps

    technics st-s7.jpg

    st7.jpg

    s7output.jpg
     

     

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  2. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    907
    Location:
    Beverly, MA
    That cap looks pretty bad. FM will be OK. FM is OK in the PS too. You could also use Wima or Kemet 2.2uf film caps instead of Silmics for the output cap replacements.
    Searching AK, i see some people have used the OPA2604, why not give it a try?
     
  3. Synchro-bias

    Synchro-bias New ClassA

    Messages:
    671
    Location:
    Australia
    Thanks for the reply and help 39cross , Would be cold in MA, heard about the big freeze in the US
     
  4. FauxHall

    FauxHall Super Member

    Messages:
    1,523
    Location:
    Abu Dhabi, UAE
    I swapped out the output opamp in a Sony St-J75 with that OPA and it was an improvement.

    Note that Mike also added a larger power reservoir cap for the opamp and a small resistor on its feed from the rail to limit power inrush. He put in a socket so I could swap any number of opamps in.

    Opamps are cheap so rolling them can be a fun sport.
     
  5. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    907
    Location:
    Beverly, MA
    yes it's cold here, -14C at the moment.

    Be sure to use a socket for your opamp as FauxHall mentions.
     
  6. FauxHall

    FauxHall Super Member

    Messages:
    1,523
    Location:
    Abu Dhabi, UAE
    It's a bit chilly here in Abu Dhabi too!

    I think the lows are dipping to 65 deg F in the mornings. Days highs are only about 75.

    Tried to swim in the apartment's outdoor pool last night but just too darn cool.
     

     

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  7. Synchro-bias

    Synchro-bias New ClassA

    Messages:
    671
    Location:
    Australia
    Thank you FauxHall - , so any cap near i can increase capacitance, so i will get an adaptor socket to swap but am glad the OPA2604 goes nicely , anything is better than a AN6552 which i have atm. Voltages are pretty low in current 5v max

    Thank you 39cross, shall do, geeze that is cold, been a cold winter, shame our winters in Australia seem to be more on the warm side these winters :(

    That is pretty cool, but not sure if it was the UAE or SA, but there was snow in some mountain town one winter either SA or UAE. ITs all 80 F days here lately though this morning feels nice and cool so running my equipment
     
  8. FauxHall

    FauxHall Super Member

    Messages:
    1,523
    Location:
    Abu Dhabi, UAE
    amptramp likes this.
  9. Synchro-bias

    Synchro-bias New ClassA

    Messages:
    671
    Location:
    Australia

    Thank you Faux Hall, i forgot to get an opamp so used the free postage no min spend at RS
    LME49720 dual opamp , was cheap but min voltage is only 2.5v so is better suited i think to the opa2604
     
  10. FauxHall

    FauxHall Super Member

    Messages:
    1,523
    Location:
    Abu Dhabi, UAE
    Here's a cut-and-paste from a 2014 posting of mine

    When Mike refurbished my Sony ST-J75, he pulled the old op-amp (the audio output amp), a NJM4560, installed a socket, and reinserted the old op-amp. He also put in a larger "power tank" electrolytic cap, stacked metal film bypass caps, and a resistor on the line from the rail to the cap to limit in-rush current.

    I've had my local tech order some equivalent op-amps that will fit with his next Digi-key bulk order and plan on some chip swapping once they arrive. Here's the ones I ordered and their catalog prices:


    Texas Instrument OPA 2134 $3.42

    http://www.digikey.com/product-detail/en/OPA2134PA/OPA2134PA-ND/254686

    Analog Devices OP275 $2.71

    http://www.digikey.com/product-search/en?mpart=OP275GPZ&vendor=505

    Texas Instruments LME49720 $3.07

    http://www.digikey.com/product-detail/en/LME49720NA/NOPB/LME49720NA/NOPB-ND/1647708

    Texas Instrument LM4562 $3.07

    http://www.digikey.com/product-search/en?mpart=LM4562NA/NOPB&vendor=296


    STMicro LM833 $0.59

    http://www.digikey.com/scripts/dkse...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
     
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  11. Synchro-bias

    Synchro-bias New ClassA

    Messages:
    671
    Location:
    Australia
    The LME883N is in both my Techhnics mash cd players, sound very nice in stock form though the output is just a BA4960 or something like that, i changed them for LME48960 and the other player OPA1642 fet

    Nice choice there, will be interesting to hear the results, i got my LME49720 today, wasnt good prices but 5.63 or something about RS but shipping was free :D

    That says having to spend 60 to get free post that is nice of your local tech to do that, mine was good like that also we are friends now, and he makes DACs and out of repairs.

    Sounds some interesint mods to your sony outputs. I can see the last capacitors in the signal path 180ohm and 3.3 K, wouldve been nice to try Dale Resitors CM-55 s
     
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  12. FileFixer

    FileFixer Well-Known Member

    Messages:
    545
    Location:
    Zagreb/Croatia
    Into my SL-PS770D is M5238 chip on as first stage from DAC and sum for its output is RC4580. On previous 770A model on that all places is LM833. I think that is direct substitution for these two op-amps. Output on 770A model is same as your output with BA4960 but on 770D is RC4580. All resistors and capacitors is same on both model A and D. I`m thinking to replace all of these Op-amps for some other Op-amps, maybe OPA2132, OPA1642, AD826, LM6172 or some better. I dont want to change anything except Op-amps and also I dont know what is best matched Op-amp for direct substitution?
     
  13. Synchro-bias

    Synchro-bias New ClassA

    Messages:
    671
    Location:
    Australia
    Hello FileFixer,
    That sounds a nice player, more high end than my PG440A, ad it has the LM833N after the dac ( afraid to change that one) so changed the BA4960 for a OPA1642 opamp and put film caps crosscap with bypass 10uf in place of the output bipolars. If you are good with solder you could try to change the M5238, its a FET i think like the OPA1642.

    When i wrote to Texas industries for help, they have a forum, and you can ask an engineer a quesiton. This was for my P447A and PG440A.
    His words were the LM833N "should be compatitible"
    https://e2e.ti.com/support/amplifiers/ti_precision_labs_op_amps/f/1000/p/532148/1936883
     
  14. FileFixer

    FileFixer Well-Known Member

    Messages:
    545
    Location:
    Zagreb/Croatia
    Thanks for info. I checked over the internet on some Russian forums and many people use OPA1611/1612 as differential amp right on output after DAC. Schematics on SL-PS770D have different configuration on DAC output then on SL-PG440A but it is very similar.
    On 770A version Low Pass chip was be BA4560 but on 770D version Technics replace this chip with RC4580 as direct drop in replacement. Everything else is stay as before except capacitor on feedback line and place 6.1 kOhm resistor on its place. As I know on that way they remove L.P. filter and stay only as buffer before output but to me this dont look that this have many sense for that when previous RC4580 may to stay also as buffer.
    I`m thinking that OPA1612 may stay in place as first stage as output on DAC and then following with OPA2134 as summing and buffering amp. Last chip is not needed anymore.

    This is schematics from SL-PS770...

    [​IMG]
     
  15. Synchro-bias

    Synchro-bias New ClassA

    Messages:
    671
    Location:
    Australia
    Sorry for the super late reply i was overseas, then i got back and didnt get back here till now.
    This thread put me off changing the LM833M in my Technics SL-P477a

    I can tell you i have the OPA1642 in one amp phonostage and OPA1612 in another amp phonostage, the OPA1612 seems a bit better to me anyway. Remove filter caps and also muting transistors I upgraded my resistors also RC55 or CMF55. Less opamp the better, i think Lampazitor likes less opamp.
    http://audiokarma.org/forums/index.php?threads/cd-player-modding-what-did-i-do-wrong.450812/
     
  16. FileFixer

    FileFixer Well-Known Member

    Messages:
    545
    Location:
    Zagreb/Croatia
    Thanks for your answer. in the last few weeks I dont have too much time and till today I dont touch anything inside CD Player but I have OPA1612 and OPA2134.
    Now I going to read that thread... ;)

    Many thanks...
     

     

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