DIY FL and FR Pre Outs on Sony AVR STR DN1050

Discussion in 'Hi-Fi Stereo Systems & Separates' started by HomerA, Mar 23, 2018.

  1. HomerA

    HomerA
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    Hi All,
    just wanted to share with you what I have found out on this and what I intend to do. a) because its interesting, b) cos it is no where else on the net and C) cos if I am wrong hopefully some one will point it out to me ;-)

    So my AVR, Sony STR DN1050, doesn't have pre outs.... too much hassle to buy a new one and I like sony and none of them have pre outs, so I want to create some on my avr....

    I found the old schematics online.... and as you can see from the second photo (page 54), I have found the chip that handles all the source switching and volume control.... it is IC421 which is a BD3470KS2 (this took a fair bit of time as I had no familiarity with the drawings.) This is usually the point people mention to connect to. Older boards had physical connections and components to handle volume control, but more modern AVR's have it all in a chip.

    If you look to the bottom right of this pic you will see Sub woofer audio out (pre out) and if you trace it back you get to pin 15 on the chip. (The Legend shows that a red arrow without fill, is analogue audio rather than digital) Next to that is OUTFR and OUTFL (13 and 14) and these are the Audio (pre - power amplification) connections that get fed to the power amp section. If you trace these lines up you get to connection 20 & 19 which go to another part of the main board (on page 51).

    The first pic is of page 51 and on here (bottom right) are connections 19 and 20 (from OUTFR and OUTFL which are fed into all the power Amp components...... obviously I want 'Pre' outputs, so just before the power amp stage, so I need to connect somewhere between pin 13/14 of IC421 and the power amp components for FR and FL.

    now it is not a good idea to solder to the pin of a chip (might damage the chip) so I have looked for a suitable point and on Page 51 you can see the OUTFR (connection 20) hits a 10uF capacitor and then goes to R787. On this board these resistors are mounted standing up so if I solder to the top of this Resistor I will have my Front right Pre out point. Do the same for OUTFL and pick an earth point. Connect cables, twist and feed outside of the case (may do a more permenant solution later) and bingo you have pre Outs. These need to be RCA connectors (female in the future for a more fancy solution, actually screwed through the back panel somewhere) and I can plug direct into my Integrated Amp as a source to feed the speakers.

    I was thinking of putting in some fancy circuitry, as in the sub woofer out circuit, but this new connection is not a floating point and is taken past a 10uF cap (to avoid any dc pass through) so to be honest it doesn't need it. I might add a 1kohm resister in series with the output (as with the sub woofer connection) just to help with loading but not sure yet. I am downstream of R787 which is a 1kohm resistor so I don't think there is a need.

    This will do away with any need, mentioned in a previous post, for speaker cable switches and means I can listen to powerful sounds from my avr but also to stereo music from either my avr or my other sources CD player etc, :)

    If you have any further thoughts feel free to let me know.
     

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  2. muljao

    muljao
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    Wow, seems like a lot of knowledge and effort. Good luck with the project
     
  3. HomerA

    HomerA
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    that sound like a lot of wives when we mention buying HiFi....... ;-)

    but thanks for the words of encouragement.... :)
     
    Last edited: Mar 24, 2018
  4. HomerA

    HomerA
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    Warning: The following post is not a tutorial and if you attempt the same on your AVR, then I am not responsible if you blow it up or damage it [emoji4]

    SUCCESS!!!!! [emoji4]

    So I took the lid off my Sony DN1050 and was presented with the digital board. Photo 1. This was fairly straight forward to remove and needed to be taken off, as you can see by the third photo, where you can see all the parts I need to get access to are under the digital board. I had to remove all the screws attaching the HDMI connections and a few other ones and then on the inside Photo 4, disconnect a few of the cables Photo 1+2 and unscrew the digital board from its fastenings. This meant I could lift the Digital board away and reveal the main board. Photo 5 + 6. I had to remove the Wi-Fi board to get access to one screw. This just lifted off its connector once unscrewed.

    Photo 7 is a close up of the Caps and resistors that I wil need to solder to. I needed Resistor 787 for FR and 637 for FL.

    Now I wanted to do a tidy job with very little damage or change to the original AVR but still leave an easy way to connect and disconnect my Integrated Amp. After looking at the shematics I worked out that you could connect the Pre out points discussed earlier (OUTFR and OUTFL) to the Audio input points SAT/Cat V on the back of the AVR. This would mean the pre out signal would be fed back into the main selection chip, but this would not be a problem, because if this input was ever selected, it would form a 0v loop which is no problem. (Clearly I can no longer use SAT/Cat v as an input source). I could then use the female RCA connections as my 'pre out' connections for FR and FL. So SAT/Cat v have become my pre out connections.

    So I cut too short wires Photo 8 and tinned each end ready to solder. I then located the Resistors I needed to connect to (photo 9 and 10) and scraped off the coating on the resistor legs and soldered on the two wires onto the Resistors and then onto the large legs of the input points (SAT/Cat v) as Pre Out connections (photo 11).

    The rest of the photos show the wires and then the AVR after putting it all back together.

    Then onto the testing. I setup the system so the pre outs (photo 18) were connected to the inputs of my integrated Amp (photo 19) and with my Amazon echo connected on bluetooth I played music through the AVR onto my IA and into my speakers. Bingo! All worked. Video 1 shows the first test.

    I did some measurements and found that the AVR on vol level 30 gave a db of about -35. So I then connected the speakers through the IA and adjusted the vol level of the IA to give a db level of about -35. This was at about 12 ocock (approx half way). So I can play my avr and the vol levels of the speakers via the IA should match the old vol levels and blend in nicely with the vol levels of the other speakers. [emoji4]

    Hopefully this all makes sense. Any questions, let me know.
     

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    Last edited: Mar 25, 2018
  5. HomerA

    HomerA
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    rest of the photos.....
     

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  6. HomerA

    HomerA
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    How do I upload a video of the final test with Preouts and my IA connected with a little bit of Dire straits? [emoji4]
     
    Last edited: Mar 25, 2018
  7. Rambles

    Rambles
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    :thumbsup:Seriously impressive work. Excellent achievement.

    With the video, you could upload it to You Tube and then post a link here.
     
  8. HomerA

    HomerA
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    Thanks @Rambles :) I forget how good the Arcam Delta 90 AMP is :) I can tell a difference even on Amazon Music streamed over blue tooth to my AVR. The Amp just gives a fuller sound :)

    Youtube video Test on this
     
  9. HomerA

    HomerA
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    Forgive the tiny sound of my iPhone recording. Just wanted to show my first test with my new Pre outs :)
     

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