Parasound dac800, what are those diodes doing?

cortico
cortico Posts: 587
in DIY, Mods & Tweaks
Hi, so I cracked my dac open to take a look inside, while inspecting, I noticed that one resistor had been replaced with two diodes in series.

I know resistors control current and diodes are supposed to reduce voltage, but can't figure what the intention is... Any clues?

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Comments

  • [Deleted User]
    [Deleted User] Posts: 7,658
    It is possible they are zener diodes, establishing a reference voltage. Are there part numbers?
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  • cortico
    cortico Posts: 587
    Thanks so much Kenneth,

    I have found the schematic, so the two diodes (1N4002) are replacing the R316 (1K5 Ohm 1% 1/4) resistor. It appears to be connected between power switch and 4 pin of IC305 (TC74HC73P).

    urbzhoq6ki0y.png


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  • [Deleted User]
    [Deleted User] Posts: 7,658
    That is a complementary metal-oxide semiconductor (CMOS) flip flop logic chip and pin 4 is the Vcc (operating voltage, 2.0 to 6.0 volts needed) connection. I imagine they are using the forward voltage drop of 1.0 volts times 2 for 2.0 volts on pin 4. I suppose you could measure this, if you are curious.
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  • msg
    msg Posts: 10,120
    C - you think this was a repair or a factory deal?
    why wouldn't they just have used a resistor? is that a difficult spec to find?
    I have one of these DACs. I can check mine to see if it's the same. curious.
    I disabled signatures.
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  • txcoastal1
    txcoastal1 Posts: 13,300
    May have been a back feed issue as diodes are directional
    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
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  • cortico
    cortico Posts: 587
    edited December 2015
    thanks, this picture I found online shows the resistor... it could be a factory tweak to correct some imbalance.

    btlfhn3tgnp1.jpg
    Post edited by cortico on
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  • cortico
    cortico Posts: 587
    You know, this diode thing sparked my curiosity.

    This DAC is in fact an improvement over my CD player alone. It sound very detailed, yet smooth. Low frequencies go much deeper than before. There is more realism on vocals, guitars and drums. I can pick up new overtones and note decay on electric guitar breakup sounds that weren't there before on usual tracks. l...

    I like it to listen jazz, old blues and classic rock. On more modern rock and grunge guitar stuff (Pearl Jam comes to mind), I feel necessary to back the mids knob a notch to mellow things out a bit.

    It's not the last tecknology flavor but its a very good mid 90's DAC.
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