Adcom 5400 DC Offset

Drenis
Drenis Posts: 2,871
edited April 2013 in Electronics
So while tackling a speaker mod today, I decided to check the DC offset of my Adcom 5400. I set my meter to 200m on DC Voltage and got some weird readings. (Disclaimer - My meter just wouldn't sit at a stable reading of 0 when trying to conduct this. Cheap POS)

After 10 minutes of idling with nothing hooked up:

Left Channel: 68.7
Right Channel: -0.0

Wtf?? SO I powered it down, re-checked my settings, powered up and checked again after 30 seconds or so...

Left Channel: 78 (Was slowly dropping. Stopped reading at 72ma)
Right Channel: -2.2

Something is not right. The left channel is a bit over that magical 50 number but its the right channel that scares me. Is that normal?

Regardless, I have always thought the left channel sounded louder/fuller if I can use that term than the right channel. I have been meaning to take this into my amp guy here for a check over. I will probably do this quite soon as I don't want either amp or speakers to go POP! I should note that I removed the jumper between the negative terminals before taking these readings.
Post edited by Drenis on
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Comments

  • FTGV
    FTGV Posts: 3,649
    edited April 2013
    70 mv is a bit on the highish side but not dangerously so.I'm not familiar with your amp but it may have a pot for offset adjustment.As for the -2.2 mv ,offset can be either +or -since the the power supply is dual polarity.
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  • Drenis
    Drenis Posts: 2,871
    edited April 2013
    Thanks for the reply. Pretty much my thoughts. I didn't know about the polarity of the power supply fact though.

    The amp is in flawless condition and never been serviced or recapped. Runs luke warm to the touch more so on the left channel. Amp stays on 24/7.

    Overall, it's about time for a service!
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  • FTGV
    FTGV Posts: 3,649
    edited April 2013
    Drenis wrote: »
    I didn't know about the polarity of the power supply fact though.
    Since the gain circuits are powered by both a + and - DC voltage the offset can be either polarity.You should find a copy of the service manual for your tech so he can also follow the proper biasing produre for that amp.
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  • Drenis
    Drenis Posts: 2,871
    edited April 2013
    FTGV wrote: »
    Since the gain circuits are powered by both a + and - DC voltage the offset can be either polarity.You should find a copy of the service manual for your tech so he can also follow the proper biasing produre for that amp.

    Apparently he already has it. Loves working on Adcom gear too. Same tech I bought my Carver from some time back. I spoke to him upon acquiring this amp regarding a check-up. I've just been complacent with making time to go get it done.

    I will ensure that he does in fact have guidelines just to be safe.
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