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adcom 585 - redundancy in circuit?
adcom 585 - redundancy in circuit?
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Old 7th May 2004, 05:47 PM   #1
rhyno is offline rhyno  United States
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Question adcom 585 - redundancy in circuit?

proceeding under the premise that there is no perfect part....
i was looking at the schematics of an older nelson pass design that i own (adcom 585) and i see that in addition to a slow start circuit, he also has wired a coupling capacitor (4.7uf) and resistor (1k) as the first things the input signal sees.

now i understand that the coupling cap is there to remove any DC that a preamp might send. but given the soft start circuit (and assuming good turn-on procedure: preamp 1st, amp 2nd), should this C-R network even be in the signal path? seems like a great way to lose transparency w/ no benefit to me...

also, given the coupling cap, i also see that the design has 4 dc-rail fuses on the output stage (which, i would assume, would blow prior to substantial DC being output to the speakers).

again, how redundant is all this? (i'm apt to leave the fuses, as i can get nice silver plated fuses that sound fast & nice, but remove the coupling cap, as i think that any cap will impact the sound more than the DC rail fuses will).

i'd like to pull the cap as i assume this will improve transparency, but i'd love some advice on if i should pull the cap, the C&R, or neither. (as i'm not sure the purpose of the resistor in this network). (and i can live w/ the risk of DC output from the preamp, as i'll always turn it on first.)


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Old 7th May 2004, 06:42 PM   #2
Nelson Pass is offline Nelson Pass  United States
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adcom 585 - redundancy in circuit?
I don't recall designing a 585. More likely it was a modified
version of an earlier circuit I did, however some resistance
in series with the input is generally a good idea to prevent
oscillation in a system, either from a preamp that doesn't
want to look at the base of a transistor directly, or vice versa,
or to help reduce the possibility of pickup from the output
of the amp back to the input.
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Old 7th May 2004, 11:10 PM   #3
rhyno is offline rhyno  United States
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Default thanks, one more question

thanks for the advice.

given the requirement of the resistor, is it still a safe assumption that the coupling cap can go?

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