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Do I have an impedance problem? (passive pre)

post #1 of 12
3/5/04 at 7:45am
Thread Starter 
I recently picked up a passive preamp and as soon as I hooked it up, I thought it didn't sound as good as with my NAD integrated as pre. Then I read an article saying that the output impedance of the source should be really low. I'm not sure what the output impedance of my m-audio revo is but my cdplayer is at least 10k ohms, NOT LOW. Symptoms of this are supposed to be smeared transients, highs that are damped.

And I think that's exactly what I'm hearing. The midrange is fuzzier and muddier than before and the soundstage is less focused. Highs don't sparkle as much. I heard this before reading anything on passive pres.

Is it in my head? Or should I count out passive preamps for my system? If so, this passive pre will be going up on the gear forum...
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post #2 of 12
3/5/04 at 8:43am
Your Sony should be a very good source for passive pres and is able to drive long runs of cables without problems. Are you having too little volume at all?

Just wondering, what passive pre are you using? Have you gotten a chance to let it break in yet? You got to give it some time for the sound to open up if it's brand new. Also what are your cable lengths? Are you going from your CD player to passive pre to your amps?
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post #3 of 12
3/5/04 at 3:53pm
Thread Starter 
I have PLENTY of volume. This thing is friggin loud. My power amp also has a sensitivity setting so I don't think volume would ever be an issue. In any case, I have it set to the most insensitive setting

Cable run is 6ft radioshack shielded RCA to 1/4" TRS cable. CD Player to passive pre to poweramp.

The passive pre is a 2nd hand Adcom SLC-505. It should be fully broken in.
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post #4 of 12
3/5/04 at 9:33pm

Re: Do I have an impedance problem? (passive pre)

Quote:
I'm not sure what the output impedance of my m-audio revo is but my cdplayer is at least 10k ohms, NOT LOW.
What? your preamps' output impedance is 10,000 ohms????

I was told that the average is 600 ohms.

Just to give you an idea my preamps' output impedances are 17ohms, 47 ohms and 60 ohms.
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post #5 of 12
3/5/04 at 10:01pm
Thread Starter 
nono, my cdp's output impedance is 10k ohms.
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post #6 of 12
3/6/04 at 7:40am
I am unfamiliar with the Adcom passive pre so I can't help you too much. But what I CAN tell you is that just because the Adcom doesn't work for you doesn't mean OTHER passive pres won't work in your system. When it comes to passive, people try an inferior product and then go on to generalize that passive is no good.
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post #7 of 12
3/6/04 at 7:55am
Quote:
Originally posted by ooheadsoo
nono, my cdp's output impedance is 10k ohms.
Are you sure about that? That sounds insanely high. There's another recent thread a question regarding passive pres, and the poster was also confused about his sony's output impedance, due to the way it's written in the manual.
http://www5.head-fi.org/forums/showt...hlight=passive

If it says "load impedance" like for BrokenEnglish's case, then it means the minimum input impedance of your amp (the load), I think, which would make much more sense.
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post #8 of 12
3/6/04 at 8:43pm
maybe those symptoms are related to the additional cable you need to connect the prestage to your poweramp. have you tried some cable-rolling yet?

Quote:
Originally posted by fiddler
If it says "load impedance" like for BrokenEnglish's case, then it means the minimum input impedance of your amp (the load), I think, which would make much more sense.
well... it's a sony...
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post #9 of 12
3/6/04 at 8:51pm
Sony is generally one of the best cd players you will find at driving passive preamps so it's definitely not the problem.

I just notice the radio shack cable part where there's a 1/4" is involved. That might be the main problem.
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post #10 of 12
3/6/04 at 9:17pm
Thread Starter 
Well my pro audio power amp only takes 1/4" input and XLR (standard pro inputs.) My radio shack cable worked fine and dandy for my NAD pre. Anyone know of a better rca to 1/4" cable?

In any case, I THINK I've figured out how to get my system sounding good again. I bumped up the sensitivity of my power amp and *HEY* the magic's back! I think it sounds pretty good, back to normal
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post #11 of 12
3/7/04 at 2:10am
/me bashes ooheadsoo on his head.

Well glad you worked everything out. Instead of getting a rca to 1/4" cable how 'bout a RCA to balanced cable?
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post #12 of 12
3/7/04 at 2:39am
Thread Starter 
The 1/4" can be balanced, but the RCA end isn't, so there's no point, right? I don't think the radio shack 1/4" is balanced but I didn't think there would be a point.

BTW, I have a REALLY STUPID question over here that may be of interest to other guys in my situation looking into getting a subwoofer coupled to this system. The whole problem is the dang 1/4" input on the poweramp making getting a typical Y splitter cable very inconvenient...

http://www5.head-fi.org/forums/showt...threadid=64125
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