What's a normal output impedance for a CD player? - diyAudio
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Old 17th August 2003, 05:40 PM   #1
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Default What's a normal output impedance for a CD player?

I just tried plugging my CD player (Technics SL-PG100, modified) *directly* to my DOZh, for the first time, and it makes a strange crackling noise (almost like clipping) with strong signals... i measured them and were well below the maximum input signal of the amp - "something's weird at the input" i thought, so i checked on Google and found out that this line of players have an output impedance of 1kohm (???). Is this normal? The amp works perfectly with any other audio source i've tried (Sony CDP, CDROM, tape decks, etc).
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Old 17th August 2003, 06:36 PM   #2
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Default Re: What's a normal output impedance for a CD player?

Quote:
Originally posted by Lisandro_P
I just tried plugging my CD player (Technics SL-PG100, modified) *directly* to my DOZh, for the first time, and it makes a strange crackling noise (almost like clipping) with strong signals... i measured them and were well below the maximum input signal of the amp - "something's weird at the input" i thought, so i checked on Google and found out that this line of players have an output impedance of 1kohm (???). Is this normal? The amp works perfectly with any other audio source i've tried (Sony CDP, CDROM, tape decks, etc).
1k's not at all unusual.

Marginal connections (cables, solder joints, etc.) can sometimes bring about the crackling noise you describe. Do you have another amp you can try the Technics with?

se
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Old 17th August 2003, 06:37 PM   #3
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Default Sounds kinda high.........

But what you really need to know is its current driving capabilities. Only way to do that is to measure it. They assume that you are using the standard IHF load of 10 kilohms, and x pF. At least, they used to.

Jocko
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Old 17th August 2003, 06:47 PM   #4
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Default Re: Sounds kinda high.........

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Originally posted by Jocko Homo
But what you really need to know is its current driving capabilities.
What could they possibly be using that it wouldn't be able to supply a few milliamps?

se
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Old 17th August 2003, 07:33 PM   #5
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1k seemed pretty high to me, so i thought it MIGHT had something to do. I spent a couple of afternoons doing various mods to it; it has the DAC practically integrated to the transport and both digital and analog signals are then picked by a separate board. For the analog path there's an opamp gain stage (where i did most of the mods) and a discrete buffer. I didn't even bother to check it, i mean, if there's a buffer it can definitely supply a couple of mA. I was thinking of bypassing the buffer but now i'm not quite sure... I don't think the mods i did have much to do with this issue either (improved psu, bypassing caps, changing electrolytics and bipolars for plastic caps where possible, higher values for coupling caps, etc).

PS: The Technics works fine with my dad's amp. As a matter of fact, it's quite a sweet sounding deck.
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Old 17th August 2003, 10:05 PM   #6
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Were you using the same interconnects when you ran it on your dad's amp? And are you getting the crackling in both channels? Also, how absolutely sure are you that the input sensitivity of your DOZ is at least equal to or greater than your CDP's output?

se
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Old 17th August 2003, 10:42 PM   #7
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The DOZh that you speak of, that is the DOZ headphone amp is it not? If so you've got a pretty high input impedance, around 100k I do believe, so if a CD player cannot suply enough current to drive a 100k load there is a problem I would say. That buffer wouldn't be there if it couldn't drive such a load, because then it would be rather useless.

I'm guessing there is another problem here.
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Old 17th August 2003, 10:57 PM   #8
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Yes, yes and yes. The Doz for headphones has an input sensitivity of 1vp-p; the deck spits about 2vp-p, but with the volume control (a 100k log pot) the signal during these noises is arround 0,6 - 0,7v (p-p).

I'll reopen the deck tonight and play with it some more, to see if i can figure this one out...
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Old 17th August 2003, 11:36 PM   #9
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Quote:
Originally posted by Lisandro_P
Yes, yes and yes. The Doz for headphones has an input sensitivity of 1vp-p; the deck spits about 2vp-p, but with the volume control (a 100k log pot) the signal during these noises is arround 0,6 - 0,7v (p-p).
Ah, ok. That's what the "h" meant. Thought it was a typo.

When you said you were driving it directly, I thought you meant directly without any volume control.

How are you verifying the numbers you gave above? Just a DVM or do you have a 'scope?

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I'll reopen the deck tonight and play with it some more, to see if i can figure this one out...
Good luck.

se
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Old 17th August 2003, 11:40 PM   #10
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With an analog multimeter - i'm a starving studient who can't afford a decent scope I have a nice digital one but those are useless in these situations...

As for directly, well, that's as direct as i can get without ending deaf - i have no volume control in the amp itself.
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