2. amps-preamps
  3. 1203297523

Getting back to members on passive vs active lines

I found a buffered passive linestage for really cheap for experimentation. It is a Harman Kardon AP 2500 preamplifier with a passive linestage option (switch) made between '93-95' so minimalistic that it doesn't even have a balance control. Input impedence is 33k ohms;output impedence is 300ohms. I also have Rothwell attenuators in lieu of the Endlers which are again backordered--at the preamp's inputs and at the amp's inputs. It sounds really good, a lot better than the Celeste in the same set-up which I had figured out was being driven into distortion by the amp's low input impedence. The same with the CD player to preamp. The CD player's output impedence was too high and preamp's input impedence too low. So the system likes the H/K in passive mode better than it likes the active Celeste. And I'm not getting the anamolies at the low end of volume that I expected. The Rothwell's are dull as advertised, however. But Gregm was essentially correct in saying that a passive linestage won't work for me, because I don't have enough volume on the Telarc 1812. I have enough on all other CD's I've tried. When I get stepped attenuators, mybe I can decrease the attenuation enough so that I will have enough volume. But a CD player with 10K ohms impedence is a problem. Moral of story: match components within parameters before buying. Thanks to everyone for the info and help and for challenging me. I really needed to learn all this stuff. Comments welcome. Lynne
arnettpartners
6 responses Add your response
eldartford
4,262 posts
 
A CD player with 10K output impedance!!! What brand is that? 10 OHMS is quite possible with SS electronics, and less than 50 is typical. Even old tube preamps ran 600 ohms.
arnettpartners OP
312 posts
 
It's a Harman Kardon HD7600ll made between '90-'92. I bought it like new in the box from a member a few months ago. It was highly regarded but I couldn't afford it back then. It ran circles around my Simaudio Moon Equinox--made it sound and look like the Kling-ons made it. So I sold the Moon. I keep checking that spec but it says 10k ohms@2V. What determines output impedence? Is it the internal impedence of the amplifier section or is there a buffer at output? I know a power amp would ideally have zero output impedence. Also phono stages usually had 47K ohms at about .75-1 V.
rodman99999
6,126 posts
 
The output impedence of your CD player will vary with frequency. IE: My BAT VK-D5's output impedence measures between 880 to 910 in the middle and high freqs, but goes to 8475ohms at the lowest(single-ended). Balanced- it's 980s to 1200s, and 17kOhms at 17hz. Of course- that's with a tubed output stage. Don't forget- The 1812 Overture has some monster transients on it with the cannon shots(read- VERY wide dynamics swings). If the music had been recorded at normal levels, the shots would send your woofer's voice coils across the room(well- maybe that's a slight exaggeration). I have the original Telarc record. Back then people were wondering why they had so much trouble tracking those cannon shots. Then they realized the cutting stylus had hit the stops when they cut the master. Basically the groove had a square wave cut in it.
rodman99999
6,126 posts
 
Addendum: SS output impedances would be more stable than tubed. My CD player employs no buffers at all. Here is a review, and measurements comparing the outputs of two Cary CD players, the same except for one employing a tubed output section. Notice the difference in output impedance and the variation of impedance/freq of the tubed unit.(http://stereophile.com/cdplayers/1005cary/index5.html)
arnettpartners OP
312 posts
 
Rodman99999, Thanks. I found the review/test results on the Cary. I haven't found a review yet on the 7600 but it would be interresting to get measurements on it. I did remove the Rothwells from the preamp's inputs and I think maybe I won't need them with the preamp's 33k ohms impedence compared with the Celeste's 12k ohms. It's hard to tell because the preamp is only starting day 2 of break-in. That would probably give me enough gain for the cannons.I don't have the vinyl disk but even the CD engaged the amp's protection circuitry at moderate-loud levels when I played it on the Sim. It doesn't with the 7600ll. But maybe then the impedence spec is conservative on the high side.
arnettpartners OP
312 posts
 
Addendum: I get it. Output impedence is a characteristic of frequency and is effected by components ie tubes or ss components. Hope I stated that correctly.
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