Check the impedance ratings at frequency extremes

Posted by jsm71 (A) on March 2, 2012 at 13:54:28

In Reply to: Thx. I too asked for those data. posted by jeffreybehr on February 29, 2012 at 21:52:04:

I too thought that I did my homework when I bought the Cary preamp. Its stated output impedance is 440 ohms. Sounds pretty low. When I complained about weak bass on this site more than one person suggested a possible impedance mismatch and one person directed me to review a Stereophile review that I read, but ignored the testing section.

Testing graphs that Stereophile is famous for showed frequency response curves against multiple input impedances. The only acceptable curve was against 100k input impedance. The 10k curve was really bad! My Mac amp rated at 20K looked on paper to present some issues. Listening did indeed bear that out. I got bass rolloff using the Mac amp. Not a good match. That drove me to find an amp rated at 100K ohms. Once I had that good matchup all is wonderful.

To quote the Stereophile article for my preamp: "The output impedance in the midrange and treble was usefully low, at 370 ohms, but this rose at 20Hz to 6.8k ohms, due to the limited size of the output coupling capacitors. This will prematurely and audibly roll off the bass with power amplifiers having an input impedance of much less than 20k ohms."

Those output inpedances that are stated in spec sheets are across the bulk of the frequency curve, but not at the extremes. My Cary preamp as one example is a great preamp, provided it is mated well to the amp.

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Follow Ups Full Thread

Topic - Amplifier Modifications - Hawk28 06:34:14 02/29/12 (25)

RE: Amplifier Modifications - giantnutz 20:26:12 03/09/12 (2)

RE: Amplifier Modifications - jsm71 07:07:29 03/10/12 (1)

RE: Amplifier Modifications - giantnutz 19:41:00 03/11/12 (0)

RE: Amplifier Modifications - giantnutz 07:35:20 03/03/12 (0)

RE: Amplifier Modifications - Alex M 01:50:01 03/02/12 (0)

Yes, I had that need. - jsm71 14:07:38 02/29/12 (0)

RE: Amplifier Modifications - Hawk28 11:41:01 02/29/12 (5)

RE: Amplifier Modifications - wheezer 12:18:13 03/02/12 (0)

Thx. I too asked for those data. - jeffreybehr 21:52:04 02/29/12 (3)

Check the impedance ratings at frequency extremes - jsm71 13:54:28 03/02/12 (0)

RE: Thx. I too asked for those data. - Hawk28 05:34:18 03/01/12 (0)

Food for thought. - FenderLover 22:35:23 02/29/12 (0)

RE: Amplifier Modifications - Palustris 10:51:07 02/29/12 (0)

'Loading' a preamp with a poweramp, input impedance, and the load resistor - jeffreybehr 10:33:05 02/29/12 (5)

Goldpoint shows how to accomplish this... - wheezer 12:12:10 03/02/12 (0)

RE: 'Loading' a preamp with a poweramp, input impedance, and the load resistor - Palustris 11:11:58 02/29/12 (3)

Perhaps I should have written 'poweramp system' instead of just 'poweramp'. - jeffreybehr 21:46:17 02/29/12 (0)

no,,,, that makes perfect sense - bwb 14:29:39 02/29/12 (1)

RE: no,,,, that makes perfect sense - Hawk28 16:24:28 02/29/12 (0)

It is usually set by a single resistor from input to ground, very easy to change /nt - bwb 07:20:31 02/29/12 (5)

RE: It is usually set by a single resistor from input to ground, very easy to change /nt - ahendler 09:29:38 02/29/12 (1)

RE: It is usually set by a single resistor from input to ground, very easy to change /nt - Palustris 10:42:12 02/29/12 (0)

RE: It is usually set by a single resistor from input to ground, very easy to change /nt - Hawk28 09:15:38 02/29/12 (2)

RE: It is usually set by a single resistor from input to ground, very easy to change /nt - Karma16 03:26:24 03/02/12 (1)

RE: It is usually set by a single resistor from input to ground, very easy to change /nt - Hawk28 05:39:35 03/02/12 (0)

Follow Ups

Check the impedance ratings at frequency extremes - jsm71 13:54:28 03/02/12 (0)

Check the impedance ratings at frequency extremes

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