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I used to think passive preamps were superior to active preamps given right the setup, but

my recent evaluation of a modded old SS preamp has me a little befuddled.  I've evaluated $10K+ active preamps in the past and was never impressed especially given their cost.  In general, I've found passives to do better job. I know there's ongoing debate on this.  But here's a very illuminating video on the subject by Bascom King, one of the legends of high end audio.

https://youtu.be/HHl8F9amyY4
dracule1
dracule1 OP
1,043 posts
 
Paul79, I really didn’t think anyone would be interested because it’s no longer made and is considered mid fi to most. It’s the Acurus RL11 that was modified. Acurus was considered the little cousin to Aragon. The stock preamp is nothing to write home about, but once it’s modified to be direct coupled and run in Class A with better output mosFETs and power supply upgrade, etc, it beat every passive I have in almost all categories of music reproduction important to me.
dracule1 OP
1,043 posts
 
Georgelofi,

"Except for some tube output sources which have ridiculous high output impedance (more than >1kohm). Or some ClassD amp that are very low input impedance (less than <10kohms). These users usually find something wrong with the sound of passives, and say active preamps are better, oblivious to the fact that they had an impedance mismatch with the passive they used."

Yes, I completely agree.  Most of my sources have output impedance less than 100 ohm and my amps have input impedances 50k to 100kohm. Although my tube DAC has output impedance ~1.6kohm, it still sounds great in my setup using passive pre.

georgehifi's avatar
georgehifi
4,966 posts
 

1.6Kohm could also sound fine so long as the amp is still over 33kohm, because the 1.6kohm has to drive the combined load of passive + the amp.

If you have say 33kohm amp and 10kohm passive that's a combined impedance the source sees of just under 8kohm, a 1.6Kohm source will drive this no problem as the ratio is still 1:5, but a ratio of 1:10 is the really the minimmum one should aim for, and then it could sound even better instead of fine.


Cheers George

dracule1 OP
1,043 posts
 
George, sometimes it's just too much of a hassle to match your system to a passive preamp, although you can get some great results when all the stars align. Sometimes an active can be as or more rewarding without the hassle.  As it stands now, I like both in my system, but the active pre just does more for me overall.
georgehifi's avatar
georgehifi
4,966 posts
 

Not really, like I said over 90% of systems are a perfect match for a 10kohm passive, it's the few oddball high impedance tube output sources that are the trouble.

eg: like the well know "cottage industry" dac with a 12AX7 output tubes at 3kohms!!!, the 12AX7 was never meant to be an output tube buffer. High gain input tube for phono/preamp/poweramp stages yes but an output tube?? Really?? 


Cheers George 

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