2. amps-preamps
  3. 125047-818

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
1,085 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
10,312 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
1,085 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
10,312 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 

mitch2
3,894 posts
 
It is not just about gain but I believe also about control of the interconnects, impedance matching and frequency variations with impedance.  The passives I have used include several resistor types (including Endler direct to amp - i.e., no interconnect) and Bent-type TVC, but not LDR.  All had excellent clarity but all missed out in the areas of bass drive and tonal depth compared to my reference, which is a no-gain, buffered preamp with a Shallco attenuator using great-sounding AN tantalum resistors, Lundhal coupling transformers and an outboard choke-filtered power supply.  My conclusion was that even with a 4V source, amps with 100K ohm input impedance, and short, balanced interconnects, the passives were not able to match the tonal saturation of the buffered preamp.

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