2. amps-preamps
  3. 153702-525

Looking to Try a Passive Preamp

I am looking to try a passive preamp in a system using a Audio Mirror Tubadour III DAC having an output impedance of 1.5K - 2K ohms  and a BEL 1001MK5 amplifier having an input impedance of 22K ohms. I am interested in this approach due to having a problem with EMI and RFI interference with my tube based active  preamp which may become a subject of another thread herein.

I own a Schiit Audio SYS passive. My concern is, given it's input impedance of 10K ohms and it's output impedance of 5K ohms may make it not the best fit. I understand that the input impedance of the SYS and Bel amp are added to give the total impedance that is 'seen' by the DAC, the combined 32K+ impedance due to SYS/amp/2pairs interconnects and that should be OK.  I am concerned about the output impedance of the SYS which to my limited understanding seems too high. Am I correct on any of this? 

If I am correct in my concern with the SYS I am interested in finding another passive pre having input/output impedance better suited to my system. Suggestions sought.

Thanks in advance for any help. Mike
 
mesch
jmolsberg's avatar
jmolsberg
467 posts
 
Does that output impedance seem pretty high for the dac? 
georgehifi's avatar
georgehifi
10,312 posts
 
mesch
jmolsberg



No good for a passive with up to 2kohm dac output impedance and his power amp at 27kohm input impedance.
He needs an active preamp best would be a Schiit Freya with "passive" "tube" or "solid state" selectable outputs. Ideal because all with low gain.
And if the OP ever changes the dac to one with a nice low output impedance the the Schiit passive mode could be used to great effect.
https://www.schiit.com/products/freya-1

Cheers George
someonenew
8 posts
 
georgehifi nails it again. Bravo!
holycannoli
2 posts
 
mesch OP
3,394 posts
 
Yes, the output impedance for the DAC seemed high to me. This is the information I received from Vlad at Audio Mirror. Also the output impedance for the SYS seems high. Is this so?

As to input impedances, am I right that the input impedance 'seen' by the DAC would be the sum of the input impedances for the DAC and AMP? 

Also the BEL input impedance its 27K ohms not 22K ohms. Did not catch this in my edit. Thanks George.

I am enjoying the DAC. My Jolida pre has an input impedance of 100Kohms so the DACs output is no problem. I was enjoying the pre until the RFI/hum problem. Will be calling Jolida to to see what can be done. I replaced the Jolida with the preamp section of my NAD C356BEE. This combination provides silent background. 
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