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August 10, 2020, 11:11:15 PM

Author Topic: Fix with Passive Preamp and 300B Amp ?  (Read 1646 times)

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Offline chuck999

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Fix with Passive Preamp and 300B Amp ?
« on: December 29, 2014, 10:30:29 AM »
Have single driver speakers built using Fostex FE206E (from Planet 9) and huge Sachiko double horn cabinets.  They sound fairly nice with my 300B amp but have always suspected they might benefit from some baffle compensation ...

Am using a passive preamp (home built with goldpoint 25k resistors).  Amp has they typical 100K input impedence. 

Any experience or suggestions regarding use of the Fix with a passive preamp?




4krow

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Re: Fix with Passive Preamp and 300B Amp ?
« Reply #1 on: January 31, 2018, 12:30:00 PM »
 Just remember, the Fix has a 4db insertion drop. I am wondering if there will be enough drive for the power amp. 

Offline Paul Birkeland

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Re: Fix with Passive Preamp and 300B Amp ?
« Reply #2 on: January 31, 2018, 01:33:38 PM »
Am using a passive preamp (home built with goldpoint 25k resistors).  Amp has they typical 100K input impedence. 

This isn't all you need to consider.  If your 300B amp has something like a 12AX7 sitting at the input, the miller capacitance is going to tax the high frequency response of your system when you factor in the impedance of the passive driving it, and adding in the cable capacitance.

If your amp has a pentode (wired as a pentode) at the first stage, this issue will be greatly decreased.

You could also consider changing the 100K resistors at the input of your amp for 250K resistors, but this isn't going to help if the input capacitance is too high. 

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man