Can input sensitivity be easily changed?

[glynnw]

Can the input of the soft start Paramount easily be changed to about 1vRMS?  I realize "easily" is a relative term - for me it would mean changing 1 or 2 items only.

[Paul Birkeland]

Yes, you can install a voltage divider made of two resistors at the input of the amplifier.  IIRC, the sensitivity is a little different for the 300B and 2A3, which would you like to pad down to 1V?

[glynnw]

300B - 8+ glorious watts of power

[Paul Joppa]

Too be perfectly clear, sensitivity must reflect both input and output - for example, with a 300B Paramount, you might want "1v input for 8 watts output" or perhaps "1v input for 1 watt output".

[glynnw]

Here's my goal.  I own a DSpeaker 2.0  dsp unit which has amaximum  output voltage of 1.65 vRMS.  It was an early model - later they increased this to 13 vRMS.  So I cannot use it to drive the Paramounts to full volume, while my Cosecant DAC, with 2.0 vRMS output does drive the Paramounts to full volume.  I have tried other amps with input sensitivity rated closer to 1.0vRMS and they work fine and give plenty output voltage when driven by the DSpeaker.  If I can get the Paramounts to give full output when driven by something like 1.0vRMS input voltage I can use the DSpeaker unit on them.  That is my goal, since these amps are my best sounding amps.  Hope that makes sense.  My other alternative is to sell the DSpeaker and buy a new one, but that could cost up to $500 net, which is a bit spendy.

[vetmed]

Check the Bottlehead product page for the Paramount where it states full output with 1.56V input for 300B. With a 2A3 you only need slightly less than 1 volt for full output. So with your Dspeaker 2.0 dsp unit's 1.65V maximum output you should be just able to drive the Paramount into clipping

Robert Lees

[Paul Joppa]

vetmed is correct; that's why I was asking about exactly what you meant. In this case, I think "full output" means "loud enough for me with my music and speakers". You will be clipping on full-scale peaks, but only a few dB which is normally inaudible with SETs (they overload more gracefully than high-feedback amps).

Paramount with the 12AT7 driver, version 1.0, had a sensitivity of 0.9v for full output with 300Bs. The 12AT7 bias is too low to use the adjustable operating point, making it less than satisfactory with the direct-coupled 2A3, but in 300B form you should be able to get it to work satisfactorily with the soft-start board (ver. 1.1). It requires a new 9-pin socket with different wiring - conceptually easy, but probably a bit frustrating! Just take your time.

[glynnw]

I'm just going to leave the Paramounts as they are and buy a new DSpeaker processor if I feel I need to use DSP on the Paramounts and main speakers.  For whatever reason, when I do put the DSpeaker unit into the circuit between the passive preamp and Paramounts, the maximum volume is noticeably lower than when the DSpeaker processor is not there.   I am not convinced I would really benefit greatly from applying DSP to the main speakers anyway.  On just  the subs the DSpeaker makes a huge difference - highly recommended. Thanks for the advice.