Can Foreplay III Extended bass be made "tighter"

[glynnw]

For the past month I have been experimenting with a passive bypass in my ForeplayIII Extended, coming out of the unit just after the volume control. I want to avoid the passive vs active controversy here - for many reasons I have decided in most cases that my system is just happier with the Foreplay active.  It lets me play the music stupid loud at times.   However, there is one area of sound reproduction where the passive, in my system, excels.  The bass response, especially noted when a bass guitar is featured, is just tighter when the passive mode is used.  This is obvious to me and also noted by a friend.  It was particularly apparent one afternoon when I was sitting outside the sweet spot to one side.  We're not talking louder or more bass - just that the leading edges of the notes were faster - more impact.  Other than a low value Russian teflon cap parallelling the Auricap coupling cap, the electronics of my unit are stock.  Any suggestions on what I might try to tighten up the bass?  Amps are Paramount 300B.

[Grainger49]

That is an interesting observation.  I can't yet wrap my head around the low frequency response being tighter with the FP III as a passive. 

But I know that the active stages of the FP III add "Drive" that a source alone doesn't have.  I would expect better dynamics and lower noise with the active stages in there.

I infer from the thread title that you FP III has the Extended option, yes?

[2wo]

Well tube rolling is the first thing that comes to mind.

Something you might try is reducing  the size of the coupling caps. This may sound counter intuitive but you figure that Paul has calculated the -3db point to be pretty low, maybe lower than you need for your application. Try

[Paul Joppa]

How exactly is the passive implemented? What I'm getting at is the output impedance of the passive level control - is it the stock Foreplay (Sweetest Whispers) or some other arrangement? If stock, where is the signal taken from? And what is the load on the passive? I take it you go straight to the Paramounts; what cable and how long?

I have an idea or two but it would depend on what drive impedance you actually need.

[glynnw]

I am  going direct into the Foreplay through one of the inputs from which I have removed the resistor.  I am using a Welborne Labs remote volume control- resistance (measured from RCA input plug positive to RCA output plug positive) varies from 25 K Ohm to 30 K Ohm at full volume.  The passive output comes off terminals 17 and 37.   Cables are homemade solid silver a meter long.  Don't know capacitance, but these replaced Nordost Red Dawns, which are known for low capacitance.  To go from passive to active I just move output cables to different plugs - input stays the same.

[Paul Joppa]

OK, then the highest output impedance is probably 6.5K or so. That's OK with a short, low capacitance cable.

My thought was to take the Foreplay output from the first stage plate rather than the second stage cathode, eliminating the cathode follower. That would raise the impedance to a bit over 12K, which may be too high for the cable, but is close enough to give it a try.

If that sounds promising, we can talk about using a different tube to get the impedance down without going through the cathode follower. That would of course be a major circuit change (!) and is less flexible about driving challenging loads, but your cables and the Paramount are anything but a challenging load.

[glynnw]

I appreciate the offer, Paul, but I think changing the tube type would be too complex for me. If it weren't for Doc's superb photography, I'd never be able to assemble these kits. Perhaps some tube rolling will get me closer to what I want. Thanks, again.