Adding passive output to Foreplay III

[glynnw]

The computer program I am using for playback, XXHighend, has a volume control so I have been playing around with bypassing the preamp.  However, I still need the Foreplay to drive the long subwoofer cables.  Is it possible to safely add a set of output jacks to the circuit just after the volume control and then use both the passive and regular output jacks at the same time?  This would let me use my remote to control volume and balance with the Welborne Labs unit I put in the Foreplay.

[Grainger49]

EDITED:  You can but remember the FP III volume controls are wired differently.  You would be putting the input of your computer, if that is what I understand you will be wiring to, in parallel with the 15k Sweetest Whispers.  If it has a high enough impedance that won't be a problem unless this connection injects noise into the grid of the first stage of the FP III.

I wonder why you want to tap in after the SW instead of before.  I probably are not getting this straight in my head.

[glynnw]

Hi Grainger -  The signal going to the Foreplay is from a Wavelength Brick DAC.  I am not using Sweetest Whispers in my Foreplay - I replaced them with a remote control from Welborne Labs that lets me remotely adjust volume and balance.  I tend to be a bit insane about getting balance adjustment to my liking.  If I add a set of outputs after the volume/balance control before the signal gets any amplification, I will effectively have a passive preamp within the Foreplay.  I have made a passive like this before, so I can get it to work.  What I do not know is what effect this will then have on the active section of the Foreplay if I use both the passive and regular amplified outputs at the same time.  My goal is to drive the Paramounts/main speakers passively, the 2 powered subs from the regular preamp outputs and retain simultaneous volume and balance control over both.  I may need some form of buffering in front of the passive outputs (like the 1K resistor on the second pair of regular outputs) but I don't know enough to figure it out.  I am hoping that someone can tell me it will work if I do it in a certain way.

Thanks

[Paul Birkeland]

I must ask, why not drive the sub and the amps with the Foreplay? 

[Grainger49]

Ok, I have it concerning your volume/balance setup.  I think a remote is a excellent idea.  Are you saying that instead of using the FP III for your main amps you just want to use the Welborne passive and use the tubes in the FP III for the sub?

Then if so the only thing to look out for is picking up noise because you are connecting to the FP III input grid.  Use the STP and ground on end of the shield.  You will have the input of your Paramounts in parallel with the input, but it is pretty high, 249k ohms.  This arrangement puts a lot of wire right at that input grid.  This would include the cabling to your Paramounts.

BTW, the second set of outputs on the FP III is for feeding an active sub.  Is there a reason you don't want the FP III before your Paramounts?

[glynnw]

Here is why I want to try running the Paramounts off a passive preamp.  A couple of weeks ago I purchased locally a 35 year old Sansui CA-3000 preamp, with the intention of simply reselling it on ebay at a profit.  This unit has a reputation with some vintage gear lovers as being one of the best old preamps made.  Of course, I had to test it and to my surprise, I found it sounded good and, to my ears, beat the Foreplay in a couple of areas, notably leading edge transients, like on a cymbal and some drum recordings of snare drums.  At the same time, the developer of XXHighend was commenting on his site that since he had added a volume control to the XXHighend music player, he had disposed of his preamp.  So I hooked the Paramounts up directly to the DAC and liked what I heard - it again gave me faster transients (or whatever).  However, my 16 bit DAC only gives me 6 dB steps on the player's volume control, the subs didn't work well off the passive and I really don't want to give up my remote, so if I can wire in these passive outputs I can screw around comparing several combinations quite easily.  And best of all, it costs nothing.

[Grainger49]

Glynn,

Thanks for the explanation.  Again, I get it now.  Since Paul B didn't say there would be a problem I would say go ahead.  Like you say, you have nothing to lose and it is free.

[Paul Joppa]

I don't see a problem either, as long as the Welborne is comfortable with the cable capacitance. There would be an issue with the Whispers as normally configured in the Foreplay - as Grainger said, that is an unusual arrangement. (You would have to re-configure the Whispers as a conventional potentiomenter.)

[glynnw]

DONE!  Really easy - just used input 3 (which I never use) and it is now Passive Output 1. The volume is too low for rock n roll, and I didn't test it with the subs (too much trouble readjusting the volume) but there is less noise and a bit more detail retrieval - just noticed the vibrato in a singer's voice that I had overlooked before.  Unfortunately I live on a street of 5 acres lots, so during the day there is ALWAYS a lawn mower going somewhere, but this should be great for late night listening.  And switching between the 2 choices is just simple as can be. 

One more question - the volume control has an input impedence of 25K, with the inline 33K resistor I get a reading of 58K.  Would changing the 33K resistor to a 10K give me any volume increase?  I only use 1 input, so I could change the second one and have a choice of input resistance.  But if it will make no appreciable difference, there is no point.

[Paul Joppa]

One more question - the volume control has an input impedence of 25K, with the inline 33K resistor I get a reading of 58K.  Would changing the 33K resistor to a 10K give me any volume increase? 

Assuming the 25K control is configured as a standard potentiometer, you can reduce or even eliminate the 33K series resistor, and you will get more gain that way. The Welborne manual ought to make that more clear, but I'd be surprised if this were not the case.

If you have a couple clipleads at hand, just short out the 33K temporarily and see if it works. Everyone should have a pack of clipleads on hand!

[glynnw]

Thanks paul.  I removed the resistor, it all works great and is now loud enough for 99% of my listening.  Thanks.