Foreplay II Tape Buffer Question

[dannyr]

Hi, I have a Foreplay II that I converted to unity gain thanks the instructions VoltSecond was kind enough to post on the web. Now I really enjoy the preamp where before I always felt that it had way too much gain for my system.

http://www.siteswithstyle.com/VoltSecond/Foreplay_Unity_gain/Unity_gain_Foreplay.html

Now I'd like to take advantage of the unused triode on each tube for a buffered tape loop so that I could hook up my Technics SH-9010 Parametric Equalizer for light tone control detail when needed.

Anyway, on the above page in the instructions/schematics for "Variations of Mod 2" detailing how to implement the tape buffer it recommends a CF C4S replacing R2 going from pin 3 of the 12AU7 but I already have one in place of R1 from Pin 8 of the tube. Should I add another in place of R2 from Pin3 with each tube having two CF's or use a 33K sense I already have one CF installed on each tube?

Any help/advice/encouragement is greatly appreciated.

Thanks

Dan

 

[Paul Joppa]

It will sound better with the C4S. When the loop is used, the signal goes through both triodes, so both should sound as good as possible.

My dental hygienist has a poster that says "only floss the ones you want to keep" - that's a good analogy; only use C4S loads for circuits you want to sound good.

 

[dannyr]

Hi Paul. Thank you so much for the reply. So it's okay to use two C4S CF's on the same tube then or would you use one CF and VA in the below circuit?

http://www.siteswithstyle.com/VoltSecond/Foreplay_Unity_gain/UNITY_GAIN_V2_MOD_2_DUAL_SCH.gif

Dan

 

[Paul Joppa]

Yes, both cathode resistors R1 and R2 can be replaced with CF-type current sources.

The circuit shown is not a tape loop, it's a buffered tape output. That is, the tape out is the unattenuated signal from the selected source (phono for example) The main output is the same source, after attenuation by the volume control. You'll need another set of RCA jacks and a switch to connect the volume control to the equalizer instead of the phono. I assume you know this, but just in case someone finds this thread in a search I thought I ought to mention it.

 

[Grainger49]

There is an equalizer loop back or tape monitor input and switch missing from the schematic also.