Zu Soul Superfly

Gopher:

Check "Watt's New" at www.firstwatt.com: select F1J

Nelson Pass is upgrading the F1 to the new Jfets used in the J2: free for original owners (you pay only frieght + cost of shipping box), small charge for 2nd owners, etc.

Might be your answer for more texture and image density.

If interested, contact nelson@passlabs.com to get on the upgrade list; include the serial # of your F1.

(I'm going to try the Soul with either a F1J or the J2 later this year. If you upgrade the F1, I would appreciate your comments on the combo.)

Gopher:

I mentioned to you on 7/06/2010 about upgrading your F1 to the F1J. I've read here since that you are going to do so. One potentially huge difference (problem?) for you, especially if you are using a tube pre: the input impedance for the F1 is 100K ohms single-ended and the F1J is 15K ohms (note at www.firstwatt.com under products it says 100K and 10K respectively, clicking on F1J it says 15K single-ended). Rule of thumb (from conrad-johnson): pre output impedance < 10% x amp input impedance, i.e. your pre must be less than 1500 ohms or you will probably lose some of the low-end frequency. You might want to send an email to Nelson Pass at nelson@passlabs.com and discuss this, especially if your pre has an output impedance greater than 1500. I'm anxious to hear what you think of the Soul/F1J combo, if and when you finally upgrade.

Gopher:

You will not have a problem. Your are telling me that your pre output is 700 ohm which is less than the critical number of 1500 ohms for the F1J. 10% x 15000 ohms = 1500 ohms (F1J input single-ended impedance is 15K ohms (K=1000) or 15000 ohms. 700 ohms < 1500 ohms, so you will have no problem. Now, I'm assuming that the person who will be updating your F1 will be doing what Mr. Pass does when he updates a F1. To be safe, have your guy contact Mr. Pass via email and discuss it with him.