Zu Soul Superfly

The rule of thumb is 10:1, that is, the input impedance is 10x the output impedance between the two components. I've also heard the rule of thumb is 20:1, but hey, it's a rule of thumb right, so the truth is probably somewhere in the middle, somewhere between 10:1 and 20:1.

MM Preamplifer has 700 ohms output impedance
700 ohms * 20 = 14Kohms
F1J amplifier has 15Kohms input impedance

14K < 15K

So you should be good.

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.

OK, I think I mis-read you and was concerned about input impedance.

Nelson Pass was goodly enough to post step by step instructions for the conversion on diyaudio as he does with all the Firstwatt deigns.

Step by step:

1) You match up a pair of SemiSouth R100's or equivalent and
drop them in for Q1 and Q2

2) You eliminate the Zener diodes

3) Raise the input cap values to 10 uF

4) Replace R1 through R4 with 22 ohms

5) Replace R5-R8 with 47K ohms

6) Set the bias pot to +14V on the Drains

All Greek to me, but I sourced the R100s from a group buy on diyaudio and have a competent friend willing to do the update.

Off topic--or back on topic, rather. These Soul Superflys have been the single most meaningful upgrade to my system. I'm listening many hours daily virtually every day. I'm really confused as to why Zu speakers have been so controversial over the years. Based on what I read on forums, I really expected them to have a weird sound but they sound very right to me, making real music.

The other owners really need to chime in! I feel like I'm all alone here.

Mrs. Gopher needs to post those pictures and we need to hunt down and stalk all the other owners.

Mike

Gopher,
"I'm really confused as to why Zu speakers have been so controversial over the years."

Because they were :

A- New to the Game

B- Mixed with many early 21st century Chinese copy gear, and or companies plagued with tech issues and name smearing early in the internet game. Most "Audiophiles" never saw a web page until early 2000's... Stereophile magazine, and too good to be true were the run of the mill advertising of the time.

C- And possibly the most controversial they heavily marketed direct, and with single driver wide band, no crossover voodoo. Which is like Tubes or vinyl to the mass marketed even upper scale boutique customers.

D- Entering a highly saturated audio market virtually at the peak of internet sales, Forums, and the revival of Vinyl... Who knows!