J6 and J7 jumpers, and other thoughts!

[dtrax]

Let me preface this post in saying I'm a relative newb when it comes to circuits. I can look at a schematic and know the difference between a resistor and a capacitor, but when it comes to design and functionality of many of the components I'd be lost. However, I'm patient and can follow instructions, so I haven't had any problems so far with my SCA pre's. I've built two N72's and one J99 at this point...

So, 2 nights ago I finished one of a pair of J99's. It works like a charm; no issues at all. Anyways, tonight I'm in the process of building the 2nd and I stopped at step 9 (installing the headers and jumpers). Going back to my first J99, I realized I hadn't installed the jumpers at J6 and J7. According to the instructions, these jumpers allow the servos to be switched out of the circuit for adjustment. I guess I'm confused/naive about the function of the servos. For some reason I was thinking these jumpers switched in/out the SC99 opamps?!

In any event, I did some crude audio tests with various jumper settings. In regards to J6/7, I *think* I can hear a difference with them in and out. With them jumpered as pictured in the instructions, I feel the sound has a bit more detail - but I could be completely full of sh!t. LOL

I also tested the input impedance settings and output loading, using a Mojave MA201 FET mic and my voice. I found that at 300 ohms, this mic responded with far more detail in the midrange than with a 1200 ohms. The recommended setting is 1200, but I totally suggest trying out both.

Switching the output load jumper in and out of the circuit had a small effect as well, although not as noticeable as the input impedance. When switched out, the mids are a bit more "gritty". In the circuit, the tone just seems more "refined", for lack of a better term.

Well, thats about it! Just some rambling thoughts I wanted to share with the class. Back to building!

P.S. As if it hasn't been said enough, these pre's kick serious ass!!!

[tpryan]

I also tested the input impedance settings and output loading, using a Mojave MA201 FET mic and my voice. I found that at 300 ohms, this mic responded with far more detail in the midrange than with a 1200 ohms.

Are you sure you're just not reacting to the extra 6dB of gain?

[dtrax]

I also tested the input impedance settings and output loading, using a Mojave MA201 FET mic and my voice. I found that at 300 ohms, this mic responded with far more detail in the midrange than with a 1200 ohms.

Are you sure you're just not reacting to the extra 6dB of gain?

Initially I thought that as well, but then I recorded and level matched them. Sure enough, there's a difference. Night and day? No, but enough to perhaps make it worth while to add a switch in future. After a bunch of experimenting, I ended up using 1200 ohm input and 600 ohm load output and calling it a day.