Two J99's Output different on both

[Nu-tra]

Hi Tim or anyone that can help. I am getting ready to seal up my chassis when I noticed my outputs volume of my j99's are different from each other. Both are set to -18 +18 but the volume is louder on my newer one that has the bias trim section. Any thoughts?

[Nu-tra]

EDIT. My older j99 without the bias section is louder. Any thoughts.

[Nu-tra]

anyone have any ideas? I want to close my chasis up

[tpryan]

The latest rev is set up so gain matches the other modules more closely. I don't think you have a problem.

[Nu-tra]

ok thanks what if I wanted to sum through it? Just have themes rev one louder?


Nigel tuffnel

[tpryan]

You can easily trim the gain to match. You could also swap the old rev gain resistors to match the new ones.

[Nu-tra]

sorry tim
I'm a hack. Which resistors are they? What procedure to chane the gain?

[Nu-tra]

Hi Tim

If it's not too much trouble. Can you tell which resistors to change and what values to change them to?

Thanks in advance.

[Nu-tra]

Does anyone know?

[tpryan]

You can change R5 - R9 and R11 - R15 on rev 3.3 and 3.4 to match R8 - R11 and R18 - R22 on rev 3.6. If it's not clear how to do it from the schematic, it's probably not a good idea to try it yourself. Realize also that changing the gain resistors still won't make a matched pair, since the sum of R1 - R4 on rev 3.3 needs to equal the sum of R3 - R7 on rev 3.5. That total resistance sets the input impedance, which is 1200 ohms for rev 3.6 but slightly lower for older revs. R1 - R4 would have to be recalculated to match the higher impedance and still retain the 5dB steps.

[Nu-tra]

What voltage/gain do you recommend I set the older rev J99 to? Will this affect the preamps performance/headroom?