SoundCraft spirit channel mod

[aviel]

Interesting..

what exactly did you recap?
did you keep the same values?

 

[bernatvm]

Interesting..

what exactly did you recap?
did you keep the same values?

I changed all the electrolitics in the psu, I think there are 9 of them or so. I kept original values

 

[bernatvm]

Just recaped first channel and modded the insert to be direct out (as shown previously in this thread). Also cleaned the fader and some of the pots. Only thing left is the 75Ohm resistor, which I don't have spare.

I'm thinking about modding the eq, I feel like 100Hz is too high for a high pass filter. Manual says is R22 and R23 where I should look for that kind of effect. Also, I thought maybe changing the low band to a shelf instead of a bell and rising a bit the Hi band freq, lots of posibilities... anyone have any ideas?

 

[aviel]

I plan on lowering the hpf as well, would likw to take it down to around 60Hz. Another thing that i would like to do is actually having a bypass switch for the eq. By looking on the scope i realized that even if the eq pots are at 0db, the frequency of the middle still affects the signal.

Still no practical idea on how to modify the eq though.

Do you hear a difference between the modded and unmodded channel?

 

[bernatvm]

Sitll had no time to buy R75 ohm for the direct output, so I haven't mounted it yet. I'm planing to do an A B comparison with some line source form my interface into modded channel vs unmodded channel. Will publish results in this forum  :

 

[aviel]

i didnt use another 75ohm one, i reused the one already there

 

[bernatvm]

First you need to isolate the connector from insert line by cutting PCB traces going to tip and ring pin.
Then, you should connect directly premp's output to C22 with a wire, and then the post fader signal from C21 to R34 .
The new resistor connected from ring pin to ground is used for the output impedance balancing of your new "direct"output.
You can connect it to the ground if you wish but the output signal will be then unbalanced.

I think you need two of them, the one already there (R34) should remain. moamps please correct me if I'm wrong!

 

[moamps]

I think you need two of them, the one already there (R34) should remain. moamps please correct me if I'm wrong!

You're right.

 

[moamps]

I plan on lowering the hpf as well, would likw to take it down to around 60Hz. ....Still no practical idea on how to modify the eq though.

Just  add 39nF  film capacitor on each C11 and C12.
http://sim.okawa-denshi.jp/en/OPseikiHikeisan.htm

 

[aviel]

i still dont get why you need that 75Ohm resistor along with C22., it looks like it was there to help with the return, since it is not used, why keep thrm?

 

[moamps]

i still dont get why you need that 75Ohm resistor along with C22., it looks like it was there to help with the return, since it is not used, why keep thrm?

http://www.epanorama.net/newepa/2010/02/23/unbalanced-to-impedance-balanced/

 

[bernatvm]

Is there any reason to change cap values vs change resistor values on modifying the hpf? For me is much easier to find good resistors than caps (local bussined film caps are not good)

 

[moamps]

Is there any reason to change cap values vs change resistor values on modifying the hpf? For me is much easier to find good resistors than caps (local bussined film caps are not good)

The resistors define the load of the HPF to the previous stage in the pass band. So they shouldn't be too low (IMO, under 5k).

 

[bernatvm]

Any film cap brand/model recomendations?

 

[moamps]

Wima MKP10  5% would be sufficient.

 

[bernatvm]

Moamps, do you know any web page or book I can check to understand the eq of the desk?

I'm good with all the math involved but i don't know how to find the numbers and formulas.

 

[moamps]

...do you know any web page or book I can check to understand the eq of the desk?

Don Lancaster - Active Filter Cookbook