Lasselakken
Active member
- Joined
- Nov 11, 2006
- Messages
- 43
I plan to do some recapping and maybe a few mods on an Allen & Heath System 8 mixer. My mixer is a Mk1, but here I have been using the Mk2 schematics since they are mostly the same. I have been reading quite a lot on these kinds of jobs, and have come up with a plan for the input modules. I’d love to get some input from you guys, though.
Electrolytic caps
I have marked the electrolytic capacitors on the attached schematic, and here is what I plan to do:
I plan on using mostly Panasonic FC electrolytic caps.
On top of that I plan to bypass all electrolytics in the signal path with 0,1uF Wima MKS2 on solder side of pcb.
Should I be changing the 10uF coupling caps to higher values too?
Could C8 and C9 be changed to a smaller value polyester cap? (Wima does make 10uF polyester caps, but they are much more expensive). Could other electrolytic caps be substituted by polyesters?
Transistors
Would it be a good idea to change out the transistors (Q1-4) and if so, what would be good replacements?
ICs
I also plan to do local power rail decoupling at the ICs by adding a 0,1uF Z5U cap between +/- (pins 4 and 8) and ground for each IC.
Later on, I will try different op amps like OPA2134, LM833 or LME49720. Any suggestions or warnings regarding ICs would be very welcome. Can I expect any improvement from just changing the old TL072 to new ones?
PSU
I’m aware that the original PSU is too weak to handle more power hungry ICs and I plan to upgrade it (probably just building or buying a new one).
Actually my first move will be to recap the master channels, but I think that once I have a good plan for the input modules, I can apply same principles to the master section.
Please chime in with any suggestions.
Electrolytic caps
I have marked the electrolytic capacitors on the attached schematic, and here is what I plan to do:
- C1+C2 – 10uF line input – no change, just some fresh 10uF
- C3+C4 – 47uF Mic input phantom blocking caps – change to 220uF
- C7 – 220uF just after mic gain – change to 1000uF
- C8+C9 – 10uF just after transistors – no change, just some fresh 10uF – or could these be changed to polyester caps 2,2uF, 3,3uF or 4,7uF?
- C11 – 10uF coupling cap – no change, just a fresh 10uF
- C13+C14 – 100uF on power rails – change to 1000uF
- C23 – 10uF coupling cap – no change, just a fresh 10uF
- C27 – 10uF coupling cap – no change, just a fresh 10uF
- C29 – 47uF at insert return – no change, just a fresh 47uF
I plan on using mostly Panasonic FC electrolytic caps.
On top of that I plan to bypass all electrolytics in the signal path with 0,1uF Wima MKS2 on solder side of pcb.
Should I be changing the 10uF coupling caps to higher values too?
Could C8 and C9 be changed to a smaller value polyester cap? (Wima does make 10uF polyester caps, but they are much more expensive). Could other electrolytic caps be substituted by polyesters?
Transistors
Would it be a good idea to change out the transistors (Q1-4) and if so, what would be good replacements?
ICs
I also plan to do local power rail decoupling at the ICs by adding a 0,1uF Z5U cap between +/- (pins 4 and 8) and ground for each IC.
Later on, I will try different op amps like OPA2134, LM833 or LME49720. Any suggestions or warnings regarding ICs would be very welcome. Can I expect any improvement from just changing the old TL072 to new ones?
PSU
I’m aware that the original PSU is too weak to handle more power hungry ICs and I plan to upgrade it (probably just building or buying a new one).
Actually my first move will be to recap the master channels, but I think that once I have a good plan for the input modules, I can apply same principles to the master section.
Please chime in with any suggestions.