fun with paralleling film caps in a Mackie console

[emrr]

Some of you will wonder why: Mackie 32-8 console with film bypass caps added to audio signal coupling electrolytics. I did this in stages, and compared sound as I went. First a pair of channels to compare against stock, then the more important parts of the master section, then the rest. I wound up doing the whole console in two or three sessions. Maybe 10 total hours of actual labor. Many more analyzing the circuit board drawings and marking the terminals before starting; maybe $120 worth of caps. I felt it was a significant improvement in clarity, distortion, and 'speed'. The console already had a good bit of age on it, and that may well have bearing on the improvements realized.

cap prep stages; x 600ish. These had to be floated off the back side of the circuit boards, and match the spacing of the existing electrolytics:

channels:

master section:

 

[MartyMart]

WOW !
That's looks like a lot of work Doug and I have a candidate from 1998 right
in front of me !!
Are they all 104's ( 100n ) ?
You just attached them to the solder legs of the Electro's that poke through
the PCB, that must have been quite "fiddly" to say the least !

Regards,

Marty.

 

[haima]

phew! your're a brave man doug. i tip my hat to you.

i'm glad you were able to make an improvement!

:guinness:

 

[emrr]

Funny I can't remember what the value was; smaller than I'd have liked. Maybe as low as 0.022. I still have some leftover's in the bag, so I'll check the part #s. At the time I used the largest value and smallest footprint I could find. They were much less fiddly than I expected, and getting the technique down wasn't too bad. I recall the through holes seeming fairly large and well defined, and they gave a pretty steady foothold, considering. I really didn't want to go through with this, but curiosity got the better of me and I felt the improvements, even on a channel strip, warranted further work. I'd already gone in to deal with dead master section switches, so I had an idea about the guts. I was surprised especially that the EQ's suddenly seemed to have a much finer degree of control; +1 could be heard as a change, which really wasn't before. YMMV.....

 

[MartyMart]

I was thinking of getting rid of my 32-8 but someone always pops up and
says " NO don't do that " and I get reminded of what it cost me at the time
( £3,200.00 ) - the better part of $7000 !
It needs some surgery, I keep loosing the master out on the left side, which
I think is either the main gain pot or the fader / both !!

Having not "opened her up" is the master section a PITA to get to ??

Respect,

Marty.

 

[emrr]

Not too hard to get to; mainly labor of pulling console, pulling back, pulling all knobs, pulling board. Component replacement is like micro-surgery though. I had to cut a few pots and switches into little pieces and extract the remnants. Really thought I was going to burn up the board and damage some traces. You really need the official Mackie maintenance CD with all the drawings, so you can plot it all out in your head first. I assume they still sell the CD documentation. I had it all printed out into a giant 11" x 17" book I could mark-up with a red pen. Lots of sharpie guide marks on the boards as I went.

 

[jensenmann]

I´m currently doing that sh*t to my Matchless and my M2500 including total recapping and partially reswitching and repotting. That´s quite a bit of work.
The caps I´m using are Wima 100nF. They are very small and fit practically everywhere.

The Matchless is running now and the bypass-cap-job did a very good job in the Mastersection. The improvement in the channels is not that huge but I guess when everything is done it will add up.

 

[jpuhhuh]

This has me wondering. Is benefit the result of increasing the capacitance? Or is it a result of the paralleling of existing caps?
And how does that work in theory?
Thanks for the explanation in advance.
JP

 

[gyraf]

Simplified: High-frequency transfer - where the electrolytic caps are weak because of their rather high ESR - is taken over by the film-cap.

Jakob E.

 

[Svart]

I think it's a debatable topic. For poor quality 'lytics, the films might do something but I don't think anyone has every really proven that they "improve" the response. I would simply say that they "change" the audio in some cases. Audio frequencies are generally below the worse-case 'lytic cap "filter" created by it's ESR. ESR tends to be a problem when large currents are flowing such as power supplies but I've not seen an audio test show that ESR was the main problem. It seems that the circuit impedance reacts with the ESL and ESR of the cap more often than the cap doing the damage on it's own. As we all know, simply popping a part on a board because it fits and because it's cheap gets you nowhere. You wouldn't stick an opamp in your circuit without knowing it's input impedance, why would anyone stick an unknown cap on the board? It might work, but is it working correctly?

 

[emrr]

In this case, comparisons of channels 1 and 2 with channels 3 and 4, before and after addition of film caps to 1 and 2, showed a clear improvement in 1 and 2. I had kind of hoped it wouldn't, but it did, and I proceeded to do more.

 

[clintrubber]

If you're using the mic-preamps, how about the big el-cap in series with the gain-pot ?

There's not much to be done there w.r.t. adding film-caps (polarizing the cap might be an alternative if there's mod-urge), but of all el-caps it'll be the most dominant contributor I expect. It's just on its own though, so the accumulated contributions of all smaller caps that can be 'filmed' might still be very noticable.


Regards,

Peter


But please let's conclude it's not worth it... I mean, if I still have it then, I don't feel like 'filming' my MX8000 in a few years :twisted:

 

[emrr]

I don't use the mic preamps; think I did the caps around that part anyway.