SSL 4000 G-Series Install - a 4 year journey!

[Artur D'Assumpção]

Awesome!!!

[Nick]

Hi Marcmozart,
great work. 

Could you explain better this mod you've done to the VCA card?


VCA Card (top left) on which I increased C9 to 220uF and added MKP Bypass-Caps 0,01uF on C8 and C9 (soldered to the back of the PCB)G-Series Channel Amp Card (top right) and Dynamics in the front.

regards

Nick

[marcmozart]

Read more here, it all goes back to some comments audio modding "guru" Jim Williams made on many occasions:
http://forum.sslmixed.com/index.php?topic=261.msg2161#msg2161

EDIT: Also see Pat's post below - he explained it really well.

1. The coupling caps in the signal path are there to filter out DC, they act like a High Pass Filter. Increasing the value of the coupling caps moves the frequency of the "High Pass Filter", and also it's phase shift, lower (C9 was 10uF before, now 220uF). I can measure extended low end after changing the value.

2. The added "bypass"Film-cap could be called esoteric, but it is said to improve the higher frequencies and transients. Basically, the added value of capacitance is so small that it doesn't change the value, but the added smaller Film Cap reduces the inductance in the higher frequency range. I'm not qualified enough to explain it properly, but I kinda understand what it's doing.
It certainly doesn't hurt and my recapped channels sound very clean on the VCA path. In fact the low end of my VCA path measures better than the Monitor Path (haven't changed any Cap Values on the group card yet).

Try to google "coupling caps film bypass jim williams".

Here's a link that goes more into detail:
http://www.gearslutz.com/board/geekslutz-forum/578503-bypass-caps-air.html

Once my entire console is recapped, I will experiment with 1 or 2 channels that have some heavier mods, like replacing the 5534/5532 OP-Amps with LME49710/20, which have such a low DC Offset that interstage coupling caps might not be required (they are important on Input Cards, Inserts, etc.).
But that might change the character of the console and brings other issues to the table (like high frequency oscillation), so it gets very experimental.
I would love to have more modding discussions on here, just to learn what parameters can be influenced.

Hi Marcmozart,
great work. 

Could you explain better this mod you've done to the VCA card?


VCA Card (top left) on which I increased C9 to 220uF and added MKP Bypass-Caps 0,01uF on C8 and C9 (soldered to the back of the PCB)G-Series Channel Amp Card (top right) and Dynamics in the front.

regards

Nick

[PMcC]

Hi Marcmozart,

You must surely rank as deeply inspirational to many silent, and non-silent, observers out there, you should be rightly proud of your great work and thanks for sharing it.

On the capacitor subject, electrolytic caps have an overall impedance characteristic that includes so called 'parasitic' elements two of which are ESR (effective series resistance) and ESL (effective series inductance). It is the ESL component that results in the capacitor effectively looking like an inductor at high frequencies, not good!

The ceramic, or film bypass, capacitor types have much lower ESL so when connected in parallel with the electrolytic, the combined inductance is greatly reduced, good...similar to when a high value resistor is paralleled with a smaller value resistor.

At least one assumption is in evidence here, that is the ESL of the electro Cap is greater than that of the bypass Cap...

Mods that I have implemented into various circuits in my 'senior' 4000E include getting shot of as many electrolytic capacitors as possible...enter the DC servo loop. With a little care and attention to design details, this mod is relatively straight forward and truly rewarding sonically.

I like the NE5534, any other fans out there?

Pat

[marcmozart]

Thanks for the feedback, Pat! So the bypass cap reduces the inductance of the Electrolytic Capacitor at high frequencies, right? I'll correct that in my post! And, agreed, I too love the sound of the 5534.

[marcmozart]

The never-ending story... recapping G-Series EQ-Cards, one of the easiest jobs as most caps are huge, easy to desolder, and non-polar (you can insert them any direction).

When recapping, I usually do a bunch of the same cards, while keeping a "reference" at hand to quickly confirm the correct values.



Bypassing all Coupling Caps with a WIMA MKP 0,01uF. As you can see, these Bypass Film Caps go on the backside of the PCB in parallel to the Non-Polar Coupling Caps (these Film Caps are also Non-Polar).
Need to do a listening test comparing the cards with bypass to those with no bypass. This run will have the bypasses...



Done... those four EQ-Cards took about an hour, including desoldering, cleaning the cards and recapping.

[Artur D'Assumpção]

Amazing job Marc!

Please let us know about the results on those listening tests!

Cheers,

Artur

[Spanzor]

How did they turn out?  Thinking of modding a few channels. 

What's the deal with the monitor path?  I haven't A/B'd mine against the dangerous...

[marcmozart]

How did they turn out?  Thinking of modding a few channels. 

What's the deal with the monitor path?  I haven't A/B'd mine against the dangerous...

To be honest I'm not really hearing a difference 

[mg73]

Glad to hear, saves me a lot of time when I will recap....

[Spanzor]

haha!  Thanks Marc!