SSL servo files

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

DrFrankencopter

Well-known member
Joined
Jun 3, 2004
Messages
405
Location
Ottawa, Canada
I've got my SSL servo files located here:

http://members.rogers.com/ingridandkris/SSL/SSL_mod3.htm

Plz feel free to achive them!

(Note: the document was written in MS Word, so its not really nice and web ready. the best wayto make it readable is to size your browser margins to the width of the figures, that way text doesn't wrap aroundthe sides)

Cheers,

Kris

PS: The new site has given me the drive to wanna finish this sucker!

oh, and the mods that I did to my Peavey VMP2 preamp are here:

http://members.rogers.com/ingridandkris/peavey_vmp/Peavey%20VMP.htm
 
I've seen the term "SERVO" used on preamps. Like the Jensen Twin Servo, etc...

Can you explain what a "servo" is with regards to preamps/audio gear?

Thanks!
Owel
 
Noun

1.

servo - control system that converts a small mechanical motion into one requiring much greater power; may include a negative feedback systemSynonyms: servomechanism, servosystem
That is according to Websters Dictionary.
In modern audio usage, the term servo is a feedback stage to eliminate DC
offset in amplifier stages.
Why is that important?
In older circuits, DC offset was eliminated by coupling capcitors.
That's OK.
But if you are building something that has a lot of stages, like a mixing desk, then
the room used up by lots of high quality audio coupling capacitors becomes difficult,
so there is a tendency to use small capacitors aka electrolytic, tants, etc.
These have horrible audio characteristics, and electrolytics dry out over time
as the electrolyte evaporates.
The servo circuit, a negative feedback integrator, for the expense of one extra op amp,
pretty cheap nowadays, can eliminate the capacitor problem.
I use them extensively when I design stuff, unless I specifically want a vintage
sound.
Dave M
 
hi Kris,

I'm using a CAD maxcon2 console that is servo based design and I like
it's ch and master ch sound. (the aux/sums not so much)

I looked at your paper and I see that the last schematic is showing an input buffer uses an opa604. Whenever I try 604's in the audio path I find the results unfortunate. The upper mids seem to loose their presence or
balance.It seems the gains of purity from servo would be negated or
does the opa604 sound different in a servo design?

To me the old standards like 5534/2 and tl072 change the sound less.

This may be a can of worms to get into but I'm so curious.....

cheers,
Lance
 
I am very interested in the Peavey VMP2 mod, but the link you posted does not work. Any way I could sneak a peek at that info?

Thanks.
 
Yeah, that's just a schematic error....the opamp I've been working around is the Forssell DLR-1. I just had finger troubles with my schematic software (Electronics Workbench...yuk).

Cheers,

Kris

PS: There's nothing really special about the op-amp that I chose for the buffer...you can really stick whatever you want there, just pay attention to whatever feedback compensation it requires. The servo itself is pretty much independant of the buffer op-amp. Maybe choose an opa627 if you want low noise for the servo (works well at high impedance), or an OPA177 if you want absolute DC precision.
 
really great work Doc !!!


don't you think the curve of the 1pole filter is a little bit too flat ??

I think I will use this 12db hp filter for my ssl, but I didin't tried it yet..

http://users.otenet.gr/~athsam/variable_filter.htm


do you think it would be worth the work to integrate your new designed input buffer on an extra pcb and connect to the existing G ssl board
or is it to complex, so that a completely new ssl pcb would be the best??


cheers,
matthias
 
Hi Guys, thanks for the feedback.

The peavey link no longer works because Rogers (my ISP) is now affiliated with Yahoo and are doing advertiser based web space. I have the peavey details on my computer at home, but I have some problems that I need to work out with those mods (seems to be a little bit of a tendency to ring...but might be because I was running the 1/4 out and XLR out at the same time). I can make that one a pdf as well....but I'd like to make sure its a good mod first.

As far as the DC fitler goes, 6 dB might be too shallow...I suppose time will tell. Maybe I'll put a switch in for -6 or -12 dB. For layout, I intend on doing a whole new audio path PCB (new VCA's, and Forssell 992 output amp with servo). You can keep the Gyraf SSL board as a SC board, or use the sidechain that I'm working on. But don't expect it anytime soon since my life has gotten real busy lately (new baby, new house....)

Cheers,

Kris
 
no prob...

do you know if there is an easy way to modify the onboard sidechainfilter of the ssl to switch from 6 to 12 db?? or do I need an extra filter circuit for that ??


mat
 
Hi!

Thanks a lot for posting this Kris - great reading.

You don't happen to have a link to the old Audio Amateur servo article - I would love to take a peep at it?

Cheers Tom
 
I think I will use this 12db hp filter for my ssl, but I didin't tried it yet..

http://users.otenet.gr/~athsam/variable_filter.htm

which op amp would you use with that circuit? any?
and how about making one of the 5k6 resistors a bit smaller, so the two 6db curves don't overlay completely, resulting in a more gentle roll-off? should sound better imo.
 
I know this is old as hell but does anybody still have the Servo mod .pdf around?  The link for it is down(probably has been for quite awhile)

thanks,

-casey
 
I second that.  In fact, I noticed a reference to an Amateur Audio article on servos as well.  If anyone has that, I'd be interested.
 
I've seen mention of the email account, but I don't know how to access it.  Is there a meta on this?  Or am I missing something?
 
Back
Top