SoundSkulptor EQ573 Highshelf

Awrange · Aug 12, 2021

Hey guys!

Like many others I started getting into building analog gear during Covid lockdown. First some guitar pedals, then some 500 rack gear and recently the LA2A from analogvibes.
One of the 500 units was the 1073 style preamp from SoundSkulptor. Shortly after, i built the SLQ51X, to have some eq options. It's really nice but I also want some "broader strokes" eq in my arsenal. I'd love a couple of BT50s from CAPI but they have been out of stock for ages and now I'm contemplating to maybe get the SS EQ573s instead.

There is not really much useful information on how these things sound, so if someone has experiences with these units it would be amazing if you could share them.
What I'm especially interested in is the highshelf. It looks like the original EQ uses an inductor for every band while the SS unit only uses an inductor for the low and mid band (Link to the EQ573 schematic if someone is interested https://www.soundskulptor.com/docs/eq573-ii-schematic-01.pdf).
I'm not sure, how much that is affecting the sound and if that is a "make or break" component.
In case it is, would it be possible to easily modify the highshelf circuit to incorporate the missing inductor? The unit seems pretty cramped and that last inductor might not even fit in there but I'm curious if it could theoretically work

TwentyTrees · Aug 13, 2021

Awrange said:
What I'm especially interested in is the highshelf. It looks like the original EQ uses an inductor for every band while the SS unit only uses an inductor for the low and mid band (Link to the EQ573 schematic if someone is interested https://www.soundskulptor.com/docs/eq573-ii-schematic-01.pdf).

While I've no experience with Sound Skulptor's take on the 1073 EQ, the topology looks correct on a cursory view. The original 1073 only has inductors in the high pass filter and mid band (where it had two inductors - most modern versions combine these into one), with the high shelf and low shelf being RC filters without inductors. So you wouldn't need to worry about adding any inductors to this version, as none appear to be missing.

Indeed, with many more EQ points to choose from in the high and mid bands, and with to my mind more sensible choices in the HPF range, the Sound Skulptor version certainly looks a lot more versatile than the original. I can't speak to how it sounds, though.

Awrange · Aug 13, 2021

@TwentyTrees Thanks so much, I did not know that it was like that in the original units.
I just looked at the schematic again and you're totally right, the high pass filter and the mid band are using the inductor.

The reason for my question is that I read a post on this gearspace thread
https://gearspace.com/board/so-much...nd-skulptor-eq573-eqp501-vs-neve-api-ssl.htmlwhere a poster stated that he liked this don classics eq unit more than the ss because of an additional inductor in the highshelf.
After reading that I looked up several other clones and the original RND unit and found that they indeed all use three inductors.
Maybe they changed the design at some point?

TwentyTrees · Aug 13, 2021

The poster on GS is mistaken, as the schematic on the Don Classics website shows no inductor in the high shelf there. In fact, if there was an inductor then it most likely wouldn't be a high shelf - inductors are generally used in studio EQs to obtain a bell / peak response, though the 1073 is an obvious exception.

As I mentioned, the original 1073 did indeed have three inductors - one for the HPF, and two for the mid band. In many modern versions, those two inductors for the mid band are replaced with a single inductor with more taps. There is likely to be little functional difference.

Basically, the Sound Skulptor unit isn't short-changing you on inductors.