XS902 - now with added "everything" PDF!

[Dr nEon]

Hi !

I'm studying the pdf rev 3a , and have noticed a small discrepancy between the overlay and the pcb trace.

On the photo of curtis' prototype , there is a boxed film cap mounted horizontally , between R51 and R54 . The pcb trace makes provision for this with two 5mm spaced pads , but on the overlay and bom , this cap is omitted.( The faint trace on the overlay doesn't have those pads)

I think it is a 100nF/50v ???

Was it intentionally left out , is it an error on the overlay , or is it an optional part ??

It seems to be doing the same job as C22 , I think...

I suspect it's a relic from the prototyping stage , but it would be nice to get confirmation!

cheers!

nEon

 

[Curtis]

Hi Neon,

Well spotted.  I missed it myself.  All that capcitor is used for is decoupling the positive supply rail to IC3.  C22 is doing the same job, but it won't hurt (or enhance for that matter) if you decide install that spare cap either.  Choice is yours.

100nF MKT or ceramic will work fine.

I'll aim to fix up the PDF file next opportunity I get.

 

[Dr nEon]

Hi Curtis!

Ok , cool ! Good to know that....I'm still hoping to find sometime soon, to etch a board and try this one out!

This is such a nicely documented project , very clear and easy to follow..should be a breeze!

cheers

nEon.

 

[Dr nEon]

Ok i promise , one final question for Curtis , before I get started:


If the xs902 is used in an unbalanced situation , presumably there will be a 6dB level drop. 

Are there any resistor values which can be changed to compensate for this?

In the case of the calrec eq,the input resistors could be lowered in value to give an extra 6dB boost,and IIRC the vca inputs on the ssl comp could be switched to compensate.

I imagine it will be possible, but looking at the xs902 schematic , I can't see an obvious place where this could be done...

Any thoughts?

Cheers!

nEon

 

[Curtis]

Hi Neon,

Increasing resistors R5 and R6 to 10K will correct for an unbalanced input connection by +6dB.  This will also reduce the high frequency rolloff of the first stage from 66kHz to 33kHz.  The drop in frequency may not be so much of an issue to some people, but if you want to pull this rolloff back up to 66kHz replace capacitors C29 and C30 with 220pF aswell.

 

[Dr nEon]

Aha!..got it...thanks very much Curtis!

I've been putting 0dB/+6dB switches on the rear my units ,and may also do the same here , but maybe not if it involves switching small capacitances too.... a little "internal jumper" setup may be neater...

I'll try the build with both resistances and see if the hf roll off is actually an issue.. probably not if the slope doesn't extend down anywhere near the top of the 'audio' band ,as it were...

I'm more poised to give his a go , now that I've acquired, for free , a nice old scope..it's an Advance OS15, fine for learning,but the snag is 100mv/div is it's best shot at sensitivity..I have a x10 buffer amp , but I suspect I'm still gonna have to find a more appropriate scope when it comes to doing symmetry trim of the 2252 RMS modules , looking at the datasheets , we're looking at around 8mv , right?

Thanks again!

nEon.

 

[Curtis]

You can always install the 220pF caps instead of 470pF, and switch resistors R5/R6 like you describe.  The rolloff would then be 141kHz when run balanced (R5/R6=5k1), or 66kHz unbalanced (R5/R6=10k).  I reckon most people would be hard pressed to hear this difference 

Regarding the scope, as long as you can "see" the output of the 2252 it should be good enough.  Off the top of my head I can't remember the exact scope resolution required, but the output of the 2252 only has to look "sinusoidal-ish" for optimum symmetry.  I haven't tried running the XS902 untrimmed, so you may find that setting VR3/VR4 to mid rotation makes very little difference compared to setting it perfectly.

 

[Dr nEon]

Excellent!..that's great info,everything i need to get goin'!

So hopefully I'll etch a board up over this holiday weekend..

If any troubleshooting is needed on the actual build , I'll set up a help thread on the Lab..

And of course I'll post some feedback on the xs902 when I'm done..

Many many thanks again,Curtis ,for the very clear answers!

Cheers

nEon

 

[Luny Tune]

This is awesome, Curtis! Thanks for that project. Of all the de-essers out there this was the exact one I'd wanna have. I was just playing with the thought of adapting the design myself (now that the LA-4 has left the nest) and then I see that I don't have to. Excsssssssssssssellent!!!

Thanks a bundle!

 

[erikb1971]

Hey Curtis...

looking great, Iam adding this one to my ultimate tracking monster:

1073 mic pre
902 de-esser
1084 eq
1176 compr

Tnx!

 

[emrr]

Any builds?  Secondary field reports?

 

[Davo]

I built one awhile back... Curtis did a nice job laying everything out, but after everything's said and done (moneywise,) I should've picked up the real thing and racked it:

http://www.vintageking.com/DBX-902-De-esser-Cards-used

and it looks like they're going for a couple hundred each on evilbay

plus, I had a bugger of a time finding the double reverse log pot... ended up getting one from Colin (audiomaitenance) in the end.

cheers,
Dave

 

[emrr]

I can imagine that being true, cost/effort considered. 

Hadn't noted the pot so far, have to consider that bit too. 

Thanks.

 

[peterc]

Seems like all the links are dead.....

Anyone have the files?

Thx

 

[Davo]

I just uploaded them to the groupdiy gmail account.

Cheers,
Dave

 

[haima]

the original cards do come up very cheap on ebay... might be the easiest option!  8)

 

[shot]

I'm reviving this old thread!

All the documents from this thread are gone. Can someone upload them again?
Since it's still in "drawing board" section, does it work? Has someone built this baby?

I'd be very interesting in giving a try if I can get the documents of this version.
There's only rev3a.pdf in another thread still available, but this "everything" version is missing.

 

[emrr]

think it's in the tech docs section

 

[shot]

Oh! Yes! It is!
Thanks emrr!

I got confused since there's an older topic on building the first version with this same pdf attached (rev3a).


Anyone built this latest revision?
Just to check if there's any newer tips and updates before I start.

 

[Joe_caithness]

Bump,

Does anyone have pics of a finished build?

Interested in seeing if a stepped mastering friendly 902 esque thing can be made