SB4000 Support Thread

[ruckus328]

the input level and output level on are quite off.  The input level is about 5dB lower than the output. 

Then you didn't follow the very first step of the calibration procedure, which is adjusting for unity gain.

 

[ruckus328]

Hi minor_glitch  thanks, I did and the calibrations worked fine mostly.  Except I ran out of travel on the pots to get the t1 and t2 exactly but it's really close.  There is something wrong with the threshold, it acts really strange after about 11 dB compression.  Not sure what I did wrong, and where I should start troubleshooting.  I checked solder joints and they looked good??

Any ideas would be greatly appreciated!!
I'm so amazed at the design of this compressor, it's really really cool! 
Thanks!!  Greg

What are you using for a test tone and what are you using to measure the voltage?  Test tone needs to be 1khz or it won't calibrate properly.  If the meter you're using doesn't meaure True RMS then your calibration will be incorrect as well.  You should not run out of turns or come even remotely close.

Otherwise just pretrim VR5/VR10 to 5K2 and VR6/VR9 to 2K3 and call it a day (measure resistance between Pin 1 square pad and the wiper).  If you already have these pots installed you'll need to temporarily remove U6 & U7, as well as disconnect the ribbon cable to get an accurate resistance reading.

 

[ruckus328]

Thanks minor_glitch - That's the same for me.  T1 was off by around .2 and t2 was perfect.  When you run a signal into the compressor (on bypass) do your input and output levels match?  On my unit if I feed a -10 signal in, it comes back to my DAW (PT 192) around -15 or so...  Sound fishy to me?  So when I'm compressing I need to use a little more of the make up knob then I would normally use with a SSL comp...
Have a great day
greg

??  When unit is bypassed it's a relay hard bypass.  There's no way your input and output signals can be different.  If so it's a daw/interface issue, not the compressor.

 

[etheory]

Ah bugger, thanks Ruckus, it's always the info you want that you skip over accidentally.... sorry 

 

[Wembley]

Just thought I'd add for the people who are looking for fish paper to put under the transformer, McMasterCarr has reasonably-sized sheets for around $4.  The stock number is 8490K11.

 

[etheory]

Well, I fired up my unit last night and it works!  I didn't do the full calibration procedure yet, just the pre-calibration as per the circuit diagram ( which, truth be told, is probably very close to a correct calibration anyway ), but, it sounds amazingly good.  Like, insanely good....

It's not a "hard" or "crunchy" sound ( well, yet anyway, I know I can tune this via calibration ) and it's not "clinical" either, necessarily.  As it's set up now it actually sounds quite smooth and I guess, in a single word "precise".  It seems to "impose" it's timing over the source material in a really really nice way.  It really does sound phenomenally good.  And my unit, even with the lid off, is deathly silent, with no appreciable background noise, hiss or what have you, at all.  Very very nice stuff.  I can't wait to share some sound samples with you all after I've had a little more time with it.

I am looking to do a proper calibration tonight.  I love watching that analog meter jump around - it's beautiful stuff.

Thanks again!

P.S. if you got the meter from the diypartssupply kit note that you don't need to solder the resistor only for the 100uA meters ( I think it's a 330K one ).  I ALMOST made that mistake, but a thorough check before turn-on found that and I cut it out.

 

[etheory]

FYI. for those who are unlucky and unable to get the diypartssupply kit supplied nuts to fit the bourns pots like me ( your mileage may vary I am aware that many others have had success with this ), I managed to find a supply of perfectly fitting nuts in Australia from element14: http://au.element14.com/jsp/search/productdetail.jsp?SKU=1774585

 

[bieckmusic]

Thanks Ruckus!!!  I need to get a meter with true Rms.  The unity calibration calibration worked fine, it was more a problem with the led meter.  I need to check calibration on my digi 192.  Greg

 

[etheory]

Here is some example audio I recorded through the unit for testing ;-)  I'm liking what I am hearing....

http://soundcloud.com/evolutionarytheory/evolutionary-theory-sb4000

 

[Neil]

Anyone had trouble calibrating their meter to show the right level of compression? Sending a -20 dbfs 1 kHz tone out of ProTools and compressing it -10 db it seems like I run out of room on VR17. I have to crank it all the way clockwise and the analog meter is still about a dB off at best.

 

[minor_glitch]

Anyone have a recommendation for shielding the toroid from other gear in my rack? 
I have a Chameleon Labs 7802 I want to place directly under this comp, but the 7802 is laid out backwards with the toroid on the opposite side, leaving the output transformers directly underneath the toroid of the sb4000. 
I'm getting serious hum around -40db through the 7802 when I turn on the sb4000.
Would a couple sheets of mu metal be the best solution?

 

[etheory]

Have you checked that there is a electrical connection between the earth connection on the star ground and EVERY panel of the entire case?
Technically in a metallic case the farady shield produced by the earth connection should be pretty strong provided it is connected to all panels across the entire case.
Another suggestion is to try and run each device off of a separate mains circuit to see if it's an electrical intereference ( due to something like back-emf feeding back into your supply ) issue instead of an electro-magnetic one.

 

[minor_glitch]

Yeah I sanded the heck out of every connection point and checked for resistance between the star ground and each point.
I pulled the 7802 out of my rack while both units were powered up and the noise decreased as I pulled it away from the sb4000.  So I think it's safe to say the toroid is to blame.

 

[ruckus328]

So I think it's safe to say the toroid is to blame.

Meh, maybe, maybe not.  There's been about 200 SB4000's built and who knows how many thousands of GSSL's (Which generally share a very similar topology), and this is the first time I've (personally) heard of an issue like this.  Have you tried putting any other gear next to either one to see if the issue re-manifests?  Could be the output transformers on your 7502 are ultra sensitive (and it doesn't help have this reversed-from-usual topology).  If it were me I'd try cracking open the 7502 and slapping some mumetal over the output xfmr's.

Just for the hell of it, try pulling the XLR cables from each (while leaving them plugged in the other of course) and see if the issues persists.  Also, turn the SB4000 sideways and hold it in your rack so the toroid from the SB4000 is over top of the output transformers in the 7502 (but this way the 7502's toroid won't be below the SB4000 PCB, eliminating the possibility that this is the culprit.)

 

[minor_glitch]

Thanks ruckus, I'll give your suggestions a try.
I just quickly checked with another piece of gear, a Pre-73 preamp.  It's a half rack unit, so I turned it on while under the main board side of the sb4000, then slid it over towards the toroid side.  Sure enough the hum increased by about 8db when it was under the toroid.
I'll probably try some mu metal, or just build another piece of gear with the toroid on the right side to stick under there.haha
Hmm, come to think of it, I wonder if it would happen if I put the 7802 above the sb4000 instead of below...
I'll get back to you!

 

[minor_glitch]

Ok tested it a few different ways. 
I stood up the sb4000 and hovered it over the output transformers of the 7802 like you suggested.  The noise pretty much disappeared.  It seems the hum only occurs when the output transformers are directly above or below the sb4000's toroid.  No problem when the side of the toroid is facing them.
I didn't even have to turn on the 7802.  I unplugged everything on both units except the outputs on the 7802, turned on the sb4000 and the hum was present on the 7802's outs.
I'm starting to think the problem is just the wacky backwards design of the 7802 combined with its cheap output transformers.  I've attached a photo so you can see its layout.

I was growing tired of the 7802 anyhow, so maybe this is a sign that I should sell it!

 

[ripgtr]

I finished mine a few weeks ago. Worked right off. I really liked how the board was organized. Other than a LOT of soldering, it was pretty easy.

I had some mixes, all in the box. I have been playing with them for months, trying to finish them. I must have had 6 or 7 VSTs on the mixes trying to get the to sound right. I ran the mixes through the SB4000, x2 compression, never over 8 dB. Man, fixed them up really nice, took the ugly edge off. I then ran some light eg (added some air and took out some 300 Hz mud), put a light limiter on to catch the peaks and the mixes sound so much better.

This thing rocks. I even went back and redid some of the mixes, hitting a few problem tracks ( a couple vocal and one guitar, a couple of snares) and it really smoothed them out.

I really like this thing! 

 

[sonic02]

Hi Ruckus,
About to wire up the power trafo (VTP36-1390 25VA, 36.0V @ 0.69A, 18V @1.38A parallel - as per ptownkid kit)) 1st project and have never done this before, sh*t scared of blowing myself up and damaging all the hard work. Can you give me some advice on wiring for 240V. At the moment, my understanding is:

Primary for 240V
1)  Brown to top pin on Power Switch
2)  Blue to N (Neutral) on IEC (Mouser 693-6200.2200 – ptwonkid kit)
3)  Wire (18awg) from centre pin on Power Switch to L (Live) on IEC
4)  Wire (18awg) from Earth on IEC to Star Ground
5)  Tie Grey and Purple together (solder, heatshrink etc…) and leave unconnected
6)  There are two smaller (reduced) pins on the IEC connected by a metal strip, think they are fuse links, but unsure?

Secondary
Black, Red, Orange & Yellow (Black closest to BR1).

Hope this will help others who may be finding this part of the project a little intimidating. The rest is fairly straight forward. Great setout/design too ruckus.

Cheers, Stuart

 

[sonic02]

just to clarify above post, the trafo is Triad Magnetics, digikey part no. 237-1327-ND.

 

[earl]

Hey Mike my circuit is passing audio and all voltages mentioned in previous posts look good.  Following the sidechain like you said
to do.  no compression.  Is there a quick test to do on the "that" chips in the sidechain circuit to determine if they are hosed? 


        EDIT :  had 100k instead of 100r for r118.  Fixed a whole bunch of stuff... squish... squish... Thanks Mike i followed your
                                                                                  advice on the sidechain circuit to find it.