SSL 4K channel dynamics. (And more in future). PCB's/kits: Available!

[Catrunes]

https://drive.google.com/file/d/1DfL79vHjS-A_nVupGeDZOyc97u0VPD_9/view?usp=sharing

do you have the standoff lengths for the meter board by chance?

 

[duantro]

do you have the standoff lengths for the meter board by chance?

Good question. Anyone know of standoff measurements for the meter board?

 

[Ricardus]

Since I've been building SSL preamps, and I'm involved in an SSL channel EQ project, I was wondering if anyone had done the channel dynamics module. So I guess here is my answer!

 

[duantro]

Anyone have tips for assembling  the ribbon cable connectors?  When I pressed mine together the female connectors exploded. I have more on order.

 

[Ilya]

The trick here is to apply even pressure. You can do it with the vice. Also, there's a special instrument, not that expensive, but for on-offs it's not worth it.

 

[duantro]

Thanks. I ordered 8 more. Hopefully that’s enough to get it right!

 

[Ricardus]

Anyone have tips for assembling  the ribbon cable connectors?  When I pressed mine together the female connectors exploded. I have more on order.

I messed one up when I tried to make one by hand not long ago. I'll be getting the crimper one of these days.

 

[duantro]

Vice did the trick on the ribbon connectors. Almost ready to calibrate. Need to pick up some meter leds and it’s calibration time

 

[duantro]

Well it looks like my stand-off measurements won’t work. The ribbon cable connectors are too close. It appears the the standoffs for the main pcb need to be real short! I tried 5/16” and it looks like it needs to be almost 1/2 that.
Edit, it looks like 1/8" on the bottom and 1" between the main board and the meter board.

 

[duantro]

I have one of my units working and calibrated, the second one passes audio but can't calibrate compression to register anything on the meter or audibly. Also the gate seems to be registering on the meter, but can't hear anything happening. I did have CPS1 (220uf) cap in backwards that wasn't happy. I replaced that and seem to be getting proper voltages on sockets. Any thoughts on where to check? maybe I'll see if I have any extra 78L05's around and swap those.

 

[12afael]

It happen to me something similar. One of the diodes was backwards on one of the precision rectifiers. It can be many things really but that was in my unit.

 

[duantro]

I found a bad solder on the relay, signal at last! Time to calibrate
Compressor calibrated, but it looks like gate threshold/vr3  isn't doing anything. Time for more searching...

 

[duantro]

OK, I've found some differences in some voltages. Attachment has my voltages of the working unit in blue, and the one that doesn't open up the gate in red. Can anyone see what is shorting the voltages?
Where does the -5 vdc  come from at r41?

 

[12afael]

What voltage do you have at the set gate pot? Does it change??

 

[duantro]

What voltage do you have at the set gate pot? Does it change??

Thanks for the reply! R31 has 15.41vdc on trimmer side, the same as the working one. And 0vdc on the other side. I took most all voltages and only posted the ones that differ from the working one.

 

[Electrobumps]

Here's my calibration procedure per the SSL documents and Igor's schematic. Please feel free to correct anything I got wrong, because I am far from 100% sure I've done this correctly...


2. Send a +14 dB 1k sine wave (this is the first part I may have done wrong... I'm assuming this is in dBu, which according to my console manual is -4 dBFS. I set my DAW sine generator to -4 in this case to make the +14 dB).

Jason, thanks for your explanation of the alignment the procedure while it creates a working compressor which sounds good I’m not sure the reference levels are correct.

If we look at the our 500 series schematic compared to the original schematic we have a newly designed i/p and  o/p section.  Our i/p and o/p circuits do not exist in the same way in a console as there is much more complex routing and signal flow. 

If we look at Igor’s schematic it is states next to TP2 SET -5VDC  @ 1.55 RMS.  If we reference 1.55rms at TP 4 and then align the compressor  It does not matter if we use dBm, dBu or if our DAW is -18dbfs or -14dbfs or any other reference level, we just need to reference 1.55rms. 

When I line my compressor up to +14dBu I see -4.33VDC at TP2 and 3.84rms at TP4. 

I also found that when referencing +14dBu the trims were very close to the extent of their ranges.  Aligning to 1.55rms also seems to make more sense relative to the trim pot.

In operational terms if you are recording signals at close to 0Vu in your DAW.  I find lining up to +14dBu does not give as much range on the compression threshold.

My method is as follows.


1. Set the compressor as the per the SSL manual. *
2. Send a 1khz test tone to the compressor adjust the level of your tone in your DAW to see 1.55rms at TP4. (take a note of the tone level in your DAW or save the setting to recall later at step 11)
3. Adjust VR2 to get -5VDC at TP2. This sets 0dB

I then continued as per the manual / Jason’s notes but with 1.55rms reference to set gain VR1 and set gate VR3. 

5. Turn your threshold control all the way down (-20) so that you're seeing the GR maxed out. Back your sine wave off until you see no compression. Clear your meter peak in your daw.

6. Raise the sine level until you see the first GR meter LED come on. Take a look at the peak reading in your DAW at this point. (Mine was -25.5 at this point).

7. The SSL Docs say that the level should stay fairly constant (within +/- 1 dB) as you raise the sine level from here (because your ratio is at infinity). Mine did not do this at first- Once my compressor started limiting at -25.5, the level made it up to like -23.9 or something like that. This is how you know you need further adjustment...

8. ...in which case, the documents tell you to adjust the "gain preset" (I guess 'preset' means 'trimpot' in British... I speak American =P). The trimmer in this case is VR1... You'll adjust VR1 to correct this.  Lower your sine level until there is no more Gain Reduction, then clear out your DAW peak meter again. Raise the sine until you see some GR, make note of the peak level at that point, then continue raising. If the output level doesn't go past 1dB, you've made the correct adjustment. If it got WORSE, you need to turn the trim pot the other direction =P

9. Once you've met the condition that the output stays within +/- 1dB of where it is when GR begins, your compressor is set! Change your ratio to the lowest setting (1:1)

10. Set the expander settings to those specified in the SSL docs.

11.Send a 1khz test tone to the compressor to see 1.55rms at TP4.

12. Adjust VR3 until the signal passes through the gate. (this was easy). Once this is done, put your range control to its minimum setting.

13. Sym Adjustment. I stumbled upon this by accident! The output, when viewed in the cubase channel settings, showed multiple harmonics of 1k (2k, 4k, etc). This is the distortion that the SYM trimmer is supposed to remove (I guess... tell me if I'm wrong!) I'm including an image of what it looks like before adjustment.

14. Adjust the SYM preset until those extra harmonics go away. If you go too far, they begin to creep back up. Find the happy medium.

For Symmetry I used a plugin in my DAW called SPAN https://www.voxengo.com/product/span.  Waves PAZ will also work. 

*settings of compressor do not effect TP2 VDC level.  However these setting make sense to test the attack switch and then to follow on and setup the gate.

SSL manual link https://pdfslide.net/documents/611-calibration.html

 

[jasonallenh]

Wow,    I came back to reference this to recalibrate my cards and I return to find your significantly better instructions!

I do have a couple questions though-

1) what do you do if you don't have VR2?? I used the THAT chip instead and the schematic references the other chip in the notes you're referring to.

2) I was able to set the same reference level, but I cannot reduce VR'2 to  get -5VDC at TP2. Instead, I just set my reference level per your instructions, and then used the SSL procedure to set 0DB (Create a 4db decrease when switching in). The THAT portion of Igor's schematic does refer to this point as "set 0db, so I am assuming this is still ok even though this ended up giving me about 4.8VDC at TP2 instead of -5VDC. I thought maybe the PCB was arranged so that either option you choose uses one half of an opamp, but the schematic says that's not the case. It's behaving like a compressor though! and you're right, the comp does behave better.

3) Cubase's default channel eq will show the harmonics so you can set the SYM pot, no plugins needed!

I'm entirely self taught, so if you have any other thoughts, please jump in. I think between the two of us, the SSL manual, and igor's docs, we have a full calibration procedure for either option ;D

By the way- to the person asking about standoff sizes for the meter board: I never got standoffs for my meter board............. I just put a couple machine screws through the pcbs with nuts on either side to hold the meter board in place. At least this way it's infinitely adjustable. I would rather use standoffs though...

Jason, thanks for your explanation of the alignment the procedure while it creates a working compressor which sounds good I’m not sure the reference levels are correct.

If we look at the our 500 series schematic compared to the original schematic we have a newly designed i/p and  o/p section.  Our i/p and o/p circuits do not exist in the same way in a console as there is much more complex routing and signal flow. 

If we look at Igor’s schematic it is states next to TP2 SET -5VDC  @ 1.55 RMS.  If we reference 1.55rms at TP 4 and then align the compressor  It does not matter if we use dBm, dBu or if our DAW is -18dbfs or -14dbfs or any other reference level, we just need to reference 1.55rms. 

When I line my compressor up to +14dBu I see -4.33VDC at TP2 and 3.84rms at TP4. 

I also found that when referencing +14dBu the trims were very close to the extent of their ranges.  Aligning to 1.55rms also seems to make more sense relative to the trim pot.

In operational terms if you are recording signals at close to 0Vu in your DAW.  I find lining up to +14dBu does not give as much range on the compression threshold.

My method is as follows.


1. Set the compressor as the per the SSL manual. *
2. Send a 1khz test tone to the compressor adjust the level of your tone in your DAW to see 1.55rms at TP4. (take a note of the tone level in your DAW or save the setting to recall later at step 11)
3. Adjust VR2 to get -5VDC at TP2. This sets 0dB

I then continued as per the manual / Jason’s notes but with 1.55rms reference to set gain VR1 and set gate VR3. 

11.Send a 1khz test tone to the compressor to see 1.55rms at TP4.

For Symmetry I used a plugin in my DAW called SPAN https://www.voxengo.com/product/span.  Waves PAZ will also work. 

*settings of compressor do not effect TP2 VDC level.  However these setting make sense to test the attack switch and then to follow on and setup the gate.

SSL manual link https://pdfslide.net/documents/611-calibration.html

 

[jazzboxuz]

are boards for these available anywhere?

 

[duantro]

I just saw that Frank has these on his store now!
https://shop.frontpanels.de/navi.php?k=59

 

[jazzboxuz]

excellent, just ordered! thanks!