[BUILD] CAPI VC528 ML2~500 Series~Missing Link 2~Official Support Thread

[jsteiger]

OK, I would like you to check continuity at the pins of each relay. You will have to do this from the bottom of the PCB. The attached screenshot is a view from the top side of the PCB so keep that in mind when looking at the bottom of the board.

In BYP, pin 3 should connect to pin 2 and pin 8 to pin 9.

In ACT, pin 3 should connect to 4 and pin 8 to pin 7.

Check both relays.

 

[Sparqee]

First of all let me say thank you for all your help Jeff.  You kept me from feeling adrift on a sea of ignorance.  Your troubleshooting process was specific and easy to follow.  However.... it seems that my final solution was..... magic.  :/  I'm not sure I believe in elves that come to my workbench late at night and fix my broken projects but.... <shrug>

Let me back up.  Yesterday I took the PCB out of the metal L bracket to inspect the solder points.  Today I hooked the PCB up to the test jig and got correct results from testing the relay pins.  I didn't expect that so I ran my sine wave sweep though the module and lo and behold I got an excellent frequency response through my analyzer plugin.  I ran more tests: bypass in and out, filters in and out with varying slopes and cutoff points.  All of it looked excellent on the scope.  I ran some music through the module and it sounds fantastic.

I'm not one to look a gift horse in the mouth but.... WTF!?  I seriously pondered over whether my testing had been flawed but from the beginning I could hear the extreme low frequency roll off.  I tested the module in two different 500 racks and I checked the freq response of my converter, patchbay, rack and other 500 modules.  I tested the VC528 after swapping the DOAs and got different but equally messed up results.  Yesterday the bypass switch did not affect continuity between edge pins 2&10 or 4&8 yet today bypass is working correctly.

Yesterday I did touch my soldering iron to the solder points on the bypass switch and the relays.  Perhaps my memory fails me and I didn't retest after that?  I thought I was being pretty thorough as I went through step by step. Testing after each change.  I also hot touched the legs on one of the DOAs but again I could swear I tested after that and got no improvement.

Well, the most important thing is that I now have my VC528 working beautifully.  Yesterday I went ahead and ordered a couple of prebuilt 2520's from Scott Liebers but that's ok.  I'll use them when I build my second VC528.    I suppose I'll put one of his and one of mine in each module for balance and hopefully I won't have so many problems with the second build, or if I do perhaps my late night elves will sneak in and fix that one as well.  <shake head>  Really.... it's enough to make me question my sanity.

Thanks again.

 

[OOstudio]

Hello all,

I just built a module. I ran the calibration, and everything is fine. I didn t have the time to test the ML2 in a session, but I think that it will be a great tool in my studio.
I just have a question. I have a doubt on the booster amp. Unity gain is ok. And when I turn the knob, the sound decrease. I understood that it's 3 db more, but i m not sûre. Somebody can confirm ? It seems logic with the sens of rotation of the knob.
Thanks a lot.
Luc

 

[jsteiger]

Luc, I am not exactly sure of your question?

 

[OOstudio]

Excuse my french  . I ask if it s normal that the output signal decreases when I turn the trim knob from 0 to 3.

 

[jsteiger]

Oh yes, this is as designed. The trim switch is configured so each step from 0 is another -.5dB. 

 

[OOstudio]

Great. Thanks à lot Jeff. I don t know why I had this doubt. Maybe because of the name "booster amp".
So, Everything is fine. As usual, very good kit, easy to assemble, and super quality!

 

[OOstudio]

Hi all.
I just finished my second ml2. I will calibrage this second unit tomorrow.
I d like to be sure that i understood the use of the j2.1 jumper regarding the link for bypassing 2 units.
My rack is a 51x rack from Volker.
2 questions:
-Must I use the link jumper on the rack backplane ?
-Must I use the link jumper on the both units, or only on one of them (to create a master / slave fonction).
Thank you in advance.
Best.

 

[jsteiger]

Hi all.
I just finished my second ml2. I will calibrage this second unit tomorrow.
I d like to be sure that i understood the use of the j2.1 jumper regarding the link for bypassing 2 units.
My rack is a 51x rack from Volker.
2 questions:
-Must I use the link jumper on the rack backplane ?
-Must I use the link jumper on the both units, or only on one of them (to create a master / slave fonction).
Thank you in advance.
Best.

To link the bypass function between 2 ML2 modules, flip the backplane switch (or shunt jumper) between the 2 slots. Then move both of the DC link jumpers on both ML2 modules to Y for yes. This way, one bypass switch will indeed activate both modules into bypass (or not).

 

[fragletrollet]

Whatever happened to the rest of Chunger`s log?

 

[jsteiger]

Whatever happened to the rest of Chunger`s log?

I know he became very busy with his mic's. I will ask him. Last I heard he was pretty much done with this build/pics.

 

[kvothe]

Hello everyone!
I went ahead and build 2 ml2 last week, now I am doing the pre-power measurements for the o to c sockets of the doas.
On A3: c-o 520kohm
On A4: c-o 1.5mohm
In the PDFs it is said to be the same reading for both, or doesn't it matter as long as it is over 100kohm?
All c-v measurements are ~250kohm

Have a great day everyone!

 

[jsteiger]

Those will be fine.

 

[kvothe]

Thank you Mr Steiger,

I went ahead and calibrated rv1, but with rv2 I am can only get to about 1.3dB over 0. The pot clicked and I need another 5 turns i would guess. (Anticlockwise)

Anybody had a problem like that? Otherwise everything is working correctly and I will put the next one on the table to check.

Kind regards, Kvothe

 

[jsteiger]

.....but with rv2 I am can only get to about 1.3dB over 0. The pot clicked and I need another 5 turns i would guess. (Anticlockwise)

This is not right. Something is wrong somewhere. There should be plenty of adjustment available. Are the opamps kits or pre-built?

 

[kvothe]

Thank you for trying to help.

They were kits, gar2520  already in use with my vp28, I also checked with 3 different pairs of red dots, still the same readings.

The other unit has the opposite problem, very little level when active, rv2 does not change anything and the fader only works until ~-34, then no gain changes until 0. From 0 to 12 again, more level, but not enough. It looks like trim is working. Filters do work, but every change clicks or pops.

Again your help and the help of those who already build a kit is very much appreciated.

I will chek my soldering and could post pictures of the areas where the problems are most likely.

Thank you!

 

[kvothe]

I touched up every solder joint on the second unit, but no changes in behavior. When the unit is in bypass, it passes audio normally. When active the fader has no real use except for the very first click and the clicks after 0.
Could the fader be damaged, or maybe the relays?

Could someone help me out?

 

[jsteiger]

It is extremely unlikely that there's a problem with the fader switch. The bypass is a hard relay bypass which directly couples the input to the output so no signal runs thru the module. I suppose pulling the opamps and toggling between bypass and active would tell you if the relays are working properly. With no opamps installed, no signal should pass when in active.

 

[mxz174]

I've already sent an e-mail to Jeff, but then I came across this support thread and figured I'm post it here as well.  Just in case Jeff would rather respond here, or when we figure out the fix I can let everyone on this thread know so they have more information to go on.

I built a pair of VC528 ML2s.  One checks out perfectly.  All knobs, filters, the fader, switches all work great.  CMM worked and done and unity gain adjustment completed.  The module sounds great!

Now the other one is almost perfect as well.  Same deal that all features work just fine, and the module itself even sounds very good when music is put through it.  The only problem is the unity gain adjustment.  I'm in the right range but can't quite get to unity gain.

I'm using a 1kHz sine wave input.  The input level is coming out as -13.4dB.  The full range of the adjustable pot takes the output from -22.2dB to -19.4dB.  I have the trim spot clicking but can't get higher than -19.4dB. 

On the 'good' module my range of adjustment goes from -15.1dB to -12.3dB.  So the full range is right about the same for both modules, just that the one has a lower overall offset.

I've tried testing out both modules now with a handful of different op amps and get exactly the same results for both, so I know it's not the op amps.

Here's another interesting piece of the puzzle, on the resistance tests i always get ~200kOhm on each of the +V and -V to C points, as well as the O to C points EXCEPT on the one module that is 'bad'.  On that module the O to C resistance for A4 (booster op amp) is 4.5M Ohm.  Now I know that the trim pot is controlling the output level of this op amp... so this looks like it could be the key to what's going on.

If Jeff is out there listening, or anyone else for that matter that has experience here let me know if you have any ideas.  As I said both modules sound really good as is on music, if I can just get that unity gain level up a bit on the second module I'll be in business!

 

[trumanaudio]

Ok, hopefully someone out there can stear me straight!

I've got a Missing Link.

I have a 400Hz sine running into the test jig, test jig into the ML, then into another channel on my DAW

The unit is active with the fader and trim set to 0

With the CMRR switch engaged on my daw, I can use RV1 to achieve the lowest value.

When I disengage the CMRR switch and try to adjust for unity gain, using RV2, nothing changes.

What could possibly be wrong? I'm using two gar2520s and I don't know where to start to look for problems.

Thanks.