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

[grievousangel]

Any idea why I am seeing ~ 4VDC at the ML2 output? This seems like an usual  failure point ... has anyone seen this before?

This happens only if ML2 is active and A3 or A4 is installed.

First thought was something related to K2 (relay that by-passes A4/T2 ouput. Looking in this area now.  Appear OK so far. I checked all diodes for proper junction voltage drop, all OK.

I am also looking at the DF.1 (A1 and A2).

Not likely a bad 2520 right? I see the DC when either A3 or A4 is plugged in.

CMR adjustments would have no bearing on this correct?

Since this is  a coupling capacitor design, I would think a electro capacitor related issue, but test OK so far.

TP V+ / TPV- read as expected, ie. ~ Input voltage.

Suggestions?

Thanks.

 

[SoundStudio412]

The overall concept is identical to the first version. Most people have been buying my Extension Jig which has the proper R's fitted to it as well as instructions. There is a pic in the ML2 Assembly Guide that shows where to measure the signal.

Is there any more detailed information on the CMRR final adjustments? I'm really struggling to understand the directions and can't find any other resources on this.

Thanks,
-G

 

[jsteiger]

4 volts of DC at the output is not likely since the final output transformer would be blocking DC. I suspect you have a problem with the relay circuit.

 

[grievousangel]

4 volts of DC at the output is not likely since the final output transformer would be blocking DC. I suspect you have a problem with the relay circuit.

Thanks. I'm digging around in the relay circuits now.

 

[grievousangel]

Has anyone building a ML2,  found  their Elma fader with the rear PCB wafer (SMT side)  NOT facing  the front faceplate?

It was posted a little while back that his gain structure was off a few steps due to due the SMTs on his Elma were facing the ML2 faceplate and NOT the rear. He said it corrected his problem.

My Elma's wafer PCB SMTs are facing the front which seems to agree with Elma's Web site product date sheet.

I am having  some ML2 issues and ran into his post while checking the ML2 post out.

Later.

 

[calaverasgrande]

Is the CAPI test jig required?
I've already got a test jig I use for various 500 series builds. It has banana jacks for power and input/output. As well as some 600:600 transformers to go between it and unbalanced test gear when needed.

However I notice the CAPI jig has a switch and a couple 1k resistors. Do I need to short some pins or load them to correctly do the CMRR procedure?

 

[grievousangel]

Is the CAPI test jig required?
I've already got a test jig I use for various 500 series builds. It has banana jacks for power and input/output. As well as some 600:600 transformers to go between it and unbalanced test gear when needed.

However I notice the CAPI jig has a switch and a couple 1k resistors. Do I need to short some pins or load them to correctly do the CMRR procedure?

Yes.

For CMRR procedure, SW1 needs to be active to insert the two matched resistors (~750 to 1K) to route equal levels of test input signal (400Hz to 1KHz) + present Noise to both IN+ and IN- of ML2 Receiver DOA. With input voltages seen as 'common-mode', [It] improves the usefulness of resulting CMRR adjustment. This 'adjusted' measurement value is not actually the CMR Ratio, but is a reflection of the receiver DOA's ability to reject common-mode signals, i.e., adjust for minimum voltage at test point. I think I got all that correct. Good Luck with your project.

 

[calaverasgrande]

Thanks that makes a lot of sense.

 

[grievousangel]

Thanks that makes a lot of sense.

Let me know how ML2 turns out. What was the minimum voltage after adjustment, ie. approaching -70dB or a little better? This is as 'good' as I am aware of. If passing signal, anywhere from maybe -50dB and up is OK as I understand.

Are you planning on building two ML2? One for each bus? I have two ML2.

BTW, Initially I had some confusion on where to take the measurement. Instructions were slightly different (in terms of actual component locations) between the initial ML2 and current version as the kit was upgraded years back. Where did you take measurement? Output of A3?

Jeff has designed and manufactured fantastic hardware!

Later

 

[grievousangel]

Thanks that makes a lot of sense.

Just curious, is your ID pic a pottery wheel?

 

[calaverasgrande]

Just curious, is your ID pic a pottery wheel?

It is a picture of the infamous "Demon core" device which caused two severe radiation poisoning incidents at Los Alamos in the 40's.
https://en.wikipedia.org/wiki/Demon_core
Gonna get to the ML2 later today. And yeah I'm eventually buying another kit, but I have a rule about finishing backlog before I buy new projects. I have a lot of backlog.

 

[Hillie]

Started putting together my ML2, but of course messed up the sticker on the big knob. I saw it was a snug fit, thought "I have to pay close attention" and instantly proceeded to mess it up. Can I order the stickers separately, or would folks recommend just a drop of paint?

 

[shabtek]

use adhesive tape in case you need to change something (again)

 

[Hillie]

Jeff added a sticker when I ordered 2 VP26 kits, thanks Jeff! But.... I decided to paint, with model/hobby store paint. I used Tamiya white primer, Testors green enamel for the green knobs, Tamiya X14 sky blue for the blue knobs (matched the blue on the CAPI logo sticker I got with the order nicely, but a bit lighter than the knob stickers) and Tamiya X22 gloss clear coat. Takes orders of magnitude more time to do, but I had my mind set to doing this, so I just had to.

Of course I took off the sticker from the small trim knob and then realized it's drilled all the way through, ouch! So it looks slightly odd, but I also painted the end of the switch, so it doesn't show too badly.

Pics:



Small question about the signal flow: I understand one of the transformers obviously sits at the output, but where does the second transformer come in? Between fader section and filters?

 

[jsteiger]

Small question about the signal flow: I understand one of the transformers obviously sits at the output, but where does the second transformer come in? Between fader section and filters?

It is just before the channel fader.

 

[grezvani]

[[EDIT 4/4: Solved] I had not heard back on here or by email so went ahead and pulled the followers where I suspected the issue was, and sure enough I just completely missed soldering one of the transistor leads on one of them. Soldered that and now works great. So, if anyone is seeing a problem between T4 and T5 on the ML2, look at your followers.]]

Hi,
I got a couple VC528 ML2s a couple weeks ago, built the first one and it works great. Got the second one done and it is passing a signal, but very low level and distorted. Is there trouble shooting info with info about the test points available for ML2? I can find it for ST2 but not ML2 and it is very different.

All buttons and switches are working, the filters work from what I can tell, and I have ruled out the op amps (both pairs of op amps work in the functional one, but no difference in the bad one). Took voltage readings to ground with sine wave at -4 dBU at around 250 Hz or something, Trim and fader set to 0. The good one is the first column:

T1: 2.5 2.5
T2: 2.5 2.5
T3: 4.4 4.4
T4: 1.1 1.1
T5 1.1 0.2
T6 1.1 0.2
T7 1.1 0.2
T8 1.1 0.3
T9 2.4 0.5

So based on the location of TP5 and the traces I am thinking that there is something off around followers, but from what I can see and test without pulling them they seem ok, and they are so simple I am not sure what would have gone wrong that would cause this. Any thoughts on where to look from here? Trying to avoid pulling the followers unless I know that is where to look for the issue.

BTW, I sent Jeff a message through the CAPI website but I know he is out working on his house so not sure if he is responding now, thought others here might be able to help to save him the effort.

Thank you!!!

 

[abeLovesDIY]

Sorry to be dense. But I am trying to calibrate a unit. If I am using the CAPI test jig and sending the unit a 100Hz tone at 10dBu, what am I adjusting R1 to read on a DMM?

 

[jsteiger]

Sorry to be dense. But I am trying to calibrate a unit. If I am using the CAPI test jig and sending the unit a 100Hz tone at 10dBu, what am I adjusting R1 to read on a DMM?

The lowest AC voltage reading you can get.

 

[abeLovesDIY]

The lowest AC voltage reading you can get.

Thanks so much.
My DMM is set to measure AC between the Cathode of C7 and Ground. With the test jig switched in, I can't get any AC rating. with the switch out, I get ~.399. Is that a sign that something is not correct?

What should the settings on the module be for the CMRR test?

 

[abeLovesDIY]

I have built six of these. Four work great, but two have low/sputtery output. Is there a good spot I should start looking at?