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

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grievousangel

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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

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Feb 20, 2020
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jsteiger said:
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

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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

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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

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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?
 
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grievousangel

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Oct 4, 2017
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Location
Statesboro, Georgia
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.
 

grievousangel

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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
 

calaverasgrande

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Jan 15, 2015
Messages
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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.

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.
 

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