[BUILD] CAPI LC53A~500 Series~Love Child EQ Kit~Official Support Thread

[HMPS]

Jeff is awesome with support in case you were wondering.

Ok I have two units one is loud and one is soft.

I checked the R's in the amp section like you suggested and they all check out.

How can I check the OP amps & discrete voltage followers?  Where else should I look?

Thanks
David

 

[dandeurloo]

try swapping the op amp and followers from the loud one to the quite one and see if you can track down what might be causing the volume difference.

 

[HMPS]

swip swapped all op amps, they all give out same reading, so the difference must be somewhere else. . .. but where?

 

[HMPS]

"louder" eq
Negative C2 = .017 ACV
O of A1 = .017 ACV
O of A2 = .018 ACV
O of A3 = .018 ACV
O of A4 = .018 ACV
neg C12 = .018 ACV

Softer

Neg C2 = 0.017
A1=  .017
A2= .018
A3= .018
A4= .017
Neg C12 = .018

So they match pretty closely...

OK.

I would start by taking some measurements from the properly working module. After injecting a signal, take a measurement of your choice at the output of each amplifier stage then see where the gain increases in the hot module.

1st reading: negative side of C2 on the Main PCB.
2nd reading: output pin of A1, DF on CB PCB
3rd reading: output pin of A2, DF on CB PCB
4th reading: output pin of A4, DTO5 on CB PCB
5th reading: output pin of A3, DTO5 on CB PCB
6th reading: neg side of C12 on the Main PCB

Those are in signal flow order.

We'll figure out the problem stage and go from there.

 

[emrr]

Check output transformer secondary connections

 

[HMPS]

The soft at C12 measures .018 pins 2 &4 measures .019 on the loud
they measure the same on the soft.

Perhaps swap output transformers and see if that does the trick?

 

[emrr]

perhaps see if they are connected correctly and ohm out the same before anything else.

 

[HMPS]

Ok swapped transformers and the loud is now soft and soft is now loud, which leads me to believe the output transformer is the culprit.

Where should I test for unity gain?  black ground, red to in pin 2 and then black ground, red to out pin 2?

 

[emrr]

Ohm out the transformers IN CIRCUIT and report.  It sounds like everything else is ok. 

 

[HMPS]

Ohm out the transformers IN CIRCUIT and report.  It sounds like everything else is ok.

Thanks for the suggestion.

I'm a newbie and haven't found any instructions on how to ohm out the transformer.

I assume set DMM to Ohm to measure.

How do I ohm out the transformer?

 

[emrr]

compare the resistance of the windings with your meter.  Transformer does not have to be disconnected. 

 

[HMPS]

I used mono out from my daw into the LC53A.  I was using trs out from the headphones to it, which I believe was giving the wonky readings.

Adjusted to 1.223 ACV

Used a different slot and clamped black down to a ground jumper on the 51x.

Checked +16v it read out.

These are the readings

unity gain unit

Input mono out from Daw at 1.223v

c2 .598
a1 .597
a2 .593
a3 .406
a4 .404
c12 .406

output

black 2 red 4 1.2 V


Signal Loss unity

c2 .598
a1 .597
a2 .592
a3 .408
a4 .405
c12 .398

output black 2 red 4 .129V

 

[jsteiger]

I don't know why I am not getting notifications to this thread. I have been receiving other ones?    :'(

Anyhow, I have been helping via email which HMPS has been posting here as well. Turns out that he does have a short between two of the secondary leads on one of his 2503's. The constant 180mV readings at the test points were throwing me off but once he got thru that, it was easy to verify where the actual problem was. These trafo problems happen but are thankfully very few and far between.    I am posting a replacement to you today David. 

BTW guys, if you are using a DMM for these ACV measurements, make sure you know the frequency response of your particular model. Most have very poor response at 1k which can throw you for a loop. 400Hz is usually a better choice but sometimes that is too high. You can also easily verify by measuring the output of your generator at different levels to make sure your DMM is reading properly.

For example, to test your DMM you can use this calculator here http://www.sengpielaudio.com/calculator-volt.htm This will also give you an idea of the internal operating levels of the amplifier stages. The receiver stage does drop the input level by appx 6dB.

 

[kante1603]

Hi,

Doug meant you should ohm out the windings in circuit.
The transformer has one primary and three secondary windings,look here,took it from the parts list on Jeff´s site:

http://www.classicapi.com/catalog/images/gallery/2503/2503-specs.pdf

Set your DMM to "ohms" and measure the pairs like this:

Primary:      Brown---Red=?
Secondary:  Orange---Yellow=?
                  Green---Blue=?
                  Violet---Gray=?

Cheers,

Udo.

Edit:OOOOPPPSSSS,double posted,excuse me Jeff

 

[jsteiger]

Hi,

Doug meant you should ohm out the windings in circuit.
The transformer has one primary and three secondary windings,look here,took it from the parts list on Jeff´s site:

http://www.classicapi.com/catalog/images/gallery/2503/2503-specs.pdf

Set your DMM to "ohms" and measure the pairs like this:

Primary:      Brown---Red=?
Secondary:  Orange---Yellow=?
                  Green---Blue=?
                  Violet---Gray=?

Cheers,

Udo.

Edit:OOOOPPPSSSS,double posted,excuse me Jeff

Haha no worries Udo. Thanks for chiming in. Good info to have up here anyhow.

All of his windings were around 8.5 ohms as expected. He did have an internal direct short from Violet to Orange which is not good.... :-[

 

[number2]

how nice to have all the baggies separated for each PCB.

how nice to have all these pictures, detailed instructions and warnings!

quick shipping, quick email responses....so far my experience has been GREAT with classic api ! I give an A+ at the moment

 

[mulletchuck]

ok, currently doing a build of 4 of these guys.  I finished up until the Unity Gain test.  all 4 units have 0.4db of gain.  I'm feeding from my DAW a -6dbFS 1Khz Sine, and my audio interface input is showing a -5.6dbFS signal.    Is that worth worrying about?  Seems negligible.    Also, this was using a 1731 in A2, and a 2520 in A1

Also, jeff, in your build guide, you say to install 1 op-amp in A2 before the unity gain test.  It wasn't until i installed both op amps that the units would pass unity gain(sort of).  When i had only A2 populated, the unit lost about 16db of signal.    And to support this, chunger's pics show him using 2 opamps when he tests for Unity Gain. 

 

[kante1603]

Hello Chuck,

A nice job you're doing there!
I would say 0,4 dB is negligible low for unity gain difference,I wouldn't care for that.
My readings have been very close to yours.
Same at chungs builds after loading them correctly,hahaha......
And for unity gain test,yes,all DOAs,followers etc. must be installed.
I asked Jeff on how the bypass works,he replied as follows ( see reply #47 in this thread):

The In/Out switch simply lifts all of the LCR networks from their respective connections to ground. The signal still flows thru all of the opamps, followers and the 2503.

So all good I think,rock on,I swear you'll love them (that's what their name stands for!)

Cheers,

Udo.

 

[jsteiger]

...Also, jeff, in your build guide, you say to install 1 op-amp in A2 before the unity gain test...

Yes indeed Chuck. I said that assuming that the opamp in A1 was still in place from the CMR calibration. If I said to install both opamps for this unity test, you would have said " but Jeff, I already have an opamp in A1"!!  ;D

Like I said on FB, the .4dB is nothing to worry about and some small variations are to be expected. All 4 of your units are the same so I would say you are golden! Carry on. 

 

[mulletchuck]

just finished mine!
Fully tested, and fully functional.  The two on the left use 1731s, and the two on the right use 2520s!