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

[Indecline]

Just wanted to add that another love child lives! 8)

My buddy built the boards and I did the dt05's and voltage followers. After finding a faulty 2520 (that I built :-X ) it fired up first errr.. Second shot!

Thanks jeff!

 

[Quantum J Audio]

Hi

Just been using these on various bits and really liking them, Smooth EQ.

Just strapped them across the mix buss and one unit is 1.4db hotter,  when the EQ is out.  Is this normal for two units to differ so much?  As it is enough to noticeably skew the image on the mix. 

Thanks
Iain

 

[jsteiger]

No this is not normal. It sounds like maybe the shunt jumpers for the lo-z/hi-z load do not match from unit to unit. The typical setting will be hi-z load. If it's not that, I would put the 2 side by side and compare each and every resistor. Any 2 proper units should be within .2dB or better.

 

[BricktopRecording]

I just finished my build and have a couple issues-

Signal passes through but the output is loud and a bit distorted both with the EQ engaged and disengaged-  I'm thinking this may have to do with my CMRR adjustment but I'm not exactly sure,  I can hear the filters working when I cut/boost, engage HP/LP, etc.  Has anyone else run across this? 

Second,  the cut/boost switches seem to be a bit off,  its hard to explain- but they seem to function normally until I get to lets say -8db and it sounds like it jumps to +8db, but the whole way there it will be cutting until that point.  Is this fix as just moving the stop pins?

Thanks
Pete

 

[jsteiger]

Pete

The CMRR adjustment will not cause distortion. It must be something else. It could be opamp related. The first trhing I would do is swap out opamps especially if they were kits. Use known good working opamps that you have tested in another build like a preamp.

If you scan early in this thread, I give some probe points to "step" thru the circuit so you can measure ACV and see where things go wrong.

It doe sound like you have some GH pins in the wrong locations.

Cheers, Jeff

 

[BricktopRecording]

Thanks Jeff,  swapped the op amps with ones from working pre's and I'm still getting the super loud blown out sound.  I check earlier in the tread for the ACV points.

 

[jsteiger]

I would check all of the R's around the opamps. Sounds like maybe something got swapped around.

 

[BricktopRecording]

All the resistors on the main pcb near the opamps are correct,  though R6 & R7 measure about 3.6k in the circuit but are the correct 10k when out.  Could this be a potential issue?

 

[jsteiger]

No since you can't accurately measure an R while it's in circuit. You would have to lift one end.

I think you will have to find the test points that were mentioned near the beginning of this thread. Measure those for ACV while injecting a balanced signal as was discussed back then. If you only have a DMM for this, I would suggest using a lower freq, something like 400Hz.

 

[Unit7]

Hello,

I'm super excited to have this eq completed soon! I have my power supply pcb build to the point of needing to calibrate the cmrr and was hoping someone might be kind enough to verify my method before I dive in. I've garnered information from the assembly aid, the vc528 cmrr guide and from this thread to devise the following plan:

- Connect "special cable" to signal generator with +/- 500Hz sine wave. I'm assuming I can use a plug in my DAW as a signal generator.
- Adjust output for 1 volt AC as measured using a DMM with red probe to pin 2 and black pin to pin 1 of special cable.
- Connect special cable to card edge (input) of power supply pcb: I plan to use my API 500V as a power supply with the pcb inserted into the first slot and simply connect the cable to the xlr input. I'll empty it of all other modules and position it for the "easiest" access to the pcb. Please let me know if this is bad.
- Connect to input of DAW via XLR with other end of cable altered with aligator clips, etc... to connect pin 2 to negative side of C2 and pin 1 to the common terminal of A2, being sure to have installed a known-good op amp into A1. It's my understanding that I may have to also connect pin 3 to the common terminal of A2 if I don't see a signal.
- Power up and follow adjustment instructions.

I'd be grateful if anyone could give me the thumbs up on this approach or point out any flaws/suggestions.

Thanks!

Jason

Just wanted to check that I get this right... Using this method, does it mean that I could do the cmrr without a dedicated oscilloscope and use my Purple Sweet Ten as power supply when testing?

 

[jsteiger]

Yes it should work. Just be careful.

 

[Unit7]

Yes it should work. Just be careful.

Thanks Jeff!
I'll be careful

Except for making the special cable with the two resistors, for the cmrr test I thought about making a cable for connecting the board to the DAW input: Two millmax pins and an alligator clip on one side and a male XLR on the other. Millmax pins connected to pin 1 & 3, and alligator clip to pin 2.
Would that work?

 

[jsteiger]

Sorry, not sure I follow you exactly....

 

[Unit7]

Sorry, not sure I follow you exactly....

Sorry,
Instead of saying 'Except for making…' perhaps  i should have said 'In addition to making'…
To be able to do the test with the board in my Purple rack, for convenience I thought it would be a good idea to also solder a cable for connecting the board to the input of my DAW.
Edit: Clarification: To be able to connect this cable to the PCB board in my Purple rack without the risk of the alligator clips slipping and causing damage I thought of soldering two millmax pins directly on the cable (to be connected to DOA C connectors - one of them optional as stated in your instructions) and one alligator clip (to be connected to negative side of C2). On the other end of the the cable - male XLR going in to my DAW for measuring.
Still unclear?..

 

[kante1603]

Sorry, not sure I follow you exactly....

Sorry,
Instead of saying 'Except for making…' perhaps  i should have said 'In addition to making'…
To be able to do the test with the board in my Purple rack, for convenience I thought it would be a good idea to also solder a cable for connecting the board to the input of my DAW.
Edit: Clarification: To be able to connect this cable to the PCB board in my Purple rack without the risk of the alligator clips slipping and causing damage I thought of soldering two millmax pins directly on the cable (to be connected to DOA C connectors - one of them optional as stated in your instructions) and one alligator clip (to be connected to negative side of C2). On the other end of the the cable - male XLR going in to my DAW for measuring.
Still unclear?..

Hi,
if I get it right you want to do the cmrr calibration with the module mounted inside your rack?
If so it might be way better to use an extension-cable and have the module laying on the side in front of you.
Or connect it to an external +/-16 vdc psu.
But you must have the module parts accessable.
About extension cables,you can easily do it on your own (I made it this way using some edac connectors and prototype boards) or get cheap kits to build one pretty easy.They'll help you with troubleshooting/calibrating/matching for stereo tracking etc. on other modules too.
Just my 2ct.....

Udo.

 

[mulletchuck]

just do what I did for testing the module.  Unscrew the backplane of your rack and pull it out from the side/top/bottom walls so it's all by itself. 

 

[Unit7]

Udo and Chuck, thanks for the suggestions! Really appreciate it!

I'm new to DIY, and I'm not (yet) building anything but complete, 'ready to build' kits, so I'm not planning to buy bench PSU, oscilloscope etc, if I don't really have to. I've built Horvitz's chorus and 550A eqs, and now plan to build a pair of LC53As and a VP28. Then if I like them I'll add more units from time to time.

I've got my Purple rack mounted and hooked up in my rack in my studio and need it to be operational for my work. Demounting, unhooking and demounting the rack itself, and then all back again seems a bit inconvenient and time consuming for my situation.

Udo, yes, if possible I'd like to do the test with the pcb board in my Purple rack (placed in my studio rack, accessible via the patch bay), and your suggestion with the extension cable seems good. I'll look into that!

But if I could solder another cable for the CMRR test I believe it would be much more convenient and time saving for me.

By now, I've read Chunger's superb guide in this thread, Jeff's CMRR and LC53A aid doc five times and my brain boils!..

Please bear with me and help me starting from square one, with these couple of questions:
- For the CMRR test, it's possible to do by routing the signal from the PCB board to the input of a DAW for measuring, correct?

- If the above is correct, the connections should look like this:
PCB board A2 Common terminal -> DAW XLR input, pin 1
PCB board Capacitor 2, minus side -> DAW XLR input, pin 2
PCB board A2 Common terminal -> DAW XLR input, pin 3, OPTIONAL

Correct?

Thank You!
Paul

 

[kante1603]

Hi Paul,

yes,looks correct for me.
Picking up the common at A2 is just because it is easy to reach.In general you can use any common point in the circuit for that.So attaching a piece of wire to a fresh doa pin and plugging in to the common point at A2 is o.k.
Connecting the common to pin 3 on the xlr too as an option depends on whether your interface input is floating or not.
Looking good so far,keep us posted,

Udo

 

[Unit7]

Hi Paul,

yes,looks correct for me.
Picking up the common at A2 is just because it is easy to reach.In general you can use any common point in the circuit for that.So attaching a piece of wire to a fresh doa pin and plugging in to the common point at A2 is o.k.
Connecting the common to pin 3 on the xlr too as an option depends on whether your interface input is floating or not.
Looking good so far,keep us posted,

Udo

Great, thanks Udo!
I'm still waiting for the VP28 to be in stock at cAPI before I'll order it and a pair of LC53As, so I haven't started to build yet, except for eight GAR2520s made this weekend. But now I'll be able to prepare those test cables!

Follow up questions:
- Does Steiger's special CMRR cable require a shielded cable (for pin 1)?
- Is there any reason why Chunger uses a cable with so many leads? On Jeff's drawing it seems a simple shielded instrument cable would do the job
- Would 'my' test cable (desribed in my last post) require/benefit from the use of a shielded cable? In that case, on which pin?
- I've checked my plugin collection in ProTools (HD) and Logic and don't find a good measuring tool that displays dB continuously and in two decimals. Any recommendations on a really cheap plugin for Mac OS 10.6 that will do the job?

 

[sharpeleven]

Two more Love Childs alive and well here.

Everything went well with the build except the calibration part left me scratching my head for a while until I figured it out. you basically have to build two cables for the cal procedures and the rest is easy.

The LC's sound good! I got blisters from turning those knobs...!

All red dot op amps. Lows feel a bit loose, mids/high are very smooth sounding.

thanks, Jeff, for creating yet another great tool!!