[spaceboss]

Calibration questions

This is a really well put together kit, and has been an enjoyable build so far.

I'm getting close to the calibration step on my build. I've built the test jig, and looked for precise instructions on how to use it--without any luck.

I'm still not confident that I know what to do. I know how to send the appropriate test tone out of my daw and into the XLR input on the chassis.

Where I get fuzzy is the output. From the picture on step 5 of the Final adjustments, I see the two yellow alligator clips and I know where to put them.

My questions are:

1. Is it just one alligator cable that is jumpering the positive end of C2 to the resistor?
2. If not, where do the other ends (not pictured go)? To get the signal back to my DAW do I use the XLR out on my chassis, or do I take the output from somewhere else?

Thanks.

All the best,

James

[jsteiger]

James, the instructions for using the Extension Jig are written in the silk on the jig's PCB. As for monitoring the output, you will clip onto the points shown in the pic linked in the Assembly Guide. The output signal will be unbalanced and need to go directly to your convertors and into your DAW. The positive lead will clip to the cap shown and go to pin 2 of your convertor's XLR. The ground connection is being made by clipping onto the end of the R shown in the pic. That will go to pin 1 of your XLR. Pin 3 will float and have no connection.

[kato]

James, that's not a jumper. It's two separate test clips that both happen to be yellow.

http://www.classicapi.com/catalog/images/553F-build/553F_assy_aid_29.jpg

The one going to the electrolytic is the audio out + and the one on the resistor is the audio out -.

edit: whoops Jeff beat me to it.

[spaceboss]

Thanks Kato and Jeff!

That is much more clear now.

[pitol678]

Hi, I am just wondering about how difficult and what equipment is needed in order to learn how to calibrate the 553 (and other kits). I'm fairly handy and Ive put together some of the simpler kits but I don't even know where to start to learn this skill. Maybe that's my answer?

Any resources anyone could point me to would be much appreciated, thanks!

[kato]

Hi, I am just wondering about how difficult and what equipment is needed in order to learn how to calibrate the 553 (and other kits). I'm fairly handy and Ive put together some of the simpler kits but I don't even know where to start to learn this skill. Maybe that's my answer?

Any resources anyone could point me to would be much appreciated, thanks!

Needed: An XLR jack, two resistors, and some wire. 

Follow the instructions on making a "special cable" (page 2 of this PDF) - but not the rest of the instructions as it applies to a different module. But instead go back to the 553 build manual for how to calibrate.

I output the module straight to powered monitors and listened to the sine wave blaring in the room while adjusting the trim pot. Enjoy!

[pitol678]

Thanks Kato, Really??!? that seems really simple unless I am misunderstanding. So I dont need a sine wave meter, just my ears?

[kato]

You just turn the trimpot till the sinewave disappears. It's very obvious when you've hit the perfect spot because as you continue to turn it, it gets louder in either direction. It's the "common mode rejection" setting so it's bucking out noise that's equal in both lines - in other words, sound that's not supposed to be present in your audio signal but gets picked up the electromagnetic interference and other junk.

You don't even need a sinewave generator. I found a free sinewave generating app and output via miniplug from my laptop into my "special cable" into the 553F.

[spaceboss]

Okay. My unit powers up, but will not pass audio, regardless of whether the eq is in or out. So likely there is a short somewhere maybe? I'm regretting not buying pre-made op-amps, so I could rule those out. Is it too late to do so once a kit has been purchased?

My pre-flight measurements all exceed the measurements that they should exceed. Some of them appear to substantially exceed them. I'd be happy to provide pictures, voltage measurements or anything else that could be useful. I have an unbalanced audio probe that I've used for de-bugging guitar pedals.

This was my third 500 series project, the other two fired right up--so I guess as a relative newb I was due for a trouble shooting adventure.

If anyone has any advice on where to start or what to check, I would genuinely appreciate it.

All the best,

James

[jsteiger]

Do you have other opamps from your other modules? That is always the first thing to rule out, after rack slot, associated cabling and converter settings.

[kante1603]

Hello James,

welcome to the forum.
To rule the doas out tear them out and do the initial voltage checks.With your dmm set to dc put the black probe to a 0vdc point (the audio/psu ground) and check the voltages at the doas sockets.
What do you get?
Jeff has preassembeled doas at his shop btw.,if that helps.
I didn't get what you meant saying all measurements exceeded what was to be expected.Did mean supply voltages,right?

Let us know,

good luck,

Udo.

[spaceboss]

Do you have other opamps from your other modules? That is always the first thing to rule out, after rack slot, associated cabling and converter settings.

Hi Jeff. My other units use 990s. Would those work as drop in replacements for 2520s? They have the same pin configuration. Rack slot and cabling have been ruled out.

Udo thanks for the welcome. In the build guide there are instructions for measuring resistance across the Op-amp sockets while the unit was unpowered. That's what I was referring to.  I'll post the exact resistance measurements in case anything sticks out. I'll also test the voltages at the sockets per your suggestions tomorrow after work.

I appreciate both of your responses, I know your time is valuable.

James

[jsteiger]

Yes you can swap in 990's. They will run fine in both spots of the 553F.

[spaceboss]

Well it was definitely an opamp. It works fine with the 990s.  I did manage, to break off a millimax pin on a good opamp though.  It's a good thing I'm not a brain surgeon.

On the plus side I know which opamp was funky, I'm going to reflow the solder and see if that helps.

Thanks for the help!

[jsteiger]

I just modified the instructions.

[spaceboss]

I got mine up and running last week.

This a beautiful sounding Eq. The high-pass, low-pass and subtle wide band bumps are great for tracking. Just the right amount of knobs for quick-good decision-making.

My op-amp mistake was one that I can put in the long--make this mistake only once file. 

While putting together a hybrid amp to act as a place holder for the 2520--it dawned on me that the voltage regulators are not the same part and are not interchangeable.  (It would have occurred to me earlier with a more thorough read of the BOM.)

So after some fun times with a desoldering pump and braid, I was able to set things right. It's good to know my soldering skills weren't the culprit--only my ability to carefully follow directions. 

Thanks for the fantastic kit and Eq!

[Mishegas]

Hello,

Long time builder (destroyer) -first time poster!

I hoping someone can help me with this - Just got done with a 553F (awesome build!) and was preparing to calibrate. (The *Pre-Flight Measurements* checked good,  all V+/V- were 150kOhms+- and C>O on A2  was 55ohms...)

Installed the OpAmps (2 SL red dots), plugged in the jig, (CMRR switch off- EQ out)

Anyhow, I had the 553F in the powered-up jig for maybe  a minute or so as I was looking for a BNC>alligator to hook to a freq gen when I noticed that the transistors on the A2 red dot were *really* cooking! I know they sometimes can feel a little warm but in this case I could barely touch them without permanently branding a SOT-package profile on my thumb.

I switched the SL's with some known-to-work GAR2520's- same deal.

Specifically it's the MJE172 (reddot) and the BD140 (gar2520) that are really baking.

Obviously -I've unplugged the whole thing and haven't continued the calibration...

This can't be normal? Just for the sake of comparison- I've just fired up some VP28's and a LC - and the transistors in those are a little warm but *nothing* remotely close to this & frankly I don't wanna go any further and discover I've just deep fried some DOA's!

Anybody know what this could be?

!Thank you in advance for any guidance or advice!

[kante1603]

Hello and welcome to the forum.

With no Doas installed I'd check the dc voltages at the sockets first,maybe the psu ground is gone for some reason?
Also are the voltages on the test jig o.k.?

Best regards,

Udo.

[Mishegas]

With no Doas installed I'd check the dc voltages at the sockets first,maybe the psu ground is gone for some reason?
Also are the voltages on the test jig o.k.?

Thanks Udo,

The DOA sockets show +/- 15.4vdc at V+/V- both A1 & A2.

Jig seems ok - tests identical to the actual card edge connector

I've had the 553F mounted directly in a BAE rack-...(A2)DOA  still really *hot*

?

[jsteiger]

Can you desolder all of the leads for the 2503 and measure the DCR of each winding? Set your DMM to a range of less then 100 ohms.

That would be:
red to brown
orange to yellow
green to blue
violet to gray