JMan

Re: TC-500 // Versatile Tracking Compressor for 500 Series.
« Reply #40 on: February 22, 2021, 10:52:33 PM »
Well, I finally got around to soldering the last couple joints and going through the calibration.  In typical fashion for me, everything mostly worked, but I ran into a few issues.  I guess I am the only one who did, since this thread has been pretty silent except for me.   :-X

Anyway, I apologize for what is going to be a long post, but I'll try to be concise.  I built two units, and while they both actually sound quite good, each of them has some kinks that I need to work out.

Unit A: This one pretty much worked from the jump.  However, two things struck me as odd.
 
-Peak reduction meter was able to be accurately set to display the -3 dBfs during calibration.  However, when running actual audio (something other than a test tone) through it, the meter seems to display a fixed relationship to the Peak Att. knob position -- to put that in clearer terms, the LEDs will change predictably as the Peak Att. knob is turned, but they do not move in relation to musical dynamics.
-Second, and probably less important, when I went to trim the VCAs for distortion, the Voxengo plugin showed literally ONLY my 1k test tone -- no harmonics, no 2k, nothing to adjust like what is in the picture in the build guide.  Just my sine wave.  Should I be using a different type of signal?  Anyway, I don't pick out any audible distortion when running music through it, so this is likely just fine.

Unit B: This one had more issues.  I'll preface everything by saying that it's possible I fried one or both of the 2181 chips on this one when soldering them to the adapter board, so if that sounds like a likely culprit for these symptoms, it wouldn't be unreasonable.

-GR_Cal trimpot has no effect on LED meter.  Fully CW or CCW, nothing changes.  Luckily, the meter tracks quite accurately without adjustment, so I guess that's okay...
-Peak Attenuation does not work at all.  Even set to max, signal in and signal out are identical.  PK meter also shows nothing, predictably.
-VCA 1 - Voxengo plugin shows no distortion again, but this time, nothing at all happens if I adjust the pot, not even to the fundamental of the sign wave. 
-VCA 2 - Shows some 2k harmonic, which I can reduce by turning the pot CCW.  I can literally just turn this until the 2k disappears entirely, it never seems to go back the other way.  I guess that's good?

Anyway, again, sorry for the long post.  I'm just trying to be complete.  Happy to receive any suggestions or thoughts you might have.


elskardio

Re: TC-500 // Versatile Tracking Compressor for 500 Series.
« Reply #41 on: February 27, 2021, 08:54:08 PM »
Sorry JMan, I just saw your post. Notifications are not working with my account...

-Peak reduction meter was able to be accurately set to display the -3 dBfs during calibration.  However, when running actual audio (something other than a test tone) through it, the meter seems to display a fixed relationship to the Peak Att. knob position -- to put that in clearer terms, the LEDs will change predictably as the Peak Att. knob is turned, but they do not move in relation to musical dynamics.

Does the Peak attenuator works? Does it compress the incoming signal when you lower the control? What DC voltage do you read at the junction of R78 - R79 ? You should have around 0.6V



-Second, and probably less important, when I went to trim the VCAs for distortion, the Voxengo plugin showed literally ONLY my 1k test tone -- no harmonics, no 2k, nothing to adjust like what is in the picture in the build guide.  Just my sine wave.  Should I be using a different type of signal?  Anyway, I don't pick out any audible distortion when running music through it, so this is likely just fine.

You need to lower the "Range Lo" setting in the plugin preferences to see the full frequency spectrum. Then you should be able to precisely trim the VCA.




-GR_Cal trimpot has no effect on LED meter.  Fully CW or CCW, nothing changes.  Luckily, the meter tracks quite accurately without adjustment, so I guess that's okay...

What DC voltage do you read at the junction of R48 - R49? You should have around 1.1V



-Peak Attenuation does not work at all.  Even set to max, signal in and signal out are identical.  PK meter also shows nothing, predictably.

First lets test if the Detector works (4305 IC). Send a test tone to the module's input. Measure the DC voltage at R52 as shown in the picture. You should have a small reading in mV. If you do, play with the signal generator's volume to see if the DC voltage move.



Is the Gain working on the unit? If its working properly, then VCA2 is fine.

JMan

Re: TC-500 // Versatile Tracking Compressor for 500 Series.
« Reply #42 on: March 01, 2021, 12:36:32 PM »
Thanks for your reply! 

I'll check all of those points this evening and report back.  I'll email you in addition to posting here, since your notifications aren't working.
« Last Edit: March 01, 2021, 04:43:22 PM by JMan »

JMan

Re: TC-500 // Versatile Tracking Compressor for 500 Series. New
« Reply #43 on: March 01, 2021, 05:13:31 PM »
UNIT 1

Does the Peak attenuator works? Does it compress the incoming signal when you lower the control? What DC voltage do you read at the junction of R78 - R79 ? You should have around 0.6V

The peak attenuator appears to work when sending a test tone.  It reduces the signal as expected by adjusting the control knob.  However, after watching its behavior while running musical material (as opposed to a test tone), I'm thinking that it may be working more like a gain knob, just turning the whole signal down.  The meter LEDs seem to reflect this as well.  I will send you a video via email, because maybe it is easier to see it than to understand how I am describing it.  It will also light up if I turn the knob down even if there is no audio running through it.

DC voltage at junction R78/R79 is more or less as expected, 0.637 V.

You need to lower the "Range Lo" setting in the plugin preferences to see the full frequency spectrum. Then you should be able to precisely trim the VCA.

Fabulous!  I hadn't used the plugin before and I couldn't find that control.  VCAs are now successfully trimmed.

So, this first unit is working and fully calibrated, and the only outstanding oddity is the peak reduction meter.


UNIT 2

What DC voltage do you read at the junction of R48 - R49? You should have around 1.1V

I'm reading 1.16v DC at this junction.  Something else must be wrong here...

First lets test if the Detector works (4305 IC). Send a test tone to the module's input. Measure the DC voltage at R52 as shown in the picture. You should have a small reading in mV. If you do, play with the signal generator's volume to see if the DC voltage move.

WHOA.  Okay, with DMM set to measure mV, I got "OL," so I set it to volts and boom, -6.4v DC.  If this is meant to be millivolts, I'm obviously way off.  I did play around with the level from the tone generator, and the voltage changed by a few thousandths, but clearly the issue is bigger than that.

Is the Gain working on the unit? If its working properly, then VCA2 is fine.

This was odd.  The gain knob shifts the panning.  When running a signal through the unit with gain at 0, the image comes back into the interface/DAW panned hard right.  As I turn the gain knob up, the signal slowly shifts back to center.  I don't think there was any actual level gain, though.  So I guess I toasted VCA2 when soldering?
« Last Edit: March 01, 2021, 05:30:23 PM by JMan »


 

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