SB4000 Support Thread

[sr1200]

I dont think you'll get any voltage if the unit isn't in stereo mode...  but in order to trouble shoot, EVERYTHING should be installed (backwards or not).  There are relays that route the signal, and not having a switch in there may be causing the relay to be in the WRONG position.  If you put the switch back in, flip it and see if you hear the relay engage/disengage. 

 

[jandoste]

I have a 47K resistor in the "47 or jump". Should I pull that out and replace it with a jumper?

use a jumper! I had the same problem...

 

[ruckus328]

check your diodes

actually, check that your caps are not backwards also...

All of my caps are are in proper polarity. Diodes all check out the same (Using diode function mode testing .600 - .699 in one direction and 1. in the other direction) without de-soldering one leg. Is removing one leg necessary to test my diodes if they all test similarly?

I'm getting either +/-12VDC or +/-15VDC or both on all of my op amps. I also get one leg of each op amp with a small voltage that corresponds to a control on the front panel. I'm pretty sure my power is getting everywhere nice and clean.

My bargraph is not lighting up with the -20db signal being fed, but lights up during power-up/down. No change in the signal to my DAW no matter what I change on the front panel.

Any other tests I can do to rule out issues?

Drjoe -

1) Is the unit passing audio in both bypass and engaged modes?

2) Is makeup gain working?

3) Did you jumper the resistor by the threshold pot that says "47K or jump"?

If your makeup gain is working, this might be a case of you're not feeding it a loud enough signal and/or you didn't jumper the resistor mentioned.  You say -20db but you don't say dbwhat.  If you're talking -20dbu, that's way too low of a signal, and the bargraph wouldn't light up, and you probably wouldn't be able to get her to compress either (even if you did jumper the resistor)

Thanks for the response, Ruckus.

Yes, the unit passes audio in all modes and whether it's on or off. I get the same steady signal back into my DAW no matter what I adjust on the front panel.

Makeup gain is not working. Nothing on the front panel is affecting the signal, though I detect voltage changes on the op amps when turning knobs.

I have a 47K resistor in the "47 or jump". Should I pull that out and replace it with a jumper?

Sending -20db from the signal generator plugin in protools set to peak. -20dbfs? The same signal sent through a dbx576 registers as -22 on the VU meter. Even when I boost the signal to where it clips the 576, I get no meter activity on the SB4000.

I flipped it over and hit a few suspect joints with a re-solder, but no change.

Dr Joe - sounds like you have multiple issues (with likely multiple sources), so taking it one step at a time - Yes, you need to take the 47K out and jumper it.  That will solve one issue but not everything, but it's a start.  You should feed it a louder input signal for this stage, -22dbfs is too low for troubleshooting.  Feed it a hefty signal (like -10 to -5 or so) so it'll be easier to trace.

You're gonna need to break out the schematic, this is easy, it's just follow the dots.  Just referring to the Left channel - Audio signal comes in at top left hand side of the schematic, through a couple caps/resistors, and then through the reciever IC (U3), then through the 22uF cap (C73).  After this cap the signal splits and goes to the VCA's and also branches off to the sidechain (The arrow labeled "L_SCIN").  Look down at very bottom left hand corner of schematic, you'll see where "L_SCIN" continues, it goes to the relay (K5) and also at this point is where it hits TP8.  If you are not getting any signal at TP8, then you know your problem is at one of the components before TP8. 

If your makeup gain is not working, I would suspect either:

a) your ribbon cable has an issue

b) Bad solder joint/backwards component somewhere around the TL072

c) You did not properly install the jumpers around the audio VCA's

Try what I said above and let us know how you make out, good luck, don't worry you'll get it figured out.

 

[bieckmusic]

hi everyone! 

I'm still stuck on my compressor...    I'd be so appreciative if anyone has any more suggestions...
Well, I checked everything on the control board, and around TL072 and fixed a few more solder joints and it's working way better but still not perfect.   

The compressor is still slamming like crazy when it gets to around 10 dB compression...  ???

Do you think I should purchase a few replacement op chips to try, some TL072s?  Do you, or any one, have any additional thoughts??

thx
greg

 

[Harpo]

Yes, the unit passes audio in all modes and whether it's on or off. I get the same steady signal back into my DAW no matter what I adjust on the front panel.

Makeup gain is not working. Nothing on the front panel is affecting the signal, though I detect voltage changes on the op amps when turning knobs.
....
I disconnected the key input switch to rule that out and I've tried all other combinations of buttons to be sure they weren't wired backwards.
I'm still not getting any AC voltage on TP8 - TP12.

Double check your bypass switch, connection to J11, resistor value of R1 (51 ohm) and the relay K4.
Your unit is in a steady bypass mode. You'll get no different behaviour until you get this relay K4 engaged, so signal reaches your compressor input.

 

[drjoe]

Yes, the unit passes audio in all modes and whether it's on or off. I get the same steady signal back into my DAW no matter what I adjust on the front panel.

Makeup gain is not working. Nothing on the front panel is affecting the signal, though I detect voltage changes on the op amps when turning knobs.
....
I disconnected the key input switch to rule that out and I've tried all other combinations of buttons to be sure they weren't wired backwards.
I'm still not getting any AC voltage on TP8 - TP12.

Double check your bypass switch, connection to J11, resistor value of R1 (51 ohm) and the relay K4.
Your unit is in a steady bypass mode. You'll get no different behaviour until you get this relay K4 engaged, so signal reaches your compressor input.

YES! I had swapped the 51R with the 510R at R137. Now I'm compressing and my bargraph is working. Thanks for the tip!

Now I'm trying to calibrate the unit and I'm getting different levels between channels. When adjusting unity gain, I can match my DAW with the Left side, but my Right unity control at VR1 is maxed out and I'm getting almost +10db when I engage the compressor. Both VR1 and VR2 have the same value between wipers, but I notice the label on the top of the trimpots is different between them. One says VR1 says 54U and VR2 says 545. They came in the same bag labelled as 50k trimpots but I'm thinking the labeling means there is a mistake.

CV Level calibration went fine, but I stopped there until I can figure out this L/R problem.

Also, the compression is super dirty. I can push the gain very hot and it sounds clean, but any amount of compression and it starts sounding distorted. I'm not sure where to begin tracing that down.

 

[drjoe]

Sending a 1k test tone from my DAW through the comp, back to the DAW.

With the compressor in bypass I'm seeing -14.1db on LEFT and  -11.5db on RIGHT on my DAW

When I engage the compressor, I'm reading -3.6db on LEFT and -9.2db on RIGHT. (+10.5 / +2.3 respectively)

With the comp in bypass and no signal being sent, I'm reading -70db (noise) on the LEFT and clean 0db on the RIGHT.

I've checked most of the components between the input and the VCAs. Not sure what to try next.

 

[Harpo]

Now I'm trying to calibrate the unit and I'm getting different levels between channels. When adjusting unity gain, I can match my DAW with the Left side, but my Right unity control at VR1 is maxed out and I'm getting almost +10db when I engage the compressor. Both VR1 and VR2 have the same value between wipers, but I notice the label on the top of the trimpots is different between them. One says VR1 says 54U and VR2 says 545. They came in the same bag labelled as 50k trimpots but I'm thinking the labeling means there is a mistake.

+10db probably being +10dB digital full scale, calibrated to whatever level. VR1 and VR2 have the same value at whatever ohm reading between their start and wipers would give you a clue what you might be missing (wipers are at virtual ground). If you had these trimmers installed without their pretrim value as adviced from pg.1 of the assembly document and the schematic, but wiper towards their zero ohm setting, you might have blown one or both audio VCAs.
With your mains wire disconnected and keeping your trimmers soldered in circuit for measurement, pull out your audio VCAs U11 and U17 and dial in the trimmers resistance to 30K by measuring ohms between trimmer VR1-pin1 or TP10 and audio-VCA U17-pin1 for the right-side and between trimmer VR2-pin1 or TP8 and audio-VCA U11-pin1 for the left-side.
Put the VCAs back in. You might have been lucky and they survived, if this was the initial reason for misbehaviour.
Double check all resistor values (there might be more mixed up), especially around U3, U12, U8 and U5, U18, U4.
Double check your jumper settings to match your type of VCAs.
Reconnect your mains wire and try calibrating again.

 

[whomper]

Just finished assembling the unit and gone through calibration. Everything went smooth.

Trouble is, when sending audio to the unit, the audio is distorted more and more based on the compression amount. When hitting 8db, I get noticeable distortion in the signal.

When activating the unit with threshold full CW (no compression), the sound is as clean as the input signal, only when increasing compressions do I get increased distortion in the audible level.

It does not matter what the other settings are at, the distorted sound is apparently a function of the compression amount.

The LED bar graph does not seem to be consistent between IN and OUT. When sending signal and activating the unit, although the DAW sees the saw level coming in as going out, the bar graph displayes a different level when switching between IN and OUT modes.

Have enclosed two screen captures of a 1KHz sine wave, first without compression engages (unit activated) and the second with 8db compression. There seem to be an increase in harmonic content of the sine wave and it changes its color; i.e. it does not only decrease in level, but it becomes somewhat phased as seen by the additional harmonic content that gets emphasized.

Thanks,
Whomper

 

[whomper]

Second file, 8db compression.

EDIT:

Have done some more research into the issue:
1. With a 1KHz signal U16 (TL074) pins 8 and 14 exhibit a 2KHz signal when compressing. The 2KHz signal is also present in the ATTACK_OUT going into the VU as well as the control boards in some pins.
2. With music, Pins 7 exhibits no signal with 0db compression, and a distorted signal with 8 db compression. Pin 1 exhibit distorted signal without compression and as compression is applied, the signal gets totally distorted.
3. TP11 has a good signal. So does PIN12.
4. The issue is symmetrical in both channels, i.e. U15 shows same behavior as U16.

Is this behavior normal? What could exhibit a signal multiplication and distortion?

Thanks,
Whomper

 

[band_master]

hey everyone,
is anyone else in the market for a case for this project from http://diypartssupply.com/? It seems Ptownkid may have been having some email problems and we just need to get around 20 people in order for him to do the run at the metal shop. reply here if you need one?

BD

 

[sr1200]

Wouldnt it be more appropriate to have people post on Ptowns page rather than here in the support thread?

 

[band_master]

fine by me. here is the link: http://www.groupdiy.com/index.php?topic=36609.0

 

[druu]

Hi

I've nearly completed the boards, just waiting on some replacement parts. I have a couple of questions, still fairly new to this stuff:

Anyone running the Serpent Quad VCA boards? I'd like to confirm which jumpers on the VCA section need to be populated, so far I have JMP8 and JMP9 installed but none of the ones on top. Is this correct? I was supplied THAT2181B chips for all.

Secondly, on the control PCB, should JMP7 be jumped?

Also, is anything supposed to be populated in J19 (3 pin)?

That's it for now but will probably have more!

Thanks in advance!

 

[druu]

One other questions re: the quad vca boards, what should the pot be trimmed to?

 

[whomper]

Guys, any tips to help me isolate the issue I have having posted a few posts ago would be greatly appreciated...

 

[ruckus328]

Hi

I've nearly completed the boards, just waiting on some replacement parts. I have a couple of questions, still fairly new to this stuff:

Anyone running the Serpent Quad VCA boards? I'd like to confirm which jumpers on the VCA section need to be populated, so far I have JMP8 and JMP9 installed but none of the ones on top. Is this correct? I was supplied THAT2181B chips for all.

Follow table on schematic for DBX202 (Gold Can), it should also be indicated on QVCA BOM which jumpers to install, so yes JMP8 & JMP9 on backside of board.

Secondly, on the control PCB, should JMP7 be jumped?

Yes

Also, is anything supposed to be populated in J19 (3 pin)?

J19 is Bargraph Connector, it's how signal/power is brought to the bargraph from the main board.  Look at wiring section on build manual.

 

[ruckus328]

Just finished assembling the unit and gone through calibration. Everything went smooth.

Trouble is, when sending audio to the unit, the audio is distorted more and more based on the compression amount. When hitting 8db, I get noticeable distortion in the signal.

When activating the unit with threshold full CW (no compression), the sound is as clean as the input signal, only when increasing compressions do I get increased distortion in the audible level.

It does not matter what the other settings are at, the distorted sound is apparently a function of the compression amount.

The LED bar graph does not seem to be consistent between IN and OUT. When sending signal and activating the unit, although the DAW sees the saw level coming in as going out, the bar graph displayes a different level when switching between IN and OUT modes.

Have enclosed two screen captures of a 1KHz sine wave, first without compression engages (unit activated) and the second with 8db compression. There seem to be an increase in harmonic content of the sine wave and it changes its color; i.e. it does not only decrease in level, but it becomes somewhat phased as seen by the additional harmonic content that gets emphasized.

Thanks,
Whomper

Not really sure what I'm looking at here, the 0db compression jpg does not depict a clean signal, that is a fair amount of distortion.  First thing's first, narrow down whether problem is in audio path, sidechain, or both.  Make sure you Unity Gain Pots are adjusted for unity gain (they should be somewhere around centered)  Did you install the correct jumpers in audio VCA section?

If so, remove Audio VCA's, and temporarily jumper Pin's 1 & 8 at each audio VCA.  Feed it a 1K signal, look at it on freq analyzer, you should have clean signal (no harmonic nodes).  Report back.

 

[whomper]

Have removed the left channel VCA and rewired pin 1 to 8. The output signal at the XLR is clean.

 

[drjoe]

Now I'm trying to calibrate the unit and I'm getting different levels between channels. When adjusting unity gain, I can match my DAW with the Left side, but my Right unity control at VR1 is maxed out and I'm getting almost +10db when I engage the compressor. Both VR1 and VR2 have the same value between wipers, but I notice the label on the top of the trimpots is different between them. One says VR1 says 54U and VR2 says 545. They came in the same bag labelled as 50k trimpots but I'm thinking the labeling means there is a mistake.

+10db probably being +10dB digital full scale, calibrated to whatever level. VR1 and VR2 have the same value at whatever ohm reading between their start and wipers would give you a clue what you might be missing (wipers are at virtual ground). If you had these trimmers installed without their pretrim value as adviced from pg.1 of the assembly document and the schematic, but wiper towards their zero ohm setting, you might have blown one or both audio VCAs.
With your mains wire disconnected and keeping your trimmers soldered in circuit for measurement, pull out your audio VCAs U11 and U17 and dial in the trimmers resistance to 30K by measuring ohms between trimmer VR1-pin1 or TP10 and audio-VCA U17-pin1 for the right-side and between trimmer VR2-pin1 or TP8 and audio-VCA U11-pin1 for the left-side.
Put the VCAs back in. You might have been lucky and they survived, if this was the initial reason for misbehaviour.
Double check all resistor values (there might be more mixed up), especially around U3, U12, U8 and U5, U18, U4.
Double check your jumper settings to match your type of VCAs.
Reconnect your mains wire and try calibrating again.

I did pre-trim all values before firing it up for the first time. However, since the R UNITY trimpot wasn't achieving the results I needed, I did open it fully, potentially frying the VCA. When I followed your instructions, both trimpots where around 47k after attempted calibration. I spun them back to 30k, reinstalled the VCAs, and nothing changed.

I removed the VCAs once again, jumped pin 1 to pin 8 on each VCA, and fired it back up with a 1k tone. When I engage the compressor, my right channel jumps 15dB on my DAW meter (I'm using PAZ Frequency). The left channel remains the same.

Here's a link to a file on soundcloud of a 1k test tone while making adjustments. I left comments to let you know which controls are being changed.

http://soundcloud.com/joestulpin/sb4000-1k-cal/s-aLr9M

As you can hear (and see if you download the file and open in a DAW), the compressor being engaged causes the spike on the right channel only, but the compression is crushed and distorted on both channels. My assumption is now that both VCAs are fried (I have 2 more coming in the mail today), but I don't know where to look for the problem regarding the right channel. I'm afraid to install the new RIGHT VCA in case that spike fries it again. Perhaps I'll replace the LEFT VCA only and see if my noise clears up on that channel?

All problems aside, while playing music through the unit, I can hear the good qualities through the noise. I can hear the kick start thumping when I adjust the HPF, and I can tell it's doing the right thing behind all that junk. I can't wait to hear it working properly.