SB4000 Support Thread

[MaNiAC]

Thanks for your answer, Harpo.
I'll get into the build as soon as I can

 

[MLAudio]

Added a 5K resistor in series with VR17 and all is well in the land of gain reduction metering. For those who want or need this fix, here is what I did. I cut the trace on the back side of the PCB between C121 and VR17 Pin 1 (CCW) and then soldered the resistor on the backside between those points. This allowed me to correctly complete Calibration Step 4) Meter/Ratios with the 1ma (slightly less in reality) Hairball compression meter.

"for an easier fix an about 3K3...4K7 fixed resistor at the meter terminal" would have done the same without cutting a pcb trace.

You are absolutely right. I thought about that at first, but since my gear is always moving around from trucks to venues to studio (I do mainly live recording), I didn't want anything flopping around. For most people your suggestion is the best.

 

[dacapitan]

I have the unit passing clean audio in bypass mode and with the compressor in, gain seems to be working fine but threshold only shows any sign of compression at extreme levels (-20) which I think can be explained by the problem below. I have begun to calibrate the unit but I have run into a problem at step 3.

I get a reading of 0.740VAC at TP 8 and TP 10

I get  0v reading at TP11 and TP12 with no effect from VR7 & VR8.

I have tried to look for solutions through the thread and noticed  Mica had the same issue, but the conversation led to a dead end. I know ruckus328 did mention to buzz out from The input to TP11 & 12

-- but I must admit I am not that great at reading schematics either. I am struggling to understand where the XLR input meets the Internal Left and Right Side Chain on the schematic, so I can attempt to buzz it out? Any help would be appreciated

I really am trying my hardest/best to understand this, having completed 4 builds this has by far been the most challenging and patience testing.

 

[Harpo]

I have begun to calibrate the unit but I have run into a problem at step 3.

Mikes or mine (see previous page)?

I get  0v reading at TP11 and TP12 with no effect from VR7 & VR8.

Unit powered on, HPFilters set to off position,  External key disabled, sine test signal connected to XLR-inputs ?
Check for same AC voltage U2a-pin1 as TP8 and same AC voltage U1a-pin1 as TP10.
Check for same AC voltages arriving at the 20-pin connector J6/J18-pin11 and pin18.
Check for same AC voltages arriving at the 2x6 HPF switch poles pin1 and pin7.
Check for same AC voltages arriving at the 20-pin connector J6/J18-pin13 and pin17.
Check for same AC voltages arriving at the external key relais K6-pin4 and pin9.
If any of these tests fail, fix it (bad solder connection, broken part, connector not connecting, ...) before continuing.
Now adjust TP11 and TP12 for same AC voltages by trimming VR7 and VR8.

 

[dacapitan]

I have begun to calibrate the unit but I have run into a problem at step 3.

Mikes or mine (see previous page)?

I get  0v reading at TP11 and TP12 with no effect from VR7 & VR8.

Unit powered on, HPFilters set to off position,  External key disabled, sine test signal connected to XLR-inputs ?
Check for same AC voltage U2a-pin1 as TP8 and same AC voltage U1a-pin1 as TP10.
Check for same AC voltages arriving at the 20-pin connector J6/J18-pin11 and pin18.
Check for same AC voltages arriving at the 2x6 HPF switch poles pin1 and pin7.
Check for same AC voltages arriving at the 20-pin connector J6/J18-pin13 and pin17.
Check for same AC voltages arriving at the external key relais K6-pin4 and pin9.
If any of these tests fail, fix it (bad solder connection, broken part, connector not connecting, ...) before continuing.
Now adjust TP11 and TP12 for same AC voltages by trimming VR7 and VR8.

Thanks for the reply Harpo - I appreciate it alot,

I have tested all the points you have mentioned above and get the same Voltage as TP8 and TP10

Although I get 0v at K6-pin4 and pin9 but I get the same voltage as TP8 and TP10 at K6-Pin10 and Pin3 according to the datasheet below

http://www.mouser.com/ds/2/418/NG_SS_108-98002_W_P2-196265.pdf

Which according to the schematic would make sense as to why there is no voltaqe at TP11 and TP12.... but the question now is, how to get the voltage to carry from k-6 Pin3 and 10 to Pin4 and Pin9?

 

[Harpo]

Although I get 0v at K6-pin4 and pin9 but I get the same voltage as TP8 and TP10 at K6-Pin10 and Pin3 ...
but the question now is, how to get the voltage to carry from k-6 Pin3 and 10 to Pin4 and Pin9?

... External key disabled, ...

This. Your unit is switched for sidechain operating an external key signal (with obviously no external signal present) and the relais K6 seems to be operating correctly to do so.

 

[dacapitan]

Although I get 0v at K6-pin4 and pin9 but I get the same voltage as TP8 and TP10 at K6-Pin10 and Pin3 ...
but the question now is, how to get the voltage to carry from k-6 Pin3 and 10 to Pin4 and Pin9?

... External key disabled, ...

This. Your unit is switched for sidechain operating an external key signal (with obviously no external signal present) and the relais K6 seems to be operating correctly to do so.

Spot on Harpo! The way I understood the key switch to work is obviously in reverse to what I thought. Cant thank you enough!! You are so helpful - very much appreciated!! 

 

[Bowie]

Does anyone know what might cause the gain knob to be bypassed/non-functioning??  I have fully functioning compression and the bargraph monitors the input.  But, no matter where I have the I/O switch or the Gain knob, the output doesn't change.  I can hear it, but it's not adjustable.  Any help is greatly appreciated.
Thank you.

 

[Harpo]

Does anyone know what might cause the gain knob to be bypassed/non-functioning??

12VDC across the makeup pots outer pins?
Pots center pin varying voltage between 0...12VDC when you turn from CCW to CW position?
Same DC voltage arriving at the 20pin connector J18 pin10 and J6 pin10?
Same DC voltage arriving at left side of R123 (other/virtual ground side of R123 will measure 0V)? 

I have fully functioning compression...

Obviously not.

...and the bargraph monitors the input.

By default setting the bargraph is monitoring the right side output. Feeding both the left and right side with different program level would show this input/output and left/right side selector for the audio level bargraph operating correctly (or not).

But, no matter where I have the I/O switch...

Nothing to do with the units compressing function.

...or the Gain knob, the output doesn't change.

Audio output (assuming you are referencing this) with program signal above threshold will change with different ratio settings, no matter what makeup gain is dialed in. At least your unit is not in hard bypass mode, else the bargraph at any I/O L/R setting wouldn't response.

I can hear it, but it's not adjustable.

Whatever you may hear doesn't make much sense in this context.

 

[Bowie]

Does anyone know what might cause the gain knob to be bypassed/non-functioning??

12VDC across the makeup pots outer pins?
Pots center pin varying voltage between 0...12VDC when you turn from CCW to CW position?

First, thanks for taking the time!!  I have someone waiting on the completion of this build and I'm under pressure to finish it.
As far as the pot, yes, measurements go from 0-12vdc when panned.

Same DCvoltage arriving at the 20pin connector J18 pin10 and J6 pin10?

It there any way to measure this without removing the main and panel boards and measuring them at the solder joints underneath? 

Same DC voltage arriving at left side of R123 (other/virtual ground side of R123 will measure 0V)? 

Yes, it's 12vdc at one end of the resistor and 0 on the other.

I have fully functioning compression...

Obviously not.

The compression itself is functioning.  I can hear it working correctly and responding as-expected to changes in threshold, ratio, etc.  It's the make-up gain and output metering that are non-functional.

...and the bargraph monitors the input.

By default setting the bargraph is monitoring the right side output. Feeding both the left and right side with different program level would show this input/output and left/right side selector for the audio level bargraph operating correctly (or not).

That has me even more stumped because it's definitely the input signal I'm seeing.  The reason I can tell is that it does not change under heavy compression.  The bargraph meter level does not go down when heavy compression is implemented, leading me to believe that it's showing the input.  Also, these levels remain exactly the same when I flip the I/O switch.
The left and right selection works correctly though and shows different levels for the left and right channels. 

But, no matter where I have the I/O switch...

Nothing to do with the units compressing function.

Correct, I didn't think it would.  But, I expected to show the input and output levels respectively (unless it's reflecting something else that I'm not aware of).

...or the Gain knob, the output doesn't change.

Audio output (assuming you are referencing this) with program signal above threshold will change with different ratio settings, no matter what makeup gain is dialed in.

Yes, but what I am saying is the the Gain knob has no influence on the sound.  It is not functioning, not affecting the gain at all when tuned.  It's as if it's not even hooked up, but when I measured it, it's measuring 12vdc when open and 0 when closed.

I can hear it, but it's not adjustable.

Whatever you may hear doesn't make much sense in this context.

What I am hearing out of this unit is normal audio compression that behaves very much like the SLL buss comp I worked on years ago.  However, my Gain pot isn't working at all and the meter only shows input, even when it is switched to the output setting.

Thanks again for the help, I hope I was able to clarify the specific issues taking place.

 

[Harpo]

Same DCvoltage arriving at the 20pin connector J18 pin10 and J6 pin10?

It there any way to measure this without removing the main and panel boards and measuring them at the solder joints underneath? 

Same DC voltage arriving at left side of R123 (other/virtual ground side of R123 will measure 0V)? 

Yes, it's 12vdc at one end of the resistor and 0 on the other.

0...12V DC offset arriving at R123 proves the 20pin connector pin10 conducting and 0V at the opamps inverting input shows usual behaviour of a working opamp. Measuring the inverting summer U13-pin7 without audio signal should show a varying negative voltage between 0V and -1.935V when varying the makeup pot. Case not, reflow the bad or missing solder connection of R123 (correct parts value 620K ?).

It's the make-up gain and output metering that are non-functional.

But GR-meter is working correctly ? (VR17 dialed in for too low resistance might shunt down U16c)

...because it's definitely the input signal I'm seeing.  The reason I can tell is that it does not change under heavy compression.

You measured this? You wouldn't be the 1st. with missing solder connection at relais K7.

The bargraph meter level does not go down when heavy compression is implemented, leading me to believe that it's showing the input. Also, these levels remain exactly the same when I flip the I/O switch.

Describing previous assumption of a maybe bad solder connections at K7 (or SW3 or R130 parts value/solder connection) that prevents the relais to switch over for metering input side. Different from other compressors, the ratio circuit already injects a gain loss compensating voltage depending on ratio setting.

 

[Bowie]

Same DCvoltage arriving at the 20pin connector J18 pin10 and J6 pin10?

It there any way to measure this without removing the main and panel boards and measuring them at the solder joints underneath? 

Same DC voltage arriving at left side of R123 (other/virtual ground side of R123 will measure 0V)? 

Yes, it's 12vdc at one end of the resistor and 0 on the other.

0...12V DC offset arriving at R123 proves the 20pin connector pin10 conducting and 0V at the opamps inverting input shows usual behaviour of a working opamp. Measuring the inverting summer U13-pin7 without audio signal should show a varying negative voltage between 0V and -1.935V when varying the makeup pot. Case not, reflow the bad or missing solder connection of R123 (correct parts value 620K ?). 

It's the make-up gain and output metering that are non-functional.

But GR-meter is working correctly ? (VR17 dialed in for too low resistance might shunt down U16c)

...because it's definitely the input signal I'm seeing.  The reason I can tell is that it does not change under heavy compression.

You measured this? You wouldn't be the 1st. with missing solder connection at relais K7.

The bargraph meter level does not go down when heavy compression is implemented, leading me to believe that it's showing the input. Also, these levels remain exactly the same when I flip the I/O switch.

Describing previous assumption of a maybe bad solder connections at K7 (or SW3 or R130 parts value/solder connection) that prevents the relais to switch over for metering input side. Different from other compressors, the ratio circuit already injects a gain loss compensating voltage depending on ratio setting.

Thanks Harpo, I checked/adjusted VR17 and it was ok.  On U13 I wasn't sure what pin-7 was but I check the ones that might be it and didn't see any negative voltage, just levels close to 0.  Before taking the main board out to re-solder I tried experimenting with some things.  I went to give it a listen and run some test tones and discovered that my problem is compounded now as I'm no longer getting compression on the output signal, though the meter shows every nuance of the compression.  It changes as I adjust the with the threshold, ratio, stereo/mono, sidechain, etc so I know it's reflecting actual compression.  But, it's not apparent in the output signal.  The output signal now just sounds like a several db reduced version of the input.  Does that give you any ideas who what might be going wrong?
Thanks.

 

[Harpo]

On U13 I wasn't sure what pin-7 was but I check the ones that might be it and didn't see any negative voltage, just levels close to 0.

U13=TL072. Its output pin7 is sending control voltage to the audio-VCAs. No high voltages here (50mV/dB). Just follow the pcb traces to the audio-VCAs, beginning with R118 (with maybe buffered voltage attenuators 6.1mV/dB for THAT218x VCAs in between) and look out for shorts and/or wrong/missing jumper settings for your secret type of audio-VCAs that might shunt down your control voltage. (I have neither an idea of your populated parts nor your signal level or if this misbehaviour might be frequency related from wrong value fitted caps).

...though the meter shows every nuance of the compression. It changes as I adjust the with the threshold, ratio, stereo/mono, sidechain, etc so I know it's reflecting actual compression.

Sidechain hopefully seems to be error free then. After removing possible errors on their way to the audio-VCAs and if sidechain- and audio-VCAs are the same type, you might pull one sidechain-VCA and exchange it with an audio-VCA to exclude a broken audio-VCA.

 

[Bowie]

On U13 I wasn't sure what pin-7 was but I check the ones that might be it and didn't see any negative voltage, just levels close to 0.

U13=TL072. Its output pin7 is sending control voltage to the audio-VCAs. No high voltages here (50mV/dB). Just follow the pcb traces to the audio-VCAs, beginning with R118 (with maybe buffered voltage attenuators 6.1mV/dB for THAT218x VCAs in between) and look out for shorts and/or wrong/missing jumper settings for your secret type of audio-VCAs that might shunt down your control voltage. (I have neither an idea of your populated parts nor your signal level or if this misbehaviour might be frequency related from wrong value fitted caps).

...though the meter shows every nuance of the compression. It changes as I adjust the with the threshold, ratio, stereo/mono, sidechain, etc so I know it's reflecting actual compression.

Sidechain hopefully seems to be error free then. After removing possible errors on their way to the audio-VCAs and if sidechain- and audio-VCAs are the same type, you might pull one sidechain-VCA and exchange it with an audio-VCA to exclude a broken audio-VCA.

Thanks, I've been pulling it apart, triple checking for correct component values, shorts, correct jumpers, etc and I'm really at a loss.  It still has no audible compression even though it can be seen on the meter. What might cause the signal to come through uncompressed even though the compression meter is showing what looks to be normal compression behavior as I adjust the knobs?

I can post any other pics that might help.

 

[sr1200]

Just a thought, and i did this on one of the ones i built.  The Inputs are the ones in the MIDDLE of the board the outputs are on the left (if looking at it from the front)  If you hook it up in reverse it passes audio in bypass but no compression.  I spent a day trying to find errors once only to realize this.  Very embarrassing moment in the shop lol.

 

[Bowie]

Just a thought, and i did this on one of the ones i built.  The Inputs are the ones in the MIDDLE of the board the outputs are on the left (if looking at it from the front)  If you hook it up in reverse it passes audio in bypass but no compression.  I spent a day trying to find errors once only to realize this.  Very embarrassing moment in the shop lol.

When I initially wired it I had done that too, but caught it before hooking up the main board.  Thanks for the help though.

I'm starting to think it must be a component failure as I've going over this board an endless number of times.  I really hope it's my own error as it would be easier to discover.  I feel extremely bad for the person I'm building this for.  I've never been stumped like this before.

  Does anyone know how to get a hold of Serpent Audio?  I received an email when I had a pre-sale inquiry but after the sale I cannot get any emails returned.  I even tried different accounts in case of an aggressive spam filter.

 

[sr1200]

Mike can be very difficult to get a hold of.  Double check the orientation of all your IC's and what VCA are you using (that or the little boards?)

 

[Bowie]

Mike can be very difficult to get a hold of.  Double check the orientation of all your IC's and what VCA are you using (that or the little boards?)

I checked the IC's a number of times. The vca is the serpent supplied THAT 2181b.
I'll post some pics later today.

 

[Bowie]

Here's  some pics, any thoughts as to why I'm seeing compression and not hearing it would be greatly appreciated!!

 

[sr1200]

hard to tell in that pic, but do you have the right jumpers jumped in the VCA section?