SB4000 Support Thread

[wave]

the wires coming off the transformer arent the rails (well, not yet atleast) Your rails are the +/- 12v +/- 15v and your 0v is your reference.  So if your meter is standard... black probe on the 0v and red probe on the rail youre testing.... and DONT cross the streams!

Thanks sr1200.  I think I understand the rails now, still not sure where to place the black probe.  I feel like I am so close! 0v is where?

J4-3 0V
j5-2 0V (isolated)

 

[David R.]

Thanks Wave!

 

[mica]

U sure youre in the right mode mica?  did you try switching the stereo/mono switch?

Im sure im in the right mode.. If I wasn't tp10 wouldn't have any voltage on it right? anyway I have tried turning buttons on and off but still no readings.. I'll try replacing TL072 next..

Im unsure now.. the "IN / EXT IN" switch needs to be at "EXT IN" for step 3 right? And the "EXTERNAL SIDECHAIN" button needs to be off (not pushed in)?

My XLR inputs now read:
LEFT: 2.29V
RIGHT: 2.23v
(In step 2 - both bypassed and enganged - Step 2 seems OK)

STEP 3:
Im now getting:
3.1v at TP8
3.7v at TP 10
3.7V at TP 12
but still no voltage at TP11..

Also my LEFT channel is way lower than my right channel in my daw, in stereo mode. (If i go to mono they even out..)
If i turn up the makeup gain only the LEFT channel responds (in both modes)
Basicly: the right channel doesnt move..
After my TL074 "accident" i have replaced all TL074 and the TL072. PSU voltages are correct..

Im kinda' stuck now

/Michaael

 

[sr1200]

im thining you may have your ext in and in switch wired upside down, and keep in mind that SSL mode is when the mono/stereo button is OUT if wired properly.... i think lol.

 

[David R.]

[/quote]

J4-3 0V
j5-2 0V (isolated)
[/quote]

OK, got it.  Also, and please correct me if I am wrong, but 0v is the ground.  I am trying to be as clear as possible to make sure I understand the theory behind the circuit for future builds.

I just powered up the power supply section and all looked good.  Connected to the main board, looked good.  Woo hoo!  Now to hook up an audio cable.

 

[wave]

This is from another thread

Thanks Ian and Dave for your patience - I apologize for my thickness.  :-[ Earth and 0v had me confused. Otherwise, I think I'm good to go and will report back in a few days (I hope).

No need to apologise. There are many many people who are similarly confused and it does not help that the terms ground, earth, chassis, signal ground and 0V are often used interchangeably and hence connected together in places they should be.

The principle purpose of 0V is as a return path for signal current within a device.

The principal purpose of chassis (earth or ground) is as a screen around your circuit. The screen picks up external interference and routes it safely and separately away from signal currents. If you (accidentally) route interference through 0V wires you get noise and earth loops which is why it is important to connect the two together at one point only.

In the good old days of transformer balanced inputs and outputs this worked fine and there was absolutely no need for any signal current to flow in screens. But today, with electronically balanced input and outputs the ins and out are actually differential rather than balanced so this important property has been lost with the result that people now get hum loops even in so called balanced circuits.

Cheers

Ian

 

[wave]

U sure youre in the right mode mica?  did you try switching the stereo/mono switch?

Im sure im in the right mode.. If I wasn't tp10 wouldn't have any voltage on it right? anyway I have tried turning buttons on and off but still no readings.. I'll try replacing TL072 next..

Im unsure now.. the "IN / EXT IN" switch needs to be at "EXT IN" for step 3 right? And the "EXTERNAL SIDECHAIN" button needs to be off (not pushed in)?

My XLR inputs now read:
LEFT: 2.29V
RIGHT: 2.23v
(In step 2 - both bypassed and enganged - Step 2 seems OK)

STEP 3:
Im now getting:
3.1v at TP8
3.7v at TP 10
3.7V at TP 12
but still no voltage at TP11..

Also my LEFT channel is way lower than my right channel in my daw, in stereo mode. (If i go to mono they even out..)
If i turn up the makeup gain only the LEFT channel responds (in both modes)
Basicly: the right channel doesnt move..
After my TL074 "accident" i have replaced all TL074 and the TL072. PSU voltages are correct..

Im kinda' stuck now

/Michaael

For step 3 the EXT IN should be off (down) and the INTERNAL SIDECHAIN should be out (not pushed in)

Dave

 

[sr1200]

Unless of course you wired the switch upside down like i did on both of my units where EXT IN was really in and IN was really ext in lol  does that make any sense.  hahaha

 

[mica]

I've tried switching between every possible combination and still no voltage on TP11.. My wiring looks good on the switches.. The left channel is still way lower than the right but responds to increase from the gain knob both in mono an stereo. The right channel doesn't move in any mode..

 

[sr1200]

Was the unity gain adjusted? (actually...) do the unity gain pots make any difference?

 

[mica]

Yes.. Step 1 and 2 are good.. The unity gain is set and measured with True RMS DMM. Same values both engaged and disengaged using the trimpots..

 

[sr1200]

OK so then under what conditions is the signal lowering?

 

[druu]

I had a similar issue but turned out to be my dodgy soldering on my cables, one of the wires had disconnected. Try swapping the inputs on the rear and see if the voltage is any different?

 

[mica]

I tried switching cables on the input PCB (L<->R). Still no voltage at TP11..

 

[mica]

OK so then under what conditions is the signal lowering?

In stereo mode one side is 1/3 of the other channel. In mono, they are the same. When i turn up the gain knob, only one side increases, both in mono and stereo mode.. Both channels gets a 1khz signal at same level.. switching cables didn't help (L to R). I have EXT IN/ IN switch down, (but have tried up as well).. No matter what: no voltage af TP11, so im still stuck at calibration step 3..

Any way to rule out that one or more of the THAT2181 chips are blown? I did make a mistake with the TL074 chips earlier.. Im just trying to isolate the problem

 

[sr1200]

hoping you put the right resistors in the right places... if it seems right in mono mode but is off in stereo mode that should narrow things down quite a bit.

 

[mica]

Well its (kinda') working.. Threw it a drummix and it's compressing just fine, but the right channel is gone. At one point it was there but at low volume, but now its gone again. If i go to mono mode (Internal sidechain button pressed in) the compression seems to disappear.. In mono, only the Gain knob seems to work.
Both meters seems to be working, and all knobs (I think..) in stereo mode. TP11 still has 0V..!!

Does it make any sense?

/M

 

[sr1200]

in short... no it doesnt make sense, but theres gotta be something very wrong.  you may have to check all your chips especially if one was blown or you put one in backwards. (i did that on my second unit and nearly lost an eye... the chip exploded and sent shrapnel across the room)

 

[Harpo]

In stereo mode one side is 1/3 of the other channel. In mono, they are the same. When i turn up the gain knob, only one side increases, both in mono and stereo mode.. Both channels gets a 1khz signal at same level.. switching cables didn't help (L to R). I have EXT IN/ IN switch down, (but have tried up as well).. No matter what: no voltage af TP11, so im still stuck at calibration step 3..

Any way to rule out that one or more of the THAT2181 chips are blown? I did make a mistake with the TL074 chips earlier.. Im just trying to isolate the problem

At least two different issues.
Double check jumper settings J1 populated, J2 and J3 not populated, resistor values R77,R83,R84,R105, cap values C84,C100, solder connections and VCA U11 fully pushed into its socket. Both audio VCAs receive the same control voltage from U13b, so one side no makeup gain, there will be a difference behind U13b-pin7 and the audio-VCAs or the audio-VCA U11 is broken, if 'one side is 1/3 of the other channel' is the left side. If its the right side, its the corresponding part from right side.

For your 'no voltage at TP11', trace backwards with audio signal present, measuring AC voltages of relais K6-pin9, K6-Pin10, with HPF-control switch set to 'off' the 20pin-connector pins 11,13 both sides making connection, U2A-pin1, TP8/9/10 all the same voltage reading in oxford-mode or TP8/9 same reading and TP10 0V reading in mono-mode.
Voltage coming back, the last checkstep before will be the faulty, wrong or poorly soldered part. Maybe broken or not switching relais ....
Good luck.

 

[mica]

I re-seated the U17 (right VCA) and presto! I have audio on both channels again..
I redid step 2, and whent on to step 3 of the calibration, but still nothing on TP11.. Any way to measure K6 from the top? Otherwise i will have to dismount all wires to be able to turn it around.. In that case: what do I need to connect to be able to test K6 relay? Just PSU or do i need to connect everything with the main PCB upside down?