SB4000 Support Thread

[jamesn81]

Here is an PDF file with vector versions of MONO, or M / S (for the Sidechain button) and COMP (for the Compressor button) if you want to have them glow with the word on the switches (kinda like the original unit). 

They are 9.6mm square which seems to fit perfectly in the switches that are given as part of the kit.

 

[dd64]

Hi
I'm a new DIYer.
I've a (stupid?) question and I can't find the answer.
The sb4000 is a stereo comp.
So why is there only a mono led meter?
Is it possible to put a stereo led meter (and still the switch for In/Out meter)?
Thanks

 

[druu]

Yes it's stereo. There is another toggle switch for Left/Right.

 

[druu]

Has anyone tried replacing the threshold and gain pots for stepped switches? I know the PCB would probably need hacking up but anyone tried?

 

[Winetree]

Upon testing the power supply I accidentally touched probes and saw sparks.
I replaced all regulators, diodes and bridge.
Voltages are good except on the -12 volts I'm getting -19 v.
No adjustment available should I check resistors? Any suggestions?

 

[Harpo]

Any load connected to this -12V rail? (a temporary 1K - 1K5 resistor between 0V and -12V would draw enough mA that the vReg behaves, if it isn't broken).
Replaced diode D29 fitted with correct orientation ?
Else diode D29 has blown short or the 7912 vReg is broken.

 

[Winetree]

No load connected. does there need to be a load to read correctly or wake up 7912?  All other voltages good.
Replaced 7912 vReg, D29 diode (correct orientation) for the third time and checked 10R resistor good.
-12v still reads -19.75 vdc
Have replaced almost all parts except Caps.
Any other suggestions?

 

[Harpo]

No load connected. does there need to be a load to read correctly or wake up 7912?

Maybe you missed this "a temporary 1K - 1K5 resistor between 0V and -12V would draw enough mA that the vReg behaves" ...

Replaced 7912 vReg, D29 diode (correct orientation) for the third time

No idea why you are replacing probably working parts ...

Any other suggestions?

At full moon dance around your unit three times, then throw a dead cat over your left shoulder while shouting out loud 'buggadi buggadi' ...
.
.
.
.
.
.
.
or just croko clip a temporary load resistor across this rail so you know it is working correctly when connected to your circuit as previously said.

 

[Winetree]

It's another month till a full moon, I don't dance, I'm allergic to cats, and i don't speak that language.
A simple answer is yes it needs a load to read correctly. I'll try the resistor to test
before connecting to main P.S.B.
Thanks.

 

[druu]

I think you took Harpo a bit too seriously, lol.

Harpo might seem like a machine but I can assure you he's human too (he's made a joke with me before which caught me off guard - think of it as brain relaxant haha).

 

[EmptyMusicBox1]

HI

I have a new question about the SB4000 :

the out and Vu Level of the Oxford is "offset" than the GSSL Mode ?

 

[jonathanmorbin]

Hi,

Wandered if anyone had any thoughts on this problem.

My Tilt 1 circuit is compressing a lot more than it should be and with the trimmers i cant get it down to 10db of compression. I have another working unit and if i feed them the same signal the differences i get are on the input of U7 (pin 1). On the correct unit i get 2.3vac and on the non working unit i get 13.2vac. All other voltages match pretty well. on the unit that doesnt work, every other part functions correctly, T2 works fine as well. i have changed c53 and c56. the resistors all measure correct and the trimmers also measure correctly in this part of the circuit.

Any ideas?

Jon

 

[sr1200]

Have you tried fully recalibrating the unit?

 

[jonathanmorbin]

Yes i have recalibrated the unit a couple of times and i still have the same problem. on this build i have not populated the bargraph section but i dont think this should be a problem.

 

[Harpo]

...and on the non working unit i get 13.2vac.

Seems the opamp is running open loop. With opamp U6A and/or U7A pulled (you didn't say its the left or right side misbehaving), measure resistance between opamp-pins 1/2. Reading with a not broken trimmer, proper soldering and no broken or lifted pcb traces should be about 12K (sum of 6k8 plus dialed in trimmer value). When reseating the pulled opamp, double check all opamp pins are in their socket (when a pin bends inwards it doesn't connect. From murphys law it will be the pin that causes the biggest misbehaviour).

 

[jonathanmorbin]

Its both left and right sides. they both measure the same.

With the ic's pulled between pin 1 and 2 i can get 6.8k-16.8k as i would expect. on both L and R. im really unsure where to look for this problem. I changed U6 and U7 with ic's i knew were definitely working so that is not the problem.

 

[Harpo]

As you just ruled out, feedback loop should work, so fault must be in front of opamps summing node. Double check parts values of R3,4,7 and R21,20,19 for 150k,15k,1k. Most likley at least one of each group will be (maybe a decade) too low, causing excessive gain.

 

[jonathanmorbin]

Resistors all look where they should be. I have just noticed a possibility though. C31,41,28,36 have this written on them.

U15J63

does this mean they are o.15uF? they are supposed to be 1.5nF so im wandering if this is the problem. unfortunately i dont think i have any 1.5nF lying around so i cant test it yet.

 

[Harpo]

Yepp. 3nF (=1.5nF||1.5nF) needed for HPF -3dB @ ~53kHz with voltage gain of 12. Your paralleled 150nFs set this HPF @ 530Hz instead.

 

[MarioXLR]

Hello all. I'm thinking in get this unit. Anyone knows the cheapest way to get the parts? I mean, buy the kit in Europe? I don't mind to buy in US if there's a way to don't pay customs...