GSSL HELP THREAD!!!

[gyraf]

so the short is actually the Pot itself?

Only when the pot is turned to one extreme. Turn it to the middle and re-measure.

Your problem is probably in something loading the -12, not the +12.

Double-check connections and component values..

Jakob E.

 

[BladeSG]

Thanks Jakob, that is correct with the pot turned to one extreme it shorted and in the middle not.

Found something I think is weird, the 1M8 resistor on the Control PCB was only reading 680K. So I replaced it with a new one from the same bag as the original (rechecking before I soldered it) and it's the same. Only reading 680k when I measured it at 1.806M before I soldered it. Is this normal? Doesn't seem right to me as the 1M2 above it reads 1.2M.

Steve.

 

[gyraf]

Bladesg,

You can't measure the 1M8 in-circuit - look at the schematic; it is paralled by other components. The 1M2 is not (unless ratio switch is at 1:10 position)

Generally, if you measure resistors in-circuit and get an unexpected value, you have to lift one leg of it and re-measure in order to avoid this type of paralleling-problem...

Jakob E.

 

[BladeSG]

Thanks again Jakob, that makes sense.

The only other thing I can comment on so far is that for some reason the longer the Main PCB is powered up for (without Control PCB attached) the lower the +15V Rail becomes. The -15V rail is staying constant at -15.1V. The + Rail starts at +14.83 and after about 5 minutes gradually drops to about +14.20, although I did see it go below 14V at one point.


Thanks for your patience Jakob.

Steve.

 

[gyraf]

How are your +/-12V rails doing?

Are you drawing current for a meter lamp? If so, try removing that for now.

Are your 7815/7915 regulators getting too hot to touch? In that case, they may need a bit of heatsink (isolated from each other!!)

Jakob E.

 

[BladeSG]

With Control PCB disconnected

-15.1V @ -15V Rail
+14.2V @ +15V Rail

-15.1V @ Rail outside Left VCA parallel to 2 47K Resistors.
+11.96V @ Rail between 78L12 & 100nF Capacitor
+11.96V @ Rail next to Sidechain VCA and 3K9 Resistor.
0V @ Rail between TL072 & 100R Resistor
0V @ Rail between 7915 and 1000uF Capacitor.

*The 7915 is getting too hot to touch

With Control PCB connected

-4.3V @ -15V Rail
+14.8V @ =15V Rail

-4.2V @ Rail outside Left VCA parallel to 2 47K Resistors
+12V @ Rail between 78L12 & 100nF Capacitor
+12V @ Rail next to Sidechain VCA and 3K9 Resistor
+0.7V @ Rail between TL072 & 100R Resistor
0V @ Rail between 7915 and 1000uF Capacitor

* The 7915 is not getting as hot with the Control PCB connected, hence the +15V Rail is not dropping.

No meter or meter light has been connected yet.

I cannot find a -12V Rail. I probably don't know enough about electronics and probably shouldn't have done this project. Thanks again Jakob and everyone else for your patience. I will certainly consider buying new PCB's and starting over.

Steve.

 

[BladeSG]

I should also mention that I have not soldered a power LED to the Control PCB, as I was going to put a power switch with light.

Steve.

 

[gyraf]

Trace the -12V rail from the -12V regulator, the 79L12. Check where it goes on the control pcb. On the control pcb, it is the bottom trace that goes to the threshold pot. Check that this does not short to anything - including chassis and the 0V line that is right next to it where it connects to the main pcb.

Measure -12V voltage with/without control pcb connected.

Use an ohmmeter to check for continuity between 0 and - on the control pcb (see the pdf layout file for reference)

Jakob E.

 

[BladeSG]

Thanks again Jakob. I measured -12V from the - output pin (that goes to control PCB). The fault is intermittent now as I was getting +12V & -12V and also +14.8 & -15.1 even with the Control PCB attached. I noticed that fiddling with the Bypass Switch and Threshold and MakeUp pots cured the problem momentarily. I also noticed that turning Threshold pot past half way yeilded the longest periods of normal operation ( and yes this thing sounds sweet when it's not distorting).

When the Control PCB is disconnected I'm always getting -12V at the - output pin. With the Control PCB attached it fluctuating between -12V and -4V.

I'll try changing these pots and Bypass switch tomorrow and see if it makes a difference.

Steve.

 

[BladeSG]

Here's something funny for you all.

I was just in the process of re-soldering some joints on the Control PCB and a couple on the Main PCB in the hope there was a bad joint somewhere.

Now the -15V Rail is OK even when the Control PCB is connected. However the +15V Rail now drops to +5.4V when the Control PCB is connected.

And no I did not have the polarity of the DMM probes around the wrong way, even I thought this at first until I double then triple checked it.

I'll have another look tommorow.

:grin:

 

[Mendelt]

Thanks for helping me with my led-display question last week seem's i'll be using an LM3914 with a linear scale. I have another one for you if you don't mind.

I was planning on building two compressors in one 2u case to keep costs down.

Is it possible to drive two compressors from one powersupply? How much current does one compressor draw? I saw you can draw approx. 1A from the 78/912 and 78/915's but i have no idea what one compressor would need.

To make matters worse I would like to drive a couple of led-bars to display input signal and gain reduction and I would like to drive these from the same powersupply too.

thank you,
Mendelt Siebenga

 

[gyraf]

Mendelt,

You could have +/0/-15V supplies on one board, and link these to the second board. But you'd need to do some thinking to get it right - it may be easiest to just use two psu transformers.

For the meter, I think a separate psu would be safest - noise and all.

Jakob E.

 

[Mendelt]

I was hoping I could use one transformer connected to a seperate board that provides +/- 15 and +/- 12 volts to both compressors (the PSU schematics look kinda easy to build separately on a stripboard).
But maybe thats not such a good idea after all. :?
I think i will try using one transformer to power both psu's on the boards. I can then try to make my own psu for the led-stuff.

thanks,
Mendelt Siebenga

[quote author="gyraf"]Mendelt,

You could have +/0/-15V supplies on one board, and link these to the second board. But you'd need to do some thinking to get it right - it may be easiest to just use two psu transformers.

For the meter, I think a separate psu would be safest - noise and all.

Jakob E.[/quote]

 

[gyraf]

If you build an off-board powersupply - which is not a bad idea - you should make it +/-15V only, and keep the +/-12V regulators on the PCB's. This because you need a stable local reference.

Jakob E.

 

[BladeSG]

Just done some more fault finding and it now seems apparent that the +15V rail is dropping intermittently with and without the Control PCB attached. The one thing I have found is that even with the + & - 15V rails being as they should the sidechain VCA's Pin 5 is always @ -8.7V.

I also found that Pin 4 of the TL074 always gets +12V so long as the +15V rail is @ +14.8V. Pin 11 of the TL074 fluctuates with and without the Control PCB attached from -12V and then drops to about -6V. This pin 11 can be at exactly -12V and pin 5 of the SC VCA still at -8.7V.

When Pin 11 of the TL074 is showing -6V the voltage at pin 5 of VCA also drops below -8.7V to around -5V.

I'll have a rest from it for a while and get back to it later tonight.

Steve

 

[BladeSG]

Done some more testing with the control PCB disconnected. Also re-soldered most of the main PCB's points and replaced the TL074, SC VCA and the 22uF 25V Cap outside SC VCA that leads to the 79L12.

Found the 15V Rails OK. Just noticed that the left and right VCA's are only getting about -8V at pin 5 but the full +15V at pin 7. NE5534's in left and right VCA's are getting correct voltage. NE5532's & NE5534's in the I/O section are getting correct voltage too. SC VCA does also get +12V @ Pin 7.

Look at it again tommorow. :sad:

Steve.

 

[BladeSG]

I didn't take into account the resitor that is in line of the -V input to VCA's, so they're likely to be OK.

If there is a short cicuit somewhere on either PCB is it possible for the voltage to drop between the rectifier (W04) and the Regulator's (7915 & 79L12?

Checked the 1000uF Cap and 10R resistor between W04 and 79L12 and they seem to be working fine. replaced 79L12 just in case.

Is it also normal for the negative output of the W04 to fluctuate up to -24V when using ground as reference? The voltage here varies wildly from anywhere between -9 and -24V intermittently and sometimes actually sits at -15V as I think it should.

To me this doesn't seem normal.

Any help would be greatly appreciated.

Thanks,

Steve.

 

[BladeSG]

Thanks guys.

 

[Twin-x]

Are 1000uF/50V ok or do they have to be 35V

Second question i ordered NE5532 but i got NE5534P from the company.
The NE5534 i order were NE5534N

Is the NE5534P the same as the NE5532????

 

[gyraf]

1000uf/50V is alright, if you can fit them on the PCB. Higher voltages are always alright.

And no, NE5534 and NE5532 are different opamps. '34 is a single, '32 is a dual.

Jakob E.