[gyraf]

Kent,

Look at the schematic.

Even though this is a feed-back design, there's no DC feedback path. This means that we are either looking at noise disturbing the sidechain, or one of the DC-blocking capacitors are leaking..

Check for DC at point "C" without signal. If there's DC here with no signal, then either you have some HF oscillation or the 22uF electrolytic in the input of the sidechain rectifier is leaking DC (the one after TL074 pin7).

Check DC at the output of the A/R timing buffer, TL074 pin8. This should follow the signal on point "C" plus some timing - metering actual GR.

The threshold pot only adds some extra gain to the sidechain VCA, so whatever messes up must be a signal present at the input of your sidechain.

Try tracing your signal through the unit - for both AC and DC.

Check your supply voltages - specially the +/-12V should be stable and noisefree..

Jakob E.

[skrasms]

Hey, does anyone know if this meter will work? It says it's for 0-1mA DC and I know it'll fit in a single space rack case. I don't know how to tell if it's linear though. I'm pretty new to all this electronics stuff, and have never put a meter in anything, so please pardon any ignorance. If that meter doesn't work then does anyone know any others that can be found in America (aside from the Behringer) and will work?

[tubejay]

I have a stupid transformer question...  I just bought this transformer:

http://www.digikey.com/scripts/DkSearch/dksus.dll?KeywordSearch

I'm getting ready to finish building the powersupply section of the SSL compressor, and am a little stuck on getting the transformer wired correctly.  I've never actually had to build a power supply.  Every project I've built in the past has either had an external supply or operated off of a battery (guitar pedals).

Here's my understanding of how I'd do it.

One, tie the yellow and red wires together, and then tie the black and violet wires together.  The yellow and red go to hot on the 120v outlet and the violet and black go to negative.  

Then I tie green and brown together.  Then red and blue together.  Those then go to the rectifier?  

It shows ground coming off of the middle of the transformer.  That's the part I don't understand.  Is that just connecting to the metal part in the middle of the transformer where the screw goes?

Sorry for the super basic question, but I've never built a power supply before.  So I've never had to wire a power transformer.

Thanks,

Jay

[gyraf]

Skrasms,

Welcome to GroupDIY!

Yes, that meter will work fine, providing you get it in the mentioned 1mA version.

Tubejay,

That link dosen't work..


Jakob E.

[tubejay]

Tubejay,

That link dosen't work..


Jakob E.

Sorry, that's Digikey part number TE62063-ND.

Thanks!
Jay

[Twin-x]

If i don't wish to use xlr connectors how is the wiring for jack plugs? Erm to add to this i mean 2 pole offcourse so it will be unbalanced.
I don't use mics or anything. Just plain simple for my drum computers.

[gyraf]

On the input, connect XLR pin3 to ground, pin2 to tip.

On the output, leave XLR pin3 unconnected, and pin2 to tip.

Jakob E.

[tubejay]

Tubejay,

That link dosen't work..


Jakob E.

Sorry, that's Digikey part number TE62063-ND.

Thanks!
Jay

[Twin-x]

On the input, connect XLR pin3 to ground, pin2 to tip.

On the output, leave XLR pin3 unconnected, and pin2 to tip.

Jakob E.

Thanks but i don't really understand. According to the pcb layout on your site you have the pins that should go to the XLR plugs. I wish to use Female Jack does this mean i connect

bal input left + to tip jackplug left input
bal input right + to tip jackplug right input
bal input left - to ground jackplug left input
bal input right - to ground jackplug right input
bal input 0 remains unconnected

bal output left + to tip jackplug left output
bal output right + to tip jackplug right output
bal output left - unconnected ?
bal output right - unconnected ?
bal output 0 remains unconnected

Is this what you mean? I appoligize for this very noob question.

[kent]

OOOOOOkay here's what I have so far:

There's DC after pin 7 on the TL074.  There's DC after the DC blocking cap of said pin 7.  There's DC at point "C" after the FWR.  THis all goes up and down with the threshold pot so it's not shorted to a power rail somewhere.
I swapped out the DC blocking cap on pin 7 of the '74.  No change.  Of course the meter goes back to "0" when this is removed.
The +/-12V supply reads OK on my DMM.
I'm thinking this must be the HF oscillation Jakob mentioned.  I have a scope which my father bought for my birthday so I'm still figuring it out.  He got it used and it only goes up to 500kHz.  Is this enough to find the HF problem?  If I stick it on the input to the sidechain I don't see anything.

kent

BTW - it's a B- meter

[Livingroom]

Hi Kent.

I am having the exact same problem with my ssl clone. Measuring the DC at the same points gives the same result as you mentioned. If it's HF osc., then how do I get rid of it? Could it be some of the components around the 074 that causes it?

All voltage rails seem to be fine.. could it be a problem with the sidechain vca?

[gyraf]

A 500KHz scope should be plenty to find HF instabilities.

What voltage and polarity are the DC voltages around the sidechain rectifier input (before and after the 22uF)?

Be sure to mount the 22uF according to the polarity of the DC at that point.

Jakob E.

[Greg]

Tubejay:

My toroid is actually an Avel from Parts Express, but yours will do just fine. Here's what you need to do to wire it.

On the primaries:
Tie yellow and red together and that goes to your common (not GND).
Tie black and violet and that goes to the hot (115VAC/120VAC).

On the secondaries:
Tie red and brown together...
Then measure between green and blue and you should have approximately 30VAC.

When you go to connect to the Main PCB, the red/brown (which are connected together), go to the middle point of the three. Connect green to the outside and blue to the one on the inner part of the board.

Basically we're connecting the primaries is parallel and the secondaries in series.

Let me know if anything is unclear.

[tubejay]

Thank you very much Greg!!!  That makes a lot of sense!

 :guinness:  :sam:  :guinness:  :sam:  :thumb:

[Nele]

Hi,

Just finished building my SSL clone. Works perfectly but there is a small hum problem. If I leave the input unplugged and turn up the make-up gain you can hear some hum. Is this normal? I have to turn up the volume to hear it but it is pretty annoying. It's also present with inputs plugged in. When I disconnect the switches-pcb it's gone but I suppose that makes sense (no controls..).

I've used a toroid transformer, tied chassis and mains ground to one of the input grounds. gave each input/output it's own earth from pcb.

Any suggestions?

thanks,
corneel

[Greg]

Nele:

Regarding the inputs:

Do you have one wire from the board going to one input ground, which is then jumped over to the other, then chassis/GND.

Or do you have two seperate wires (one for each) coming off the PCB to the input connectors GND, then one of those going to chassis/GND?

Also, did you use nylon or plastic seperators/insulators between your standoffs and PCB?

Sounds like your have a ground loop of some sort.

Also, how do you rails look... any excess ripple?

[robomatique]

Nele:

Do you have one wire from the board going to one input ground, which is then jumped over to the other, then chassis/GND.

Or do you have two seperate wires (one for each) coming off the PCB to the input connectors GND, then one of those going to chassis/GND?

Just what I was going to ask, which is the right connection/grounding?

Robert

[Nele]

I have two wires going from both input grounds to the board. Same with the outputs. I also tried using one wire but that made no difference.
Using separators also doesn't solve the problem.
btw: the hum disappears in bypass-mode.

[gyraf]

Be sure that your whole chassis is grounded. The sidechain is quite high-impedance and thus hum sensitive.

When you check for hum and noise, do so with shorted inputs to avoid external hum pickup.

Jakob E.

[Greg]

Nele:

Do you have one wire from the board going to one input ground, which is then jumped over to the other, then chassis/GND.

Or do you have two seperate wires (one for each) coming off the PCB to the input connectors GND, then one of those going to chassis/GND?

Just what I was going to ask, which is the right connection/grounding?

From my understanding it's the first, but it might not matter. If you look at the GSSL I just finished, I only have 5 wires (red ones) coming from the input connector, then the input GNDs are jumped together, which then goes to my chassis. I did this as to attempt to create only one path to GND. You can see this clearly by looking at the pics I originally posted. Follow the link below if interested:

Greg's GSSL

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