GSSL HELP THREAD!!!

[dukasound]

Hi
I assembled my GSSL and look at this on my bench :grin:

First, I measured voltages and I have:
+14,94VDC
-15,25VDC :?: :?
+11,98VDC
-11,98VDC.
I used 2x18V transformer and I saw 22,6VDC after rectifier.
Because I still didnt receive 2180 I put 2181 with modyfing: 1M to 680K, remove 10K and linked with wire. Also 68ohm is omited. Because I havent any instrument to measure distortion I set trim 50K to measure min voltage on middle who is connected to 680K.
Than I put some music and set ratio 2:1 and if I set high gain reduction the sound wasnt bad. Gain is different in a relation of attack and release
Also I test with sine wave and watch on my mixer VU. If I had full scale reduction I saw on my mixer ?20db. I tested with Make-up on CCW position. If I put Make-up full CW I saw 0db.
This big meter is 1mA. Next I will try to test ratio and maybe S/N.
I havent any hum.
Does anyone knows input and output specification (sensitivity, impedance, etc)?
Thanks to Vili Lampas who send me boards.
Duka

 

[Flundran]

I followed the THRESHOLD signal with my multimeter, and it seems the signal is shorted out right after the 220K resistance.

I looked at the SSL schematic and compared with spec. sheet of the tl072. It seemed to me the tl072 should be mounted the other way around. So I did that and powered up. Nothing happend, no voltage anywhere on the PCB.

I've measured my toroid trafo in every way I can think of. It seems that it's broken. Is toroids fragile in general??? I would think the toroid would be the last thing to break...

/Flundran

 

[gyraf]

Flundran,

The '072 should be mounted like shown in the layout .PDF and on the component overlay. Mount it wrong, and it dies.

The 220K's goes to the inverting input of TL072. This is a "virtual ground" point, that will always be at 0V because of the feedback resistor. If you have to measure, measure at the opamp output. Nothe that pin numbers for the two opamps in the 072 are swapped on the schematic.

Jakob E.

 

[Flundran]

Nothe that pin numbers for the two opamps in the 072 are swapped on the schematic.

This is what's been confusing me...

If you have to measure, measure at the opamp output.

I have to measure on this compressor to find out what's wrong and why it won't work.


/F

 

[super5-56]

Hi everybody and thanks for a great place!

I´m about to finish my first DIY project, and except for a bug with the threshold control and a minor ground hum, I´m quite happy with myself''

The problem is that the threshold control doesn´t affect the signal at all. The unit is compressing very nice, but the compression is starting when I feed 0.1v into it and when I reach nominal level at .775v I can barely recognize the input signal anymore. I have read about every post around here, and have tried to swap VCA´s, 072 and 074 without any sucsess. The values at the Threshold pot are like they´re supposed to be, and all the power rails show decent values(+15.2, -15.2, +11.97, -12.21).
I have also measured a lot of resistors and looked all over the PCB´s with magnifying-glass for shorts or cold joints but I haven´t had sucsess so far.
So... any bright ideas at where to look?


thanks
/kjt

 

[gyraf]

KJT,

Look at the schematic. The threshold pot is a voltage divider that adds a DC voltage to the control voltage going to the sidechain VCA.

The 50K threshold pot is connected between +12V and -12V. So you should have a voltage at point "F" that can be varied from +12 to -12 by turning the threshold pot. Next is the 220K resistor that mixes (adds) this voltage with the CV that comes from the timing circuit, and controls the sidechain VCA.

Try tracking these voltages. Note that pin numbering for the TL072 is swapped on the schematic relative to the PCB.

Jakob E.

 

[super5-56]

Hi an thanks.

I´ve checked the +/-12v at point "F" and also at the 220k resistor and can´t find anything suspecios. But at the other side at the 220k I have next to nothing regardless position of the threshold control. Is this right?
I have of course lifted one of its legs, and I measure it to be 218k.
I have also checked the PCB´S for shorts with my meter, but are not doing any progress.
I happend to put my finger at the left corner backside(Resistors 1M2+1M8 and the other beneath+ the threshold pot wiring points) of the control PCB, and I suddenly got some action on the threshold pot.
Think I have put in the right values on components and really don´t know where to look now:-(


/kjtl

 

[gyraf]

[quote author="super5-56"] But at the other side at the 220k I have next to nothing regardless position of the threshold control. Is this right?[/quote]

Yes, it's right. You're measuring at the input of a virtual-ground summer. The feedback resistor will make sure that the inverting input is at the same voltage as the non-inverting input - which is grounded.

Measure at the output of the 072 opamp to get useable results.

Jakob E.

 

[super5-56]

[quote author="gyraf"]
Try tracking these voltages. Note that pin numbering for the TL072 is swapped on the schematic relative to the PCB.[/quote]

:green:

Tracking was the thing. I had populated with a 470K instead of 470R and will probably need glasses before I start another project ''

Thanks for all your help, now I just have to trace the minor 50hz hum.

/Kjtl

 

[[silent:arts]]

Hi all, finished populating my GSSL Board (thanks Jakob fort the project, Gustav fort his quality PCBs) and measured and tested the boards the last three days. Passes audio, sounds great, measuring is good for just a PCB with no housing.

But I have problem / question according the Threshold settings: setting Threshold to 0dB (disconnecting the wiper of the Pod), feeding 0 dBu to one channel (avoiding the addition of coherent sinus signals) I have 14 dB gain reduction. I could fix this modifying the Threshold Pot, but I don?t think this is normal, and I want to understand where my fault is. I checked components, shorts etc for three days now, and I can?t find anything.

It would be interesting what you people measure at some points on your units, because I have some strange values I don?t understand: TL074, Pin 14 (feeding 1kHz @ 0 dBu, Threshold at 0dB) I measure -7,55V in Bypass, -0,93V when switched in. TL074 Pin 10 = -1,69V (unit switched in).

Any experience with your unit or hints would be interesting. I read all 41! Pages of this thread with no result according my problem ? and while I think I have a problem the unit sounds still great!
:grin:

 

[gyraf]

Hi [Silent],

The threshold function in the SSL is threefold:

First, there is the voltage added to the rectified control-voltage by one-half of the ratio switch. This is because the designers wanted to acheive more-or-less the same GR when switching ratios - providing that your mixbus was loaded to around 0dB. We keep this artefact in the clone - just as we keep just about everything else in this well-proven design..

Second, there's the voltage drop of the 1N4148 between TL074 pin14 and Point"C". This is the actual threshold that has to be overcome in order to start compressing.

Third, there's the gain of the sidechain VCA, that is set by adding a voltage from the threshold pot with the actual "feedback" voltage coming from the rectifier.

In all, I think your voltages are in the right range - allthough I don't currently have a prototype to measure exact voltages on..

TL074 pin14 in bypass has no "feedback" path, as the connection between the rectifier and the timing is interrupted by the bypass switch - so wierd sidechain voltages when bypassed is natural, and not necessarily out of order.

Anyone else with an open clone?

Jakob E.

 

[[silent:arts]]

Hi Jakob - this was fast ...

ok, the voltage drop (same conditions, 1kHz @ 0dBu, one channel): I have -0,93V at pin14, -1,69V @ point "C". (is this a drop ???)

I think I have too much gain in the sidechain VCA.

 

[gyraf]

Too much gain in the sidechain VCA will show very easily as a ratio that goes beyond 10:1 - often even beyond inf:1, meaning that raised input level will diminish output level. So it's an easy test to do to confirm that everything is alright...

Jakob E.

 

[[silent:arts]]

At 10:1 I have a ratio beyond inf:1 (+2dB input dimish 0,2dB output). because of the "SSL ratio measuring" thread I thought I will fix this later that way, but may be it's part of my threshold problem.

 

[[silent:arts]]

OK, I fixed the Ratios with Steffens solution. Now I have exactly 1:1.95, 1:4.1 and 1:10.

I think my Threshold is still too low, with wiper disconnected the 1:10 comprression starts at -14dBu input @ one channel.

BUT the compression curves have their crosspoint at ca 0dBu Input. Is this ment to be the Threshold ???

Anyway, I just ordered two other PCB sets to compare. If this is normal I will have to mod the Threshold to start from 0 to + 20dB.

 

[gyraf]

I think it's normal behaviour - but if you like, the threshold is easily altered by either changing the series resistor and/or adding a resistor at one of the pot's ends..

Jakob E.

 

[[silent:arts]]

Thanks Jakob.

I think my understanding of Threshold is maybe different from the one SLL uses. But just like "MakeUp" or "Gain", it's just labeling. And for a bus compressor it may even makes sense the way it is.

 

[cannikin]

Hey Guys; Well my GSSL is up and running...

THe right channel is working perfectly.. actually sounds amazing!

THe problem I'm getting no Signal through the right channel. I have checked my solder looking for bad joints solder bridges and incorrect wiring but can't find anything...

Where - what should I look for next....

Help!

 

[gyraf]

Same procedure as described several times before..

Jakob E.

 

[chrissugar]

Hey cannikin

I wrote a step by step description about how to isolate the problem in two threads, one for Hulk and one for J Hall.
Find those threads and try to do those tests.

chrissugar