GSSL HELP THREAD!!!

[mitsos]

non shorting. 

 

[Alessio]

I've probably found out how to have more gain!
If I put a variable resistor (and I adjust it for bigger values. es. 200k) after the 100k resistor that is connected to the negative feedback of the TL072 can I have more make-up coming out from the unit?
Is there a risk to damage something?

Thank you!
Alessio

 

[Alessio]

I would like to use WIMA caps for my next SSL.
But how can I know witch cap I have to replace with the WIMA ones?
All the electrolitics?
Witch caps are the ones where the audio goes through???

Please help I really dont know how to find out...
Thanks,

Alessio

 

[mac]

Alessio,

I have built three of these now so my experience is only limited to these, but my understanding of the circuit is that some of the 0.1uf caps in the input and output stages and VCA stages will impact upon the audio path, but some are decoupling caps. I used wimas throughout these stages and cheapo films in the sidechain and psu sections.

Not sure swapping out all the electros for film is a wise idea depending upon what they are doing in each part of the circuit. Search back through the thread for 22uf and 100uf.... there is some chatter about using higher quality electros in certain places.

(easy way i have found to do this is to use the "print" feature and then cut and paste into a word doc - so you can search for individual terms through a long thread like this one)...

good luck,
Mac

 

[Harpo]

I've probably found out how to have more gain!
If I put a variable resistor (and I adjust it for bigger values. es. 200k) after the 100k resistor that is connected to the negative feedback of the TL072 can I have more make-up coming out from the unit?
Is there a risk to damage something?

Yes and yes, and higher frequencies might miss some compression above 2.6kHz with feedback resistor 100K in series with your 200K rheostat when dialed full cw for tripling the audio-VCA control voltage for -(makeup - sidechain).

For your Wima caps, have a look at parts dimensions for maybe a moderate sized single 1uF/63V cap. Ignoring parts cost, you'd need 100 of these in parallel to substitute a single 100uF electrolytic cap for the same hpf response. Elcos in your direct audio path are 4* 22uF at input, 2* 22uF after the line receivers and 4* 100uF at output. Thats 532* 1uF caps in parallel in a then probably larger than 1HE case, and due to total caps surface area making a pretty good antenna to pick up any garbage. Using bipolar caps in these spots or 2 back to back elcos with center tap biased to a supply rail might be more successful if you want it to sound different, maybe/not neccessarily better.

 

[Alessio]

Thank you Mac and Harpo...
so... I'm a little confused now

About the gain:
I've probably exaggerate saying 200k variable resistor, I actually need a little more make-up I dont need to tripling it. So If I add let's say 50k can I have more make-up without any problems?

About the caps:
I thought about WIMA because I know that SSL and Manley use them in their products and I saw some pictures of Gssl in this thread with those... I dont understand why I cant replace the 22uf and the 100uf with WIMA with the same values... I'll check better tomorrow I dont have the GSSL documentation with me right now.

Thank you,
I'll let you guys know!

Alessio

 

[Alessio]

Ok, so I've finally understood the problems with wima caps: capacitance and size!!!
So like Mac suggested I'm gonna replace only the 25 caps 0.1uf with these (the smallest I can find): WIMA polyester 5% 63V size:2.5 mm W x 7.2 mm L x 6.5 mm H. Mouser part: 505-MKS2.1/63/5.
The Polypropylene are too BIG!

Is that correct? Can you confirm?

Thank you very much!
Alessio


- I'm still thinking about the gain modification. Harpo what do you think?

 

[Alessio]

Anyone?
Please  :

 

[Harpo]

Alessio, when you increase the 100K feedback resistor from this summing stage, the 100pF cap across this resistor would have to change as well for comparable result. The dangerous part in this spot when using a trimmer is, this might fail open circuit or the wiper looses contact for the blink of an eye and the opamp will/might throw out a voltage only limited by its connected supply voltage. This + or -12V will be reduced by the voltage divider in the following substitution circuit when using a THAT2180/2181 or DBX2150, but not enough to not exceed the +/-1V VCAs limits of delta Ec+/Ec-, so this VCA will get damaged.
Another drawback is, that you boost the applied DC voltage from the ratio setting with rectified and timed audio signal at double frequency riding on top as well.
Decreasing the 620K between wiper from make-up pot and inverting input within limits might be the easier and less dangerous way.
Just my 2ct.

 

[Alessio]

Thank you Harpo, I dont wanna risk to damage anything so I'll try to decrease the 620K right before the Make-up Pot! I could actually use a 1Mohm trimpot or something like that... I'll let you know!
I want do this because I've added a "Threshold range" control to the unit so I can destroy the sound!  ;D

Last thing about the caps: I'm gonna replace with WIMA or Mallory caps only the 25 caps 100nf. You think its a good idea?


Thank you soooo much!

Alessio

 

[Harpo]

Alessio, if your plan is only a 1M trimmer to substitute the 620K, watch the trimmers initial setting. (I'd probably use a maybe 240K with 470K trimmer in series.)
The make-up pot is a voltage divider, voltage at wiper varying between +12V and 0V. The following inverting summing stage has gain set by -(Rfb/Rin) = -(100K/620K) = -0.161, so at output of this opamp stage the voltage varies between (+12V* -(100K/620K)) and (0V* -(100K/620K)), giving -1.93V .. 0V. Depending on ratio setting and audio level, the other input, coming from sidechain will be summed in this stage as well to a more or lesser degree. Imagine your 1M trimmer dialed into a low resistance position, maybe 10K, could be even lower down to zero. Just replace the 620K with this maybe 10K in the formula above. Your opamp won't throw out -120V, but it will try to do so and is only limited by connected rail voltages. The prementioned 240K might not match your plan, but will limit this to -5V.

I won't get into a debate about your Wima or Mallory caps. For bypassing electrolytic caps in the audio path with foil caps, both are well respected, unfortunately I never heard a difference with or without bypassing. For your 100nF caps connected between IC supply pins and 0V I'd use ceramic caps because of their lower ESR. They cost less and do a better job in this position.
As always YMMV.

 

[mitsos]

OK, so I removed the turbo wires going to the main board, soldered the 47K back in place, and the GSSL came back to life. So, I messed up something in wiring up the turbo. But, I did some small tests now and my threshold pot doesn't do much of anything. I have the 47K in series with the leg that goes to +12V, get a variable voltage at the 220K resistor on the PCB, but 0V on the other side of it.  And of course, no voltage change on pin 1(?) of the TL072.

Also, turning the makeup pot changes the voltage at the pin7 of the TL072 by 1.48V, from 0V (CCW) to -1.48(CW). Makeup pot wiper measures +12V (CW) and 0V (CCW)

Ground reference for the above is the jumper between where the 15V regs and the large lytics would go (neither of these are stuffed on my board, btw, I am using an external PSU).

Any tips where to look?

thanks!

 

[Harpo]

.., get a variable voltage at the 220K resistor on the PCB, but 0V on the other side of it.

Opamps inverting input is virtual ground. Current, not voltage.

And of course, no voltage change on pin 1(?) of the TL072.

Might be a solder bridge between pins 1/2.

Also, turning the makeup pot changes the voltage at the pin7 of the TL072 by 1.48V, from 0V (CCW) to -1.48(CW). Makeup pot wiper measures +12V (CW) and 0V (CCW)

Input resistor between wiper and inverting input 820K instead of 620K?

 

[mitsos]

Harpo, you're a genius.  I didn't realize the inverting input was a virtual ground even though I've been reading that every day for the past few days in these SSL pages... Anyway... good news is it's all good. There was in fact a solder bridge... not between pins 1-2 per se, but between the other side of the 100R and the inverting input. That is, the 56K and 100R were connected on both sides...

Also TL072 pin7... The resistor in question is, in fact 620K.  After clearing away the above solder bridge, pin 7V changes with makeup gain pot from 0V to -1.91V wrt same ground point as my post above.  Is this OK?

It seems to be working fine, I was getting insane pumping yesterday, and that is all cleared up, no pumping so far in any settings.  I think I'll enjoy it for a couple of days before I try the turbo again. Just too lazy to go through this again this week.

Thanks again harpo!

 

[Harpo]

There was in fact a solder bridge... not between pins 1-2 per se, but between the other side of the 100R and the inverting input. That is, the 56K and 100R were connected on both sides...

A TL07x is not that amused to drive such a heavy <100R load. Thank to its inventor, opamp output is short protected by internal current limiting resistor.

Also TL072 pin7... The resistor in question is, in fact 620K.  After clearing away the above solder bridge, pin 7V changes with makeup gain pot from 0V to -1.91V wrt same ground point as my post above.  Is this OK?

Perfectly close to my calculated 0V to -1.93V from 4 posts above.

It seems to be working fine, I was getting insane pumping yesterday, and that is all cleared up, no pumping so far in any settings.  I think I'll enjoy it for a couple of days before I try the turbo again.

 

[mitsos]

Ok, two days passed... Enjoyed it and finally stuck the turbo on again (ade sure not to short that 100R this time) and
BAM! it works! very very cool. Now gonna have to put it through some tests.. and find me some more turbo boards cuz I have some more SSL boards to stuff! 

THANKS again Jacob and gustav, harpo and everyone else who's posted in these 150 pages!

 

[Alessio]

I have 6 EAO switches 01-281.025. they are 120VAC 5A.
Can I use them for the "power on" of the GSSL or I need 15A???

Thank you,
Alessio

 

[mitsos]

Those should be fine. 

 

[Alessio]

Ok, but the standard outlet is not 120vac 15 Amps?

 

[Harpo]

I have 6 EAO switches 01-281.025. they are 120VAC 5A.
Can I use them for the "power on" of the GSSL or I need 15A???

Thank you,
Alessio

From http://de.farnell.com/eao/01-281-025/pushbutton-switch/dp/4527999?Ntt=eao+01-281.025 these are rated 250VAC / 5A.
If this switch is only used for turning on the GSSL mains and not your whole studio, fridge and whatever else, 5A will leave you enough safety margin.
Online data might be buggy. What voltage and current rating is stamped on your switch?
What is the mains voltage in your gallaxy/planet/continent/country?
(updating your profile with your location data might better help others to help you)