SSL comp question to Jakob

[gyraf]

:razz:

 

[clintrubber]

Ehh, what's worse than Beh. ?

3.5mm plugs I'd say...


And worse than that, hmm,

... Beh.-gear using 3.5mm plugs ?!

 

[chrissugar]

"And worse than that, hmm,
... Beh.-gear using 3.5mm plugs ?!"

I don't think such thing exists. Even Behringer can't go that low. :green:

chrissugar

 

[Svart]

i'm intrigued at what problems may arise from cutting the ground loops from the PCB. i've worked on projects that picked up radio stations from ground loops just a inch or more in total diam. When i CRANK the output of my finished SSLs and also CRANK the console channels, i hear what sounds like radio static, which is more organized than background radiation static.... am I just hearing things?

i'm currently populating 2 more GSSL pcbs and the finishing parts will be here next week. I would like to try cutting the ground loops and seeing what happens.

Gyraf: Any idea what to expect based on your prototyping experience?

:guinness:

 

[Svart]

oh and kinda off topic but in the emulation circuit, there is a 100pf cap parallel with the 1k*. is that feedback stabilization? what would happen if I increased to 220pf?

 

[clintrubber]

oh and kinda off topic but in the emulation circuit, there is a 100pf cap parallel with the 1k*. is that feedback stabilization? what would happen if I increased to 220pf?

Please have a look earlier in this thread. This 100pF even needs to be 100nF. Jakob explains the reason why there was still 100pF in the schematic.

Bye,

Peter

 

[Svart]

thanks peter, my bad for not reading that fully. I was more intrigued by the ground looping issues...

however, i am used to seeing multiple grounds on the high speed boards my team has designed. we use power ground plane, and a secondary ground plane for digital that is coupled at one point(usually at the A/D converter) through ferrite. this seems to hush any digital bouncing on the analog ground, and keep noise from the digital ground. should we look at this for future boards, keeping audio ground separate but coupled through ferrite to the power ground?

:guinness:

EDIT: I thought about it for a little bit and I guess this style of grounding isn't really needed since most of the designs here are used with differential supplies and ground isn't one of the rails... I guess it would only be useful for single ended supplies?

still wondering about the ground loops though..

 

[Svart]

any more ideas before i give cutting the loops out a try?

 

[Svart]

ok, to ease everyone's tension.... over the weekend I cut the ground loops on the pcb and did some measurements..

ground loops left alone
faders@unity
GSSL@unity
-70db with slight hint of 60hz

ground loops cut
faders@unity
GSSL@unity
-71db with slight hint of 60hz

I don't see much improvement in noise floor or 60hz hum from cutting the ground loops.

EDIT: I must say though that I've taken time and effort to make sure my rack is as noiseless as possible. Your results might vary. don't mistake noise coming from another source as an issue from any single place like ground loops on PCBs or ground loops in systems, they can come from one box or ALL of them together!

cheers! :guinness:

 

[radiance]

Thanks for cutting!

 

[rafafredd]

Did you cut on my proposed places?

NY Dave said he would give a try on pointing good places to cut...

 

[bblackwood]

[quote author="Svart"]ok, to ease everyone's tension.... over the weekend I cut the ground loops on the pcb and did some measurements..

ground loops left alone
faders@unity
GSSL@unity
-70db with slight hint of 60hz

ground loops cut
faders@unity
GSSL@unity
-71db with slight hint of 60hz[/quote]
Are all SSL clones that noisy?

 

[matthias]

definately not !!

I actually have two of them (more to come soon and they are really quiet... no noise, hum or anything... !!

 

[Svart]

I cut similar places Rafafredd, but not exactly where you suggested. My console is normally -75db to -80db with no inserts. I think -70db is fairly respectable and i've heard from people who used the originals that they aren't really that quiet to begin with, that what I am seeing is average. However, each person's results will vary with all the variables between systems.

Matthias: Are you talking about normal usage? When my faders are @unity you cannot hear the GSSLs at all. I meant to say that the 60hz hum is only audible when you turn the gain on the box and the console up enough to hear it.

 

[rafafredd]

Well, maybe you could try a beefier connection fro board to chassis ground. Generally those big solid copper non shielded cables makes resistance very low and can make some units quieter.

 

[matthias]

@ svart: makeup gain full cw... faders up... no gain no hum

 

[daArry]

Hey...

Just to be -sure- before I bolt these boxes in the rack with regards to the 100nf/100pf capacitor count...is this correct:

http://notapplicable.co.uk/audiolab/ssl/ssl-caps-issue.jpg

Which makes 25 100nF (which is whats noted in the parts list) and 10 100pf (9 mentioned in parts list tho). The 2 circled are again ones which now ought to be 100nf too ye?

Thanks!

 

[gyraf]

No, those are the 5534 compensation caps (pin5-8). The ones in question are the caps paralleled with the feedback resistor at the same opamps.

Jakob E.

 

[Rogy]

Hi all,

Just ordered a set of SSL comp PCB's for my first DIY attempt...

I was comparing the original SSL comp schem and the Clone schem and found some differences.

First of all the "A" connection of the Ratio switch is drawn different in the Clone schem than on the original. I think the Clone PCB is equal to the original schem; can somebody confirm?

Second: One of the Ratio switch resistors has a value of 1.5 M on the original and 1.8 M on the clone. is this a change on purpose?

The both schematics are here with the things to clarify marked in red:

http://users.pandora.be/Rogy/SSL%20clone/ssl_82e26%20Q&A.JPG
http://users.pandora.be/Rogy/SSL%20clone/ssl_sch%20Q&A.JPG

Thanks in advance!


Rogy

 

[gyraf]

Hi Rogy,

Yes, there's some small differences between pcb's and schematics. The PCB's are known working..

I always implement changes on pcb first to check for intended function, but I'm not good at following up with schematic changes..

Jakob E.