signal to noise in the GSSL comps.

[Repairman]

The ratio mod has been discussed in another tread.
i've changed the 100K resistor fedding the makeup amp to 122K and tthat put the ratios allmost spot on.

Remember when measuring S/N to drive the unit to 1% THD and then measure the noise relative to this level. (ca. 22dBu)

 

[Greg]

I would definitely recommend performing the ratio check... I feel that the unit is much more usuable at 2:1, 4:1, and 10:1 for drum and 2 buss compression.

 

[dufo]

[quote author="Repairman"]The ratio mod has been discussed in another tread.
i've changed the 100K resistor fedding the makeup amp to 122K and tthat put the ratios allmost spot on.

Remember when measuring S/N to drive the unit to 1% THD and then measure the noise relative to this level. (ca. 22dBu)[/quote]

Interresting I will try this maybe as well. Anyone else found the same difference once swapped out ?

 

[j.hall]

[quote author="Kev"]
I think Dave may have been looking for a specific noise like a mains induced hum or buzz.

By looking at the spectrum ... or even zoom in on the output with lots of gain you may idenity the noise as something specific.
[/quote]

back on topic......

that makes more sense kev.

it's for sure not full bandwidth "white noise" type sounds.

like i said, i've been sick with the flu and now trying to catch up on a few things, i'll try to get some images of the noise and a few pics of the inside of my unit and post them soon.

i need help on this. and appreciate those of you that are helping me!!!

 

[Kev]

[quote author="j.hall"]..
it's for sure not full bandwidth "white noise" type sounds.

like i said, i've been sick with the flu and now trying to catch up on a few things, i'll try to get some images of the noise and a few pics of the inside of my unit and post them soon.[/quote]

"white noise" but not full band width ... ??

take it slow and one thing at a time.
Jakob may pass by with a few ideas
but
we will find some common ground as this stuff is important and even though it is a relatively simple project, there is still many components
and
anyone of then could be a factor of ten out.
That could screw things up but the project would still work

... if you get my drift

it's all good
:thumb:

 

[j.hall]

i meant it wasn't white noise sounding. but it doesn't sound like ground hum either.

i should have some time this week to mess around with it....maybe i can get a graph of the noise and post it.

 

[gyraf]

Remember to short/terminate the inputs, when measuring noise figures..

Jakob E.

 

[j.hall]

update.

i finally found some time to investigate this further.

i tried a few different ways of testing the noise floor and kept getting the same result.

the noise is a hum, but not 60 cycle ground hum

i had my tech (who is building one for another guy) take a look at mine as i feel this is over my head at this point.

he cut all the ground loops on the PCB and that did nothing, so he jumpred them all back together.

he tried a few other things (changing out all the chips and VCA's) and that did nothing.

he finally put the mother board of his comp in my chasis and the hum went away.

so now we're thinking it has to be a bad solder joint or a solder bridge or something like that.

anything you guys can think of that would cause a fairly low level hum to get into the audio path let me know.

 

[gyraf]

bad psu regulation? broken regulator? were all supply voltages within specs? A half-broken opamp with very poor PSRR?

Jakob E.

 

[j.hall]

the PSU was within spec last time i checked it (about a month ago) i'll check again.

my tech replaced all the chips, and opamps and the problem didn't go away, so i assume that means they were all fine to begin with.

i'll start checking the PCB's under a magnifying glass tonight and see what i can find.

hopefully i find a solder bridge and it will be an easy fix.

 

[gyraf]

..an electrolytic in the supply the wrong way around?

 

[j.hall]

highly unlikely as i checked all those four times before the first power up, and again after i found the noise.

but hey, i'm only human

keep the ideas coming, i'm taking notes and will check all this stuff.

would it help if i could tell you what frequency range the hum is in?

also, if i turn the threshold all the way down the meter bumps up to -2dB of gain reduction.

it doesn't move at all, just bumps up to -2 and stays there.....so i figure the noise if getting in prior to the gain reduction circuit and not just on the output amps.

also, i figured out that pulling the input molex connectors off the PCB did nothing. so it's not in the input path.

and unplugging the daughter board (if i remember correctly) killed the noise as well.

would that mean i should focus on the daughter board?

 

[Svart]

yes please tell what the frequency of the hum is.. sometimes you will get 60hz hum at some other multiple of 60hz, like 120hz and so on..

 

[j.hall]

all right, i made a note to look at the hum on my RTA.

 

[Kev]

can we get a picture of the inside of your box ?

I know you have had a friend look at it but it might be nice to see what we are talking about on the off chance there is something simple in xl and ground and chassis wiring.

 

[j.hall]

i'll get the picture up tonight. my tech has built two of these on his own thus far so he's sort of familiar with the unit at this point.

not saying he's the guru of this design.....but he isn't approaching this from scratch.

i'll get the pic up so you guys can see if anything is a glaring mistake.

i'll probably post the pic uncompressed so you can zoom in with some decent resolution.

 

[j.hall]

RTA has been taken

http://download.prosoundweb.com/~j.hall/StudioPics/SSLrta.pdf

one interesting thing to note.

this RTA is of the left channel output with the gain at full blast.

i switched over to the right channel output and got nothing like this RTA. the right channel as a slight rise at 125 and 250 and that's it.

so i'm fairly isolated to the left channel.

pics to come.

 

[j.hall]

i found some old pics i took for myself.

they are pretty decent

let me know if you want any other shots and how you want them taken

http://download.prosoundweb.com/~j.hall/StudioPics/SSL3.JPG

http://download.prosoundweb.com/~j.hall/StudioPics/SSL4.JPG

http://download.prosoundweb.com/~j.hall/StudioPics/SSL5.JPG

http://download.prosoundweb.com/~j.hall/StudioPics/SSL6.JPG

http://download.prosoundweb.com/~j.hall/StudioPics/SSL7.JPG

 

[j.hall]

all right, all solder points look good to me.

i used 2180's for the VCA's so they are pre-trimmed.

i read somewhere that it was OK to fully load the VCA section minus the trim pot and just drop the chip in.

i'm wondering if that is a mistake and causing me trouble.

but that doesn't really explain why i'm having such trouble with just the left channel.

maybe i'll gut the VCA sections and rebuild them

anythoughts?

 

[Kev]

[quote author="j.hall"] ... let me know if you want any other shots and how you want them taken ... [/quote]

just wanted to see how the xl's where wired to see if there was anything obvious with the grounds and the way they were looped together.

It might be possible to bypass the VCA section to check you have a clean I/O. The 4 opamps just unbalance and then re-balance so fault finding through there should be easy ... ???