GSSL HELP THREAD!!!

[vertiges]

Bluzzi,

By the way, which VCA'S have you chosen ?
(I took the 2181AL)

Yes for me too, the days are so short ! I'd love to work full time on this project... but you know... :wink:

Don't give up !

eD

 

[vertiges]

I'm still trying to figure out about my little hum problem.

I read in this thread that it can be caused by a "too small" power supply.
Before running some further tests I would like to know if the PSU I'm using : the Amveco 62053 (Digikey : TE62053-ND / It's a 15V-0-15V, 0.500A -- 15VA.) is strong enough ?

I intend to use 3 leds (1-2 volts). One connected directely to the control board and the two others connected to the outputs of the power supply (with the adequate resistors) before the rectification stage.

The leds are not connected yet.

Another question : I'm using a 400mA 250 Volts Slo-Blo Fuse. Is that Correct ?

Thank you,

eD

 

[guavatone]

g has 315mA in the schematic so 400 should be fine. I think fast may be better though.


BTW I just finished my first GSSL and had a short of -15V to GND. these pads are very close together on some spots and I had just a sliver of solder touching which was the problem.

 

[vertiges]

Guavatone,

Congratulations for your first clone !! :thumb:
Will you post some pics ?

Maybe I should try a 315mA... I imagine as far as it doesn't blow when I switch the unit on it's OK. (But I will connect the leds before)

It's a stupid question but, where or how can we measure to total amount of current drawn by the circuit ? (I read in this this thread that there is a peak when powering the circuit on especially with the toroïdal PSU)

eD)))

 

[Bluzzi]

[quote author="vertiges"]Bluzzi,
By the way, which VCA'S have you chosen ?
(I took the 2181AL)[/quote]

I'm using the 2180LB.

jim

 

[vertiges]

I've finished my first GSSL... (of 2 or maybe more... :wink: )

I'll try to make time to post some pics...

Everything works perfectly but I've still got a little hum... I just can't get rid of ! I've been able to take it 20 dB down by adding a additional wire from the main PCB (connected to a ground point close to the bridge rectifier) to the star ground, but it's still there. It's quite low, but if I turn the gain up, it's getting higher...

The hum is there :

1) even with the bypass
2) even with the control board disconnected
3) when I add the 2 leds, it even gets a very few dB more... (Normal Is suppose)
4) I made all these tests with the inputs shorted. The box closed or opened does'nt change anything.
5) I made the "classic" ground wiring described many times in this thread.
6) All my voltages are normals.
7) I checked and rechecked and rechecked again for broken traces, cold solders, wrong component values... Everything seems normal.
8) I tried to chase the source of the hum with a prob (cap + resistor as described by Jakob) and a computer speaker. I got a kind of noise when testing the power rails, but it's not a hum, it's more like a very soft, silky white noise... I got very big static hum on the pin 1 of the VCA's (all of them). I don't know what that means... but nothing else...
9) the only moment the hum disappears (excepting when I switch the unit off :green: ) is when I take off the THAT from the VCA's and when I put two wires from pin 1 to 8 to bypass them. Can I conclude that my hum comes from the sidechain part of the circuit ?
10) I tried to replace the 7815 and the 7915 regulators. Nothing changes...
11) Ha yes, I forget, I tried to move the power supply transformer... nothing. I can even put the PCB just above, the hum doesn't get any louder.
12) My hum belongs to the 60 Hz family, it's not a static noise.

Is someone have a suggestion...

Some other considerations :

a) It took me so many hours to build this first one !!! I was a bit naive before starting... :wink: But something is sure : the second one will be ten time sfaster !
b) The "metal work part" is a pain in the *&?/"@+!!@ !!! :evil:
c) This forum and all the people inside are great !!! :thumb:

And a few more questions :

1) I use 3 2181AL VCAs. I changed the 3k9 to 5k1 in the Left-Right VCAs but I left the 3k9 in the sidechain section as this last one is powered by 12 volts instead of 15. Is it correct ? Some did the change some did not...
2) I bought the chassis from Par-Metal. I noticed that it's composed by metal panels painted with non concutive paint. So I did sand (meaning I remove the paint) the surface under the heads of the screws for being sure
every part was connected together and to the ground. Was it a good thing to do ?
3) A very weird question : I've got a 80 pounds Golden Retriever and he's very nice, but he looses a lot of his hairs... :grin: There are some of them stuck in the rosin from the soldering on the PCB ! Could it be the source of the hum ?

Thank you,

eD

 

[Bluzzi]

Conductive dog hair eh? I doubt it.

But to clean just try a hard toothbrush on the solder side of pcb. Sorry I can't help more until at least finish one successfully.

I'm almost there myself on #1 of 2.

I have everything wired now but the AC.

Don't get discouraged if its only a hum. It will get solved.

jim

 

[guavatone]

[quote author="vertiges"]
It's a stupid question but, where or how can we measure to total amount of current drawn by the circuit ? (I read in this this thread that there is a peak when powering the circuit on especially with the toroïdal PSU)

eD)))[/quote]

I stand corrected, slowblo is the way togo

I wouldn't worry about an exact 315mA -400mA is fine... but I am using a 700mA since I had one

 

[vertiges]

Guavatone,

Yes, Slo-blo is the way to go :thumb:

 

[vertiges]

Jim,

I'm not discouraged at all... :wink:
I know I will kill that hum !

A toothbrush... it's a good idead... :thumb:

Have finished your 1st one ?

eD)))

 

[guavatone]

vertiges, can u take a pic of your wiring to see if the hum is from audio interacting with AC supply wiring?

If it's a toroid try rotating it to see if hum level changes.

 

[vertiges]

guavatone,

Thanks for answering...

I use a toroid, and I tried to move it. Nothing changed. As I say I can even put the main PCB 1/4 inch above the toroid, the hum doesn't increase...

Basicly my wiring is exactely the same as "matta" described is this thread : http://www.groupdiy.com/index.php?topic=18855&postdays=0&postorder=asc&highlight=difference&start=0

(third picture from the top)

In addition of the wiring of Matta, I left the PIN 1 of the Left input XLR wired to the 0 of the INPUT of the PCB. (and the Pin 1 of the Left input XLR is linked the PIN 1 of the Righ input XLR and after goes to the start point).
So this way I know, My main PCB is linked by two points to the ground start and make a big ground loop... But that's the way I can reduced the hum the most.
Actually I get the hum down at lest 30 dB down just with the wire which links the center of the three pin input of the toroid supply (the zero reference) with the star ground (I hope you follow me). The other link described above just gives me a few dB down more.
I tried so many different things !!! Each time I link the ground from the main PCB which is around the sidechain section I get those 30 dB of reduction. So I guess my problem is somewere in the Sidechain. I tried to reheat all the solder points. I tried with another VCA, TL72, TL74. Nothing changed...

eD)))

 

[guavatone]

Ed, I am having my own problems with this build. So far hum and low signal. This is going to be "fun" to scope out!

I have seen all thes hum post and haven't found common solutions other than references to ripple. And there seem to be wuite a few people using separate PSU's. I have 1000uF PS caps, maybe try to fit 2200?

My Regs are a little off from 15V, 14.6V IIRC.

 

[vertiges]

Guavatone,

Inspired by this thread : http://www.groupdiy.com/index.php?topic=18855&postdays=0&postorder=asc&highlight=difference&start=0&sid=05445f848f3b486404d87279b4c82538


I've ordered a few MNAT's PCBs for building external PSU.
I hope that will solve that little hum problem.


And about your problems try to follow the instructions of chrissugar in this thread : http://www.groupdiy.com/index.php?topic=6338&postdays=0&postorder=asc&start=0&sid=3eefe7bb08d04cf4e191c7794ff76076
It's a great procedure for troubleshooting !

eD)))

 

[vertiges]

I was thinking about using them for the 25x100nF one's :

WIMA MKS2 0.1/63/5 (.1UF 63V 5% 5MM)
http://www.wima.com/EN/mks2.htm

Are those correct ? :roll:

Thanks,

eD

 

[gyraf]

They look right..

 

[vertiges]

Thank you Jakob !

eD)))

 

[ChrioN]

I got a problem with my GSSL. Shouldn't I get 6 dB gain reduction when I get half the inputvoltage on the output? The GR meter shows 16dB gainreduction when my multimeter reads half the input voltage at the output xlr... this with the make up gain CCW (no make up)
Meter is a Sifam 1mA with the correct resistor. As a matter of fact it is a Sifam VU meter...is that the problem?
Other than that the unit works good, no noise or wierd behavour.

 

[Bluzzi]

I feel really stupid for asking this but its AC and I don't want to go further until I straighten this out first.

I'm using Amveco Xfr model 62083. Its my first toroid connection.

For 115vac operation the primaries must have the Yellow and Red together and the Black and Violet together. That I have done and I get no problem.

Its the secondaries I'm getting confused. If I connect in series (Red and Brown are connected together, lets call it center tap ) I get around 17.5vac from the other 2 leads relative to the center tap.

So now what happens to Ground? I thought AC Ground goes to center pin of GSSL's AC 3 pin connector?

If I measure my secondaries relative to ground I get 80vac, more on the other secondary!

So am I supposed to connect the center tap to the center pin of GSSL?

I've finally got one of the GSSLs wired up. All I need is to connect AC now to start testing. Also, should I remove all the ICs and VCAs before applying AC?

Thanks

jim

 

[vertiges]

Jim,

I used the Amvenco 62053. I suppose it should be the same color code. On the secondary, I did connect the brown and green wires as OV (center pin of the three pins connector on the PCB) and the blue and red wires as V+ V-

eD)))