GSSL HELP THREAD!!!

[Nele]

grounding all of the chassis might be a problem. I bought mine at thomann.de and it is painted with none-conductive paint. so there isn't a connection between the different parts that make up the case. I have the bottom and back plate grounded but this didn't make any difference.

could the problem be my capacitors? I used nichicon HD series for the 22uF ones. when I touch them in the input circuit you can hear an extra, louder and heavier hum.

 

[Nele]

Hi,

I did some more testing. The hum is 50Hz so there is probably some grounding problem. As the hum is also present in bypass mode (less audible but cranking up the make-up gain explains the higher level in active mode) I suspect the input stage. Could it be that the input caps, 22uF, are responsible? It isn't the input plugs (jacks in my case) because on disconnecting the noise is still there.

Caps used are nichicon HD:
http://www.nichicon-us.com/english/seihin/pdfs/e-hd.pdf

 

[gyraf]

Nele,

No, it's not the input caps.

Do you have hum even with inputs shorted to ground/0V?

If so, I would check the powersupply. Check that voltages are correct, and that the +/-15V are clean, without hum.

Jakob E.

 

[Nele]

with inputs shorted to ground hum is still there.

plus 15 V reads 14,97 V
minus 15 V reads -15,45 V

minus regulator used: KA7915

How do I check for hum in the powerlines without a scope?

thx, corneel

 

[gyraf]

To me, it looks like your 7915 is problematic. They're rarely off by more than 0.2V when thry're allright.

---

You could maybe check for hum on the power lines with a 1uF polyester capacitor in series with a cable going to an amplifier, and a 10K resistor shorting from after the capacitor to ground. The capacitor lets AC through, but blocks the DC voltage.

Connect amplifier input ground to your device-under-test's 0V, and use the free end of the capacitor as a probe.

Remember to keep amplifier volume down, as there will be a VERY loud click when you attatch/detatch the "probe".

And don't use an expensive amplifier/speaker for this - there still is a real possibility that it can be damaged.

Maybe a cheap computer-type powered speaker would be a good tool for this?

A setup like that could also be used to trace signals through a circuit - making it much easier to trace errors.

Jakob E.

 

[Nele]

I replaced the 7915 and now it reads -15,24V. Still humming. Both regulators are pretty warm.
Might it be the transformer? I used a clairtronic 15VA 2 x 15V toroid.

 

[gyraf]

Check DC voltages at the outputs of the opamps associated with audio - the 5534's and the 5532's at the in/out section. DC should be less than ~50mV on all output pins.

How is your +/-12V acting?

How much hum do you have?

have you mounted the power transformer in some distance from the pcb? Does the hum change when you move the transformer around?

Do you draw supply current for a meter light? If so, how much?

Jakob E.

 

[Greg]

[quote author="gyraf"]To me, it looks like your 7915 is problematic. They're rarely off by more than 0.2V when thry're allright.[/quote]
Gyraf:

I asked this question a while back when I originally powered up my clone. My positive rail is giving me 14.87VDC. Would you suspect a prolem? I haven't noticed any hum or excess ripple. Does that seem low and do you recommend anything?

Thanks.

 

[gyraf]

Greg,

No, +/-0.2V is no cause for concern.

Jakob E.

 

[kent]

Alrighty, after having a long weekend away I've gotten back to my SSL problem so Jake, oh great guru of all things SSL (no offence, Keef), let me run these numbers by you.

these are with the threshold from CW to CCW respectively and no input signal:

pin 3 on SC VCA
.25V -.05V
pin 7 of the TL074
-4.8V -10.6V
after the 22uf blocking cap
-.04V -1.04V
pin 1 of TL074
.5V 1.8V
junction of diode & 20k on TL074
.1V 1.2V
junction of diode & 1M on TL074
-4.4V 1V
pin 14 of TL074
-.4V 5V
"C" connection to PCB
-.2V -4.7V
pin 8 on TL074
-.1V -4.5V
pin 1 on TL072 (it's pin 1 on the schem but really pin 7 on layout - a minor annoyance)
-1.7V -2.7V
pin 7 on TL072 (once again pin 1 on layout)
3.4V -.8V

Threshold control sends a nice +/- 12V. Nothing on the 2150 input (pin 1). Also, it takes a big spikey jump right before I hit full CW but I'm guessing a flakey pot which I can change later.

Any insight? I'm not sure what to look for if it's oscillation. If it's supposed to look like a wave riding on some DC on my scope I don't see anything but I'm most certainly a newbie with that thing.

cheers,
kent

 

[gyraf]

Kent,

If you have down to -10V on TL074 pin7, output of the sidechain vca I/V converter circuit, there surely is a problem here.

And it's a DC problem, not a oscillation problem.

First of all, replace the 22uF right after TL074 pin7, as the one there has been reverse-biased and is probably faulty. When mounting a new one, reverse it's polarity, so the plus side points away from TL074 pin7.

We'll need to look for the source of this DC voltage before the or at the sidechain VCA.

Try swapping the sidechain VCA with one of the audio VCA's to rule out a broken VCA. Bear in mind that they are mounted opposite ways around.

What DC voltages do you have before and after the two 47K resistors adding the sidechain VCA input together?

What DC voltages do you have on the two input NE5534's outputs, pins 6?

Jakob E.

 

[Nele]

Hi Jakob,

Here are my voltages:

NE5534 input (pin 6): -1,0mV and -1,6mV
NE5532 output (pin 7): 1.0mV and 1.3mV

12V seems ok: 12,08V and -11,90V. they do get pretty hot!

moving trafo doesn't help

no meterlight...

the hum is pretty low. only audible when cranking the mixer up all the way but it is noticeable.

 

[Svart]

quick question on hooking up makeup pot and bypass switches.. the area on my boards are a little unclear how they should be hooked up. anybody got a picture?

 

[Greg]

[quote author="Svart"]quick question on hooking up makeup pot and bypass switches.. the area on my boards are a little unclear how they should be hooked up. anybody got a picture?[/quote]

Did you look at the PDF from Gyrafs site that shows the PCB layout and component overlay? There are diagrams there that show how the pots and bypass switch are connected.

 

[Svart]

thanks, i didn't see those before. however i am looking to wire it up without makeup defeat or use a simple toggle switch. is there another way to do this that what is shown?

 

[kent]

Success :green: !!

After checking voltages on my input amps and seeing that they were happy I swapped the VCA in the sidechain. Voila, happy meter. I did a quickie sound check here at work and it all seems OK. I'll do some better tests with my stuff at home but so far it looks good.

Thanks, Jakob.

cheers,
kent

... now on to that 1W amp!

 

[Greg]

[quote author="Svart"]thanks, i didn't see those before. however i am looking to wire it up without makeup defeat or use a simple toggle switch. is there another way to do this that what is shown?[/quote]

If you don't want makeup defeat, then just use a jumper on the Control PCB. If you do this, you will always have makeup gain. If you want to use a seperate switch for makeup defeat, then just take the two points for makeup defeat out to a switch. That's exactly what is being done as shown by Gyraf... it's just that the bypass and makeup defeat switch at the same time.

 

[Svart]

thanks, now that you mention it i see it.

cheers!

 

[Greg]

Hi, I posted this in another thread but this is probably where it should've been posted:

I don't think I'm getting unity gain through my unit. I'm using the 27k resistors... it appears that I'm losing about 5 dB. I traced the signal after the debalancing stage to the 27k and nothing is lost there. It's odd becuase last night I was having the same trouble, then all of a sudden I was at unity gain. It seemed to go to unity gain after I did a big frequency sweep (but that could've been coincidence). So I powered it up this morning and I was back to the 5 dB loss. Any suggestions?

FYI - I used the unit and it sounds great. No distortion or crackling or noise/hum or anything like that.

Also, I'm using a multimeter so I'm only looking at RMS values because I don't have access to a scope at the moment. Is that ok?

 

[gyraf]

Greg,

Are you sure you have the balanced in/out's set correct when measuring with unbalanced test equipment? (-input to ground, output measured between + and -)

alternatively, try using your unit with a normal balanced input/output under "realistic" conditions and see how levels are..

Jakob E.