The official G9 help thread

[sonolink]

Any chance someone can help me with this, please?
If I'd like to change the original 12V/50mA pilot light for a 4,4V/50mA would I be ok by putting an 88 Ohms resistor on the positive side of the light?
Thanks

 

[Harpo]

Any chance someone can help me with this, please?
If I'd like to change the original 12V/50mA pilot light for a 4,4V/50mA would I be ok by putting an 88 Ohms resistor on the positive side of the light?
Thanks

(12V - 4.4V) / 0.05A = 152 ohm will be the resistors min.value.
(12V - 4.4V) * 0.05A = 0.38W, so this resistor should be rated for at least 0.5W.
This 152R (next avail.standard value 160R or 180R) in series with your light for an at least 7.6V drop could be connected to either side of your bulb. This value might apear still too bright, so you might increase it to taste.

 

[sonolink]

@Harpo
Thank you very much indeed. Of course I should have calculated the resistance needed for a Voltage drop of 7,6V!! I don't know how I came up with 88R...still too much of a beginner in circuit analysis...I think a 220R will probably work ok.
I very much appreciate your time and help and definately owe you a beer 
Cheers
Sono

 

[PeteSanders]

I just noticed (  :-[ )  that the 10-pin header on the control panel isn't ordered the same as the main board and I had been wiring them straight across.


I changed one channel's cables so the labels are matched with the identical ones, and now have different-sounding wrong things happening. 

More is going right on the straight-across channel - brain fatigue setting in; going to bed... nuh.....

 

[gyraf]

I just noticedthat the 10-pin header on the control panel isn't ordered the same as the main board and I had been wiring them straight across.

..but they are..

 

[sonolink]

I just noticedthat the 10-pin header on the control panel isn't ordered the same as the main board and I had been wiring them straight across.

..but they are..

They're not on my boards either, Jakob. I have Audiokitchen Rev#1 2002 boards bought a few weeks ago.
10-pin header on my main boards are as follows Left to Right:
NC, P48, Line, From 12V, From 48V, Out-, Out+, Trafo +, Trafo -, To Outamp
10-pin header on my control boards are as follows Left to Right:
NC, P48, Line, From 12V, From 48V, Trafo +, Trafo -, Out-, Out+, To Outamp
Unless this is meant to be like that, Trafo and Out connections seem to be interchanged

 

[PeteSanders]

OK,
thanks; back to the straight-across-wiring then.

Channel 1 is mostly working good now; A couple things to fix. No noise probs.

Ch 2 needs work.

Is that unconnected trace from P1 to the bottom of the Phase switch supposed to be left unconnected?

Looks like it's not needed.

 

[mattyblue]

Has any ever tried the 12av7's in their G9?

 

[sonolink]

I just noticedthat the 10-pin header on the control panel isn't ordered the same as the main board and I had been wiring them straight across.

..but they are..

They're not on my boards either, Jakob. I have Audiokitchen Rev#1 2002 boards bought a few weeks ago.
10-pin header on my main boards are as follows Left to Right:
NC, P48, Line, From 12V, From 48V, Out-, Out+, Trafo +, Trafo -, To Outamp
10-pin header on my control boards are as follows Left to Right:
NC, P48, Line, From 12V, From 48V, Trafo +, Trafo -, Out-, Out+, To Outamp
Unless this is meant to be like that, Trafo and Out connections seem to be interchanged

So are they meant to be connected straight forward or i.e: Out- to Out-, Trafo+ to Trafo+, etc?

 

[gyraf]

10-pin header on my control boards are as follows Left to Right:
NC, P48, Line, From 12V, From 48V, Trafo +, Trafo -, Out-, Out+, To Outamp
Unless this is meant to be like that, Trafo and Out connections seem to be interchanged

You're right - this is a pcb overlay error that I didn't spot before.

The connectors are meant to go straight over between main pcb and control pcb, 1:1

The marking error only affects absolute polarity of output signal (like flipping the phase switch) - so this is not the problem you're having.

Jakob E.

 

[PeteSanders]

Help!

I don't know what I did, but now my power is escalating; I replaced the IC's, checked diodes and resistors for the power sections - they seem OK.  HT now starts at about 300 and climbs fast; unregulated is higher, p48 gets up to 60v, 12v gets 15v.  I haven't let it stay on very long.  Power was working OK before this, generally was working and sounding good.

When this happened, I was pursuing a little voltage present at input xlr on ch 2; I found that, when the inst jack is selected, the ch 2 relay measures with a short across where the D107 diode is (when the power is off).  But the ch 1 relay gives the coil impedance .288 for all three selections.  I have the omron G5V-2-DC12 ones.  Which channel's relay is the way it's supposed to be?   

I don't know if these happenings go together or not;  the voltage still rises if I don't select the DI jacks.

 

[gyraf]

As mentioned several times before in this thread, measure voltages under load, i.e. mount the tubes and let them heat up (~30sec.) before trusting your reading.

Jakob E.

 

[PeteSanders]

Tubes were in;
This morning the HT voltage wasn't a problem - I think it was my meter & battery - a lot of readings had been moving around.  Maybe tube seating.  I hesitate to blame crystal meth or tequila. 

I'm getting a grip on the other issues; am not whimpering anymore.



Pete

 

[gyraf]

..make sure to heatsink the 7812 very good, or it will overheat and then power down - leaving the HT to rise because of lost heating and thus lost load.

Jakob E.

 

[ianmgull]

Quick question. How important is it to heatsink the TIP121 (48v phantom transistor)? I don't have very much space and I thought that this one doesn't generate much heat. Do you guys think I can get by without a heatsink on this? Thanks!!!

 

[tmuikku]

Hi all!

I bought almost finished G9 from Gustav some time ago. I wired it up and everything seemed to work (voltages seem right, passing audio, all controls work as espected). The unit did not give that much gain with either channel and cranking first stage gave nasty sounding distortion. Since then I really haven't had any time to start troubleshooting until today.

I hooked up a sine generator (unbalanced connections between G9 and my soundcard). If I hook scope to xlr input pin 2 and DI socket there is a lot of attenuation and phase shift, the lower the frequency the worse. Same when measuring from output.

Now, is this something to do with my poor scoping skills, interfacing, bad tubes (tried to swap them, both channels behave similarly) or some fault in the build? I just checked most of the resistors and verified that transformers are correct type (OEPs in cans). All connections to control boards seem to be right and no solder bridges spotted. I also read this thread through and there were about 3-5 people with similar issues PeteSanders and mamiti naming a few but no one got any answers...

Unfortunately I don't have a camera right now to take pictures. I don't have screened cables yet for XLR in/out connections. Grounding is done with all XLR pin 1 to starground and DI socket is wired with screened cable as per oscillation fix mod thingy. What should I test and try next? All help appreciated!

Edit
I've attached an image: pink noise from sound card to G9 input (input to DI looks about the same) and G9 output back to sound card. The roll off slope does not change when fiddling with G9 gain settings... Why there is such a roll off, what can cause it? Also with 100Hz sine this thing seems to distort pretty badly and much much earlier than with say 1000Hz tone.

 

[Grooveteer]

I finally finished my first G9. (it's been on the shelf for 2 years)

Funny thing: gain steps 1-4 are OK.  After that (5 and up) the signal gets weaker. This happens on both channels. I've checked the resistor values around the gain switch and they are correct.  HT voltage is a nice 243V.  Does anyone have an idea what this could be?  '

Thanks,

G

 

[Kingston]

Edit
I've attached an image: pink noise from sound card to G9 input (input to DI looks about the same) and G9 output back to sound card. The roll off slope does not change when fiddling with G9 gain settings... Why there is such a roll off, what can cause it?

Turn the SPAN FFT "slope" setting to 0.0 dB. You're looking at a 3dB per octave tilt on the FFT display only. nothing to do with the preamp.

 

[tmuikku]

@Kingston, hahaa, your are right! But I wish it was the only fault... Here are pictures with white and pink noise (some freeware generator, crest factor was on setting 1.42:1 if it matters? Don't know what that is, some bottom boost?) to DI and line input. The upper screen is directly from DA out to AD in for comparison and the screen below is DA -> G9 DI -> AD with both gain potis at 12 o'clock.

The third picture with three screens is mains hum on top (line input connected but no signal), middle is with white noise to line input and the bottom is pink noise to line input. Low cut seems to be working but it is not on. Can some faulty capacitor do this?

white noise

 

[tmuikku]

same with pink noise ( this is because there is that low end boost in adda loop, changin crest factor seemed to boost more)