The official G9 help thread

[steppenwolf]

I just looked up the specs for the M9 and it says it has 200Ohms output impedance and is a transformer less design so it should be pretty different than the G7...
Anyone has already tried to run a G7 through a G9?

 

[gyraf]

Anyone has already tried to run a G7 through a G9?

Yes. And it ain't no problem :grin:

Jakob E.

 

[steppenwolf]

Great! Thanks!

 

[crazytooguy]

Hi all. my G9 has a lot of buzz and hum in the output, and I think it's coming from the power supply. I have all the grounds starred through the channel one input XLR. Here's a scope pic of the output at max gain

And here's the heater 12V. The HT 245V looks very similar.

Just in case it's useful, here's the input to the 12V regulator

When I first hooked everything up, there was a short to ground in the heater circuit and it trashed the regulator. It's been replaced, but is it possible that the diodes or the smoothing caps are wrecked as well? Is it just easier to replace them and see if it helps? Thanks!!

Pat

 

[tony dB]

To add to the mic choice ...
this preamp is killer with all mics I've tried so far. AKG 461 with omni capsule sound very close in room and spaceyness as compared my Neum 149 (tru another -UA-! preamp).

Have also a very little hum on 50 and 100 hz (seen on analyzer - hooked up my G9's are dead silent!) what I need to sort out, but I believe this issue came up already so many times, that the solution is to be found in this thread.

 

[steppenwolf]

Hi guys!

My g9 is close to be finished but there are some problems with the transformers.
I'm using one 2x15V 50VA toroid and an 2x12V toroid at 50VA.
I hooked up the first 15V transformers to the mains and connected one pair to the ECC82 heater terminal and the other pair to the 48V terminal.
Everything works fine. I'm getting 12V on the heaters and 48V phantom.

But as soon as I connect the secondary of the second trafo to the 15V of the previous it begins to hum and it draws around 650mA with nothing connected???
I tried to connect just one pair of the secondary of the second tranny in case I messed up the phase but I'm still having the same problems.

I thought I could have a defective transformer but when I connect the second transformer straight at the mains it works fine an puts out around 14V idle so it can't be the transformer...
Has anybody an idea what the problem could be?

Thanks!
Stefan

 

[steppenwolf]

Hi guys!

The transformers problem is gone. I inserted a 4 Ohm resistor between the secondary of the first tranny going into the primary(secondary) of the second. That lowers the voltage down a bit and everything settles fine.

But I observed two problems and they make me a bit nervous:

1)

The voltage rating of the 10uF cap just after the 1k in the 245V line is 250V.
When I turn on the G9 the voltage rises up to around 280V AFTER the regulator until the tubes heat up a bit and begin to consume some mA and than settle around 245V. I'm afraid that this overshoot will kill the cap...
What do you think?

2) Phantom power:
I feed the phantom power circuitry with around 16,5VAC and I get more than 80VDC after the last diode. The cap attached to it rates 63V like in the schematic. That's again too much.
Same behavior on your G9?

Would be nice to here from you!
Best,
Stefan

 

[steppenwolf]

Hallo!
I finished my G9 a few weeks ago and I'm really happy with the outcome!
(PICS soon)
The only little issue I have is the following:
With both the Gain and the Volume Knob cranked and nothing connected to the inputs I get a tiny bit of white noise on one channel (that is perfectly accepteble) but on the other channel I'm getting some random crackling noises and I can hear voices sometimes so I think it's RF interference...
Both input and output trannies are shielded as well as the wires.
Do you have any suggestions on how to improve that or should I keep it as it is? It's defenitly not bothering me as it is low in level...

Thanks,
Stefan

 

[maxime]

hello,
I may be wrong but I don't understand the reason (except a ground loop) for the ground (0V) jumpers on the pcb. the ground path is already complete without these.
anyone knows the reason behind the existence of these two jumpers?
(one jumper is right aside the r26 resistor, the other aside the r31)
best
maxime

 

[ognam2]

Hello....
I ordered a custom trafo for my g9 like this:

Prim: 230V - Sek: 220V(60mA) / 15V(1A) / 15V(10mA) toroid
(do you think the values are OK?)

so I will have one instead of two....
My question is, if it would make sense to place it outside of the chassis....
Maybe to prevent hum?
Would be no problem because it is molded in a plastic can and can be mounted easily with one screw....
what do you think?

Jonas

 

[gyraf]

15V/10mA makes no sense.

You'd want something like 50V/30mA for the 48V phantom power (and change the phantom power circuit accordingly)

Jakob E.

 

[ognam2]

You think pahntom power needs more than 10mA?
I just thought about to take some kind of a "plug and play" Trafo for the circuit that you made... (one of the custon one cost the same like two standards) because I bought the pcb from gustav and can´t change the pcb design anymore to have a new phantom circuit.
I know that there other possibilitys, but is there any reason why it is not good just to feed your circuit with 15V?

so maybe 15V/30mA for this?

cheers Jonas

 

[ognam2]

or is there an easy way to modify the circuit. what is wrong with the way that I thought about?

thanks!

Jonas

 

[ognam2]

I´m a little bit confused now...
What is the right value for the phantom circuit trafo?

 

[gyraf]

I have not tried to calculate the needed current of the 15V-winding driving the P48 voltage-tripler.

To play it safe, just use another 15V/1A winding - the cost probably will be the same or cheaper than a low-current winding.

Jakob E.

 

[ognam2]

1A for Phantom? I guess thats really "safe"... ;-)
I thought that it would be more expensive if the winding is made for more current.... well I will ask the trafo guy....

thanks

Jonas

 

[JimiH]

Ok I have a new problem.

I was using my G9 with a small condensor mic and happened to notice the oscillation problem in both channels with the gain up high. I decided to fix this in the usual way and it worked a charm for channel 1. Now channel 2, only a distored signal was being passed (same mic) so I decided to open 'er back up and see what all the fuss was about. I had the lid off and I was making a few measurements when I noticed that the temperature of the 12 volt regulator was shooting sky high and smelling funny (it was either that or the diodes before it, they were also getting rather hot) and that it was also touching the case, as in the insulating washer had slipped out and past my observation when I was screwing it all back up.

So anyway the 12 volts cut out once the regulator reached about 140 degrees C (yes I know, I let it go all the way up without turning it off, shame on me) and the audio subsequently also cutout. I know that the 12 volts cut out as my power indicator and heaters turned off suddenly. Before this happened however there was a humming like a ground loop coming out of the speakers, the cheap speakers that I was not worried about ruining if there was a massive pop by the way.

So my question to you out there, whoever you may be, is this: can a dodgy heater voltage regulator be the culprit in my hum issue? Does no heater voltage = no sound? I would assume this to be the case as there would probably be no heaters in thermionic tubes if they weren't needed. Can loss of heaters cut the sound this quickly? I guess my G9 needs a new 12 volt regulator...

As a side note I should probably mention the fact that once I had everything open and "jiggled" about a bit channel 2 seemed to work as well as channel one did, albeit with the hum and loss of sound once the 12 volt regulator cutout...

 

[steppenwolf]

I would suggest to solve one problem after the other. maybe the shutting down regulator causes the trouble, maybe not.
You might need a bigger heatsink.
I used an old CPU sink that is pretty big. After a few hours on, it's still gets really warm. BIG heatsink needed here...
Cheers,
Stefan

 

[JimiH]

Yep yep. I have it bolted to the case which seemed to work fine before this little incident. It used to be on for up to 6 hours a day, no trouble. Thanks though. I might try a different heatsink anyway.

 

[JimiH]

Hey everybody, again.

My G9 has a new problem. I fixed the regulator and it no longer cuts out, but now it humslike a little bitch. It never used to do that. but here is the funny thing. Both channels hum the same, but with the output volume all the way down, there is no hum... Anybody experienced this yet? I am at a loss as to where this could be coming from, especially considering that it didn't do this before I burned out the heater regulator.