The official G9 help thread

That would seem a likely cause.
I checked all the resistors both visually (by color code) and with a VOM before soldering them in, but I'll check again.

I carefully checked all the resistors both visually by color code and by measurement with a VOM, and all seem to be correct (based on the Gyratec IX rev 8 schematic). The GIX conveniently used the same numbers as the G9 for all parts.

The only resistors I could not measure in place were the input (-48, line pad) and the 10k outputs across the output transformer secondaries, but those color codes are correct..

Except for the output being so low, everything seems to be working OK - the step attenuator is increasing the signal in regular steps, the output pot acts as it should, the output even clips when you put a signal through it and turn everything up. The internal signals all look as they should when fed a sine wave.  It's just the output is really weak. What are normal P-P voltages at the output of V1 and V2 at clipping?

T1 is an OEP A262A3E and T2 is an OEP A262A2E and due to their pinout, there no way to insert them incorrectly in the PCB.

As I mentioned, I've tried different tubes and even different tube types. I'm really puzzled as to what to check next. 

mhuss said:

The only resistors I could not measure in place were ... and the 10k outputs across the output transformer secondaries, but those color codes are correct..

Click to expand...

You wouldn't be the 1st reading a resistors colour code backwards (especially these 10K parts values with 1% tolerance) ...

Thanks for the suggestion, good point, but I've noticed there's usually a larger space between the brown '1%' band and the other four (value) bands.  The tolerance band is also often a bit wider than the other four.

However, this is why I always check the value of 1% resistors with the ohmmeter before soldering them in -- mistakes do happen. The tests above were just a recheck of the assembled unit.

Hey,

I got a little problem with my G9. One channel doesn't work at all, no signal comming out. No matter what Input is selected.
It worked before, but after some fiddling around and changing transformers, it doesn't work anymore.
I undid the changes, swapped transformers, changed XLR's, changed output cap, switched tubes, still no signal...
Channel 2 works fine. I also measured voltages and compared, and to the last resistor R30/R130 all voltages are almost the same...
The weird thing is, sometimes, but very seldom it still worked for short time.
Does anybody know, where I should look at or what the problem could be?

UPDATE: swapped relays, now I got very, very little signal but only when in MIC mode.
So signal seems to come through, but really low, thin and distorded.
Any clues?

..small crack in pcb copper conductor somewhere? Beep-test everything (EVERYTHING)

Jakob E.

Hey Jakob, thanks for your suggestion. Will try that!
But if there was a crack, wouldn't the voltage also drop somewhere?
I swapped a few more components, and now I don't even get 48V at the XLR's anymore, not even on the channel that worked before... I will order two new relays, and see if that will help.

Sorry, for double post.
But Jakob, am I right, that at R42 there should be 48V?

yep, 48V across R42

Hmm, than there also lies the problem... I have nothing at R42.
At the TIP121 I have 50V on B, 90V on C and 0V on E.
There should be 48V on E all the time, right?

EDIT: OK, got 48V again, one leg of the TIP121 was broken. So fixed that.
But I still got next to no signal on channel 1... Hope that the new relay will fix that.

EDIT 2: Got it!
You were right, bad connection. After I read that, putting a TRS in the DI will break the signal, I put one in the working channel and it was almost the same as in the bad channel. Really low, thin signal. So I thought it had to be something with the DI.
After swapping the DI jacks and resoldering the connections there was still no signal. Than I did a continuity test, and voila, the "ATT" pin on the controll board made no contact. Fixed that, fixed the whole problem. Now I got plenty of good signal.

Thanks alot Jakob!!

Hello people,

I hope this is not a too dumb question but is it possible that cheap power transformers come already broken?
I built the PSU for my G9 and chose cheap power transformers (12-15€) for them. When I had assembled the whole PSU, I wanted to measure all voltages before assembling the rest to prevent future confusion if something is not working. And I actually ended up getting wrong or no voltages at all. So I disconnected the power transformers to measure without load and even then, wrong or no voltages. This is what I measured:

Heater (supposed 15VAC): 17,8 to 18,1 VAC
HT Line (supposed 220VAC): around 0VAC, sometimes up to 0,003VAC
Phantom (supposed 15VAC: around 0VAC, sometimes up to 0,004VAC

I don't get it. I triple checked and the Multimeter was set up correctly and the soldering connections of the multiple secondaries for the Phantom Power circuit were also fine.

Only thing I can think of, is that the power transformers are shit. But before I buy new ones, or this one which has both in one (https://www.don-audio.com/G9-Audio-Power-Trafo-Sec-230V-15V-12V-Integrated-Shielding) I want to make sure it's the only possibility.

Thanks in advance!!

Check with the beeper is there continuity between proper windings.
Check both transformers separate at normal conditions do you have at secondaries double 15V and double 12V.

For the future order custom made (one) transformer with proper secondaries and you will be happy and pay less.
I can give you contact for manufacturer which makes toroids for audio equipment use.
Secondaries:
220V
45V
15V

Cost is circa 50euro without shipping.

ln76d said:

Check with the beeper is there continuity between proper windings.
Check both transformers separate at normal conditions do you have at secondaries double 15V and double 12V.

For the future order custom made (one) transformer with proper secondaries and you will be happy and pay less.
I can give you contact for manufacturer which makes toroids for audio equipment use.
Secondaries:
220V
45V
15V

Cost is circa 50euro without shipping.

Click to expand...

Thanks! That would be great, as a back-up, if the testing shows that they are actually broken. If you send me the contact, would be awesome. However, one, probably stupid, question as it is my first G9, for what the 45V secondaries? The Heater or Phantom Power circuit?

For the phantom - you can just use normal rectifier instead voltage tripler.
Always you can order with 15V (instead 45V) and use tripler, but the price is the same so what for bother with multiplying voltage?

ln76d said:

For the phantom - you can just use normal rectifier instead voltage tripler.
Always you can order with 15V (instead 45V) and use tripler, but the price is the same so what for bother with multiplying voltage?

Click to expand...

Yeah ok true, but as I got it and the rest of the PSU assembled already, I would probably go for the 220VAC, 15VAC, 15VAC version. For next time good to know, though.

You can always remove five diodes and four capacitors (or just disconnect D12) and use bridge rectifier screwed to enclosure.
It's simple
I will send you later contact on PM.

Question:

I've noticed that the charge across the two large high-tension capacitors in my unit drops quite rapidly after power-off. I know this because I'm careful to measure and discharge them before reaching into the case.

Does this type of leakage indicate a problem of any kind?

Hello once again,

I built the PSU of my G9 completely now and I am very happy to have the right voltages for the heater (12,01 V measured) and almost for the Phantom Power (48,93 V measured).

However, with the HT Line I measure around 275v instead of the needed 245v. Does anyone know where this problem can arise from? I am trying to find the problem myself at the moment, but until now I haven't been able to find it.

Any help would be appreciated.
Thanks!

@A-Ape        do you have ps loaded with rest of circuit; you should have some kind of load or voltage may be high\regulators may fail\to regulate

Audio_Ape said:

Hello once again,

I built the PSU of my G9 completely now and I am very happy to have the right voltages for the heater (12,01 V measured) and almost for the Phantom Power (48,93 V measured).

However, with the HT Line I measure around 275v instead of the needed 245v. Does anyone know where this problem can arise from? I am trying to find the problem myself at the moment, but until now I haven't been able to find it.

Any help would be appreciated.
Thanks!

Click to expand...

If you measuring PSU only without the rest of the circuit, then it should be correct. WIth the load (tubes) voltage should drop.