The official G9 help thread

[burglar]

Hi Folks,

I have a problem with my G9.  Channel 1 is working fine.  I move the tubes over to test channel 2 and when on 48v, gain positions 10 & 11 have a dramatic drop in gain.  My initial thought was incorrect setup of the switches but everything seems to be fine with a dynamic mic.  Any thoughts on what could cause this in one channel only??

Cheers 

 

[Paperweight]

What's the voltages around the 12AU7s on each channel?

 

[burglar]

When you say around what do you mean?  Which points do I need to measure?

Cheers

 

[burglar]

Just to rule out any problem with the control board i swapped it with the control board from channel 1.  The problem remained so it is definitely something on the main PCB.

Any other thoughts on what this might be??  If I am to compare voltages around the tubes between ch 1 and ch2 can I take them directly from the tube socket legs?

Cheers

B

 

[burglar]

bump

 

[mhuss]

hi, I have a pair of GIX-51X  pres I recently finished (different form factor, but same preamp circuit). In MIC mode with both gains maxed, I'm getting about 43 dBv gain (~48mv p-p in / ~6v p-p out) from the first grid of V1 to the plate of V2. Is this low or in the ballpark?

 

[gyraf]

when on 48v, gain positions 10 & 11 have a dramatic drop in gain.  My initial thought was incorrect setup of the switches but everything seems to be fine with a dynamic mic.  Any thoughts on what could cause this in one channel only??

Hard to guesstimate. Probably a short somewhere? Compare voltages on the two channels at same setting?

In MIC mode with both gains maxed, I'm getting about 43 dBv gain (~48mv p-p in / ~6v p-p out) from the first grid of V1 to the plate of V2. Is this low or in the ballpark?

Don't know the 51x-version - the original gives some 57dB gain mic in to line out. A bit dependent on variation in tubes.

Jakob E.

 

[burglar]

when on 48v, gain positions 10 & 11 have a dramatic drop in gain.  My initial thought was incorrect setup of the switches but everything seems to be fine with a dynamic mic.  Any thoughts on what could cause this in one channel only??

Hard to guesstimate. Probably a short somewhere? Compare voltages on the two channels at same setting?

Where should I be taking my measurements from?

 

[Audio_Ape]

Hello folks,

I ordered all the parts for my first G9. One question that came up when planning everything is about the assembly.
Couldn't find a related link, so asking myself:

As there is no "real" PSU anymore and the toroids are connected to the main PCB directly, is there a specific order I should assemble the components? I mean normally you would first build the PSU and connect it to the empty main PCB to measure if all voltages are correct. Anything to take into consideration here as different zeners and other components on the main PCB regulate the voltages?

Thanks in advance!
Best wishes

Nik

 

[ln76d]

I see the real PSU in G9, maybe you have wrong PCB
Solder all components, make all other connections, connect transformers and use.
For example am using toroid 200V/15V/45V instead two - less work, similar price.

 

[Audio_Ape]

No yeah, obviously there's a PSU but it's not separated. You don't have a separate PSU PCB. That's why I'm asking but o.k.
Thanks for your help!

Another thing I came across: What fuse did you guys put into the IEC connector? Absolutely no information on that found. Obviously I don't wanna go too low in amps and need to replace the fuse every 2 days but risking my unit to melt by using a fuse with too many amps is also not my plan... Any info?

Thanks in advance!
Nik

 

[ln76d]

No separate PSU pcb is a big plus - less work - but this is of course my opinion only.
Look on the schematic again

1A T (slow blow - or whatever is called in english).

 

[Audio_Ape]

Yeah no definitely, I like it too. Just got a little confused but I think it's all clear now.

And ok cool thanks for that!

 

[ln76d]

Just carefull solder all components and don't make a mistake with the values and there is a big chance that it will work from the first powering
Jakob design is really great, PCB well designed so the chances to burn anything are really small.

 

[Audio_Ape]

Thanks a lot In75d ! 
I guess, I'm going to be fine!
One other thing that confuses me now while doing last checks:
On the components list, it says C16, C17 and C18 need to be 1000u/25V Caps, while on the PCB it says 1000/35V.
Got 25V Caps now, are they right or should I get 35V ones?

EDIT: Also C3 and C103 are different. On the PCB stated as 220n, they are stated as 470n in the BOM and schematics. Any info?

Thanks in advance!
Nik

 

[Majestic12]

Thanks a lot In75d ! 
I guess, I'm going to be fine!
One other thing that confuses me now while doing last checks:
On the components list, it says C16, C17 and C18 need to be 1000u/25V Caps, while on the PCB it says 1000/35V.
Got 25V Caps now, are they right or should I get 35V ones?

EDIT: Also C3 and C103 are different. On the PCB stated as 220n, they are stated as 470n in the BOM and schematics. Any info?

Thanks in advance!
Nik

25V electrolytics are fine.
It doesn't make a big difference if you use 220n or 470n in those spots, just use what you already have ordered.

 

[ln76d]

I used mostly 150nF if i remember correctly. Rest also ok

 

[Audio_Ape]

Thanks a lot In75d ! 
I guess, I'm going to be fine!
One other thing that confuses me now while doing last checks:
On the components list, it says C16, C17 and C18 need to be 1000u/25V Caps, while on the PCB it says 1000/35V.
Got 25V Caps now, are they right or should I get 35V ones?

EDIT: Also C3 and C103 are different. On the PCB stated as 220n, they are stated as 470n in the BOM and schematics. Any info?

Thanks in advance!
Nik

25V electrolytics are fine.
It doesn't make a big difference if you use 220n or 470n in those spots, just use what you already have ordered.

I used mostly 150nF if i remember correctly. Rest also ok

Thanks guys!

 

[mhuss]

I have a pair of GIX-51X pres, identical circuit to the G9 but in a 500 rack format (one channel per unit).  Many people have successfully built these, so I know the basic PCB/design/etc. is sound. Vcc is about 240VDC.

Both of these have a very weak output signal, optimistically -28db  output with gain and output both at maximum and using a dynamic mic for input.  On 10/10, the output is distorted, as you would expect. At 7/7, cleaner (but even weaker!) output.

I'm using the OEP transformers. Voltage gain is perhaps 42dbV from the input of V1 to the output of V2. The signal looks okay (clean sine wave in and out).

I tried different ECC82/12AU7  tubes, it made no difference. I tried an ECC81/12AT7 in V2, but it just made it much noisier, no real gain improvement (V1 gain is controlled by NFB, so a higher gain tube won't help). 

Any idea what I should check for?  Both preamps are acting identically, which makes a wiring error more unlikely (unless I'm very consistent in making my mistakes!)

 

[gyraf]

Consistently wrong resistor value somewhere maybe?

Jakob E.