The official G9 help thread

[audiophreak]

  from 1954U1
Ah, so, being maybe power supply related,
I'd try first to swap C25 and C125.

  in the G9 parts list, C25/C125 are called "HT NOISE FILTER"  my newbiness... I don't know what that does  :-[

  But at this point, its as good a starting point as any. I think instead of swapping caps, I know so far, that this is confined to the right channel, so I think I'll replace one component at a time, maybe stare at the schemo for a few  hours and try to follow the right channel audio path

Thanks so much for the insight,
                                          Chip

 

 

[gemini86]

the schematic only shows one channel, so you'll just need to go by the component numbers, eg- C4 = C104 on the second channel, so once you establish which channel you have wired as you 'right' channel you can figure out where stuff is.

 

[microc]

Hi Guys,
I have almost completed my G9. The one thing remaining is getting it to work! When I fire it up I get a bit of hum, and a oscillation (at aprox. 8kHz, not sure, my oscilloscope is old) when the gain switch reach maximum.  ???
I’ve had some problems: I used wrong resistans (R34), so the 245V vas 20V. I changed the R34 to a correct value, and I change the TL783 and R33-37 aswell incase of any damage. I also checked C14 and C15. C14 and C15 is at 100uF/350V  Low Impedance Aluminum Electrolytic Capacitors (http://no.mouser.com/Search/ProductDetail.aspx?R=UCS2V101MHDvirtualkey64700000virtualkey647-UCS2V101MHD ). Could this have any influence at the system, should I change to big oil caps instead?
Now,all the primary voltage are correct. I also had some earth problems, but after reading all the post about earth, I’ve got it sorted out.
After reading all the posts about connection to XLR, I’m pretty sure that’s correct too.

So I guess I have to start unsolder all my components to check them (would be frustrating! :-\) if anyone of you don’t have a clue. ???

Thanks for your help and tips  ;D
Best Regards
Jens

 

[flintan]

So, in doing some digging around, is the edcor XSM a suitable input transformer? Is this transformer susceptible to noise due to lack of shielding?

Using an unshielded transformer for mic input does not sound like a good idea to me. Will most likely result in hum, noise and/or oscillations..

 

[flintan]

Another input transformer question.. I have some old Lundahl LL3815 (yes 3815, not 1538..). There is no data sheet for it but its turns ratio is 1+1 : 5 and each primary measures 5Ω DCR, the secondary measures 70Ω DCR.

I'm about to finish a G9 and need som input iron for it but i have a feeling these are too low Z for a tube pre. Anyone have a clue if it's worth trying them? Maybe it's better to save these for something like a JE-990 based pre instead..

 

[gemini86]

On the gyraf site there is a link to Kev's g9 build, (don't know who kev is...but anyway) He used OEP inputs and outputs, with NO shield cans, resulting in, well not much difference, to I don't think the non shielded cans will present TOO many problems that can't be sorted out with proper power transformer placement. Also, the most common cause for the HF oscillation is the long wiring/track for the instrument input jack, it's almost a foot long all together.

08. Jan. 2007: If you run into problems with oscillation on the highest gain settings, try running the connections to/from the front panel High-Z jack connector "directly" from the relevant points on the PCB - by cutting the PCB traces, and running a length of shielded cable directly to/from the jack. See this image for reference!! http://www.gyraf.dk/gy_pd/g9/G9-EDIT.GIF

 

[audiophreak]

Hi,
  Quote from Gyraf's G9 page :

"Note that OEP's HAS to be in screening cans, including the output trafos (that are not canned on the pictures, sorry). Without it, I've had oscillation problems because of the high gains and bandwidths involved."

...hope this helps,
                    Chip

 

[microc]

Thank you gemini86 and audiophreak !
My wiring from the instrument input jack is about 1/2inch, I will try to cut the trace on the board then. I use Lundhal trans, not OEP, my bad not telling
I had forgot kev's projects, I will check it out again. Anywho, thanks, I check in later =)

EDIT: I was just slightly afraid that I had blowed some tubes...

EDIT 2: After reading kevs page again, I notised that he got oscillation problem, and he knew wich wire who caused it. I use very thin wires, with very little isolation around. I will try to replace them with quality wires.

EDIT 3: (I'm the edit-guy from downstairs) I changed C14 and C15 from 2x100uF to 2x330uF and it's now working like a preamp Still a bit noisy. I'm reading this http://www.groupdiy.com/index.php?topic=15513.0, hoping to solve the problem xD
Thanks guys

EDIT 4: I got ridd of "all" the hum of 50Hz. Only abit hizz/hush left, but I think it will go away with better wires.

 

[guitarguy12387]

Just out of curiosity, has anyone tried replacing the output pot with a stepped attenuator? What do ya think? I may have to make one anyway, figured while i'm at it, may as well try it if it will make an improvement...

 

[stanz]

In regards to using an Edcor XSM for input transformers, and them making noise, I am going to chalk this one up to lesson learned. After unmounting them and moving them around, position was crucial, but at best, I could only get it to a barely tolerable hum. Obviously, the input is very sensitive and these are not shielded enough. The position where the least noise is, it is not possible to mount. I am going to get some Cinemag mic input transformers, as they are clearly the correct part. I know, getting something cheaper is not always cheaper.

 

[Kir_For_Pleasure]

Built my first G9  8)
Fired it up tonight and absolutely nothing happend ?? i have done some measuring and my conclusion so far is that toroidal 1 15v got 230vac and the secondaries have 15vac, one of them to each insert of 15v of the pcb, i have measure at the links of the card with no current as result ??
First tip besides quit buiding ??

 

[gemini86]

Built my first G9  8)
Fired it up tonight and absolutely nothing happend ?? i have done some measuring and my conclusion so far is that toroidal 1 15v got 230vac and the secondaries have 15vac, one of them to each insert of 15v of the pcb, i have measure at the links of the card with no current as result ??
First tip besides quit buiding ??

Are you getting 15v? 230v? a picture of your wiring would maybe help make things clearer?

 

[audiophreak]

Hi,

  The G9 was my first large project and have since completed a GSSL. The power trans configuration and hook-up was ( and still is ) confusing to me. I found this link that was plain enough for me to understand, so I'm sure it will help you and others. 

  On the G9, T1,the primaries are configured for your mains voltage to dual isolated secondaries ( top middle diagram ) connect one secondary to the 15v that is next to the HT 220v, then split the second secondary, one split to the 15v that's next to the LED feed and the second split feeding the T2 the other way round into paralleled secondaries ( lower right diagram ) then take the primary of T2 connected in series ( second in from lower left diagram ) to the 220v on PCB. This is how I connected mine and its been working flawlessly for the last 6 months, and it sounds AWESOME ! 

  hope this helps,
                      Chip

http://www.diyfactory.com/data/transformer_connections.gif

  ps, I printed this diagram out and pinned it to the wall in my shop  and have referenced it MANY times  ;D

 

[Kir_For_Pleasure]

My connection

 

[Kir_For_Pleasure]

the primary on the T1 have to be in serial !! trying again !

 

[peterc]

Check the second transformer, should be black/orange together & yellow/red together.....

 

[Kir_For_Pleasure]

yes i had that wrong on the sketch *sorry*
played my bass throu it know for a hour and its sounds really nice =)

 

[audiophreak]

Hi All,

  A little embarrassed, but I found that the cause of the low end loss in the right or #2 channel of my G9 was a poor connection at the CD player RCA connector  :-[
Thankfully I found it before tearing out and replacing components... just some of whats left of my hair  ;D  been running it for last week or so just to make sure and all is well.

Thanks for all the suggestions and support,
                                                            Chip

 

[sjekkih]

Yes I tried setting the gain at max and the out low, but the G9 is too clean

I will try changing R10. I understand the NFB loop consept now, but what is this talk about pads and pots at the output transformer?

BTW, is there a big difference between a tube mic and a regular condenser one?

Thanks for the guidance

Hi, I tried changing R10 to get more distortion in the gain stage, I doubled R10, without any significant difference in the audio signal. Any other ideas to mod the G9 for a dirtyer, tubier sound? Or should I go for a new  preamp without NFB loop.

Anyone know anything about sound diffrence tube mics vs regular condenser, when you want some warm distortion?

 

[SaMpLeGoD]

Hello! I'm have some questions about the G9... hop you can help me:

1) Could someone post again the fix for the high frequency oscilation? the JPG links aren't working
2) Anyone used flat cables to connect between the main PCB and the Front Panel one without problems?
3) I'm planning to use the OEP for output and the VTB9045 for inputs, is this help to get rid of the low cut problem with OEPs in and out?

Thanks a lot everyone!!

Eddie