The official G9 help thread

[PavelB]

My version. There were a lot of problems, but everything worked out well. Noise -96dB. Thanks to the author for the information provided. I liked some of the engineering solutions, replaced others with my own.





1 chennel version:

 

[gyraf]

wow, that is really beautiful in it's own strange aesthetic...

How did you do the 2u front panel decoration? Is it engraved-on-powdercoat or is it something else?

/Jakob E.

 

[PavelB]

Hi Jacob, thanks for your posts. The panel is engraved on my CNC, V-engraver 4mm, the depth is slightly greater than the thickness of the coating.

 

[drumminkiger]

Maybe this has been discussed to death somewhere, but I was unable to find it. If someone were to spend a couple extra dollars on a few fancier capacitors, like Mundorfs, where would they be the most use in the G9 circuit? Or is it good money after bad? I was also thinking about springing for some dale or the like resistors for the audio path.

 

[gyraf]

IMO it would probably be a waste of money - just use decent polyester caps where ever possible, and you're good.

/Jakob E.

 

[drumminkiger]

Thanks for the reply!

One other question, do we need to make any changes to the power supply when using the Don Audio 230/15/12v transformer? I'm imagining a change in D13-16, or does IC2 take care of that for us?

 

[gyraf]

you'll really need to ask Don about that

/Jakob E.

 

[drumminkiger]

Okay, in case anyone wants to know in the future, according to Aaron from Don Audio "This shielded toroidal is wounded for the G9 project and there should not be changed anything but it makes sense to check the values after the rectifier but usually you don´t need an adjustment."

So I'll build it as planned, and make sure my voltages look good with tubes installed. Just waiting for the power transformer to make it through US customs.

 

[drumminkiger]

After a few days of messing with it I think I've got it pretty much there. I did the DI mod from the get go, then relocated the B+ and Heaters to the external PCB after getting the noise some people experience and traced down a few other small errors. It's as quiet as it should be and sounds great.

 

[Clbraddock]

I've been trying to learn about tube circuits in general before building a G9 and I have a question mostly for learning purposes. In looking at the G9 schematic, I notice there is no grid stopper. I understand that there isn't always a grid stopper (especially on transformer mic pres) but was still curious if the lack of grid stopper would allow high frequency noise into the first gain stage when using the hi-z input. Does the circuit have some other mechanism to achieve the LPF effect a grid stopper would normally perform?

 

[gyraf]

grid stopper would be for hf stability - and with ecc82 we simply do not have a gain-bandwidth high enough for that to be an issue

..also C6/106, the 68pF in the feedback loop ensures stability at low gains..

 

[Clbraddock]

Is there a bom with the capacitor lead spacing anywhere? My pcb hasn’t arrived yet, but looking at pics it looks like there a quite a few different cap sizes (physical size).

 

[johnchantler]

Here is a spreadsheet I made with cap dimensions and lead spacings in preparing for my own recent parts order

https://www.dropbox.com/s/qdympa7qhlsjojz/GYRAF G9 BOM.numbers?dl=0
Will add it here as text when I’m back on proper computer.

 

[Clbraddock]

Here is a spreadsheet I made with cap dimensions and lead spacings in preparing for my own recent parts order

https://www.dropbox.com/s/qdympa7qhlsjojz/GYRAF G9 BOM.numbers?dl=0
Will add it here as text when I’m back on proper computer.

That is excellent! Thank you so much for sharing!!

 

[johnchantler]

here it is attached as a PDF, too for when that link eventually dies...

cases for mine arrived today from Frank so looking forward to getting these closer to done.

 

[Clbraddock]

Are the cap voltage ratings on the BOM in VAC or VDC? Normally, I assume VDC but this circuit is higher voltage than other preamps I’ve built so I wanted to double check.

 

[gyraf]

I always rated VDC, the AC rating is much more "elastic" in definition

 

[rankot]

View attachment 84296
My version. There were a lot of problems, but everything worked out well. Noise -96dB. Thanks to the author for the information provided. I liked some of the engineering solutions, replaced others with my own.

Which tubes did you use? 12AU7 or something else?

 

[Clbraddock]

Where are people in the US getting pcbs from? I ordered from analog classics over a week ago and it doesn’t appear anything has shipped. I emailed asking for a status update also no answer. Their reverb page only lists a single potentiometer for sale, so I’m starting to wonder if they are still in business.

 

[johnchantler]

I got my boards from analog classics back in October. Took 3 days to ship (and then ~ a month to arrive here in sweden)