The official G9 help thread

[Deepdark]

Quick One for you Jakob, or anybody: Simply out of curiosity, do you have any idea why I can't get more than 41.5v (phantom power) (measuring from between ground and xlr), while HT is 241V and heaters are 11.95V. Maybe it's related to the fact my transformer are 50VA each and I feed secondary 12V with 15V. Probably nothing to care about, but simply to have any idea.

I got 90V after rectifiers. When looking at the schematic, we see that we have to set the right voltage before TIP121. The circuit is a zener diode voltage regulator setup, so D6-56V zener would be there to set our voltage at about 56V, R40 is there to drop a little current, PR1/R41 is our load, and Voltage across PR1/R41 must eb the same as the voltage across the zener diode, right? If I'm set at 41V at max, so how can we explain the gap between 48v and 41v? Maybe because my voltage is higher than the 60V specified, the excess is dissipated as heat through the zener and influence it's performance??

 

[gyraf]

With a zener that actually is 56V, and a functioning TIP121, you should be able to trim to 48V - at no load, i.e. no mic connected. Once you connect anything that uses p48, voltage will and should drop (because of the 6K8's).

Jakob E.

 

[Deepdark]

Never mind, i got 48v. Forgive the brain fart  ;D

 

[Deepdark]

Looks great! Do you have an overview of the whole device? Why did you opt for different transformers?

Here it is. Overall view of the thing

 

[JingleDjango]

Thanks, Deepdark. That'll be a great reference for me when I get the time to wire mine up.

I made myself a little capacitor discharger with a 10W resistor and a couple (insulated!) alligator leads. If I've had the device powered up and I want to get in to work on it, do I need to be careful to discharge any capacitors other than C14 and C15? Do I need to sweep the entire board?

 

[Deepdark]

You're welcome. The only things remaining is to put some tyrap around group of wire to get them group and clean and put some new tubes in it and bingo. Pretty happy with the unit.

 

[JingleDjango]

Also, can you tell me what gauge wiring you're using to connect the terminal strip to the board? I was going to order several colours of 18AWG but maybe that's overkill? All I have at hand is 22AWG.

 

[Deepdark]

I use 22ga, rated 300V, I got some 600V, too. You'll probably be fine with your 22ga

 

[JingleDjango]

I only need to wire everything up at this point. Unfortunately, the instrument jacks I bought (http://www.neutrik.us/en-us/plugs-jacks/m-series/nmj4hc-s) are wide enough that they get in the way of the control PCB. I can't get the PCB close enough to the front panel to fit the threading of the switches in. I'm not sure if I should carve away a part of the PCB to make room or order more jacks. Shipping is so expensive. . .

 

[JingleDjango]

I think I answered my own question. : Yay Dremel tool.

 

[JingleDjango]

I need to double check one aspect of my power wiring with someone more experienced because I want to avoid serious problems.

I'm using this terminal strip to make all the connections between my toroidals, and running the power rails out to the board.
-In the green circle, you see the two pairs of wires from the 2x12v transformer secondary coils. (BLK/ORG, RED/YEL)
-They are connected on the other side of the strip to secondary B from the 2x15V transformer.

 

[JingleDjango]

(image is the same as above, viewed from the bottom)
-Running away from there, connected to the same side as the YELLOW and ORANGE wires belonging to the 2x15V transformer, I have a pair of narrower gauge wires to carry to the 15V terminal on the far right of the PCB, above C113.

I have it wired like this to try to keep things well organized inside the chassis. I'm unsure if this is quite the right way to go about it, though. If anyone could take a glance to reassure me, I would appreciate it!

 

[JingleDjango]

Finally, I'm reposting the transformer wiring diagram so all the pertinent information is collected here for reference.

I'm not using these exact transformers, but my two transformers use the same colour scheme as the Avels depicted in the diagram.

Thank you.

 

[JingleDjango]

I ended up using the two spare terminals in my strip to do a simpler wiring that I could be more confident with. The unit worked almost perfectly on first plug-in. No smoke or worrying smells or sounds. This was very reassuring because this is my first time working with tubes or high voltages!
Here are some relevant details:
PCB from http://pcbgrinder.com I was a little disappointed that their board didn't include the spare power supply board in Jakob's files. Otherwise there were no problems whatsoever with the PCB.
Case and front panel from collectivecases.com. The enclosure is great. I wish the front panel had a hole drilled for an indicator light. I may still add one myself in the future, but for the time being it's not a priority. The silkscreened paint on the front is delicate and scratches easily. Frankly, I'm not in love with the look of this panel but it was the cheapest and most convenient I had access to. If I build another unit, I will probably order from http://www.frontpanels.de/.

Transformers are all oep with the shielding cans. I haven't used the preamps other than to test that they work, so I can't comment on the sonic characteristics of these.

Capacitors were a grab bag. In the future, I would seek out WIMAs where applicable because they are known to fit the board better. I have no opinion about whether capacitor selection affects the sound much.

For the power supply capacitor bank, I would especially look for the physically smallest electrolytics possible. This part of the board gets crammed.

Initially I had P48 in only one channel. I traced this back to a switch I had installed incorrectly. I removed the switch and reoriented it and this solved my issue. There was an intermittent connection causing drop outs in ch.2. This was caused by using a crimp type connector to connect the output pot to the control PCB. I corrected this problem by removing the connector and soldering directly to the board. I haven't had the chance to check the instrument jacks yet, but everything else works great.
NO perceptible hum! After reading so much about this issue, I was concerned that I might have to do a lot of re-tooling my completed build to minimize unwanted noise or hum. This was not an issue at all. I credit everyone who contributed to this thread and others with providing case studies and advice.

Before starting the build I compiled a folder of images from this thread of other people's successful builds. This was the most helpful resource when it came to figuring out the practical issues that would come up (ie. grounding, ways of organising the internals, general wiring, component selection, etc.). I'm going to post a bunch of pics I took of my build in the hopes that they'll be useful to someone like me.

I apologize in advance for monopolising  the thread. I think I've said it elsewhere, but in the interest of preventing dead links in the future, I'll be uploading the photos as attachments. Unfortunately, I can only do this one per post.

Finally, I'm donating $10 to the website as a way of acknowledging Jakob's contribution to the knowledge base. I wish I could afford to give more. Thank you, Jakob.

 

[JingleDjango]

Overview 1

 

[JingleDjango]

Overview 2

 

[JingleDjango]

Overview top

 

[JingleDjango]

PCB close 1

 

[JingleDjango]

PCB close 3 from back

 

[JingleDjango]

PCB close 4 side