The official G9 help thread

[spudstyle]

Today, I changed the wires between front panel jacks and PCB. I use microphone wire but the noise is still here
No noise when I'm in line or mic mod but when I plug a jack, noise is present ! I don't understand why.
The case was opened, it can be a problem as the U87 project ?

 

[gyraf]

no, if it gets noisy with a jack is plugged in, the noise comes in through the jack - simple as that. Reason is the very-very high input impedance at the instrument input.

Try shorting the jack inserted to verify that hum goes away.

Jakob E.

 

[pzjones]

Hi Everyone. This is my first post on the DIY forum and it marks the completion of my Gyraf G9 Micpre. I wanted to thank everyone who has provided me with hints and tips over the past couple of months and of course to Jakob for his design and patience, Gustav for his PCB and kit, and Dan for the case and panel. All the voltages were good at power up and the phantom power was adjusted to 48volts. I used Avel Lindburg encapsulated toroidals with additional hum protection in the cases. 12v and 15v at 30VA. They make them just across the border in Wales so it was easy to talk to them and pick them up. I was careful stuffing the board and made sure that the wiring was correct and the Lorlin switches had the correct stops. Heater voltages are good as is the HT. I did the inst input mod and then cut the cables going from the pcb 5 pin connect to the front panel PCB. they were very sensitive. I made a ground bus for the XLR's and connected to the IEC earth. Did not bother with shielded cable for the output wiring.The unit is quiet and sounds great on Ac guitar with plenty of gain available. Transfer Function through Smaart shows no problems with Freq Response and shows the filter slopes when the hp filter is engaged. All together really pleased with the sound and should be able to check it on vocals later this month. I attach a pic. Once again many thanks.

 

[gyraf]

Hi pzjones,

Welcome to groupDiy!

That is a very pretty and clean build you have there! Love the color!

And thanks for the clear positive feedback on the project - from time to time I wonder how many potential builders we scare away by having this huge all-problems-thread: To an outsider or a beginner it could look like there are endless problems in DIY'ing a project like this.

Very nice to know that it also goes according to plan - and I'm sure you're not the only one - we just rarely hear from people that don't run into trouble

Jakob E.

 

[spudstyle]

no, if it gets noisy with a jack is plugged in, the noise comes in through the jack - simple as that. Reason is the very-very high input impedance at the instrument input.

Try shorting the jack inserted to verify that hum goes away.

Jakob E.

Possible that my G9 is not properly grounded ? It is a bit noisy but acceptable with other sources.

I wire all XLR pin 1 together and one of them to the star ground. Xlr input 1 on PCB to the star ground too and the main ground to star ground. Something is missing ?
Or the problem can be my not encapsuled transformers ? And I use 2x15v cause I don't have a 2x12 in stock.

 

[phelar]

Just want to say thanks to everyone here for the help with my G9.
It´s dead quiet now. It´s hard to say where the noise came from, maybe the old Mbox.

I have tried it in two different professional studios and it sounds wonderful.

...and thanks Jacob for a nice sounding circuit.

 

[boab]

Hi

This is one of my first posts. I have been lurking around for 2 years now and have finally got to the stage that I am nearing completion on my first G9 (and SSL comp).

I have had a good look for similar problems, but I cant find the same thing, so I am posting here!

My G9 works! but only when I have it in series with a lightbulb (on live) and have my soldering iron on(in the same circuit).
In this situation I am measuring around 145VAC at the iec inlet, 10vac (twice) and 160vac from the transformer onto the board. The unit works and the HT is around 180vdc.
When I switch the lightbulb out the circuit. The LED fades the tubes fade and the voltages go up. I have 228vac at the iec socket, 17.1vac (twice) and 275vac coming out of the transformers on the HT I have 358vdc.

I made an error when I was in a bit of a rush and didnt have the circuit diagram to hand (stupid I know!) I had the transformers wired incorrectly and had 160vac (instead of 220vac). I also had one of the off board caps(C15)the wrong polarity. I tried it in series with a lightbulb, but R33 smoked but didnt blow (it measures ok but could be my problem)

The components I have used are IC1 - TL783C, IC2 L78S12CV, T1 Tip 121.

I dont have the exact voltages to hand(updated to correct voltages) but I hope you can get the idea from this any ideas what to look for/ where to check & measure?

Thanks in advance for your support.

Great project by by the way!

Boab

 

[gyraf]

I don't quite follow the lightbulb setup.

If your 12V (heaters) fade at full voltage, it's probably because your 78S12 gets too hot and shuts down.

Make sure to heatsink properly - e.g. to the chassis - but REMEMBER to mount it electrically insulated from chassis. You need a TO220 mount kit for this, consisting of a sheet of insulator and a plastic insert for isolating the mounting screw from the 78s12.

Jakob E.

 

[boab]

Hi Jakob,

Thanks for your speedy reply.

To clarify, the lightbulb (which can be switched in and out) is wired in series with the live before a dual socket on my bench. It acts as a current limiter to stop blowing up broken things when testing them, if something is faulty and draws to much current the light bulb glows. It also saves your soldering iron as when not in use you can just switch the bulb on and the iron cools a little then when you need to use it the switch the light off and the iron heats up again. Its an old trick from an ex ferrograph/ valve amp repairman/ designer who trained in the 60's and know his stuff.

The problem is that it doesnt just fade, it just turns off instantly as soon as I bypass the light bulb. The heatsink isnt hot and IC2 isnt hot. I cant measure a voltage out of the IC, could it be from over voltage? Im a bit concerned about the HT being so high also!

Thanks again

Boab

 

[stevan.siemens]

Just an update here. I finally had some time to work on this build after a hiatus of some length. I did the trace cuts, and redid my grounding, and my preamp is fully functional. There is a bit of hum, but not really significant. I've also got a bit of buzz picked up in my second channel from the power supply, so I need to put up a shield between that pot and my transformers. Sounds great with the G7 mic!

 

[boab]

Good News Update!

I replaced the resistor and removed and re-applied some more heat sink paste to IC2 and it works!

Thank goodness for the light bulb or I would have fried a few more components. see link below for recommendation

http://www.richardsradios.co.uk/repairing.html

Voltages are measuring fine now also.

Just got to mount it in a nice case now and get into the studio.

Thanks for your help. this is a great project!

Boab

 

[Wowa]

Hello everyone. Today finished my G9 project. Here are some photos:










Later I'll try to record the sound samples.

 

[Wowa]

Reamp using the G9.
Recording chain:
DIY Tube guitar amp - Bogner 4*12 (V30 speakers) - SM57 - G9 preamp - RME Fireface UC.

http://12ax7.ru/G9/G9_KSE_REAMP.mp3

 

[MeToo2]

Reamp using the G9.
Recording chain:
DIY Tube guitar amp - Bogner 4*12 (V30 speakers) - SM57 - G9 preamp - RME Fireface UC.

http://12ax7.ru/G9/G9_KSE_REAMP.mp3

I listened carefully to the sample you posted, and it seemed to contain an excessive amount of noise.  8)

Nice build.

 

[Wowa]

Reamp using the G9.
Recording chain:
DIY Tube guitar amp - Bogner 4*12 (V30 speakers) - SM57 - G9 preamp - RME Fireface UC.

http://12ax7.ru/G9/G9_KSE_REAMP.mp3

I listened carefully to the sample you posted, and it seemed to contain an excessive amount of noise.  8)

Nice build.

Hi, thank you very much for the tip. Noise associated with reamp and with the grounding problems in my home Studio. Today has recorded a live example:
http://12ax7.ru/G9/G9_Time.wav
Without reamp

 

[bruce0]

I don't have this on my build.
...

Maybe you can probe with a 10Meg scope for any DC offsets before and after the pop?

Turns out that I don't have this problem either.  I found that the popping and clicking had to do with tube microphonics, and changing out 2 out of 8 tubes, and bolting the preamps down, and now the pops are gone (I can reproduce the pops but only while the tubes are heating up).

Sorry for the bad info.  Shorting and non-shorting both sound about the same now.

 

[gemini86]

Reamp using the G9.
Recording chain:
DIY Tube guitar amp - Bogner 4*12 (V30 speakers) - SM57 - G9 preamp - RME Fireface UC.

http://12ax7.ru/G9/G9_KSE_REAMP.mp3

I listened carefully to the sample you posted, and it seemed to contain an excessive amount of noise.  8)

Nice build.

Hi, thank you very much for the tip. Noise associated with reamp and with the grounding problems in my home Studio. Today has recorded a live example:
http://12ax7.ru/G9/G9_Time.wav
Without reamp

I think he was poking at the music being noise... I thought it sounded great. (I'm an A7X fan, so I can dig it)

 

[MeToo2]

Reamp using the G9.
Recording chain:
DIY Tube guitar amp - Bogner 4*12 (V30 speakers) - SM57 - G9 preamp - RME Fireface UC.

http://12ax7.ru/G9/G9_KSE_REAMP.mp3

I listened carefully to the sample you posted, and it seemed to contain an excessive amount of noise.  8)

Nice build.

Hi, thank you very much for the tip. Noise associated with reamp and with the grounding problems in my home Studio. Today has recorded a live example:
http://12ax7.ru/G9/G9_Time.wav
Without reamp

I think he was poking at the music being noise... I thought it sounded great. (I'm an A7X fan, so I can dig it)

Sorry. Yes, it was a joke. Thought the  8) would make that clear.

Your clips sound damn fine, and whoever it is can really play guitar.

 

[spase]

can i use metal film resistors 1/4W 1% everywhere? expect on those places where i need 1W or 2W.

 

[gyraf]

yes