The official G9 help thread

[gemini86]

do they just blow up, or do they light up, then explode?

at 100k there should be barely any light.

Tell us exactly how it's hooked up, and where...

 

[braeden]

do they just blow up, or do they light up, then explode?

at 100k there should be barely any light.

Tell us exactly how it's hooked up, and where...

Yeah that's exactly what I thought...
They light up and then explode (go up in smoke).

I've taken the +/- supply from the PCB to a breadboard into the +/- rails on that, and then plugged in a resistor in series with the LED. The LED is the correct polarity etc.

Also... is there any reason why I would be getting an extremely insignificant amount of gain from the instrument jack? I plugged in my bass to the D.I. and there is hardly any gain at the highest gain/full output setting.
I have cut the traces as per the example in Gyraf's G9 documentation, the microphone input works fine including the phantom voltages etc.

Edit: After recording some kick drum through an AKG D112 which usually has a fair bit of low-end to it with other pre-amps (API 312) it appears that the pre-amp is lacking a lot of low end, suggestions?

Thanks guys

 

[braeden]

Here's a picture of the frequency response of the left & right channels.

http://i.imgur.com/k2mzS.jpg

This doesn't look right at all for a 1Hz-20kHz sweep :/

 

[gemini86]

In regards to the LED problem, what do you mean by + and - rails? you're just using the greater supply, right? 12v?

 

[G-Sun]

PSU Question:
If I have 230V in my mains. Why should I use a torroid to get 15V AC and then another one to get back to 230V?
Why not take the 230V out of the mains and use one torroid to get the 15V?

 

[gemini86]

PSU Question:
If I have 230V in my mains. Why should I use a torroid to get 15V AC and then another one to get back to 230V?
Why not take the 230V out of the mains and use one torroid to get the 15V?

because the transformer is there for your safety...

If you accidentally electrocute yourself, (not as difficult as you may think) the transformer will limit current to a less 'instant death' level. If you went directly from the wall, a quick zap would dump whatever amperage the circuit will carry until the breaker or fusebox trips...

I said this before a few days ago, maybe it should be a sticky... NEVER take power directly from a wall outlet without isolation from a transformer. If you like, you could use a 1:1 isolation transformer. I haven't had much lick finding cheap ones here (may be a different story in 230v country) so step-down transformers or tube specific power transformers are the way to go.

 

[braeden]

In regards to the LED problem, what do you mean by + and - rails? you're just using the greater supply, right? 12v?

The greater supply? I'm running two wires from the PCB where it specifies "TO LIGHT 12V/50mA +/-" straight to the LED. 50mA is obviously too much current, so shouldn't an appropriate value resistor lower the current so I can use it for an LED?

Here's a measurement I did today of the left channel, D.I. input.

And a sweep with the microphone XLR input

Is this typical of the G9 frequency response curve? It sounds pretty good to me, lacks a bit of low end though but it sounds nicer than the API 3124 in my opinion which is a little too full bodied.

And here's the API 3124+ freq. response for those that are interested...

The G9 seems to have enough gain to blow me away but the API 3124 has an excessive amount of gain, to the point where it makes the G9 look weak... is this right or have I done something wrong?
Any comments are appreciated!

Thanks

 

[gemini86]

Sorry, my phone autocorrected me...

meant 'heater' supply... I have no clue why you would be popping LEDs on a 12v supply. Even running at 10mA which is about hald the typical max rating, you should only need 1k current limiting resistor. Are you sure you aren't using a 100ohm resistor instead of a 100k?

---

I do know that some feel the G9 is lacking in the low low end... but if it sounds good to you, why ruin it for yourself and run a frequency response sweep?

 

[G-Sun]

PSU Question:
If I have 230V in my mains. Why should I use a torroid to get 15V AC and then another one to get back to 230V?
Why not take the 230V out of the mains and use one torroid to get the 15V?

because the transformer is there for your safety...

If you accidentally electrocute yourself, (not as difficult as you may think) the transformer will limit current to a less 'instant death' level. If you went directly from the wall, a quick zap would dump whatever amperage the circuit will carry until the breaker or fusebox trips...

I said this before a few days ago, maybe it should be a sticky... NEVER take power directly from a wall outlet without isolation from a transformer. If you like, you could use a 1:1 isolation transformer. I haven't had much lick finding cheap ones here (may be a different story in 230v country) so step-down transformers or tube specific power transformers are the way to go.

Thank you!
I didn't plan to take the ac directly out of the wall, just curious
(Sorry for not seeing your previous answer)

 

[gyraf]

G9 frequency response will depend on 1) transformers used for the build, 2) source impedance of whatever driving it's input transformer.

I've only measured Lundahl versions, which gives you something like 34Hz-30KHz @ -3dB, 200 Ohms source into mic in.

OEP transformers are different, less lows, but sonically attractive in another way.

Jakob E.

 

[braeden]

Jakob, while you're here... when I was conducting the frequency sweep measurement, I noticed that when I do not have a 1/4" mono plug connected to the D.I. input and I record the sine sweep through the XLR input the response looks the following way (in blue) when it should look like the red. However, when I plug a cable into the front (even without any connection on the other end) it produces the expected frequency response.

(Gain is on the highest setting, no HPF, positive phase, all the way clockwise on the output pot and the input switched to mic)

Why is this? could this be the result of a faulty relay? It happens on both channels so I doubt both relays would be faulty  :-\

It's annoying, I want to wrap this project up and get started on my 1176 :-X

Thanks Jakob

 

[gemini86]

PSU Question:
If I have 230V in my mains. Why should I use a torroid to get 15V AC and then another one to get back to 230V?
Why not take the 230V out of the mains and use one torroid to get the 15V?

because the transformer is there for your safety...

If you accidentally electrocute yourself, (not as difficult as you may think) the transformer will limit current to a less 'instant death' level. If you went directly from the wall, a quick zap would dump whatever amperage the circuit will carry until the breaker or fusebox trips...

I said this before a few days ago, maybe it should be a sticky... NEVER take power directly from a wall outlet without isolation from a transformer. If you like, you could use a 1:1 isolation transformer. I haven't had much lick finding cheap ones here (may be a different story in 230v country) so step-down transformers or tube specific power transformers are the way to go.

Thank you!
I didn't plan to take the ac directly out of the wall, just curious
(Sorry for not seeing your previous answer)

I don't even know if I had said it in this thread. So no worries. There are a few really old guitar amps that used the wall voltage directly, but I wouldn't plug a guitar into one without addingan isolation transformer first. They also typically didn't havea three prong chord either, so you run the risk of having your guitar  strings floating at hv if something goes wrong.

 

[Orphin]

I have a question concerning the tele jack/line input. On the PCB there is from, to and ground. How do I wire this to the tele jack?

 

[gemini86]

You're going to want to look up the Di mod.

 

[Orphin]

You're going to want to look up the Di mod.

Huh?

 

[gemini86]

Sorry, i'm on my phone right now so, I can't provide the courtesy of doing it for you, so you'll have to use the search function (or google for that matter) and look up the DI mod. It involves citing the traces on the pcb and wiring the jack directly to the board with shielded cable to correct some hum issues associated with that part of three circuit.

 

[audiophreak]

Hi , Look  towards the bottom of page 34 of this thread , the graphic you're looking for is there. 

 

[gemini86]

Thanks audiofreak, mighty helpful of you!

http://www.groupdiy.com/index.php?topic=17980.msg448605#msg448605

 

[audiophreak]

Thanks audiofreak, mighty helpful of you!

http://www.groupdiy.com/index.php?topic=17980.msg448605#msg448605

  You're  welcome  .....  its nice to get one right every now and then    ;D

 

[Orphin]

Nevermind the mod. Right now I need to figure out what's wrong.
I've wired like this:

To --> tip of tele jack
From --> tip of tele jack that breaks when plug is inserted
Ground --> ground

I only get a faint sound from a guitar when I plug it in. It also seems as it doesn't matter if the routing switch is set to line or mic.
However, with a mic inserted to the XLR input the routing switch seems to work as it is supposed to.