G9 assembled - major issues

[netcastle]

I have finally finished assembling my G9. It took three months to get it together. When the moment of truth arrived, I was let down. Here are the problems I am experiencing.

1. No audio (this is the biggest problem). I grounded the input xlr's (pin 1) and the ground from the from iec connector to a single point on the chassis.

2. Massive oscillations at at ten and eleven clicks on the gain dial on the left channel (farthest from the power supply), and on the right at eight, nine, ten and eleven. The oscilations occur regardless of whether the selctor is set to Line, Mic or 48. However, when an instrument is plugged in there are no osciations at any gain setting in either channel.

3. There is noticable hiss on both channels.

4. With the volume all the way up I can detect 60 cycle hum faintly through the left channel and much more distictly on the right.

I built this project using Gustavs PCB, and I sourced the parts using both Byron's and Paul Stephen's list. The tubes I bought from Triode and were tested. I am using only two 100uf 350v caps. All of the onboard componets are not soldered flush to the board and the bigger caps where left standing about one half inch above the board. I did not use a heatsink on all componets when soldering.

I am inclined to believe that many of these problems could relate to grounding. I am greatly confused by proper grounding of this unit. If other's of you can clue into these problems please chime in. I would really love to join the club of happy G9 users.

Tim

 

[CJ]

Don't worry, all new projects start this way when testing. One problem at a time.
Our crack team of G9 techs will get you happy with this unit.
cj

 

[Emperor-TK]

Check that your control PCB hook-up to the main board. The symptoms that you describe sound consistent with having those connections reversed. Do you get any sound when you use the instument in jack? That would also indicate this situation.

-Chris

 

[netcastle]

No. The wires are correctly aligned. There is no sound from the instrument jack.

More info:

I used 110:110 15:15 30VA toriodals and OEP tranny's. I soldiered the cans in place by filing the metal on both part of the can and carefully running a bead around the edges. I only soldered two side of each can and not four and I fear the the cans are not entirely secure.

The tubes do glow when powered up.

The 78S12 is sinked to the chassis via a metal L bracket. The bracket itself is electricaly connected to the 78S12 but is isolated from the chassis with a thin piece of cardboard and a nylon nut and bolt.

Question: Shouldn't the outputs be grounded as well?

Tim

 

[gyraf]

Question: Shouldn't the outputs be grounded as well?

No. They share ground with the inputs, connected directly at the xlr's.

Jakob E.

 

[Rob Flinn]

Are the group of 5 wires from main boards to control pcb`s done with shielded wire? I had some problems initially because of this that are consistant with the trouble that you are experiencing. It only seems to be the group of 5 wires that give this problem.

There is also a thread entitled "G9 problems" which may be worth taking a look at.

 

[netcastle]

No, these wires are not sheilded. I will try this.

As far as grounding goes, pin 1 on both the inputs and outputs should be connected, and this connection should terminate at only one point on the chassis and this is the same point at which the power is grounded. Isn't there a grounding path already on the PCB that the inputs are connected to?

Tim

 

[gyraf]

[quote author="netcastle"]No, these wires are not sheilded. I will try this.

As far as grounding goes, pin 1 on both the inputs and outputs should be connected, and this connection should terminate at only one point on the chassis and this is the same point at which the power is grounded. Isn't there a grounding path already on the PCB that the inputs are connected to?

Tim[/quote]

There is a ground at the input connector. This goes to the XLR's pins1, and to chassis at one of the XLR inputs. This is also where you mount the mains guard ground. It's all described before - try searching some..

Jakob E.

 

[netcastle]

I'm sorry if I sound naive and I certainly don't want to waste anyone's time. I have looked at all of the literature available for this unit. Perhaps its just that I don't understand the concept so much as the actual application. However, I am reading further. I think that I may have bit off more than I could chew, but I am going to make this thing work regardless.

Tim