The official G9 help thread

[Godders]

[quote author="CurtZHP"]How does one say "Duh!" in Danish?[/quote]
Düh?

:green:

Cheers

Nick

 

[CurtZHP]

I've got a few pictures of my G9 construction on my website. Check them out and tell me what you think!

http://www.zerrohouseproductions.com/

Go to the preamps page.

 

[Sandersonic]

Hi Everyone,
I've decided to build a G9 and have been slowly working my way through this thread to avoid asking any redundant questions. I've allowed myself the shortcut of ordereing pre-made PCB's from Gustav and will begin buying components soon. One question I wanted to ask is if anyone has modified the design to allow for toggle switches instead of rotary switches for the Input, Phase and Lowcut switches? It looks feasable when I look at the schematic, but when I look at the control board layout it seems a bit more complicated.

Thanks!

 

[laiben]

Hi,

Sorry to report so late. I swapped two OEP output transformer and then the other channel got the same problem, so I concluded that one of the output tranny was dead. I ordered another tranny from Farnell and last night I put the new tranny to the dead channel now it works! The only problem is I got the oscillation when the gain is at MAX. I chopstick it and the oscillation change when I move the cable to the direct jack socket (I already used the "cut-the-trace" approach to avoid the oscillation, but I didn't cut the trace on the pcb. I don't want to damage the pcb just because I can always "fall-back")

Tonight I will try to re-solder the jumper cable to the jack socket to see if it helps.

BTW, what can I do with the dead output transformer? I don't think Farnell will give warranty on the used transformer...


laiben

[quote author="laiben"][quote author="gyraf"]DC points arenot that bad off - Maybe a short at the transformer solderings?[/quote]

It is very hard to desolder the transformer from the PCB to check.. hope not the solder goes into the shield when I put the mu-metal sheild on the OEP... will report the result.[/quote]

 

[jdr]

last night I put the new tranny to the dead channel now it works!

:thumb:

the oscillation change when I move the cable to the direct jack socket (I already used the "cut-the-trace" approach to avoid the oscillation, but I didn't cut the trace on the pcb...)

From the pictures that you posted a few pages back, it looks like you aren't using shielded cable to connect the intrument jack to the transformer and cap. Try using shielded cable instead (ground the shield at one end only). If that doesn't work by itself, then cut the traces. I think that even if you have connected wires to bypass the PCB traces, that the uncut traces will still be able to induce oscillations in the circuit...(?)...

Hope that helps,
John

 

[laiben]

Thanks for the tips John. Actually I already replace the jumper wire with shield cable, the problem still exists. Tonight I will cut the trace!!!


laiben


[quote author="jdr"]

last night I put the new tranny to the dead channel now it works!

:thumb:

the oscillation change when I move the cable to the direct jack socket (I already used the "cut-the-trace" approach to avoid the oscillation, but I didn't cut the trace on the pcb...)

From the pictures that you posted a few pages back, it looks like you aren't using shielded cable to connect the intrument jack to the transformer and cap. Try using shielded cable instead (ground the shield at one end only). If that doesn't work by itself, then cut the traces. I think that even if you have connected wires to bypass the PCB traces, that the uncut traces will still be able to induce oscillations in the circuit...(?)...

Hope that helps,
John[/quote]

 

[laiben]

I cut the trace on the pcb, now the oscillation is gone!

However when I test the noise level of the preamp, when both gain and volume is at MAX and no mic is connected. Though my ear hear nothing from it, it gives around -85db (ch.1) and -90db (ch.2) of noise in my Tracktion.
Screen capture is here. The peak frequency is about 40hz. Is that normal?

 

[laiben]

I remove the direct jack jumper cable and short it directly on the pcb, the noise still exists. So I can conclude that the noise is not introduced by the jumper cable. Also I notice that when the phantom power is on the noise is a bit louder (on the DAW, my ear still cannot hear the noise).

So, am I done now?

 

[Ilya]

I'm not sure if this is an issue... I've just built a PSU for G9 (no other components on the board yet), and everything seems to be fine except one detail. I'm seeing a suspiciously high voltage after the tripler and befor the collector of TIP121. It measures in the 80-85V range. After the regulation it's 48 though. Now, my concern is that those lythics are specd for 63V and 85 is much more than that. And I can't get it how 15 (ok, 16.5 'cause the PSU is unloaded) turns into 85 which is almost 6 times more. Is this because I have no load connected? Or have I screwed something?

 

[originalmusician]

Could someone straighten me out on Skylar's G9 wiring diagram? The primaries of the first transformer are connected in parallel (i.e. 115v). Power then flows across the to the secondaries. Now BLK and ORG are 0v and Red and Yel are 15v. Is this correct so far?

If so, The Yel 15v wire connects to the board and then to the Blk/Org secondary of Transformer 2. Keeping in mind that Blk and Org are 0v on transformer 1, wouldn't we want to connect the 15v yellow wire to Red/Yel of transformer 2 instead of Blk/Org?

 

[josh]

I can tell you that mine is hooked up exactly like that and is working good.

 

[originalmusician]

Okay, thanks for replying. The more I look at it, the more correct it seems. It makes sense that I would want the 110 on top and bottom of primary of transformer 2 as opposed to the middle. It took me a while to get that. I'll hook it up as shown. :grin:

edit: And thanks to Skylar for making this diagram. It has been extremely helpful.

 

[originalmusician]

Well, I managed to slam the thing together, but it turns out I don't have the correct length 1amp fuse to fire it and see if it smokes. I'll have to go to radio rip tomorrow and pick some up. The waiting is killing me, but at least I managed to get this far. This pre is a heavy solid piece of hardware and is more impressive looking when built than I was expecting. I can't wait to see how it sounds. :grin:

 

[originalmusician]

Progress update: I got the fuse and fired the G9 up. The good news is nothing smoked. But I do have a few problems. The right channel oscillates on the last two gain setting when in mic mode. I think I read when this happens to cut the traces and wire the line ins directly?

The left channel works fine up until the 4th or 5th gain click, and then the gain knob has no affect from there until the top of the range. I'm guessing the problem originates from the switch or its card as the tone of the pre is not affected. The switch just stops increasing the gain after the 5th click. I guess the best way to find out is to swap the gain cards and see if the problem reverses channels.

Despite these problems, both channels sound excellent. This pre has a very strong tube flavor on both the mic input and line input. Obviously that's because it's a tube pre, but I guess I'm saying that the sound is very flavorful, classy, and distinctive. This is an excellent project, and I am really grateful to Jakob for providing us DIY guys with the opportunity to build a piece of studio equipment of this caliber. To put it mildly, I love this thing! :grin: :guinness: :sam: :thumb: :green:

 

[laiben]

Use "cut-the-trace" method, it works on mine.


[quote author="originalmusician"]Progress update: I got the fuse and fired the G9 up. The good news is nothing smoked. But I do have a few problems. The right channel oscillates on the last two gain setting when in mic mode. I think I read when this happens to cut the traces and wire the line ins directly?

The left channel works fine up until the 4th or 5th gain click, and then the gain knob has no affect from there until the top of the range. I'm guessing the problem originates from the switch or its card as the tone of the pre is not affected. The switch just stops increasing the gain after the 5th click. I guess the best way to find out is to swap the gain cards and see if the problem reverses channels.

Despite these problems, both channels sound excellent. This pre has a very strong tube flavor on both the mic input and line input. Obviously that's because it's a tube pre, but I guess I'm saying that the sound is very flavorful, classy, and distinctive. This is an excellent project, and I am really grateful to Jakob for providing us DIY guys with the opportunity to build a piece of studio equipment of this caliber. To put it mildly, I love this thing! :grin: :guinness: :sam: :thumb: :green:[/quote]

 

[originalmusician]

Thanks, I used the cut-trace method, and it solved the oscillation problem completely!

Interestingly, switching the Lorlin cards did not change the problem with the gain maxing out at position four of the left channel. Up till position 4, the gain is actually a little louder than the right channel, but after that, it does not increase. Switching front panel cards had no effect. I'm currently at a loss.

Also, when I cut the traces and put things together, I lost ground to the main board. If I run a ground wire from the power Cap ground to chassis ground, things get extremely quiet. But otherwise, the board is floating free of ground. This one seems easier to diagnose than the left channel gain problem, so maybe I stand a chance of figuring it out.

It looks like I have a lot of work to do. I'm not real good when it comes to electronics, so I appreciate any advice or feedback. :thumb:

edit:

Gain problem plan of action: Next I'll check the wires between the front panel card and the main board. If that doesn't work, It looks like I'll be getting really familiar with the schematic and begging for info :grin:

 

[gyraf]

Up till position 4, the gain is actually a little louder than the right channel, but after that, it does not increase.

Look at the schematic of what the gain switch does. It depends on a voltage divider - the feedback resistor (R10 - 47K) and then the variable resistor to ground.

If this divider dosen't work (i.e. wrong/missing/shorted parts), then you only have the first four "attenuating" gain steps to work with.

Jakob E.

 

[originalmusician]

[quote author="gyraf"]

Up till position 4, the gain is actually a little louder than the right channel, but after that, it does not increase.

Look at the schematic of what the gain switch does. It depends on a voltage divider - the feedback resistor (R10 - 47K) and then the variable resistor to ground.

If this divider dosen't work (i.e. wrong/missing/shorted parts), then you only have the first four "attenuating" gain steps to work with.

Jakob E.[/quote]

Hi Jakob:

Your post was very helpful. I think I've traced the problem to either a bad C7 or a bad solder joint at C7. I was going to pick up a couple of new caps anyways as the ones I am using are too big to fit the board. I don't think I can get Wima's but Digikey should have something that will work.

Interestingly, my meter reads 75v feeding the C7 caps. I'm using 100v rated caps right now but the schematic lists these at 63v. Do you think my high reading is problem with my circuit? Should I stick with 100v caps or should I try to bring the voltage down that is feeding the caps?

Thanks! :grin:


Edit: I had an extra Wima 100v cap for C7 laying around, so I soldered it in, and it fixed the gain problem. I think I'll pass on buying new caps that fit the board better and call this good. The pre sounds fantastic!

 

[Stagefright13]

Hey have a look at my new G9! Tell me what ya think and be honest. I can take it...

But seriously any tips? I think I am gonna cut the traces from the get go. But other than that any advice would be welcome. And thanks in advance everyone. I am VERY excited about this one! Something about tubes and trannys just gets me psyched! And thanks Gyraf for making something like this available for everyone. You Rule!
:thumb:

 

[originalmusician]

[quote author="Stagefright13"]But seriously any tips? I think I am gonna cut the traces from the get go. But other than that any advice would be welcome. And thanks in advance everyone. I am VERY excited about this one! Something about tubes and trannys just gets me psyched! And thanks Gyraf for making something like this available for everyone. You Rule!
:thumb:[/quote]

Good idea to cut the traces from the start. I thought I had the noise out of my line ins, but when I finally got my studio back together, I discovered I still have a problem even after cutting the traces. So I still have a little work to do there.

The sound of this thing with a guitar plugged in is excellent (OEP trannies). It has a very sweet flavor to it that inspires a playing style that is distinct from any of my guitar amps. It is mellow, sweet, tube flavored, and compressed.

Plugging my 5 string bass in doesn't produce as good of result as my Groove Tubes Brick. The upper strings sound great, but the lower two strings are muddier than the Brick. Perhaps this is a problem with my G9 and doesn't show up on others? I'll have to try my 4 string bass and see if this changes my opinion.

As far as mics go, my g9 is very saturated. The sound is excellent, but it is characteristically tube distorted even at the lower settings. This could be a problem with my particular build, but right now I'm thinking, if it is broken, don't fix it. IOW, it sounds cooler than sh!@

I picked up Purusha's case for this thing, and I'm really glad I did that. Not only does it take a lot of work out of the assembly, when you are done, you have a high quality looking unit.

Take your time when you solder the boards up. Upstream care will save a lot of downstream headaches. Truthfully, there is enough info already posted to put this thing together without too much agony as a lot of people have already done most of the work for us. The only hitch is going to be if you solder something incorrectly. Then you are in an entire new ballpark where instead of paint-by-numbers, you have to understand why things work the way they do. But depending on how familiar you are with electronics, that can actually be a good thing. Just be careful with the high voltages. My caps drain down pretty fast once the thing is shut off, but you definitely want to check them with a meter before tinkering. Be extra careful when the unit is actually turned on and you start tinkering around inside measuring voltages etc. Okay, I have to admit, I only got shocked by this thing one time--so far :guinness: :sam:

I'm aware that you probably are a lot more familiar with electronics than I am. I'm pretty much just putting the voltage shock stuff and other basic stuff here just as a general warning to others.

One thing I'm unsure of is that my big power caps (c14, c15) don't measure evenly. I have 240v on one and 270v on the other. Does anyone know if this represents a problem?

Good luck, this is a really super cool piece of gear! :grin: