The official G9 help thread

[rock soderstrom]

Thank you Jakob, yeap right, ohm numbers say nothing from themselves. I will finally end up with OEPs. But i am thinking of also trying a pair from a local well known winder old man here, for one channel, just for experiment. He can  wind them for me in any ratio and specs desired for really low cost, a few bucks both like. He usually builds power and power out trannies for valve circuits and is well known for this here. Different story i onow but he has also built some  in and out audio trafos in tube pres and mics for other guys with  good results as they say. So why not taste too?
I know he uses M6 core, open type and told me he could get about 20-20K, 0db ( ???). Didn't spoke a lot about inductance when i mentioned to.
So according to your scheme what would you suggest i could tell him wind? I know again it's very generalized and vague but just a starting point. Don't hurt experimenting i guess. And if they don't "pass the tests" i could probably use them for smthng else in the future.
Told him about 1:5 (600:10K) for input and something like 4:1 (2400:600) for output. 250-300mV and passed him the scheme. He understood we have to do with mWatts here indeed. What other points should i mention to him?

Peace.

I wish I had such a winder here in Berlin!

Your math is wrong.
The impedance is quadratically related to the turns ratio. For example, a 1: 5 transformer has 600: 15K impedance, i.e. multiplied by 25.  A 4: 1 transformer has an impedance of 10K relative to 600R, i.e. divided by 16. The 2400: 600 you mentioned would be a 2: 1 transformer.

 

[Philip_BlueFX]

Hello.
I have two questions on the G9 builds.
Firstly, I noticed most builds use big, out of the board smoothing capacitors for the +HT.
I am building mine on point to point fashion instead of a PCB and I used a couple of Samwha 100uF/350V THT (they go at 0,70€ at tme.com). Scope says that my ripple ~4mVpp which is pretty fine. Is there a reason I should upgrade to a better quality (I found some Nichicons at 5€ each, same value) caps when ripple aint an issue?

Second question is about a noise issue I have, regarding my output valve. I should add that my build is a single channel G9. Also, I do not have the in-out transformers yet. I have built a balanced/unbalanced circuit with OpAmps for the in-outs but my noise issue is present either with, or without the balunbal circuit.
Noise Problem: I get pink noise out of the SRPP Tube as shown in my spectrum analyzer (through Studio One). I poked around with my oscilloscope and I believe that this noise starts at the SRPP output (pins 1/7/8 of V2) and is not present earlier. I tried to switch the valves with one another with the same results.
Also the noise level is affected by the volume knob and not by the gain.
Would this be a component issue? Could this be the out impedance not matching the SRPP?

With the original ll5402, what's the impedance that the V2 "sees"?
Thanks for any helps.

 

[gyraf]

Noise is everywhere - how much do you have exactly, and how much did you expect there to be (from the involved impedance and the gain)?

This thread is meant for support of the DIY-project - it's not really within the scope of this to trace possible errors on heavily modified or altered circuits. Perhaps Drawing board is a better place for such undertakings?

/Jakob E.

 

[Philip_BlueFX]

Well, it didn't occure to me to be honest. I'm taking this to the Drawing Board.

What about my capacitor concern? Is there a reason I should upgrade even if I don't have high ripple issues?

 

[HerbertR]

Hi, I have also finished my G9. Except of one Problem everything works fine. The Unit sounds great.
I have a static 100Hz Hum Problem. It is independend from Gain and Output Pot settings. Not really high but a little bit to much. Same on all two channels.
What I also have recognised is that the twoTransformers (15v and 12V) also make a little bit louder Hum-Noise Vibration in the Case than normal builds from me. But this depends on where they are placed in the Case. Yes, I did the Oszillation Mod with cutting the traces and using a shielded cable
To get rid of the 100Hz Hum I have tried a lot of things:

-checked the grounding schematic like recomanded:.  ICE-> Starground<-Pin1 InputXLR<PCBGround, All other three Pin1 XLRs connected to one Input XLR, you can can connect, disconnect.... No changing improvement with the static 100 Hz Hum
-replaced the Regulators 7812 and 783, no changees, Voltages seem to be correct / HT Out 246VDC,  after 12V StepupTransformer about 305 Volt AC the three Zener show good Voltage Values 270/250/250V,
12V DC shows 11,9V
-replaced the Reservoir Caps to higher Ones with 450V 470uF, no change
-I also replaced the 12V Transformer, no change with the static hum
-resoldered all Joints...

One thing to mention - I am using actually 5x11V Zeners in serial till I get my 56V Zener for the 48V Phantompower. Can I also try a 62V Zener to get rid of the static hum to test till I get my 56V Zener deliverd?

I would really appreciate it if someone had a few ideas. BR

 

[HerbertR]

I am using new JJ Tubes. Could they cause the static 100Hz Hum Issue?

 

[HerbertR]

Hi, I have solved after hours the "static hum 100 Hz" Problem. There is a link anywhere in this Thread to that Issue.

So I also canceled the HT+ Supple on the Mainboard and "outsourced" with additional PSU PCB Outcut from the Controlboard. I only outsourced the HT, not 12V DC Supply. This 12V DC Part remained in the Main PCB.
Here are my Summary of recommanded to get rid of Oscillation, Hum and Noise:

- Outsourcing of the HT+ PSU Part at the Mainboard using the small remaining HT+/12 additonal PSU PCB, the 0V connection from the big ReservoirCaps goes in my Build directly to the Star Ground - Grounding of the these Caps on dedicated Connection has caused the most 100 Hz Hum

- Useing the recommanded Grounding Schematic with Pin1 Input to the Ground

- Useing shielded Cables for all Audio Lines like XLR Connections, Instrument Connections/Oszillation Mod, drill all other Cabels especially for ACs, ...

-Do the Oszillation Modifikation, this mod is in most cases absolute Necessary to get rid of the that

- Check the Instrument 6.3 Jack if "To and From" is reversed or try to reverese the Cables if anything feels not common like additonal Hum if using the front Jacks...

- check if you use the OEPs - the Cans should have a connection to the Ground or they are very sensitive!

-Transformers as far as possible away from the Tubes, Audiotransformers, XLRs...

By the way I am not a Electrical Engineer and this Build was really hard to get a propper working Unit. This piece is an excellent sounding Unit, behaved clean sound. Sound very expensive...
And yes, a first Quicktest show that the OEPs have from 60Hz to 20kHz a very linear Frequency Response. Under 55Hz to 20 Hz they are causing a Bass Roll off of about 3-4 dB at Line Mode with Line Level, 0dB 0,775V Output. So you should think about it, if you need this Lowend Range, or you prefer this little extra Preparation for the Mixing....

 

[HerbertR]

The Additonal HT/12v PCB

 

[HerbertR]

PCB

 

[HerbertR]

Nearly finished and perfectly working...

 

[gyraf]

..beautiful..

Is that case from Frank?

/Jakob E.

 

[HerbertR]

Yes, he is a good man. He corrects  also the (most) mistakes made in in my .fpd s, like colours, ....

 

[Philip_BlueFX]

Hey, on a 2+2:1+1 Transformer, this kind of winding should result in a 4:1 output.
Am I totally wrong? 1st windings in series while 2nd wirings in parallel.

Also, what is the need for the 10k resistor on the 'phase reverse' switch?

 

[gyraf]

yes, it's wired 4:1. The loading resistors tames spikes when switching polarity

/Jakob E.

 

[Grooveteer]

My G9 is coming along nicely. 

There is a slight hum (that goes away when I flip polarity on one of the channels by the way). 
The grounding is as in my beautiful MS paint artwork in attachment.

I only have a ground connection to the PCB on IN 1.  I think this is supposed to be OUT 1 (not in)

Is that likely to be the problem?

DI traces are cut, and since I will not be using the DI I have closed the circuit with a wire bridge on the PCB

I'm using a shielded toroid and a MU metal shield around it. (probably overkill, but I had it laying around)

 

[earlfsmith]

Looks nice! I'll be starting my mine in a few weeks once all the parts are delivered. I'm building two units. Thanks Jakob for this project! 

 

[innercityman]

Hi,

I decided to build the 245V Ht and 12VDC psu out of the board as I can't get rid of the famous 100HZ noise. I read on the thread that it was the solution. Unfortunately when trying to separate the switch boards I broke some traces on the spare psu board so I throw it away at the time. I'm gonna build the circuit from a blank board following the schematic and trying to copy the spare psu board layout, anyway... Can someone who did that help me in this build ?

I have few questions, mostly about wiring psu board to the main one...

- Where's the best place to connect the 12V heater on the main board ?

- Do I have to cut some traces ?

- From where do I take 0V ground on psu board... Chassis or board ?

- Is it better to connect 0V of both 470uf reservoir caps to chassis ground ? Does it improve noise issues ? I did that with my classic build but no improvement with 100HZ noise.

Thanks for your help.

 

[innercityman]

Ok I found out, sorry for the stupid questions.

I decided to just move the 245VDC out of the board first and see if it solve the 100HZ noise issue. If not, I will move the 12VDC too on another board. And if not, I'll try to replace it by a regulated LM317 AC/DC converter psu board. I've read that it's a noise free 12VDC solution for a lot of builds.

 

[innercityman]

Can someone help me please ?

As I said before, I've built the 245VDC psu out of the board and as soon as I powered up the unit the bridge rectifier blew up with smoke. I had the same behaviour with the on board psu. Each time after fire up, I had a little smoke cloud coming from D17 to D20 diodes. So, I disconnected the power trafo and measured tensions coming from it.  This is the expensive big one dedicated to the G9 from Don Audio, and I got around 310VAC from the first secondary. My opinion is that this transformer is faulty.

What do you think ?

Thanks for your help !

 

[rock soderstrom]

Can someone help me please ?

As I said before, I've built the 245VDC psu out of the board and as soon as I powered up the unit the bridge rectifier blew up with smoke. I had the same behaviour with the on board psu. Each time after fire up, I had a little smoke cloud coming from D17 to D20 diodes. So, I disconnected the power trafo and measured tensions coming from it.  This is the expensive big one dedicated to the G9 from Don Audio, and I got around 310VAC from the first secondary. My opinion is that this transformer is faulty.

What do you think ?

Thanks for your help !

Your transformer is fine. Without load the AC voltage is higher.

The problem is somewhere in your build. Smoking rectifier diodes is sign for a very low resistance betwen HT and Ground, probably a dead short.

It is pretty hard to help you from the distance. Check your build again and show some photos of it.