The official G9 help thread

[Marvel]

Hello,

My first post to the forum. I'm Marcin, I'm from Poland and I specialze in building tube guitar amps.

I'd like to thank Jakob for this fantastic design. And Gustav for PCB's.

I built the G9 for a friend and he is very satisfied with the result.

Couple of pics below, they may be of some help for somebody.

Regards,

--
Marcin

 

[baol]

Hi, about xlr outputs: I'm using a mic cable, 2 wires plus shield. I solder the 3 strands on the xlr leeds, but on the other end it seems the middle pin it's not connected, have I got to leave the shelding un-solded?
thank you
Andrea

 

[baol]

...one more: now about toroidals.
They both have 1 primary and two secondary.
I'll connect one of the primary to the main switch and his secondary to the terminal block close to 13-16 diodes. But I have no idea about his other secondary.
Same for the other toroid.
I connect the primary to the "220" terminal (close to 13-16 diodes too), but no idea about his secondary.
thank you for this too.
andrea

 

[knight84]

Hi, I just have finished a G9 with a friend. As I finished tested and sorted out some weird problems. I am new to DIY and electronics, I might be missing simple things and question sorry for that.

This problem is only on the first channel . When using dynamic mic., the gain settings work fine. But when switch off as the mic is at the cable, on the highest settings I have a noise like radio frequency. Have it only at the highest 2 settings. When mic is on, there is no noise and the gain switch works fine and sounds nice. With a conderser needing 48V there is no problem. With a condenser with ex PSU, the noise is again on at these gains and the mic signal is also cut. The signal seems to be only negative value and nearly constant gain as I saw on my DAW.

My second problem is, the phase switch changes the sound quality and the sound gets thinner mostly losing low end.
This happens on both channels.

Lastly, I dont know the best way to measure the max gain but I am comparing G9 with Warm Audio WA12 and comparison gave me that it gives around 52 db max. I wish it better have 4-5 db more to use lower input setting while singing into my dynamic mic. The 2nd channel might be 2 db louder than the first one but not sure about it. I used lundahls and telefunken nos 12AU7.
By the way, it sounds very very nice. Nice sparker but no sizzle and nice low end with definition. I loved the sound quality.
As I said dont have experience and having difficulty on troubleshooting. Any idea will do help me! Thank you
Barbaros

 

[bruce0]

"Noise like radio frequency" . Please explain.  Do you mean you "Hear the audio from radio channels, actual clear or indistinct music or voices" or do you mean "you hear a high pitched whine like someone tuning an old radio in a movie"?

 

[knight84]

Yes it is like a high pitch sound like tuning an old fm radio. When I move my hand in the box around the tubes or touch caps the sound is changing. Also amplitude increases and decreases with the pot.

 

[bruce0]

I don't know what you are touching, but this thing has 250VDC in it, and some things you would only be able to touch once before you die.

As to the sound I don't think that is RF interference, I think that is a noisy tube, but wiser folks could chime in.

If it is radiation... then think switching power supplies.  Turn off dimmer lights, move computer power supply blocks away, close the metal enclosure it is in, these could all make a difference.

Is this with the input terminated (150ohm load or a mic plugged in)?

 

[knight84]

I know where the 245 V are on the circuit but will be more careful thank you. Yes it occurs when the mic plugged in. Can it be about this?: We used EMI filtered power in and we took the middle legs of the tubes to the ground on the circuit.   
We did some measurement with ossiloscop by the way. To 50 mV input we got 21-20V output. That is 400 times of input. I guess this is lower than 9*6=54dB.
Barbaros

 

[bruce0]

it is important to test with mic plugged in or with the input terminated by a resistor across Pin 2 and pin3 (150 ohms typical).  Under those conditions (with the shield grounded) the mic cable is a poor antenna.  So I don't think you are hearing RF


Unless..... you are un-terminating it....In your post, when you say "But when switch off as the mic is at the cable..." do you mean that you are turning a switch off on the mic itself?  Under those conditions is the mic still terminating the input? I don't know.

I have a simple male XLR with a resistor soldered across it, rather than a mic.  It is useful for testing, takes 5 minutes to make if you have a Male XLR connector lying around.


You say it only happens on one channel...  I have heard whines from a noisy tube at high gains.  If you switch channel 1 and channel 2 tubes, and the problem moves, then it is a noisy tube.

Have you tried swapping out the tubes for other ones? 

I know where the 245 V are on the circuit but will be more careful thank you. Yes it occurs when the mic plugged in. Can it be about this?: We used EMI filtered power in and we took the middle legs of the tubes to the ground on the circuit.   
We did some measurement with ossiloscop by the way. To 50 mV input we got 21-20V output. That is 400 times of input. I guess this is lower than 9*6=54dB.
Barbaros

 

[knight84]

it is important to test with mic plugged in or with the input terminated by a resistor across Pin 2 and pin3 (150 ohms typical).  Under those conditions (with the shield grounded) the mic cable is a poor antenna.  So I don't think you are hearing RF


Unless..... you are un-terminating it....In your post, when you say "But when switch off as the mic is at the cable..." do you mean that you are turning a switch off on the mic itself?  Under those conditions is the mic still terminating the input? I don't know.

I have a simple male XLR with a resistor soldered across it, rather than a mic.  It is useful for testing, takes 5 minutes to make if you have a Male XLR connector lying around.


You say it only happens on one channel...  I have heard whines from a noisy tube at high gains.  If you switch channel 1 and channel 2 tubes, and the problem moves, then it is a noisy tube.

Have you tried swapping out the tubes for other ones? 

Thank you very much. Today we changed the 470 nF caps with better ones. The noise when the mic is plugged while the mic is switched off is gone now. Happy for that but still have the phase switch problem.
The phase switch changes the spectrum of the sound. It looses some components of the spectrum. And still have a low amplification value. Around 400 times.

 

[bruce0]

You mean the 470nf at C5? Hmm.

As to phase switch changing frequency response.  Check for shorts around the relay.  But it is on both channels so maybe that is not likely.

400 times is what 50db?

Perhaps your gain and phase issues are related.  Some of the gain comes from the transformer step up.

What specific transformers are you using?
Have you got them wired right?
If PCB mount, have you switched input and output transformers or something?

Thank you very much. Today we changed the 470 nF caps with better ones. The noise when the mic is plugged while the mic is switched off is gone now. Happy for that but still have the phase switch problem.
The phase switch changes the spectrum of the sound. It looses some components of the spectrum. And still have a low amplification value. Around 400 times.

 

[baol]

Hi, who can explain me how to link the 2 "external" capacitors to the 245V terminal?
I'm using two JJ 50/50UF 500V radial caps, they have 3 eyelets and I don't know how to connect them toghether and to the terminal.
About the light: there is an output for a 12v light, are too much for a led?
thank you all and good easter.
Andrea

 

[knight84]

Hi, who can explain me how to link the 2 "external" capacitors to the 245V terminal?
I'm using two JJ 50/50UF 500V radial caps, they have 3 eyelets and I don't know how to connect them toghether and to the terminal.
About the light: there is an output for a 12v light, are too much for a led?
thank you all and good easter.
Andrea

As I know they should be minimum 100uF (can be larger). We used silicon gun to fasten it on the floor of the case. There are better ways done, like using a fastener for caps. For connection, the positive sides go separately to the pcb inputs dedicated for them (C14, C15) The negatives of each caps can be connected to each other with a cable then from one negative point, you can connect it to the negative point on the pcb ( the point between positives).

Barbaros

 

[knight84]

You mean the 470nf at C5? Hmm.

As to phase switch changing frequency response.  Check for shorts around the relay.  But it is on both channels so maybe that is not likely.

400 times is what 50db?

Perhaps your gain and phase issues are related.  Some of the gain comes from the transformer step up.

What specific transformers are you using?
Have you got them wired right?
If PCB mount, have you switched input and output transformers or something?

Yes C5 and C3 changed and noise problem solved. I measured the gain values with signal generator from DAW. Yes the first channel has 50dB and second has 50.5 dB max. I used Lundahl option, and telefunken ecc82. I saw a post of Jacob saying that, with lundahls the max gain is around 55-57 db. It seems 6dB lower than the target. Maybe the tubes maybe some bad caps have voltage leakage. But as there is a consistency over the channels, tubes may not be the problem. Hard to find nice caps in my country. When I have some other options, I am thinking to change a few ones.
Barbaros

 

[baol]

thank you knight84, I will follow your directions.
Have you any idea about using a led as light? are too much the 12V from the board?
thank you

 

[knight84]

I think you can find 12VDC indicator led light. I saw red and green ones a lot in local shops.

 

[knight84]

You mean the 470nf at C5? Hmm.

As to phase switch changing frequency response.  Check for shorts around the relay.  But it is on both channels so maybe that is not likely.

400 times is what 50db?

Perhaps your gain and phase issues are related.  Some of the gain comes from the transformer step up.

What specific transformers are you using?
Have you got them wired right?
If PCB mount, have you switched input and output transformers or something?

Yes C5 and C3 changed and noise problem solved. I measured the gain values with signal generator from DAW. Yes the first channel has 50dB and second has 50.5 dB max. I used Lundahl option, and telefunken ecc82. I saw a post of Jacob saying that, with lundahls the max gain is around 55-57 db. It seems 6dB lower than the target. Maybe the tubes maybe some bad caps have voltage leakage. But as there is a consistency over the channels, tubes may not be the problem. Hard to find nice caps in my country. When I have some other options, I am thinking to change a few ones.
Barbaros

I just realized that I forgot the diode next to the relays. Might that be the reason. The LL1528 have two wiring options and one has twice amplification of other(1:2.5 and 1:5). So that sound logical but the transformer legs were constraint to fit on the pcb and the pcb circuit uses the 1:5 option. I will change the relay and see what happens. And I can not be sure about 10 uF 63 volt caps' real value. It says DME F100 CDEC 106K on it but nothing else. Anyway I guess the first action I should do is put the missing diodes.

Barbaros

 

[wolan42]

Last week I finished my Espresso machine.
A Gyraf G9 Preamp.
It was this sort of frightening buildings.
I have to keep in mind the high voltage.


Got the case from Frank end of last year. The PCBs two years ago from Gustav.
It is build with the OEP transformers and moded Inst. input.


After checking all the wires and contacts for several times,  I switch the Preamp on without tubes.
No exploding capacitors, no burning fuse and no smoke. And I am still alive.
Checking the voltages show nothing wrong.


Test with old, not so expensive, tubes on my Apollo Interface.
Okay the tubes are noisy, but it works.


Change the tubes to NOS Silvanias.


No Noise and an amazing sound with one of my moded U87 Copies.
I plugged my Sandberg Bass in.
Wow. I am really thinking about to use it as bass preamp instead of my Glockenklang preamp.


Today we tested it in the studio with my Matador C 12 with Beesneez CK12 capsule.
A fantastic couple. Mac, the Studio owner, now want exactly this combination. ;-)
I will build the next one with Haufe In- and Output transformers.


Thank you to Jakob to share the design, to Gustav for the PCBs, Frank for the frontpanel and the community for the help threat.

 

[wolan42]

The next picure, sorry I don't know how to insert more than one.

 

[wolan42]

3rd one