G9 noise and hum problem

[Wolferl]

In supplement to my message from May 17:

With the new replaced TL783 I did measurements with an analyzer software and the hum @100Hz is really a bit lower. About -95dB - this is 10dB better than with the former TL783. So this IC has big tolerances in ripple rejection...

But even -95dB@100Hz is still audible, because this is a permanent hum without influence of gain and output level. :roll: :twisted: What happens if I replace this IC with another ...? :?

 

[maxime]

hi
my sony mxp 2000 (which has good noise specs) has the output noise at about -80dB... look no further -95 db is more than adequate!
you don't mention where the signal destination, and maybe your problem lies there (-10 dB consumer input level equipment for example)
best
Maxime

 

[ioaudio]

you could try to leave out the regulator and replace it with a (2w) resistor. something like 10k, maybe less for two channels.
measure volts after the rectifier and milliamps after the regulator for finding the correct value. add another rc stage for more ripple rejection. dont forget a bleeder (something like 150k 2w)
when i breadboarded the g9 for testing i did this (couldnt find a tl783 at that time)

 

[Wolferl]

@maxime
Noise is not always noise in the same meaning. My G9 has a permanent output level of about 95dBu@100Hz + harmonics up to 2k at no gain. When I compare this to a cheap T1953 i got:

F(Hz); G9(dB); T1953(dB)
50; -99; -100
100; -94; -113
150; -108; -114
200; -99; -123
250; -108; -114
300; -115; -126
...
So you see, the G9 has same 50Hz hum + harmonics but much more 100Hz hum + harmonics and this is audible - it doesn't matter if the next stage has consumer or pro level.

@ioaudio
Good idea! I will check this.


Regards and thanks to all,

Wolfgang

 

[tony dB]

if you disconnect the mixer behind this from the mains earth, do you get a difference? Sorry if I'm way of here and your measuring/listening without mixer.

 

[Wolferl]

Thanks anyway tony dB!

In the meantime I mounted a switch at the back panel to lift the ground... :grin: but in most situations this is not really neccessary.

 

[pstcho]

Hello, i made several G9 through the years, my first was in 2006 i think

i replaced the tubes a couple of time since then and they have been used quite a lot

since some days, i have a weird hum at 50Hz coming up after some minutes of use ( 15-20 minutes )

It is the same on both channels

When i put all volumes and gains down, the main hum drops significantly but still exists, if i reverse the phase on one of the 2 channels, the hum disappears, when gain and volumes are up, with phase reverse i dont get rid of it, so the hum is well amplified and distorted by the tubes

i compared voltages with my other builds and everything seem fine more or less 5% so i guess it is very fine

i tried to replace the tubes and no difference

Any advice where to check ?

thanks for the help

 

[VerreyckenGerd]

I just finished my G9 and have mains hum without any harmonics on th higher output levels.
While using condenser microphones this is no issue due to the high signal from the mic but when preamping passive guitar/bass it is an issue. Did you guys find a solution?

 

[ruffrecords]

It sounds to me like both of you are running the output too low. -95dBu hum is a very respectable figure and if the output is running at 0dBu then the hum will be totally inaudible. I suspect your interface is too sensitive so you are forced to use the G9 with a lower output. For example if your interface clips at 0dBu and you record normally at -18dBu then the G9 will be running at -18dBu and the signal to noise will suffer the same.

What interfaces are you using?

Cheers

Ian

 

[VerreyckenGerd]

I use a pair of MOTU 828 MK2's and am convinced (I could be wrong) to fully understand how to  utilize the best signal to noise / headroom /suturation / noisefloor of a preamp.  The next thing I gonna change is some extra high voltage caps. I only used 100µF as mentioned in the BOM on the gyraf site. After building I noticed 220µF in the schematic afterwards. I suspecxt this could improve the situation.

 

[ruffrecords]

I use a pair of MOTU 828 MK2's and am convinced (I could be wrong) to fully understand how to  utilize the best signal to noise / headroom /suturation / noisefloor of a preamp.  The next thing I gonna change is some extra high voltage caps. I only used 100µF as mentioned in the BOM on the gyraf site. After building I noticed 220µF in the schematic afterwards. I suspecxt this could improve the situation.

I hope you are right. However, I looked all the way through a MK2 manual and nowhere does it give any information about the analogue performance or the input levels it can handle. I even looked on their web site under tech specs and again absolutely zero info on the analogue side. As I said before , -95dbU output noise is a very respectable figure for any analogue device so if this level sounds noisy to you then there must be something wrong with your gain staging.

Edit: Exactly how are you measuring the output noise of the G9?

Cheers

Ian

 

[VerreyckenGerd]

Solved,

A pair of 460µF 450V 105°C United Chemi-Con caps arrived and solved my hum problem completely.
I haven't done any measurements. Only used my ears  on this one. Now it is dead silent.

Thanks for the support.

 

[biosynth]

Solved,

A pair of 460µF 450V 105°C United Chemi-Con caps arrived and solved my hum problem completely.
I haven't done any measurements. Only used my ears  on this one. Now it is dead silent.

Thanks for the support.

thanks for this info, will try that. (I have hum issues with my four G9 pre)

 

[biosynth]

It's nearly perfect about noise

One tip for future builders: be very carefull about power switch, put its cables as far as possible from front pcb. Also put shortest cables possible between torroidals power transformers and main pcb. These improvments have contributed for lowering 100HZ noise in my situation a lot more than "star ground mod" and "fat C14 C15 caps mod"

:-*