J99 buzz

[kid]

I have a CH01 with 2 A12's in slots 1 & 2 and two J99's in slots 3 & 4. Slot 3 with either J99 has a buzz when the gain is up at around 9. I am at 9 because I was using a Beyer M160 ribbon mic recording a mandolin. I checked the front panel and I definately took off the white paint around the holes. What else might I try to eliminate this problem?

[davidkakon]

I have the same problem with my beyer and my j99's. Its most likely something interferering with the PS, do you have any racked units above or below the preamps?

[kid]

I do have a rack of 4 N72's below it. I took the J99 rack out of the rack and still have the same problem. Is there a way to post audio samples of what it is I am hearing on this forum?

[Jarek]

I have the same buzz on mine J99's output. It seems that it has something to do with the power supply. My N72's or A12's do not have these symptoms.

I have 220V 50Hz out of the wall. In shot below you'll see the output of U2 pin 6 (yellow) and trannies secundary output just before the bridge.
http://www.borasband.nl/pics/TEK00001.bmp

The second shot is the output glitch magnified. Amplitude gets pretty high. That's what you hear.
http://www.borasband.nl/pics/TEK00000.bmp

Output of J99 is connected to ADC input. J99's input is floating. Connecting a mic lowers the glitches but they're still audible.
The gain switch and fader are full open.

As you see the glitches have double freguency of the power supply => 100Hz. I couldn't see those interferances at any of the power lines with my scope.
Could anyone confirm 120Hz buzz in America???

I've checked component values on the preamps. They're OK.
Both of my J99 channels suffer this way.
Tim???

[davidkakon]

im sending my case to Tim at the end of the month to add 2 more n72s, I asked him to look at my j99s. He suggested it might be a power supply issue

best
david

[Category 5]

Mine do it too, although not noticably with most high output mics. It's death for my ribbons though, since I need max gain and at that level the buz is almost as loud as the source.

I am interested as to whether a psu modification could correct this.

Shane

[tele_player]

Using ProTools , my two J99's into line inputs 5 and 6 on Digi002, at max gain with nothing plugged into the input, have a 120Hz buzz (US 60Hz mains). These are in positions 3 and 4 (counting from the power supply) of the chassis, and the amplitude of the buzz is noticeably higher on #3.

Things to note:
- noise measurements shouldn't be done with an open input
- I didn't measure the amplitude of the noise
- I didn't swap the positions of the #3 and #4 preamps to determine if the increased amplitude is the result of proximity to the power supply.

[Jarek]

My J99s are in slot 3 and 4 as well. I've noticed indeed that the buzz on channel 3 is stronger.
My rack is open anyway so I'll swap 3 and 4 just to see if buzz amplitudes will move with PCB.

I'll connect an external power supply to see if the buzz is caused by PS02 or not.
I've tried to tracked down the source of the buzz in J99 but I can't see anything. Buzz show up on pin 6 of U2, power lines are clean.
Nevertheless the buzz goes in sync with the power. It looks like as
soon as the large caps on PS02 have to deliver HF sweep is generated.

Got to go. I'll post the results asap.

[Category 5]

Mine are in slots 7 and 8, but I just noticed that all the modules have the buzz when at full gain.

I tried unplugging everything in the proximity but it doesn;t decrease the buzz. It seems if I run independent of my snake the hum is reducede, but I don;t get the hum on my MP20 even with the snake so I'm not sure what's up.

It only affects me when I try to use the ribbons, but I have been wanting to use the J99 for my ribbons and have been stuck using the MP20. Using condensors the signal is WAY higher than any preceptable buzz and teh sound of all 3 modules is sweet as it gets.

Shane

[vocalworld]

Hi,

I have ordered 6 of the J99 some days ago and now I am waiting for them. But the postings in the moment concerning the buzz make me uncertain if I had done the right choice of preamps. I hope that Tim will find a solution.

I had some trouble with a Focusrite ISA 428 preamp some months ago. There were some crosstalk problems between the 4 channels. It seems that Focusrite has this problem with all ISA 428 and they are working on the problem now. But I have given my 428 back to the seller and hoping now to have luck with the J99!?

The J99 has Lundahl trannies as the ISA 428 has them, too. Maybe there is an influence from the transformer of the power supply into the lundahl trannies? Could this be? Concerning my 428 I could messure also an interference of the double frequency. But in my case with the 428 there was no influence from the power transformer however the signal from one channel to another was going over with the double frequency.

Maybe someone has an idea how to test if there is an interference from the power transformer to the lundahls?! Its just an idea.

Mathias

[Jarek]

I didn't have much time today but I've moved my first J99 to 8th channel position. The buzz ampl. dropped by more than factor 2.
Channel 4 buzz is now louder than the 8th. The PCB from 8th channel in slot 3 is making more noise than the 4th.
So the buzz amplitude vary with PCB position in rack and it's not a PCB's property

Often the diodes (and their switching behaviour) are blamed for any HF sweeps. Tantals or low F discs are then used to shortage them (HF interf.) as they have very low internal resistance. But there are tantals already present at every power line for opamps used in J99.

I'll try external power supply asap.

[Jarek]

Power supply is to blame. You can simply test it by turning fader and gain full clockwise. Listen to the buzz, then switch the off power. The PSU has enough capacitance to keep J99 working for a while.

I'm gonna change the bridge for soft-recovery diodes. I think that this can help. I'll post the results.

[kid]

Is anyone else experiencing this? Tim is this something you are looking into? I need to redo my Mandolin session and would like to use my ribbons with the J99's. I guess I could make another harness and move the J99's as far away from the power supply as possible. I would hope there is a more elegant solution.

[Category 5]

I mentioned in another thread, but thought I should post this here too. the noise issue is starting to sound like a bigger issue here than it really is. With 70db, at FULL gain "yes" you can hear some buzz, but in 98% of situations, especially with condensors it should never be a problem.

Also, anyone think that twisting the transformer wire pairs might help with the issue? I have yet to see a commercially released preamp that does not have the pairs twisted.

Shane

[kid]

Hey Shane,

I do think this is a big issue. I understand that the pre's have an enormous amount of gain that will often not be used. But the fact of the matter is I can not use a pair of Beyer ribbons with these because of the buzz. My gain was up at 9, not fully clockwise and this was not acceptable. I bought the J99's to do small chamber group recordings and with a buzz like this they are not useable. I wish Tim could chime in here with some ideas.