J99 buzz

[davidkakon]

i have a/bd the J99 with Boulder preamps which I believe were the original twin servo preamps made by Deane Jensen. They sound very similar if a little more open on top, but the Boulder had 0 buzz. I also bought these for acoustic music and almost always put a ribbon mic on a string instrument. So far I have not been able to take advantage of theses terrific pres in this context because of the buzz in the last few clicks.

I am sure there will be a solution soon, Im just happy that its not just me!:)

best
david

[Jarek]

I swapped the bridge.

I've used SBYV27-100 diodes. These are ultra fast, soft recovery diodes. The buzz dropped the amplitude about 20 maybe 25%. So this won't solve the problem.
I started to move around the PS02 and found the best place for the ps:
About a 100 meter from the rack!!!

Moving the PS02 outside the rack solved the buzz. Probably the EM emision from the tranny causes the interferance. Audio trannies are kind of coils so they pick em fields and produce this buzz.
This explains why external PS solved the problem as well.

The question is how to kill these electro magnetical fields before it reaches the preamps. Tim places a metal box around the tranny and metal, grounded wall between the PS and preamps. But this isn't enough and should be done better.

I've compared the buzz with my DTC preamp at 72dB. DTC is quite, no buzz at all. I think something as the Faraday cage will help a lot but the guy is gone and won't contribute to this forum.

Tim???

[davidkakon]

I dont mind having my PS external, but 100 Meters seems like a lot. I dont even have 100 Meters in my studio!

is this a typo? did you mean 1 meter?

david

[Jarek]

You have to build a new studio .
I think it was about 20 cm. that was sufficient.
I don't know what distance exactly should do. I'm not serious about moving the PSU out of the rack. I think some magnetic shielding to stop the EMI should be used.
What I see is that slots 1,2,3,4 suffer from EMI. The field is generated probably by the tranny. I looked inside few preamps and compressors. What you see is that the power supply (and the tranny) are as far away as possible from audio path, especially from audio transformers. DTC or Purple MC77 have trannies placed on the other corners of the rack.

I'll try to place few extra grounded copper plates between the PSU and 3rd slot. In meantime maybe someone else will come up with the solution. The best will be to catch any electro magnetic fields right up by the tranny.
Then you're talking about MU magnetics shield materials. They are used i.e. in osciloscopes to protect the screen from EMI.

[Jarek]

I've almost got rid of any hum.
I've placed J99 in slot 7 and 8 as these preamps are most humprone. You won't hear this kind of buzz on N72 or A12. I think that Jensen output trannie is picking up the e-magnetic field. Cinemag trannies have nice copper shield. Maybe this is what helps.

I changed the diode bridge for soft recovery diodes. This had effect as well. Further I've fasten about 20 pcs. 1 mm. thick iron plates between the trannie and the rack.
This shield stopped em field to almost undetected levels. At my first preamp (slot 3) I have very small buzz at full gain (rather A12 or N72). If you use condensers you won't hear it. Channel 4 is free of any hum.

Hope this helps. The best would be some MU shield but these are pretty expensive.

[tele_player]

Doesn't your power transformer have the mu metal shield? Mine does.
Or are you suggesting mu metal shields somewhere else in the box?

[Jarek]

I had to change the power trannie because of 220V here in Europe. 22V wasn't enough to drive regulators without the ripple. New tranny is bigger so I moved the mu shield behind the thin "wall". However the shield only wasn't enough to stop all EMI. Maybe my new trannie has higher em emision?
The metal material used for the shield has very good properties though.
Does anyone know were this shield comes from, where can I buy few more of these???

[jimbob]

So is everyone still having problems with hum on the J99? Is there a solution to this dilemma? I want to get a J99 to use with low-output ribbon mics but I'm afraid of hum problems (I'm also a newbie at DIY and I"ll probably start with the simpler A12).

Thanks!
Jim Bob

[tele_player]

The new PS03 is a very different design, and (I believe) should take care of the noise.

Reports from J99/PS03 users?

[yavuz]

I did not notice any noise but then again, I put them in to the 7th and 8th space in the rack after reading al the posts.
So, I do not know if that is the reason.

My C84s buzz a little when the gains really high with sm 57 or sennheiser MD - 421 MK II.

[tele_player]

It's important to mention whether you've got the PS02 or PS03.

[yavuz]

I have PS03.

[tpryan]

My C84s buzz a little when the gains really high with sm 57 or sennheiser MD - 421 MK II.

Have you read my replies in this thread and this thread? You should be able to get your C84s dead quiet no matter where they are in the chassis. Same with the J99s.