Re: DBX 3BX DS - can some low level hum be inherent?

[62vauxhall]

Since the year 2000 I have used a DBX dynamic range expander beginning with a 2BX series I. It was replaced by a 3BX series III which remained in place for several years. Two years ago, for some reason, I placed an absentee bid on a lot of three different 3BX units and won them. The lot consisted of another 3BX III, a 3BX I with remote and the 3BX DS.

During an initial quick listen, they all worked and I left the remote 3BX I installed in the system.

An occasion arose which had me scrutinize the 3BX DS more closely and that revealed a hum none of my other DBX expanders exhibit. It manifests with the preamp’s volume about the 12 o’clock position and is only noticeable when no signal is passing through it.

Connecting it’s chassis to the pre-amp’s chassis changed nothing.

It’s a naive notion but since no amplification that I know of is contained within the unit, I am wondering “why the hum”?

If anyone who uses a 3BX DS can comment if theirs produces a hum with no signal present and when volume control is up fairly high, I would be interested in learning what, if anything, you are hearing. And if it’s correctible, I’d be keen to know how.

For me, determining a source for hum has been somewhat elusive.

FWIW the older remote 3BX I is pretty much hum free as were the others which saw duty for any length of time.

 

[Lavane]

How old is the DS? The power supply caps may need replacing? Maybe take a good look at the solder joints. Might be a cold or cracked ground solder joint?

 

[62vauxhall]

How old is the DS? The power supply caps may need replacing? Maybe take a good look at the solder joints. Might be a cold or cracked ground solder joint?

Thanks!

No idea of age or it’s history other than it belonged to a former CBC engineer cum hoarder. After his passing all his stuff went to auction and there was a lot of it.

Very few lots were individual items, mostly groups of 3, 4 or more. I had an eye on a particular Sony pre-amp but did not want nor could I afford 3 of them plus a power amp.

My thought too was that something within the power supply might be to blame. New caps would not be a difficult tentative fix

And examining PC board ground points should also be a fairly easy chore.

 

[qdrone]

Check the solder joints where your inter connect Jack's are. If you grasp the inter connect and wiggle it where the jack goes in does the hum increase or go away?
I had this problem with a 3dbx, the solder was cracked, I ran a soldering iron over solder and cemented the solder over crack and fixed it.

 

[62vauxhall]

Check the solder joints where your inter connect Jack's are. If you grasp the inter connect and wiggle it where the jack goes in does the hum increase or go away?
I had this problem with a 3dbx, the solder was cracked, I ran a soldering iron over solder and cemented the solder over crack and fixed it.

Thanks for tip! Popped off the top earlier, wrote down which capacitors are in the PS and will be removing the board on Friday. That's the soonest I can spend any time on it.

I noticed the heatsink can be wiggled a bit as can the shaft of the Transition pot so will invstigate those more closely too. .

 

[mbz]

Often helpful to know if it's mains 50/60Hz or rectified 100/120Hz hum pointing to problem before/after rectifier...
Record hum and load into audacity or similiar, easier to use an oscilloscope...

 

[Lavane]

Check the solder joints where your inter connect Jack's are. If you grasp the inter connect and wiggle it where the jack goes in does the hum increase or go away?
I had this problem with a 3dbx, the solder was cracked, I ran a soldering iron over solder and cemented the solder over crack and fixed it.

Good idea. Especially with jacks that are soldered to the board. I see lots of them now where the ground ring on the jack just clips into the plastic part of the jack. I had one pull right out removing a cable.

 

[62vauxhall]

How old is the DS? The power supply caps may need replacing? Maybe take a good look at the solder joints. Might be a cold or cracked ground solder joint?

Check the solder joints where your inter connect Jack's are. If you grasp the inter connect and wiggle it where the jack goes in does the hum increase or go away?
I had this problem with a 3dbx, the solder was cracked, I ran a soldering iron over solder and cemented the solder over crack and fixed it.

Well, you two nailed it.

The common/ground pins of the RCA out jacks had poor or distressed solder connections. I reflowed solder onto all RCA jack pins and the hum is gone. Since I'd already purchased new electrolytics for the power supply, they got replaced too.

 

[Lavane]

Awesome. Good to hear it was something simple.

 

[qdrone]

Carver is famous for cracked solder too fyi. Glad to hear it was an easy fix.