How to add a subwoofer to a Spectral system?

microstrip

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May 30, 2010
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Interesting Micro...I have a soft, steady ground loop hum...cannot figure out why. (BTW, it is a loud ground loop hum unless I select the 'Float' option on the Robert Koda K15EX preamp.

What I do know is that disconnecting the IC from the preamp to the Sub solves it immediately. I was hoping that this Jensen Sub-2RR would therefore solve it. Any thoughts on whether that is a fair assumption?
Yes, the Jensen will probably solve it. Did you try the questionable operation of trying the subwoofer with a cheater plug that disconnects the mains ground? It is a good way of diagnosing.

You must get rid of this hum - even if minimal it can affect sound quality seriously!
 

LL21

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Dec 26, 2010
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Yes, the Jensen will probably solve it. Did you try the questionable operation of trying the subwoofer with a cheater plug that disconnects the mains ground? It is a good way of diagnosing.

You must get rid of this hum - even if minimal it can affect sound quality seriously!
Hi Micro,

Thank you! Interesting question...if you look at the plug outlet on the back of the Velodyne there are only two plugs...so is that in effect 'not grounded' anyway. I have noticed on another sub (REL?) (JL Audio?).

Does this in any way change your mind about Jensen possibly working in my case?

And yes, definitely want to get rid of this hum! At night, I can hear it from 25 feet away when the room is dead quiet. However, during the day it is not so noticeable with people outdoors, etc.
 

microstrip

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May 30, 2010
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Hi Micro,

Thank you! Interesting question...if you look at the plug outlet on the back of the Velodyne there are only two plugs...so is that in effect 'not grounded' anyway. I have noticed on another sub (REL?) (JL Audio?).

Does this in any way change your mind about Jensen possibly working in my case?

And yes, definitely want to get rid of this hum! At night, I can hear it from 25 feet away when the room is dead quiet. However, during the day it is not so noticeable with people outdoors, etc.

Did you try reversing the neutral and phase in the power plug?
But the Jensen (or a similar transformer) should solve the problem anyway. Lundhal also have excellent units. Are you using balanced connections?
 

LL21

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Dec 26, 2010
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Hi Micro,

How do I do that...just turn the plug 180 degrees when I plug it in?

The Velodyne DOES have balanced inputs (and the Robert Koda is Balanced out)...however, I have tried to use them and for some reason, it put the Gryphon into protection instantly. I am sure it was probably my fault for overlooking something...but now I dare not use the Balanced so I am SE only on the input to the Velodyne.

I believe that the Jensen is full accommodating of balanced out to SE in anyway so hopefully fine. I will simply go balanced out into an XLR-RCA adaptor...and then go SE all the way to the Jensen and from the Jensen to the Sub. Make sense to you?
 

microstrip

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Hi Micro,

How do I do that...just turn the plug 180 degrees when I plug it in?

The Velodyne DOES have balanced inputs (and the Robert Koda is Balanced out)...however, I have tried to use them and for some reason, it put the Gryphon into protection instantly. I am sure it was probably my fault for overlooking something...but now I dare not use the Balanced so I am SE only on the input to the Velodyne.

I believe that the Jensen is full accommodating of balanced out to SE in anyway so hopefully fine. I will simply go balanced out into an XLR-RCA adaptor...and then go SE all the way to the Jensen and from the Jensen to the Sub. Make sense to you?
This means that your Velodyne XLR is injecting DC or noise in the output of the preamplifier - be careful and also have your XLR cable checked. Probably this Velodyne / cable problem is related with the hum. But we can't exclude that the hum is generated by the subwoofer.
Even with the Jensen you can go XLR/XLR - it isolates the units.

And yes, just turn the power plug.
 

LL21

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Dec 26, 2010
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This means that your Velodyne XLR is injecting DC or noise in the output of the preamplifier - be careful and also have your XLR cable checked. Probably this Velodyne / cable problem is related with the hum. But we can't exclude that the hum is generated by the subwoofer.
Even with the Jensen you can go XLR/XLR - it isolates the units.

And yes, just turn the power plug.
Thank you. I have just spoken with my local dealer who has inquired about Jensen. I will keep you posted! It would be great if it were such a simple fix!
 

acousticsguru

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Feb 17, 2014
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Thank you. I have just spoken with my local dealer who has inquired about Jensen. I will keep you posted! It would be great if it were such a simple fix!
Be sure to let us know how this works out for you! Keeping fingers crossed!

Greetings from Switzerland, David.
 

LL21

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microstrip

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May 30, 2010
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Thank you. I have just spoken with my local dealer who has inquired about Jensen. I will keep you posted! It would be great if it were such a simple fix!
Supra sold some isolation transformers for computers that will work just for testing - see if you can borrow one of those or similar .https://www.cinenow.fr/articles/22935-supra-ags-10k-humbuster a1.jpeg

But first you should get a voltmeter and check the voltages at the XLR input of your subwoofer. Very simple to do - put the negative (black probe) inside pin 1 and check for DC voltage in 2 and 3 with the red probe. Then do the same for AC mode.
 

LL21

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Dec 26, 2010
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Thank you! I checked and they are the same cost as the Jensen Sub2RR apparently here...i will ask my dealer if he happens to have any kind of hum buster type product that might be a good 'test'.
 

Paul54

New Member
Mar 11, 2021
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I had a serious hum issue with a recently added sub that only had a unbalanced connection option. A 2 meter sub cable had no hum, two different brands of 12 meter sub cables produced significant hum but one was slightly quieter than the other. I plugged my preamp and sub into the same circuit and the hum level did not change. I thought about the potential rf interference from a high voltage power line behind my residence running in parallel to my cabling producing this interference - because of the cable acting as an antenna.
So i purchased a Jenson isomax sub model that accepted an xlr in to a rca out. A 12 meter xlr cable connected to my preamp lfe out connected to the isomax then to my sub with a 0.5 meter cable produces zero hum. That worked for my situation.
 
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LL21

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Dec 26, 2010
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THanks, Paul54! So I now have the Jensen in...but unfortunately while it reduced the hum a bit, it still exists. I am running quite a long 25' cable from the preamp (SE cable with XLR adaptors which also have some kind of 'blocking' to protect feedback from the sub back into the preamp)...to the Jensen...and then a 1.5m cable from the Jensen RCA-RCA to the Sub.

Given what you have said about length of cable which I know can sometimes be a problem, I will look into potentially shortening BOTH cables since we do not need 25 feet any longer (we used to in the old house).

Fortunately at this stage from the listening position while I can hear the hum (annoying)...in truth, it does not even register on the meter when measuring...31db with or without the system on. In fact, even 1m from the speaker the room measures 31db with the system on or off. Quieter during the late evening. So manageable, and hopefully someone can fix when lockdown ends.
 

Paul54

New Member
Mar 11, 2021
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THanks, Paul54! So I now have the Jensen in...but unfortunately while it reduced the hum a bit, it still exists. I am running quite a long 25' cable from the preamp (SE cable with XLR adaptors which also have some kind of 'blocking' to protect feedback from the sub back into the preamp)...to the Jensen...and then a 1.5m cable from the Jensen RCA-RCA to the Sub.

Given what you have said about length of cable which I know can sometimes be a problem, I will look into potentially shortening BOTH cables since we do not need 25 feet any longer (we used to in the old house).

Fortunately at this stage from the listening position while I can hear the hum (annoying)...in truth, it does not even register on the meter when measuring...31db with or without the system on. In fact, even 1m from the speaker the room measures 31db with the system on or off. Quieter during the late evening. So manageable, and hopefully someone can fix when lockdown ends.
Just to add a bit more to my experience. The xlr cable i am now using is the canare l-465 which is supposed to be good for for noise rejection. With the various rca subwoofer cables I tried I had a noticeable hum and a much lower intensity buzz at the sub (the buzz almost sounds like a small cooling fan - not sure if there is a fan to cool the sub’s amp or if the amp itself has a slight buzz ?)
The hum volume increased with the sub volume setting but the buzz does not.

Any way the hum did disappear with the isomax using a xlr cable, but the very slight buzz did not. I can hear the buzz a few inches from the sub but i cannot hear any buzz near any seating. I could hear hear the hum at the seating positions.

I really cant say if the xlr cable being balanced and supposedly less susceptible to interference or the isomax transformer was responsible for the hum elimination. If the sub had an xlr input i would be able to answer that question.

I am not a technical expert on the source and control of system noise in sound systems . But unfortunately the 69 Kv power-line boarding my property produces measurable ELF that i am sure is not ideal for sound systems (and probably me too).
 

LL21

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Dec 26, 2010
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Thank you! That probably means at some point I need to investigate a proper XLR connection. The Velodyne does actually have an XLR input but I once had a huge problem using it (RCA with an XLR adaptor) where the moment I plugged it in, the amp went into protection. Someone guessed there was back EMF from the sub into the preamp and the into the amp. Not sure if that is correct but suffice to say, not being a techie, i never used it again. perhaps under proper technical supervision, we might try it again with the Jensen.
 

robbyd

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Dec 23, 2015
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Would it not depend on whether your subs can take a high level input?

I wondered about taking it off the speaker inputs...

or possibly using tape-out function on pre to feed the signal?

regards
 

robbyd

Well-Known Member
Dec 23, 2015
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uk south-east
yes I know. Right now I'm feeing the tape out signal from 30sv into another pre, through RCAs, that then splits subs and main signal. So essentially a two way active. Why? Because the 400s are connected to main outputs and I only have XLRs.
Not using the Spectral power amps at the moment though, and cabling complications (MIT requirements) would make that tricky...
 

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