Help with hooking up unbalanced sub to balanced outs

[Category 5]

I am using a Presonus central station passive switcher for my monitors. I have a hafler P1500 running Dynaudio BM6ps on channel A. I just got a SWEET Velodyne subwoofer that I want to run off of channel C (recommended by Presonus for sub use since C and A can both be selected at the same time).

The problem is, the Velodyne Sub only has unblanaced RCA ins. I thought it was simple and just connected a pair of TS to RCA cables to the Velodyne and all was sounding good with no hum.

The problem is, when I switch in speaker A with speaker C, the volume of A drops significantly. When I switch off C the volume goes back up. Hmmm. When I have C selected and I switch A off the sub (C) doesn't change volume, but A loses volume when C is switched in.

So I figured it out. The TS to RCA cable is tying cold to ground, which is what I have always done when running balanced outs into unblanced gear. But since the mains also share hot, cold, and ground with output C, when they are both switched on (passive architecture) I am effectively passing cold to ground on input A as well - whenever I switch on input C.

Viola...there's the reason for the significant signal loss when using both the sub and the mains. Mind you the input impedance of the sub is 65k, so it should not pose much of a drain at all.

SO MY QUESTION IS THIS

How can I hook an unbalanced sub to balanced outs, without tying cold to ground? Can I just use a TRS cable with no wire connected to cold? This would give me hot and ground, and cold would be isolated from the sub so it wouldn't affect speaker A!

Or will I have to come up with some kind of output transformer to isolate the sub from the A input. If I hook it up any other way I won't have a single volume control for both speakers, so I have to figure out how to hook both A and C up to the Dynaudios and Velodyne at he same time.

Thanks!
Shane

P.S. The Velodyne sub kicks some serious ass, and was only $138 us plus shipping NEW. It is called VX-10 and despite being a 10" with 150watts only, it is one heck of a sub!

 

[PRR]

> Can I just use a TRS cable with no wire connected to cold? This would give me hot and ground, and cold would be isolated from the sub so it wouldn't affect speaker A!

Woofer hot to Velo Tip.

Woofer ground to Velo Sleeve.

Crank woofer gain 6dB.

SInce this is apparently a Balanced (not Floating) output, that should work.

 

[Category 5]

Thanks PRR! You're one of those guys that just has the answer to everything. Thanks for sharing the knowledge!

Shane

 

[Category 5]

Yeah Jakko. For studio use the VX-10 is WAY more powerful than you need. I have to set mine on very low power for it to blend seamlessly.

It does have a great woofer, and the cabinet is very robust and well designed. The only caveat is the unblanaced ins, but that is to be expected from ANY hi-fi sub design. The amp in the VX-10 is supposed to be pretty nice as well. All I can say is this little thing has enough bass to get the job done.

Maybe for home theater in a very large room it wouldn't cut it, but it would take a pretty large room.

Also, why do you need 2? One is enough. The input impeance of the VX-10 is pretty high. I bet you could use a simple splitter to feed both the BM6s and the VX-10.

Shane

P.S. The BM6s are damn nice arent they!?

 

[Category 5]

Jaakko,

Did yours take a long while to break in? Mine were VERY harsh and unpleasant for a couple of days. In fact, My Audix sounded so much better I was beside myself.

I did the thing where you put the speakers face to face and invert the phase of one while feeding a mono signal. I did this for about 15 hours and it DID help a bit, but it took quite a lot more use before they really loosened up.

now they sound phenomenal and I can't even imagine not having liked them. I guess those rubber surrounds are stiff when the speakers are brand new.

i made a new cable with the ring on the TRS foating and now the BM6's and Velodyne are getting along fantastic. You can't hear the sub at all, but when you turn it off you all of the sudden hear whats missing. THey blend seamlessly.

Shane