Boomzilla's Journey (ongoing)

[Deleted]

Feb 13, 2014 17:41:33 GMT -5 hemster said:

Feb 13, 2014 17:10:11 GMT -5 @bmoney said:

Cheater plug?

Per his earlier post, he tried that already:

3. Used an ungrounded power cord to power the sub = still hums

Oops

[Boomzilla]

I think that the sub is working properly - no need to bother PSA. Whatever's wrong is wrong at my end. How do I know? Because when the sub was plugged into the monophonic "sub out" jack of the Oppo, it was dead silent, even at maximum gain setting. It's only now that I'm trying to run stereo inputs that the hum problem occurs.

I've tried running the crossover, phase, and volume pots up & down. Only the volume affects the hum.

A "cheater plug" is one where the ground prong is removed from the AC plug, and the device ground floats on the ground voltage of the component it's connected to (in this case, the Oppo player). This is often used to advantage in pro gear where many, many more devices are involved in the system. What's typically done is that one and only one device is grounded and all others ground through that device. This method is called "star grounding."

I know that if I were running this sub from a single sub feed, there would be no hum. If I had two different subs, each driven by a single channel of the Oppo, there would be no hum. Only the stereo feed to the single sub creates a hum.

So far as I know, I can't just jumper the two channels together. Since the Oppo's outputs are used to feed both the stereo amplifier and the subwoofer, doing so would essentially short the right and left channels into a mono signal. Yes?

On the other hand, since the balanced XLR outputs are used to feed the power amp and the unbalanced outputs feed the sub, would making a common signal of the RCA outputs actually make the XLR outputs mono too? I'm not too sure of how the Oppo's circuitry handles the different outputs. There's actually a THIRD set of outputs on the Oppo that I might employ... In addition to the "stereo only" XLR & RCA pairs, there's also a 7.1 set of RCA outputs. If I used the 7.1 right and left front channel outputs (set to full range, and variable output), maybe I could common them with a Y-cable without affecting the stereo outputs?

In any case, I doubt that using a Y-cable on the 7.1 outputs would affect the stereo-only XLR outputs, so that's my next attempt to tame the hum. We'll see...

[monkumonku]

Feb 13, 2014 17:53:16 GMT -5 Boomzilla said:

I think that the sub is working properly - no need to bother PSA. Whatever's wrong is wrong at my end. How do I know? Because when the sub was plugged into the monophonic "sub out" jack of the Oppo, it was dead silent, even at maximum gain setting. It's only now that I'm trying to run stereo inputs that the hum problem occurs.

I've tried running the crossover, phase, and volume pots up & down. Only the volume affects the hum.

A "cheater plug" is one where the ground prong is removed from the AC plug, and the device ground floats on the ground voltage of the component it's connected to (in this case, the Oppo player). This is often used to advantage in pro gear where many, many more devices are involved in the system. What's typically done is that one and only one device is grounded and all others ground through that device. This method is called "star grounding."

I know that if I were running this sub from a single sub feed, there would be no hum. If I had two different subs, each driven by a single channel of the Oppo, there would be no hum. Only the stereo feed to the single sub creates a hum.

So far as I know, I can't just jumper the two channels together. Since the Oppo's outputs are used to feed both the stereo amplifier and the subwoofer, doing so would essentially short the right and left channels into a mono signal. Yes?

On the other hand, since the balanced XLR outputs are used to feed the power amp and the unbalanced outputs feed the sub, would making a common signal of the RCA outputs actually make the XLR outputs mono too? I'm not too sure of how the Oppo's circuitry handles the different outputs. There's actually a THIRD set of outputs on the Oppo that I might employ... In addition to the "stereo only" XLR & RCA pairs, there's also a 7.1 set of RCA outputs. If I used the 7.1 right and left front channel outputs (set to full range, and variable output), maybe I could common them with a Y-cable without affecting the stereo outputs?

In any case, I doubt that using a Y-cable on the 7.1 outputs would affect the stereo-only XLR outputs, so that's my next attempt to tame the hum. We'll see...

Just to clarify, you are using the Oppo's main left and main right RCA outputs to feed the sub? So the sub has a left and right channel input that it blends and extracts the signal to output based on the crossover you set?

[Boomzilla]

Feb 13, 2014 18:23:55 GMT -5 monkumonku said:

Just to clarify, you are using the Oppo's main left and main right RCA outputs to feed the sub? So the sub has a left and right channel input that it blends and extracts the signal to output based on the crossover you set?

That's correct. In fact, the Oppo has THREE "main" outputs - a stereo-only XLR pair, a stereo-only RCA pair, and the Right-Front and Left-Front of the multi-channel analog outputs.

I've solved the hum problem by using the Right-Front and Left-Front outputs into a "Y-cable" that then sends the combined signal to the subwoofer mono input. The "stereo-only" RCA outputs feed my Crown power amp (with its volume pots cut back to 50% on both channels).

Using this configuration, I have no hum AND the levels match between the sub and the mains.

Sound? My-Oh-My, YES! This sounds much, much differently than without the sub...

Now this opens an entirely NEW can of worms... Even with a preamplifier in the system, there is no way to alter the subwoofer level relative to the main signal level. In other words, I can split frequencies between the satellites and the sub, but I can't alter relative volumes. That means that even with an XSP-1 in the system, the main speakers will continue to be FAR louder than the sub. Stated another way, this sub doesn't have enough gain to keep up with the combination of a high gain amplifier (the XPR-2) and sensitive speakers (Klipsch Heresys).

Therefore any one (or more) of several things must happen:

1. I'll need to use an amplifier with its own volume attenuators (Either of my Crown "Pro" amps or a Mini-X)

2. I'll need to use less-sensitive speakers

3. I'll need to add a second subwoofer (doubles the SPL for the voltage delivered from the preamp's output jacks)

4. I'll need to insert attenuation at the input of the power amp (Control Freak or fixed attenuators that are volume matched)

Recommendations?

[garbulky]

Adjust the gain on the subwoofer to balance the sound with the speakers. Then increase the entire volume with the XSP

[Boomzilla]

Hi Gar - Even with the subwoofer volume all the way up, it can't keep up with the speakers. That's the problem in a nutshell.

And yet one additional thought about subwoofer level:

I do have a "Pro" 1/3 octave equalizer sitting in my closet. If I were to run the mono full-range signal to the equalizer prior to feeding the subwoofer, I'd have the opportunity to not only amplify the bass signal using the equalizer's circuitry, but also accomplish both some slight room correction via the sliders...

This bass boost alone might allow use of the XPR-2 again rather than the Crown amplifiers. The Klipsch Heresys, whose exuberant dynamics are such a good match for the slightly restrained XPR-2 become slightly strident sounding in my room with the (also highly dynamic) Crown PS-400. The room may be a contributor to this, and the ATS company has promised me some feedback by Monday as to room treatments.

Therefore, later today (Friday 14th), I'll install the equalizer & see what I can get. I have high hopes that some of the room non-linearity (peaks only) can be tamed with judicious equalization cuts. I know better than to amplify dips... I also have better sense than to try boosting frequencies below the roll-off of the (vented) subwoofer.

I'll report on how the (equalized & boosted) PSA HV15 works. I'm a tad disappointed that the sub's gain is insufficient to keep up with my speakers, but I'm probably a "one in a million" case:

Most use their subs with an AVR that won't need any more boost
Most use their subs with less sensitive amplifiers than my XPR-2
Most use their subs with less sensitive speakers than my Klipsch Heresys

Even so, a "low-gain / high-gain" switch on the sub would have been nice.

So yet another question for the Lounge - Should I buy a second sub?

[garbulky]

This is strange B'zilla that even with the sub recieving full range outputs they can't keep up with the klipsch.

The immediate thing that I think you need to rule out is that....is this really a problem with the klipsch sensitivity or not. Because all the fixes appear to hinge on that. It is the most likely possibility but also a strange one. So let's make sure of "Most use their subs with less sensitive speakers than my Klipsch Heresys"

To do so stick your deftechs in there and see if the sub is now shaking the room without EVER thinking that it could be a bit louder. And I do mean oh my goodness I need to turn this thing down fast type. If it's not doing that, there's something else going on. so to be clear - it shouldn't be "now the bass is balanced" - it should be TURN it down it sounds too overpowering.

[Boomzilla]

When I use the Crown amp (with the volume cut back on the amp's own pots), your response is EXACTLY what I get. My issue (as Chuck Elliott instantly identified, having had the same experience) is that a high-gain amplifier and high-sensitivity speakers ALWAYS outplay subwoofers (unless the subs are specially designed to compensate).

And I'm 100% sure that my statement about most people using less-sensitive speakers than the Heresys is also true. Klipsch says the Heresy speakers put out 97 dB at one watt at one meter. The average Home Theater speaker is designed for "high sensitivity" so that wimpy AVRs can drive a bunch of them, and they average 90 to 93 dB at one watt at one meter. That four to seven decibel advantage for the Heresy is HUGE in terms of sensitivity (it's a logarithmic scale).

Combine that speaker sensitivity with an amplifier that has 600+ watts of output per channel and 29 decibels of gain, and the combo gets loud QUICKLY!!

Yes, the DefTechs will match the subwoofer (even with the XPR-2 driving them) because they're rated as 92dB sensitive, but actually run a bit less. When I get a preamp that will do bass management, I'll plug in the DefTechs and see how they do. Since I'm currently running satellite speakers full-range and cutting in the sub below, the Heresys are a safer match (because they're air suspension & won't flap the drivers below their loading).

In any case, the system is up & running now with the sub & without hum. Feel free to drop by & listen.

[garbulky]

Thanks!

[Deleted]

i would email or call Tom V. he welcomes setup issues. have you tried a dfiferent sub cable?

this doesnt sound right. I had the XV15 with Klipsch RF3's (98db) and the XPA5 32db gain.....I had no issues...I am not convinced its your speakers/amp combo thats the issue...but I could be way off base lol

[pop]

Feb 14, 2014 7:26:32 GMT -5 garbulky said:

Thanks!

"feel free to drop by and listen"

That means, "hey come over and fix this"

In my family we call this being Popovicked.

For instance. Let's say I just bought a new BBQ and don't want to put it together so I call my buddy.

"Hey I am smoking some baby back ribs tonight wanna come over and eat them"

"sure"

He gets there and has to help me put the BBQ together to eat the ribs. Popovicked

I like your style boom!

[Boomzilla]

Expertise (and a good set of ears) are where you find them. Now if Cindy Crawford was an audiophile...

[Boomzilla]

Feb 14, 2014 7:48:50 GMT -5 @bmoney said:

i would email or call Tom V. he welcomes setup issues. have you tried a dfiferent sub cable? this doesnt sound right. I had the XV15 with Klipsch RF3's (98db) and the XPA5 32db gain.....I had no issues...I am not convinced its your speakers/amp combo thats the issue...but I could be way off base lol

Thanks - I've done EXACTLY this - Mr. V. has been emailed & I'll post his reply. I've tried several sub cables. What was your preamp? If you used an AV preamp and auto setup, then the levels were adjusted for you.

[Deleted]

usp-1

but then very shortly after i got the psb's

[Boomzilla]

If your setup works, bmoney, with 98dB speakers and a 32dB gain amp, then mine should work fine too. It doesn't. I tried the equalizer to see if I could get additional boost - no go. The equalizer apparently doesn't so much boost signal as cut it. The setup IS working with the Crown amp dialed back to 50% gain. We'll see...

[Deleted]

im now very interested in what Tom has to say ....looking forward to hearing how this will be fixed

[Boomzilla]

Tom's reply:

1)Unfortunately the only thing I can think of here may be adding a "gain box" to the subwoofer signal chain. Something like the ART CLEAN BOX. www.subwoofer-builder.com/cleanbox/cleanbox.htm. Conversely you can add signal attenuation to the main speakers but I'm guessing you'll want to keep that signal path as "pure" as possible. A potential additional benefit may be eliminating the ground loop issue too.

2)The cheater plug on the subwoofer won't help as the amplifier is a modern "ungrounded" variety (no ground prong). Could you describe the connection progression when connecting the subwoofer to the stereo signal? What components are used for the 2 channel portion of the system? Have you tried a cheater plug on the Oppo?(assuming the oppo is used as the "2 channel" preamp).

3)You are correct. If you purchase a second XV15 within 6 months of the original purchase we deduct 10% from the price of the second unit. This makes it $719(including shipping).

Tom Vodhanel
Power Sound Audio
Power Up!

[DYohn]

a preamp would likely help.

[Boomzilla]

Feb 14, 2014 11:26:00 GMT -5 DYohn said:

a preamp would likely help.

On order.

However - The preamp offers frequency division only - not relative level adjustment between the two parts of the frequency spectrum once separated. I do expect the preamp to help with dynamics. I don't particularly expect it to make any difference at all in the subwoofer level matching. If the preamp were an AV unit, then, yes, level adjustment would be possible. With the stereo preamps that offer bass management, however, I don't see any level matching options. Are they there & I missed them? Thanks.

[Deleted]

you are correct, there are no level matching options...I was concerned about this as well. but was not an issue, at least in my set up