SUB OUT VOLTAGE mismatch problems on Receivers

Mike Kao

Second Unit
Joined
Oct 31, 2000
Messages
277
I've heard of many people experience voltage mismatch problems when using pro amps to power their subs and connecting them to the sub out on their receiver. Unfortunately I've had the same bad experience with my previous receiver, the Harman Kardon AVR-510. B/C of the voltage mismatch, output drops significantly and requires the use of an external boost device. Using a buttkicker II and a crest pro amp, I connected the amp to my receiver's sub out only to first discover this problem... the problem precisely being that the sub signal drops. It required a sub setting of +10 (highest setting possible) and insane volume levels to get decent feedback from the buttkicker. I thought it may have been the amp, so I tried using two other brand amps (Samson and QSC), and experienced the same problems.

Upon adding an SVS sub to my setup, I would encounter yet the same headache. I had previously used a Midiland sub in my setup that I ripped off my COMPUTER SPEAKERS (S2 4100), and quite honestly it outperforms the SVS, even when the SVS is driven at insane volume levels with the +10 sub setting! That gives you an idea of how bad this voltage mismatch problem is.

Some have used the $50 Radio Shack SA-155 to boost the signal to the amp, but quite honestly it's quite a crude, cheaply constructly device that undoubtly degrades the signal. I've gone down the same route only to return the device a few days later.

I've become and sick and tired of dealing with these problems so I finally decided to get a new receiver... one that doesn't exhibit these problems. As much as I LOVED the harman kardon (it really was a wonderful receiver), and in fact I even wanted to give the AVR-520 a try just in case it somehow miraculously doesn't have the problem, I really have to move on.

So my question is, who here has experienced the same problem with their receiver? Please list the brand and model. Hopefully such a list may be useful for many others as well!
 

Wayne A. Pflughaupt

Moderator
Premium
Joined
Aug 5, 1999
Messages
6,584
Location
Corpus Christi, TX
Real Name
Wayne
Mike,

I've become and sick and tired of dealing with these problems so I finally decided to get a new receiver... one that doesn't exhibit these problems. As much as I LOVED the harman kardon...
I doubt that changing your receiver will make a difference. The problem is he fundamental differences in signal voltage between pro and consumer audio equipment.

A much cheaper solution to buying a new front end would be to look into a budget pro audio crossover from Behringer, or perhaps a nicer used one from e-bay from the likes of Rane or Ashly, to name a few. It could connect between the receiver and amp function as a “line driver.” Not to mention, most pro crossovers these days have excellent 24dB/octave slopes with Linkwitz/Riley alignment, far superior to the standard fare that comes with a receiver or pre-pro.

Bruce,

I didn’t see anything at the link about the SVS Black Box being an interface (or signal booster) between a receiver and a pro amp – did I miss something?

Regards,

Wayne A. Pflughaupt
 

Luke M

Grip
Joined
May 1, 2002
Messages
15
This is a general issue with interfacing ANY consumer equipment with ANY pro equipment. You have to use a voltage level shifter (NOT AN AMPLIFIER! Sheesh whoever told you to use a RadioShack amp is an idiot) to convert up to pro levels.
 

brucek

Second Unit
Joined
Dec 29, 1998
Messages
335
Luke,



You have to use a voltage level shifter (NOT AN AMPLIFIER! Sheesh whoever told you to use a RadioShack amp is an idiot) to convert up to pro levels.
Maybe saying they were an idiot is a bit harsh. A level converter that you recommend is fine, just as a voltage amplifier would be fine. This is a high impedance voltage bridge interface, an as such, doesn't require any high "current" devices, so the voltage can be amplified quite effectively and inexpensively.



The SVS black box is a good device that will do the job. I also recommend the Paradigm X-30 which provides high quality 13dB's of gain. This is perfect for the consumer to pro conversion. It also provides a nice volume control and variable phase control. I use this device myself.

http://www.paradigm.ca/Website/SiteP...trolunits.html



The voltage amplifiers have the added benefit of properly impedance matching this interface. The trouble with the passive level converters are that they require strict adherence to input/output impedances. Since they are a simple step up transformer, they reflect their gain in the form of lowered impedance to the source. So a 10:1 transformer will relect a 20K amplifiers input impedance as 2K to the source. I wouldn't want the output source impedance of my preamp to be very high. It would result in a nice little low pass filter (not that we're too concerned in a sub situation though).

These passive level converters also convert the single ended to common mode - not too many subs have XLR balanced inputs......



Personally, I'd recommend the voltage amplifier (although the Radio Shack one may be a bit cheap).....




brucek
 

Cliff

Stunt Coordinator
Joined
Aug 4, 1998
Messages
55
brucek,

I have taken your suggestion about incorporating the X-30 into my setup, which also includes a receiver (Yamaha RX-V1), a parametric equalizer (Symetrix 551E), and a sub amp (Samson S-1000). I have a question about the sequence of connections between the receiver and the sub amp. Since both the equalizer and amp are pro gear, I would think that the most logical sequence is receiver -> X-30 -> equalizer -> amp. However, for logistical reasons, I have the connections going from receiver -> equalizer -> X-30 -> amp. Thus, the cabling switches back and forth between -10 dBV and +4 dBu a couple of times. Does this matter? Am I compromising performance, safety, or longevity of the equipment using the sequence of connections I have? I would appreciate your thoughts.

Thanks,

Cliff
 

Bruce N

Second Unit
Joined
Feb 13, 2000
Messages
349
Here's what it says on that page:
18dB of active gain allowing your surround receiver to drive virtually any consumer or pro-type high-power amplifier
Isn't that what we're looking for here?
Cliff,
I have the same type of setup and I put the X-30 before the EQ.
Pre/pro > X-30 > EQ > Amp.
Bruce
 

brucek

Second Unit
Joined
Dec 29, 1998
Messages
335
Cliff,

I answered this question a few weeks ago (except the EQ was a BFD). I don't know the 551 to well, but I suspect the answer applies the same. Here's the advice I gave:

OK, well then it would be best to place the line amp between the BFD and the SVS power amp for several reasons. Feeding the line amp from the processor is a bad idea.

Use the -10dBv switch setting on the BFD...

The BFD is not an amplifier, it's a unity gain device. Since it's digital and you're feeding an ADC/DAC chain you want to optimize its input level to take advantage of all the bits available. By this I mean to take maximum advantage of the dynamic range provided by the analog to digital converter in the BFD or any ADC for that matter, you need to provide it with a maximum input signal level that takes advantage of the greatest number of bits to represent the resultant voltage samples.

If the range from your weakest signal to the strongest signal was only half the required maximum input level, you would be robbing yourself of dynamic range and subsequently increasing your signal to noise level. To get the most out of this system you would like the maximum signal sent to the BFD to "just" not turn on the red LED. If the yellow LED comes on in explosions etc, that would be fine. The BFD has no compressor or limiter on its input, so you can easily overdrive it and clip the output.

This means once you've reached and set this level, you can't increase the level any more even if you wanted to. So it's the output analog signal that you want to amplify, not the input signal which is easily set to optimum by your processor into the EQ.

The BFD's unity output (or less if filters are applied) can then be amplified to your hearts content with the line amp. If the line amp can create 18dB gain, then it will "all" be available to you, instead of being limited if you placed the line amp before the BFD.
Processor > 551EQ > X-30 > Sub Amp

brucek
 

Cliff

Stunt Coordinator
Joined
Aug 4, 1998
Messages
55
Thanks, Bruce and brucek. The Symetrix 551E is an analog equalizer and therefore has no ADC/DAC processing. Neverthess, input level must be held within some optimal range, and thus the issues brucek described for the BFD are somewhat applicable to this device as well. But there does seem to be one difference: the 551E has a control for boosting or cutting input level up to 15 dB. In fact, the manual suggests using some boost when feeding a signal from a -10 dBV device (such as my receiver). I am actually doing this in the hookup I described above, where the receiver's sub output is fed directly into the equalizer.

So, I assume that as long as the input level to the equalizer is appropriate, my setup is okay in which the equalizer's output is fed to the X-30, and the gain control on the X-30 is used to boost the signal to the amp. I guess my concern about the alternating sequence of the device types (-10 dBV, then +4 dBu, then -10 dBV, then +4 dBu) is not a problem.

Thanks again.

Cliff
 

brucek

Second Unit
Joined
Dec 29, 1998
Messages
335
Cliff,

So, I assume that as long as the input level to the equalizer is appropriate, my setup is okay in which the equalizer's output is fed to the X-30, and the gain control on the X-30 is used to boost the signal to the amp.
Yep, that is the correct setup. I had the time to look at the 551 and it's a very nice unit - good specs. The input line stage can compensate very nicely for various input levels (consumer or pro). This control combined with the processors sub out control can be used to set your optimum input level.

Then you are free to adjust your X-30 without worry of overdriving the 551. The X-30 then gives you freedom to have front panel convenient access to sub volume and phase.

brucek
 

Forum Sponsors

Forum statistics

Threads
345,164
Messages
4,732,567
Members
141,395
Latest member
Georgiastevenson