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Low bass extension


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#1 Russhomeaudio

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Posted 12 December 2005 - 08:23 AM

I am into home audio and have speakers that are difficult to control so I borrowed a Crown K2 amp from a retailer to see if it would provide the control I was looking for without fan-noise.  I'm bi-amping with a musical fidelity amp used for the top end and K2 for bottom end, which includes a bass driver in the main speaker and matching subwoofer on each side (left and right).  My Osborne speakers go very low and I love the low bass they put out.  I adjusted the level of the bass by setting input sensitivity on k2 to 0.7v (mus fid amp is 1v) and using dials on front to scale output back to a similar level I was used to with previous amp (another mf).  

As expected, the K2 with its incredible damping factor by home audio standards was fantastic in controlling these speakers.  However what surprised me was that compared to the five other power amps I have tried in the same set up (musical fidelity, arcam, carver etc) the bass is far less extended with the K2, which contributed to the sound feeling a little cold and clinical.  This was quite noticeable and does not seem to fit with the frequency range specs on the datasheet.  I would have thought the 8hz high-pass filter would not be playing a role in the  20hz range.   The control is so good that if the high-pass filter is to blame I would buy amp and have it removed if this is feasible.  Can anyone explain this?

#2 DGlass

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Posted 14 December 2005 - 09:13 AM

The K2 is a great amp for use with low end in a home system. I know of many people that use it for such including myself. There may be another reason for this in the system as you are using "Pro Audio" gear with "Consumer" gear. I would make sure you are doing the wiring correctly to go from Unbalanced to Balanced connections. Our "Amplifier Application Guide" has a great section of wiring digrams. ( http://www.crownaudio.com/pdf/133472.pdf )
I would also check that the Preamp has enough output voltage as you may have a bigger problem getting the proper amount of signal to the amp. You must know the output line level signal of the pre amp in order to set up the proper system gain. Some Crown amps have fixed input sensitivity, while others have adjustable settings from .775V, 1.4V and 26 dB.

Using a K series amp you have two choices for input sensitivity, 1.4V and 26dB. In other words, in the 1.4 volt setting, you need to supply 1.4 volts of signal with the input attenuators turned all the way up (no attenutation) in order to get full out put of the amp. The 26 db setting would require   volts)

What if your preamp only puts out .5v of signal. The K2 will pass audio, but nowhere near what the amp is capable of doing. In order to get the full output level of the amp, you will have to add a pre-amp between your preamp and the input of the K series like a Rolls “MB-15 ProMatch” (www.rolls.com) or an ART “CleanBox” (www.artproaudio.com)  . It will take an unbalanced -10dBu signal and raise it’s level to balanced +4dBu (1.23V nominal) which will work very well with the K series

#3 Russhomeaudio

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Posted 16 December 2005 - 07:57 AM

Thankyou David for your response.  I had noticed on the net that people seem to uise the K series amp for low bass, such as driving subwoofers, which seemed to be at odds with my experience as you imply. Please note that i am entirely happy with output level of most of the bass range, just not the lower bass such as less than 30hz odd.  

The manual for my preamp cites the following specs: Sensitivity (for 1v RMS output) = Line 220mv; Analogue input impedance= 10k; output impedance (all analogue outputs)=50R; Maximum output voltage =10V rms 20Hz-20khz.  The manual for my other  power amp that is designed as a sister to the preamp has specs: Input Sensitivity=1000mv; and Input Impedance=31KOhm.

One thing to note is that I only have a single RCA for each channel from preamp and because I am bi-amping, I purchased a 'splitter' which is like a double adapter--I plug a single RCA into preamp left channel and it splits the signal into two lines, one that I plug into a power amp channel to be used for top end and the other into a different power amp channel for bottom end.  I added an adapter to this male RCA so it would fit in K@2 socket.  Does this splitting have an impact on impedance?

Because power amp says Input sensitivity=1000mv, I set switch on K2 to 0.775v and adjusted gain back until overall bass level for most bass (ie 30hz and up) seemed about right.  However, the lower bass was not very prominent and if I adjust gain to max, the mid-bass is too much and low bass still too little.   This is in comparison to other respectable power amps I have tried.

I have had a look at the wiring docco you send and need to read it again as I dont really understand how to suss if i have the balanced thing wrong--no reference to this in manuals of my current amps.  Any further advice would be greatly appreciated.


QUOTE(DGlass @ Dec 14 2005, 09:13 AM)
The K2 is a great amp for use with low end in a home system. I know of many people that use it for such including myself. There may be another reason for this in the system as you are using "Pro Audio" gear with "Consumer" gear. I would make sure you are doing the wiring correctly to go from Unbalanced to Balanced connections. Our "Amplifier Application Guide" has a great section of wiring digrams. ( http://www.crownaudio.com/pdf/133472.pdf )
I would also check that the Preamp has enough output voltage as you may have a bigger problem getting the proper amount of signal to the amp. You must know the output line level signal of the pre amp in order to set up the proper system gain. Some Crown amps have fixed input sensitivity, while others have adjustable settings from .775V, 1.4V and 26 dB.

Using a K series amp you have two choices for input sensitivity, 1.4V and 26dB. In other words, in the 1.4 volt setting, you need to supply 1.4 volts of signal with the input attenuators turned all the way up (no attenutation) in order to get full out put of the amp. The 26 db setting would require   volts)

What if your preamp only puts out .5v of signal. The K2 will pass audio, but nowhere near what the amp is capable of doing. In order to get the full output level of the amp, you will have to add a pre-amp between your preamp and the input of the K series like a Rolls “MB-15 ProMatch” (www.rolls.com) or an ART “CleanBox” (www.artproaudio.com)  . It will take an unbalanced -10dBu signal and raise it’s level to balanced +4dBu (1.23V nominal) which will work very well with the K series
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#4 bluecatsound

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Posted 29 December 2005 - 06:11 PM

the main problem you have is that you are sending full frequency range to the subwoofer. for proper biamping, you need to use an active crossover. this would send only the low freq. to the subwoofer, and higher freq. to the other speakers. depending on your subwoofer, you would only want to feed it a signal below about 100hz.

#5 DGlass

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Posted 30 December 2005 - 02:08 PM

How are you Bi-Amping?
Does the sub speaker have a built in crossover?
If all you are doing is sending the same signal to two separate amplifier inputs they will be amplifying the same signal. Unless there is a crossover someplace  the sub speakers would still be trying to reproduce the High Freqs. and the Mid/Hi boxes would still be trying to reproduce the Sub Freqs..  blink.gif
The frequency crossovers for Bi-Amping could be done by either having an Active electronic-crossover after the preamp or with Passive crossovers built into the boxes. But without using a crossover of some type the boxes are not truly Bi-Amped.