Servo-Controlled Amplified Bass

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,599
225
1,190
Seattle, WA
www.genesisloudspeakers.com
There are still many audiophile who erroneously believe that the bass performance of the main amplifier does not matter when using Genesis loudspeakers as they have a built-in servo-controlled bass amplifier. Conversely, they think that it is a waste of money to buy a better power amplifier or one that has better bass control because the bass performance would not be reflected in the speakers with active bass.

That is outdated thinking. In true active systems, there is no crossover in the woofer and hence the sound of the amplifier used will change the sound of the woofer. All crossing-over is done between the preamplifier and all the power amplifiers used.

My designs are different. There is a low-pass filter for the woofers and a band-pass filter for the midrange (sometimes an additional band-pass for the mid-bass coupler), and a high-pass filter for the tweeter. The low-pass filter plus servo-controlled amplifier for the woofer has the same 'sound' as the band-pass and high-pass filters used in the crossover of the rest of the loudspeaker. The active low-pass filter plus servo-controlled amplifier for the woofer is designed with the same group delay as the band-pass filters used and high-pass filters used. This is how I achieve coherence across the entire sonic spectrum.

Hence, whatever amplifier that is used will have its sound translated to the entire loudspeaker. All the professional reviews of my designs have mentioned this coherence and seamlessness and the sound of all the drivers (include the active ones) being cut from one sonic cloth.

With the Genesis loudspeakers, you hear the 'sound' of any amplifier you use. For example, when you use a Single-Ended Triode tube amplifier, you hear what the bass of that amp sounds like. With a large solid-state amplifier, you hear the sound of that bass too. This is also why I do not allow for bi-amping or tri-amping via multiple pairs of binding posts. All the most disastrous systems I've heard have had different amplifiers for the various parts of the loudspeaker because the audiophile thought that a low-powered solid-state amp for tweeters plus a SET tube amp with "golden midrange" plus a monster solid-state amp for the woofers would lead to sonic nirvana.

In a recent demo at a customer's room using the G2.2 Junior with built-in amplification, we had the Viola Bravo monoblock amplifiers and a Gryphon Mephisto stereo amplifier (both about the same price). When we switched amplifiers, the biggest difference we all heard on switch-over was in the tonal character of the bass. Then, we had to sit down and concentrate to hear other differences. But the low-bass differences swamped the listening session - even though the bass is already self-powered and the higher power of the Mephisto should not have made a difference.

G2Jr's in Penang.jpg
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,067
8
0
Dallas, Texas
Nice setup.

When you switch out amps with different gain, how do you adjust the powered woofer's level?

I've never measured an amp's group delay. Could an amp's group delay significantly change the group delay between the band pass and the powered woofer?

There are still many audiophile who erroneously believe that the bass performance of the main amplifier does not matter when using Genesis loudspeakers as they have a built-in servo-controlled bass amplifier. Conversely, they think that it is a waste of money to buy a better power amplifier or one that has better bass control because the bass performance would not be reflected in the speakers with active bass.

That is outdated thinking. In true active systems, there is no crossover in the woofer and hence the sound of the amplifier used will change the sound of the woofer. All crossing-over is done between the preamplifier and all the power amplifiers used.

My designs are different. There is a low-pass filter for the woofers and a band-pass filter for the midrange (sometimes an additional band-pass for the mid-bass coupler), and a high-pass filter for the tweeter. The low-pass filter plus servo-controlled amplifier for the woofer has the same 'sound' as the band-pass and high-pass filters used in the crossover of the rest of the loudspeaker. The active low-pass filter plus servo-controlled amplifier for the woofer is designed with the same group delay as the band-pass filters used and high-pass filters used. This is how I achieve coherence across the entire sonic spectrum.

Hence, whatever amplifier that is used will have its sound translated to the entire loudspeaker. All the professional reviews of my designs have mentioned this coherence and seamlessness and the sound of all the drivers (include the active ones) being cut from one sonic cloth.

With the Genesis loudspeakers, you hear the 'sound' of any amplifier you use. For example, when you use a Single-Ended Triode tube amplifier, you hear what the bass of that amp sounds like. With a large solid-state amplifier, you hear the sound of that bass too. This is also why I do not allow for bi-amping or tri-amping via multiple pairs of binding posts. All the most disastrous systems I've heard have had different amplifiers for the various parts of the loudspeaker because the audiophile thought that a low-powered solid-state amp for tweeters plus a SET tube amp with "golden midrange" plus a monster solid-state amp for the woofers would lead to sonic nirvana.

In a recent demo at a customer's room using the G2.2 Junior with built-in amplification, we had the Viola Bravo monoblock amplifiers and a Gryphon Mephisto stereo amplifier (both about the same price). When we switched amplifiers, the biggest difference we all heard on switch-over was in the tonal character of the bass. Then, we had to sit down and concentrate to hear other differences. But the low-bass differences swamped the listening session - even though the bass is already self-powered and the higher power of the Mephisto should not have made a difference.

View attachment 19274
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,599
225
1,190
Seattle, WA
www.genesisloudspeakers.com
Nice setup.

When you switch out amps with different gain, how do you adjust the powered woofer's level?

I've never measured an amp's group delay. Could an amp's group delay significantly change the group delay between the band pass and the powered woofer?

Thank you.

The Genesis speakers have one set of binding posts, so that the included amp gets the same signal as the passive crossover. That way, switching amps does not require adjustment of the speaker. Nevertheless, some adjustment is needed when high output impedance amps are used. Hence, I do provide for this with user adjustable gain and low-pass frequency.

Initially I was surprised too with group delay on various amplifiers. With some amplifiers, it isn't even constant with frequency and power! Measure a few, it would be interesting to say the least.
 

racerxnet

Well-Known Member
Apr 30, 2014
76
25
323
Gary,

If you recommend amplification to the bass towers, then why have built in amplification in the bass servo? What happens to the servo amplification when powered separately? I am curious with my Genesis 2 system.

Mark
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,599
225
1,190
Seattle, WA
www.genesisloudspeakers.com
Mark,

The amplifier in the servo-system is part of a feedback loop. Hence, unless you know the amplifier characteristics it is impossible to make the servo-control system function accurately. With your Genesis 2, even the woofer cables are inside the feedback loop. Hence, it is important to design everything as a whole.
 

racerxnet

Well-Known Member
Apr 30, 2014
76
25
323
Mark,

The amplifier in the servo-system is part of a feedback loop. Hence, unless you know the amplifier characteristics it is impossible to make the servo-control system function accurately. With your Genesis 2, even the woofer cables are inside the feedback loop. Hence, it is important to design everything as a whole.

If that is the case then I need to go from the PreAmp, to the Power Amps then to the servo control for proper operation. Would that be correct. Also, do you recommend the same wattage for all 4 amplifiers?

Mark.
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,599
225
1,190
Seattle, WA
www.genesisloudspeakers.com
Mark,

All 4 amplifiers have to be identical. But are you going to bypass the Servo Amp supplied with the Genesis 2? It is possible..... but do you have an electronics designer developing the servo-control circuit to work with the amplifiers you are using?
 

racerxnet

Well-Known Member
Apr 30, 2014
76
25
323
Mark,

All 4 amplifiers have to be identical. But are you going to bypass the Servo Amp supplied with the Genesis 2? It is possible..... but do you have an electronics designer developing the servo-control circuit to work with the amplifiers you are using?

Hi Gary,

As stated above in the chain for connection I would be using the servo as stated. I just wanted to confirm the connections as listed. Hope that clarifies this.

Mark
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,599
225
1,190
Seattle, WA
www.genesisloudspeakers.com
You only need one amplifier for the midrange/tweeters in addition to the servo-bass amplifier. Then, from the power amp to the servo-bass amplifier you use this:
http://genesisloudspeakers.com/gcable_bass.html

The old company used to drive the servo-bass amplifier from the preamp.
 

racerxnet

Well-Known Member
Apr 30, 2014
76
25
323
Gary,

Is there a schematic for the Bass interconnect and termination used.

Thanks,

Mark
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,599
225
1,190
Seattle, WA
www.genesisloudspeakers.com
Gary,

What watt resistors are you using?

Different sizes and different brands/types will sound different. If you are going to make these interconnects yourself - you're going to have to try it out yourself. I'll always tell you what I do. How I achieve my sound, you'll have to pay for :D
 

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