Gilmore Audio Raptors are wonderful

Gilmore Audio Raptors are wonderful!

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Posted by Al Sekela (A) on July 08, 2006 at 15:41:12

In Reply to: Anyone using class D power amps (UcD, ICE, NuForce, etc.) on Magneplanars ? posted by beppe61 on July 8, 2006 at 05:14:15:

These are 500 watt per channel monoblocks that stay cool no matter how much power your Maggies demand. Mine are MG-20s.

In order to audition them, I had to rewire my crossovers to go back to full-range operation (I formerly used hybrid biamp with separate amps and cables for bass and mid/treble). The rewire is now a tri-wire setup with the tweeter crossover and cables completely separate after the spade connectors.

Even with the stock Magnepan outboard 132 microfarad midrange high-pass caps and bass low-pass (with augmented R-C filter on the bass panels and replacement mid/treble crossovers), the sound is better than anything I had before. I thought I had good bass-midrange integration before, but the control offered by these amps tames several speaker resonances and gives a bass and midrange delineation that is hard to believe. Their output impedance is far lower than the InnerSound amp, and they use no feedback to be confused by stored energy in the speakers.

I was concerned that the class-D operation would cause treble veiling, but these amps are the cleanest and quietest I've heard in my own or any other system. They use a chip set made by a well-known manufacturer, but have linear power supplies to avoid the noise issue with switching supplies.

It is too soon to say anything definite about the noise rejection, but they seem to be more immune to the RF noise in my environment than my previous setup (OTL monoblocks for mid/treble and InnerSound ESL-300 for bass).

Very highly recommended!

∑ Glacier Audio products page (Open in New Window)

Agree. I misunderstood andyr's intent

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Posted by Al Sekela ( A ) on July 11, 2006 at 14:25:30

In Reply to: Re: Hi Andy, posted by morricab on July 10, 2006 at 15:34:57:

and answered his further question in private e-mail.

While the resistive load is friendly to a wide variety of amps, Magnepans do require very low output impedance in the amp to control their stored energy issues for the best sound. I'm auditioning the Gilmore Raptor switching amps and the improvement in palpability is wonderful to hear. If someone were to attempt to model the stored energy issues (panel resonances and room air resonances), the equivalent circuit would be complex and specific to the room.

In my limited experience,

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Posted by Al Sekela ( A ) on July 17, 2006 at 14:39:17

In Reply to: Then, are we better of with a "digital" amp with high damping factor for the bigger maggies ?? posted by Dr.Jazz on July 17, 2006 at 04:15:24:

the Gilmore Audio Raptor monoblocks running my MG-20s full-range give the best performance I've had.

My previous setup was home-made OTL monoblocks (essentially, tweaked Atma-Sphere MA-1s) running the midrange and treble through upgraded crossovers, and an InnerSound ESL-300 running the bass panels through the stock Magnepan outboard low-pass filters. I thought I had good integration through the bass/mid crossover region, and even enhanced the performance by adding R-C filters to the bass panel inputs.

However, the Raptors made clear to me how important it is to damp all the Magnepan internal resonances, both in the bass panels and in the other elements and in their interactions.

To use the Raptors I had to rewire my crossovers. I use the mid/treble high-pass in the outboard Magnepan box to feed the midrange crossover, and a separate wire from the spade connector to run the tweeter crossover. This avoids the problem with the stock setup, where the treble has to go through the big, ugly midrange high-pass capacitor bank, and is a well-known tweak. My present setup is tri-wired, with no connections shared following the spade terminals at the amps.

The treble is cleaner, and the detail retrieval superior, compared to my OTL amps. The midrange palpability is superb, and the bass is wonderfully clear.

With proper timing of the output devices, a good switching amp connects the load either to a DC supply with low internal AC impedance, or to ground. Thus, the damping is always as good as it can be. Linear amps, on the other hand, have damping limitations imposed by their feedback networks regardless of how many output devices they may have. The OTL monoblocks (with no global feedback) have a fairly high output impedance that depends on the number of tubes employed. The Atma-Sphere MA-1 circuit dissipates 500 watts per monoblock continuously, and is about the largest such amp I could accommodate in my house. There are larger models with more tubes, but I would not be able to stay in the same room with them for long.

The Raptors have linear power supplies, so they are not degraded from the close proximity of the switching supplies found in most switching amps. Switching supplies generate enormous levels of RF noise. I've found that RF noise in linear amps is a major detriment to realistic reproduction, and that it gets in to do damage through all the ports. I have not tried undoing my RF noise treatments, but I believe the Raptors are much less susceptible to RF noise than my previous setup. They reveal all the problems with the AC supply to my Wadia 861 source, and have allowed me to find ways to make that device cleaner.

I'm still early in my evaluation, but I think I've found amps that are better than what my tweaked Maggies can reveal. I never thought that would happen.

Tone quality is superb!

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Posted by Al Sekela (A) on July 18, 2006 at 12:08:19

In Reply to: Re: In my limited experience, posted by morricab on July 18, 2006 at 02:03:24:

All my tweaking efforts on the OTL monoblocks were directed towards making the sound more natural as well as improving the resolution. Their sensitivity to RF noise, together with my strong local RF noise sources, led me to a lot of power line and noise source treatments as well as audio system treatments to reduce the effects of the noise,

By good fortune, I had just found some tweaks that removed most of the remaining RF noise artifacts from the OTL monoblocks when the Raptors arrived, so I was able to compare the amps' tonal qualities without the slight grit that always made the artificiality of reproduction obvious.

The best way to describe the comparison is that the Raptors have all the naturalness of the OTL monoblocks without the response dips and peaks created by the OTL monoblocks' high output impedance. Piano timbre is especially improved by this change, where good recordings now sound more like the real thing.

I've tried these amps briefly on a friend's SoundLab M-1s. We blew a fuse after one song because the bass sounded so good that we had the volume cranked way up. The amps' fuses are intended primarily to protect the speakers, and some users have destroyed their SoundLab back panels with them by using fuses that were too large! The performance on the SoundLabs was superior to their owner's Wolcott monoblocks, but, with only one song, I can't give meaningful detail to the comparison.

Yup.

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Posted by Al Sekela ( A ) on July 18, 2006 at 16:10:54

In Reply to: Hey, Al! Re: Tone quality is superb! posted by Webnick on July 18, 2006 at 15:32:15:

I have a mentor who is retired from the cable business. I've learned a lot from him about smooth, natural midrange sound, and how electrical noise interferes with it. He has what was the smoothest sound I'd ever heard until I got the Raptors and tweaked the AC supply to my Wadia.

The last time he visited, he took extensive notes on the tweaks I've made. He is pleased with the Maggie midrange I get with the Raptors, and admits it is now better than his.

The OTL monoblocks are not like typical tube amps. They are more neutral than most because they do not have the colorations imposed by the output transformers. I believe my tweaks made them about as resolving as the Raptors, but the bumps and dips in the Maggie response became obvious by their absence when I inserted the Raptors.

I believe there are some reviews in progress, but I'm not privy to who or when.

Correct.

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Posted by Al Sekela ( A ) on July 19, 2006 at 12:22:48

In Reply to: Re: Yup. posted by morricab on July 19, 2006 at 04:11:22:

Even with the tube complement balanced well, the output impedance is on the order of an ohm. This is why I used ZERO autotransformers with the OTL amps (thereby violating the purity of the "OTL" designation) with 4:1 impedance step up. This translates the 4-ohm Magnepan drivers into a 16-ohm load for the amps, and improves their ability to control the speakers. However, this level of control is still audibly inferior to the Raptors.

I don't know the details of what is inside the Raptors. The chip set is made by a well-known manufacturer, but is not the same as what they sell under their own name. The power supply is a linear one designed with massive margins to avoid the noise issues that come from switching supplies. The assembly is done by an aerospace house. The casework is machined aluminum and very rugged without noticeable resonances. The boxes are small but heavy.

Neither: neutral with good damping.

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Posted by Al Sekela ( A ) on July 22, 2006 at 12:07:22

In Reply to: Quick and detailed Amp for Magneplanar 20.1 or Warm & Relaxed? posted by DkB on July 21, 2006 at 23:56:31:

No amp will compensate for dynamic compression and maintain neutrality.

If the MG-20.1 is similar to my MG-20s in this regard, you can improve matters by rebuilding the crossovers and bypassing the miserable hardware and fuses.

IME, the Gilmore Raptor switching amps, 500 watts per channel, have the clearest, cleanest and most relaxing presentation. They avoid the noise issues of switching power supplies by having oversized linear supplies. The damping is as good as it can be, which is important with the large Maggies. They appear to be less sensitive than amps with feedback to RF noise picked up by the speakers and the speaker cables.

Switching amps are limited by their power supplies.

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Posted by Al Sekela (A) on July 25, 2006 at 13:31:57

In Reply to: back EMF posted by MM on July 25, 2006 at 07:27:39:

The ability of an amp of any variety to absorb reactive currents (what you call back-EMF) depends on the power supply.

In a switching amp, the "output" transistors switch between ground and the DC rail. How much the DC rail looks like an AC ground to the speaker depends on the impedance of the power supply. A small power supply will keep the amp from properly damping the speaker. With an amp rated at 15 WPC, I suspect the switching transistors are also small and have higher impedance than desired.

Most switching amps use switching power supplies, which generate lots of RF noise. This is why most of them are considered to be veiled and have an artificial midrange and treble.

I'm auditioning Gilmore Raptor 500 watt monoblocks on my MG-20s. These amps are the best I've heard. They have oversized linear power supplies, and have no trouble with RF noise or damping the speakers.

Neither: neutral with good damping.

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Posted by Al Sekela (A) on July 22, 2006 at 12:07:22

In Reply to: Quick and detailed Amp for Magneplanar 20.1 or Warm & Relaxed? posted by DkB on July 21, 2006 at 23:56:31:

No amp will compensate for dynamic compression and maintain neutrality.

If the MG-20.1 is similar to my MG-20s in this regard, you can improve matters by rebuilding the crossovers and bypassing the miserable hardware and fuses.

IME, the Gilmore Raptor switching amps, 500 watts per channel, have the clearest, cleanest and most relaxing presentation. They avoid the noise issues of switching power supplies by having oversized linear supplies. The damping is as good as it can be, which is important with the large Maggies. They appear to be less sensitive than amps with feedback to RF noise picked up by the speakers and the speaker cables.

True for stock speakers...

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Posted by Al Sekela (A) on July 31, 2006 at 16:01:37

In Reply to: Maggies at low volume posted by raja79 on July 31, 2006 at 10:32:51:

Magnepans have poor-quality connectors, wiring and crossover parts. Bypassing and replacing these things makes them work well at low listening levels. If you need speakers that work well at low levels right out of the box, then Maggies are not for you. However, if you are willing to tweak and learn, you can achieve excellent sound for much less money than similar speakers would cost.

Maggies also need amps with excellent damping characteristics to control their panel resonances and the room resonances coupled to the panels. IME, the best amps I've heard on my MG-20s are the Gilmore Raptor monoblocks. These have vanishingly small output impedance and the sense of overall control is wonderful.

I've heard SoundLabs and believe my tweaked MG-20 setup is superior at all levels. SoundLabs use overlapping resonances of individual panel sections to achieve higher SPL, and this is obvious if you've heard a setup with good control.

Not an exact match...

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Posted by Al Sekela (A) on July 31, 2006 at 15:30:02

In Reply to: Weird amp query of the day: Innersound ESL vs NuForce monoblocks on MG1.6 posted by Albireo on July 30, 2006 at 22:34:27:

I own the InnerSound ESL-300 and am familiar with its characteristics and limitations. It has a much smoother sound than the Bryston 4B-ST it replaced, but is not as clean and transparent as a good tube amp in the treble.

I'm presently running my MG-20s with Gilmore Raptor 500 watt monoblocks. These are switching amps with oversized linear supplies. The switching supplies in the NuForce and similar light-weight amps are powerful radio frequency noise sources. In fact, the NuForce had to be redesigned to meet FCC requirements because the first version put out so much RF noise. The Gilmores are the best amps I've ever heard.

Magnepan speakers are excellent radio antennas, and pick up RF easily. Even if the power amp circuit is immune to RF noise from the speaker connection, just letting it get into the chassis means it can get into your source through parasitic capacitances.

Your sonic description suggests your NuForce setup suffers from RF noise. The InnerSound is less noisy but is still somewhat sensitive to RF noise at the speaker terminals. This can be helped with R-C networks at the ends of the speaker cables, and RF damping measures on the cables and in the speaker crossovers.

Let me know if you want to correspond by e-mail on this topic. I have a lot of experience in dealing with RF noise in my system.

With pleasure!

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Posted by Al Sekela (A) on August 14, 2006 at 09:26:20

In Reply to: Anyone ditched their Class A amp for digital? posted by Dawnrazor on August 13, 2006 at 21:52:38:

I had what I thought was the most revealing setup possible, with my own OTL monoblocks driving MG-20 midrange and treble, and InnerSound SS driving the bass panels. I got detail that I did not hear in any but one or two other systems.

Then the Gilmore Raptors arrived for audition, and I realized that they deliver even more detail and with superlative control of the Maggie panel and room resonances. I've been able to resolve AC issues with my source that the previous setup obscured. The sound is much, much better. It is more relaxed and life-like than what I could get with tubes, and has better authority than what I could get with the big InnerSound as a bass amp.

Linear amps are dinosaurs. Just be sure to avoid switching amps with switching supplies.

I bought them and love them!

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Posted by Al Sekela (A) on September 07, 2006 at 15:50:41

In Reply to: Pinging Al Sekela posted by GL on September 7, 2006 at 10:26:50:

The Raptors are so neutral and well-behaved that I've been busy upgrading the cables and power cord for my Wadia. With my previous bi-amp setup, I knew intellectually that these things could be improved, but actually hearing the results is very rewarding. The previous collection of amps had enough noise problems of its own that my ability to detect progress in tweaking the CD player setup was limited.

Let me answer your questions in order.

1) Have you determined if the amps put out significant RF back through the power connection, radiated through the air, or out to the speakers. I'm talking about the Class D switching frequency.

As far as I can tell, these amps do not produce significant noise. I have noticed some changes in sound with different power cord designs on the amps, but this is likely to be due to power cord interactions with the AC house wiring.

2) Have you tried Zobel networks at the speakers yet?

Yes, my standard speaker setup is to use R-C filters at all ends of all cables. These are soldered to my DIY cables, so I've not done the experiment of removing them. I don't think these affect the amps one way or the other, but they do load the cables to reduce RF resonances that can couple back to the CD player. These are not strictly Zobel networks, but are similar.

3) Have you determined which module is used in the Raptor yet? e.g. the Icepower.

This is proprietary to Gilmore Audio. The modules are not the ICE.

4) Has the sound improved as the amps have broken in?

I can't say, as I've been like a kid in a candy store with my cable tweaks. Things are so much better from cable tweaks that any amp burn-in improvements have been swamped.

5) Do you have any further comments on the sound of the Raptors compared to the amps you had previously?

The Raptors are neutral in the same sense that the Atma-Sphere OTL amps are neutral. There is no 'tube smoothness' that robs music of honest details. However, the Raptors have more authority over the Magnepans. Quirks in playback of recordings I know well, that were due to under-controlled Magnepan resonances, are now missing. There is more palpability and poise in the presentation. The treble extension and clarity is just as good if not better.

There is also better bass definition, which includes pitch as well as sound-stage imaging of bass instruments. No doubt, I was inhibiting my system by attempting to match the OTLs on the midrange and treble with solid-state on the bass, but I perceive the Raptors have much more honest bass on Maggies than the InnerSound ESL-300. I feel that Magnepans couple so well to the room air, that the bass amp has to damp the Maggies as well as the room. Simply adding the Raptors (which are always on) improved the bass from our RPTV, which has no electrical connection to the audio system, but shares the same room air.

The Raptors are an excellent match to Magnepan speakers. The performance will be limited by speaker tweaks and cables, and not the amplifiers.

Been there, done that, bought the T-shirt...

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Posted by Al Sekela (A) on September 17, 2006 at 15:24:56

In Reply to: Maggie 20.1 with 2 Amplifiers posted by Peter_S on September 16, 2006 at 13:18:22:

Actually, my experience has been with MG-20s, but the problems are the same.

I tried to match OTL monoblocks on the midrange/treble with a solid-state stereo amp on the bass panels. I had the levels matched, and visitors commented upon how seamless the presentation was through the midrange.

Then I got a pair of Gilmore Raptor switching monoblocks (rated at 500 wpc, but with very low ouput impedance), and rewired my already modified crossovers to go back to single channel per speaker operation. The crossovers mimic the stock except the treble feed bypasses the stock midrange high-pass capacitor bank (the speakers are effectively tri-wired), and I added R-C filters to the outputs of the stock bass low-pass elements. These changes were made prior to adding the Gilmore amps, but I want to be complete about the comparison.

The sound with the Gilmore amps is so much better! The mid-bass through midrange palpability was increased very much over the bi-amp setup. The treble is clean and pure. The bass damping is far superior to what it was with the InnerSound ESL-300 bass amp.

What Maggies really need is the highest damping factor you can provide. Your proposal divides the power requirements among the amps, but does not increase the damping factor of any one of them. It will not result in improved performance, and will consume many hours of your time in trying to make it work.

The Wolcotts are fine amps within their power limitations, as Henry Wolcott is a genius who put his feedback tap inside the output transformers. This makes his amps stable with electrostatic speakers, but does not overcome the limitations of tube circuits in general. You should be able to get good modest performance with these amps if you don't care for the sound of the Odyssey Stratos. Certainly, either type of amp would be good to break in the Maggies.

Modifying new speakers is always a personal decision, because doing so voids the warranty. However, I would consider bypassing the midrange high-pass capacitor bank for the tweeter feed and the stock Magnepan mid/treble connection hardware, fuses, and crossovers. The Gilmore amps retail for $5000 per pair, and are a bargain for Magnepan power.

It's all about the tone.

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Posted by Al Sekela (A) on September 18, 2006 at 14:40:14

In Reply to: Re: Been there, done that, bought the T-shirt... posted by morricab on September 18, 2006 at 08:01:54:

Sorry that I haven't been more clear about this. I'm a music lover first and audiophile second. Some of most intense experiences I've had have been with live music, and my tweaking efforts have always been directed towards capturing more of the tone of live music in my system. When I installed the Raptors, I was captured by the gorgeous tones present in my favorite recordings.

RF noise is the major cause of harsh, cold tone in serious playback systems (along with the usual other issues), IMO. Switching amps that contain switching power supplies are compromised by the proximity of the supply. The Raptors are based upon oversized linear supplies for this reason. My OTL amps could approach the Raptors for good tone, but were more susceptible to RF noise from other sources than the Raptors appear to be.

The chip technology is proprietary, but is made by a well-known manufacturer. The assembly is done by a first-class military-qualified house.

I haven't had the amps long enough to say that they are tweak-proof. They perform so well that I've been busy cleaning up some now-obvious problems with my CD player AC supply and interconnect cables. I've found some slight resolution dependence on the details of the Raptor power cords, but that is all.

The amps use toroidal power transformers, and, like all such transformers, will buzz if the AC has enough harmonic distortion. I can tell when my neighbor uses her hair dryer on half-power! Fortunately, that is the only local AC harmonic distortion issue that I have.

No.

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Posted by Al Sekela (A) on September 18, 2006 at 14:19:00

In Reply to: Had you tried any other Class D amps with your 20s Al? posted by Webnick on September 17, 2006 at 19:40:12:

I was convinced by field reports that switching amps were fatally flawed, especially with a speaker such as the true-ribbon Magnepan.

It was a lot of work for me to rewire my crossovers so that I could test the Raptors, and I would not have done this if I did not have confidence in Mark Gilmore's designs. At least with my speakers, the Raptor switching amps deliver the best sound I've had, and I'm happy I tried them and bought them.

Another recommendation.

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