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May 2013
Superior Audio Equipment Review

Copland CTA 506 Vacuum Tube Power Amplifier
Hearing music's sadness -- the longing sigh -- as the music's essence tugs at your emotions.
Review By Ron Nagle

This is a follow-up review to Phil Gold's original review (as seen here).


Copland CTA 506 Vacuum Tube Power Amplifier  From time to time, I would pass a furniture store on the corner of 34 Street and Madison Avenue in New York City. The store specialized in Danish Modern furniture; I can't recall the stores name just now, but that must have been 30 or more years ago. My territory at the time was in midtown Manhattan fixing office equipment for Xerox. Back then, I would walk through the store just to breathe in the smell of teak wood emanating from the beautiful but unaffordable furniture. Scattered about that showroom they used a few Bang & Olufsen hi-fi systems in a static display. Upon reflection, my fondness for clean organic Scandinavian Design must have been born long since, from back then.

The Copland Companies founder and designer Mister Ole Moller tells us how he settled on the name of the company. It's pretty straight forward, Mr. Moller lives in Copenhagen Denmark ; he plays piano and is an admirer of the composer Aaron Copland. In my estimation, the CTA 506 Amplifier is a clean modern design that intimates power and yet it avoids looking like an industrial transformer. Even now, this Copland Amplifier in some ineffable way speaks to me with a defining Scandinavian accent.


The Hardware
The Copland 506 MSRP is $6,500. At this price, it is approximately one-fourth the cost of some comparable high-end hollow state amplifiers. The unit weighs 57 lbs. and measures 7.50" x16.75" x15.35" (HxWxD). It is slightly smaller than most tube power amplifiers that can produce 90 wpc. The chassis/case is constructed with heavy gauge cold rolled steel sitting on four feet. The top cover is perforated for air circulation, as are the side panels. Right in the center of that nice modern 3/8" thick aluminum front panel is the power switch. This switch is round and reminds me more of a volume control. That choice does not seem logical to me since you really cannot turn it past the (power on) twelve o'clock position. A more logical choice would be a two-position rocker switch with a matching aluminum finish. Around back at the business end of the amplifier and centered on the rear panel is the IEC power cord receptacle containing a fuse. However, there is no fuse value listed. Glancing at the back panel the first thing that will grab your attention are the very nice gold plated WBT speaker binging posts. There are three on the left and right for a total of six. They are labeled: 0/Gnd., 4, and 8 Ohms. However, the written specifications speak of a non-existent connection for 16-Ohm speakers. Additionally you have the option to connect balanced XLR or unbalanced RCA cables to the CTA 506. However, the RCA jacks on the rear deck are in a recessed metal socket. This is a very sensible idea however, one pair of RCA plugs on my old Wire World Eclipse cables were to big to fit into the openings.

Note: All of the preceding nit picking does not in any way affect the sound of the Copland CTA 506 Amplifier.


The Engine Inside
Copland CTA 506 Vacuum Tube Power AmplifierAfter you unpack the amplifier, you will need to unscrew the top cover and remove some of the packing material holding the six-pentode tubes in place. You will then be able to see a very beefy looking Toroidal transformer sitting next to a single blue colored circuit board. Near the back interior are two large standard laminated out-put power transformers. The circuit board is divided into mirror imaged left and right sections. Divided onto those two sections there are miniature triode tubes There are four 12BH7 driver tubes and two 12AT7 push-pull cathode drivers. In front, just behind the grill opening are four matched KT120 pentode power tubes. They have a plate dissipation specified at 60 watts for each tube. The KT120 is a relatively new addition to the KT88/6550 family of power pentodes. However, it is possible to get a lot more power from these tubes. That is about 200 wpc from a pair KT120 Pentodes. With the CTA 506 amplifier conservatively rated at 90 wpc, you have a very large amount of low distortion dynamic headroom. Up front the two 6550 pentodes provide active tube regulation. One tube is dedicated to regulate the driver stages and the second tube regulates the amplifying stages.  What you are looking at is a modern iteration of a time proven push-pull ultra-linear circuit patented by Alan Blumlein (No. 496,883) and popularized years later by David Hafler and Herbert Keroes. (Reference: Wikipedia) Many classic power amplifiers including Marantz, EICO, and Dynaco and my old Heathkit WM 5 Mono blocks were designs utilizing Ultra-Linear circuits.

Ultra what you ask? Well it's a clever way to use (in this case) a five element pentode tube for it's greater power handling but at the same time operate the tube so that it acts more like a triode. The Ultra-Linear circuit innovation requires adding a separate section to the primary winding of the output power transformer. This additional winding allows a portion of the output signal to be applied to the power pentodes screen grid. It can be thought of as a type of local feedback to the KT120 screen grid. The benefit is that the pentode tube can operate with much lower output impedance and with lower distortion by taking on some of the characteristics of a triode tube.

Dare I say the romance of tubes?

Ok, call me superficial but the Copland amplifier has something that will fascinate any red blooded Tubeaholic. Powered on you will see two pairs of matched KT120 Pentode tubes bracketing two 6550 pentodes placed side-by-side and visible behind the slots in the front panel. With my esthetic sense lined up in parallel with those six tubes, Copland installed six red Light Emitting Diodes (LED), that's one diode behind each tube. You could opt to turn off the front panels bright scarlet light show with a switch located on the back panel, but then that would most definitely kill the party.


Sound Advice
This very same CTA 506 amplifier was demonstrated at the 2013 Communications and Electronics Show in Las Vegas and therefore came to me "broken in" with the tube bias adjusted. Included in the owner's manual you can find the tube biasing instructions with the .036 Volt bias specifications. On the main circuit board diagram, there are four test points and four separate bias pots, one for each KT120. However if you purchase this amplifier from a storefront dealer why don't you just let the store guy's set it up for you. As received, right out of the box and before any serious listening, the CTA 506 was run in for approximately 40 minuets before it completely settled down. It took that long before the image between the speakers stopped improving and the bass tightened its dynamic grip. If you let the Amp sit over one cold night, it could take about twenty minuets for the sound to solidify. One last blurb, with those six big Pentode tubes up front the CTA 506 runs nice and hot. So you most definitely need to give this amplifier ample space to breath.

Note: Half way into auditioning the amplifier, I replaced the CTA 506 stock power cord with one and a half meter of HE II Kaplan Cable. The sound was quieted and the performance seemed smoother and less grainy.

Fire up front music out back. I usually begin auditioning any audio gear by piping radio music through it for a time. Let us start at the bottom octaves and work our way up by describing the bass response. Why? Tube (Hollow State) bass has a very defining personality that can vary greatly. In amplifiers, it can tell an awful lot about bass damping and extension. My bass reference remains Adagio d'Albinoni in G minor. This is a recording by Gary Carr and Harmon Lewis. This recording by Gary Karr and Harmon Lewis may still be available via the Cisco Music catalog [GCD 8003]. It is a duo of two instruments, an Amati bass fiddle accompanied by a large pipe organ recorded in a cavernous stone cathedral. Certainly, this recording serves as a deep bass reference, but far more importantly, it will detail bass voicing and resolution. It is not enough to rattle low bass it is another thing to capture the rich wooden textures and mournful harmonic resonance of this performance. Gary Carr's Amati bass fiddle transitioning the scales from deep bass to midrange has to be the ultimate bass resolution test. This recording is invaluable to me because it contains sustained bass frequencies that slowly decay into inaudibility. The time it takes for the organs echoed reverberation to fade gives a sense of the size of the churches stone interior. The musical selection helps analyze not just the bass transient speed but also and far more importantly, the tonal structure of the sound itself.  In that resonant stone Cathedral Gary Carr's bass seems to summon you with a mournful cry of despair. The Copland CTA 506 portrays the tumbrel nuance perfectly, you can hear the harmonic shading and wooden resonance of the Amati's body The Copland amplifier gets it right, the sadness the longing sigh, the essence of the music is free to tug at your emotions.

If this performance does not affect you than I suggest you find a good Shrink. Talk at me! I listen and evaluate mostly by listening to the sound of a human voice, It this that I know best. When the Copland Amplifier was literally dropped off I cued up the Diana Krall album, Live In Paris [Verve 440-065-109-2] Ms. Krall has a strong characteristic quality to her voice that can be hard to reproduce. Specifically, there are two songs on this CD, titled; S' Wonderful and I Could Drink A Case Of You. The three words wonderful, marvelous, and case are a good test of an amplifiers power to detail midrange minutia. Diana Krall sings these words with a very wet sibilant "Ess" sound that tells me about midrange resolution. When Diana sings   I could drink A Case Of You, she sings slowly and adds a slurring moist quality to her voice. What a great vocal interpretation, and damn how appropriate can you get ! The song was written about someone sucking booze in a (hotel) bar. She sounds a few sheets to the wind, and it's all intoxicatingly there to hear.


To describe the differences between a good solid-state amplifier and a good Hollow State tube powered amplifier is hard to do. As a matter of fact describing sharply outlined differences between tube amplifiers is an art form that could tax the skills of Shakespeare and Shelley. Nevertheless, I am duty bound to try! My reference tube amplifier is my Audio Research Classic 60. Aptly named, it is in fact a 60 wpc amplifier that uses 6550 Pentode tubes configured to operate as triodes. The respected CL60 is indeed a classic tube amplifier, and a very different beast. The CL60 projects the Adagio bass recording with a big and wide image that is much warmer and a less defined than the CTA 506. The Copland interprets the same soundstage with the bass in greater detail and with more tonal nuance. The full spectrum result is that it is better integrated with the midrange and treble. Another way to say the very same thing is to borrow Harry Pearson's coinage to describe the sound as, "Continuous".

Moving right along, my PrimaLuna PL 2 integrated amplifier supplies about 33 wpc of power. Now the PrimaLuna is yet another Ultra linear tube amplifier with a slightly different way to grab music. My PL2 has a matched quartet of NOS GE 6550 tubes (that I rolled). In a shoot out with the Copland CTA 506, the soundscape is a might smaller. That is it seems just between the speakers and not as deep. On a list of my requirements, the dimensions of a sound stage rank very near the top. Why? It is because in my small listening space the sound stage must expand to include me!

Even my cat likes the Copland amplifier!


End Think
Granted, what may be impossible and mutually exclusive would be to carve razor sharp outlines around elements contained in a performance. And then at the very same time depict that performance space as an expansive tonally rich flesh and blood event. In my estimation, laying at these two extremes you will find cold sounding "Class D" amplifiers* and at the other extreme you will find warm sounding "Single Ended Triodes".  In my estimation, the technology that combines the best of both worlds is the implementation of the Vacuum Tube Ultra linear Circuit. This will explain why it has been in so many audio components and used by so many manufacturers for the last 73 years.

Like an oenophiles predilections you may prefer a crisp fruity white wine or a warm deep red. Amplifiers can be thought of like that, it is an acquired taste. For me the flavor of this space expanding Copland Amplifier compliments my love for the organic sound of a human voice. If you would be like me, desire the best of both then go forth, and seek out the Copland time machine as it will take you there.



*Digital be a toy of engineers that have tiny little ears. They take's the music and  they chops it into tiny little bits, then they squeezes it through tiny little chips. They knows music don't need no least significant bits. -- R.N.


Review System
Speakers:  Onix Rocket Strata Mini and Aurum Cantus Leisure 2 SE two-way monitors on 24" stands, Mark and Daniel Omni Harmonizers.

Amplifiers: Audio Research CL60, Prima Luna Prologue 2, Roger Sanders ESL Power Amplifier, Audio Research SP9 MK III Preamplifier.

Analog: SOTA Sapphire Turntable, SOTA flywheel power supply, Grado Signature tone arm. Blue Point Special Cartridge

Digital: Marantz CD player DV8400, Music Hall DAC 24.3 D/A Converter


Type: Stereo vacuum tube amplifier
Frequency Response: 5 Hz to 100 kHz (-3dB)
Tube Complement: Four KT1220, two 6550, four 12BH7 and two ECC81
Power Output: 90 wpc continuous from 20 Hz to 20 kHz
Distortion: < 1% at all levels|
Signal To Noise: > 100 dB 
Overall Feedback: 17 dB
Sensitivity: 1.5 V
Input Impedance: 100 kOhms
Output Taps: 4 Ohms / 8 Ohms 
Binding Posts: Gold plated WBT 200 Ampere
Power Transformer: Shielded toroidal
Inputs: XLR, RCA
Dimensions: 17" x 15.4" x 7.5" (WxDxH)
Weight: 57.3 lbs
Warranty: One year parts & labor, 5 year parts replacement
Tube warranty: 30 days
Manufactured: Denmark
Price: $6500


Company Information
Ryesgade 25 D
2200 Kobenhavn

Website: www.Copland.dk

North American Distributor
Divergent Technologies
E-mail: divergent@divertech.com
Website: www.Divertech.com













































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