COPLAND CTA408 INTEGRATED TUBE AMPLIFIER

INTEGRATED TUBE AMPLIFIER

Even the front panel of Copland’s latest valve integrated amplifier is musical. You could play a few tunes on it if you like!

Copland really needs to have a quiet word with Danish customs authorities. My review sample, which was air-freighted to me almost direct from Denmark, had been opened and resealed by them before being loaded onto the plane. “Based on X-ray control our security personnel (…) had to open the consignment and make a manual control” said the printed note that had been left inside the carton.

I suspect the manual inspection might have been required because unlike many manufacturers of valve amplifiers, which ship their amplifiers with the valves already installed, Copland ships the four KT150 power valves in a separate box inside the main carton. I guess that all those wires and metal supports inside the valves must look extremely suspicious on an X-ray.

EQUIPMENT

The Copland CTA408’s front panel looks so plain that you could almost be forgiven for thinking it was a power amplifier, especially if it’s in its standby mode, in which mode the centrally located front panel display is just a solid black circle save for a single bright blue LED.

Press the small black round-topped push-button to the right of the display, however, and (assuming you’ve connected the power and correctly set the 240V mains rocker switch on the rear panel) the display will light up to show that you have a choice of four line inputs (identified only by the numerals 1 to 4) and a phono input (identified by a capital P). There are two extra symbols in the display, circles with dots in their centre, which appear to have no purpose at all, and which are unexplained by the sparse (eight page) Copland ‘User Guide’. Copland seems to be using a new display on the CTA408, because whereas the older display had the letters ‘SB’ alongside the blue standby LED, and ‘ON’ alongside the red ‘On’ LED, the display on my review sample of the CTA408 had no lettering alongside these LEDs at all.

The small black round-topped pushbutton to the left of the display is a ‘Tape Monitor’ button, which is a description that’s sure to mystify anyone born in the last twenty years or so. And although it might seem that tape machines are making a bit of a comeback, given the number of audiophile sites selling pre-recorded open reel tapes, only two companies in the world currently manufacture open-reel recorders – STM (formerly Mechlabor) and Metaxas & Sins, so ‘comeback’ is hardly an accurate description.

Copland’s volume control is a little intimidating, because it’s calibrated from 0 to infinity in dB, though it’s difficult to decipher this because the ‘dB’ is actually upside down at the two extremities of the control. Even more confusingly, the numerals on the dial are not prefaced by the minus symbol that’s essential in order that the 0 and the infinity make sense. But, just so we’re clear, infinity is minimum volume and 0dB is maximum volume. As for the numerals themselves that are on the dial, they go up in twos from 0 to 10 (2, 4, 6, 8, 10) then in fours from 10 to 22 (14, 18, 22) then in sixes from 22 to 46 (22, 28, 34, 40, 46), then in eights from 46 to 70 (46, 54, 62, 70) after which there’s a bit of a leap to infinity. I’ve never, ever, seen this numbering system before and cannot imagine any earthly reason for it.

Input selection is done via the rotary control at the left of the front panel, and it’s an encoder, rather than a switch, so it merely instructs relays inside the CTA408 to make the desired input selection. This circuit implementation means there’s a loud click whenever you switch inputs.

The Copland CTA408 can handle both moving-magnet (MM) and moving-coil (MC) cartridges, but as you’ve probably already guessed from my description of the front panel display, there is only one phono input. You have to select whether you want it to be MC or MM via a slider switch on the rear panel. If you choose the MC input you have a choice of three input impedances: 50 , 100 or 470 . For a moving-magnet cartridge the impedance is set at the industry-standard of 47k .

The Copland’s headphone output circuitry is over-engineered, with an output impedance of just 9 and a frequency response far exceeding that of the main amplifier, from under 10Hz to more than 200kHz. It’s all delivered from a standard 6.35mm (quarter inch) phone socket on the right-hand side of the amplifier. This is a very inconvenient location, but I guess it’s more accessible than if it were on the rear panel, which, if you’re not going to put it on the front panel, would be the only other place you could put it.

My suggestion would be to buy an extension lead with a standard 6.35mm socket at one end and a right-angled 6.35mm plug at the other, to make for a ‘neater’ look, but be warned that whenever the plug is inserted the main speaker output will be muted, so you’re still going to require easy access to the plug. It did occur to me that this might be Copland’s way of ensuring you leave sufficient space for ventilation!

Copland’s CTA408 is a very photogenic amplifier. Which is to say that it looks much more elegant and streamlined in photographs than it does when it’s in your equipment rack. It’s a big, boxy amplifier. If it were not for the need to ensure the valves are adequately ventilated, I’d suggest putting it on one of the lower shelves of your equipment rack, so you can only see the front panel, which is actually pretty good-looking, especially as you can see the glowing valves through those six horizontal slots machined into it, that for all the world reminded me of a mantle-shelf radio my grandfather used to own. The bars of alloy separating the slots are, incidentally, quite musical… or at least four of them are. If you pluck the topmost one with your fingernail, it will play a fairly pure ‘B’ on the tempered musical scale, pluck the next and you’ll hear ‘C’, while the next will sound ‘D’ and the next ‘E’. The bottom-most bar will sound ‘F’, but it’s not as ‘pure’ a sound as the others.

However, regarding the need to ensure ventilation for the valves, the chassis is so capacious, and there’s so much ventilation supplied (there are also slots on both sides of the chassis, as well as the bottom and top of the chassis… indeed the only panel that doesn’t have any ventilation is the rear panel) that I am certain there will likely be adequate ventilation so long as you leave a two or three centimetre gap on both sides of the chassis and above it.

The rear panel of the CTA408 is a bit unusual because rather than fix all the RCA terminals to the rear panel in the usual manner, Copland has fixed them directly to a printed circuit board located inside the chassis, so each one is accessed via a small circular hole drilled in the rear panel. This technique greatly reduces the amount of wiring inside the amplifier — and improves performance and reliability — but does mean that if you have a favourite RCA connector whose body is larger than the diameter of the hole (16mm) you won’t be able to use it. The speaker terminals are standard multi-way gold-plated types.

The bars of alloy separating the slots are, incidentally, quite musical… or at least four of them are

REMOTE

The infra-red remote Copland supplies (RC-102A) is interesting because it has more buttons on it that don’t work than it does buttons that do. The five buttons that work are for on/standby, volume up, volume down, and input source selection up, and input source selection down. The six buttons that don’t work don’t do so because they’re intended to operate a CD player. (Stop, Play, Pause, Track Skip, etc). This would not be unusual if Copland actually manufactured a CD player, because many manufacturers ‘re-use’ remotes across several different models because it’s more cost-effective for them (they can buy the remotes in greater quantities). But Copland doesn’t have a CD player in its line-up.

I can only assume the company has found a supply of inexpensive remotes and is ‘badging’ them. Given the number of spare buttons on the RC-102A, it would have been nice if Copland had made one of them a ‘Mute’ button, or re-purposed several of them as direct access source buttons. At least all the buttons that control the CTA408 are at the ‘top’ of the remote plate, so they fall easily under the thumb.

INTERNALS

Inside the CTA408 you’ll find the layout and design of the entire amplifier, including the PCB components, is a true delight, and apparently all the work of Copland’s own Olé Møller, who founded the company after working for many years at Ortofon. Although Møller was involved in the design of Ortofon cartridges, his principal duties with the company were involved in the design and manufacture of the cutter heads and amplifiers used in Ortofon’s cutting lathes, used to make the masters used to press LPs.

The very large toroidal power transformer is made for Copland by Noratel, which came as a surprise to me, because I would have thought that being a Dane manufacturing in Denmark, Møller would have specified a transformer from a Danish manufacturer, rather than one made in Norway. I then realised he didn’t have much option, because in recent years Noratel purchased all three of Denmark’s transformer manufacturers, Lübcke, Garre Transformere and Ulveco!

Møller does, however, use Danish-made output transformers. In fact, they’re not just made in Denmark, they’re made in Copland’s own factory in København. This is very important because output transformers are arguably the most important components in a valve amplifier… even more so than the output valves themselves.

The phono input circuitry is all housed out of sight and away from electromagnetic interference in a shielded case, right where the signal enters the amplifier, which is excellent design. I am led to understand that it uses active RIAA equalisation that uses entirely discrete components including high-spec JFETs.

The four KT150 valves are provided separately. Mine were made by Tung-Sol. Because they’re matched at Copland’s factory and the bias set for each one in its appointed position, the exterior of each valve box has a sticker (V104, V204, V103, V203) indicating in which valve socket it should be inserted. Being a mistrusting type of person, I would have preferred Copland to mark the valves themselves, because they cannot guarantee that anyone removing the valves from the cartons will then place them back in the same cartons. I mention this also because Danish customs had not only opened the carton containing the amplifier, but had also opened the valve cartons as well. I can only hope they put them back in the correct cartons! As for Tung-Sol, although the name sounds Chinese, it is a US company that took its name by tacking the first syllable from the word Tungsten (which is the metal from which the valve heaters are made) and tacking on the Latin word for the Sun (Sol), this last in reference to the colour the valves glow once they’ve heated up.

The combination of those KT150s and Copland’s customwound transformers is an aural delight

The company has changed hands a number of times since it was first established in Newark, New Jersey, back in 1907. It is now owned by the New Sensor Corporation, founded by Mike Matthews, which also owns the brands Sovtek and Electro-Harmonix. Although the company is still headquartered in New Jersey, all its valves are now manufactured in Russia under the watchful eye of Matthews’ partner, Irusha Bitukova. (Trivia factoid: Bitukova’s father was the co-inventor of the hydrogen bomb in Russia.) Irusha is also a videographer. She shot a great video that shows how valves are made that you can watch here: https://tinyurl.com/ehx-valve-manu

OPERATIONAL

Although Copland ships the CTA408 without the valves installed, as noted in the previous section of this review, I would imagine that if you purchase it from a retailer the valves would be pre-installed for you and the amplifier hand-delivered to your home, so it’ll really be a plug n’play exercise. But in the event you do have to install the valves yourself, it’s still really a plug n’ play exercise because all you need is an Allen key (not supplied), to remove the 16 screws that fix the CTA408’s cover to the chassis. (This may sound excessive, but the chassis is so large that it needs this number of fixings to ensure structural rigidity.)

Once the cover is removed, it’s simply a matter of plugging the four KT150 valves into their sockets. I would suggest using cotton gloves (not supplied) when handling the valves, but it’s not strictly necessary. The manual says the valves “have been carefully matched at the factory and the tube bias has been set accordingly.” Which for me raised the question of how the bias is reset when you replace the valves. The answer is that it’s reset using potentiometers on the PCB, a process that will require the attention of an accredited service centre.

As for the bias used, there are two methods commonly used on valve amplifiers: Fixed Bias and Cathode Bias. In a Fixed Bias type (such as the Copland CTA408) once the bias is initially adjusted to suit the electrical characteristics of the valve, it then stays the same until it’s adjusted again, such as when valves are replaced. In a Cathode Bias design the negative grid bias is accomplished by lifting the potential of the cathode using a resistor in series with the cathode so the grid bias varies according to the size of the resistor and the current through the tube. Because of this action, Cathode Bias valve amplifiers are often called ‘Auto-Bias’ designs.

Why does Copland use Fixed Bias in the CTA408? According to designer Olé Møller: “In cathode-biased output stages, the cathode resistors usually have an electrolytic capacitor in parallel, in order to prevent local a.c. feedback at this point in the amplifier. These cathode bias amplifiers, along with some more modern variants using IC servos, can have a sonic tendency towards compression and muddy bass, like other types of d.c.-servos. The Fixed Bias type amplifier is usually more power-efficient, with less compression and deeper, tighter, and freer-flowing bass reproduction.”

Copland says that because its circuit has been specifically designed so that it does not stress the valves, you can expect long valve replacement intervals. Says Copland’s Operating Manual: “The tubes are operated around 50% of their full nominal power, which considerably increases their life expectancy. The lifetime of the tubes should be at least 4,000 hours, assuming that the amplifier is switched on and off a couple of times per day.”

You do have to be firm but not overly-pushy to correctly seat the valves in their valve sockets, but it’s easy enough. I do have to note, merely because of its incongruity, that while on one hand Copland ships its valves separately so they have to be installed, and tells you how to open the case and install the valves, it seems to see no irony in the fact that it also prints a warning on the rear panel that says: “Caution! Risk of Electronic Shock. Do Not Open.” And, just in case you didn’t quite get the gist, it prints yet another warning that says “Attention! Risque de shock electronique ne pas ouvrir.”

As is usual with glass audio (I absolutely love this descriptor for valve-based hi-fi components) there’s a ‘soft-start’ circuit in the CTA408, though for this amp, I think

I’d call it a slowwwww start because after you press the stand-by button, the ‘blue’ standby light extinguishes and a red light starts flashing… and flashing… and flashing, during which the Copland is doing a selfcheck routine. This self-check takes around half-a minute (which seems like forever) after which the light stops flashing, but the amplifier still isn’t ready to go. You need to wait around another half-a-minute before you’re rewarded with sound. (You can attempt to listen prior to this, but it won’t be pretty, I warn you!)

On switch-on after the power is switched off at the rear panel the Copland always defaults to Input 1, so it would make sense to connect your most-used source to this input, but if you leave the amplifier in its Standby mode (in which it will consume less than one-watt of your mains power and none of the valves are powered-up, so it won’t eat into their service life), the CTA408 defaults to the last-used input. The one exception is if you were using the ‘Tape’ input. This input selection is always cancelled whenever you switch to Standby.

Some people reading this review might not understand the potential usefulness of the tape input, not least because I have yet to mention that there’s also a tape output, and the two comprise what was commonly known as a ‘tape loop’.

What happens is that whatever music is selected with the source selector (say A1) not only appears at the speaker outputs, but also at the tape outputs. The signal at the tape output is unaffected by the position of the volume control, so it simply ‘tracks’ volume changes of the music. This means that you can connect a recorder to the Tape Output and connect, say, an analogue-to-digital converter and, if you played back LPs via the CTA408’s phono input, you could convert your LPs to digital at the same time you were listening to them.

However, you could also send the phono signal out from the Tape Output to, say, a DEQX HDP-Express II room corrector and then take the output from the DEQX and connect that to the Tape Input. This would mean that every time you pressed the Tape button on the front panel, you’d hear your music corrected by the HDP-Express II to compensate for any deficiencies in your loudspeakers’ performance as well as for your room’s acoustics.

A tape loop also makes it very easy to conduct ‘A–B’ comparisons. For example you could easily check the ‘audibility’ of a particular brand of interconnect by simply using it to directly link the tape output terminals to the tape input terminals. With the ‘Tape’ button switched off, you’d hear the direct sound, and with the Tape button switched on, you’d hear the same sound, but through the length of interconnect. This would make it simple to choose the interconnect that — in your system, at least – has the least affect on the sound.

AUDITIONS

I was so excited by the performance of the Copland CTA408’s phono stage that I am going to lead my listening sessions with what I heard when spinning black vinyl.

First up was an old favourite (in both senses of that word) in the form of Frank Sinatra’s famous album ‘In The Wee Small Hours’. It’s been supposed that this particular album may have been the world’s first ‘concept’ album, being produced on the back of a failed suicide attempt, a divorce and the messy end of his most significant extra-marital affair, but I think Antonio Vivaldi would have a better claim with his album ‘The Four Seasons.’

Sinatra’s concept album is a magnificently unhappy album about loneliness, failure, isolation and depression that has such stand-out tracks as Mood Indigo, I Get Along Without You Very Well, What Is This Thing Called Love, Last Night When We Were Young and, of course the title track. Interestingly, the album was first released on two 10-inch discs (which I don’t have) and then on a conventional 12-inch LP, one of the first such ‘pop’ 12-inchers ever released.

Sinatra’s vocal construct on this album was a complete turn-around for him (Nelson Riddle famously said that Sinatra’s newfound ability to sing more emotionally was a direct result of his marital and other trials and tribulations.) You’ll hear all of this emotion listening to the Copland CTA408 better than you’ve ever heard it before. Along the way take the time to admire Sinatra’s phrasing and his ability to sustain almost any note, anywhere in a phrase or even within a word. It’s uncanny. The Copland also has the balance between Sinatra’s voice and his orchestra perfect.

But if you really want to hear fantastic sonics as well as fantastic music you could do no better than to audition GoGo Penguin’s ‘A Humdrum Star’ from just a few years ago. This was the band’s second album for Blue Note (hence the fabulous sonics!) but also the band’s furthest excursion from the fairly straight-ahead jazz with which they first made their name. ‘Humdrum Star’ is a fantastical meld of jazz, classical and electronica that’s so detailed you can barely believe it’s just drums, keyboards and bass. The musicianship from all three players is mind-blowingly good. If you need to test the attack and decay, dynamism, texture and tonality of a component, this should be your go-to album, and the Copland CTA408 passed all these tests with colours flying.

Time then, for some Steely Dan, so I span up ‘Aja’, partly because it’s a great album (probably their best) but also because I wouldn’t like to admit that mostly when I want to listen to Steely Dan I play my ‘Greatest Hits’ double-album from 1978 because it has pretty much all my favourite Dan tracks on them. But although it doesn’t have all my favourite tracks ‘Aja’ probably has the finest musicianship (literally dozens of the finest session musos in the US at the time played on it) of any of their albums and certainly the most going on sonically. The complex and sumptuous sound of this album was delivered to perfection by the Copland CTA408.

The fantastic sonics I heard could have been because of the synergies between vinyl and valves, the two technologies just seem to deliver better sound quality when paired. Then again it could also be due to designer Olé Møller’s passion for vinyl, and his long history at Ortofon. He has obviously put his heart and soul into the design of the CTA408’s phono stage. Just as equally, it could be due to the contributions from all three: valves, vinyl and Møller.

Being a valve amplifier, and not a particularly high-powered one at that, you will need to carefully consider the speakers you’ll use with it, not least because of the inevitable interaction between the amplifier’s output impedance and the loudspeakers’ own impedance. As a general guide I’d suggest that speakers connected to the 8Ω tap should have an impedance that dips no lower than 2Ω and it would be nice if the impedance also stayed under 20Ω for the most part. For speakers with impedances that drop below 4Ω, you’d need to use the 4Ω tap.

In my own sessions, during which I used speakers that fell into both categories, I preferred the performance of the Copland when using the 8Ω tap. I also preferred the performance when using loudspeakers with higher, rather than lower, efficiency ratings. My recommendation for this spec would be no lower than 87dBSPL and preferably higher. JBL’s fabulous L100 Classics worked brilliantly with the CTA408, for example, not only sonically but visually. (If you’d prefer a more modern-looking pair of JBLs, the Copland also worked really well with the JBL Synthesis HDI-3600s.) The Copland CTA408 also worked really well with Richter’s Wizards and Focal’s Kanta No3s.

Staying a little left-field for a moment longer, I also need to complement Møller on the headphone amplifier he’s designed for, and fitted to, the CTA408 because it, too, is a stand-out performer, delivering sound quality far in excess of what I usually hear from the headphone outputs on integrated amplifiers. I heard very fine sounds indeed from both Focal’s Stellias and Grado’s RS1s.

Once I started listening via the line-level inputs, I quickly found Neneh Cherry’s ‘Broken Politics’ had the Copland responding with a wonderfully light touch, so that her vocals came through with passion and nuance, and the kind of natural dynamic fluidity that only really good valve designs seem to manage. There was a lovely sense of space around each instrumental strand and a total lack of unwanted hardness to the sound.

Going in rather heavier with The War On Drugs’ Grammy award-winning (Best Rock Album) ‘A Deeper Understanding’ proved the Copland is able to deliver the deepest bass, the highest treble and tiniest sonic details perfectly, and all at the same time if needs be. The CTA408 revealed the signature sound of Adam Granduciel’s guitar-playing beautifully and the complexity of his melodies and arrangements. (He might, however, have spent a bit more time on his lyrics for the songs on this album. Maybe he consulted on the lyrics with Kate Bush, from whom he borrowed the album’s title.)

CONCLUSION

If you spin a lot of vinyl, you owe it to yourself to check out Copland’s CTA408 because the performance using the phono input is absolutely outstanding — you’re going to love it! Vinyl and valves are a match made in heaven. But even if you don’t spin a lot of vinyl, it’s worth checking out the Copland CTA408’s sound via its line inputs and your favourite line source because the combination of those KT150s and Copland’s custom-wound output transformers is an aural delight. Plus you can take added delight in the sound of the headphone output driving your favourite cans.

Yes, you do need to take some care with loudspeaker selection, but if you follow the guidelines I mentioned earlier in this review, you will have an enormous range of models from which to choose and trust me that if you do take the time to choose wisely, your efforts will be rewarded, because the Copland CTA408 will make certain they are. Scott Nyland

The Copland CTA408 has two taps on each of its output transformers, one 8 and the other 4 , yet Copland specifies the power output of the CTA408 into 8 and 3 loads. Irrespective of the tap you use, output power is rated at 75-watts per channel.

Newport Test Labs first measured output power using the 8 taps and 8 test loads. At 1kHz, the CTA408 exceeded its manufacturer’s specification by 23-watts when both channels were driven and by 28-watts when only a single channel was driven, returning power output results of 98-watts per channel and 103-watts per channel.

When the same tap was used to drive 4 loads at the same frequency the Copland CTA408 delivered 135-watts when only a single channel was driven and 110-watts per channel when both channels were driven.

Power output dropped off at the frequency extremes, as you can see from the tabulated figures. At 20kHz the Copland CTA408 delivered 50-watts per channel both channels driven into 8 , and 42-watts per channel when the 8 tap was used to drive 4 loads.

At 20Hz the Copland CTA408 delivered 66-watts per channel both channels driven into 8 , and 95-watts per channel when the 8 tap was used to drive 4 loads.

When the Copland CTA408’s 4 tap was used to drive a 4 load, and a 1kHz test frequency used, the amplifier delivered 98-watts when only a single channel was driven, and 87-watts per channel both channels driven. Again, the same power was not available at the frequency extremes, with Newport Test Labs measuring the both-channels driven power output at 20Hz as 66-watts per channel, and at 20kHz as 64-watts per channel.

On test, the Copland CTA408 exceeded its manufacturer’s claim for frequency response extension at both ends of the audio spectrum, with Newport Test Labs measured amplifier’s 3dB downpoints at 3Hz and 121kHz. This means that normalised, the Copland CTA408’s frequency response was measured as 3Hz to 121kHz ±1.5dB.

The frequency response across the audio band is shown in Graph 7 for both when the Copland CTA408 is driving a standard non-inductive 8 laboratory test load (black trace) and also when driving a complex load that simulates a typical twoway stand-mount loudspeaker (red trace). You can see that, when driving the 8 load, the frequency response is just 0.6dB down at 5Hz and 0.2dB down at 50kHz. Newport Test Labs measured the 20Hz to 20kHz response as ±0.05dB.

Driving the simulated loudspeaker test load, the Copland’s frequency response varied considerably, as would that of any valve amplifier, but Newport Test Labs’s graph still shows that response as extending from 5Hz to 50kHz ±0.06dB, which is an excellent result and would be perceived as ‘audibly flat.’

Channel separation was more than will be required for good stereo separation and imaging, but quite low at 66dB for frequencies below 1kHz and only 44dB up at 20kHz. Phase accuracy was also good at midrange and low frequencies, but there was a high 7.9° error at 20kHz.

Channel balance (at 1kHz) was better than 1dB (0.79dB) which is an order of magnitude less than I’d expect of a solid-state amplifier.

Harmonic distortion at an output of 1-watt into 8 (Graph 1) was, as I’d expect of a valve amplifier, dominated by a second harmonic at the relatively high level of –65dB (0.0562% THD). This was followed by a third at –82dB (0.0079% THD), a fourth at –86dB (0.0050% THD), and a fifth at –100dB (0.001% THD). As you can see, higher order harmonics (6th, 7th, 9th, 10th and 12th) are visible on the graph, but they’re all more than 100dB down.

When driven into a 4 load at the same output level, but still using the Copland’s 8 transformer tap, the level of almost all harmonic distortion components increased, with Newport Test Labs measuring the second at –57dB (0.1412% THD). This was followed by a third at –75dB (0.0177% THD), a fourth at –78dB (0.0125% THD), a fifth at –93dB (0.0022% THD) and a sixth at –98dB (0.0012% THD).

Distortion again increased significantly when output power was increased to 20-watts per channel. At this level, into an 8 test load, Graph 3 shows that the second harmonic at –46dB (0.5011% THD). The third, fourth, fifth and sixth harmonic distortion components are clustered either side of –70dB (0.0316% THD) graphing line. The next four components are mostly lower than –80dB (0.01% THD) and although harmonics are visible out to 20kHz, all are more than 100dB down.

At the same power level and frequency into a 4 load, distortion levels increased further, as you can see on Graph 4. The second, third and fourth harmonic are all above –60dB (0.1% THD), while the fifth through 10th harmonics are all above –70dB (0.0316% THD).

Intermodulation distortion at an output of 1-watt into an 8 load (8 tap) is shown in Graph 5.

The unwanted regenerated signal at 1kHz is at the fairly high level of –71dB (0.0316%), but there’s also a signal at 2kHz at –93dB (0.0022%) and at 3kHz at –112dB (0.0002%). The sideband signals at 18kHz and 20kHz are both around 80dB down (0.01%).

When output was increased to 20-watts (Graph 6) the level of the regenerated

1kHz signal increased to –56dB (0.1584%). The 18kHz and 20kHz sideband levels increased to around –60dB (0.3162%). As you can see, high-frequency sideband signals were added, along with additional regenerated signals.

Newport Test Labs measured the signalto-noise ratio of the Copland CTA408 at 81dB (IHF-A) referred to one watt and 95dBdB (IHF-A) referred to rated output, the latter figure exceeding Copland’s specification by a very healthy 5dB.

The 100Hz square wave has a slight tilt that indicates the non-d.c. frequency response of the Copland CTA408, but there’s no bending, so phase shift is low, supporting the tabulated figure of 0.5°. The slight overshoot present is more obvious on the 1kHz square wave.

The 1kHz square wave is not ‘text-book’ with a slight overshoot, albeit quickly corrected, that would seem to be partially due to a rise in the response at ultrasonic frequencies but there could be some other mechanism responsible.

The same overshoot is visible on the 10kHz square wave, seemingly ‘stretched out’ due to the different time-base on the oscilloscope. The rise-time is very fast, confirming the Copland CTA408’s extended high-frequency response. Driven into a highly-demanding capacitative load (8Ω in parallel with a 2μF capacitor) the Copland

CTA408 proved itself to be completely stable, with a quarter-height overshoot completely corrected within five cycles. While the ringing is small and quickly damped, it’s a little more than I might have expected on a valve amplifier and more like the ringing I’d expect to see from a solid-state amplifier tested in a like manner.

The line inputs of the Copland CTA408 were very sensitive, requiring an input of just 25mV to deliver one-watt at output, and just 212mV to deliver rated output. This puts overall gain at a shade more than 41dB.

The output impedance of the Copland CTA408 is, of course, much higher than for a solid-state amplifier, with Newport Test Labs measuring 1Ω at 1kHz. Importantly, despite being high, the impedance was remarkably consistent over the audio band, varying only between 0.9Ω and 1.1Ω. This means a single-figure damping factor (of exactly 8) rather than a more desirable two-figure DF (and preferably one higher than 20). Because of these impedance characteristics the CTA408’s frequency response will vary with swings in loudspeaker load impedance, so it will ‘sound’ different with different loudspeakers, depending on their design. For a well-designed loudspeaker however, the differences should not be audible, as demonstrated in the red trace of Graph 7.

Newport Test Labs confirmed that the Copland CTA408 meets the Australian standard for stand-by power consumption, drawing just 0.39-watts in this mode. However, as you’d expect of a valve amplifier, it will draw 222-watts once it’s switched on, even if you’re not actually playing music through it, and a bit more once you start listening to music. Use it at full power and it will pull around 500-watts from your 240V a.c. mains. So whenever you are not actually using it, it would be wise to switch it to its Standby mode.

Overall, the Copland CTA408 is a very well-designed valve amplifier that returned an excellent set of results on Newport Test Labs’s test bench. Steve Holding

A very well-designed valve amplifier that returned an excellent set of results on the test bench