High-End Crofts

by KeKessler.

GOOD OLD MARTIN COLLOMS- never one to go over the top - made an earth - shattering comment in his report on linear crystal copper in the October issue. Only a valve fancier would have noted MC's comments about the amazing possibilities of LC/OCX cable if used in output transformers, but it was there for all to see.

The repercussions are such that its use could disarm the most powerful of anti-valve comments, which refeers to the fact that valve amplifier users are listening through miles of cable because of transformer coupling. I can't begin to count the number of times I've heard the remark, 'You're not listening to valves; you're listening to output transformers.'

It's been pointed out that 10 metres of LC/OCX sounds like a few millimetres of 'normal; OFC cable; I won't hazard a guess as to how many cubits of the stuff are wrapped around the cores in my valve Paravicini, Radford, Grant and other heroes of mine read the piece.

MC reckons that anyone not using LC/OFC (amp manufacturers, speaker manufacturers or whoever) will be left way behind in the race toward the state-of-the-art.

Until then, there is but one alternative for valve amp lovers who don't want to hear those miles of cable between the valves and the speakers. This alternative is not as simple as replacing normal copper with the new stuff, but- by golly- it works ... though LC/OFC could render this type of amplifier redundant overnight.

Output-transformerless valve amplifiers have been around for 30 years or so, this school of amp design being firmly associated with one Julius Futterman. The late Mr Futterman perfected the viable OTL amplifier, his designs still being produced today by New York Audio Laboratories (see December issue). Though the amplifiers are massive, expensive and unwieldy, generating lots of heat and just as many hernias, music lovers and JA have been known to go quite weak in the knees upon first exposure to these most open-sounding of valve amplifiers. The Futtermans bear but one concession to safety and simplicity, and that is a coupling capacitor between the valves and the speakers.

Just as some decry valve amps because of their transformers, so do some question OTL designs using a coupling capacitor. OTL amplifiers are rare enough, but this new breed - OTL/OCL - is even smaller in number, and one of these is British. Croft, for it is theirs, don't use the wordy label 'output transformerless/output capacitorless' to describe their amplifiers, preferring instead 'direct- coupled'.

Some of you have already turned to the next page, not wanting to read about how I heated my room with LS3/5a briquets, but don't worry: the gang at Croft are not trying to create the concept of self-immolating hi-fi. There is a sensor in the amplifier to detect runaway DC. My own fears were overcome when they promised to replace my speakers, carpets, house,cat and wife if the things failed to work. What's of greater relevance is that there are-even as I write - dialogues going on between the two camps (with capacitor vs without capacitor), so the final votes have yet to be tallied.

Croft acknowledge with great respect the role played by Futterman in the world of OTL design, quite unashamedly describing the influence his amplifiers had on the Croft design. I seem to recall a conversation with Croft's Peter Bruty where he remarked that he and Glenn Croft serviced a Futterman for a friend and were so impressed by the sounds the amplifier made that they were then inspired to carry on with their own. I've heard a couple of Futtermans and can sympathise with their reactions. Hearing an OTL amplifier for the first time is not unlike hearing an electrostatic loudspeaker or a master- tape for the first time. The primary characteristics - openness an transparency - are most disconcerting, especially if you've been living with solid-state equipment.

The Croft amplifiers are whacking great monoblocks costing 2600 per pair, yielding 100watts each, and bearing 10 big fat output valves per unit. By the time you've added up all the bottles in a stereo pair, you're looking at amplifiers that really do heat rooms, and they draw enough current to make your summer electricity bill look like you've been cooking with electric bar heaters. The units are incredibly well-made, and I use the term 'hand-crafted' as a compliment; in this case, the term is not a euphemism for shabby finish.
 
"Hearing an OTL amplifier for the first time is not unlike hearing an electrostatic loudspeaker or a master- tape for the first time." 

Installation and use are of the hair-shirt school, and you've got to enjoy the ritual if you want to qualify for Croft ownership. These are not 'switch'em on and forget'em' units, and they're the closest any amplifiers get to inspiring audience participation. I suppose you could call it part of the fun.

Before you do a damned thing, make sure that all signal and speaker leads are connected. Peter Bruty did not go into great detail about what happens if you switch on before securing all but he sucked a lot of wind through his teeth, so I assume that the sight is not unlike what you hope to see on Guy Fawkes anniversery. After you've made sure that the circuit is complete, you switch on both units and leave the room for at least half an hour. I recommend a cup of coffee, with the would-be Croft listener doing the grinding and brewing to while away the warm-up period.

When you return to the room, be prepared to get hit in the face with a rush of warm air. (I learned afterwards that my room can now double quite nicely as an airing cupboard.) Before you get anywhere near the turntable, you check the two amplifiers for DC offset and bias on all 20 (10 per side, remember?) output valves.
 
I'm going to get a screaming phone call if I carry on much longer in his vein, because the ritual is that and nothing more; the actual labour involved is minimal. There are two meters on each block, as well as test switches. You test for DC offset by pressing the switch and watching for movement of the needle away from '0'; if it wanders a bit, you fine-adjust the amplifier via a pot with the special tool (a screwdriver, in fact) which comes supplied with the units. It's he same procedure for the valves when you do the biasing, and you'd be surprised just how quickly those 20 tubes can be set for operation.

I use the Crofts (I can't call them OTLs for short because that's a trademarked name) with the Beard P505 Mk II preamp, the Oracle Delphi turntable, Zeta arm, Garrott/Decca MicroScanner and Goodmans LS3/5As with Rogers LSB1 subwoofer. Speaker cables were Absolute Wire, and the signal leads were the as-yet-unnamed supercables possibly to be imported by Beard. (They were very Randall-ish, and I spent much time with them before installing the Crofts to minimise the variables.

I've got to get this off my chest or I'll never be able to deal with the sound: the Crofts have an Achilles' heel that will drive most of you nuts. I tell you this because it's my duty, not because I want to embarrass the Croft crew. Indeed, they're fully aware of this problem and are working on it at this very moment. Croft, you see, is a very tiny operation - two men, in fact - and they lack the power of, say, Krell and cannot afford to tell their toroidal transformer supplier where to get off. The Croft amps use toroidals in the power supplies, massive things the size of Goliath's bagels, and they suffer the usual toroidal ills: they buzz just like a yellowjacket in heat. I've got a so-so SPL meter, and it told me that I was getting 30 or so dB of bzzzzzz at one metre.

This noise was masked when the music came in, so I didn't mind it too much, but it really is unacceptable in a product costing 2600. It begs the solution of putting the amps in another room,but who wants to compromise sound with an extra few metres of cable? I can't apologise for it, but I will repeat that Croft intends to sort it out.

Now that that's been dealt with, I can tell you that here are units worthy of the label 'high end'. Before committing this to paper, I had the opportunity to audition at least a dozen amplifiers from the lunatic fringe, and I can say without hesitation that the Croft amplifiers are the first UK-made amplifiers I've auditioned that can compete with America's cost-no-object offerings.

But let me put this into perspective for you. Since returning from the USA, I've modified my approach to include a new form of relativity. I shall always endeavour to judge products by type rather than subject them to artificial conditions not worthy of the product. For example, I'd review a solid-state unit in terms of other solid-state units rather than compare it to valve equipment; emotions run too high and conclusions foregone depending upon the reviewer. I now look at moving-coils in terms of other m-cs, rather than compare them with m-m types, for the same reasons. What this means is that I'd rather discuss the Croft in terms of other output-transformerless designs, and this leads naturally to the Futtermans.

If the above sounds like a cop-out, let me explain something. I firmly believe that consumers have a pretty good fix on what they want, and that no amount of raving about tubes or MOSFETS or transmission line speakers or biamping will convert people not already predisposed toward a component type. So why cloud the issue when reviewing a type of component by discussing it with irrelevant criteria? Whatever, I have no choice but to examine the Crofts in terms of the Futtermans.

Unfortunately, the Futtermans I heard cost $10,000 and this four-to-one-ratio is just too much to lay on the less expensive product. Instead of lessening the Croft achievement, I'd rather praise it by describing its similarities to the OTL1, which - to the best of my knowledge - is the finest output-transformerless unit available.

The Croft has managed to duplicate two of the major strengths of the OTL1, and they are airiness and soundstage. Like the $10k wonder-amp, the Croft presents an incredibly grunge-free sonic picture, with space around the performers, a lack of 'grain' that precludes the criticism of sounding 'too hi-fi', and an overall clarity that will upset anti-valve campaigners. In the area of soundstage, the Croft rivals the very best of the American super amps, and I'd love to see the map that Dave Wilson (of WAMM fame) would draw if he reviewed these for The Absolute Sound.

The overall character is one of no character, a wonderfully neutral performer offering seamless sound from its solid lower octaves to it sweet top end. If I had to pick this unit apart, I'd have to say its greatest weakness is in resolution and fine detail, the Crofts losing some of those tiny messages that tell you what colour dress Elia wore to the session.

The delivery of the Crofts to my home also included the revised version of their dual-mono preamp. Peter said that they revised it because they heard an Audio Research SP10, and if that ain't honesty, then I don't know what is. I mention the preamp only because it is perfectly suited for the Croft power amplifiers, and I spent as much time using it as I did the Beard. Its sonic character is more in keeping with the power amps, but the Beard does add its own 'flavour', as would any other preamp. It's arguable that a power amplifier will work best with the preamp for which it was designed, and vice versa, but I prefer to see consumers tailor a sound to their own needs and tastes, and if this means using another make of component, then so be it.

The Croft power amplifiers are frighteningly good, an incredible achievement from so small a firm. If they can sort out the buzz of the toroidals, then they'll be offering us poorer folk a shot at near Futterman performance. I hope these guys make it.
 
Manufacturer's specification

Power Output
110W (20Hz to 20KHz at less than 0.1% THD into rated load)
85Wrms into 4ohms
110Wrms into 8ohms
115Wrms into 16ohms
110Wrms into 32ohms
 
Frequency response
3Hz to 200Khz (+0 -1dB)
2Hz to 200Khz (+0 -3dB)

Power Bandwidth
5Hz to 200Khz (-0dB at less than 0.2% THD)

IMD
less than 0.015 at any level from 0 to 110W equivalent power

Output damping factor
60

Signal-to-noise ratio
98dB down from 110W

Input sensitivity
1.5Vrms for rated output

Input impedance
100Kohms

Power consumption
Idle: 250W
Full power: 1000W

Dimensions
18 x 12 x 10in

Croft SeriesII OXL Amplifier

~  H1-FI NEWS & RECORD REVIEW JANUARY 1985


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