Is your hi-fi conventional? Do you run a CD player into a respectable solid-state amplifier which feeds similarly respectable ported loudspeakers? Are you happy with your conventional system and really can't be bothered with going the extra mile to arrive somewhere special? Then stop reading now, feed another CD into your digit-eater and be happy. After all, who am I to cause you to question your carefully assembled system and approach to hi-fi?
The minute I saw that Diy HiFi Supply's Brian Cherry was to launch a Directly Heated Triode (DHT) preamplifier I knew I was sunk. There would be no way I could restrain myself from getting my hands one. Don't be put off by the mention of DIY in the company name, the preamp is available fully built as well a kit and by the way Brian is Canadian with his business and life residing in Hong Kong. A fully assembled preamp will cost you a little under $2000 plus shipping and taxes.
Although I have built most of my system, I decided to review the Tram Mk2 DHT preamplifier as a fully assembled unit rather than as a kit. My reasoning was that a good percentage of the market for this preamp is likely to be for fully assembled units. Why? Because there are few DHT preamps on the market, indeed there's just one other that I know of. Given that most people into esoteric hi-fi are probably not certifiable DIYers it seems to me there should be a big market for these preamps fully assembled. My secondary motive for not going the DIY route is that I knew I wouldn't want to wait to hear what the preamp sounds like.
are no doubt wondering why I'm making such a fuss about just another preamp,
after all the market is flooded with preamps. For starters, I know of quite a
number of DIYers who have built DHT preamps, reports invariably gush about their
sound. Of course there are some people who don't get on with DHTs even in power
amplifiers. Some folk prefer the specifications of tubes such as KT88s (which
are not DHTs) to those of a 45, 2A3 or 300B (which are the more commonly known
DHTs), that's fine and I can only say that DHTs are for me. If you've got this
far into the review and don't like DHTs then now is the time to quit.
The resistors and capacitors appear carefully chosen for their specific roles in the circuit, there is no sign of skimping, Takman and Kwame resistors are present as are several flavors of Obbligato capacitors including Teflon & Tinfoil, Polypropylene & Tinfoil and Gold Film. Tube sockets are Teflon, mounted on a damped sub-chassis to damp out vibration. Bias is set via the Diy HiFi Supply in-house auto-bias module so there's no cathode capacitor to color the sound. The DHTs are heated via another in-house module; a voltage current source regulated very low noise DC supply. Think of Tram Mk2 more as a power amplifier, it's as big and heavy as an EL84 power amplifier. This preamp needs and has a power supply that would suit a power amplifier yet which is also quiet enough for a preamp.
Selection of the five inputs is via silver relays, the volume control is executed as a 128 step attenuator using a resistor ladder and FET switches. The Dallas Semiconductor DS1666 chip used for the volume control is to be found in some very high-end (expensive, e.g. $10,000+) equipment. Control is via microprocessor, which is powered via its own winding on the power transformer. This shows great attention to detail. Input selection and volume control is mainly intended to be operated via a remote. The volume control seems to be a potentiometer but it's not, it's a rotary encoder so the feel of this control is not what you get from a traditional potentiometer. Use a remote.
You don't get a remote with the Tram Mk2, you need to source one yourself indeed you will quite possibly have a suitable one already. Almost any remote for other audio equipment should work, at least for the volume control as this uses standard RC5 codes. I've seen key-ring remotes for a few bucks that should work too. Remote channel switching, if this is important to you, may require you to buy a suitable remote. Blue LEDs on the Tram Mk2 front panel usefully indicate the input selected and volume setting. I used a remote from a Meridian system to control the volume. Manual input switching is fine for me so the lack of this function by remote is ok. When I think back to the Michell Orca preamp and Alecto power amps I ran several years back I remember the remote control in particular. This was an RC5-encoded remote which was hewn from two chunky pieces of aluminum; the shape was like a smooth, flat pebble. The only function was for volume. It was gloriously tactile which provided a strong connection with the hi-fi system. This is rather like BMW putting a lot of effort into making sure switches have a good feel, this imparts a strong feeling of quality and wellbeing. I can't help feeling that a similar type of remote should be offered as an option, even if the cost is $150 to $200. Once Tram Mk2 owners become so attached what Tram Mk2 does for their musical pleasure, I feel sure many would buy such an optional exotic remote and derive great pleasure from handling it.
a few words about another special element of the preamp, the way the Tram Mk2 is
laid out endows it with a stupendously short signal path, this has to be a
significant benefit. All the signal wiring is at the rear of the chassis
connecting to the DHTs which are also at the rear of the chassis. Wiring is
solid silver, the lengths involved being of the order of 3 to 4 inches! This is
one very finely-tuned design.
Tram Mk2 With My System
In very rare circumstances you may come across a source component which can overload the 5V maximum input for the volume control. A very few DACs have huge outputs and high gain phono stages used in conjunction with high output cartridges will conceivably cross the 5V overload threshold. In the very unlikely event you have such a high output source Diy HiFi Supply can provide an attenuated input. I needed an attenuated input but I happen to have a source with a particularly high signal level, this is very unusual. It just has to be me that is the awkward one...
The nature of a DHT is that it is Directly Heated; a consequence is that you hear everything. This is both a benefit and curse. It's fantastic for signal purity but any noise or peculiarity can also be heard. The power supply needs to be mega quiet. I found the Tram Mk2 initially exhibited some ‘hum pulses', it turned out this was due to the way my electricity company monitors and maintains the mains supply by super-imposing data on the 50 Hz waveform. Diy HiFi Supply suggested a small modification to the power supply to null this out. This will I believe become a standard feature for the Tram Mk2. This is great advert for mains regeneration; I have a plea to my electricity company – just give me a clean supply! Anyway, it's fixed now and very effectively by Diy HiFi Supply.
While we're on the subject of noise I should mention tube selection. The Tram Mk2 works with 45 and 2A3 tubes, it can be relatively easily be modified to work with other DHTs too. You should be getting the impression that a DHT preamp is a sensitive and special piece of kit. So, possibly it may come as no surprise that simply any old 45 or 2A3 tubes will not do. Just because they are fine in your power amplifier running with via an output transformer doesn't mean they'll be fine in the Tram Mk2.Like I said, you hear everything with this preamp. The DHTs need to be good performers, closely matched and low noise. Diy HiFi Supply will do the screening for you. The TJ45 mesh plates I was sent were good. I happened to already have two pairs of heavily used "old stock" 45 tubes and a pair of TJ globe type 45 tubes. One pair of the old stock 45s simply didn't work, they just made screeching noises, I have to assume they were so far past their best the auto bias module was unable to get them to operate. The other pair of old stock tubes were fine, they suffer quite high-level sizzling noises, again these tubes are very well used, the upside of them is that they seem totally immune to microphonics. The sizzling noises come and go and when present can be heard during quiet music. The overall sound they produce is good but with bass sounding strangely constricted. The TJ45 globes are so microphonic as to be not realistically usable without help. The ST shape 45 sent with the Tram Mk2 fare much better being just moderately microphonic, sizzling, rushing or emission noises were originally a little too audible but now they are tamed... see the Fettling section below.
you consider purchasing Tram Mk2 as a kit, you need to be someone who is
confident in building a tube power amplifier as essentially that's what Tram Mk2
is. There are several pre-assembled
modules that you will need to install and wire up. The internals look quite
complex from the photos but in reality it is not that complex, in terms of
wiring up there is not too much to do. I would say this is a kit of moderate
complexity for someone who has built a tube kit before.
Fettling The Tram Mk2
My success with the ST shaped 45s led me to try the more recalcitrant globe 45s. I tried 65mm guitar damping instruments this time, these were positioned at the widest part of the tube. The vast majority of the severe microphonics were now tamed. However I didn't stop there, I then placed the 50mm dampers from the ST tubes on the globes, half the way up the tube. Unfortunately they slipped down the tubes as they heated up. Steve of Herbie's Lab suggested a particular silicone substance but before his email arrived I'd wrapped some Teflon plumbers tape around the tubes to create an area for the dampers to grip, which may seem a strange attribute to ascribe to Teflon but it worked, just don't wrap the tape too smoothly. I knew that Brian at Diy HiFi Supply had tried Teflon tape for other reasons, this gave me the idea. With two damping instruments in place on each tube I now had microphonics with the globes down to ST shaped tube levels. Success! I must add that in the final analysis I preferred the sound with the ST 45s.
Taming the microphonics had a side effect I didn't expect. The rustling and sizzle issues I'd noticed with no music playing dropped very dramatically. Actually there are two approaches I found worked for reducing spurious noises, one is what I already mentioned with the tube dampers, the other is to simply "cook" the tubes in the preamp for several hours. I found that if I experimented with some tube rolling the noises came back and I had to cook them again. Something inside these tubes is delicate. Any noises can only been heard now with my ear very close to my high efficiency speakers and it's mainly one tube that is responsible. As to why the dampers reduce noise my explanation for this is that there are some form of emission noises occurring in the tubes and when microphonics are an issue these emissions set off a chain reaction of sounds through the internal structure of the tube. DHT preamps are sensitive beasts but the rewards of taking care fettling them are immense. If you want a preamp that requires no thought and measures super-well then choose a solid-state textbook design. If you want something really special in the sound department and are prepared to optimize a preamp for your situation and system then you are in Tram Mk2 territory.
for build and looks the Tram Mk2 chassis is very robust, heavy gauge aluminum is used, it is well manufactured. The style is attractive in a functional way.
The front view is dominated by the large power transformer cover. So that the
signal path can be so very short the power transformer has necessarily been
placed at the front, definitely a case of form-follows-function. If the preamp
were being sold for $10,000 then more money would be invested in the chassis
style, possibly adding bling, to my taste it's better as it is. As Tram Mk2
comes in under $2000 the chassis construction and looks are very respectable, at
least to my eye.
The sound from this system is pretty darned good, replacing any component results in changes to the sound I can easily hear. I have tried various active preamps over the years, with little success. Indeed I've had a love / hate relationship with preamps. Shunt-type resistive attenuators were favored for at one time though the loss of dynamics bugged me so from time to time I would add a powered buffer but the loss of resolution always made me remove the buffer after a while, I went around this cycle a number of times. Similarly I've tried several active preamps, tube and solid-state, I've always appreciated the dynamics but felt they veiled subtlety and nuances. I've been very happy with the TVC even though this put a strain on the source, indeed I needed to ensure my phono stage had sufficient drive to cope with the inductive load of the TVC as well as 5m of interconnect. The setup has been well balanced, hugely enjoyable and has received popular acclaim, especially for its atmospheric, spacious and 3D soundscape.
In addition to swapping the TVC for Tram Mk2 I was now able to remove the buffer driving the bass amplifiers. The Tram Mk2 has no problem driving the 18kohms combined load of the bass amplifiers and LD91s along with the 5m of interconnect. My listening levels work out well using the -3db output on the Tram Mk2. Initially my view was that the sound quality was an improvement over the much loved TVC but there was more to come. I found I had problems with microphony affecting the DHTs, having resolved the microphony issues as described earlier I was in for a considerable performance lift.
Is What it's
Somehow I've now got to find a way to put across what I've heard. This isn't going to be easy, I will do my best to avoid "reviewer hyperbole", the problem I have is that I'm close to speechless about what Tram Mk2 is doing.
On Eric Clapton's Unplugged, this album always sounds tremendous. This is going sound like a terrible cliché, but after 25 years of reviewing I promise you this is the first time I have said this; playing this album through Tram Mk2 was like hearing it for the first time. Sure the bass, mid and treble sounded great, timing and spaciousness are great too. It's the musical phrasing that is exquisite; the music hangs together and makes even more sense than it did before. There is intense clarity, not juiced-up artificially with high-frequency emphasis; this is about broad spectrum clarity with amazing harmonic reproduction. Music is laid out wonderfully in front of the listener. These effects came across album after album.
With Led Zeppelin Mothership (compilation), any decriers of single-end amplification and tube amps in general should hear this through a system with Tram Mk2. This music comes across with the correct aggression, power and energy. Dynamics are as you'd hope for and there is no way the system struggled with the more complex tracks. The Tram Mk2 seems drive the music forcibly and straight through the power amps to the speakers. Single ended amps don't do rock…..yeah, right. Get the preamp and speakers right, skeptics will be amazed.
Amy Winehouse's Back to Black allowed be to hear a nice punch with good treble, often the treble on this album can sound synthetic. Timing is superb, the drums on Rehab exhibited detail and fluency I'd not heard before.
Tanika Tikaram Ancient Heart: The London Reference cartridge on the Salvation deck really kicks hard with the bass, the Tram Mk2 showed zero softness, it was powerful, fast and deep.
Joss Stone The Soul Sessions: Vocals have become very breathy, every vocal and instrumental nuance is now very apparent.
The Pentangle Basket of Light from 1969: This shows many modern recordings a clean pair heels. Heavily processed recordings are perfectly listenable but when you hear music that is well mastered the difference is not at all subtle. The clarity of this "old" recording is impressive and it's all the more apparent with Tram Mk2.
Madelaine Payroux Careless Love: Atmosphere, wonderfully luscious, what more can I say?
Charles Mingus' Mingus Ah Um: The start / stop dynamics are breathtaking, there is tremendous fluidity and the timing is metronomic.
Sonny Rollins Saxophone Colossus: Yet another truly superb sound. Picking one aspect from this album from the track Strode Road; Sonny's sax is very prominent in the mix but for the first time I could properly hear the double bass in the background. The drum skins were also clearly being worked hard, again this was easy pick out and make sense of. Sonny's aggressive sax playing style was very plainly communicated right across the album.
Overall I've found that strings have intense bite and attack, accompanied by rich harmonics that sumptuously describe not just the notes played but how they are being played.
Most of my listening is done using my Trans-Fi Salvation rim drive turntable with its Terminator T3Pro arm and London Reference cartridge as this is my highest fidelity source. Swapping over to PC Audio playing so-called "bit perfect" through a Beresford 7250 DAC produced more impressive results than I had expected. My digital setup is very cost effective, even cheap; but it does not sound cheap. A lot of the qualities I heard with my top quality vinyl source were there with PC Audio too. As you would expect the two sources sounded different but the qualities the Tram Mk2 DHT preamp imparted were plain to hear. The key point here is that the Tram Mk2 makes the best of the source you feed it from. I'm not saying it will make a lousy source sound great, it won't, GIGO applies but it's not that fussy either.
put it simply; if you care about your music you must
strongly consider this preamp. Don't let the potential need for fettling put you
off but I appreciate that it won't suit some folks. As you can tell I'm over the
moon with Tram Mk2, there's no way it's leaving my system.
We are also very happy that the reviewer hears what we hear in the Tram Mk2. When sending out such a purpose-built-for-performance piece of gear there is always some anxiety as to whether the reviewer will 'get it' or 'miss it'. The reviewer was right on reporting the few eccentricities traded for major performance gains.
The premise is simple: less is more. Use a single direct heated triode, put the signal on the grid and take it off the anode - done! However the execution was an adventure because a direct heated triode in the linestage position not only musically tells all, but reveals all, meaning ALL: electrical noise, chassis noise, microphonics, tube hiccups - if it's there you'll hear it. So to make the 'simple premise' work needs good layout and all the supporting electrical services as seen by looking at the many chassis parts and modules. In fact the Tram Mk2 would not have been possible without raiding the cupboard for one or more of each of the 'Technology Bites' active modules:
1. Power Supply: Super quiet and power on demand B+ and bias supply: this is the FCUPS module -- Film Capacitor Ultimate Power Supply, combined with a 5U4 tube rectifier. This is a dedicated power supply system using all film capacitors in a small footprint (due to the high value on-board inductance) capable of handling even many power amplifiers power supply requirements (we also use the same module in all our Monoblock Amplifiers). As the two triodes in the Tram 2 run at 32mA current each we actually have the situation where the linestage is a small power amplifier in its own right, so having a power supply that can deliver a lot of current while being quiet is very important.
2. Filament Supply: The triode filaments are powered from our Low Noise Filament Supply. With directly heated triodes the heater and the cathode are one and the same, not separate as in indirectly heated triodes, so anything attached to the heater is directly in the signal circuit, and especially audible in a DHT linestage!
3. Active Bias System: The final "audio Lego" building block in the picture is our Active Bias Supply Module. This very small but potent module draws an already very well filtered (using only film capacitors, no electrolytic capacitors allowed) bias voltage from the Ultimate Film Capacitor Power Supply. It further massively reduces the very small amount of remaining noise and uses a second order control loop to automatically adjust the tubes grid bias. This allows us to omit the usual resistor and capacitor circuit in the cathode line to ground -- to bias the Triode. This so-called cathode capacitor is a major source of colorations and, depending on the capacitor used, delivering a less than ideal sound. Instead of using this method the cathode returns directly to ground through a low value (12 Ohm) resistor that allows the Active Bias Supply Module to measure the current in the triode, all thanks to this very small (1/2 credit card size) module, which nevertheless packs a mighty punch for good sound.
4. Layout: Incidentally, if you look at the schematic for the Tram Mk2 from the manual and at the schematic of the Ultimate Volume Control from its manual, in the Tram Mk2 the signal travels less than an inch of silver wire from the RCA connector to the ultimate volume control, where it in turn traverses maybe another 2 to 3 Inches of gold-plated copper foil, one relay and our stepped attenuator on a chip. From this circuit board we use Teflon & Tinfoil Capacitors to directly bridge the signal over to the Triode, omitting any other wire. After the triode gain stage more silver wire carries the amplified signal to our Obbligato Polypropylene & Tinfoil coupling capacitor, which is bypassed with a large value Obbligato Gold film capacitor, to give good low frequency extension into low load impedances. The final step in the signal path is the resistor network that allows the different output levels to correctly match the system gain. Even with all the features built into the Tram Mk2 the signal path is actually extremely minimalist and purist. Practically all of the circuit boards contain circuitry that merely supports this minimalist signal path and allows the design to achieve its potential.
The Tram Mk2 has given us even more respect for venerable DHTs like the 2a3 and 45 from the 1930's and 1940's. They are supremely linear and dynamic devices and paint with a rich tapestry of harmonic color. From our experience with them in power amplifiers we have long known these qualities were there but with the Tram Mk2 we feel we are hearing the wholeness of the 2A3/45 sound for the first time.
Some notes relating to specific scores:
Self Noise: noise exhibited as microphonics or rushing and sizzle will be very system dependant. A little care is needed with positioning the Tram Mk2 coupled with good vibration control for the DHTs, such as with Herbie's tube dampers. Getting this wrong will result in reduced sound quality and some spurious noises. Getting it right results in a quiet preamp, not 100% silent in the way a TVC would be but easily quiet enough.
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