Review: Croft Micro 25 Basic Preamplifier, What a Bargain!
Glenn Croft, most respected UK tube guru/auteur, amongst the last of a dying breed, has certainly been around. For the longest time, he has been making excellent tube products at bargain prices. Perhaps he is as famous for the unadorned looks of his creations as his legendary OTL amps (which I had the fortune of hearing at my friend mda's place; but apparently and unfortunately Croft doesn't make them any more). Some years ago, I almost bought his Vitale preamplifier, but it took my trip to the UK this year for me to finally acquire a Croft product.
Croft Micro series Preamplifers Croft has been using the term "Micro" for his preamplifiers on and off for a long time. The latest is the Micro 25 series, I suppose an anniversary designation. His current amplifiers are simply designated Series 7, a continuation of previous efforts. I learned about the current products through reviews of the Micro 25 Preamplifier and Series 7 Amplifier (Tone, TAS).
Built The box is OK, but packing material is quite a joke (I have no idea if export versions are different) - there is no foam or cardboard, instead consisting of crumpled paper (apparently compaction is achieved by stepping-on them, as shoe marks are evident). No manual is provided. The case is very basic, but slim and solid. Lettering is a bit smeared (don't know if it is better in the non-Basic version). The knobs are cheap plastic, but you can easily upgrade them for little money so that your unit looks like the non-Basic version(s). I have no problem with the utilitarian RCA connectors and toggle switches.
Power Supply Only 4 screws hold the cover. Once inside, I have even more admiration for the built. In the power supply, unusually there are two transformers (which are the same and appear in series). I wrote Croft and was informed one was for B+ and the other heater supply. At this price point, I applaud the presence of transistors for power regulation.
Preamp section is well isolated from the power supply and is truly compact. I have no problem with the basic volume pot and selector. Like all Croft preamps. the entire preamp section is hard wired through a basic terminal strip (which may raise eyebrows), with the bigger caps anchored to the chassis. Resistor and caps used are basic but of good quality. This unusual method of construction for sure guarantees very short signal paths, but may prove troublesome should modification is desired or service needed. I cannot decipher what cables are used inside. My unit comes with 2x JJ ECC83 for the phono section and a Sovtek 12AX7WB for the line section. Since the website says 5965 for the linestage, and since 5965 is not exactly the same as 12AX7 I am not sure what is the import on sound, I wrote Croft on this. I received this reply: "...later Basics like yours can only use the ECC83 in the line stage - the 5965 has a higher heater current. The ECC81 and 5751 are other options for the line stage....". Now, that settles it - the info on the website has not been updated.
Caution! I must caution you on connection to the amplifier. Here, the Preamp Output is simply marked "Out". Adjacent to it is a "Line Out" which turns out to be what we would call "Tape Out". I mistook the latter for the preamp out and got full volume. Fortunately I was able to immediately shut down my amp so no damage was sustained. Also, as this basic model has no protective relay or auto-mute at turn-on, if you intend to use it with a transistor power amplifier you must wait a couple of minutes for the preamp to stabilize before playing music, or risk damaging your amp and speakers (tube preamps sometimes output DC at turn-on).
Driven by Wavac MD-811A, sound through my reference highly sensitive YL 4-way horns was a bit rough at first, but settled quickly. The sound was forward, quite dramatic and palpable, equally adept through both the line and phono sections. However, a bit of amelioration/smoothing with old-stock tubes was needed, as the forward natures of both the preamp and the loudspeakers could sometimes be too much of a good thing. Swapping in RCA 12AX7s did the trick for me.
In that system, the Croft proved to be highly capable. Even with 100 db sensitivity, the preamp was commendably very quiet even when phono was used. Although with large orchestral material it did not match the Shindo Monbrison dynamically, it acquitted itself quite well, with particularly impressively clean bass. With jazz and pop material, the sheer presence was quite enjoyable. Although it did not quite yield the ultimate details and at times I could detect the thinnest veiling, somehow it gives life to instruments like few preamps can - they simply sound more real. That is quite an accomplishment.
What is interesting is that, with the Tannoy, and perhaps due to run-in, the Croft acquired a refinement that had escaped me at the start. The faithful rendition of instrumental timber is still there, but now more subtle sonic textures can be heard - indeed it can be quite refined with tube rolling, if that is what you are after.
Some musical examples. When I substituted the re-issue Marantz 7c everything moved backwards. In the Beethoven violin sonata from Argerich's Lugano 2011 set, both the violin and piano became more recessed into the soundstage; the piano grew more full bodied and the violin was sweeter. But I have to confess the sense of a live event was better conveyed by the Croft, even if the tones of both the violin and piano were leaner. Playing the vinyl of Ellington's Blues in Orbit, it was obvious the Marantz 7c had more oomph, though the Croft held up valiantly.