You are here

Demeter HM1

Tube Mic Preamp By David Mellor
Published January 1998

Demeter HM1

Can an expensive valve microphone preamp like this one really make that much difference to the quality of your recordings?

Demeter, as you all know, is the ancient Greek godess of valve amplification, and as such it is her responsibility to bring warmth and life to recordings that would otherwise be made with transistors, ICs and especially anything cursed with a cold digital soul. Personally, I'm not a believer. I think you can make great recordings with any equipment that has a good enough frequency response, low enough noise, and is otherwise working properly. Music is in the artistry, not the equipment. (Am I giving the game away?) But I'm happy to keep an open mind, and if I find valve (or tube, as they say in the USA) recording equipment that really is better, then I'll use it alongside all my cooler‑running gear — if I can afford it!

Demeter the company have a long history in valve equipment, since 1980 apparently, when many people believed that valves had become extinct at around the same time as the dinosaurs. But the company persisted and, thanks to Demeter in some part, the valve is now seen by designers as another eminently usable option in the choice of active circuit devices. Valves are no longer old‑fashioned — they just have a long history behind them.

As well as the HM1 reviewed here, Demeter make the EQ1 2‑channel parametric equaliser and the HC1 mono optical compressor in the same range. Another range of Demeter products includes the VTMP2b mic preamp, VTCL2a compressor/limiter, VTBP201 bass preamp (sounds interesting), VT275 tube DI box, and even the VT275HF valve power amplifier. I think you can see that Demeter are certainly no me‑too first timers — these people are serious about their valves!


The HM1 is a straightforward 2‑channel mic preamp with no frills such as compression or EQ. Every mixing console has mic preamps built in, so there has to be a good reason for spending money on something very similar to what you already own — and you probably already have many more than you need. Either the HM1 should sound better than your console's mic amps, or it should sound different in an interesting way. (The only other main reason for owning a separate mic preamp would be that you move from studio to studio and having your own preamp gives you the confidence of consistency.) Before I give my opinion on whether it is indeed better or different, let's take a look at what it does.

Both channels of the HM1 are identical and have both mic and line inputs. The mic inputs are on the back panel, on normal 3‑pin XLRs and on balanced tip‑ring‑sleeve jacks. On the front there's an unbalanced line input. Outputs are on balanced XLRs, and jacks too. The input impedance of the line input is a desirable 1MΩ, which means that it is such a trivial load that even an electric guitar retains the brightness that is lost when a lower impedance is used. The mic input has switchable +48V phantom power (which isn't applied to the line input, so don't worry about your pickups smoking). The other switches are for phase, ‑20dB pad and low‑frequency cut — all perfectly normal, and standard provision.

Gain is calibrated from 30dB to 60dB, meaning that the lowest gain setting, with the pad taken into account, is 10dB. A volume control sets the output level, which can be as high as a specified +28dB into 600Ω (I presume they mean dBu), high enough for any purpose I can imagine. Not all mic preamps have sufficient output to drive pro equipment properly, so this is a point worth checking. An LED bargraph which describes itself as a VU meter shows the output level in 10 stages, from ‑20dB to +3dB, with a switchable extra 10dB of sensitivity if necessary. Subjectively, the ballistics seem faster than a mechanical VU meter, but it does, according to my tests, take a full 250ms to come within 1dB of full level. Fast ballistics are great for checking peaks, but some engineers prefer meters which show the effective loudness of the signal, as a traditional VU meter does quite well. In addition to the meter there is a overload LED which indicates when the gain control is set too high for the level of the input signal — that is to say, when you're risking clipping. This does, of course, register even very short peaks.

Valves are no longer old‑fashioned — they just have a long history behind them.

Build Quality

That's it for the controls. Now let's open it up and see what the build quality is like. Bearing in mind that the valves run on 200V supplies, I'll make doubly sure to isolate it from the mains first! (Don't forget that this is something that will eventually have to be done to replace the valves.) The casing has a reasonably solid feel and opens up easily. Inside, the build quality is good rather than exemplary. The heat‑shrunk shroud around the mains switch terminals seemed a little unprofessional to me, and I noticed in comparison that the mains inlet, voltage selector and fuse holder have their terminals exposed, as do the valve base terminals. To remove the valves (specially selected 12AX7As) involves placing some stress on the solder joints of the daughterboards upon which they are mounted. In the review model, one of the pins of one valve base was touching a capacitor, when there is ample room on the board for such overcrowding to be unnecessary. Overall, although the HM1 bears a CE seal of approval sticker I'm only satisfied with the build quality when, considering the price, I had expected to be amazed.

One further point to consider is that, unless this unit is permanently bolted into a rack, sooner or later the protruding plastic fuse holder is going to take a knock and be damaged. Demeter should use a recessed fuse holder, for which there is ample room. By the way, full marks for transformer‑balanced inputs. Transformers are bulky, heavy and expensive, which is why we don't see them so often these days, but transformer‑balanced equipment is not nearly so prone to hum and to do strange things as the cheaper electronically balanced alternative. Since there is room, maybe Demeter could offer transformer‑balanced outputs as an option?

When mounting the HM1 it would be advisable to leave 1U of rack space above the unit. Valves obviously generate a fair amount of heat, and in this case they radiate through slots in the top panel. Leaving space above the HM1 is for the protection of any other equipment mounted higher in the rack, as well as for the HM1 itself. The cool‑running valve has not yet been invented.


And now the real meat and potatoes. What does the HM1 sound like? Does it blow away every transistor mic preamp you have ever heard? Starting with the line inputs (a nice little extra on a unit that is advertised as a mic preamp) you may be inclined to connect your keyboards, sampler or electric guitar to obtain a little valve warmth that would otherwise be lacking, but don't think that this is any kind of overdrive or distortion box. When the overload LED comes on, it really is telling you it's time to back off the gain. Up to that point, however, it's very easy to be convinced that the sound is just a little bit better in an undefinable way, and driving the unit close to the edge can enhance the flavour. Actually this would be a very good preamp for a Fender Rhodes electric piano, since a Rhodes really does need a high‑impedance input if the sound is not to be made rather dull and unexciting (which is the way you normally hear it!). The HM1 doesn't suit an electric guitar at all, since you need the distortion and hiss of a real guitar amp (some cabinet rattles and an authentic tear in the speaker cone too) to feel you're getting the real thing. An electro‑acoustic guitar with a built‑in preamp is a different matter. My Martin guitar, which has an internal Martin preamp, sounded fine.

Having pronounced myself a non‑believer at the beginning of the review, have I been converted? Yes, I like it.

And what about the mic inputs? For over £500 apiece, they had better be good. Let me put it this way: when you record vocals straight into the desk with a good large‑diaphragm mic they sound pretty much the same as they do with a basic cooking‑quality capacitor mic — until you mix, that is. Suddenly, the large‑diaphragm mic is clearer, fuller, and the sound is incredibly more responsive to compression and EQ. That's the difference I found with the HM1. It turned a standard AKG C451/CK22 (which I wouldn't normally recommend for vocals, but it suits my own particular brand of mournful wailing) into more than a match for a mic costing three or four times as much. To see whether I could take this any further, I tried a classic Neumann U87 through the HM1. Of course, much depends on the vocalist, since you can easily come across a really great singer whose voice, for reasons that are difficult to define, just doesn't suit your favourite mic/preamp combination at all, but it seemed to me that the U87 had been taken backwards through a timewarp and had acquired something of the nature of a valve U67 or even a '47. I'm not going to promise that you will hear all of this, since it is subjective and subtle, but you wouldn't buy a unit costing over £1000 without testing it very carefully, so you will indeed be able to judge for yourself. Technically, the distortion is low (I measured it myself at less than 0.03%), which shows that valves and distortion do not necessarily go hand in hand. The noise is certainly higher than can be achieved with transistors at ‑95dB EIN (Equivalent Input Noise). A transistor preamp can achieve something like ‑127dB at its optimum gain setting.

But you don't buy a valve preamp and complain about the technical specs. If warmth could be rated objectively, the Demeter HM1 would be up with the front‑runners. If you want a mic preamp with character, in the same league as the top transistor models but with a slightly different sound, the Demeter HM1 is definitely a contender.


Having pronounced myself a non‑believer at the beginning of the review, have I been converted? Yes, I like it. The HM1 is good and it's different, so it would justify a space in my rack. In terms of value it compares with other top mic preamps, which in my opinion are all over‑priced, but if you have a spare thou or so, it's well worth a listen. You may be converted too.


  • Makes your mics sound more expensive.
  • Transformer‑balanced inputs.
  • High maximum output level.


  • Expensive (like most similar units).
  • Internal build quality is good, but should be outstanding at the price.
  • Fuse holder likely to be damaged.


Definitely good, definitely different (to a transistor preamp) and definitely worth having — if you can afford it.


£1169.13 including VAT.