Engström Monica Mk3 line preamplifier Measurements

Sidebar 3: Measurements

I measured the Engström Monica Mk3 with my Audio Precision SYS2722 system, checking some of the results with the magazine's top-line APx500. (I made sure that the inputs were set to Stereo, as indicated on the front-panel display.) The volume control appeared to operate in approximate 1.5dB steps at the top of its range and 1dB steps at lower settings. The maximum gain was 4.8dB at the balanced outputs for both the balanced and unbalanced inputs. The gain with the single-ended inputs at the single-ended outputs was –1.2dB, ie, 6dB lower, as specified. With its input toggle switches in the down position, the preamplifier preserved absolute polarity (ie, was noninverting) with both balanced and unbalanced inputs and outputs.

The Engström's balanced and unbalanced input impedances were 20k ohms at 1kHz and 20kHz, and inconsequentially lower at 12k ohms at 20Hz. At higher frequencies, the balanced output impedance was very low, at 36 ohms at 1kHz and 44 ohms at 20kHz. However, it rose to 300 ohms at 20Hz, presumably due to the use of an output transformer. The unbalanced output impedance was even lower, at 72 ohms at 20Hz, 14 ohms at 1kHz, and 18 ohms at 20kHz.

The Monica's frequency response, measured at the balanced outputs, is shown in fig.1. (Both the response and the excellent channel matching were identical with the single-ended inputs and outputs.) There is a small (+2dB) bump at the very bottom of the audioband into the high 100k ohm impedance (blue and red traces), but more puzzling is the rise in response above the audioband. This reached +4dB at 100kHz and +23.4dB at 204kHz, the highest frequency setting of the APx500's signal generator. This rise is very much lower with the low 600 ohm load (green and gray traces), and the low frequencies now start to roll off below 30Hz, but with the input impedance of 95k ohms that I measured for JVS's Dan D'Agostino Progression M550 amplifiers, the boosted ultrasonic response will be present—as will the boosted response at low frequencies. I am not sure what will be the consequences of the ultrasonic behavior, but the Engström preamplifier might be susceptible to picking up RF interference.


Fig.1 Engström Monica Mk3, frequency response at 1V into 100k ohms (with volume control set to the maximum) (left channel blue, right red), and into 600 ohms (left green, right gray) (2.5dB/vertical div.).

The Engström's channel separation was superb, at >120dB, L–R, and >110dB, R–L, below 5kHz. The Monica's wideband, unweighted signal/noise ratio, measured at the balanced outputs with the unbalanced inputs shorted to ground and the volume control set to its maximum, was a good 81.6dB in the left channel and 83.1dB in the right, both ratios ref. 2V output. Restricting the measurement bandwidth to the audioband increased the S/N ratio to 95dB, left, and 102dB, right, while switching in an A-weighting filter further improved these ratios to 107.9dB and 114.6dB, respectively. To check that the S/N ratios were not being affected by the control/power supply chassis on which it was sitting, I inserted a stack of 2 × 4s between the two and repeated the measurement. The ratios were identical.

Fig.2 shows the preamplifier's low-frequency spectrum with the two chassis separated. The left channel's noisefloor (blue trace) has a higher level of supply-related spuriae than the right's (red), though the level of the random noisefloor is low in both channels. This graph was taken with the volume control set to its maximum; the spectrum was identical with the volume control set to –20dB, as it was when I connected a wire from the ground terminal on the power supply chassis to the analyzer's ground. The highest-level spuriae in the Monica's output lay at –100dB ref. 2V (0.001%), so I would not expect them to be audible. Nevertheless, I note that JVS found that with his sensitive Wilson speakers, "a slight hum was audible from the listening position."


Fig.2 Engström Monica Mk3, balanced input/output, spectrum of 1kHz sinewave, DC–1kHz, at 1V into 100k ohms with volume control set to the maximum (left channel blue, right red) (linear frequency scale).

The THD+noise in the Monica's right-channel output reached 1%—our definition of clipping—at a high 11V into 100k ohms (fig.3), and the level of distortion below 2V was very low. This is commendable for a design that does not use negative feedback, especially as the clipping voltage into 600 ohms wasn't much lower than it was into 100k ohms. With the change of THD+N with frequency, I wasn't surprised to see that the percentage increased at low frequencies (fig.4). This will be due to the onset of core saturation in the Engtröm's output transformers. However, I was surprised to see that the distortion at higher frequencies was higher in the left channel (blue and green traces) than it was in the right channel (red and gray traces). This may well be due to the left channel's tubes not being as well-matched as the right channel's.


Fig.3 Engström Monica Mk3, balanced input/output, distortion (%) vs 1kHz output voltage into 100k ohms .


Fig.4 Engström Monica Mk3, balanced input/output, distortion (%) vs frequency at 1V into 100k ohms (left channel blue, right red) and 600 ohms (left channel green, right gray).

At low frequencies, the second and third harmonics were similar in level in both channels (fig.5), at close to –60dB (0.1%) each. At 1kHz (fig.6), the second harmonic was almost 10dB higher in the left channel (blue trace) than it was in the right, again suggesting that the tubes carrying the hot and cold signal phases were not as well-matched in that channel. (Perfectly matched balanced operation eliminates even-order harmonic distortion.) Higher-order harmonics were all very low in level in both channels.


Fig.6 Engström Monica Mk3, balanced input/output, spectrum of 50Hz sinewave, DC–1kHz, at 2V into 100k ohms (left channel blue, right red; linear frequency scale).


Fig.6 Engström Monica Mk3, balanced input/output, spectrum of 1kHz sinewave, DC–10kHz, at 2V into 100k ohms (left channel blue, right red; linear frequency scale).

The fact that the Engström preamplifier's distortion signature predominantly comprises second and third harmonics works against it having audible consequences at the levels I found. However, this will only be true if the distortion signature doesn't result in excessive levels of intermodulation distortion. With an equal mix of 19kHz and 20kHz tones at a peak level of 2V into 100k ohms, the second-order product at 1kHz lay at –66dB (0.05%) in the left channel (fig.7, blue trace) and at –74dB in the right (0.02%, red trace). The higher-order products at 18kHz and 21kHz were at the same level in both channels, –87dB (0.004%), and while more high-order products were visible in the left channel's spectrum, these are all at a very low level. The picture didn't change when I repeated the spectral analysis with the punishing 600 ohm load.


Fig.7 Engström Monica Mk3, balanced input/output, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 2V into 100k ohms (left channel blue, right red; linear frequency scale).

The Engström Monica Mk3's measured performance is dominated by the designer's decision not to use negative feedback. The higher levels of noise and distortion in the left channel than the right may well have been due to that channel's tubes not being optimally matched, perhaps due to age. However, the levels of spuriae are still low in absolute terms. I was impressed by the fact that the preamplifier was not fazed by driving low impedances, but I remain puzzled by the boosted response at ultrasonic frequencies.—John Atkinson

Engström & Engström AB
US distributor: Musical Artisans
8335 N. Keeler Ave.
Skokie, IL 60076

latinaudio's picture

Hi Jason, thanks for a wonderful review.I´m not in the camp of objectivist vs subjectivist nor in the camp of cheap vs expensive, but 60.000$ and a loud hum forced the manufacturer to send you a new unit? Oooops, what kind of value do we have here? And in the end, for a "mere" 20.000$ less the Momentum sounded as or better than the Engstrom? Thanks again, some people will save enough to buy a new car to drive to the record store :)

Jack L's picture


Yes, who really NEEDS to burn 60 grands to own a LINEamp ??
Maybe some rich & naives ?

Technically, CD/DVD/DAC/servers/phono-preamp/tuner/tape deck/TV, etc deliver output voltage (2Vrms++) high enough & impedance low enough
to drive any power amps to their max rated output powers.

So why bother to spend good money to get a lineamp? To show off peeres like owning an artifact ?

Technically, any active electronics in the signal path is a harmonic & phase distortion, noise or even hum generator, affecting the music signals going thru it.

My skeptical ears detect it. That's why I went without any active lineamp since day one decades back, enjoying bigtime my classical/pop music - closer to live perfomrance, IMO.

Unitl a few years back when I switched back from digital to vinyl as my prime music programme, I added an one-stage tube linestage (switcable from active to straight-line PASSIVE mode) to my home-brew tube phonostage, to boost up too low signal level of some vinyl recordings.

Of course, I only use quality tube: ECC82 (Mullard, made-in-Gt. Britain) for the linestage. Nothing else for better sound.

I always keep the linestage in passive mode whenever possible, particularly for many vinyl old recordings that were recorded at pretty high levels. Passive mode sounds sooo much more livelike, airy, detailed & transient-FAST than the active mode as evidenced by AB switching btween active & passive mode. Closer to live performance, period.

I am impressed by the $949 Schiit Feyer line amp which also comes with a straight-line passive mode !! This only show its desingers have done their auditon work properly with their musically awared ears, to have added the passive mode there.

Should I not be an audio DIYer, I would definitely go for Schiit Feyer lineamp for its passive mode option, price irrespective.

Listening is believing

Jack L

windansea's picture

I would expect zero hum or hiss from any preamp over $1K. My pre with 60-year old tubes has zero hum or hiss even if I crank it all the way, and that's 1200 watts through ribbons.

I didn't see any raves in this review. Just get a Shindo instead. Or Lamm or Audio Research or CJ.

MhtLion's picture

I usually don’t leave a negative comment, but I don’t think that is a good measured performance. In not a professional, but I think I know a thing or two about measurement. Such a measurement makes me believe this is a ‘fool’s toy. A toy for the fortunate but fool. Don't get me wrong. I'm more than sure this preamp sounds good and brings a lot of musical satisfaction. I never manufactured a preamp myself, but if I can sell 50 units for $60,000. Then, I will outsource a few engineers for the PCB and case design. Then, try a few different preamp layouts from the internet and play with the most expensive top quality parts. I'm more than sure such a preamp made by someone like me who knows a 'sh*t' - will sound pretty good for the ridiculous amount of money. There really aren't many bad-sounding pieces of equipment over $10k. If you use tried and true design and top quality parts - it pretty much sounds all good. And, some of them sounds particularly good in certain aspects but exhibit a clear mis-engineering in certain other aspects. Literally, anyone can produce a good-sounding preamp for $60k.

Jack L's picture


Be nice, my friend. Please do not insult whose rich & affordable as a "fool" !

Like we should not label those who love Italian fine dines as "fools" as they can afford quality food.

I would use "naive" to discrible those owners of 60-grand lineamps - taking the hefty price level as their only yardstick for quality music. The vendor who sold the lineamp hit the jackpot !

Jack L

MhtLion's picture

I did not mean to offend anyone. I did not think the readers here would have purchased it. Anyway, I have absolutely no objection to how people spend their money. Whether one puts 100k into a car, a small condo (which will be hard these days), or a diamond-decorated spoon, whatever brings joy to the beholder is good. Nor do I have beef whatsoever against people enjoying this preamp. It's just the measurement here seems to suggest that it's not a particularly well-engineered product for the money.

Jack L's picture


I see yr point.

Yet bench measurement alone won't tell you how good/bad it will sound.
It is what you hear that matters.

Likewise how come a tube amp that measures some 5% THD still sound so good to our ears vs a solid-state amp measured 0.001% THD ?

Likewise how come I don't mind paying much more for my vintage Telefunken ECC83s & British-made Mullard ECC82 for my phonostage & linestage ? All tubes of same model should measure same data, right?

Listening is believing

Jack L

Auditor's picture

Indeed, if the device sounds great, it's all that really matters. But in the case of this preamplifier, we're talking about a clearly audible problem: the thing hums!

But measurements can show problems that the buyer should know about even if they aren't clearly audible. In this case, the differences measured between the right and left channel seem to indicate the unit didn't go through the necessary QA before shipping. Engström should ensure their tubes are well matched. Especially at this price.

Jack L's picture


Yes & no.

Yes, bad QC could be a reason.

No, bad transit can also make it defective on arrival.

Jack L

MhtLion's picture

I respect your opinion, and I agree that good tube amps with 5% THD can sound like a dream. What I'm seeing in these measurements is not the THD, nor the harmonic distortion. After all, harmonic distortion is expected from tube equipment. What I'm seeing is the odd behaviors such as high-frequency noises, left vs right channel imbalance, and most importantly the possible RF interference. I spent some of my careers testing the signals of the backbones of the internet using industrial/scientific-grade testing devices. Of course, I cannot directly relay my experience to consumer audio. The science and technology of consumer audio for the most part lag a good 50 years compared to their industrial counterparts. I cannot nor should apply the rigorous signal testing standards to the consumer audio - there is just no need for it. That being said, when I see/read equipment possibly picking up the RF interference - I cannot avoid thinking the engineer behind the product may not have the necessary training when it comes to electrical engineering for signal processing. Setting the RF interference aside, I still think it has way too much high-frequency noise and too great of channel imbalance. The only positive thing I can say from the measurement is that the noise floor is surprisingly low for tube equipment.

Jack L's picture


YES, audio designers/builders nowadays should tackle RFI/EMI noises discretely due to WiFi, the prime source of "RF interference", is everwhere today.

RFI/EMI is airbborne. So effectively shielding is a must. No digital or pulse mode modulation power supply should be used in any analogue andio electronics, e.g. preamps, frquency equalizers & power amps.

Interior powerlines (hidden behind finished walls/ceiling/floors) are huge antenna loops for RFI/EMI noises. Any audios plugged into the wall AC outlets will receive RF noises as free bonus.

Just like drinking out of a sewer !!!

So powerline conditioners are indispensable to stop RF interferences getting into our audios. Yet NOT all power conditioners are angels as some of complex designs can affect the AC power currents passsing thru on top of hefty pricing - impair the music reproduced.

My very cost efficient way is having dedicated powerlines hooked up direct to the electric breaker panel to my audio rig. So such short & direct powerlines are isolated from the household powerline loops & therefore free with RFI/powerline noise contamination.

So no need of any bulky & costly complex power conditioners, which may possibly affect the sound as well.

So I only installed simple LCR inline poweline noise filters, each for each of the 4 dedicated powerlines (3 for analogue audio & one exclusively for digital audio - so NO more analogue-digital 'crosstalk'.

Such inline powerline noise filters (made in England) provide effective RF insertion loss up to 52dB @32MHz & 36dB @1,000MHz & well beyond ! I've purposedly chosen those simple LCR conditioners is to ensure they would NOT affect the produced music besides being very affordable.

Be RFI/EMI/powerline-noise smart !!!

Jack L

Auditor's picture

The last thing I want to have beside me when I'm trying to enjoy some music is my smartphone. I don't want screens and notifications to break my concentration; and I doubt I'm the only person who feels that way. It's a nice feature for those who don't mind having their phone close by. But seriously, to make that the only option?! (Other than getting up, that is.) For this price they could have thrown in a remote, too.

Jason Victor Serinus's picture

Roon and all other playback software I've ever used rely on apps controlled by phone, tablet, or computer. In my case, I finally called Apple and learned how to turn off notifications. Nothing flashes across my iPad screen any longer, and I hear no sounds from callers. Instead, I read liner notes on my pad, control sound, and take in music without disturbance.

Auditor's picture

I understand that most people now use mobile applications to control their music. However, there are still quite a few "dinosaurs" out there who only spin vinyls or CDs and who don't necessarily want to have to keep their phone close by just to turn the volume up or down without getting out of the armchair they're comfortably sitting in. It's a nifty feature that Engström have included, agreed. But I don't like the fact they don't also offer the possibility of having a traditional remote. It's nothing major but it's a minus.

windansea's picture

reminded of something Art Dudley once said of remotes, in Stereophile:
One of the best things about the Luxman preamp is something it doesn't have: a remote handset. I detest those things. Every time a review sample arrives with a remote handset, I feel like going for a drive and throwing it out the window the way Americans used to do with their lunch bags and soda cups before the TV commercial with the crying Indian. Caveat venditor.

Charles E Flynn's picture


Jason Victor Serinus's picture

I think I missed it when it was initially posted. Another recording review is coming tomorrow.

Charles E Flynn's picture

There is a brief excerpt from this work at https://www.linnrecords.com/recording-pergolesi-stabat-mater-0 (track 4). Singing is heard only in the last few seconds, but "jaunty" does seem fitting.

romath's picture

A preamp is a control device, not a streamer where there's need for a screen to sort through multiple choices. Your 21st century comment is really off base.

Jason Victor Serinus's picture

By the way, who's on first?


romath's picture

As a preamp, a mobile computing device shouldn't be necessary: what if the user doesn't have a server/streamer, but is playing via something like an Oppo, and just wants to control the volume? Contrary to the comments left above, the idea of having a separate remote control is not the mentality of a "20th century dinosaur," it's just practical (practicality is whose on first for me). Not designing in that possibility reminds me of a lot of the dashboard electronics now being put in vehicles, making things more complicated while claiming simplicity. To each their own sense of practicality. Oh, I didn't know "remote" had a homophone.

Btw, after reading Jim Austin's op-ed about live music and what we actually hear through our systems, your introduction of the three preamps as sounding dramatically different seems apropos.

tonykaz's picture

Comparing three Ultimate class & price products seems an overly indulgent luxury.

I listen to gear like this keeping them in mind as Operatic Voices. ( something like the Three Tenors performing on One Stage )

Getting tube gear to this level is easiest ( to me ), just get rid or replace the underperforming bits, audition as many tubes as can be found, replace as much as possible with silver, find a recording studio builder to supply good sounding wire, audition Capacitors and install a good Star Ground system.

Tubes will always win a big Comparison but tube performance deteriorates demanding a constant search & purchase system that can drive any audiophile insane. ( Tube hunting is a worthy hobby in & of itself )

Settling for acceptable sounding SolidState Gear is my lonnnnnnnnggg term solution.

Chasing or hunting Pavarotti levels of Audiophile performance is an endless expense, I guess that I've learned to live with the Michael Bolton level and I suspect most folks live with and are happy with the Sound Quality from their Televisions.

I've observed, over the decades, that people ( doctors & dentists ) who buy gear like this don't have the skill sets to keep their gear working properly or to get it to sound good, at all. This kind of stuff isn't 'Plug-n-Play'.

Nice little Snow Story that I counter with a March Swim in my Solar Heated Florida Pool ( weightless Nirvana )

Tony in Florida

Awsmone0's picture

Well as a doctor I spend a lot of time on set up, and happily maintain my equipment , and have a good set of soldering equipment and have built my own crossovers , and set up an active crossover system on my own
After 8 years in my current room I still find things to improve
Please keep your generalisations and profiling to yourself thanks

tonykaz's picture

Well, good on you for taking the time to detail your hobby.

You are not typical of my world where successfully educated folks usually don't have the time to focus on a hobby like sound ( or the inclination ), they typically own Airplanes and Golf Memberships.

I admire you for owning a Soldering Iron and would like you to mention which one you've settled on, I own quite a few but prefer a temperature controlled model designed for circuit repair.

As far as opinions go, your brief letter to me to keep my opinions to myself is itself an opinion ( in an opinion section of an opinion magazine ). The point of all this is to share opinions, isn't it ?

Thanks for taking the time to report on your personal experiences in sound reproduction gear & active crossover construction .

I'd love to hear you opinions on Cramolin Contact cleaners for low voltage signal degradation prevention.

Tony in Florida

georgehifi's picture

Ya got that right! a "matched good quality" passive, will have better dynamic ability, less colouration, frequency response from DC to MHz+, and far better distortion figures than any of these can do.


Cheers George

Awsmone0's picture

I think this review raises the thorny issue of what is an amplifying device for?

As preamplifier serves several function
To act as a volume control
A source switching device
To sufficiently amplify or reduce the volume to the amplifier
To act as a buffer between source and output without manifesting frequency response errors

I don’t think the aim of an amplifier is to editorialise the sound ?

Perhaps there should be a different section for products that editorialise the signal, given some manufacturers preference to use zero feedback and consequent measurement challenges

I note the lack of multitone testing in Stereophile measurements which would show real world impacts of poor IMD imho

tonykaz's picture

The Pre-amp is the 'Singing Voice' for the electrical transducer recreating the recorded music.
The Amplifier is the Megaphone
The Loudspeaker Transducer system and the room attempt to recreate the recorded experience

Of course this is a simplification of the complexity of each tiny piece's contribution or detraction from original sound quality.

Analog gear, in my decades of opinionating , strives to IMPROVE the sound quality of recorded music whilst Digital folks seem to crave accuracy of sound quality. ( I kinda prefer improving the SQ ).

Audiophiles and Stereophile readers have always seemed to be Underfinanced and under educated in all things Audio whilst Recording Studio Engineers are over-achievers in all things Audio.

We Civilian music lovers can be amazingly successful with the low price point gear like the little Schiits but still admire the fancy Blue Light Mac Gear our higher Caste love to show-off.

We all could probably duplicate systems that Bob Ludwig or Bob Katz describe building for their workings but they have vast experience, help from Manufacturers and the ability to commit a few hundred thousand dollars in their Studio + the Electronics that they tend to build themselves .

Stereophile Magazine is now bringing us wonderful reviews about the Streaming Technology that's replacing 33.3, tape, CDs, DVD, Blu-ray and most of the other devices that I now see on the shelves of Goodwill and Salvation Army.

We're in an Audiophile Revolution that will allow us to toss all our media into Waste Management's Vast Landfill system.

I didn't see this coming in 2011 at RMAF.

Tony in Florida

Jack L's picture

Bingo !

Jack L

Awsmone0's picture

Well Mr Tony from Florida

Don’t own a plane, a super yacht or a beachfront property ;) and I hate golf!
My favourite past time is music, actually trained as a professional musician at one stage , and hifi !!! Sorry to disappoint …… your profile
Contact cleaners is a bit left field but ….
Clearly clean contacts are important if they change impedance in impedance critical interfaces

I cannot recommend a specific brand, but have had great success with a simple trick of using a low abrasive/grit pad on important connections, of late I have had an interest In graphene as a contact enhancer, I have a few bottle of various contact enhancers in my cupboard but found the effects less than subtle and not overly desirable in my experience

As to soldering irons I use of course a temperature controlled iron, and lead free silver solder from Cardas if memory serves

I am unclear on your exposure to doctors, but perhaps your exposure and opinion is coloured and or biased, and that is an opinion imho lol
Funny but there are a number of doctors I know that also did engineering and or physics before medicine perhaps the practice and education in USA is different and less rounded ?

georgehifi's picture

Can you please name the " https://youtu.be/YTY26k0CA0I?t=5 " that made up this eyebrow raising "audiophile" phrase?

Cheers George

Anton's picture

I don't think I have ever said this before, but..."Not even if it were free."

Side note: which audiophile case is best for an iPhone being used to control the Hi Fi? I suppose we should expect one from Synergistic Research soon!

windansea's picture

Well,the case looks clean in a euro way, and the copper color does seem like the shade du jour.
But I wouldn't want this in my signal chain.