Analog Corner #300: Boulder 2108, Consolidated Audio Monster Can Boulder 2108 Measurements

Sidebar: Measurements (from October 2020, Vol.43 No.10)

In his review of this very expensive, very heavy, American-made, two-box phono preamplifier in the August issue—the 2108 with its 2110 power supply costs $52,000—Michael Fremer enthused over its sound. "The 2108 produces both a sense of soaring exultation in the upper registers and gritty drama in the lowest one," he wrote, adding "Boulder detractors who think their products are too analytical, sounding dry and bleached, ought to give the 2108 a listen." Intrigued, and remembering how well Boulder's previous flagship phono preamp, the 2008, measured back in 2002, I suggested to Stereophile's editor-in-chief, Jim Austin, that I measure the 2108 and write a follow-up review.

I measured the Boulder 2108 phono preamplifier (serial number 12213) with my Audio Precision SYS2722 system (see the January 2008 "As We See It"). As the 2108 has balanced inputs, I floated the signal generator's balanced output from ground. For logistical reasons, I measured with the preamplifier chassis sitting on top of the power supply chassis.

Each of the 2108's three inputs has a plug-in "personality card" (actually, two, one each for the L and R channels) to set the gain, cartridge type (MM or MC), loading (resistive and capacitive), and whether the demagnetization feature is turned on or off. I performed a complete set of measurements using Input 1 and repeated some of the tests with Input 3. First, though, I measured the 2108's output impedance, which was an appropriately low 100 ohms from 20Hz to 20kHz.

For Input 1, with the personality card set up as I received it (MM, low gain, with a 100 ohm resistor soldered in place), the gain at 1kHz was 31.55dB; set to high gain, it was 10dB higher. This is significantly lower than Boulder's specifications of 40dB (low) and 50dB (high). Note, however, that my measured gains will be reduced by the voltage-divider action of the Audio Precision's balanced output impedance of 40 ohms and the Boulder's input impedance, which turned out to be 100 ohms rather than the usual 47k ohms typically used for a MM cartridge. Remeasured at Input 3, which offered input impedances of 50k ohms at 20Hz and 1kHz, dropping to 25k ohms at 20kHz, the gain measured 48dB, which is suitable for a MM cartridge. With Input 1 set to MC, the measured gains were 57.3dB (60dB specified) and 61.2dB (70dB specified), but again these will be reduced by the interaction between the AP's output impedance and the MC mode's input impedance, which I measured as 110 ohms across the audioband. The lower a moving-coil phono cartridge's source impedance, the closer the 2108's gain will approach the specified values.

Fig.1 Boulder 2108, Input 1, MM, low gain, response with RIAA correction into 100k ohms (left channel blue, right red), with high-pass filter set to 10Hz (left cyan, right magenta), and to 20Hz (left green, right gray) (1dB/vertical div.).

All the 2108 inputs preserved absolute polarity, with the XLR input and output jacks connected with pin 2 "hot." The RIAA correction was almost perfect, with superb channel matching (fig.1, blue and red traces). The high-pass filter was bypassed for this measurement. When I repeated the response measurement with the filter set to 10Hz (cyan and magenta traces) and 20Hz (green and gray traces), the gain dropped by almost 1dB and the response rose above the audioband. In this respect, the 2108 behaved almost identically to the original 2008.

Fig.2 Boulder 2108, Input 1, MM, low gain, response into 100k ohms with FFRR correction (left channel blue, right red), with Columbia correction (left cyan, right magenta), and with EMI correction (left green, right gray), all ref. RIAA preemphasis (1dB/vertical div.).

As the 2108 offers FFRR (Decca/London), Columbia, and EMI equalization as well as RIAA, I remeasured the response with each of these settings. As the input signal had RIAA preemphasis applied, the responses shown in fig.2 are what you get when you play a modern RIAA-equalized LP with these historical corrections. FFRR (blue and red traces) tilts up the response by >3.5dB above 10kHz and down by >4dB below 40Hz. Columbia (cyan and magenta traces) suppresses the treble by 1dB, boosts the midrange by 1.2dB, and rolls off the low bass. EMI (green and gray traces) also tilts the response but less than the FFRR.

Fig.3 Boulder 2108, Input 1, MM, high gain, output spectrum, DC–1kHz, ref. 5mV input (linear frequency scale).

Channel separation was superb, at >95dB in both directions across the band. Spectral analysis of the Boulder's low-frequency noise floor with Input 1 set to MM and high gain (fig.3) indicated that both random noise components and power supply–related spuriae were all low in level, though there was a little more 60Hz component in the left channel (blue trace) than the right (red). The Boulder's unweighted, wideband S/N ratio, measured with Input 1 set to MM low gain, was a very good 67.3dB in the left channel and an even better 73.3dB in the right channel, both referred to an input signal of 1kHz at 5mV. Restricting the measurement bandwidth to 22Hz–22kHz increased the ratios to 74.5dB, left, and 77.5dB, right, while switching an A-weighting filter into circuit increased both ratios to 82dB. Switching the MM gain to high reduced the S/N ratios by 9–10dB, the amount of the additional gain. Similarly, setting Input 1 to MC, low gain setting, reduced the S/N ratios by 12dB, left channel, and 5.5dB, right channel. Switching to high gain didn't result in any further reduction in S/N ratio in MC mode.

The Boulder preamp's overload margins were superb but were affected by the gain setting and whether the input was set to MM or MC. In the best case, MM low gain, the margin was an astonishing 44dB across the audioband ref. 1kHz at 5mV. This dropped to 34.3dB in MM high gain mode. With the input set to MC, the margins were 38.9dB, low gain, and 28.6dB, high gain, both ref. 1kHz at 500µV. These margins are all still excellent and equate to the preamplifier output clipping at 30V RMS into 100k ohms!

Fig.4 Boulder 2108, Input 1, MM, high gain, spectrum of 1kHz sinewave, DC–10kHz, into 100k ohms for 10mV input (linear frequency scale).

Distortion was vanishingly low in level. With Input 1 set to MM high gain and with a 1kHz signal 6dB higher than the nominal MM reference level, the only harmonic visible above the noise floor was the third, and this lay at –109dB (0.0004%) in the left channel (fig.4, blue trace) and –114dB (0.0002%) in the right channel (red). This graph was taken with the easy 100k ohm load impedance.

Fig.5 Boulder 2108, Input 1, MM, high gain, HF intermodulation spectrum, DC–30kHz, 19+20kHz into 100k ohms for 100mV peak input (linear frequency scale).

Reducing the load impedance to the current-demanding 600 ohms didn't increase the levels of these harmonics at all. Intermodulation distortion, with an equal mix of 19kHz and 20kHz tones, at a peak input level equivalent to 1kHz at 10mV, was also extremely low in level, with no second-order difference product at 1kHz (fig.5). Overall, the performance of the Boulder 2108 on the test bench reveals it to be an extraordinarily well-engineered (though expensive) phono preamplifier.—John Atkinson

Bogolu Haranath's picture

Hopefully, there won't be any October surprises this year in 2020 :-) ........

Ortofan's picture

... will prove to be much more precise and measure (with an inverse network or pre-equalized test signal) much flatter than what Hi-Fi News found for the $5K "economy model" Boulder 508.

In that regard you'd be far better off with the $1,500 Parasound Halo JC3-Jr.

Jack L's picture

...... an inverse network or pre-equalized test signal" quoted Ortofan.

So what even if the RIAA measured zero error. You think your ears can detect better sound ?????

Good sound or not is not based on the absolute RIAA accuracy !!!!

Better sound is based on the design of the RIAA gain stages involved.

IMO, the best phonostage design is built of PASSIVE RIAA equalization, not conventional 'active' RIAA EQ using loop feedback. It is the active loop feedback screws up the music signals. I know because I design/built my phonostages with PASSIVE RIAA EQ which blows away conventional RIAA feedback loop design sonically.

For phonostages, LESS active stages BETTER will be the sound. Don't believe the very wrong concept of more stages will better sound. It is the contrary technically & sonically.

My signature logo here shows the very very compact phonostage I design/built many years back: SINGLE one gain stage with PASSIVE RIAA EQ
followed by a single-gain-stage linestage. More than enough voltage gain to drive any power amps.

Simplicity delivers better sound.

Listening is believing

Jack L

alvind's picture

I would normally roll my eyes at a comment that mentions measurements without any associated listening. But as an owner of the Boulder 508, I can say the measured upper midrange push is clearly audible when listening through the 508. On a front end that already leans in the direction of lean/analytical (AMG Giro, AMG Teatro) the Boulder is enough to push things over the edge on a good portion of my vinyl collection. On some records the presence boost (as I'll refer to it from now on, as its almost an identical effect to turning a tone/presence control up) is actually an improvement, particularly with simple and sparse arrangements. But on other records it is enough to make listening less than pleasurable - the extra upper mid energy can actually obscure detail, making it harder to hear texture and reverb tails. It can also push the sound stage so forward that it begins to sound a bit 2D.

Considering how good the 508 is in almost every other aspect, its a love/hate relationship I have with it at the moment. I have listened to a PS Audio Stellar phono in the same system, which sounds far better balanced in terms of its RIAA EQ, but I prefer the boulders overall signature (or lack of signature). I by far prefer the highs on the boulder which sound substanially more artifact free. Not to mention the bass is tighter and more articulate on the 508. At least in my system.

I have recently performed a little experiment, by piping the 508 through a Lynx Hilo running FabFilter to compensate for the presence boost. The result was quite eye opening. If the RIAA was a bit flatter on the 508, it would be more than good enough to be an "end game" phonostage for me. As it is, I'd have a hard time letting it go due to the stuff it does well. I just wish it was possible to send the thing back to Boulder for them to mod a bit more accuracy into the EQ, but I guess you cant have it all on an 'economy' model.

Ortofan's picture

... flat (+/- 0.1dB) frequency response from a $500 phono preamp, such as the Clearaudio Nano Phono, then there's no reason why Boulder can't deliver comparable performance at ten times the price.

Have you actually asked Boulder if they could adjust the EQ to make it more accurate?

JHL's picture

Are you of the school that regards simple loudness uniformity as the de facto only measurement? I know that in your case that's not true. So who cares if a thing isn't utterly flat?

Get this: We can't even arrive at a decision which kinda sorta maybe flattish response the speaker must make to pass muster. Nobody can say, in all the din about speakers, which loudness uniformity graph constitutes The Holy Accurate Speaker. And if we could we couldn't hear it.

But phono stages? Oh my goodness. Look, flat does not conflate with 'performance'.

We're funny sometimes.

Spla'nin's picture

Would have liked to have seen the comparo include the Yipslion MC SUT + Zesto Allasso SUT in the mix .. but thanks for the Cinemag input.

tonykaz's picture

I've seen this many times previously.

An owner of ultra pricy xxxxx tries out some comparably modest gear change to discover his flabbergastingly expensive gear now suddenly performs much better.

I can't help wondering why the previously wonderful gear is so weak by comparison?

Why not get dam good advice from someone in the first place?


Does the performance of ultra gear have a Half-life like the Synthetic Oil in our car?, like the suspension in our Koetsu that relaxes a bit too much after a few months of careful playing?


The ultra gear wasn't the ultra a performer that we earlier and impulsively convinced ourselves of.

On the other physical hand, our ears & nervous system develop pronounced shifts in perception that lead us into changing our opinions about how things actually are.

I ask: are any of our Opinions useful, since they seem to change as our lives advance?

It somehow seems a bit unfair for outfits to present pricy improvements to folks who's hearing systems are probably 8 db. down in the lower octaves and another 8 db. down in the upper octaves. Perhaps a 16 band equalizer from the Pro-Audio folks should now be an Audiologist calibrated part of our Music Systems.


When a curious bystander observes a prominent improvement we might question how good our gear was in the first place.

Tony in Venice

Ortofan's picture

... design (for high-output cartridges) all settled about 45 years ago?

If you're using a low-output cartridge, try a Jensen MC-2RR for $600.

nirodha's picture

"Before you whine about the price, consider that $29,000—the 2008's price when it was introduced—is $41,330.08 in today's dollars. So, the 2108 is really only about $12,000 more expensive. Don't you feel better?". In short, no, I don't. Either you are looking down on poor sods like most of us who can only read about products like these, or calling Boulder greedy bastards ;-)

Jack L's picture

............Don't you feel better?". In short, no, I don't. " quoted nirodha.


Give me a break, for $52,000 to buy a preamp built with op-amp IC chips !!!!!!

As a veteran HOBBY audio amps designer/builder for decades, the LAST gain components I would use are op-amp chips, thanks for my huge love of music backed up by my electrical/electronic background.

Why? An op-amp chip is built with many bipolar junction devices (or transistors) with tons loop feedbacks. This makes the music signals (built of complex waveforms of high order harmonics) to go thru this op-amps NOT as smoothly as discrete devices, like discrete FET, transistors or triode tubes!!!

I only gain devices I did, do & will be using for building audio amps re only TRIODE tubes, period.

Why? Triode tubes are the only LINEAR gain devices which get entire sets of linear signal transfer curves. Bipolar junction devices & op-amp chips ALL get non-linear signal transfer curves with a kink or 'knee'on each & every one of them. So this will limit the signal swing to avoid going into distortion zones!!!!

Sonically, IMO, op-amps sound clinical, apparently due to their built-in non-linearity & multiple feedbacks. My critical ears can tell even I were blindfolded. Triodes, being their inherent linerity, sound so natural & musical.

Listening to linear devices is believing

Jack L

Ortofan's picture

... the following articles?

Jack L's picture


Bench measurements always use sinewaves as test signals instead of real music signals. So apple to orange comparison as an audio amp amplifies music signals, NOT not sinewave test signals.

So what if the data of an op-amp chip measured 'perfect', it does not tell us at all how these chips would handle realtime music signals.

As said above here, technically, an op-amp is built of many bipolar junction devices (or transistors, FET etc) with tons of loop feedback.
It is the too many gain stages & loop feedback that screw up the proper passage pf the complex music signals comprising high orders of harmonics. Critical ears, such as mine, can tell.

Less no. of gain stages with ideally ZERO loop feedbacks, provide fast passage of complex music signals with much less harmonic distortion, crosstalks & phase distortion as occured in an op-amp.

We must understand measurement todate bears very litte, if not zip, relevance to what our brain perceive the music.

Listening is believing

Jack L

Ortofan's picture

... what sort of test signal might meet your criteria for a "real music signal".

A square wave contains "high orders of harmonics".
Is that sufficiently "complex" for you?
But, it's also just the sum of multiple sine waves of different amplitudes.

How fast does the "passage of complex music signals" need to be?

Does having "ZERO loop feedbacks" really result in "much less harmonic distortion"?
Can you name an amplifier with "ZERO loop feedbacks" that has "much less harmonic distortion" than an amplifier with "tons of loop feedback"?

Your stated preference for tube amps suggests an acquired taste for "second harmonic sauce".

jimtavegia's picture

I am sure it is wonderful sounding, but to need this to play a $20+ LP to gain enjoyment is, well I don't really know what to say. If your turntable is $20-$50K, is that enough of a front end to make this worth it?

I would think you would need the best turntable/cartridge combo to justify this purchase and the rest of your system must be top notch as well, but since the sound of all the A+ gear is not the same, what is the "right sound"?

I am glad I don't have to worry about this issue. I will never own a half-million dollar system. My 73 year old ears could not appreciate it.

I hope that those who can afford it will truly enjoy it. I feel confident they will. I am glad there are engineers who will push the envelope higher as the trickle down engineering may help many others.

volvic's picture

I have four turntables, all magnificent sounding (the fourth one will be setup shortly). Since I work from home nowadays, like all of us, I was spinning a record and was thinking how similar all of them sound. One a simple LP12 with Ittok LVIII MK2 sounds great and is bested by another one which has a better tonearm by just a few degrees - nothing major. The same with the cartridges; one has a top of the line Audio Technica which is a nice cartridge but it isn't that much better than the Shure V15 MK V MR's I got in rotation, and that I have owned for the last 30 years. The other issue is that I was able to buy these tables in the last ten years, as I can now afford them. But I am almost 55 and is my hearing going to get better to warrant paying thousands more for a better preamp or power amp or phono preamp? Just for a few degrees of improvement? I thought about all this reading this review. I have no doubt it is phenomenal, but if I were to bring it into my apt and plug it in would it be revelatory to my 55 year old ears? I have yet to hear any uberly priced gear that made me want to go out and buy it because it massively improved the way I listen to my music. However, it is always possible. I guess I should audition it.

volvic's picture

I don't want to sound overly critical because I am not. My dad who is still around sometimes throws me words of wisdom that make tremendous sense. He tells me just to keep one turntable and enjoy my music. But I like others on these pages, love the gear. I have nothing but respect for these people that create this equipment; that actually build them from scratch, out of passion and love for the music. I also get why the prices are high in this day and age. Do not want to knock Boulder or any company trying to enrich our musical appreciation, just that there have been few pieces of equipment that moved me and some of it wasn't all that expensive.

Bogolu Haranath's picture

MF could review the $72k Soulution 755 phono pre-amp, and do a comparison test :-) .......

NeilS's picture

I deleted my comment - I had misread the article. My apologies for any confusion.

jimtavegia's picture

My only other comments is how I test my hearing in the most simple way. I use recorded vocals to determine the "clarity" issues for all of my pedestrian gear. I will admit that the best phono stage I have ever owned was the Monolithic Sound with the power supply. I have never owned a phono cartridge over $500, my best being a Shure Type 5 MR, long gone with the Dual CS 5000, and now use a Shure M97 and a Ortofon OM30. All of this part of the proletariat landscape of audio for sure, yet I know that many have worse.

When I stop being able to understand the words a singer is trying to pronounce I know it is probably me, but on many albums I have no issues so I know it is me probably most of the time, not all, and my record playback system some of the time and I don't think that a phono stage would fix this without upgrading everything I own and start over totally new.

One of my favorite albums is Mary Chapin Carpenter's scenes From The Movies, great music and great story telling. I have a hard time understanding her singing with all formats, but my HD Tracks 2496 download is a big improvement and my new, very affordable Project S2 DAC a big help using my old disc spinners for a transport. If I listen on my AKG K701 cans it is better still. I have this same issue with Norah Jones on some albums.

I would also bet that the "mastering" for all of these formats is totally different which is also a part of it. I also know that it is not the fault of my gear for my hearing loss. There are probably many audiophiles my age (73) with the same issue.

That is why I really appreciate Michael doing all of his cartridge and cable tests with sound samples as downloads so I can make a hearing determination which might work better for me. I do pretty well p;icking out what the better is by vote of many of you. There is probably no cartridge or headphone too bright for me.

I will probably make one more change of phono stage and cartridge before I kick, but I am not getting my hopes up that it will be life changing. I don't know if even a $5 grand upgrade would do that with the HF loss I have.'s picture

Thanks for the information! So many of our customers love music and like information on sound systems. We will share this link on our website.

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Bill Stevenson's picture

On the basis of this review I bought one of these and it arrived just a few days ago. Wow! Cartridge is a SoundSmith Experion and phono stage is a Conrad-Johnson TEA1, series 3. I can't believe the improvement in imaging, detail, bass control. No down side that I can hear, not edgy. BTW, I am 72 years old and can't hear like I could 20 years ago, but I can hear this not very subtle improvement. Thanks Mikey.


Bill Stevenson
West Palm Beach, FL

Bogolu Haranath's picture

What speakers are you using? ..... Just curious :-) .....

Bill Stevenson's picture