PrimaLuna DiaLogue Three preamplifier Measurements

Sidebar 3: Measurements

I measured the PrimaLuna DiaLogue Three using the Audio Precision SYS2722 system (see www.ap.com and the January 2008 "As We See It"), as well as my vintage Audio Precision System One. The maximum gain at 1kHz into 100k ohms was lower than the specified 12dB, at 9.67dB in the left channel and 9.9dB in the right. The preamp preserved absolute polarity (ie, was non-inverting), and the input impedance was very high, at >150k ohms at all frequencies. (I can't be more precise because the voltage-drop method that I use to measure input impedance becomes increasingly inaccurate for impedances above 100k ohms or so.)

The DiaLogue Three's output impedance is specified as a high 2500 ohms; I measured 2400 ohms at high and middle frequencies but 4000 ohms at 20Hz, which will be due to the limited size of the output coupling capacitor. (A coupling cap needs to have a high value, but the desired plastic-film types are also physically large.) As a result, the frequency response into the punishingly low 600 ohm impedance will roll off prematurely at low frequencies (fig.1, cyan and magenta traces), reaching –3dB at 28Hz. Into 100k ohms (fig.1, blue and red traces), the response is flat to below 20Hz, though the ultrasonic response is curtailed compared with the condition of low load impedance. At –0.25dB at 20kHz, however, this will have no audible consequences. This graph was taken with the volume control set to its maximum, and a 0.23dB channel imbalance can be seen. Repeating the measurement with the control set to unity gain (2:00) gave the same imbalance, which suggests that it is due to an intrinsic difference in gain between the two channels rather than to volume-control mistracking.

Fig.1 PrimaLuna DiaLogue Three, frequency response at 1V with volume control at maximum into 100k ohms (left channel blue, right red) and 600 ohms (left cyan, right magenta). (0.25dB/vertical div.)

The PrimaLuna's low-frequency channel separation was moderately good, at 90dB in both directions at 100Hz, though the separation decreased to 45dB at the top of the audioband. The unweighted, audioband noise levels, measured with the input short-circuited but the volume control set to its maximum, were low, with a signal/noise ratio of 87.5dB in the right channel but 80dB in the left. Switching an A-weighting filter into circuit increased both ratios to 97dB.

The DiaLogue Three appears to use only a limited amount of negative feedback, as the plot of its THD+noise percentage against output voltage reveals a steady increase of the former into all loads (fig.2). While the low-level THD+N is low into the higher impedances, dropping below 0.1% below 330mV or so, this graph indicates that loads below about 3k ohms are best avoided with this preamp. Even so, the THD reaches 0.58% at 2V into 100k ohms, about the highest level the preamplifier will be required to deliver in practice. The small-signal THD+N percentage remains constant with frequency (fig.3).

Fig.2 PrimaLuna DiaLogue Three, distortion (%) vs 1kHz output voltage into (from right to left at 1% THD): 100k, 10k, 3k, 600 ohms.

Fig.3 PrimaLuna DiaLogue Three, THD+N (%) vs frequency at 300mV into 100k ohms (left channel blue, right red) and 3k ohms (left cyan, right magenta).

Fortunately, the spectrum of the distortion is heavily second-harmonic in nature (fig.4). This graph also shows the slightly higher level of random noise in the left channel (blue trace), and the highest power-supply component is the third harmonic at 180Hz, which lies at –97dB left and –100dB right. This is presumably due to magnetic leakage from the power transformer, but is too low in level to be audible, even when the signal level drops to 300mV (fig.5). The only disappointing aspect of the DiaLogue Three's measured behavior was with the high-frequency intermodulation test, where, even at 300mV, the equal mix of 19 and 20kHz tones resulted in a 1kHz tone at –46dB (0.5%). However, the higher-order products at 18 and 21kHz lay below –70dB (0.03%).

Fig.4 PrimaLuna DiaLogue Three, spectrum of 50Hz sinewave, DC–1kHz, at 1V into 100k ohms (left channel blue, right red; linear frequency scale).

Fig.5 PrimaLuna DiaLogue Three, spectrum of 50Hz sinewave, DC–1kHz, at 300mV into 100k ohms (left channel blue, right red; linear frequency scale).

The PrimaLuna DiaLogue Three's measured performance is related to its low-feedback tubed circuitry; but taking that into consideration, it gets a clean bill of health.—John Atkinson

COMPANY INFO
Durob Audio BV
US distributor: PrimaLuna USA
2504 Spring Terrace
Upland, CA 91784
(909) 931-0219
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COMMENTS
Hoser Rob's picture

Hmmm ... that sounds just like tube standby mode to me.

I applaud the fact that they have a standby mode, and that it's automated, but it amazes me why that's not more standard nowadays.  It used to be.

And with the quality of today's tubes it should be standard, especially for power amps.  Not preheating the filaments really decreases tube life.  I can't believe how much costly tube gear doesn't do this.

maury's picture

I just ordered one of these, along with the DiaLogue Severn Monoblocks. They'll be here next week, but I still have to get my speakers here so I can't try them yet!

Pete's picture

Hi there.

Thanks for the honest review.

But why do you compare so speciffically to a pre amp 4 to 7 times the price? Wouldn't it be the same to compare it to an amp of say $400,00?

And then stating the differences?

In this way, allthough I insist on honesty and realism in audioreviewing, I always get the feeling that it is still not a very good amp. That it is 'only mid range' you will buy. Or am I the only one that feels that?

Why not compare this 2,6k amp a little bit more to Tube Pre Amps of about 2 to 4k? Or heck: even up to 6 or 7k? Instead of 10 to 18k? More from an upgrader's perspective?

Of course we still all do want to know how it compares to 10 to 18k amps... But the remark about the bass remains a bit unfair I think.. Even if you 'haste to remind'... It sticks with me anyway.

Because I look for an upgrade! I come from 'lower'. I have a top class Tentlabs cd player of $4600 (please do review sometime!) and a Power Amp of about $3300.

My Pre Amp is a modified Rotel RC 995 of about $1000. So although this thing is still surprisingly good, it's still also my 'bottleneck'. I know I have some very top class speakers allready too and my room and setup are other topics of course (not bad at all).

So I'm looking for a Pre Amp upgrade: say about $2600! So I want more comparison to 2-4k amps, not speciffically to 10 or 18k amps, reviewing a 2,6k amp... 

Allthough it's a fair remark and I'm sure you meant that it is very good at it's price (which you also stated..), in my humble opinion you still end the review with a touch of 'looking downward' on this amp.. And I don't say that because I'm dutch just like the amp... But because I'm 'looking upward'...

Anyway. You're not a salesperson for Prima Luna (neither am I). So thanks for the effort and for the honest information.

Maury: how are they?

Et Quelle's picture

This thing is good looking for a pre-amp under $3,000. Why do others look like small simple metal boxes with tubes on top; AVM looks average though. If stereophile raves over it, then it I trust their opinion even though I would jump at the chance of an audition at a dealer. That tells you a lot, but half of what it will sound like with my interconnects, non thousand dollar speakers and components. The only way is to buy everything in the artice (a dream) or just buy the Dialogue 3 and see.

DLKG's picture

I hope you answer this question.  Why is it that you can get an integrated Primaluna for only a few hundred dollars more than the pre amp alone?  I've also read rave reviews about the integrateds but would I be better off with the pre amp and using my existing (Hafler Transnova)?  I guess I'm finding it hard to believe that a pre amp with a few hundred dollar amp section could be as good as a separate amp even though it's really old.  Primaluna price points makes things very confusing.  Not just that but the fact that I have not found. A dealer where I can compare the integrated and the pre amp with a separate amp.  

 

DLKG

myvpi@aol.com

 

 

 

 

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