T+A PA3100 HV integrated amplifier Measurements

Sidebar 3: Measurements

I tested the T+A PA 3100 HV with my Audio Precision SYS2722 system (see the January 2008 "As We See It"). The review sample did not have the Tone Control/Room Correction module fitted and neither did it have the optional PS 3000 HV auxiliary power supply. I looked first at its behavior via its line inputs, mostly with the volume control set to its maximum of "99," and then at lower settings. (The volume control operates in accurate 0.5dB steps.) The front-panel meters are correctly calibrated, a power of 1W into 8 ohms being shown as "1W." I preconditioned the amplifier by following the CEA's recommendation of operating it at one-eighth the specified power into 8 ohms for 30 minutes. At the end of that time, the heatsinks were very hot, at 131.6°F (55.4°C), and the top panel's temperature was 103.6°F (39.8°C).

The maximum gain at the loudspeaker outputs was 40.6dB for the balanced inputs, 45.6dB for the single-ended inputs. At the headphone outputs, the maximum gain measured 20.7dB and 25.7dB, respectively. The maximum gain at the preamplifier output was 14.45dB for the balanced inputs to the balanced output and 13.4dB for the unbalanced inputs to the unbalanced output. The PA 3100 HV preserved absolute polarity (ie, was noninverting) at all of its outputs.

The PA 3100 HV's unbalanced line input impedance is specified at 20k ohms, which was confirmed by my measurements. The balanced input impedance was 41k ohms. The preamplifier output impedance was 44 ohms across the band for the unbalanced output, 89 ohms for the balanced output. The headphone output impedance was a moderately high 47 ohms across the audioband—50 ohms is specified—meaning that low-impedance headphones will not be driven optimally by the T+A amplifier.

The amplifier's output impedance was 0.15 ohms at 20Hz and 1kHz, rising slightly to 0.17 ohms at 20kHz. (The measured values include the series impedance of 6' of spaced-pair speaker cable.) The modulation of the amplifier's frequency response, due to the Ohm's law interaction between this source impedance and the impedance of our standard simulated loudspeaker, was minimal (fig.1, gray trace). The small-signal bandwidth into resistive loads with the volume control set to its maximum was flat to 20kHz, and there was no overshoot or ringing with the amplifier's reproduction of a 10kHz squarewave (fig.2). Channel matching was excellent and maintained at lower settings of the volume control. The response at the headphone jack and the balanced preamplifier output was flat in the audioband and –2.5dB at 200kHz. At the single-ended preamplifier output, the response was down by 1.5dB at 100kHz.


Fig.1 T+A PA3100 HV, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).


Fig.02 T+A PA3100 HV, small-signal 10kHz squarewave into 8 ohms.

Channel separation via the line inputs (not shown) was excellent, at 90dB in both directions below 2kHz and still >80dB at the top of the audioband. The wideband, unweighted S/N ratio, taken with the unbalanced input shorted to ground and the volume control set to its maximum, was a good 69dB (average of both channels), ref. 2.83V output into 8 ohms. Restricting the measurement bandwidth to the audioband increased the ratio to 78dB, while switching an A-weighting filter into the circuit further improved the ratio to 81.1dB. The level of the PA 3100 HV's noise floor depended on the volume control setting. With the control set to its maximum ("99"), low-level supply-related spuriae at 60Hz and its odd and even harmonics were visible in the amplifier's low-frequency output spectrum (fig.3, green and gray traces); these were lowered by 10–15dB when the control was set to –20dB ("79") (fig.3, blue and red traces).


Fig.3 T+A PA3100 HV, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms with volume control set to "79" (left channel blue, right red) and "99" (left green, right gray, linear frequency scale).

T+A specifies the PA 3100 HV's maximum continuous power as 300W into 8 ohms (24.8dBW) and 500W into 4 ohms (24.0dBW). With both channels driven and using our definition of clipping, which is when the output's percentage of THD+noise reaches 1%, fig.4 indicates that the amplifier clipped at 318Wpc into 8 ohms (25.0dBW). The T+A amplifier also exceeded its specified power into 4 ohms, clipping at 525Wpc (24.2dBW), again with both channels driven (fig.5). (I don't hold the AC wall voltage constant for these tests. With the amplifier idling, it was 121.6V; with the amplifier clipping into 4 ohms, the AC supply voltage had dropped to 117.9V.)


Fig.4 T+A PA3100 HV, distortion (%) vs 1kHz continuous output power into 8 ohms.


Fig.5 T+A PA3100 HV, distortion (%) vs 1kHz continuous output power into 4 ohms.

I measured how the PA 3100 HV's distortion changed with frequency at 20V, which is equivalent to 50W into 8 ohms, 100W into 4 ohms, and 200W into 2 ohms. The THD+N percentage was very low into both 8 ohms (fig.6, blue and red traces) and 4 ohms (cyan, magenta traces). It did rise above 0.1% into 2 ohms (green, gray traces), but there was no rise in THD+N in the top octaves, which implies a commendably wide open-loop bandwidth. The distortion was predominantly the second harmonic (fig.7), with the higher harmonics decreasing in a linear manner with frequency (fig.8). Despite the good high-frequency linearity seen in fig.6, there was a greater amount of intermodulation distortion with an equal high-power mix of 19kHz and 20Hz tones than I was anticipating (fig.9). However, the highest-level intermodulation products still lay at or below –70dB (0.03%).


Fig.6 T+A PA3100 HV, THD+N (%) vs frequency at 20V into: 8 ohms (left blue, right red), 4 ohms (left cyan, right magenta), and 2 ohms (left green, right gray).


Fig.7 T+A PA3100 HV, 1kHz waveform at 50W into 8 ohms, 0.044% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).


Fig.8 T+A PA3100 HV, spectrum of 50Hz sinewave, DC–1kHz, at 50Wpc into 8 ohms (left channel blue, right red, linear frequency scale).


Fig.9 T+A PA3100 HV, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100Wpc peak into 4 ohms (linear frequency scale).

Overall, the T+A PA 3100 HV performed very well on the test bench. It exceeded its specified power, and while distortion is not especially low, it is commendably consistent with frequency and consists primarily of the subjectively innocuous second harmonic with higher-order harmonics declining with increasing frequency.—John Atkinson

T+A elektroakustik GmbH & Co. KG
Planckstrasse 9-11, 32052 Herford,
East Westphalia, Germany
US/Canada sales: David Schultz
(207) 251-8129

LTig's picture

Really, all measurements done by JA are within the cited specs. Although THD could be lower from a technical point of view (at least for this price) IMHO it's not audible in most real world situations. I'm not so sure about the latter regarding IMD because IMD is not harmonically related.

It's a pity that the room EQ module was not included for review. It's probably the best investment one can do when buying it (at least I can say that I never had better sound in my living room than after using room EQ with my Classé Sigma SSP mk2) so testing it to see if enabling it has more advantages than disadvantages would have been important for many audiophiles.

a.wayne's picture

Seems like another great product , distortion vs freq is excellent even thou oddly square wave response does let on to some slewing, open loop gain must be excellent. Nice to see power meter readings are accurate as many are not doing so today , would have liked to see lower 8ohm power say 200 rms for better current drive ..


a.wayne's picture

Plugging this amp into a power conditioner , instead of straight to the wall may require a second subjective review opinion ..


windansea's picture

did this company bother to check what T&A means in the USA?

JRT's picture

If you look at their website, they clearly state in English that, "...T+A stands for Theory and Application in the field of audio technology." Same meaning here as there.


eriks's picture

Just to clarify something, many old master paintings look dark because they are old, not because they were intended to be dark. Their original palette is often quite different than what we see today. See if you can find the digitally restored Mona Lisa for instance. Wow!

Herb Reichert's picture

but the Rembrendts in the Metropolitan Museum (NYC) are fresh as new after a very long very careful "cleaning"


Jason Victor Serinus's picture

was painted by Leonardo da Vinci. Nonetheless, here's an article that shows a cleaned Rembrandt. While the face itself is more brightly illumined, the background is still dark. https://www.frick.org/sites/default/files/archivedsite/exhibitions/rembrandt/conservation.htm

eriks's picture

The Mona Lisa was by da Vinci. My point to use her was any time we are thinking about how painters worked, or what they intended we should include the natural aging process in our consideration.

I used da Vinci specifically because the digitally restored Mona Lisa is startling. The Rembrandt you pointed out is more luminous and detailed after restoration. Yes, the background is dark but the impressions can change. :)

tonykaz's picture

Single Brand Music Systems have always seemed logical .

I wouldn't want a Car made up of parts from a great many unrelated and unconnected Manufacturers, who would?

Decades ago, I imported the beautiful Meridian Product Line, I also loved LINN's simplicity and logic.

Your T&A piece seems a capable All-in-one Music System that my wife wouldn't mind having in our ( her ) living rooms vs. the scattering of unsightly boxes & wires that kinda makes my gear look like a Picasso designed system which probably has much in common with our typical basement dwelling ( banished ) audio hobbyist. ( I no longer have a basement but do have a Semi-attached/detached shed ).

You covering these Integrated Amps is making darn-good sense, they are clean solutions to everyman's dilemma: how to make mysterious gear look good & work properly ?

Thank You, nice work !

Tony in Venice Florida

JRT's picture

" Single Brand Music Systems have always seemed logical. I wouldn't want a Car made up of parts from a great many unrelated and unconnected Manufacturers, who would?"
- Tony Kaz

You are now forgetting the many OEMs supplying that industry that you used to work in? eg. Dana, Tremec, Z-F, JTEKT-Torsen, Brembo, Koni, NSK, Recaro, Bridgestone, etc.

Likewise most electronics assemblies.

tonykaz's picture

There are thousands of OEMs supplying.

The one Brand like Chevy designs, builds, distributes, services, warrantees, organises Sales Dealerships as well as advertises and does Bank Financing.

Chevy also owned it's OEMs and efficiently sold them off!

I love and admire the Single Brand Gear like B&O, LINN, SCHIIT, etc. I just don't own one but my wife would certainly choose one. I did own and love an Electrocompaniet System.

My issue is that I tend to meet and like a manufacturer, I impulse buy his product which will probably replace something that I'll end up selling in Asia ( for a small profit ).

I personally prefer shirt pocket Audio Gear running 16/44. Selling Audio Gear is an escape strategy hobby powered by eBay technology, ( an exciting 21st Century development )! I'm not storing any of my loved audio gear, it's all loooooonnnnngggg gone.

By the way, Chinese gear mostly has No Brand Names to speak of ( or re-sale value for that matter ) The Chinese want Brand Names like JBL, vintage McIntosh, etc.

Tony in Venice Florida

Ulfilas's picture

I do find it a bit off-putting how JVS has to constantly mention how much more expensive his own equipment is.