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Stampfl Stressless AM-Receiver
 

From Heinz Stampfl's workshop comes a device that caused a lot of discussion and misunderstanding before it went on sale. The “Stampfl Stressless AM receiver”.
When prospective buyers look at this receiver, the “must have” function is immediately activated in their minds. The white lacquered housing and the colorful display heighten expectations and make it stand out from the gray-black crowd. If you step closer to the device, the knowledgeable eye will recognize that it is a pure AM radio. Why no SSB, is the first thought. In the flood of today's all-rounder devices, the Stressless stands out with a downgrade.
What is the reason for this?
The philosophy of the “Stressless” is reception of pure AM modulated radio stations on long wave, medium wave and short wave. Switch on, tune in, lean back and enjoy. No long rummaging through the bands. The target group of the “Stressless” is the classic program listener.

The most important key data of the Stressless

-- Operating mode: AM
-- Frequency range: 100 kHz - 30 MHz
-- Principle: Double super, IF 21.4 MHz, 455 kHz
-- AM bandwidth filter LT455 HTW = 6Khz
-- Automatic switching preselector with 1 low-pass filter and 4 band-pass filters
-- Frequency display: 5” TFT LCD display, 480 x 272 pixels, resistive touchscreen
-- 50 frequency memories
-- Signal strength display: Single LED
-- Intermodulation IM3: +20 dB
-- Sensitivity: 100 kHz - 30 MHz, 12 dB S/N at -101 dBm, mod. 1 kHz, 80 %
-- Antenna connection: BNC socket
-- Power supply: 11 - 15 V-DC, 360 mA
-- Dimensions: Width 305 mm, height 120 mm, depth 185 mm
-- Weight: 1.7 kg
-- Local oscillator: SI5351, 30 MHz TCXO

Scope of delivery:
-- Stressless kit

The “Stressless” kit

The AM receiver is supplied as a kit. All circuit boards are pre-assembled, eliminating the need for time-consuming soldering and adjustment work. The receiver only needs to be screwed together and a few wires soldered. The manufacturer writes in the instructions that this kit is aimed at amateurs and beginners. Nevertheless, a certain degree of dexterity and understanding of the technology should be present. The assembly time is approx. 1.5 to 2 hours.


The housing and the circuit boards

The white lacquered housing shells are made of aluminum and are a perfect fit. The front panel and rear panel of the “Stressless” are made of circuit board material. The prefabricated circuit boards are of good quality and neatly finished. The trained eye will notice a few things. Firstly, there is the 5-stage preselector. This offers good antenna compatibility and largely protects against out-of-band interference. The other is the optical tuning encoder from Copal. This high-quality encoder guarantees an extremely long service life. Nowadays, the majority of encoders used are mechanical, which stop working properly after a short time. The well-known JRC NRD-525/535 shortwave receivers had the same Copal encoders installed. Next is the 5” TFT touchscreen. This is of very good quality and by no means a cheap part. Then there is the loudspeaker from Visaton. This quality loudspeaker promises good sound. You can tell from details like this that the manufacturer has not cut corners.

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The smart exterior

Let's take a look at the stylish receiver in its assembled and ready-to-use state. With its white lacquered housing and colorful display, it is literally crying out to be touched! But before we indulge in some stress-free listening, let's take a closer look at the receiver. There is no beauty without flaws! This is also the case with the “Stressless”. The housing screws selected by the manufacturer are not attractive and do not do the device justice. The screws on the front panel in particular are bulky and inappropriate in terms of color. The tuning knob is made of aluminum, but with a diameter of 32 mm it is unfortunately a little small and not very easy to grip. The small finger recess is not deep enough. In addition, the tuning knob protrudes too far from the front panel. The volume knob would fit in better with the concept if it were also aluminium and the same color. Apart from that, the Stressless makes a solid impression.

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The display

The central point of the receiver is the 5” touchscreen display. All receiver functions are set there. After switching on, the welcome screen appears with the setup button. Pressing this immediately takes you to the simply structured settings menu.
Possible settings:
-- Reset function. Device is reset to original settings. Memory is retained.
-- Encoder pulses 50 or 100 pulses per revolution of the tuning knob.
-- Tuning after exiting memory mode: Last set memory or last set VFO frequency.
-- Color settings of the display fields, function buttons and frequency display.

Below: A few examples of the color settings. Other color combinations can be set.

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Working with the Stressless

Operating the Stressless is easy and quick to learn. If you tap on the frequency display, you can enter the desired frequency in KHz directly. Tapping on “Rundfunk” below the frequency display takes you to the frequency band input screen. Here you can tap directly on the desired band. The Stressless has two VFOs. This is practical if you want to compare a station on the parallel frequency. If you want to adjust the frequency in 1 MHz steps, press the arrow buttons above the Memo button. The frequency is then adjusted using the tuning knob.
If the touchscreen is not touched, the display switches back to the main display after 5 seconds.
The experienced program listener knows his favourite frequencies and stores them in the 50 frequency memories. Once this is done, you can use the tuning knob in memo mode to conveniently tune through the memories without interrupting the audio.

The range of tuning steps caused some surprise. What is the point of the 100Hz & 2.5KHz tuning steps on an AM receiver? The assumption is that the software comes from another Stampfl receiver and has been modified for the Stressless.


 

Tuning the frequency with the small tuning knob is a little tough. If the tuning knob were slightly larger, turning it would be easier. The volume of the Stressless can be turned up very loudly without the audio clattering. The volume control should be operated carefully, as the volume is already very high in the lower control range. The highlight of the receiver front is the great display. It responds very well to touch. The inputs are well accepted even with a gentle touch. There is also the red “Field” LED. This starts to light up at around S9. For transmitters that come in at S9+20dB, the LED lights up fully. It has no real use. The switchable loudspeaker with the switch on the front is practical. The Stressless is overdrive-proof! Even with the vertically operated MegaDipol MD300DX, which delivers really fat signals, the Stressless remained calm.


Audio playback

No test without comparison! I compared the Stressless with my Icom IC-R75, which has Kiwa modifications built in. The R75 sounds much brighter than the original due to the modification in the audio path. The AGC has also been significantly improved.
In direct comparison with the built-in loudspeaker, the Stressless sounds mercilessly bright and leaves the R75 behind in terms of sound. With medium and strong stations, the Stressless shines with its crystal-clear audio reproduction, which unfortunately has little bass. If the signal level of the transmitter falls below a certain value, the AGC of the Stressless no longer regulates. The transmitter becomes quiet and the audio sometimes has a bright background noise. If you listen with headphones or connect stereo active speakers to the headphone output, the Stressless produces a kind of pseudo-stereo sound. It seems to be a kind of 2-channel mono. In any case, the audio gets a certain width. This effect is very pleasant with medium and strong stations. If the level decreases, this effect is more of a disadvantage. If you don't like this effect, you can use a jack stereo/mono adapter to make the audio sound mono.

The Stressless offers an audio frequency response up to approx. 14KHz, the R75 stops at approx. 7.5KHz. These recordings were made with a microphone directly on the device speaker. No antenna, only the noise generated by the receiver.


Audio frequency response Stressless
Audio frequency response Icom IC-R75 Kiwa Mod.


Reception comparisons

Second 0 - 10: Stampfl Stressless
Second 10 - 20: Icom IC-R75 Kiwa Mod.

Chaine 3 - 252khz
 R. Tunis Chaine Int. - 963khz
 Darc Radio - 6070khz
 HCJB Voice of Andes - 7365khz
 TWR Africa - 9500khz
Voice of Vietnam-RUS - 9730khz
 		Media Broadcast - 13660khz
 Radio Vatican - 13830khz
 R. Exterior Espana - 15520khz
 R. Algerienne - 17700khz
Radio Tamazuj - 21485khz

 

Conclusion:

The Stampfl Stressless AM receiver is an exotic product! For the pure program listener without DX ambitions, it is a practical receiver of very good quality. The Stressless masters the main discipline, the reception of medium and strong AM stations, without any problems and sounds pleasantly bright, unfortunately with too little bass range. If the signals fall below a certain level, the signals become quiet. This seems to be caused by the AGC. Thanks to the preselection, no clipping effects could be detected. The Stressless, which is available as a kit, has its good points but also a not-so-good point. The reception of somewhat weaker stations should be a little better.

Source of supply: Stampfl Elektronik

posted: 25.05.2024
 

 

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