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Testbench - Davoli UP100+100 Dual Slave Amp


Test Report on: Davoli UP 100+100 Dual Slave Amp
Test Date: 5th March 1975, £156.60

Davoli have been in the musical equipment business since Athos Davoli founded the company in the thirties.

They have grown into an international concern; their United Kingdom post (Davoli (U.K.) Ltd.,) is based at Park Royal, London NW10.

The UP 100+100 is a very compact unit containing two identical 100 watt RMS slave amplifiers which share a common power supply. The only controls are an on/off switch and a mains voltage selector. The other front panel fittings are an input, an output and two fuses for each amplifier together with the mains input plug, a mains outlet socket and a removable 'mains earth' to chassis link.

The inputs are compatible with almost all mixers and guitar amplifier slave outputs.

The outputs will drive full power into 8 ohm speaker loads or a little over half power into 15 ohm loads. They are not suitable for driving 4 ohm speaker systems.

The slow blow fuses fitted are of the unlikely 3.15 amp rating. It would be a very good idea to carry some of these as spares. Mains input is via a standard Euro connector and a continental mains outlet socket is provided for feeding other equipment.

The removable earth link may assist in solving the hum due to earth loops problems which many groups suffer when the overall system has multiple earths.

Construction


Construction is unusual but rigid and very practical. The whole back is a heat sink, assisted by heat loss from the top and bottom panels. Although the main construction is of metal, the end plates are of wood. The most surprising feature is its small size for two such powerful amplifiers. It is only 6 inches high, 7½ inches deep and 15½ inches long.

The main electronics are mounted on two glass fibre printed circuit panels, one for each amplifier.

The general standard of construction is quite good, but on the printed circuit boards some components are 'stood on end' or on long wires. This is not uncommon in domestic products but the practice is not consistent with readability in equipment which will have to survive frequent 'humping'.

RESULT TEST CONDITIONS REMARKS
Power Output 109W ® 10% total harmonic distortion The amplifier had to be run well into clipping
81W @ 1% total harmonic distortion to get 100 W RMS output; Not that an odd
RMS power @ 1KHz ½dB matters from a practical point of view.
Output Protection Good The output protection clearly worked well but a slight DC offset on the output found a weakness in our measuring technique.
Distortion Total Harmonic 0.045% incl. background noise Measured at 1 KHz and 50% rated power Very good - Hi-Fi Standard.
Band Width Flat 20Hz to 20KHz Sine wave at 70% full power and at 1 KHz. Very wide band with 3dB at 60KHz. Flat throughout audio band.
Signal to Noise Ratio -86dB RMS Sine wave power at onset of clipping to RMS noise wideband. Good and would have been even better if only noise in the audio band had been taken into account.
Square Wave Test Very clean response without ringing. Rise time 5 uS approx.
Capacitive Load Test O.K. 1 KHz Square Wave, 1uF across 8 Load. 15% overshoot and 2 overshoots before settling. This indicates the amplifier has been designed with a good stability margin.

Conclusion


With both amplifiers driven at full power with sine waves, which is a far more severe test than using for 30 minutes music, the heatsink was found to get too hot to touch but not hot enough to endanger the transistors.

The small size of this unit will make it an asset to any group. Apart from reservation about components stood on end on the printed circuit board, there seems to be no reason why it should not have a long and trouble free life.

Owing to its small size and high power rating good air flow is important, so give it breathing space.

The unit is capable of delivering high power signals which are far above and far below the audio range. It is undesirable to feed these into a speaker system because they can damage the speakers. (See Goodman's Power Range notes). However, the problem is easily solved by putting a low pass filter (2 components) in the speaker box. The pre-amplifier should have suitable high pass filtering.

Test Equipment


Oscillator; purpose built sine wave generator, total harmonic distortion measured at 0.005%.
Total Harmonic Distortion Factor Meter, Sugden JE S1452.
Advance OS250 Oscilloscope with calibrator.
Resistive loads 2% tolerance, 4, 8 and 16 ohms.
Level TM3 milli-volt meter.
Power measurements are correct to ±10%
Sensitivity measurements are correct to ±0.5dB.



Previous Article in this issue

Testbench - Carlsbro Super Stingray Combo Amp

Next article in this issue

Guitar Check


International Musician & Recording World - Copyright: Cover Publications Ltd, Northern & Shell Ltd.

 

International Musician - Apr 1975

Donated & scanned by: Mike Gorman

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Soundcheck

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Amplifier > Davoli > UP100+100 Dual Slave

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