About the Gazember 2x 160W 303

The Quad 303 160W RMS per channel. Part two.

Last Thursday, on Valentine’s Day, I was in Antwerp, as Stefaan sent me an interesting e-mail (nothing to do with Valentine). A customer sent us a Quad 303/33/FM3 set for a check up, all bought from the man whose name should not be mentioned on this blog, (only this time).

Yes, the "Gazember" 160 W 303 was on our workbench. The pictures on Ebay reveal a 303 in a sorry state, in real life as well I can say now. The output capacitor banks are "glued" to the chassis, with wood glue, so they where rattling inside the cover of the 303 after transport.

The extra capacitors on top and beside the original power supply capacitors where held together with an elastic band.

The original trimmer pots where still in place after 40 years.

The solder work is below any standards.

So far for first impressions.

Technical review:

The regulated power supply has been removed, including the 40411 transistor.

The emitter resistors are halved in value by soldering a second pair over the existing ones.

The standard number of current limiter diodes is unchanged.

All the output transistors are replaced with MJ15003, which in itself is a good idea.

There are two rectifier bridges screwed to the chassis, with more extra diodes soldered on top of it.

All the wirering and the soldering looks unprofessional.

Measurements:

Instead of measuring with constant input voltage whe measured the maximum output before clipping, the way it should be done according to IEEE definitions.

If you let the amp clip until the level of square wave output, "almost" any RMS voltage is possible.


A 1 KHz test signal was applied.

The results:

16 Ohm 24W RMS both channels
8 Ohm 42W RMS both channels
4 Ohm 62W RMS both channels

Technical analysis.

By using the wrong (in our opinion) secondary windings from the transformer, combined with the voltage selector on 240V, you will get a power supply voltage of 70 V DC without load.

With two channels at full power, the voltage drops to 62 Volts DC.

This explains the lower performance with an 8 Ohm load compared to a standard Quad 303.

As a result of halving the emitter resistances the theoretical current limit doubled. This explains the result at 4 ohm load.

There may be 3 possible reasons why "Gazember" made the mistake to state the 303 had 2x 160 Watt RMS:

• He was confused between Ac Peak-to-Peak Voltage and RMS Voltage. Power into 4 Ohm = output voltage under load (both channels) Square / 4.


• Output-power is defined as power before "clipping" or before 1% distortion


• The power-supply has to be able to deliver the total power. In the case of a Push-Pull like the 303 this is 200% to be on the safe side. A 2x 160W would need a 640W PSU.

Advice.

It could be possible that whe are looking at a "Monday-morning" product. So check those units before you buy them, if you like what you see, buy it.

Until it is clear under which conditions the amplifier should be measured in order to produce the promised results, and it has been checked by an independent lab, I have very strong reservations.

And there is still the issue of the "misinterpreted graph" (see my comments in the first article).

Joost Plugge

The original Joost Plugge text - not for publication - can be obtained via info@dadaelectronics.eu only. You will need Joost's agreement to publish parts of the text.

Stefaan

Gazember - continued

Andy Williams added the following information:

I am also involved in the upgrading of QUAD amplifiers and during the course of this I have seen a Gazember. The owner of this had owned it for around 12 months and said it had been returned for repair two or three times and had eventually lost faith in the product.

Opening the case revealed the original 30 year old power and output caps had several low value caps soldered in parallel and the original caps had finally ruptured and leaked onto the circuit boards causing the amplifier to fail yet again. The original large capacitors should have been replaced when serviced, to not do so is just penny pinching and is not in the customers interest as the amplifier would be no more reliable than a non serviced 30 year old 303 which is not what the customer would expect after spending money on his Quad.

The old trimpots were still in place as was the original rectifier bridge however the power supply board had been removed and the current limit increased by removing half the turns on the wire wound emitter resistors and putting them back in place. New resistors of the correct value would have been far more professional and actually easier to fit - again penny pinching at the customers expense. The resistors windings are no longer in contact with the ceramic former and would be far more prone to failure than a new resistor.

I looked at his ebay shop recently and notice he is now selling QUAD's valve powered equipment - I would like to express my concerns to prospective customers of the high voltages involved in valve equipment and the required safety measures that should be followed when upgrading or repairing such equipment. My advice would be to ensure that whatever they purchase, if it has been modified or repaired that it has been done so by experienced qualified technically competent people and not someone who's past record shows a distinct lack of electronic knowledge and know how. These amplifiers can be very dangerous if the work is not competently carried out and could pose a serious electric shock hazard to children as well as the owner.

Regards Andy Williams

Quad 306 Upgrade-service & DIY Kit launch

Dada Electronics launches the Quad 306 Revision-service and the Do-It-Yourself kit. They will be available in the European, USA and Australian Ebay-shop.

The input-filter and the DC Feedback circuit are upgraded to the Quad 909 quality-level.

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Low-noise 1% Metalfilm resistors give less noise on the base of the input-transistor. The TL071 opamp in this amplifier is not replaced as it is not in the signal-line and so it has no impact on the sound quality.

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All 4 zeners in both channels are decoupled with 100 nF MKT, thus eliminating HF ripple and further improving signal/noise level of the zener's output voltage.

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The old 4700 µF Power-supply caps are replaced with new 6800 µF caps with low ESR. The higher capacitance reduces ripple and increases stability of the PSU voltage.

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Finally the input-sensitivity is adapted to modern standards. The original value was 0,375 Volt which is much to sensitive for modern preamplifiers or input-sources. As this is done by increasing the local feedback of the input stage, as Quad did also in the later 707 and 909 models, this also improves overall signal to noise ratio.

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The kit and the service are available in Dada's Ebay-shop, just click on the links in the article above.

If you want a (free) copy of the upgrade/revision manual just send an e-mail to info@dadaelectronics.com.

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Stefaan & Joost

Listening session

Hans Aussems (NL) upgraded his 2 303's to monoblocks with Dada Electronics' High-end boards. He wrote:

Hi, Stefaan,

Yesterday I visited an old friend after a long time. I know him since we studied Hobo and Fagot at the conservatorium. What we also have in common is our love for listening to music and audio equipment.

I took my 2 Quad 303 monoblocks to listen to them with with his vintage 7-ties Tannoy Dual-concentric speakers which are completely revised by a Tannoy-guru from the UK.

I have to say I was very impressed by those speakers! Despite of my Electrostat-ears this was a very pleasant experience. Many modern loudspeaker-builders could learn a lot from this.

But the best is yet to come: the Quads.

After listening a while via my friend's Rega amplifier we connected the Quads. What a great sound!

The sound is tranquil at all times, without sharp edges or turbulence but with a lot of power and authority. What a dynamic can be realised with those speakers! We couldn't do anything else than listening to our music, stopping was not an option.

The Rega clearly was the lesser one, it did not have the fineness or the natural sound of the Quads.

At the end of the session we also compared with a tube-amplifier but this one had too much unrest, sharpness and distortion.

My friend is completely convinced now of what I knew already: the great capacities of the 303. You can soon expect a new order for a set of 303 Highend-boards.

Hans