Amp explosion!
- Thread starter foxwelljsly
- Start date
Tony L
Administrator
The 306 has a (I think thermal) cut-out too, so would have likely complained if pushed too loud for too long rather than cooking/exploding.
PS It also needs pointing out that if this particular amp has Net Audio boards it isn’t a Quad 405 and other diagnostics need to be applied. I know they changed the 303 into something entirely different that had little connection to the original design beyond much of the casework. No idea about the 405, but I’d have expected them to redesign it as that was what they were selling.
PS It also needs pointing out that if this particular amp has Net Audio boards it isn’t a Quad 405 and other diagnostics need to be applied. I know they changed the 303 into something entirely different that had little connection to the original design beyond much of the casework. No idea about the 405, but I’d have expected them to redesign it as that was what they were selling.
S-Man
StrivingON
Actually it's the other way round, the original can dissipate a surprising amount of power, see fig 1 here:
http://www.meridian-audio.info/public/quad_405_test_reports[2314].pdf
The 1/3rd power both channels driven is a VERY stiff test,
Astonishingly thorough review!!!!
However, the 405 was not designed to drive 4 Ohm loads - see the power output tests. Not sure how much more power the Mk2 coud manage into 4 Ohms.
It would be interesting to know what NetAudio has done to the design. But removing the protection features (if they have done) is very risky with one pair of output transistors and 50V rails... as has been argued (both ways!) in the DIY pages.
Arkless Electronics
Trade: Amp design and repairs.
I believe it is Keith Snooks "Mod 3" design. An "ultimate" version of the 405 with everything learned from the 405-2, from Bernd Ludwig's work, and Snooks own work incorporated.
405-2 gives about 140W into 4R
AmadeusMozart
R.I.P.
That's why after a mega expensive amplifier went full rail and destroyed even more expensive speakers (which could not be fixed unlike the amp that was fixed under warranty) I left the solid state scene and went tubes.
No big amplifiers needed, just use sensitive speakers.
chiily
PFM Special Builder
I must admit it is some of the comfort I take from switching to valve amps, no DC on the amp's output.
foxwelljsly
Me too, I ate one sour too.
I think the crowbar protection was still in situ. Rob at amplabs reckons he might have a couple of original 405/1 boards I can drop in, so if I can refurb the case, I will may look to do that and install his speaker protection modules.
AmadeusMozart
R.I.P.
Or have what the Kef Reference R101 has: At the crossover input are four 100uF bipolar capacitors. Not only shields the drivers from DC but also protects the woofer from being fed too low frequencies.
foxwelljsly
Me too, I ate one sour too.
Fully serviced Quad 606 now in situ and all is well. And sounding very splendid. New smoothing caps and many other caps OC now replaced. Speakers are fine.
Arkless Electronics
Trade: Amp design and repairs.
Seems very likely that protection was present and worked then.
Arkless Electronics
Trade: Amp design and repairs.
Several KEF speakers over quite a time span had a largish electrolytic in line with the woofer and whilst yes it gave protection from amps going DC the reason for their presence was as part of the bass alignment. It worked well but was a bit of a bottleneck to ultimate SQ.
AmadeusMozart
R.I.P.
Modelling in LtSpice did not show much impact on the bass. But likely you are correct - it might have an impact on SQ, I've not compared it side by side.
Arkless Electronics
Trade: Amp design and repairs.
You can only model the crossover on LTspice... the Thiel-Small parameters of the bass units, effect of the cabinet tuning/reflex port etc all form part of the bass alignment. The increasing impedance and phase shift with falling frequency of the capacitor works in combination with these other parameters to give the lowest bass extension for the driver/cabinet size/tuning but a fast roll off below this point.
Some of our speaker designers may be able to add more!
davidsrsb
pfm Member
The capacitor will certainly change the bass response amplitude and group delay, so it will sound different. The impedance dip between the two port resonance peaks will become an amplitude dip. Which is correct will depend on the crossover and driver design. I presume that the KEF engineers added cost for a good reason.
Arkless Electronics
Trade: Amp design and repairs.
Like I said it enables a specific bass alignment and, counter intuitively, extends the -3dB point
AmadeusMozart
R.I.P.
Perhaps if you were to model it then you might discover the impact is not as big, I only observed a 1db dip from 150 Hz down to around 15 Hz where there was a couple of dB peak around 10Hz.
And if you have both HF and bass behind the capacitors then there is no difference in phase between them.
And I know enough about the parameters and using those for modelling with Martin Kings' spreadsheets for MLTL's. But have now reached an age to give it all away and only use the knowledge for repair or safeguarding my expensive equipment.