I knew this would happen. It started as a simple exercise in down-sizing. Moving to an Apartment would clearly mean my Hi Fi had to be rationalized.
In the process, I have bought a Sugden Bijou Headmaster to pair with my Quad 405, which drive my Stax Headphones. However, I have been trying to find precisely what point the 405 dumpers come into play, the hope being I could operate the amp below that threshold, thus keeping it in class A.
Consensus of opinion suggested it probably wouldn’t work. However, early experiments show, maybe I can drive the Stax for comfortable low level listening, without invoking the Current Dumpers. I was “Buoyed” by a comment made by someone on WAM who also has SR - 3 headphones, when he suggested ~10 watts should be enough to drive them.
Having read an article by some Guru on Stax products, his suggestion was to leave the amplifier/SR - 3 & SRD - 5 adaptor on to allow the headphone bias to Stabilize. “This would balance the audio level in each ear - speaker”, which I have found to be absolutely correct.
In doing so, my 405 has been reaching Electric - underblanket temperature when quiescent.
Driving the 405 with at a modest level with classical material, raises this temperature by an, as yet unmeasured amount. However, whilst listening to less intense music, at a soothing level, the 405 heatsink temperature drops below the quiescent value it stabilises at when left on overnight. There is a technical reason for this and I must refresh my memory on the subject: having spent decades working on high Power Broadcast Transmitters, it will take me some time to claw it back from my brain.
Maybe, someone can spare me the task if they themselves can recall what is going on. In essence, I believe, it is because when driving the 405 below the “Class A Threshold”, the RMS power it consumes is less than when it is Quiescent. Thus the reduction in heatsink temperature. I intend to get some temperature probes into the amplifier to take some proper readings.
Which now leads on to what I feared all along, when I first decided to buy a new Pre- Amplifier to replace my 33. I could not believe my luck when I got a pristine Bijou Sugden - the remote control was still unused and on the whole the amplifier looks brand new. I knew this exercise would lead on to yet more expense!!
Initially, I wanted to see if the 405 could deliver, or could be modified to deliver enough class A power for the needs of the Stax. As I say, consensus of opinion and a couple of emails to Quad suggested this wasn’t going to be possible.
It was then I though, if indeed I can currently drive the Stax at low level and keep it operating in class A, at what point then does the Quad 606 transition over to it’s Dumpers. That question remains unanswered as does the one in the direction to which I am being taken - the Quad 909?
Not having used the Stax for years while my Spendors stood idle for some time pending our move, it was a real revelation to find my 405 when married to the Sugden could produce such sublime audio in the Stax. This should also reflect in the fact that, even when driven by the 33, the 405 now holds the Spendors in an iron - grip, extending the bass even lower and bringing superb clarity to the mid - range. So much so, I intend to hook - up the Spendors in the next few days to see exactly what the Sugden does to improve on that.
I have spent the last 2 - 3 weeks trying to find a second hand Class A power amp, to no avail - what is available is too expensive, particularly as there are no guarantees generally given with second hand. I could tolerate that, if prices reflected the chance that amplifiers may need servicing/repairing. But they don’t.
So the price of a second hand 909 will still leave me enough to send it off to Quad for servicing, given they have looked after my 303/33, vintage 1971 and my 405, which I bought second hand in 2004. It seems to me, even with the cost of my Suggie, it and a 909 would still rate as a steal.
Plus, the 909 would be more in keeping with the “Bauhaus” styling of the Sugden.