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I am the second owner of an original Threshold 800A amplifier, bought it second hand 6 months old almost 30 years ago and it is still running strong. Nelson Pass sure knows how to build amps, I am currently running this in my second system but I do switch it into the main one at times. Never has this amp failed to impress me with its smooth romantic sound and powerfull bass, however a few years ago I got into tubes and for now I am playing with that in my main system. I have almost always run this with a tube pre although now I am using the ultra revealing Placette Passive pre with it, love that remote control, lazy I quess. Anyone else still enjoying there 800A?
Follow Ups:
i MIGHT be trading my 8 month old Quad 909 for a 400A that was factory modded to STASIS-3. it was also serviced a year ago or so.what does the stasis-3 and the 400A sound like? are they cold, warm, harsh, smooth, etc.?
There is some similarity in the design of the Stasis series and the original current dumping Quad 405. Both involve using a small high quality amp directly connected to the outputs of a larger current source. The Stasis 3 uses a class A front end amp with a cascoded AB output stage using 16 matched output devices per channel. Consequently, it employs no protection circuitry and uses a much larger power supply than the Quad. Weighing 50 lbs, it is built like a tank.Sound? Short answer: perhaps a touch lean in the lower midrange but very smooth. Exceptionally clean at the top. Can drive very difficult loads such as the reactive environment of electrostats where I used mine for many years. It does not, however, clip gracefully. It will sound brittle if you push it too hard. Mine has been utterly reliable for 26 years. Although it was not experiencing any problems, I decided to replace the power supply caps about six months ago.
I have some scans of the product brochure and schematic if you are interested. Send me an email and I'll send those to you.
i'm curious. upon reading, there are two camps. some dig the 400a better, some like the stasis-3 better. what's the difference? the 400a is all class-A and the stasis is A/AB? both are cascode, right?
I fixed it so you could. There's about 9 MB of stuff.
Tony
I got mine for 175.00 from a friend of mine who bought it new in 1977.All I replaced in it to get it working was the big filter caps and one was open causing the amp not to come on but I did blow 6 of the output transistors in a staggerd fashsion and it was my own fault because when the filter cap was out,I put to large a fuse in for testing and it took out six of the 24 outputs in the one channel.
The motorola outputs only cost me 1.35 and 1.65 each..I bought a whole channels worth to have on hand from hamilton avnet being they were so cheap...It takes the 2n5876 and one other one escapes me at the moment I think its a 2n also..Anyway about two years ago I changed the smaller caps on the power supply board which cost hardly nothing..I use this amp for bass on my big subs with the martin logans at times and I have also used it on the imf sacms full range..Its a nice classic piece for what I have in it but I like the later threshold stuff better like the sa2s and sa3s.
I noticed on my amp the button you push in for on/off seems to take it to standby only.I think I might have to chnage the triac.
The toggle switches in back are a little strange to but overall its a hell of an amp.
Very nice.
Personally I haven't heard new or vintage tubes that sound better than good solid state gear.
but I remember it well. I worked for a hi-fi shop in the 70s that carried Threshold gear. The 800A would dim the lights in the room for a moment upon turn on. That is a special amp having been Nelson Pass' first commercial design which introduced the concept of sliding bias Class A operation. It had no trouble driving the owner of the shop's Dayton-Wright electrostats which were known to be difficult to drive.Similarly, I use tubes in the main system, but still enjoy an '81 Stasis 3 amp with the vintage double Advent system. Problem free, but I elected to replace the power supply caps a few months back given its age.
You ought to send an email to Nelson Pass and tell him of your experience. He is a laid back, approachable kind of guy who would likely enjoy hearing from you about your 800A. You can find his email on any of the Pass Labs' sites or at DIY Audio in the Pass forum.
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