Proton D1200 power amplifier

wingman0121

Active Member
I used to have one, its "100 watts" per channel rating is hilarious since it has 7.3dB worth of headroom. How come amps don't come with huge headrooms anymore? Is it because things got less expensive to build amps that can output higher power constantly instead of just for a few milliseconds of musical peaks?
 
the Proton is a beast... I just bought one a few weeks ago and the matching 1100 pre... a pretty pair... and to put things into perspective... I own Krells and Aragons...
 
Personally, I believe the commutating amplifiers were simply not reliable enough in the long term and had difficulty into low impedance loads. They also used extra componentry and more complicated PSUs along with at least another pair of filter caps- all cost money. Pretty much every commutating amp I have worked on (everything from the protons, to NADs(powertracker/PE), Kenwood basics, Pioneer A80/90s, Marantz AVSS etc) were only slightly spectacular when they worked and that wasn't ever for long. Low impedance speakers became the norm and most of these amps had to be forced to run the LV rails for 4 ohm speakers. If you were brave, you'd run the 8ohm setting (the HV rails) on 4/6ohm speakers and run the risk of the thing blowing up. The switching circuits were also prone to introduce spikes in the waveforms when toggling between the LV and HV rails.

The proton was one of the earliest and arguably the best of any I ever heard/owned. The 100w rating is FTC and even that was conservative, but throw a 4 ohm reactive load on it and you could be picking up the pieces. It was fun to see 400+watt peaks from it though!

I would bet most of the commutating rail amps of the 1980s are in landfill now.
 
Dug up some old picture of my old beast... those smaller caps in the middle are 22,000uf :yes:


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1986 October 6-12th on those big caps. She's doing well for 27 years!

Yeah, but these amps are all hitting the age where they start to become problematic. Many Proton amps from that era are sold as not working on eBay or have broken RCA input jacks (they weren't screwed to the case or anything, just held on by solder joints). Mine leaked brown fluid from one of its huge caps while it was on, thankfully I caught it right away and nothing went haywire and I just have to replace it (ordered it from Proton). Mine was the earlier version that's bridgeable, I ended up selling mine because it was sort of falling apart and I didn't know who to bring it to for repairs at the time.


But I really enjoyed those big power meters... not so big to look obnoxious like the Onkyo M-504, and not so small that it seems pointless. In the dark all I can see is this red laser needle moving with a shade of green glow in the back. The green is darker than the green found in Yamaha CR series of receivers, just dark enough so it isn't distracting for home theater. It is very easy to wire a switch to turn the lamps off should one feel the need to do so. The needle moves according to the average dB instead of peak figures so you'll never see this meter spaz out like some do, there's a sense of grace to it.
 
Hi,

I dont know if theres still any life to this thread but I have a question. I have a d1200 which i thought i had fried but apparently hadnt..long story. I bilought a nos adcom gfa-5400 which is rated at 125wpc into 8ohms....it drives my new alon 1 speakers well. Later this week im having a couple weak caps replaced and plan on switching the adcom for the proton to see how it sounds. This leads to my question. Many people make the comment that with the headroom over 7 db, the 100 watt rating is a joke....what exactly does insinuate? How much wattage

Scottdoes this amp truly put out?
 
Taken from a stereo review test report; "The effect of the circuit is to give a 100 watt amp the ability to deliver very high power outputs for several hundred milliseconds instead of the 20 milliseconds called for in the dynamic headroom standard."
The one they tested clipped at 153 wpc @8ohms but delivered 593 wpc @8ohms for those bursts. This means it's not only a fairly powerful amp but it's also got lots in reserve for dynamic peaks. This is why I referred to it's 100 watt rating as a joke.
 
Its interesting to note that some manufacturers under rate thier products while others bend every rule and play every trick in the book to over rate their stuff.....what would an amp of similar attributes cost today? Im thinking at least 2.5 x the cost...I cant wait to see how it drives my alon 1's...thanks for adding that data.

Scott
 
They were only $599 new in the 80's. It's a great concept and I don't know why no one other than Nad to a certain degree ever made a similar design. Dual mono, insane amounts of power at 2 ohms, lots of headroom and nice looking meters make for a damn nice amp imo.
 
My adcom gfa-5400 which I bought as nos a month or so back is rated at 125 wpc @ 8 ohms but its got 1.7 db of headroom...its a nice sounding amp and I have no complaints but the proton seems much more musical to me and when im playing jazz with a lot of highs., it seems more sonic (if thats the right term).....as soon as the two caps are replaced on the proton its being moved back into its rightful spot.....the adcom will be a worthy back up amp....
 
I believe Proton used the term DPD "Dynamic Power on Demand" to describe the circuitry that allowed the amp to make those dramatic headroom outputs.

Proton also gave some equally impressive ratings for 4 & 2 ohm but I have read -on several occasions - these amplifiers were prone to fail when driven hard into these loads.
 
I believe Proton used the term DPD "Dynamic Power on Demand" to describe the circuitry that allowed the amp to make those dramatic headroom outputs.

Proton also gave some equally impressive ratings for 4 & 2 ohm but I have read -on several occasions - these amplifiers were prone to fail when driven hard into these loads.

DPD as measured in their lab; 595 into 8 ohms, 1187 into 4 and 1,800 into 2 ohms.
I can assure you the 1200 can take being driven very hard into a 4ohm load for hours without getting hot or showing any other signs of distress. And it can also do this deed with one of it's output transistors unsoldered in from the factory. One side of the amp would get slightly warmer than the other but mine ran for many years in that condition before that oversight was discovered about 5 years ago.
 
Basically its reserve dynamic power makes it sound like a much, much bigger amplifier without the cost involved to buy an amplifier that can do 500+ watts a channel. The downside is it is not designed to sustain its dynamic peak power for more than half a second (300 milisecond to be exact), which can become a problem if you use it to run subwoofers for home theater or have bass-heavy material and you like it loud.

The idea is cool and the amplifier sounds great to my ears, but you just have to be careful because it can blow out speakers quite easily if say, you dropped the tone arm or the preamp sent a nice loud pop due to oxidation of the volume control or things of that nature. It's like a smooth long island ice tea, it'll give you a good buzz but it'll also knock you on your arse if you try to be a fish.

That said, I wouldn't hesitate to give the D1200 two thumbs up.
 
When I got mine last year, I looked on a auction site and several had sold in the $200 range...I looked last week again as I was thinking of grabbing one for parts if the price was right and I couldnt believe it...a couple fetched $400 and a bunch went for mid $300's....quite a jump from last year....also amazing that they can still fetch 60-70% of thier initial value from 25 + years ago...
 
I never owned the D1200 but I still have the D940 receiver I bought new back in the late '80s.

It's in semi retirement now but the main amp section never gave a lick of trouble and still works fine to this day.
 
The proton actually replaced my kyocera r-611 and was my first jump into seperates....the difference was like night and day (albeit the kyocera was 70 wpc). That kyocera has been used as my main, my preamp, and now as my tuner using the tape outs....the kyo's amp is no slouch as this was a $900 plus receiver in early 80's but the proton brings out sounds that ive never heard before....I know its not true hi end but its going to hopefully keep me happy for another year or two until I can afford to make the next big step....
 
I used to have one, its "100 watts" per channel rating is hilarious since it has 7.3dB worth of headroom. How come amps don't come with huge headrooms anymore? Is it because things got less expensive to build amps that can output higher power constantly instead of just for a few milliseconds of musical peaks?

The peak headroom this amp is capable of is because of its unusual power supply design.
DPD isn't just a label its a functional circuit, which monitors the signal and controls the supply.
Normal supply rail voltage is just over 50 volts. But when signal levels start to hit high peaks,
the supply rails will shift upward as high as 100 volts, feeding it what it needs to help complete a peak signal demand without clipping.
 
Does anyone off the top of thier head know of any modern ss amps that might be the second coming of the d1200 ? 100 watts with uber headroom and two channel....
 
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