Oh, and for semi conductor devices, amplifier circuitry analysis and calculations get Fundamentals of Semi Conductors by Floyd. That should be at the university too.
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Transistor for Powerful Class A Amplifier
- Thread starter mike7877
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- Thread Starter
- #22
The transistors are in, I bought 16 of them in case something happens in the future.
The guy is just too "busy" and because I'm his "friend" he has to do the other stuff first (he does single handedly run the entire shop (parts) and repairs though
About the fuse - I don't think the fuse blew doing the 2 ohms x2 power test, just the 1 ohm, and the 1 ohm didn't blow 'til over 1kw
edit: I think the fuse could be increased if one wanted to use 2 ohm speakers- the fuse is probably sized for protection for 4 and 8 ohm operation (the official spec in the manual). Under no circumstances should two 4 ohm speakers be drawing more than 1100 watts from a +/- 58V supply, something would have to be broken (or shorted). I actually think that if it was being used for music, the 10A fuse would be fine for driving 2 ohms speakers. Personally I wouldn't run the amp with 2 ohm speakers - the decreased performance and probably decreased lifespan, plus the extra heat would be toooo much!)
That's cool that you did warranty for them, that job sounds awesome.
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- Thread Starter
- #23
Super duper. Once the amp is repaired you should not need those transistors unless a catastrophe happens again... LoL.
IC. Lotsa juice.
It certainly is a refreshing break from Sony service and repairing Soundstream and Coustic monster car amps to get a nice home amp and preamp in for service where the repair is done by the hour and they just want it back in proper working order and are not afraid of paying. I thoroughly enjoyed heating up the load resisters with Kinergetics gear.
I don't know the backstory. My understanding is that it was a deep sea electronics communications devices development company that branched off into making some very cool audio gear. Why it went away is beyond me. I liked the gear so much that I had 2 KBA75 amps and my buddy of the time had a KBA75 and a KCD-40 CD player.
- Thread Starter
- #26
I'll be extra extra careful in the future. Hopefully nothing happens...
I have a CyberPower medical UPS with isolation transformer for its protection and 100% DC removal waiting (I didn't have issues, it's just something I like for my Toroids, like my Arcam A18 and A32.
- Thread Starter
- #27
Maybe quiet new laws (thinking CA, EU, US) prohibiting the selling stuff not "x" efficient or in category "x" which consumes more than "x" power. I have a feeling with how over the top they are about things, you couldn't sell, a class A amp over 40WPC commercially in North America in 2025. Probably not since at least 2013.
Do you know if the KBA75 was basically the same design as the 280 but smaller? Or were they different designs entirely?
Do you still have your KBA75?
Old_School_Brad
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I wasn’t familiar with Kinergetics amplifiers -they look serious. Will keep an eye on the used market..
It happens to all/most of us. One second things are going good and then BZZZzzzzzz and things went wrong... LoL. I never fried a amp like that but I took the 40,000 micro farad + and - power supply rails to the forearm and bent my prescription frames and glasses and had a big red welt on my face because my arm smacked me really hard when the muscles deflected upon being electrocuted. It was a Kinergetics amp that bit me. So be careful with those big fat caps that are in the kind of power supply you are going to assemble.
A nice piece.
I don't remember the exact specifics of the differences in circuitry other than they share a similar layout with the fan cooling and stuff. It's been ~31+ years.
No I sold my platinum version in the green anodized finish and wow does that thing look nice under the lights up close...Lol. Then after a move I bought the 2nd KBA75 in the black rack mount version. I got the 2nd one from ebay as a works but shuts down after a short time issue. It was the cooling fan issue. Somebody had put a series resistor on the fan to slow it down/quieten it and the amp would heat up and auto shut down. I removed the resistor and voila... perfectly operating KBA75.
- Thread Starter
- #31
They don't come up often. I got mine used from a local hi-fi store. The guy who used to own it died, and since he went to the store all the time (and I guess his wife didn't share the hobby, because if she did, having no spouse anymore is no reason to give up your ability to play back your music collection through a high fidelity system... IMO) she brought all his stuff to the store to sell (since they also buy and sell used gear). It was almost 20 years old when I got it - I think I got a great deal: $900.
I knew it was going to need new caps within probably 3-5 years, and after that it would last another 20-25. Normal [good quality] receivers' bulk capacitors can last 35-40 years, think mid-70s Pioneer SX-950/1050/1250 level quality. Those caps, as long as the thing wasn't habitually left on unnecessarily, can last that long because most of the time it's drawing only 40-60 watts.
But with a class A amplifier, you're essentially at 100% load all the time. Because of this, and Kinergetics' ethos, instead of the necessary ~700VA transformer for the KBA-280, they put in something 1200-1400VA (estimated from its size). They could also get away with two 30,000UF caps - my 140W class AB Arcam A32, for example, only has 2x 10,000uF caps, but instead of engineering to the problem, they over engineered, to guarantee a long-lasting low-maintenance product, and used FOUR 30,000uf caps.
I've been looking periodically for another KBA-280 because I'm converting my speakers to active from passive and I need two more channels of amplification, but to no avail...
Going off memory I think it has a 1kVA transformer in it.
Nice plan. I've had active home audio and it really is nice to have that calibration control and PEQ too.
- Thread Starter
- #34
I'm looking forward to it! And with being able to change the crossover point - I want to move it down ~350Hz. And make everything perfect (obviously... hahaha)
I also think it'd be so useful for finding the optimal crossover points of a speaker before making its passive crossover (I sometimes build speakers. It's been a while since my last, but I'm in the process of finding tweeters for a pair of woofers.)
Once my Digiface USB arrives some time in the next couple weeks, I'll be good to start experimenting!
Using the power test metering that I just found in Stereophile for 8 Ohms @ mono operation @ clipping w/ 1%THD w/1kHz the power supply has ~53VDC plus and minus so a total DC potential of ~106VDC. So be careful with that baby...LoL. It can hurt.
Old_School_Brad
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You're correct, they all appear to be very rare!
There was a run of them for sale for a few years and they where selling for about $600 to $1200 for a kinergetics amp of any model
and they all got snapped up... i never see them for sale now
Old_School_Brad
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I've set an alert on Hifishark, but I'm not very optimistic.
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I've read many textbooks and looked at countless design documents and sadly I can't say I've ever seen what you are after, but I can understand why you would want it.
What happens when you learn this stuff over many years is you become familiar with some common circuit "chunks" which get used over and over again. Things such as "long tailed pair", "current mirror", cascode etc. become familiar. In all these cases the resistors and transistors are doing their normal thing, but the result of the circuit is different.
You may find it useful to study the design of an op-amp, because these tend to have many of the common elements in them and there are excellent detailed studies about them which break down their functions and explain what they are doing.
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