I’ve just repaired and restored this lovely Krell KAV-300i integrated amplifier. Read on to find out how I did all that, and why they are such a superbly engineered amplifier.
Krell still proudly builds amplifiers and other high-end gear, from their base in Orange, Connecticut, USA. Established in 1980, they set about manufacturing a range of really different hi-fi equipment, aimed squarely at the top end of town. That’s where this KAV-300i was built.
All Krell gear that I’ve had the pleasure of working on has been superbly well-engineered, well-built, using the highest grade components that you’ll see in consumer-level equipment. This of course means it wasn’t (and still isn’t) cheap. And that’s where the KAV line came in…
Krell released the KAV-300i, as far as I can tell, in around 1995. It has the same distinctive build and materials as seen in amps like the legendary KSA-150, that I owned and restored. That means it’s carved out of blocks of gorgeous anodized aluminium and held together with stainless steel fasteners. I’m not kidding. You couldn’t build it better if you tried.
The difference here is that everything is downsized – capacitors, heat-sinks and ratings are smaller, as is the 2RU chassis. Compared to my old KSA-150, with roughly the same power output, the KAV-300i is diminutive.
This of course means that the KAV-300i cost less to make and was affordable for many more folks. There are still many of them around due to the superb build quality. They really don’t build much like this anymore.
This particular KAV-300i matches her power amplifier partner, the KAV-150, both owned by my customer and here for service and repair.
Specifications, as always, courtesy of the Hi-Fi Engine:
Power output: 150 watts per channel into 8Ω
Frequency response: 1Hz to 100kHz
Total harmonic distortion: 0.3% (trust me, wildly pessimistic!)
Signal to noise ratio: 95dB (line)
Dimensions: 475 x 387.5 x 92.5mm
Accessories: remote control
Year: 1995 – 2000
Stereophile wrote a great review of the KAV-300i, back in the day, definitely also worth a read if you are looking to get one of these.
OK, let’s get down to it. This KAV-300i was in original condition which is great, but she was misbehaving. The main fault was distorted audio. I found a number of issues with this unit, mostly related to capacitor aging. The unit also exhibited issues with the board-to-board pins and pin header connectors. There were also a few dry joints for good measure.
Krell have been very kind over the years, assisting me with service documentation, where they have it and are happy to release it. A big thank you to Patrick @ Krell because, without that stuff, working on gear like this is much more difficult.
As always, I start with disassembly, inspection and cleaning.
I tend to work through equipment in a logical sequence, so it makes sense to start with the preamplifier board in this amplifier.
Power Amplifier Board
Now to get stuck into the board where all the heavy lifting is done. This amplifier and power supply board is a gorgeous one-piece fiberglass board. Typical of Krell is the absolute minimal use of wiring. The preamp board is connect to the main amp board by pins and pin headers. Power comes up through the board stand-offs, a really nice touch and highly reliable over the long term.
Power Supply and Underside
I replaced literally every electrolytic capacitor in this amplifier, simply because so many I tested were bad. As mentioned, I used only lab-grade components from Nichicon, Panasonic, Nippon Chemicon, CDE, Kemet etc, to guarantee long service life for her owner.
Reassembly & De-Bugging
Time to put her back together. Thanks to Krell’s incredible tolerances, everything just fits, like it should.
After reassembly, I spend considerable time testing, adjusting and then even had to pull her apart again. I tested every single semiconductor on both boards, just to ease my curiosity, because of some occasional distortion that still seemed to be there.
I re-cleaned and prepped the board-to-board pins and did a little more re-working of joints and testing of resistors and transistors. Finally, she went back together again and tested perfectly, actually way better than spec.
Testing & Measurement
A word or two about testing. I like to be able to quantify things for myself and for my customers. It’s if I can send an amp home with a clean bill of health and some measurements to verify that. To that end, I’ve invested, over the years, in the test and measurement instruments needed to characterise this stuff properly.
Here’s a good example of this, in the final testing and debugging of the KAV-300i. I feed in signals of known purity and amplitude, and measure them again at the output of the amplifier. In a crude sense, this proves that signals pass all the way through. But it tells us a lot more than that.
Measuring distortion of the waveform output at the speaker terminals, whilst the amp is driving a load or is open-circuit tells us a great deal about the health of the amplifier circuitry. In this case it helped me to diagnose a problem and fix it. It takes the guesswork out of debugging and troubleshooting, to be able to see with my own eyes that something I changed has dramatically reduced the distortion of a waveform passing through and amplifier.
The extraordinarily low measured distortion of this KAV-300i, is a testament to the design and the work I’ve done to restore this wonderful amp.
So that’s a look at the complete restoration of a Krell KAV-300i. I hope you’ve enjoyed this and found it informative. Don’t forget you can contact me (Mike), right here on my contact page, for assistance with your hi-fi gear.
Till next time!