Krell KAV-280p Preamplifier Repair

Krell KAV-280p Preamplifier Repair

Here’s a nice little repair and power supply overhaul I recently made on a lovely Krell KAV-280p preamplifier. Let’s call this the first article in #Krellmonth!

The modest Krell KAV-280p may not be a high-end preamplifier in Krell terms like the Krell KRC-HR or Krell PAM-7, but what it lacks in tech and high-end parts, it makes up for in solid build quality and the durability that older Krell products are known for. And before you ask, no I don’t know exactly what #Krellmonth is, but let’s just say I hope to figure that out and write a couple more articles as part of it.

I’ve been so under the pump with customer work that I thought I’d create this relatively brief article on my repair of this lovely little KAV-280p. I chose the KAV-280p because it’s just a good preamp, well-made and unassuming. Because of that, my work on her was relatively straightforward compared to some of the jobs I see here, as is writing about this little beauty.

If you’d like to watch my accompanying video, view it here:

KAV-280p
The Krell KAV-280p, as she came to the workshop

Specifications & Further Info

FREQUENCY RESPONSE: 20 Hz-20 kHz +0 dB, -0.04 dB; 0.2 Hz-300 kHz +0, -3 dB
SIGNAL TO NOISE RATIO: >98 dB “A” weighted, >90 dB wideband
TOTAL HARMONIC DISTORTION: 20 Hz-20 kHz <0.004%
GAIN: 6.2 dB single-ended output, 12.3 dB balanced output
OUTPUT: 9 Vrms single-ended output, 18 Vrms balanced output
INPUT IMPEDANCE: 43 kOhms single-ended, 86 KOhms balanced
OUTPUT IMPEDANCE: 120 Ohms single-ended, 240 Ohms balanced
POWER CONSUMPTION: 22 W standby, 25W on (wow..!)
INPUTS & OUTPUTS: RCA and XLR
DIMENSIONS: 17.3w x 3.5h x 17.3d in; 43.8w x 8.9h x 43.8d cm
WEIGHT: Shipping 22.0 lb., 10.0 kg; Unit only 16.0 lb., 7.3 kg

Note the impressive specs such as the low output impedance, RCA and XLR connectors, excellent signal to noise ratio and wide bandwidth. Also, note the stupid high standby power consumption figure, more on that shortly.

This isn’t a KRC-HR or PAM-7 as I’ve said, but it’s not trying to be and that’s something I like about it. More can be found about the KAV-280p and its partner KAV-2250 amplifier in this great review from the Absolute Sound.

Issues

This Krell KAV-280p presented with one curious issue. The owner would power it up and it would mysteriously turn itself off after 15 – 20 minutes, for no apparent reason. The preamp had been looked at by a tech who said there was nothing wrong with it and it went home and continued doing the same thing.

Krell KAV-280p

I found a few issues here, the main ones being the deterioration of the early generation surface mount capacitors in the power supply and the resultant need for a full power supply overhaul. Dust and dirt inside the case, corrosion of pin headers and connectors were incidental and also needing attention.

KAV-280p
Decent-sized toroidal transformer, lovely, serviceable design using heavy-duty connectors, this era of Krell gear was just starting to go bad, but this old girl is still OK.
Krell KAV-280p
Duuuuusssst…
Krell KAV-280p
Dust, crappy SMD capacitors and heat, a recipe for failure, albeit over a fairly long time in this case. These SMD parts all measured terribly. There were a couple of other issues here too.

SMD caps, especially early ones, hate heat. The KAV-280p has a standby mode where it uses – wait for it – 23 Watts continuously, vs 25 Watts when powered on… Really, Krell? It’s great that we can save 2 W by turning this off, but that’s really only great if the preamp uses 2 W when turned on!

I don’t know about you, but I really like my equipment not to use energy and generate heat when I turn it off. Going from 25 W to 23 W power consumption by turning this off is lame at best. Why even have a power switch?! So the 280p runs warm even in standby, wasting a ton of power and killing the crappy early SMD capacitors.

Ridiculous Standby Mode

So the Krell KAV-280p uses almost exactly the same amount of power when turned off as it does turned on, I kid you not. It basically makes the ‘off’ feature redundant. Just accept that turning it off is essentially the same as leaving it turned on, minus 2 watts. It’s therefore on 24/7.

I calculated that leaving this preamp in standby for a year will cost you exactly $57.91 AUD, here in Perth. That’s with it turned off, sitting in standby! Over the 20 years since the owner bought this, that’s $1158 AUD at today’s tariff, with the preamp switched off!!!

It goes without saying that this is just silly. High power consumption in ‘soft-off’ standby modes was common back in the day and manufacturers gave all sorts of reasons like “It will sound better when warm” etc. TVs, coffee machines and loads of other things are sipping power in your home right now when ‘turned off’.

I agree, hi-fi equipment will sound better when warm and there’s a really simple way around this for any concerned owner. If you want the benefits of your equipment sounding better when warm, simply turn it on an hour or two before seriously listening to it! That’s what I do, it works well and saves a ton of power.

Repairs

Working with surface mount or SMD capacitors can be tricky. You need some very fine soldering tools and good skills to remove the old parts and install the new ones. This has to be done without disturbing other parts nearby, especially other SMD parts. Get this wrong and you’ll damage the irreplaceable board faster than you can say “damn”!

Krell KAV-280p
Obviously, it’s out with the power supply after good high-pressure air dust. Naturally, I tested the SMD capacitors on the mainboard and they were OK. Being further away from the heat saved them.
KAV-280p
Again, great modular design and, apart from that SMD area in the middle, a good power supply to work on. Whilst the SMD capacitors were dead,  I replaced all the through-hole capacitors with premium new parts whilst I was at it.
Krell KAV-280p
First, I washed the board, then I installed some really good high temp, low ESR through-hole capacitors, similar to but better than the originals.
Krell KAV-280p
Then, I desoldered the SMD capacitors, measured them again and prepared the PCB for the new SMD parts. Here, I’ve cleaned, fluxed and prepped the pads with premium leaded solder for the new capacitors. Yes, leaded solder IS better, period.
Krell KAV-280p
This is the finished Krell KAV-280p power supply, cleaned and with all new electrolytic capacitors, ready for reinstallation.
Krell KAV-280p
These new capacitors will last another 10 – 20 years with normal use. I recommend turning the KAV-280p off at the wall when not in use though. At 28.8229 cents per kW/hr, leaving this thing OFF in Perth, Western Australia will cost $57.91 AUD annually!
Krell KAV-280p
Love looking at the old parts before throwing them away.

Results

This was another great result I’m very pleased to say. The preamp ran for hours on my bench and didn’t once turn off, so good news there. She also sounded excellent, no doubt much better than before, after all the power supply is everything in a piece of audio gear.

KAV-280p
Here, the Krell KAV-280p sits running with her overhauled power supply, not missing a beat.
KAV-280p
A lovely looking preamp isn’t she?

The question one might ask if one didn’t know much about gear like this is “Is a repair like this worth doing?” Well, to answer than we need to know a little more about what something like this might cost to replace. I don’t know if you’ve looked for a decent stereo preamplifier recently, but they are not easy to find.

There are a ton of horrible Blue-toothy, integrated digital things you might not like very much if you love two-channel analog gear. Let’s just say that good stereo preamplifiers aren’t easy to find and expensive when you do. You’d pay many thousands to replace this KAV-280p balanced preamplifier with something similar new, so repairing it for a small fraction of that really is a genuine bargain.

Krell KAV-280p

As always, I hope you enjoyed this article and if you’d like me to look at your KAV-280p, get in touch!

Liquid Mike

At 10 I was pulling apart electronics and by 13 I'd have Dad's hi-fi in pieces when my parents went out! Later, I started Liquid Audio, a specialist electronics repairer known for detail-focused service, repair and restoration of hi-fi electronics & turntables. Keeping classic hi-fi gear alive and well is what we do. Our mission: to deliver TLC for classic Japanese, American and European hi-fi stereo equipment. In my spare time, I ride motorcycles, travel, listen to music and research interesting topics.

This Post Has 8 Comments

  1. Mike

    Did the previous tech not even blow off the dust ??? How pathetic is that !
    Also surprising to see such an expensive component use garbage SMD caps !

    1. Liquid Mike

      Correct, I doubt they even took the lid off! SMD caps are prevalent across a huge range of gear, some of the most expensive test and measurement gear from this era was filled with them and they failed miserably. SMD caps have improved over time though and modern ones are OK.

      1. Mike

        For $3500 I would expect high end audio caps not cheap SMD

        1. Liquid Mike

          I hear you, though Krell did use really good caps in the critical parts of this power supply. Like many manufacturers, they jumped on the SMD bandwagon for many good design reasons, but the parts themselves let manufacturers and owners down. There’s a bit to this and I haven’t gone into all of it but the big issue with this design is that it never turns off, the standby power consumption is just too high and that kills these guys.

  2. tim davis

    Great piece! I especially loved the term “blue-toothy”!

    1. Liquid Mike

      Thanks Tim, always looking for ways to entertain my regular viewers!

  3. Dario

    Great work, as always ¡¡¡¡¡¡¡ A pleasure to read and see your work.

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