Well, although I need to get back to work and put gearhead's 2330B back together (been on the 'puter for too damn long tonight), I'll answer this and
then get back to work.
The KA-5500 was my first amp, and I saved for it all summer of '76. Tough to do with car expenses and all, but I finally bought it on sale for $200 at Burstein-Applebee.
I even sprung for the (now rare) D5 carrying handles at $35.
No matter what, I could never break this amp, and it got dragged to many a party. At several of these, it ran for hours on end blasting out tunes at close to 40+ watts of output. Unbreakable. The only issues I ever had was from dirty switches.
This amp has a very basic phono stage with a FET differential pair feeding a PNP driver/buffer, and a simple RIAA feedback loop. The phono board is mounted
directly on the rear panel, so there is no long length of wire from the input to the first amplification stage. It sounds very good.
The preamp uses a TA7136P opamp. Kenwood was known for good build quality while keeping prices a tad under the competition, and simplifying the preamp with the use of an opamp was one way to do this. While the original opamp is 'adequate', the use of the opamp actually gives a tech with an eye towards modification a lot of options. With a little bit of juggling, the original opamp can be replaced with about any modern opamp you care to experiment with. I own two KA-5500's (one is my original from 1976), and both have the opamps replaced with Burr-Brown OPA2604's. Certainly you could use anything here you wanted, but the 2604 is a very nice sounding amp and in my experiance is not too fussy about lead length and bypassing. So in my view, Kenwood's use of the opamp is a positive, not a negative.
This unit, like most of the Kenwood integrateds, has no pre-out/main-in jacks. However, the use of the opamp in the preamp section allows the
addition of the jacks very easily, and the 5500 has a nice place to put 'em.
The stock low filter is set to take place at 40Hz, and is easily changed with the swap of four film caps to 20Hz. Unfortunately, the location of the filter means that if you add pre-out/main-in jacks, the low filter stays on the amplifier side, whereas it would be more desirable on the preamp side. But Kenwood did put a tone defeat switch on the 5500, which is very very nice, and a feature missing from a lot of low-end integrated amps.
The amp section is beautifully simple and sounds wonderful. A PNP diff-pair with only a resistor current source feeding a VAS stage, and a Vbe-multiplier bias setup feeding the drivers and outputs. The only other real criticism here is the lack of a DC offset adjustment, typical for midrange and lower end Kenwood's. Both of mine have a diode and trimpot offset added to the unit, but this was before I started fooling around with servos. I may someday add servos to them, but not exactly in a rush to do so.
As an aside, the KA-3500 amplifier section is identical to the KA-5500, and also is wonderful sounding, but the KA-3500 is hindered by an inability to bypass the tone controls. Other than that, and the lower power, it also is a nice amp.
The power supply is also nothing outragous..a single EI-core transformer with a two secondary windings..one for the lamp lighting the power meters (yep...a winding that does nothing but power one single lamp), and the other for everything else. The power supply filter caps are nice and hefty for a 55WPC amp...10,000µf x 2.
I wouldn't have hung onto this for so long if it didn't continue to impress me with its sound and build quality. Kenwood didn't seem to sell a lot of these...seems that the KA-3500 (the model below the 5500) and the KA-7300 (the model above) were too close in price and squeezed the 5500 out. But the KA-5500 still is a great little amplifier, and has very good potential for those who like to tinker...