View attachment 916072
Performed a recap and basic restoration on a small Kenwood integrated amp KA-4002 and it sounds great. The KA-4002 has a cap-coupled output, so it has a warm sound kinda like tube gear and very much so the "1970's vintage sound".
- All electrolytic caps and "noisy" small signal transistors replaced.
- Electrolytics caps in audio path replaced with Nichicon KL series or metalized film.
- All replacement caps chosen for 70% working voltage (or lower) and for best price-point (i.e. if a 50V replacement was more expensive than a 63V one, then I chose the 63V one).
- Output caps replaced with same-capacitance-value to maintain the design's same low end rolloff.
- Added snubber caps to the power reservoir and output caps.
- High-stress resistors (e.g. output transistor emitter ones) replaced with high wattage metal film resistors.
- Rectifier bridge replaced with modern version.
I built a larger spreadsheet with ALL caps, all resistors, all diodes and all transistors... just in case someone needs a reference or I get bored and OCD and replace everything with modern versions.
I stumbled across this and am working a newer version of the 4002 (it says kenwood and not trio on it) I had to restore a channel thus far, besides the entire recap and the problems so far are the noisy/severely degraded 458's
I have also done the bias trans and will be turning to the drivers as it has noise in it, like fm static. It might be the goofy protection circuit or that lone 2sc971 in the tone board - be interested in seeing what subs you have worked out.
ETA: the static noise was in the 'protection'*(more on that later)
my subs: Qe19 2SC734 --> KSC1815
Qe17,18 2SC715--> KSC945CG (you can use a KCS945CY)
* kenwood protection: in many cases on the older units is a solid state circuit with no relays that simply drains input signal to ground. I find on most, like 95% of the kenwoods that I get, that using protection - which does not means 'save the outputs' - eats itself in some way.
Also, depending on which SCM you get D5,6 is listed as 1N60 in one, 1S2076 in another and the subs would be 1N60-99 for the former or a simple 1N4148 up to a 1N4007. using 'replace what you found' methodology, I used the Ge vs Si repalcements.
Very clean sounding now. Gotta sub up the phono section and I think your KSC1845F across Q1-4 is ok.
outputs ok and considering doing the drivers..they are not symmetric given that the amp is quasi comp. The 2SC1212A is a KSC2690 in my book. do you concur?
