Evan's Audio: Repair and Sale

09/23/2026

Kenwood KA8100 power amplifier stage restoration, and volume and balance controls cleaned. Customer complaint: balance and volume controls cut in and out, movement of controls will bring the signal back. Repair: cleaned mentioned controls with Nu-trol, idling current and DC offset adjusted to manufacturer spec, tested. 1 hour. Next, after suggestion for longevity: 2SC1213 and 2SA673 replaced, 4 each, with 4 of each KSC2383 and KSA1013. Audio grade capacitors used in place of 50 year old Elna brand. Listened to for hours before and after service. Tested thoroughly before and after. Here are the measurements. Close up images from after service performance, other images from after operating point adjustment and control cleaning only. The power amplifier stage is an excellent performer, and the entire unit as well, even with old capacitors in the preamp/tuner/phono stage/power supply sections (replacement not recommended due to hours more time of work, and as you can see distortion generally did not change a whole lot after power amplifier stage recap, indication of good capacitor health). Test speakers are B&O Beovox Penta.

Aside: the unit had been “gone through” by the largest other shop in town, and I would have expected those transistors and operating points replaced and set respectively, but this was not done. I am seeing work from other technicians in my area where Rifa paper capacitors (even one cracked) one are not replaced, amplifier shutting down issue remains even after it has been in two shops, preamp cuts out and fault not found, even a for sale listing of a Pioneer SA9500 without this very model of transistor as mentioned replaced that was marked as “restored”.

09/15/2026

Restoration work I am able to perform.

Baseline THD+N at 2kHz and 10kHz tested at 1/3 power 8 ohms if there is a power amplifier stage, 630mV to 1V 2kHz and 10kHz THD+N testing with line level only equipment.

I can subtract noise and 3rd or higher harmonic distortion from the reading with an equation and raising the signal to 12kHz with a 22kHz filter, and see how much there is 2nd harmonic distortion (benign below 1% generally) and 3rd or higher harmonic distortion (much worse).

I also check -.5db points in the frequency response.

Solder joint inspection and repair if necessary, control cleaning, relay cleaning or replacement if need be, staking glue removal, amplifier DC offset and idling current and power supply voltage potentiometer cleaning and adjustment or replacement and adjustment if need be, lamp replacement if need be with incandescent or LED if desired, electrolytic capacitor replacement with Nichicon copper lead MUSE for signal path, Kemet A750 or A759 organic polymer for all other audio section, Nichicon KW or KG or ES or KZ used for power supply, KW or KG in case of 63V or higher, non audio section Panasonic FR or FM series as replacement, in some values Elna Silmic II can be used if desired, select transistors as chosen from my list of poor reliability models replaced with modern new production ones, primitive opamp replacement if desired with SX52B discrete opamp, dual or triple diode substitution with 1N4148.

I can go further: high speed rectifier diode as replacements for normal rectifier diodes, signal path non ferrous metal film resistors as replacement for ferrous resistors, polyester capacitor replacement with polypropylene, even speaker posts and rca post replacement.

After this is done, baseline testing is repeated and much more testing can be done if desired.

Even at the rate I charge, which is half of what two repair shops I have worked for in two other states charge, the bill can exceed the value of the unit. I hold myself to estimates made after the first hour of diagnosis and work the large majority of the time.

08/09/2026

Harman Kardon PA2100 after restore with Nichicon MUSE capacitors installed. 2kHz and 10kHz THD+N measurements at 5W into 4 and 8 ohms, frequency response measured 5W 8 ohms and 10W 4 ohms. Loses .14db switching from 8 to 4 ohms, 5W to 10W.

08/08/2026

Just finished a Nakamichi TA-4A servicing. High THD amp… don’t have a good FFT setup right now (Cosmos ADC DM will solve that) but with my Audio Precision I measured .1% THD+N at 1W, 60W .056%, 8ohms, same THD+N 1kHz or 20kHz (Nelson Pass circuits seem to have flat f-THD responses). I assume high 2H and much lower higher order harmonics. Funny thing…. Idling current for a single output device was 10.5mA for one channel and 7mA for the other channel! Way low. Spec is 25mA. Got them adjusted, checked for bad solder joints (there were none), checked for relay performance (.25W THD+N change with spanking the unit), listened to the unit on restored B&O Beovox 6611 Pentas. Total time- 1.5 hours.

08/05/2026

Adcom GTP-500 audio stages only restoration. Using audio grade parts.

08/02/2026

From Diyaudio.com, explaining reasons for my now future use of polymer electrolytic capacitors:

“Across my many projects I have finally concluded electrolytics have no business in a signal path. Not "audio grade" ones, not fresh ones, not expensive ones. The only place they still earn a seat is bulk duty behind the rectifiers where hands are tied needing thousands of microfarads. Everywhere else — coupling, decoupling, feedback shunts — it's polymer or film, and in digital I bypass the bulk cans too. I'm done, electrolytics - fired.

Took me three projects to actually believe it, for what it's worth. I resisted for a while because everyone says polymer is wrong in signal.

Here's the thinking. In a series coupling position the whole signal charges and discharges the dielectric on every note. Aluminum electrolytic dielectric absorption runs 10-15%, polymer is roughly an order of magnitude better, film better again. Dielectric absorption is basically the cap holding onto a bit of the signal and handing it back late — thats the mechanism that eats low level detail, reverb tails, room cues, texture on a cymbal. I pulled a 10µF Rubycon out of a phono input recently that measured 4.69µF with a dissipation factor near 0.8 at 1kHz. Half a capacitor, half a resistor, sitting in front of a 5mV cartridge signal for thirty years. The polymer that replaced it reads 10.2µF and about 20 milliohms.

The leakage objection needs to stop. Yes, polymer datasheets spec higher DC leakage. Read the test condition — that's measured at full rated voltage. In a coupling seat at near-zero bias, which is where most of them actually live, leakage collapses to nearly nothing and drops further as the part settles. The objection could be real for a polymer coupling a 40V tube stage but irrelevant for a buffer output at millivolts into 20k. Most people repeating the rule have never run the numbers for their own operating point. Second thing nobody says out loud -- there's no money in polymer. The audio grade electrolytic market has decades of mythology and a boutique tier at three figures a cap. A polymer is a two dollar commodity part from a Digikey reel with a datasheet instead of a story. Nobody reviews it.

In the signal path the thing that goes away is a kind of congestion you stop noticing until it's gone — the sound opens up and low level stuff that was being smeared into a haze comes back with its own texture. Bass gets tighter and paradoxically bigger, because the leading edge of the note arrives intact instead of soft. Anyone who's described electrolytics as stuffy or metallic is hearing ESR and dielectric absorption. ESR is just the cap's internal resistance, and on old electrolytics it climbs with frequency, right where the air lives. Both problems just leave.

The digital side surprised me more. Polymer across the supply rails on a DDC, DAC and clock board did more than I expected — flat milliohm ESR across the band is exactly what a regulator feeding a converter wants, and the result is a blacker background and better spatial cues. Same story on decoupling around the digital sections. You don't get "more detail" so much as less noise sitting on top of it, and the difference in how solid an image sits is not subtle.

Three components done this way now: a DAC, a preamp, a pair of power amps. Somewhere north of a hundred caps. Zero aluminum electrolytics anywhere between the DAC chips and the voice coils.”

The diyAudio Community

08/01/2026

Restore of a Pioneer SA9500II preamp/tone board. 4.7uF 50V low leakage electrolytic capacitors (Nichicon KL) can no longer be purchased from parts retailers. I only had so many in stock. So I put in as many 4.7uF polypropylene capacitors as could fit, and where they couldn’t I used some of the last of my 4.7uF 50V Nichicon KL. These polypropylenes have even lower leakage than Nichicon KL. Nichicon ES used elsewhere. 2SC1400 transistor replaced with KSC1845F. + power supply wire will need to be soldered on to the posts as it broke during handling as these solid core pioneer wires often do. This unit will be sold with the matching tuner in original wood cases when I am done with the full restoration.

07/19/2026

05/03/2026

50+ Marketplace listings. Much more unlisted. Let’s make a deal. Flat rate shipping to 48 states and worldwide shipping when calculated.

https://www.facebook.com/marketplace/profile/100004050231440/?ref=permalink&mibextid=6ojiHh