Got my first Aiwa and was pleasantly surprised by the nice warm sound. Not too fond of the design yet but it’s growing on me. I did however find issues with Dolby C, similar to what Techmoan discovered in this video: Do anyone have experience with this? I’ve done adjustments on the Dolby levels using my ears and it works much better but do anyone know how to measure for correct adjustment? I have Dolby adjustment tape but need to know resistance to apply on output, volume setting and expected voltage. Also I’m curious about the difference between the 202 series and 203? Haven’t been able to find any good info online. Also haven’t been able to find service manual except from those sites that charge for it. I have no problems to pay for it but I’m not sure about the legality re-selling those service manuals.
The issues with Dolby C are caused by incorrect Dolby levels as you guessed yourself. There will be issues with Dolby B as well, but less obvious than with Dolby C. I cannot find anything about he HS-PC203 online, I wasn't even aware that a PC203 even exists. If it uses the NJM2065 as Dolby decoder IC, the levels should be 100mV RMS @ 200nWb/m at the Dolby points on the PCB (measured directly with multimeter, without any additional load). As for the legality of those sites that charge for manuals, those have been along for a long time. I assume if there would have been a legal problem, the companies would have sued them. The only potential problem can be one of copyright, but that would only apply in the country/countries where the manufacturer has headquarters and not worldwide. Scrolling through some AIWA and SONY service manuals, I cannot see any copyright markings so it is in question if those manuals were copywrited to begin with. If others know more about this, it would be interesting to know.
Thanks @Valentin I have now adjusted and treble is much better, a slight "pumping" effect on Dolby C recordings is still there. What other factors can influence Dolby decoding? Azimuth I suppose, maybe capacitors? I've read that capacitors is a common problem on these models and I don't know if they have been exchanged. I see some flux on some places that could indicate this. Edit: I think I spoke too soon. Done some more listening now on different Dolby C tapes and it sounds really good. Great player. If I find out more details about this model I will post them here.
Capacitors won't manifest this symptom, I would not consider them as a potential culprit. While caps are a common problem on these, it is Nichicon caps the ones that are problematic. Dolby C models usually have Nippon ChemiCon caps, but just check. In regard to Dolby C, first of all you need a well recorded tape, recorded with correct bias and correct levels: the recorded levels should be the same as input levels and bias should be adjusted for flat frequency response. Of course azimuth can be a problem, but unless the lock paint on the adjustment screw has been tempered with, there's no reason to suspect the azimuth. The pumping (noise modulation) effect is an indication of incorrect levels/bias either on the recording or on the playback side. Given your statement, I believe that particular cassette was not recorded correctly. For proper Dolby C encoding you do need a deck with automatic or manual calibration and calibrate on the exact tape you are recording, otherwise you are going to obtain poor results. This is true even with Dolby B, but B is a bit more tolerant and has more margin in regard to levels. If I remember correctly, Dolby B has a tolerance of +/-5dB on levels, while Dolby C only +/-1.5dB. Don't quote me on these numbers, but from memory they were in this ballpark.
Yes, this is my conclusion also. I think this tape was recorded on my previous deck and not calibrated properly. The other tapes I tried recorded on my "new" deck sounds fine. Dolby C is tricky but the result is great once the whole chain has been done correctly.
Never even knew about the HS-PC203. Would you mind sharing some photos if you open it up. Would be lovely to know what real difference it has over the PC202. There's barely any info on this model available at all.
