Sansui BA-2000. Where is the air?

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#21
wg_ski said:
I don’t see anything in the circuit that would obviously limit the audio frequency bandwidth. Perhaps you could check the frequency response of the amp it is being compared to. It may exhibit ultrasonic peaking making it sound “airy” or “extremely detailed”. Just a simple 1kHz small signal square wave is very telling - if there is overshoot or ringing at the leading/trailing edges is indicative of peaking. Even if the peak is waaay above 20kHz it can subjectively affect the sound (It will affect the IM distortion spectrum, and that is measurable). Also, if the Sansui has severely rounded edges to its square wave response it probably is rolling off too soon. If that happens I’d be looking for resistors that shifted or electrolytics that have gone bad. From what I see in the schematic that shouldn’t be happening.
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Of course this makes sense and the sansui frequency resonse specs corroborate this but mine and many others subjective impressions do not agree. Perhaps its the rest of the "curve" that distorts the subjective impressions such as heavier bass and low mids. The amp has been fully recapped and all the fusible resistors have been checked and replaced as necessary.
 
#26
Use quality parts; The nichicon uhe series is great for electrolytic replacements. Use high precision, low noise, and temp coefficient resistors in place of the fusibles. If you have the proper equipment, check the all the transistors and replace if necessary.
 
#27
@rjb5191 Thanks! I had already ordered bunch a parts. Will be using Nichicon UPW's for much of it, especially in the power supply. Using Nichicon UKL's in the sound path. Some of the smaller value 1uF - 3uF electrolytics I will replace with films. I got replacements for all the fusible resistors, using KOA Speer metals with the correct link leads and new spacers. I will replace all the suspect VD1212 diodes, and all the 2sc1313 transistors. The other transistors I will check. I am going to stay with the original Sanken output transistors for now, I backordered some suitable replacements: they will take months to get but it will be good to eventually have backups available. Based on some other people's builds, I will use Nichicon 15K uF 100V (Mouser part 647-LNR2A153MSE) capacitors to replace the big screw terminal caps. Also will replace all the fuses and the two relays.

This amp sounds "pretty decent" unrestored, hooked up to a CA-2000 I completely recapped along similar lines. Trying to imagine what it will sound like after it is comprehensively restored. Should be nice, will share my thoughts once it is broken in.
 
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