Virtus
Member
For this reason, I have no choice but to use the 8650 solely as a power amplifier. It sounds great, but the preamp is its weak point.
Yamaha B2 - the "why" and the "how" of a comprehensive rebuild
- Thread starter rottalpha
- Start date
-
- Tags
- v-fet yamaha b-2
Sparkplug
Super Member
Sounds like a physical issue to me not an electronic one …
spaghetti
Active Member
@Sparkplug apparently you're right.
Yesterday evening, moved by curiosity for our pre-amp issue I decided to troubleshoot my TA-8650. After a few seconds sound started to quickly fade away, especially on one channel. So I grabbed my screwdriver and started to remove the top cover, side burns, and the faceplate. I losened the front part with all the pre-amp boards and moved it a bit. Sound came back immediately. Looks like a contact issue. The preamp section is a rat nest of cable connectors going from one board to the other, I believe even minimal oxidation can lead to these kind of issues. I haven't found the exact culprit, but my hunch is it's one of the connectors that link the bottom left board with the long one over it. When the preamp section is properly secured, these connectors end up being pushed slightly by a vertical metal plate separating the preamp from the PSU section. Another reason may be cold solder joints, but when I got the amplifier I cleaned and inspected all boards and these should not be an issue here.
Yesterday evening, moved by curiosity for our pre-amp issue I decided to troubleshoot my TA-8650. After a few seconds sound started to quickly fade away, especially on one channel. So I grabbed my screwdriver and started to remove the top cover, side burns, and the faceplate. I losened the front part with all the pre-amp boards and moved it a bit. Sound came back immediately. Looks like a contact issue. The preamp section is a rat nest of cable connectors going from one board to the other, I believe even minimal oxidation can lead to these kind of issues. I haven't found the exact culprit, but my hunch is it's one of the connectors that link the bottom left board with the long one over it. When the preamp section is properly secured, these connectors end up being pushed slightly by a vertical metal plate separating the preamp from the PSU section. Another reason may be cold solder joints, but when I got the amplifier I cleaned and inspected all boards and these should not be an issue here.
Sparkplug
Super Member
As a general rule, before starting any kind of work, you should reflow ALL solder joints, a tedious task but no way around it. Most of the time that’ll solve your intermittent and other noise issues. If nothing else, you’ll at least establish a reference line of where the unit stands physically.
Almost all of the problems with vintage equipment have some physical (corrosion, cold solder joint, broken cable/connector, dirty switches/selectors, etc.) root cause.
Virtus
Member
I’m having the same problem with my 8650. The sound cuts in and out. It might come back if I remove the cover, suddenly turn up the volume, or turn the amplifier off and then back on. But after a few minutes, it disappears again. Cleaning or replacing any parts didn’t help. Many owners have encountered this and haven’t been able to do anything about it. The suspects are the green Sony BX-269 or BX-269A chips located in the preamp section. There’s nothing to replace them with. Even if you find a donor unit, there’s no guarantee that these chips will work. The only solution may be to completely rebuild the preamp section from scratch. In general, the preamp in the 8650 is very noisy. I listen to my 8650 with a separate preamp, and the sound is excellent. Apparently, Sony was in a hurry in 1973 to produce the world’s first integrated amplifier based on V-FET transistors, and this led to an imperfect preamp section.
Sparkplug
Super Member
I disagree, semiconductors usually either work or they don’t, there’s no in between since there are no moving parts, only P-junctions, N-junctions, so on and so forth. Most probably the interconnections between different parts, transistors, etc. have issues. If you start the clean up systematically, at some point you’ll find the culprit. Good luck.
Last edited:
I do no disagree but what we are speaking about here are hybrid opamps. Typically noisy, or simply out cold, but I would not rule out other symptoms
Sparkplug
Super Member
I thought of clarifying and saying the same thing also but didn’t want to hijack the thread into Sony stuff any further. But yes, in those hybrid ICs any number of things could blow and render them unusable or greatly degraded. Maybe that’s what @Virtus was referring to. That’s also why I don’t buy amps with hybrid ICs in them.
When doing 800Mhz to 900Mhz cellular amps, had the same experience with high power hybrid ICs, at the drop of a hat, they’d blow completely or get degraded performance.
Yes, the symptoms you are describing are hinting to the IC suspects, but could also be something else. That said, if you had the unit inspected already and it was determined it is the ICs then we can put the debate to rest. This would not be the only 8650 with these issues.
Not necessarily. The ICs can be redesigned with modern parts. The original hybrids use both op-amps and a j-fet buffer stage in the same encapsulated package. Jfets from that period are known to start leaking, produce crackling noise, be very sensitive to changes of ambient temp, etc. We know this also from Yamaha to some extent. The input diff of the B3s or the dual sony jfet pair of the B2. So it is rather an aging and part speciffic issue rather than a Sony design issue.
Yes, it sure looks Sony wanted to top Yamaha with being the first on the market with a vfet amplifier....or we can also say that Yamaha was dragging their feet.
Yamaha B1 was bing demoed and was market ready in '73, but Yamaha waited to bring it to market untill the beginig of '74. The way I see it, good for Sony.
BUT, I would not say that Sony cut corners with the engineering of the preamp of the TA-8650. It is a part and aging speciffic problem.
You should make an exception for this one when you can
Sparkplug
Super Member
Yep, right after I get my second B-2 and a B-3 after that, I’ll be sure to look into this …You should make an exception for this one when you can
I do want to get a Sony TAN-5550 V-FET power amp at some point though …
US7IGN
Active Member
This was a very common situation with Soviet hybrid chips, which could have problems right from the factory due to poor manufacturing quality. Then they were guaranteed to fail.
An example of replacing such a chip Самодельная «микросхема»
Last edited:
Mr. Yamaha
Not so much Yamaha lately...
Awesome information when translated to English
I would Dm Pete @rottalpha .
More LED trivia
For C-1, the original incandescent bulbs need to dissipate about 5 watts, hence the intense heat at the front of the c-1 above the vumeters
Also, the light is concentrated in the middle of the dial.
With the LED strip, light dispersion is significantly improved
And the heat dissipation is reduced ~20x
The installation is not necessarily difficult but it is not drop in either
For best results I daisy-chained the two LED strips 5v x 2 which can be powered up straight from the rectified 8v AC of the original feed to the incandescent lightbulbs. This is done in the new PSU of the C-1, in my case, but can be done as standalone with not too much hustle.
Now let’s talk about B2 and UC-1 LED strip conversion
For both applications I am using 12v LED strip
Because I need a flat surface to attach the strip to,
I made an adapter - the adapter varies between the B2 and UC-1 but it serves the same purpose
The B2 solution requires clipping onto the chassis, where for the UC-1 I am able to use existing mounting screws holes.
The end result is the same: a flat surface to mount the LED strip
I will eventually carve this out into its own post about mounting strip LEDs but for now, it should provide enough direction for the curious minds.
For C-1, the original incandescent bulbs need to dissipate about 5 watts, hence the intense heat at the front of the c-1 above the vumeters
Also, the light is concentrated in the middle of the dial.
With the LED strip, light dispersion is significantly improved
And the heat dissipation is reduced ~20x
The installation is not necessarily difficult but it is not drop in either
For best results I daisy-chained the two LED strips 5v x 2 which can be powered up straight from the rectified 8v AC of the original feed to the incandescent lightbulbs. This is done in the new PSU of the C-1, in my case, but can be done as standalone with not too much hustle.
Now let’s talk about B2 and UC-1 LED strip conversion
For both applications I am using 12v LED strip
Because I need a flat surface to attach the strip to,
I made an adapter - the adapter varies between the B2 and UC-1 but it serves the same purpose
The B2 solution requires clipping onto the chassis, where for the UC-1 I am able to use existing mounting screws holes.
The end result is the same: a flat surface to mount the LED strip
I will eventually carve this out into its own post about mounting strip LEDs but for now, it should provide enough direction for the curious minds.
Attachments
Last edited:
Asmodeus2112
Super Member
Awesome work as per usual. Thank you for sharing!