Yamaha B2 input switch/attenuator bypass

Reviving this old thread due to the need to fix some intermittent switches on my B2. Love my B2 but the cleaning of relays is not my thing. Here's the bottom line:
Is it possible to use existing input RCA jacks but bypass all attenuators, switches and relays that may cause issues? All I need is pure amp functionality with VU meters functioning -- is this possible with the B2? If so, can someone help me out?
thanks,
Herman
Anything is possible :) Welcome to the forum!
One answer you might not want to hear is that If cleaning a relay is too DYI for you, then the rest of the equation does not apply in your situation.

Do yo have someone that can help you with your B-2?
 
Hi,
I have cleaned the relays and I've had the amps services at a audio service shop. This works for a while but then they start to act up again and sound cuts in and out. Jiggling the front selector/mute switch takes care of the problem. But the bottom line is I don't want anything that is not needed. Best to bypass any areas of potential problems. Just need amp functionality! Don't mind DIY, as long as it's not a temporary fix, which cleaning the relays is.
 
Hi,
I have cleaned the relays and I've had the amps services at a audio service shop. This works for a while but then they start to act up again and sound cuts in and out. Jiggling the front selector/mute switch takes care of the problem. But the bottom line is I don't want anything that is not needed. Best to bypass any areas of potential problems. Just need amp functionality! Don't mind DIY, as long as it's not a temporary fix, which cleaning the relays is.
well, there are no relays in the selector circuit, not on the original selector circuit. If proper relay were part of that selector, none of these issues would manifest.

The relays you cleaned or replaced, are located on the output to the speaker lines. Removing the relays, removes a very important function of the delay circuit that protects your speakers against transient currents during start-up. You could be frying a tweeter or two once in a while... Many commercial amplifiers lack the automatic delay circuits. Look at how the sound engineers deal with start-ups. I would personally not remove those relays.

back to the selector....
The selector also switches VCC for the A/B relays but if those contacts are bad, then the relay coil would not engage all together, so as long as you hear the relay click, the selector does a satisfactory job for A/B relay selector.

The problems you are experiencing are related to the input source selector lines. Here you are most likely dealing with issues related to oxidation deposits on the contact pads of the selector switches OR with degraded contact effectiveness of the potentiometers. It is usually BOTH.
These, if cleaned properly, would allow the amp to work for many more years. If cleaned with abrasive materials that remove some of the contact plating or create deep abrasions that limit the contact surface / contact effectiveness, then you end up with poor contact or no contact shortly after cleaning.

There is a way to by-pass the entire assembly, keep the pots and remove the switches, keep the switches and remove the pots, basically any combination you need. In this forum you should find the exact way others have done it.

There are a couple of very important variables to consider when sending a source signal straight to the driver boards and a third variable specific to B-2
1: you will have no capacitor coupling, thus not protected from DC coming down the line.
2: you will have high inductance coming through that line, thus unwanted noise if the line is not terminated.
3: specific to B2: if eliminating the rear RCA connection to the chassis, you need to wire the ground from the PSU board to each of the driver boards with a separate wire. This however has additional unintended consequences related to the original ground loop design (subject to more research and a broader topic).

side note: The selector assembly of the B-2 is it's Achilles heel. Instead of being fully eliminated and have a bunch of knobs and switches with no use, Ideally, the entire assembly would be redesigned and fitted with proper, hermetically sealed relays for source selector duty, in order to maintain all existing functionality but not suffer from any signal degradation.

Good luck with whatever you choose. The B-2 is one of the best sounding amplifiers you can find and worth bringing back to prime.
 
I always said that cleaning relay contacts is not the best , replacing them by new is much better
yes, replacing the relays is a better solution if the relays are compromised. But if the problem persists after, then I suspect his issue is not the relays but the signal source selector.....even though he is only describing the speaker OFF switch. That switch only controls the 12v to the relay coil. If the relay coil clicks on and off in response to the switch,.... and that can easily be heard, then the problem is not with that switch...If the relay coils do not engage in response to the switch, then the problem is the switch and in that case cleaning the relay contacts or replacing the relay all together would make no difference.
B-2 only has two, commonly available relays that are easily accessible and and ruling them out as a problem, is as easy as replacing them.
However, in most cases I have seen, I found the signal selector switches or the pots to be the real issue.
 
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Thanks guys. I do love my B2 and want to get it working.

Let me describe the problem better:

The sound from one channel cuts in and out. At the same time the VU meter is moving, showing input signal with no interruptions. Selecting different input effects the VU meter activity but NOT sound coming out.

What does help bring the sound back more consistently is turning on and off the "sp off" switch, a few times.

My guess is that the relays need replacement. Is this assumption correct? If so, what is the relay make model I need to order?

thanks,
Herman
 
Also, the relay coil does click when I engage and disengage "sp off". I can't tell if both coils are clicking but I do hear a click.

So after more testing here are my findings.

toggling the input selector OR the volume control pots does not bring sound back.
toggling "sp off" or "A / B" speaker selector buttons DOES bring sound back.

Relays issue?
 
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Relays issue?
From your description and my experience I'm thinking yes.

You could try moving your speakers to the B side for a test; the B relay will likely need replacing too if the A one does but it probably won't have the exact same issue. That being said, YMMV. :)
 
He just wants to know which model relay to get.

https://www.mouser.com/ProductDetai...Safety/LY2-0-DC12?qs=ImaqFqjHA4neXVcLhtW8XA==
This should work. For future reference, the trick to getting information from the vfet boys' club here is to take a guess and then wait to be corrected.
Now that I've done this, hopefully someone else can confirm. :D

Obviously be very careful working on your B-2 and double check your work 35 times etc. No second chances.
 
>>For future reference, the trick to getting information from the vfet boys' club here is to take a guess and then wait to be corrected.
Gotcha.

Does Avionic still do work on B2 amps?
I have looked but Echowars does not seem to hang out here or at Diyaudio. So I gathered this list of recommended parts to replace:

Relays: Omron LY2-0-DC12
replacing the stock zeners (D205 and D206, 30V 1W zeners)
ALL the 2SC458 transistors (in the +/-85V regulated supply)
?? replace 2SC458 with Fairchild KSC1845 or Fairchild KSC945L (i can't find any KSC945L online)??

D203 and D204 with a series-pair of 1N4148's for reliability's sake.
?? meaning one diode soldered in series with another, and one end of each diode goes to PCB??

Should I replace all electrolytics or certain ones that are more important?

adjust the bias to 60 to 70mV. Factory spec 40mv

Please confirm that these are correct and if if you can, answer a few questions above.

Thanks guys!
Herman
 
Hello

Does Avionic still do work on B2 amps ? I don't see any reason why he will not

Relays: Omron LY2-0-DC12 yes replacing is better than cleaning
replacing the stock zeners (D205 and D206, 30V 1W zeners) can you explain why you want to replace a working component ? because it is 40 years old ?
ALL the 2SC458 transistors (in the +/-85V regulated supply) again and again , no (see my previous post about this story )
?? replace 2SC458 with Fairchild KSC1845 or Fairchild KSC945L (i can't find any KSC945L online)?? the better sub for 2SC458 is 2SC1815 . 2SC1845 will work too, but the best sub is 2SC1815 (don't tell me that it is obsolete, this is not true)

D203 and D204 with a series-pair of 1N4148's for reliability's sake. ??? Who told you that ??? semi-conductors are not tubes
?? meaning one diode soldered in series with another, and one end of each diode goes to PCB?? that's "in serie" mean

Should I replace all electrolytics or certain ones that are more important ? Replacing capacitors will not improve the sound except if your old cap are bad (dry, leakeage etc...) I n one 40 years old unit I will recommend to replace them all .

adjust the bias to 60 to 70mV. Factory spec 40mv !!! why do you want to increase the bias ?? YAMAHA recommend 40mV , B2 bias should be adjusted for this value and no other

B2.JPG
 
I have seen a couple of people running the B2 with higher bias (and fans on the top) and reporting that the sound quality improves.

I assume that will make it run more on A mode.

I have my newly restored B2 running at factory spec bias and it doesn't run hot at all. With such big heatsinks as it has, running so cold seems odd.

Really wondering what is to be gain with the higher bias setting.

Nelson Pass has recommended running at least one of his amps, not a set bias value but at a 50 degrees celsius, wondering if we can apply that to the B2...



Hello

Does Avionic still do work on B2 amps ? I don't see any reason why he will not

Relays: Omron LY2-0-DC12 yes replacing is better than cleaning
replacing the stock zeners (D205 and D206, 30V 1W zeners) can you explain why you want to replace a working component ? because it is 40 years old ?
ALL the 2SC458 transistors (in the +/-85V regulated supply) again and again , no (see my previous post about this story )
?? replace 2SC458 with Fairchild KSC1845 or Fairchild KSC945L (i can't find any KSC945L online)?? the better sub for 2SC458 is 2SC1815 . 2SC1845 will work too, but the best sub is 2SC1815 (don't tell me that it is obsolete, this is not true)

D203 and D204 with a series-pair of 1N4148's for reliability's sake. ??? Who told you that ??? semi-conductors are not tubes
?? meaning one diode soldered in series with another, and one end of each diode goes to PCB?? that's "in serie" mean

Should I replace all electrolytics or certain ones that are more important ? Replacing capacitors will not improve the sound except if your old cap are bad (dry, leakeage etc...) I n one 40 years old unit I will recommend to replace them all .

adjust the bias to 60 to 70mV. Factory spec 40mv !!! why do you want to increase the bias ?? YAMAHA recommend 40mV , B2 bias should be adjusted for this value and no other

View attachment 1641309
 
Clinic-audio,

Due to lack of complete and verified "B2 rehaul parts list", I compiled the list of parts based on a post from Echowars in this forum:
https://audiokarma.org/forums/index.php?threads/ew-mods-for-yamaha-b-2.307226/#post-3805054

>>replacing the stock zeners (D205 and D206
In your opinion I do NOT need to replace?

>>ALL the 2SC458 transistors (in the +/-85V regulated supply) again and again , no (see my previous post about this story )
I cannot find your post about this story. can you give a link? You are saying NO to what?

this is the best one to use?
Central Semiconductor 2SC1815
https://www.mouser.com/ProductDetail/Central-Semiconductor/2SC1815?qs=1mbolxNpo8fcj1oMtxMsDQ==


>>D203 and D204 with a series-pair of 1N4148's for reliability's sake. ??? Who told you that ??? semi-conductors are not tubes
Echowars. See link to his post above.
This part does not need replacement and likely will not fail?

>>?? meaning one diode soldered in series with another, and one end of each diode goes to PCB?? that's "in serie" mean.
Do you believe these old diodes should be replaced with new one per Echowars?

>> Replacing capacitors will not improve the sound except if your old cap are bad (dry, leakeage etc...) I n one 40 years old unit I will recommend to replace them all .
Ok. Do you think its ok to replace the stock power supply caps (18,000µf 63V) with 15,000µf 63V?

>>adjust the bias to 60 to 70mV. Factory spec 40mv !!! why do you want to increase the bias ??
I never said I want to increase bias. Just listing the recommendations by Echowars and other B2 users. Do you believe best sound is at 40mv?
 
Thanks guys. I do love my B2 and want to get it working.

Let me describe the problem better:

The sound from one channel cuts in and out. At the same time the VU meter is moving, showing input signal with no interruptions. Selecting different input effects the VU meter activity but NOT sound coming out.

What does help bring the sound back more consistently is turning on and off the "sp off" switch, a few times.

My guess is that the relays need replacement. Is this assumption correct? If so, what is the relay make model I need to order?

thanks,
Herman

Somewhere I remember an owner of several B2s reporting that the fading on one channel was related to a fuse.

Here is it: https://www.diyaudio.com/forums/solid-state/74725-repair-yamaha-2-a.html#post1018519
 
>>For future reference, the trick to getting information from the vfet boys' club here is to take a guess and then wait to be corrected.
Gotcha.

Does Avionic still do work on B2 amps?
I have looked but Echowars does not seem to hang out here or at Diyaudio. So I gathered this list of recommended parts to replace:

Relays: Omron LY2-0-DC12
replacing the stock zeners (D205 and D206, 30V 1W zeners)
ALL the 2SC458 transistors (in the +/-85V regulated supply)
?? replace 2SC458 with Fairchild KSC1845 or Fairchild KSC945L (i can't find any KSC945L online)??

D203 and D204 with a series-pair of 1N4148's for reliability's sake.
?? meaning one diode soldered in series with another, and one end of each diode goes to PCB??

Should I replace all electrolytics or certain ones that are more important?

adjust the bias to 60 to 70mV. Factory spec 40mv

Please confirm that these are correct and if if you can, answer a few questions above.

Thanks guys!
Herman


Before replacing the 2SC458 take a look here:
https://audiokarma.org/forums/index...toration-journey.742789/page-17#post-12371578
 
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I have seen a couple of people running the B2 with higher bias (and fans on the top) and reporting that the sound quality improves.
I could not hear a difference, but that does't mean there isn't any and have no reason to doubt the callous from other AKres that noted differences.

What I did see is only a minor THD difference (0.00xx%) on the analyzer between a channel at 40mV and the other at 50mV...nothing that anyone would hear.

I do not consider the extra heat warranted and my B-2s are at factory spec of 40mV ....for now.
 
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Clinic-audio,
thanks for the tips. I see your previous post -- 2SC458 that are rounded ( TO92 package) are OK.

Question: do any of small transistors get hot and would benefit from a heat sink?
And big power supply caps: The original ones have no visible problems or leaks. Should I still replace? If replacement is recommended, are the Nichicon KG gold 22,000μF/15,000μF both equally good or should I try to make the 22,000μF fit?
 
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