Yamaha B2 input switch/attenuator bypass

so I guess this is shielding in the loosest sense.

in my book that is shielded :)
You could of course, choose something better than Yamaha was willing to use 40 years ago, for a large production amplifier.
For the last amp I used double shielded wire, that I had laying around. Overkill, but it was available and begging me to use it for something. I am sure that purists would suggest some other fancy stuff...
 
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in my book that is shielded :)
You could of course, choose something better than Yamaha was willing to use 40 years ago, for a large production amplifier.
For the last amp I used house alarm double shielded wire, that I had laying around. Overkill, but it was available and begging me to use it for something. I am sure that purists would suggest some other fancy stuff...

I'll buy something good if I can find it - but not fanatical. While I do believe that good boutique capacitors and resistors can sound better in certain places, I do not believe in fancy silver wire with teflon coating, vibration dampers for solid state gear, and a lot of other bizarre stuff that exists out there.
 
Yes, shielded wire is a must from what I've heard. Especially because the wires run closely to a transformer.
 
Thank you, gentlemen. Working with audio electronics is not my day job, so I love how much I learn doing these projects. I picked up some shielded wire today to be installed.

One driver board is done with all new resistors in the signal path. You can see the pink Takman Rex and the elevated little blue Vishay CMF.

I ended up leaving the original R168/167 because when I removed the originals they said 2W on them, NOT 0.25W like the replacements I ordered! I expect that the fusibles in the signal path are .25W. It does not say on those Micron resistors.

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All modifications or upgrades complete now, including shielded wire connecting new inputs to driver boards. Signal meters are illuminated by 3 yellow LEDs each.
 
This is a passion and a hobby for me, Oilmaster. I put the Duelund in only to amuse myself. I think high frequency is the best characteristic of this amp, so why not?

Out of curiosity, how do you know the current through those resistors? The 47 Ohm resistors, for example, show a ~ 0 VDC drop across them on the schematic. So, current must be AC sound signal only. Are your current figures maximums or RMS?
 
This is a passion and a hobby for me, Oilmaster. I put the Duelund in only to amuse myself. I think high frequency is the best characteristic of this amp, so why not?

Out of curiosity, how do you know the current through those resistors? The 47 Ohm resistors, for example, show a ~ 0 VDC drop across them on the schematic. So, current must be AC sound signal only. Are your current figures maximums or RMS?

On those resistors you can see the maximum current is written on them and I think above that amount of current, the fuse part will blow. So you translate that to the maximum power they should be able to handle. So the current figures are maximums indeed.

But, you used 250 mW resistors in places where 500 mW resistors are required.
 
Bizarre if those are the only markings; mine (multiple B-2 and many other Yamaha units) always had their value (ohm+mA) clearly written on it.
Perhaps a previous rigid cleaning with too strong solvents?

:rflmao:Oh, this would have been too easy. Mine are bare except for the markings shown in the pictures. You're right, it's in the service manual too - which I looked at, but I guess it never registered.

So, 0.47W is the fuse blow value for those 47 Ohm resistors. While I'm not completely convinced that would require more than 0.25W in a flame proof variety, you guys have convinced me - why take any chances?

I ordered some 0.5W Vishay CMF to put there.

I appreciate everyone's help and tolerance. I enjoy these projects because they take me back 20 years to when I was studying this stuff. :)
 
Well, a couple of days of listening to this amp after the second rework and I must say, it sounds very, very, VERY good.

I do think the low hanging fruit was bypassing the selector switches and pots on the input and wiring directly to the driver boards. That made a noticeable improvement.

Did everything else improve the sound? Who knows. It certainly didn't make it worse.

So far, there is no sign of stress on R163/164/165/166. But, the 0.5Ws should be here tomorrow and I'll put them in just for peace of mind.
 
Hello

Bizarre if those are the only markings; mine (multiple B-2 and many other Yamaha units) always had their value (ohm+mA) clearly written on it.
Perhaps a previous rigid cleaning with too strong solvents ?


No , no solvents gulty here
HW20447 mean HW104470 which is a YAMAHA official part number designation 47 ohm/100mA
Same with HW29539 mean HW195390 designation 390 ohm/25mA
You can find those two values in parts list in service manual
 
The large Duelund resistor make no sense at all; R237 and R238 are part of a HF filter, to ensure that amplifier always sees at least a 4.7 ohm load at very high frequencies where the (speaker)load can be become so inductive that a real resistance fades out. In normal operation, the output signal goes through coils L201/202, not through R237/238.

I have been chewing on this for awhile. Based on my calculations, a 3uH inductor is barely showing a 100kHz signal a 2 ohm impedance.

Seems like it wouldn't have a practical effect below the 100Khz -> 1Mhz region.

Properly designed audio equipment is not generating these frequencies. Is there any realistic danger to simply replacing R237 and L201 with a straight wire?

ALSO: If you are using the B2 with Yamaha NS-1000, the tweeter has a resistor in series with it (i.e., the L-PADs). Mine has Troels Gravesens crossover, but has a solid 3.3 Ohms in series with the tweeter, so there is no chance the load will ever be purely reactive at high frequencies.

Opportunity for another "improvement" to the B2?? :naughty:
 
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What's the story on B2 power switch replacements?

My B2 has a very sticky power switch. Normally I don't use it because it is plugged into a switched power bar, but occasionally I have need to turn the amplifier off independently from my preamp. Yesterday was such a time...and the power switch broke. The metal shaft that comes out of the switch and attaches to the plastic cover physically broke. It's not a huge deal because I opened it up and turned it back on. But, still, I would like to restore the proper switch functionality eventually.

Any replacements available?
 
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
 
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