Yamaha BX-1 Mono amplifiers

Goldjazz

Active Member
Hi all,

I have an opportunity to get a pair of these rare amps. They have been refurbished and recapped and are in working order.

http://audio-heritage.jp/YAMAHA/amp/bx-1.html

I am looking at building a system with some JBL4343s, not sure about preamp yet.

Just asking for any opinions. I have seen a couple of threads here about them but not much info.

Cheers.
 
330k Yen in 1980!? That is some serious dough for mono blocks.

I wouldn't hesitate to buy those myself if the price was reasonable.
 
330k Yen in 1980!? That is some serious dough for mono blocks.

I wouldn't hesitate to buy those myself if the price was reasonable.

Yeah they won't come cheap, hence why I'm doing a bit of research. But given that they've been just been fixed up and given their rarity the price is probably reasonable.
 
Just asking for any opinions.

I don't have any direct experience but I've read lots of stuff on them over the years.

The good: When these amps are working right they sound superb. :music:

The bad: These amps run very hot and need lots of breathing room. Over the long term they usually cook themselves to death. From a service and repair perspective, their servo circuit topology and mechanical design make them a real PITA to work on. :yikes:

If it were me, the price would need to be very sweet before I'd buy them ... but that's just me. :D

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I don't have any direct experience but I've read lots of stuff on them over the years.

The good: When these amps are working right they sound superb. :music:

The bad: These amps run very hot and need lots of breathing room. Over the long term they usually cook themselves to death. From a service and repair perspective, their servo circuit topology and mechanical design make them a real PITA to work on. :yikes:

If it were me, the price would need to be very sweet before I'd buy them ... but that's just me. :D

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Yep thanks the running hot comment is coming up time and again in my research. Im sure many are aware of this site "amp 8"

http://amp8.com/tr-amp/yamaha/bx1-1.htm

The tech makes commment about the heat issue here a bit. " (basic design is bad) heat dissipation is poor, deterioration of parts early" . I am no tech but as I understand it the concern relates to the caps drying out cause they werent up to the spec of the huge heat put out.
I plan on checking the specs of the caps In the recapped unit to see if the issue has been adressed.

But yes wise words to be cautious. But just how good do the functioning beasts sound I wonder?
 
But just how good do the functioning beasts sound I wonder?

You'll just have to buy them to find out and then you can let us know what we're missing, :thmbsp:

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Class A amps--beasts, heaters, full power all the time. Yamaha B-2 had a pair for a while as I recall and I think he liked them.
 
I generally considered Levinson No series to be the most convoluted amplifier circuits I'd seen. But these go far beyond anything Madrigal thought of.
 
The pair of BX-1's that I have show few signs of heat damage - minor toasting on a few resisters. However, neither amp is functioning, so it may be that these don't have much actual operating time on them.

To deal with the heat all electrolytic's should be replaced with 105°C spec caps.

The top circuit board runs the width of the amp, and while it has a center support there is still some sagging that brings heat sinks on the bottom of the board dangerously close to shorting. Those heat sinks are not well attached and if they come partially loose they could cause a short.

I've only heard good things about the sound quality of these amps from AK'ers who owned them.
 
The pair of BX-1's that I have show few signs of heat damage

Sadly, yours are prime examples of what most BX-1's are doing these days ... and to add insult to injury, these are like the B-1 in that most tech turn and run when they see these amps coming. :beer: :D

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Complexity for complexity's sake.

The block diagram with a twin ganged 'speaker short relay' to earth could be fun- it looks like Yamaha decided an inline speaker relay was so detrimental they'd sacrifice the output stage if there is a problem.

So all we have a couple of low power, high current amps running in bridge mode to give us 100w @8ohms, each class A and we'll drop the rail voltage for 4 ohms loads because our output stage wouldn't survive otherwise, even though we've triple paralleled our MT200s.

Nothing to see here, just a tech's nightmare when it dies. The internal picture shows it all; a mess of design.

Personally, unless they were cheap, I'd steer clear of them.
 
Complexity for complexity's sake.

The block diagram with a twin ganged 'speaker short relay' to earth could be fun- it looks like Yamaha decided an inline speaker relay was so detrimental they'd sacrifice the output stage if there is a problem.

So all we have a couple of low power, high current amps running in bridge mode to give us 100w @8ohms, each class A and we'll drop the rail voltage for 4 ohms loads because our output stage wouldn't survive otherwise, even though we've triple paralleled our MT200s.

Nothing to see here, just a tech's nightmare when it dies. The internal picture shows it all; a mess of design.

Personally, unless they were cheap, I'd steer clear of them.

Thanks for the advice. They arent cheap so I think I will take your advice and pass on them, cheers. As much as I would love to have them and let everyone know what they sound like, this sounds a bit risky.
 
how much is "not cheap"? refurbished and working, with a little bit of extra fan ventilation these would be hard to beat, and they should be fairly reliable.
 
how much is "not cheap"? refurbished and working, with a little bit of extra fan ventilation these would be hard to beat, and they should be fairly reliable.

The issue is the 'refurbishing'. We have no idea what has been done with this particular pair. For some people, 'refurbishing' could be a simple squirt with contact cleaner and a dust out/wipe with a sponge, right through to a rebuild. have a look at the amp8 link further back and see what he did to make that unit reasonably reliable (hopefully).

Without having the thread moved to dollars and sense, we can't talk numbers, but for me, it'd need to be a number close to parts value if they went south and needed a rebuild. I don't think the OP wants a couple of 18kg paperweights.
 
Complexity for complexity's sake.

The block diagram with a twin ganged 'speaker short relay' to earth could be fun- it looks like Yamaha decided an inline speaker relay was so detrimental they'd sacrifice the output stage if there is a problem.

So all we have a couple of low power, high current amps running in bridge mode to give us 100w @8ohms, each class A and we'll drop the rail voltage for 4 ohms loads because our output stage wouldn't survive otherwise, even though we've triple paralleled our MT200s.

Nothing to see here, just a tech's nightmare when it dies. The internal picture shows it all; a mess of design.

Personally, unless they were cheap, I'd steer clear of them.
The complexity of the design was to achieve the best sound quality. I don't disagree that a design can be overly complex. An audio amplifier design should be a compromise between sound quality and reliability.
 
The issue is the 'refurbishing'. We have no idea what has been done with this particular pair. For some people, 'refurbishing' could be a simple squirt with contact cleaner and a dust out/wipe with a sponge, right through to a rebuild. have a look at the amp8 link further back and see what he did to make that unit reasonably reliable (hopefully).

Without having the thread moved to dollars and sense, we can't talk numbers, but for me, it'd need to be a number close to parts value if they went south and needed a rebuild. I don't think the OP wants a couple of 18kg paperweights.
Come on, you would love to restore a pair of these amps! :D
 
I have a pair of these collecting dust waiting for attention in the back. It looks like Yamaha had a bunch of parts left over they needed to get rid of. Quite frankly, I don't think the designers knew what they were doing. Either that, or they were given a set of marketing objectives and design constraints that were mutually exclusive. The front and back panels are plastic. On a $4k set of mono-blocks. In 1986.
 
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