Yamaha A-700

[JesusJones]

I picked up one of these for pretty cheap. After a I cleaned out the pots with some contact cleaner it was working like a charm. Very nice, clear sound. But not very bass heavy, which I like. But still very good.

It has this "class A" mode as well. Which I had high hopes for

But pushing the button seems to make no difference in sound. I'm not sure if it's not working or if there just isn't a BIG audible difference. Any one know or have experience with such a function?

And the main reason that I am posting is that I have 2 concerns with this amp that I'd like to have sorted out before I put it into daily use....I noticed that when I started playing music at a moderate level that the amp started to get VERY hot. Almost too hot to touch the heat sinks. This was only at moderate volume.....maybe 9-10 o'clock on the volume control. None of my other amps get anywhere near that hot. (the others MIGHT get warm)

Any one think that might be normal? Putting it into class A seemed to make it much hotter, much faster(I didn't experiment very much but that's what it seemed like)

And my second concern would be the DC offset. I noticed upon start up it was around 300mv then made its way down to 0 and 3mv. Which is good, but should I be worried about that initial surge?

I'm hoping the heat issue(if it's even an issue at all) is related to bias. I would of checked it out by now but finding a service manual is proving to be nearly impossible. (hint hint) :thmbsp:

Cheers,
Rudy

P.S. There are some nice pictures here if you wanna see what this thing is all about.
http://www.hifi-wiki.de/index.php/Yamaha_A-700

 

[Martin.Ca]

Class-A is always warm, but I suspect you need to check the idling current and do some adjustments.

I'd contact Yamaha and ask if they have a copy of the service manual

http://sportsbil.com/yamaha/a-700-s.pdf

 

[avionic]

I picked up one of these for pretty cheap. After a I cleaned out the pots with some contact cleaner it was working like a charm. Very nice, clear sound. But not very bass heavy, which I like. But still very good.

It has this "class A" mode as well. Which I had high hopes for

But pushing the button seems to make no difference in sound. I'm not sure if it's not working or if there just isn't a BIG audible difference. Any one know or have experience with such a function?

And the main reason that I am posting is that I have 2 concerns with this amp that I'd like to have sorted out before I put it into daily use....I noticed that when I started playing music at a moderate level that the amp started to get VERY hot. Almost too hot to touch the heat sinks. This was only at moderate volume.....maybe 9-10 o'clock on the volume control. None of my other amps get anywhere near that hot. (the others MIGHT get warm)

Any one think that might be normal? Putting it into class A seemed to make it much hotter, much faster(I didn't experiment very much but that's what it seemed like)

And my second concern would be the DC offset. I noticed upon start up it was around 300mv then made its way down to 0 and 3mv. Which is good, but should I be worried about that initial surge?

I'm hoping the heat issue(if it's even an issue at all) is related to bias. I would of checked it out by now but finding a service manual is proving to be nearly impossible. (hint hint) :thmbsp:

Cheers,
Rudy

P.S. There are some nice pictures here if you wanna see what this thing is all about.
http://www.hifi-wiki.de/index.php/Yamaha_A-700

Unless you have some very good hearing, The audio difference between Class A and AB is minimal. And yes Class A will run very warm..I wouldn't worry to much about the initial DC offset..Doesn't appear to be any adjustment provisions for DC offset anyway.

 

[belgianbrain]

I have this AMP and it runs HOT in class A. I only leave it on when engaging in critical enjoyment listening. Normally for background music or watching television, it's off. The unit runs quite cool then.

The sound difference is subtle. You'll pick up on it eventually, but the difference isn't big.

Mine does the same...initially you can measure 150mV or so of offset, but within a minute or so settles down to about 5 mV or less.

 

[JesusJones]

Thanks for the link!

I emailed yamaha and they emailed me back pretty quickly. They said they could mail me a copy for 15+7 for shipping+taxes. It's a little steep in my opinion. So I might just leave it be. Since it seems that running on the hot side is normal for this beast.

I will keep trying to hear the difference between AB and A. But so far I really hear NO difference. But maybe I will eventually.

Thanks every one

 

[austi15]

Listening to mine right now...it burns your hand in 10-15 minutes in class A. I've heard a difference using with my friend's dad's KEF Reference 103/2 (I think-it's the one with similar drivers to the LS3/5a- damn good speaker IMO) nearfield...but I suspect it's major contribution is in the upper mids/treble, as I honestly can't tell a difference while running them for LF with biamped B&Ws. That range was also the KEF's strong point it seemed, so that may have contributed to the relatively obvious improvement as well.

 

[BinaryMike]

In theory, the difference between class A and class B should be most audible at low volume settings. Class A eliminates crossover distortion, which often becomes a very small fraction of total distortion at full output.

 

[Raynald]

Listening to mine right now...it burns your hand in 10-15 minutes in class A. I've heard a difference using with my friend's dad's KEF Reference 103/2 (I think-it's the one with similar drivers to the LS3/5a- damn good speaker IMO) nearfield...but I suspect it's major contribution is in the upper mids/treble, as I honestly can't tell a difference while running them for LF with biamped B&Ws. That range was also the KEF's strong point it seemed, so that may have contributed to the relatively obvious improvement as well.

My CA-1010 sounds wonderful with my 103.2, I leave it in AB mode. The LS3/5a type Kefs were the smaller 101. All great speakers but the 103.2 go lower and are more efficient.

 

[belgianbrain]

Listening to mine right now...it burns your hand in 10-15 minutes in class A. I've heard a difference using with my friend's dad's KEF Reference 103/2 (I think-it's the one with similar drivers to the LS3/5a- damn good speaker IMO) nearfield...but I suspect it's major contribution is in the upper mids/treble, as I honestly can't tell a difference while running them for LF with biamped B&Ws. That range was also the KEF's strong point it seemed, so that may have contributed to the relatively obvious improvement as well.

Agreed. I hear the difference in the mids/highs. There's something about it that just sounds more life-like in class A.