Yamaha A-500 and A-520 Thread

Bratwurst7s

In The Frying Pan
Subscriber
I've been seeing a number of A-500 integrated amps (and to a lesser degree A-520) going for very attrative prices on the auction site over here.

I've been thinking of picking a few of them up to use as the core of a starter system for a few friends. Can anyone pass on anything about these amps? Weak points, things to watch out for? On paper they look like a sweet little amp flying under the radar price wise, and 70 watts would be plenty for a pair of 2 way bookshelf speakers.

Thanks and Cheers,
James
 
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Nobody?
Well, I guess that I'll be finding out for myself because I bought an A-500 and matching T-500 tuner. And ordered some deoxit.

Cheers,
James
 
Hi, since about half a year i'm owner of a a-500. i bought this because my a-700 had a crash.
my a-500 runs without any problems, its sound is clear and powerful. as speakers i use either a pair of wharfedale laser 130 or monitor audio r100 - both without any problem
 
If the A-500 is from the same line of the A-700 and A-1000 (around 1983), then yes, it is a very good mid-level amp.
 
Thanks for the replies. Yes, afaik the A-500 was made around '80-'82. I'm going to be giving it to a friend as a starter system after checking it out and Deoxitizing it. Yesterday I picked up a pair of ca 1980 Grundig Box 650B 3-way bookshelf speakers to go with it. Still waiting for everything to arrive.

One thing that I was/am concerned about is if it has the power supply cap problem like the M-50 etc. If so I'll want to r² the cap before I turn it on.

Cheers,
James
 
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I bought one new back in the 80's and replaced it with another on a few years ago when my first one went bad. I see them on the auction site and agree that they fall under the radar and are a great value. You can occasionally find them in silver.
 
I bought one new back in the 80's and replaced it with another on a few years ago when my first one went bad. I see them on the auction site and agree that they fall under the radar and are a great value. You can occasionally find them in silver.

Thanks for the info. I'm hoping that mine gets here tomorrow, but not really expecting it till Monday. Both the A-500 & T-500 are silver face. Of the ones I'm seeing in the auction site over here I'd say they are running about 60-70% silver face. I joined HiFiEngine yesterday and downloaded the service manual. There are trim pots for idle current but I don't see any dc offset adjustment.

I'm hoping that it doesn't need anything more than deoxit and idle adjustment. The guy that I'm giving it too will be over on New Years Eve and I'd like to be able to give it to him then. Considering how little people are asking for them I might just go ahead and pick up a few more in the near future.

Cheers,
James
 
My A-500 amp and T-500 tuner finally got here today. Rather, I went to the post and picked them up, as DHL was too lazy to deliver. The seller did a very stand up job of packing, with form fitting custom cut foam completely surrounding each piece. Opticly they are in near perfect condition, no scratches and only a light scuff mark in a couple of places that I believe will clean up nicely.

So far I've only stripped down the A-500 and Deoxited everything that I could think of. I was just about to turn it on and check the idle current but am now slightly perplexed because when reading the service manual it shows TP1&2 and TP3&4 as measurement points, just to the left of the trim pots VR107 & VR108. But either I'm blind or I can't find the test points on the board. Time to give it a rest and look again tomorrow I suppose.

Cheers,
James
 

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Looks nice also inside. And 12,000uF is a good value here.

I took a close look at the screws before I opened it and am pretty sure that nobody has been inside it before me. :yes: I was surprised at how little dust there was. It's all cleaned up now but I haven't put power to it yet.

The only points near the idle current trim pots that look like one could clip a test lead to are 2 posts sticking out of the top of a large ceramic resistor near (to the left of seen from the front) of each trim put. But I'm sceptical that thats correct. I'd like to take care of that before hooking speakers up but I'm stumped. I'd really like to not short something out.

I haven't the experience to know if 12,000 uF is good so I'll take your word for it. :yes: Are those the power supply filter caps?

Cheers,
James

edit: Now is when I could hope that someone like Avionic might have some advice. :)
 
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Well, nothing like diving in and just guessing. I looked and looked and saw nothing else that looked like a pair of posts to use as test points. So I clipped my test leads on that rectangular white ceramic resistor with the 2 posts sticking out of the top. In the 2nd pic of my last post you can see it just to the right of the big 12,000uF caps.

Fired up the amp and let it sit a half hour and got 34mV on the left channel and 27mV on the right. Dialed down the pots and the voltage followed, and nothing blew up. :yes: Tweaked them in to 15mV and shut it off and let it get cold. Then I did a repeat of the above to see if they had changed, the right channel showed 13 to 14mV so it got tweaked again.

I'll put a few hours of use on the amp and check them again.

And to my surprise the speakers that I bought to use with the amp were delivered an hour and a half ago. A nice pair of 1980 vintage Grundig HiFi Box 650b 3-ways. For their age they look pretty respectable, a couple of light scratches and scuffs, and one box has taken a light hit on the upper rear. All drivers work, no cone dents.

I was very happy to see these exact speakers in Pougatchoff's Grundig thread over in Speakers. So I'll be using the info found there and recapping these and adding binding posts before passing them on to my friend. Tomorrow I'll open up the tuner and deox it.

So this 34yo system is playing behind me right now and sounds pretty sweet. With a total investment of €110 for an integrated amp, tuner, and 3-way bookshelf speakers I'm grinning. My young friend that's getting this stuff should be here in an hour or so and I can hardly wait to surprise him with his 1st 2 channel system.

Happy New Year everyone,
James
 

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I haven't the experience to know if 12,000 uF is good so I'll take your word for it. Are those the power supply filter caps?

Yes, they are. The A-500 is a nice 70W/8Ω amp. Being a 34yo unit, you could increase these caps' value to new 15,000uF ones, if you want. (see bottom of the page)
But if everything is running well after the bias adjustment, I'd leave it and enjoy the amp for a while. Might worth see for a new relay. I replaced the one in my A-520 here.

Nice Grundig bookshelves. :yes:

I had a Magnat Ribbon 3 and still pursuing a Canton Karat series. :thmbsp:
 
Being a 34yo unit, you could increase these caps' value to new 15,000uF ones, if you want. (see bottom of the page)
But if everything is running well after the bias adjustment, I'd leave it and enjoy the amp for a while. Might worth see for a new relay. I replaced the one in my A-520 here.

Nice Grundig bookshelves. :yes:

I had a Magnat Ribbon 3 and still pursuing a Canton Karat series. :thmbsp:

Thanks Karl. I've bookmarked the info and will probably start with a new protection relay before it goes bad. Also, exactly which trim pots did you use? This is the first time that I've done this and noticed that the trim is very very touchy, and when I looked again after a few hours of use the right channel had crept up to 18mV. Should I also use deoxit on the trim pots? They are probably the only thing that I didn't deox.

I made a certain assumption here, please correct me if I'm wrong. The service manual stated to check the idle voltage with no input to the amp, which is what I did. My assumtion was that turning the volume completely down and selecting both front panel speaker switches to off, and no speakers connected would also be the correct thing to do. Yes? No?

I also noticed a surprising amount of source bleed through from one source to the other. For instance I connected a cd player to DAD, switched to Aux, and turned up the volume a bit and got a faint amount of music. I've never had this happen on a Yamaha amp. Is it common to these or a sign of a problem brewing?

Originally I was bidding on a pair of Canton Karat 20s but they went way out of my budget very quickly. So I settled on the Grundigs which sound pretty respectable for their age and the low price that I got them for. And they are in very good condition.

Cheers,
James
 
...

a new protection relay before it goes bad. Also, exactly which trim pots did you use? This is the first time that I've done this and noticed that the trim is very very touchy, and when I looked again after a few hours of use the right channel had crept up to 18mV. Should I also use deoxit on the trim pots? They are probably the only thing that I didn't deox.

Hi James,

Usually I replace all the trimmers in +30yo units (after full recap) with multi-turns pots from Bourns, Murata, Vishay, etc. They are normally 20 or 25 turns, so much more precise than conventional/touchy/cheap/ trim pots and are used in most Hi End amps that require good stability. These pots come in a variety of types (vertical, horizontal, lateral, square, side adjust., etc). You need to know the value of it for the A-500 (something around 2.2k I believe).
The drift/shift value you have (from 15mV to 18mV after few hours playing music) is not that much and, for an unit from 1980, it is still tolerable. I don't think deoxit the pots might help or make them be more precise/smooth. They are like this. Actually you might end up loosening them. The variation might happen because of some room temp changes/lack of ventilation, heat inside the unit, etc, for example. Or due to some aging components as well. In Summer your unit will run a bit hotter, but no worries.
If you want to replace them, make sure to preset the new trim pots at least to the proper value in ohms by measuring the old ones first - in some units it's CW turn for one channel and CCW turn for the other channel -, otherwise you'll end up frying your driver transistors (and outputs) by allowing a lot of current into them.
But don't expect that changing the pots will solve the "problem" of bias variations in the right channel. It can still occur.

I made a certain assumption here, please correct me if I'm wrong. The service manual stated to check the idle voltage with no input to the amp, which is what I did. My assumtion was that turning the volume completely down and selecting both front panel speaker switches to off, and no speakers connected would also be the correct thing to do. Yes? No?
Yes, for the A-500: volume down, speakers off and disconnected, and balance, loudness, bass, treble in flat position.

I also noticed a surprising amount of source bleed through from one source to the other. For instance I connected a cd player to DAD, switched to Aux, and turned up the volume a bit and got a faint amount of music. I've never had this happen on a Yamaha amp. Is it common to these or a sign of a problem brewing?
For the signal bleeding across sources. Well, from dirty selectors and switches, to bad grounding, to some external interference, to input capacitors... we have a variety of causes. But it can occur also with brand new gear. Yes, it can be very annoying. One "quick solution" before you trace the problem is to turn off all the other components (tuner, cassette, etc) while you are listening to your CD player.
 
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Hi Karl,
Thanks for your patience and help. I've copied all of this to a text file for the benifit of my faulty memory. At this point I'm going to give the amp, tuner and speakers to my friend to use, since at the moment the sys sounds pretty darn good, and we will be making a step by step plan for a full renovation. I will probably have more questions in the near future if you have the continued patience.

Cheers,
James
 
A-520

Now I can add an A-520 to this thread. I really didn't need it, but I was buying a T-720 tuner from the same seller on the auction site and just couldn't help myself. Considering that I got the both 2 units for €63 I'm happy.

The A-520 will be replacing an A-S201 as my PC/hobby room amp. My current JBL Control 1X hobby room speakers will be going to one of my daughters and I'm going to find another pair of those nice little Grundig HiFi Box 650b's or something similar. The A-S201 is getting sold to raise funds for recapping the A-520 and buying the new speakers.

Opening the amp I found a lot of dust but happily no signs of nicotine. The filter cap glue has done it's thing and there are signs of corrosion on at least 1 resistor (204) and a bridge next to what looks to be the rectifier bridge? Anyway that issue will get dealt with before I even turn this thing on for the first time.

I'll be looking up replacement caps in the next week or so for this and the AX-700 that I bought for my other daughter. So, lots of fun stuff going on in the coming months. I have to thank Bubo and Karl vd Berg for all of the advice and support that they've been giving me in my various projects.

More later.
James
 

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That corroded R204 resistor - 3.3k (1/4W) is in the idling current adjustments circuit for the Right channel. When you replace it then you can replace the other R203 resistor of same value (in the Left channel) with new ones of 1% metal film. Not necessary for the left channel, but why not?

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The A-520 is a nice amp. I had mine recapped but didn't replace the main 12,000uF / 56V ones, though.
At time I had a couple of minor 2,200uF / 63V new caps laying around and connected these in parallel with the 12,000uF ones (making it a total of 14,200uF per rail), so I didn't have to buy new 12,000uF ones. The stock 12,000uF ones had their value a bit lowered in time, but still under tolerance, however I decided to give them a good 2,200uF "support"...
It was a good experiment, my capacitance meter measured something around 13,800uF (stock+new), which was perfect.

But I replaced the relay as one of the channels, IIRC, had annoying intermittent sounds. I think I also replaced the stock NJM4558 opamp with my fave OPA2604 as I did with other A-450 amp, and for me that was a nice replacement. I really like sound of the OPA2604 in these Yamaha amps. I installed a 8 pin socket and tried different opamps, including the NE5532 as well... Of course, you don't have to do all this, but I had fun in trying these IC's in the preamp section.

2cpw7f9.jpg
 
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But I replaced the relay as one of the channels, IIRC, had annoying intermittent sounds. I think I also replaced the stock NJM4558 opamp with my fave OPA2604 as I did with other A-450 amp, and for me that was a nice replacement. I really like sound of the OPA2604 in these Yamaha amps. I installed a 8 pin socket and tried different opamps, including the NE5532 as well... Of course, you don't have to do all this, but I had fun in trying these IC's in the preamp section.

2cpw7f9.jpg

I am so happy to see this statement, OP Amp rolling is something the headphone guys swear by.

How noticeable are the effects of switching from op amp to op amp???

Did you rank the ones you like??
 
I have tried only 3 opamps in these amps: NE5532, OPA2134 and the OPA2604. I found the latter very open, 3-D, warmer, etc. I like the 2604. The only amplifier I had to put a 10uF and a resistor to prevent a possible oscillation was on a KA-405, but probably wouldn't need it. Some opamps seem easy driven and a few claimed that the OPA2604 works pretty much ok.

For me: OPA2604 > OPA2134 > NE5532 >>>>> NJM4558
 
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