Discussion in 'Yamaha' started by Bratwurst7s, Dec 28, 2016.
And the last of them...
I recently bought another of these amps to power a pair of Braun L 630 speakers in a system that I'm putting together for one of my daughters.
The speaker thread can be found here...
This unit has white knob markings and some interesting differences on the phono board. The 2 chokes and 2 ceramic capacitors that were soldered and glued to the bottom of the phono board in the 1st amp are now integrated onto the component side of the board. Also the wire that was soldered and glued to the bottom of the board is now mounted properly to the top side with a through hole.
This saved me an hour or so because of not having to clean the old glue off and check for damage.
The only other point to present is that I mounted the main filter caps differently this time. Using the pvc disks as stand-offs worked nicely but it took more than an hour to make them. So this time I used some 35mm x 5mm rubber o-rings glued to the bottom of the caps with rubber cement. Quick, clean and easy.
This amp had much less glue and I only had to replace 8 jumpers. No other components were corroded and even then the jumpers weren't corroded. It was just easier to remove them to get at the glue and once they were out I went ahead and used fresh wire to replace them.
Here are the filter caps mounted in place.
Looks great as always!
Did you notice any improvements after the rebuild and upgraded filter caps?
Well, the thing is that I didn't use either of the amps for any length of time before recapping and repairing corroded parts. I checked the DC offset and hooked them up just long enough to confirm that they worked. With the 1st one I was scared to use it at all after seeing all of the corrosion in it and since the 2nd one is for my daughter and I want it to be serviceable for her for a long time there was never any question about immediately recapping it.
So I really have no good idea how they sounded before working on them. However, I can confirm that they can deliver some sweet sounds now.
An odd development.
The service manual clearly shows 10mV +/- 2mV for the idle current adjustment. Looking back I see that I didn't document what setting that I used my first unit but I did set it to 10mV.
With the 2nd unit I also initially set the idle current to 10mV. The odd thing is that after hooking the amp up with the Braun's and Denon CD player the volume control was way to sensitive. It only took a very small adjustment of the volume knob to go from quiet to way too loud. Yes, I double checked that my meter was set to DC and not AC.
So I went back in and reset the idle current to 5mV as in the Yamaha A-520, just to see what would happen. This resulted in a far more normal volume tracking, similar to my first amp. This has me concerned naturally. I don't know if Yamaha made a running change without documenting it (like the changes that I found on the phono board), or if there is a problem in the amp. I'm going to have to open up my 1st amp and double check what I set the adjustment to, in spite of being certain that I set it to the stated 10mV.
At the moment the 2nd amp is working nicely at the 5mV setting but naturally I'm concerned that something is not right with this.
After repairing/restoring the speakers I actually tested them first on my 1st AX-500 and they needed a bit more volume knob adjustment than the Canton Quinto 510's need for a similar volume level (the Quinto's are what I'm using with the 1st amp), about what I'd expect considering that the Braun L-630's are larger. So it's not like the Braun's are so super sensitive that the amp is too much for them.
It's likely something else is wrong, the idle current shouldn't change how the volume works, especially not within +/-5mV.
If you change it back to 10mV does the problem come back?
For what it's worth I've had the AX-500 here and changing the bias to 10mV or 20mV didn't change how it functioned.
I'm confidant enough that you are correct that I made arrangements for the amp to come back to me for a deeper look. My daughter will be getting a RX-V567 in it's place. Actually better suited to her needs as it allows her to hook up her Playstation and TV via HDMI.
OK. So my problem actually turned out to be not a problem. Really nothing more than that the Braun L 630's are fairly sensitive and as "50w" speakers the amp just gets them loud with very little effort. It turned out that when my daughter told me that the system was less sensitive after I had turned down the idle current what she didn't tell me was that she had used the loudness knob as an attenuator.
Last weekend I reset the idle current to 10mV and tested the amp with a Denon DCD-890 CD player and a pair of JBL TLX-70 speakers. It sounds and works just fine. At least within the limits of those speakers (which I'm not overly impressed by). The amp and player are getting sold to a friend at cost and I'm giving him the speakers. Alls well that ends well.
Those 2SA1358 / 2SC3421 look pretty good devices...
... and did you recapped the AX-1090 as well?
Hi Karl! So far I haven't had any need to replace any driver or output transistors in the amps. The first one is part of my PC/workroom system and gets used regularly and sounds sweet.
I haven't re-capped the 1090 yet. I still need it in the main system at the moment for it's power amp section. I have a CX-1 pre-amp now and have it hooked up to the de-coupled power section of the 1090 until I get my M-70 working. My tentative plans are that I should be able to free up the 1090 by late spring next year. After that I'll go through it.
Separate names with a comma.