A-520 Integrated Amplifier...Problem with variable Loudness control

DrDreas

Member
I just acquired an A-520 Amp which I really quite like. The only problem is the with the loudness knob.

I'm pretty familiar with the effect this knob has on the sound as I have had many Yamahas with this feature, but the one on this amp appears to just thin out the sound until near extreme settings where it seems more normal and Deoxit has had no effect on this.

Has anyone come across a similar problem or would know where in the circuit to look for the culprit? I'm not scared of a little DIY but my knowledge is limited.

Cheers,
Dre
 
Note that I'm decidedly NOT an expert but rather a beginner that's been learning from the others here.

Having said that the first place that I would look (if you haven't recapped your amp) is at the electrolytic caps C125 & C126, 0.22µF 50v. They are in the loudness part of the circuit and are located on the main pcb directly to the left of the loudness pot.

If the problem doesn't lay there then hopefully Avionic or Karl vd Berg will be along with help.

If you don't have a service manual it can be downloaded here at AK in the Digital Docs forum.
http://akdatabase.com/AKview/displayimage.php?album=3&pos=9

Cheers

Edit: I'm using Nichicon Fine Gold caps for those, ordered from Mouser, Mouser part nr = 647-UFG1HR22MDM
 
Last edited:
Yes, check all the electrolytic caps in the loudness part of circuit. Check also for cold and/or broken solder joints.

A few 1000px (width) pictures from both component and bottom sides would help too.
 
Thanks guys, that helps! :)

When you say to check the caps, what exactly am I looking to measure, or are you talking about visual clues like swelling etc?
 
I believe that Karl means checking the caps with an LCR meter to see if their values have shifted. They will have to be removed to measure them, they can't be checked in place. And while it's nice to know for troubleshooting if their values have drifted once you have them out I would never re-install them. And yes, swelling or obvious leakage would be grounds for replacement. You are only looking at $25 or so to replace all of the caps, the protection relay, and the trim-pots with quality parts.

http://www.audiokarma.org/forums/showpost.php?p=8573423&postcount=32

Re-flowing the solder connections is also a good idea, at the age our amps have reached the solder connections tend to go bad, especially where they've had mechanical or heat stress over the years.

Cheers,
James
 
Thanks Bratwurst...I only just spotted your thread, thanks for all the shared information, very handy indeed! :thmbsp::thmbsp:
 
If the uF values are under 4.7uF it's common practice to replace the electrolytics with good film caps. These last forever under same specs and have better performance.
 
I'll keep that in mind, cheers. It's going to have to join the queue...I think one of the B110's in my concertos is playing up and still need to refoam the woofers in my NS-300x as well lol...it never ends!
 
Back
Top Bottom