Yamaha M70 Buzzing Power Supply

A

Annihilism

New Member
Last week I decided to restore an old Yamaha M70 I had lying around (bought it from the dutch version of ebay). It the the well known 250v RIFA cap blown, so I replaced it for a new one. I also had to restore the RCA jacks since they were somehow disintegrated.

After the said parts being replaced something immediately got my attention. There was a mechanical buzz coming form the power supply. It's really annoying especially when listening to music at really low volume levels. The buzz is mechanical and not coming through the speakers.

So I've read a few threads here about buzzing power supplies and it seems that most of the problems have been coming from vibrating windings in the PS. Now what I was wondering is if it's possible to repair this problem myself.

Is it possible to laquer the wires without dissasembling the power supply? Is it easy to rewind it? Maybe I can even get a replacement power supply for it.

Thanks in advance for any help.
 
Register to hide this ad
Avionic, brutal or merrylander are the resident Yamaha experts here. Perhaps a PM to one or all would be in order. :yes:
 
Annihilism said:
Last week I decided to restore an old Yamaha M70 I had lying around (bought it from the dutch version of ebay). It the the well known 250v RIFA cap blown, so I replaced it for a new one. I also had to restore the RCA jacks since they were somehow disintegrated.

After the said parts being replaced something immediately got my attention. There was a mechanical buzz coming form the power supply. It's really annoying especially when listening to music at really low volume levels. The buzz is mechanical and not coming through the speakers.

So I've read a few threads here about buzzing power supplies and it seems that most of the problems have been coming from vibrating windings in the PS. Now what I was wondering is if it's possible to repair this problem myself.

Is it possible to laquer the wires without dissasembling the power supply? Is it easy to rewind it? Maybe I can even get a replacement power supply for it.

Thanks in advance for any help.
Click to expand...

Sounds like a power transformer issue. I don't know for sure if redippng the transformer would yield any success. It would need to be removed from the amplifier and partially disassembled. You'd probably be money ahead just finding another M-70. If the unit is a multi-voltage model, you could also try a step-down transformer and operate it at 120 v instead of 220v . Might quiet it down a bit.
 
Thanks for the advice!

Well since I have a working M40 lying around wich can drive my speakers easily I guess I will use that one instead and put the M70 in our staffroom.

Next week ill be spending some time on the C70 pre amp. Going to take a while to reflow all the solder joints and bridge the broken copper bridges :yes:

The M70 is worth alot of money here in Holland since they are quite rare (you don't seem em going by as often as I see the 110 voltage models from the USA).

Oh well, I can't hear any real difference between the M40 and M70 anyway, i just like the looks of the M70 a bit more :P.
 
I have the same problem with my M-70 I have just bought
And moreover, there is some noise when pots are fully open (however it can be a question of my very efficient horns).
These two sources of noise is too much for enjoying my new toy :-(

I have a question. Did anybody solve the problem with buzzing power supply?
 
Greetings and welcome;
Avionic makes good points for repair. I guess You must be from a 220vac supply country. Okay so 'Avionic' suggests dipping. Your tranny has the plastic cover which I hope is easy to remove, then perhaps post a pic. alas no pics even on line that I can find if one has been taken.

this is a very nice 'clean' amp... http://stereonomono.blogspot.com/2013/09/yamaha-m-70.html

I've read quite a few posts on THE 'BUZZ and there have been 'diy's' who have 'poured' a mix of sorts to seal the primary back to the iron tap.. read'' both aussie to england to germany. some rewind and others have been simply isolating the transformer from the chassis with gaskets of any sort. cork to rubber. end caps as well. Some come in a quiet as kittens and others are reduced. (the damed 50-55 hz buzz) I'm referring to other amps, too.

Solvents or tars stink.. Shellac dries fast and lacquer longer but perhaps modest bake it? To recoat wires and a fast dry pour of similar may dry fast may seal the primary coil. It may be to glue the windings back together on the primary winding to the metal but if the transformer has screws? Ahh then they need to be loosened and you may have to rotate a 'pour' of material till it sets up. But a pick of the core would help on pouring or brushing etc.

The flip might be your mains caps are not 220vac for high output rated and the amp is just drawing a crap load of current. On 220 in noted countries, larger caps can 'quell' some of the hum, too. If you bump the voltage rating of the mains caps you'll bump the esr but also assure amp load/ demand.
Just the specs alone consider some pretty good rated caps at thd.
 
Thank you for showing possible actions which are:
1) dipping
2) rewinding
3) isolating
4) changing caps
I will let you know when I improve the PS.
 
You must log in or register to reply here.
Back
Top Bottom