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Yamaha M4 cutting audio at low volume

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Pedro V

New Member
Hi everyone, have plenty of questions but this is going to be my introduction here, entered the world of vintage audio with this Yamaha Amplifier from eBay in 2017, I used it with my AVR for the fronts LR via pre-out, and everything seemed to be working wonderfully for several months.

Then the problem started, it is a bit difficult to describe, but what I would notice at the beginning was that the sounds my streamer Interface was doing while navigating (small sounds when moving cursor) started cutting, like the sound stopped completely or sometimes I could hear part of the sound but it was cutting, I noticed that if I simply increased the volume on the AVR by a few dB's the sound started again, and if I start playing content that constantly had audio the problem went away.

But then again if everything became quiet sound would suddenly stop, and would not come back until something plays loud enough (kind of waking up the audio signal)

Now this issue was manageable at first but it continued to get worse, and then started affecting worse to one channel than the other, at some point I lost all the audio and changed the output to Speakers B (It has 2 speaker zones) and squeezed a little bit of more life until it still got the same problem and I had to go back to my AVR for the fronts.

At first I thought it might be something related with capacitors since most threads on vintage audio talk about needing to change those, and this is a pretty old unit (1978-1982 I think), but now that I did some more in depth searches I couldn't find anyone with the exact problem I have, I have no hum, no smells, visually everything from the top view of the unit without cover looks good.

Does anybody have a better idea of what this issue could be related to?
 
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Pedro V said:
if I simply increased the volume on the AVR by a few dB's the sound started again
Click to expand...

Welcome to AK!

This behavior is symptomatic of a degraded speaker protection relay. See the thread below for info about a replacement relay, and a minor modification needed to make the replacement fit the circuit board. (The thread is about the B speaker relay, but the A speaker relay is the same type.)

https://audiokarma.org/forums/index.php?threads/yamaha-m-4-speaker-b-output-issues.955457/

You may notice that the thread is in a forum that is specific to Yamaha, which might have been an even better place to post, but here is fine. In either forum, leading authority avionic is likely to chime in with the right answer. (Usually well before I get to it, but I'm surfing early this morning :).)
 
Wow thanks for the quick response, I missed that thread but the problem description does sound like what I have

Will post back once I get this to work
 
Since it will take a while for relays to arrive (I am in Mexico), I decided to clean them and see what happens.

Now I am getting audio only on Left speakers (both A and B), I doubt this is a problem with the relay but can investigate further.

Now I think there might be something wrong on the right speaker further down on the circuit, but I have the service manual so I guess I will need to investigate where the signal is cutting, unless someone has an idea of a typical issue on this particular amp.
 
Pedro V said:
Since it will take a while for relays to arrive (I am in Mexico), I decided to clean them and see what happens.

Now I am getting audio only on Left speakers (both A and B), I doubt this is a problem with the relay but can investigate further.

Now I think there might be something wrong on the right speaker further down on the circuit, but I have the service manual so I guess I will need to investigate where the signal is cutting, unless someone has an idea of a typical issue on this particular amp.
Click to expand...


Still think its the relay. Cleaning it you may have bent the contacts just enough to prevent good contact. Id wait for the new relays to come in.

Athanasios
 
Do you get a green LED power indication on both channels ?
 
Is your Right input attenuator control on the rear panel turned all the way down ?
 
So things I checked and tested:

1- Both right and left volumes on the back are close to the top (since I was using with a Yamaha AVR with low voltage pre-outs)
2- I only get LED power indicator on B channel, A does work but led is not working
3- Signal indicators work for both Left and Right input
4- Left speaker works on both A and B channels
5- Right speaker doesn't work on both A and B channels (switching speaker wires makes the other speaker work, so signal is not coming from both Right speaker channels)
6- Incrementing volume doesn't bring back Right signals like with previous failure

Since both right speaker channels have independent protection relays, I thought it might be odd that both are failing on the same contact, but will check and report back
 
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Pedro V said:
1- Both right and left volumes on the back are close to the top (since I was using with a Yamaha AVR with low voltage pre-outs)
Click to expand...
For testing purposes adjust both for max output..
 
Pedro V said:
2- I only get LED power indicator on B channel, A does work but led is not working
3- Signal indicators work for both Left and Right input
Click to expand...

Are you referring to the light green LED bar display ?
 
Verify all of your plug in connectors for both channels are clean and securely plugged into there proper sockets.
 
Pedro V said:
With signal indicators I mean the ones that dynamically change with content ( I think this let you know about distortion)
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No they just indicate the amount of peak output power.. With the far right red LED's indicating clipping.
 
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avionic said:
Do you get a green LED power indication on both channels ?
Click to expand...
Do both sets of green LED's indicate output or just the Left set of LED's


indicate output --- bouncing bar graph sync'd to the music output.



24471154468_aa1a550df8_b.jpg
 
So I checked again with my dad who has quite a bit of experience with electronic repairs, and turns out there was something wrong after de-soldering the relays, so it was not making proper contact, its working now :banana:

Next, I want to upgrade the terminals to support banana plugs, don't know the price of the M4 originally, but it seems odd that it has such poor speaker connectors, or maybe this was the standard in the 80s?
 
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