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AndrewT
Reply with quote  #1 
I'm having an on going intermittent fault with my Masterpiece. Just when I think the issue has been resolved it starts again. I can go days/weeks and even months without the fault happening. I have worked with Bruce to resolve the issue and replaced many parts and endlessly checked the unit without finding a problem [multi-meter only unfortunately].

Generally the issue appears as one of the following:
1/ one channel drops out into a loud hum/distortion independent of volume control 

2/ upon start up both speakers exhibit hum, generally one louder than the other, independent of volume control

I can turn the unit off, re-start and have no further problems for an extended period of time. 


System works perfectly with my spare G/G.

Any suggestions on suspected fault would be appreciated.


Drew
Reply with quote  #2 
Hi Andrew,

I built a MP over Christmas.  So, I don't have a lot of experience with it yet.

I am just curious if your problems could be related to the relay.  I removed mine (wiring and board) and took it out of the signal path completely.  My relay was causing problems in a new MP build.

With the relay removed, I'll have to be careful to turn on my MP first, wait, then turn on amp.  Shut down by turning off amp first.  I don't think that's too much trouble and am happy to have simplified the signal path and removed what seemed to be a trouble-prone mechanical component.

That's just my opinion though!  I love my MP so far.  Good luck.


Tubemon
Reply with quote  #3 
Hi Andrew
Drew is correct and I would start with the relay. You should also check your tube sockets along with the tubes themselves. Could be something simple like your tube pins need cleaning. RCA connectors and interconnect wires also come to mind.
Capt. Z
Reply with quote  #4 
Many years ago I had a similar issue with a SS amp that had some caps replaced. Turned out that one of the caps was not soldered correctly.

So as mentioned above it could be a bad connection in a tube socket, RCA connector, one of your cables, or a solder joint.
Kelvin Tyler
Reply with quote  #5 
I think in Drew's case (see other thread), apart from the blown cap on the timer board, there was almost certainly an inadvertent short to ground in the relay wiring to either the line or headphone connectors of the left channel. I understand the left channel was not working, even with the relay pulled, but sprang to life as soon as the relay wiring was removed.
The blown cap, I understand was rated at 6.3V. The timer board is fed from the 'raw' input to IC4 and this is a bit more than 6V. If the mains voltage is high, or the MP powered up without tubes present, the cap could easily be subject to over voltage and, if not quite up to par, could fail.
The only 'signal path' connections are from the relay contacts to the output sockets.
Not sure this helps with Terry's long standing issue I am afraid!
Kelvin
Kelvin Tyler
Reply with quote  #6 
Sorry, Andrew's problem, not Terry's!
Kelvin
AndrewT
Reply with quote  #7 
Thank you for the suggestions. I have removed the relay etc, will report back on the result.

For those of you building, or considering building a Masterpiece there is a slight modification that can remove a lot of pain.

I could never get the 12AU7 tubes to seat properly. The valves would sit on top of the socket with minimum insertion, for a while I assumed the sockets were of poor quality. It took a while to realise that two of the pins were essentially soldered together which did not allow any movement, or self righting.

The instructions for the build state:
23C:IC3-3 to V1-4 and 5 the accompanying picture shows the green wire looped through the two pins and soldered. Don't do this, as described above this will hinder insertion of the tube. Instead loop a wire from V1-4 and 5 to allow the pins to move freely and self align. This should be also carried out on the other channel i.e. 23D: IC4-3 to V2-4 and 5

I strongly suspect that my issues center around the 12AU7 sockets even though they now seat the tubes correctly. The sockets for the 300B tubes work superlatively, the 12AU7 sockets however feel terrible. After a bit of research I am going to replace the ceramic style with Belton glass fibre plastic filled sockets. The fit and feel of these cannot be compared to the ceramic ones which feel agricultural by comparison.

Will report back

AndrewT
Reply with quote  #8 
I have fitted the Belton tube socket. This required 3D printing an interface to align the pins to the same as the ceramic socket. I also replaced all of the resistors.

This removed the horrid hum the Masterpiece had been exhibiting, but the sound was very poor-strident and high pitched like a  cheap radio. I replaced a few of the capacitors and current sinks without any appreciable improvement.

I now strongly suspect the 220pf capacitor and will replace shortly.

 
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