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The new "My Ref" Rev C thread
The new "My Ref" Rev C thread
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Old 10th November 2017, 01:53 PM   #1971
jls001 is offline jls001  India
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Default MyRef Rev C Troubles

I've been using my MyRef Rev C (Linuxguru board + kit) for nearly a year now without trouble. The other day it went silent.

I opened it up and found that R11/1R had become open on both channels. I replaced them, powered it up on the bench, checked for offset voltage on both channels (around 7-8 mV) and connected the amp back in the chain since it was on without any obvious issues for more than one hour on the bench. On powering it up, I'm greeted by a loud continuous noise on both speakers.

Opened up once more and found the same resistors R11 had blown again. Same replaced and offsets are normal. Supplies to both opamp and 3886 are also normal.

I'm afraid to connect it back till I know what more to check.

Any advice, please?
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Old 10th November 2017, 02:02 PM   #1972
linuxguru is offline linuxguru  India
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Quote:
Originally Posted by jls001 View Post

Opened up once more and found the same resistors R11 had blown again. Same replaced and offsets are normal. Supplies to both opamp and 3886 are also normal.

I'm afraid to connect it back till I know what more to check.

Any advice, please?
I'd suspect that the opamps in both channels blew, probably as a result of a mains spike or similar. You can replace the LM318 with a TL071 for a sanity check - if it works with modest offset with a TL071, then the LM318 is suspect (By any chance, is it an LF01 hybrid discrete opamp?)

It's also worth checking your source, especially the trafo and grounding.
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Old 10th November 2017, 02:44 PM   #1973
Joseph K is offline Joseph K  Hungary
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For me, the fact that offset is ok on the output after replacement says that th lm318 is ok..

What is not Ok is the source. It seems to create a common offset on the input! That is that burns the R11
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Old 10th November 2017, 02:59 PM   #1974
jls001 is offline jls001  India
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Quote:
Originally Posted by linuxguru View Post
I'd suspect that the opamps in both channels blew, probably as a result of a mains spike or similar. You can replace the LM318 with a TL071 for a sanity check - if it works with modest offset with a TL071, then the LM318 is suspect (By any chance, is it an LF01 hybrid discrete opamp?)

It's also worth checking your source, especially the trafo and grounding.
I'm using TI's LM318, not the discrete LF01.

I have spare TL071. I'll try it. Thanks for the advice.
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Old 10th November 2017, 03:44 PM   #1975
jls001 is offline jls001  India
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Quote:
Originally Posted by Joseph K View Post
What is not Ok is the source. It seems to create a common offset on the input! That is that burns the R11
The same chain works fine with my other power amp. But in any case let me check the output of my buffer. Thanks for the pointer.
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Old 17th November 2017, 03:00 AM   #1976
mamadudin is offline mamadudin  Indonesia
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Quote:
Originally Posted by jls001 View Post
I've been using my MyRef Rev C (Linuxguru board + kit) for nearly a year now without trouble. The other day it went silent.

I opened it up and found that R11/1R had become open on both channels. I replaced them, powered it up on the bench, checked for offset voltage on both channels (around 7-8 mV) and connected the amp back in the chain since it was on without any obvious issues for more than one hour on the bench. On powering it up, I'm greeted by a loud continuous noise on both speakers.

Opened up once more and found the same resistors R11 had blown again. Same replaced and offsets are normal. Supplies to both opamp and 3886 are also normal.

I'm afraid to connect it back till I know what more to check.

Any advice, please?
It happens for my amp too, twice but always only on L-channel.. there is no differences between L & R channel except CL-60. I installed CL-60 only on R channel while the L channel does not
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Old 12th September 2018, 09:25 PM   #1977
ziffel is offline ziffel
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Hi,

What's best value for a power transformer for a stereo system Rev C for 4-ohm speakers?

I plan on buying a transformer from Antek.

I've been searching this thread but cannot find a definitive answer.

Thank you for your help - z
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Old 13th September 2018, 01:35 PM   #1978
UnixMan is offline UnixMan  Italy
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Quote:
Originally Posted by ziffel View Post
What's best value for a power transformer for a stereo system Rev C for 4-ohm speakers?
you may want to have a look at the "My_Ref Fremen Edition - Build thread and tutorial" thread.

In short, for 4 Ohm speaker it's better to stay on the low side with supply voltage, say 18 ~ 22 Vac (on the lowest end you may need to adjust the protection circuit, as there may be problem driving the relay; over ~20Vac it should work without changes).

Power rating should be around 300VA or more, as usual. More is better (within limits: up to 500 ~ 600 VA may be reasonable, even more is likely overkill).

Choose a transformer which has good "regulation". Usually it's expressed in form of % of nominal voltage (the lesser the better).
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Last edited by UnixMan; 13th September 2018 at 01:42 PM.
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Old 13th September 2018, 01:43 PM   #1979
ziffel is offline ziffel
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Great! Thank you!
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