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It is currently 11 Dec 2018, 18:45

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PostPosted: 12 Oct 2018, 21:43 
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Joined: 07 Jan 2018, 07:13
Posts: 46
Hi Bruce, thanks a lot,

Yes, I do have a scope. And to note, my power amps do not have input blocking caps and 1M resistors. Also, I have had this motorboat problem on both the left and right channels at different times so I’m inclined to think there’s not a problem stemming from either monoblock.

I will replace the diodes and try it tomorrow, I have some UF4007’s that I can replace them with.

If that doesn’t fix it, I’ll try the 2.2 cap. Also note, the 4.7 caps in there are the second set. I have replaced them the last time this happened. Would a bad ground possibly ruin them?

On my last go around with this, I ended up re-flowing all ground joints and pretty much all joints relating to this part of the circuit. I use 63/37 leaded solder.

I attached a picture of that portion of the circuit. The pic is a little older, the 4.7 caps are different now, but that part of the circuit has the same layout still. The black wire off of the bottom 4.7cap is the single ground wire for the main PS board that goes to the input jack. I can take a current pic tomorrow also.

Thanks again!


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PostPosted: 13 Oct 2018, 09:27 
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Joined: 07 Jan 2018, 07:13
Posts: 46
The Verdict,

After replacing all the components in the regulator circuit one by one, the faulty component was the 470k resistor. I’m sure this was probably the part that fixed it the previous two times. I ended up just replacing all the components those times as well.

This means that I have had 3 different resistors fail in those positions 3 times so far. Any ideal as why? I’m using 1W resistors in those positions, maybe they need to be a higher wattage?

Thanks


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PostPosted: 14 Oct 2018, 16:36 
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Joined: 04 Jun 2008, 20:59
Posts: 3854
Location: Arizona, USA
I use 1/2 watters just fine. The current in that part of the circuit is really low and they ought not have issues. It could be a bad batch of resistors. I got an assortment of carbon film ones a while back and they were supposed to 5%. 1/2 watt. About 1 in 20 was within spec and some failed in use. If the cause of the problems was the resistors then I would try another brand. Most have voltage limitations, but in my experience it seldom matters. Perhaps you have that exception.

BTW, that is a nice looking layout.

Good listening
Bruce

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PostPosted: 14 Oct 2018, 18:18 
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Joined: 07 Jan 2018, 07:13
Posts: 46
Ya, I’ll try a different brand.

I used PRP brand in those positions each time which I believe are supposed to be a fairly decent brand while being inexpensive. I use PRP for pretty much all of my amps with good luck. Must have just been a bad batch of 470k’s perhaps.

Thanks for the comment on the layout. I’m pretty happy with how the project came out all in all. Sound is beautiful except for when the resistors went bad.

Thanks!


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PostPosted: 21 Nov 2018, 11:36 
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Joined: 25 Jan 2012, 16:53
Posts: 2
HISS
Hello everyone,
I have a problem with white noise too high "HISS" with volume zero or in any position and I do not understand what can be generated
If I use Groovewatt and a self-built transistor amplifier, it's okay, but if I connect the Forewatt with ECC802S I have hiss even with shorted inputs
The schemes are the last ones
sorry for my English
thank you


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PostPosted: 23 Nov 2018, 08:55 
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Joined: 24 Oct 2010, 07:05
Posts: 282
There is a discussion starting here: viewtopic.php?f=9&t=43&start=1890#p54825
Several hints have been already mentioned. Just not to repeat them in this thread.


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PostPosted: 26 Nov 2018, 16:33 
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Joined: 25 Jan 2012, 16:53
Posts: 2
Fixed the problem, it was the fault of the LR8K4 that oscillated
thank you all


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