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Old 27th May 2010, 08:54 AM   #21
AndrewT is offline AndrewT  Scotland
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Originally Posted by Lazarus500 View Post
If i am using a 60/40 solder with flux core, is additional flux overkill?
buy 63/37 solder in two sizes. The eutectic gives better and easier results.
regards Andrew T.
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Old 27th May 2010, 01:11 PM   #22
regiregi22 is offline regiregi22  Europe
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Great Bill, you have done a great work. I will read them when I have time, and include them in the Documentation. But at a first glance, they look like an intensive analysis. I had lots of questions about the DC protection system that were not solved, now its the time

Andrew, revise your previous post quote about the relevant information posts. For any reason, they are posted in a wrong way, not showing right the links.
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Old 27th May 2010, 02:35 PM   #23
Lazarus500 is offline Lazarus500  United States
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Thanks to all! Once I realized the 3rd digit on the capacitor is the multiplier, then all capacitors fell into place. Other newbies take note.

2 of the 4 kits I received had 5% tolerance on C30 rather than 2.5% per the spec of latest BOM (Thanks Bill_P). Should I worry about that or happily move on.


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Old 27th May 2010, 02:46 PM   #24
Bill_P is offline Bill_P  United States
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5% is ok for C30
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Old 27th May 2010, 06:39 PM   #25
regiregi22 is offline regiregi22  Europe
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Because Andrew has asked me to, I will re-post Uriah's post of most useful resource links. I cannot quote it because the forum will not parse the URL links and it will show like the previous Andrew's post.

So, my next post IS NOT MINE. It is Uriah's Thank's to him, one more time.
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Old 27th May 2010, 06:41 PM   #26
regiregi22 is offline regiregi22  Europe
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Here are some questions and answers I put together before I decided whether to run the group buy or not. A huge amount of information.
Original introduction and subsequent design thread.
Can I ask the orginal designer some questions? No. He is a good guy but he no longer participates on this forum.
Thats for gerbers, boms, etc.
Single sided for etching.
The Dim-bulb Radio Tester
Lets just say that when firing it up for the first time, if you dont use this or a Variac, then dont blame anyone else if something goes 'poof.'
24V secondaries are best but 22V would be fine..
A discussion about grounding as it can be a bit confusing with this amp.
Grounding - Read this please
What pot to use?
Many caps on the board are .22uf but spec'd for .1 in Mauro's schematic. Why the change?
Dont try to improve it with the normal "tweaks". This amp is tweaked already. Leave the opamp alone. Just stop. Resist.
Fuse and switch installed correctly.
what it looks like assembled.
Can I use different diodes instead of the recommended rectification?
Should I put fuses on the secondaries?
DC offset at output of amp. Whats okay? How do I measure it?
I want the technically perfect heatsink. If you just want a guess then us a 2.5"x2.5"2" cpu heatsink.
Is it worth the build?
I want to swap my own caps. How should I do that so I dont end up over soldering the board and lifting a trace?
I have noise after putting in large input caps or just some hiss anyway, here is one explanation.
Should I do MonoBlocks? Well, I dont know but there is a discussion here.
I like cap swapping. Anything else I might like ?

Picasa Web Albums - Peter - RevC Measurem...
Some REVC measurements from Peter

From Mauro's webpage:
Passing band (typical-3db): 2Hz-70Khz
* The maximum power (8ohm): 40Wrms
* The maximum power (4ohm): 56Wrms
* Damping factor (8ohm): >200
* Relationship S/N (600ohm): >96 dB not weighed
* Typical THD (20Hz-20Khz, 1-40W 8ohm <0,05%

Cap recommendations by Dario

I have a pic of the top of the board.. pdf below
Also an eagle schematic

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Old 27th May 2010, 08:01 PM   #27
regiregi22 is offline regiregi22  Europe
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Well, here I come with the latest additions to the project Documentation:
Bill_P has provided us with some impressive measurements and writings. Of course they've been added to the compilation of the most relevant documents from this project. Thank's to him for this great effort and help.

-Added in the Bill_P folder a 20 pages paper extensive description about the behaviour of the DC protection system with simulation measurements.

-Added in the Bill_P folder some measurements he took from the 10 most relevant passive components of the circuit.

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Old 27th May 2010, 09:31 PM   #28
Bill_P is offline Bill_P  United States
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I have finished building the first board of a stereo pair and have some comments on how the build went.

In my amplifier box the back wall of the enclosure is the heatsink. The amplifier board mounts to the bottom plate and the LM3886 is fastened to the back wall (heatsink). For this to work the LM3886 must protrude past the edge of the PC board to keep the board from touching the heatsink before the LM3886 does. Unfortunately the board protrudes further than the back side of the LM3886 because the layout placed the LM3886 too far to the interior of the board. I had to straighten the leads of the LM3886 and reform them to make the chip protrude past the board edge. Depending on your heatsink configuration this may or may not be a problem but is something to keep in mind.

The heatsink for the Caddock resistor needed a fair amount of surgery. On the LM318 side two fins were removed and one fin on the LM3886 side. Wire cutter pliers are able to cut through the soft aluminum.

Capacitor C4 is supplied with 10mm lead spacing but the board layout is for 7.5mm. The location of C4 interferes with the Caddock heatsink so I formed the leads of C4 outward to span the holes for C17 and C18. Since C17 and C18 are not used, C4 was placed there to avoid the heatsink.

C5 is also a 10mm part with a 7.5mm board spacing. Forming the leads inward slightly allows it to fit in the board.

The Black Gate capacitor does not fit well in the board. The leads need to be formed inward and then it sits on R13 in an unstable position. I put two fiber washers under the Black Gate to raise it just above R13 and make the mount more solid.

R10 and R12 are supplied as 1/2W while the board takes the 1/4W size. Both resistors need the leads formed to fit.

In the relay circuit I used generic parts and avoided the cases where the supplied resistors are too large for the board layout. For the capacitors I used nonpolar Nichicon ES parts and put clamping diodes across them on the bottom of the board. I had 25V capacitors on hand but anything 10V or more is suitable. I had intended to modify the board to put in a 24V regulator for the relay but it didn't turn out to fit well with the board layout. To correct the low supply voltage problem in this circuit I changed R14 from 470 Ohms to 68 Ohms. That powers the relay with about 23 volts with a 22V transformer in the power supply. For a 25V transformer try 100 Ohms and for a 18V transformer, 10 Ohms. The diodes were changed from 1N4001 to UF4002 since the circuit needs more than a 50V diode rating.

C21 will not fit on the top side of the board so it was placed on the bottom. The leads were bent at a 90 degree angle and the cap placed on its side. The original holes for C21 were used to solder the part in.

Overall the build went fairly well. The worst of it was reforming the LM3886 leads. Using audiophile parts caused a few issues with the fit but nothing that wasn't easily handled.
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Old 27th May 2010, 11:30 PM   #29
madisonears is offline madisonears  United States
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Bill P,

Unless there is something about these boards or LM3886 chips that is different from those in the last group buy, I don't understand your comment about the difficulty of mounting the chip to the enclosure. I mounted mine directly to the enclosure wall with no problem. Why can't the board touch the enclosure wall? If anything, that might stabilize it and damp it. Rookies: if you're bending leads to get parts to fit, make certain that none of them will contact anything else or protrude over the edge of the board, or poof!

You seem very technically astute, and I don't understand a lot of what you have analyzed and posted, but I think it's great that you're looking at this circuit closely. One thing really bothers me: if so much is wrong with the protection circuit, how come so many amps work just fine? How would the "problems" that you see manifest themselves? Are the diodes meant to be marginal and fail in case of other instability? I'm not doubting your conclusions, but the evidence is pretty overwhelming to the contrary. I use a 22v xformer, and I've turned my amps on and off hundreds of times and the relay keeps clicking along just as it should.

There is definitely some cutting and fitting needed to get these fancy parts to fit. The board was not designed for some of these parts. I think that 7.5mm lead spacing was not a good design decision, but it's not a deal breaker. After a couple builds, I got pretty good at bending the 10mm leads just right! Yeah, the BG is huge compared to the space allowed for it. I pushed mine off to one side near where the input cap is supposed to go, with "L" shaped leads, supported by a small piece of foam. Rookies: that big BG cap should not be allowed to just dangle loosely. Put something under it. I didn't need to remove as much material from the heatsink I used for R3. I wonder what's different?

Let us know how it sounds!

Tom E
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Old 28th May 2010, 12:29 AM   #30
troystg is offline troystg  United States
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Originally Posted by udailey View Post
Awesome. Thanks Andrew. I hope the guys find and use the new thread.
edit: hmm the first and last link offer no information on building though...
Here was the best source for information on the Rev_C build.

Twisted_Pair did an outstanding job with the first offering.

RevC Amplifier - Twisted Pear Audio Support
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