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Old 15th May 2009, 12:28 AM   #721
soongsc is offline soongsc  Taiwan
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Donut shaped core.
For chip amp, I've used little AC->DC power blocks in parrallel with very good success.
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Old 15th May 2009, 01:28 AM   #722
bluegti is offline bluegti  United States
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Quote:
Originally posted by troystg
Like I said, pictures please.. I can compare component placement / value, wiring, everything at once.
Well I swapped boards and compared the voltages. They are pretty much the same (recommended voltages in parenthesis), so whatever is happening is happening on both boards:

-C3 -36V (-32.5)
+C8 +36V (+32.5)
+C6 +11.75V (+12)
-C11 -11.75V (-12)
-C1 -36V (-32.5)
+C2 36V (+32.5)
+C14 +16.75 (+24)

I was able to get music out of this board but there are a couple of issues:

The first time I turned on the amp, I heard an awful LOUD SCREEECH. My family upstairs called down, "what was that?" I turned off the amp immediately, checked all connections and tried again. This time... music! So, I tried turning it on and off a couple of times, no more screech. Then I listened to an entire song (~3 minutes) at normal listening levels. When I turned off the amp, SCREECH. This one was quicker than the first one but just as loud!

Also, I noticed the faint smell of burning plastic. All the caps look normal, but then I noticed the insulation of the wires that I am using for the amp input (coming from the RCA) had receded slightly. Sort of like what happens when you heat a wire too long while soldering.

Then I felt the heat sink, HOT!!! I know they are small, but since everyone seemed to indicate that these amps don't get very hot and suggested using a CPU heat sink, I didn't expect it to get REALLY HOT!

So, I've included pictures below. Any clues?

You can see the album with full size images here. Or just click on the thumbnails below to see the full size image:

Click the image to open in full size. Click the image to open in full size. Click the image to open in full size. Click the image to open in full size.
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Old 15th May 2009, 01:45 AM   #723
udailey is offline udailey  United States
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I had this same crazy sound and then burning in a chip amp once. It died instantly though. I would not fire that back up til you figure it out. Luckily this is built better than my little gainclone was.
Mine ended with a resistor on fire and burnt legs on the LM3886.
I thought mine had to do with my power supply at the time. I was using two switched supplies like soong was talking about a few posts back but they were adjustable. When you adjusted them both perfectly to 24V then ground really was 0V but I think I actually had + or - voltage on ground the day it died. So my thought is that either
1. you have one rail higher than the other which means ground is not 0V
2. you do not have your chips well insulated from the heatsink (if this is causing one of those oh shizzle moments I bet thats it). If your heatsink has the ab...........what?
I just looked at your sink. I dont think we need to think this through any further. Get a decent heatsink on there and you wont have SPIKE protection kicking in.
Uriah

edit: And if you dont use thermal paste the size of the heatsink wont help any. You must use it on both sides of your insulating pad. Also if you dont use insulating washers then your bolt will take negative voltage from your chip to the sink and it will go to ground which will leave you with a fried chip. I just dont see any paste. I see your first washer but is it a shoulder washer or a flat one?

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Old 15th May 2009, 03:13 AM   #724
troystg is offline troystg  United States
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Defiantly larger sink..

AT LEAST 5 times larger.

Send me an email with address and I will ship you some.

EDIT:

Dude, other than the HS it looks like you did a really good job assembling. <Just a quick glance though>



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Old 15th May 2009, 03:15 AM   #725
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Thanks, Troy. I'm glad that someone might benefit from my experiments and recommendations. I maintain that the quality of the input cap is paramount, and requires the most careful evaluation. Everything else is secondary, but all circuit path components benefit from improving over the adequate parts supplied in the kit.

I would expect that, given the cost and difficulty of obtaining them, exotic transformers would probably be pretty low on the list of significant improvements. I must admit I don't have a lot of experience with different types. I would like to hear the difference sometime, but I'm not gonna spend the money to find out. No doubt that power supply is important, but only to a certain point. Adequate capacity and quality of transformer is probably more important. There is really no point in cutting corners there to save a few bucks.

Dario, I'm happy to see that you removed bypass from input cap. I was thoroughly confused by your recommendation. Even though some people use them, I can't imagine a worse place to put a bypass cap. If your input cap sounds so bad that it needs a bypass, upgrade the cap.

The cost of Blackgate cap at C9 is justified, in my opinion, but I'm not sure that additional ones would be.

Any decent quality resistors, especially in signal path, are probably a worthwhile upgrade over Xicons, as cost is not so great.

I think hook-up wire and inputs/outputs contribute to sonics, and I favor adequate gauge solid OCC copper with teflon insulation. I never liked the sound of silver anywhere in my system except as speaker wire for the low end of biwiring (NOT the highs/mids!). I splurged on Vampire solid copper/gold plated output terminals, but my input jack is a PE cheapie. It's decent, but that might get upgraded to solid copper/gold plate, as well. I would prefer to get brass and other alloys out of the signal path.

One of my amps is still broken, but I've got a strategy now and I think I can get it running. I've built three good ones, so it can't be that difficult to find and fix what's wrong. Bluegti has too little voltage at C14; I have too much. Maybe I could send him a few of my extra volts and we would both have working amps.

I use a nylon bolt for connecting chip to heatsink. Obviously, no shorting problems, no expansion/contraction problems, and it's not so strong or rigid that I risk overtightening the bolt.

From his description, it doesn't sound like the problem is thermal. I think that's a symptom, but not the cause.

Peace,
Tom E
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Old 15th May 2009, 03:29 AM   #726
troystg is offline troystg  United States
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" I splurged on Vampire solid copper/gold plated output terminals, but my input jack is a PE cheapie. "

Mr. Gerald uses and likes the Vampire stuff. I changed the binding posts on my B&W 805's to some Vampire terminals and did not see any sound difference <good thing> but a HUGE convenience difference. I hated the original round binding posts and I love the hex head Vampires.

http://www.vampirewire.com/pc-46-16-bphex.aspx


Let me tell you, I called over there to order some spade terminals for a friends cables I was making and that man was a "trip". Nice guy, very knowledgeable.. But I called to order some terminals and the whole time he is telling me NOT to put the terminals on the ends of the cables because the bare wire sounds better.

Now I was NOT going to argue with him on the sound issue as I'm sure he has done extensive listening and testing, but I was doing this for a friend who was ALL about the ease of hookup. He not only definitely WANTED spades, but he wanted the spades on banana plugs so they could be plugged and unplugged as his wife redecorated....

It took over an hour to finally get 16 spades ordered and shipped. This was before HTTPS and secure internet ordering.
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Old 15th May 2009, 08:24 AM   #727
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Quote:
Originally posted by bluegti
I was able to get music out of this board but there are a couple of issues:

The first time I turned on the amp, I heard an awful LOUD SCREEECH
...
Also, I noticed the faint smell of burning plastic. All the caps look normal, but then I noticed the insulation of the wires that I am using for the amp input (coming from the RCA) had receded slightly. Sort of like what happens when you heat a wire too long while soldering.
...
So, I've included pictures below. Any clues?
I must be lucky, I've had problems with Gainclone but never with MyRef...

Your Silmics are bigger than mines...

Have you checked that C9 leads doesn't touch or are too near to anything?

Your cap has 7.5mm lead spacing vs the 5.0mm of the position so you had to bend them, right?

Quote:
Originally posted by madisonears
Dario, I'm happy to see that you removed bypass from input cap. I was thoroughly confused by your recommendation. Even though some people use them, I can't imagine a worse place to put a bypass cap. If your input cap sounds so bad that it needs a bypass, upgrade the cap.
Hi Tom!

It's nice to ear you

The cap isn't bad at all but, sometimes, even the best cap could benefit from a bypass.

For sure in this case no bypass is better

Quote:
Originally posted by madisonears
The cost of Blackgate cap at C9 is justified, in my opinion, but I'm not sure that additional ones would be.

Any decent quality resistors, especially in signal path, are probably a worthwhile upgrade over Xicons, as cost is not so great.

I think hook-up wire and inputs/outputs contribute to sonics, and I favor adequate gauge solid OCC copper with teflon insulation.
You're talking about elcos, right?

Also C6 and C11 swap (with Silmics in my case) has an audible effect that justify an expense of 0.66$

Regarding resistors I think that Xicons are already decent, to have more you have to spend more on Takmans, Dale RN55, PRP, etc.

I agree that hook-up wire makes a difference, I've used solid core copper for outputs and a nice OFC shielded cable for inputs.
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Old 15th May 2009, 09:40 AM   #728
AndrewT is offline AndrewT  Scotland
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look at page 14 of the 3886 datasheet.

Find +-36Vdc on the graph (=72V)
Go up to 8r0 loading.
Go horizontally to the far left.
@ Ta=25degC National recommend between 2.4C/W and 3C/W
@ Ta=40degC they say 1.9C/W and 2.5C/W.

For an internal heatsink with resitricted flow of cold air use the Ta=40degC.

Now find a heatsink that has double the dissipation of the National recommendation. i.e. use ~1.1C/W for each channel.

That is not 5times your existing sink, it's about 25times the dissipation.

If you mount the heatsink externally you can reduce it to ~1.3 to 1.4C/W
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Old 15th May 2009, 01:28 PM   #729
troystg is offline troystg  United States
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Quote:
Originally posted by AndrewT
..........
That is not 5times your existing sink, it's about 25times the dissipation.
...........

As always good advice, however PC heat sinks have been used since the dawn of the Overture amps and are proven to be acceptable under real world usage. They are "roughly" 5 times the size of his sink.

I don't expect him to slap 5 of his current sink on a piece of flat stock to increase the dissipation <although that probably would work>, instead I offered him some good ones that only cost an email.

With the exception of a few threads on this forum "most" of the work can be safely done in "approximation." When a hobby becomes too technical or tedious most hobbiest loose interest.

But as always you are correct, and if your advice is followed it WILL work and be "right".
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Old 16th May 2009, 01:36 AM   #730
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Quote:
Originally posted by ClaveFremen

Quote:
Originally posted by madisonears

Dario, I'm happy to see that you removed bypass from input cap. I was thoroughly confused by your recommendation. Even though some people use them, I can't imagine a worse place to put a bypass cap. If your input cap sounds so bad that it needs a bypass, upgrade the cap.
Hi Tom!
It's nice to ear you
The cap isn't bad at all but, sometimes, even the best cap could benefit from a bypass.
For sure in this case no bypass is better
Today I've removed bypasses also from SACD Player's output caps (Mundorf Zn): much better!

Tom I think you're right
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