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Old 9th April 2013, 01:37 PM   #1
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Default Beginner's Build Guide: Pearl II

Hi,

I discovered this site recently while looking to purchase a new amp. Even after buying one, I found myself coming back. I have no background in electronics or diy audio, but got interested in amplifier design while I researched for my purpose. My first thought was to take a theoretical approach, learn from books, but the complexity made me realize that I would never get to the "build" phase, so balancing book learning with doing seemed the best bet. The weak link in my system is probably my phono preamp, and 6L6 and others were very supportive and helpful, so I decided to start with a Pearl II.

My goal with this thread is not to create a guide to a great approach to building a Pearl II, as I do not have a great approach. It is really to do two things. First, it will likely help me. Forcing myself to write down what I am doing will make sure that I really think it through, don't skip steps, know what I know and don't know. Second, it is to with any luck help other beginners who are thinking of taking up the hobby. At times the threads on this site are way over my head, and I worry that I am missing things (I am) and that this will lead me to make mistakes (it has). Possibly, by going through my thought process, it will help others who are at the same level.

Also, there is the chance someone who knows what they are doing will say "you are making a mistake!!!" which would be helpful.

When I decided to build the Pearl II, I made two decisions: I would start with the power supply, and I would start with the case as opposed to the pcb and other pieces. The focus on the power supply was primarily because the parts were cheaper, so if I screwed up it would cost me less. Also it seemed less clear than the main board, so I decided that I would try to tackle it now to avoid frustration later. The case just seemed like a good idea, and it was, if I hadn't screwed it up, which I did. But that is the point of these posts, I suppose.

One last thing: this may take a while. I have work/family that keeps me away from hobbies for days at a time, and I see this process as learning first, finishing second, so I will likely go sideways and backwards at times.

People should feel free to post or send me notes, but please remember my beginner status. I will respond but won't aswer what I don't know. There are experts here who will!
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Old 9th April 2013, 01:39 PM   #2
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First post: read this!!!

Building a Gainclone chip amp power supply.

It is an intro to building a power supply. It is invaluable, or at least was to me. In fact, just re-reading it briefly made me realize I did something stupid, which I will highlight below. I don't really understand all of it, but learn more each time I look.
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Old 9th April 2013, 01:42 PM   #3
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If anyone wants, here is my BOM. I can not attest that it works, as I have not started the Pearl II part yet, but if it doesn't I will return to it.

I took the basics of this from an earlier post, but can't find it now. I am sorry not to appropriately attribute. There are a bunch of changes as some places didn't have given parts any more.
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Old 9th April 2013, 01:46 PM   #4
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Oops, wrong format: trying again.
Attached Files
File Type: doc Pearl II BOM.doc (36.0 KB, 105 views)
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Old 9th April 2013, 02:22 PM   #5
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Have you sean this thread: Building a Pearl 2
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Old 9th April 2013, 03:52 PM   #6
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Quote:
Originally Posted by MASantos View Post
Have you sean this thread: Building a Pearl 2
Yes, it is great. Highly recommended reading.
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Old 9th April 2013, 04:07 PM   #7
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So my first step was to deal with the power supply case. Sadly, I did not think this through, and focused only on the backplate--installing the ac jack, switch, fuse, and power out jack. I had no idea how to get the proper sized holes, so did some experimenting with a friend and ultimately came up with the photo below using a drill and a dremel. Note the various scratches and the slightly misaligned plug. My thoughts on tools: a drill with good bits is necessary. The dremel is very, very useful as a cutting tool (use the drill for the corners, the dremel to cut the rest), and useful if a bit tricky to use as a grinder, to get a close fit for the jacks and such. I believe that a good set of files would be helpful for this and possibly easier, so will pick one up the next time I get to the store.

If you read other build guides (this is a great example for an F5: An illustrated guide to building an F5) you will see the right way to do this. Not only do the back/face plate, but the bottom (and sides, if necessary). Lay everything out, make sure you are comfortable with where it will all go, and put in all holes, including in the base plate! I did not do this, and have a few extra holes as a result. Also, don't drill late at night after an extra glass of wine.

Were I to do this again, I would look for a combination plug/fuse holder/switch on a rectangular plate, as that would be much easier to mount. And, of course, I would lay out the various pieces prior to any drilling. On a positive note, it ultimately worked, but better aesthetics would be nice!
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File Type: jpg 101_0429.jpg (868.3 KB, 595 views)
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Old 9th April 2013, 04:29 PM   #8
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This will be my last post for a bit. The next steps were to put together the pcb, and do the wiring.

I borrowed the approach of budwiser (see Pearl Two for discussion and link), getting the PS-KIT from chipamp.com (Chipamp Power Supply Kit | Chipamp.com). This kit requires a few changes to be used in this project, but they are simple--see the manual at http://www.chipamp.com/docs/lm3886-manual.pdf. The kit has two ground outputs; they need to be jumped (giving one). It also has a resistor/capacitor pair just prior to the output (1k resistor, .1uf capacitor I believe) that must be left off. Full disclosure, comparing the power supply diagrammed in Wayne's original "how to" Pearl II guide to that of the chipamp, there are two additional pieces left on the chipamp that seem inconsistent--the 2.2k resistor and another .1uf capacitor. I left them on to be consistent with budwiser's build, but I am not sure what they do. It does work, so there is that. Soldering this up, which was a source of worry for me, turned out to be a snap.

As noted in the BOM, I got a transformer with 25V secondaries (that is, it takes wall voltage and converts it to 25V). This is not what is recommended, but I could not find a transformer with 22V secondaries anywhere. I am hopeful this will not matter, but we will see.

The last step is wiring it together, following the schematic from Wayne and budwiser's photos. It is quite straight forward, with one exception for me. I did not test to make sure I had the right pairs of secondaries (both pairs use a blue and green wire, I belive you can test their continuity but my MM does not have a continuity tester). I misinterpreted a suggestion and picked the wrong pairs. End result--many blown fuses, lots of resoldering, and a day's confusion, but eventually I realized that was where things were going wrong (using the disconnect it all, add one piece to the chain approach, wait for fuse to blow). The picture below is where I am at this point, with 35.6V at the output. This is higher than called for due to the higher V transformer (28-35 is recommended) but hopefully it will work. As noted above, re-reading the guide when I got the link to it to post above made me realize that with all the taking apart and putting back together of the wiring to diagnose the blown fuses, I had left the connections with wall voltage very poorly insulated, which is dangerous. I will fix this. But what you see below is the first actual working circuit this beginner has put together. Try not to laugh at the bad wiring!
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Old 9th April 2013, 06:11 PM   #9
6L6 is offline 6L6  United States
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This is a great thread! I love documentation like this, and your process will be invaluable to other people building a Pearl.

Remember, lots of photos is good!!!

One question - is the housing/shell of the XLR jack attached to any of the pins? You need to check.
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Old 9th April 2013, 07:27 PM   #10
Mr. dB is offline Mr. dB  United States
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Is there any particular harm in leaving the RC snubbers in place on the Chipamps power supply board?
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