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Mauro Penasa MyRefC build by Uriah
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=294
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Author:  RiGuy [ 10 Dec 2008, 19:14 ]
Post subject:  Mauro Penasa MyRefC build by Uriah

So I was doing a group buy for this board/kit. Me and a guy from CalTech. His name is Peter Schroder. He is taking care of components I am taking care of the board. I got a prototype of the board made and shipped from Malaysia and just finished populating it today. Before it got finished (because I did not have all parts yet) I started working on an enclosure and power supply. Most of the supply is actually on the board so all I have to do is mount a toroid/fuse/thermistor/plug/switch. I have both builds documented on my Picasa account. I will include one photo of each here and a link to the albums so you dont have to wait for a bunch of photos to load.
Ri

MyRef Board http://picasaweb.google.com/udailey/MyRef#

Enclosure http://picasaweb.google.com/udailey/MyRefEnclosure#
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Author:  CrazzyAbtTubes [ 10 Dec 2008, 19:37 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

That build is looking good, it looks like a large power amp of some kind, massive power supply. It must be fun to have some one else building the project with you, because I have to build every thing on my own, for example that Viking power amp project, I couldn't even find info on the net about it but I still got it to work with my mods, good luck with your partnered project. ;)

Author:  RiGuy [ 10 Dec 2008, 19:51 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

Its Mauro's design and then Twisted Pear Audio designed the boards and released kits a few years back. We are just reviving it by offering another 120 kits to a few folks. This is our test to make sure everything works and hey I get a nice amp out of it. Of course I am a good $220 into it by now without anything even fired up. Arggh! But its okay, if it works that cost will be rolled into the group buy charge to cover making sure everyone gets something that works.
Ri

Author:  Gio [ 10 Dec 2008, 19:55 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

Hi Ri, the boards look good. Would it is a lot more money to label and silkscreen the PCB? I like your progress on the enclosure. Where did you source the welders steel and how much was it?

Cheers

Author:  RiGuy [ 10 Dec 2008, 20:11 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

The proto I ordered without silkscreen and without soldermask to save money. It would have been another 60 dollars to just get those two on it. So no thank you!
The production boards will have both silk and mask.
The welders steel I got at Lowes. It was 6.23 for each 6x18 inch piece and 8.xx for the 8x18 piece. The enclosure will end up costing me more than I thought. Probably nearly 100 by the time its done. And I thought I was going to save building it myself. The oak wasnt cheap and the perforated aluminum was about 22. Then I had to buy screws, angled aluminum, bolts, and a bit that would countersink into steel. We will see how it turns out if I want to get fancy little pegs for it to stand on or if it will be a bit to burly for that look.
Its a giant and has lots of room for adding more channels, another toroid, and a pre plus I could add a pre power supply in there.
Ri

Author:  RiGuy [ 13 Dec 2008, 23:08 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

YAY! It works :)
I have to get a decent pre made up for it but it works. I am really happy about that. It has been giving me fits the last few days. I seriously got an eye tick for a day. I obsess a little bit until a project gets done.
Ri

ps I will post another pic on Picasa soon. Nothing really new to show yet. Cant really see sound and thats the only difference right now than the last pic.

Author:  Gio [ 14 Dec 2008, 11:53 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

That is great Ri. Sorry, I am not too familiar with design, but what is the gain set at? Also, does the kit come with a power supply circuit, I see one way off in the back of your photos.

Cheers

Author:  RiGuy [ 14 Dec 2008, 13:22 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

I am not sure what the gain is set at. It does come with a rectifier and power supply caps on board. All that is necessary to add is a preamp, power plugs, switch, RCAs, transformer, wire and thats about it. I am going to go wire up one of my 25k monster pots right now.
Ri

Author:  RiGuy [ 14 Dec 2008, 15:14 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

Gio,
Mauro said this at the beginning of the DIYaudio thread
Quote:
"The imput impedance of this amplifier is 100Kohm and the gain is 30 dB, for which not there are particular problems of interface with a log pot.. Suggestion to use a value not superior to 22Kohm, to avoid that the serious resistance creates an excessive high frequency cut off."

I have to say it sounds, with only one channel going so far, really really really good. Mauro claims it sounds better than some class A amps. Well, who knows I have yet to finish my F5 so that comparison is a ways off for me, but right now Bruce Springsteen is in my basement and I get a private concert :)
That was the first improvement I noticed. His voice was definitely more 'real' than with my LM3886 'regular' chip amp, which I love dearly and is way more easy to build than this thing, and cheaper to.
I really like this amp for a few reasons. Obviously right now on the first ten minutes of real listening the voices are improved. I would like to add a roll off to the highs though. The thing is a beast. I have really really screwed with it and screwed up a few things that by all rights should have killed it. I smelled smoke 5 minutes before I got it all right and it is still playing well. It waits before turning on so that I dont get that 'bump.' I like that a lot. It has speaker protection. Some of you may know from my past mishaps that this is, in my case, a big bonus.
I used a safety circuit in all my testing and the circuit is in place right now. I will NEVER, I repeat NEVER build another amp without using it. It may have saved this baby several times from cooking or maybe the amps own circuitry would have saved it, but nevertheless the safety lightbulb in my poor mans variac has lit many times and the time I smelled smoke the lightbulb lit and either saved the amp or gave the amp time to save itself. I dont know which but I am grateful to AndrewT of DIYaudio for promoting this circuit in almost every other post when he is helping newbs or pros.
You can find that little gem here: http://www.antiqueradio.org/dimbulb.htm
Ri

Author:  RiGuy [ 14 Dec 2008, 15:23 ]
Post subject:  Re: Mauro Penasa MyRefC build by Uriah

I will have to try different caps. I think it might make the drums snappier. I have to make another regular LM3886 to compare but thats a ways down the road. Sounds great but I want the drums to be more present.
Ri

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