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Old 22nd April 2006, 12:04 AM   #1
dfdye is offline dfdye  United States
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Default Possible LM4702 PCB Buy

Hello,

I have posted a proposed board based on the National LM4702 chip here that I will be ordering several prototypes of in the near future. If anyone is interested, I will be more than happy to get some extras with my order. Since this amp is still in the "new design" category, I have tried to make the board as flexable as possible to allow for a variety of components. I am sure this will not be the ultimate LM4702 circuit, but since I will be ordering parts anyway, I figured if anybody wanted to come along I would be happy to facilitate it!

I am not sure where I will be ordering from, but I know I can get boards from Olimex for ~$10 per board. Obviously Olimex doesn't put out the greatest parts in the world, but the price is definitely right for small quantities. If we get enough parts, I would love to go with Advanced Circuits or another higher quality manufacturer, but my first priority is obviously to get the boards made!

If you are interested, drop me an e-mail at dfdye at netscape dot net or click on the button at the end of this post! (or just post here and I will put you on the list)

Attached is the proposed board design, but if you are interested and would like to see something else, let me know and I will see what I can do!

Thanks!
David
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Old 22nd April 2006, 01:03 PM   #2
djkib is offline djkib  United States
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I'll take 2... How do you want paid?

Thanks for all your hard work in this development!

Peacem
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Old 23rd April 2006, 12:42 AM   #3
dfdye is offline dfdye  United States
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Hey Keith,

Thanks for the interest! Payment via paypal is usually easiest, but we can work that out after we get final prices based on actual number of boards being ordered. I'll be sure to keep everyone updated!

David
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Old 24th April 2006, 12:24 PM   #4
vinnie is offline vinnie  Norway
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Im in for 4 boards
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Old 24th April 2006, 12:34 PM   #5
PierreG is offline PierreG  Canada
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I could be interested but......
Is there a final schematic with the output transistor selected?
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Old 24th April 2006, 04:30 PM   #6
dfdye is offline dfdye  United States
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There are about 5 different output stages that people are using. The simplest is the version Russ White is using based on SAP-16's. I am playing around with some non-thermally compensated darlingstons as per the app sheet as well as some non-darlington descrete transistor options.

Though I have not finished my output stage, I have, gotten to the point where I wanted some different input stage options than what I was working with, so I figured I would make this available if anyone wanted in. Since I know a bunch of people are interested in this relatively new chip I figured I would see if anyone wanted a flexable test board for working on new designs.

I am sure as more people start tinkering with this design, there will be more output stage options available, but as of now I have not implemented a board, rather just p2p options. If you have a specific output stage implementation that you would want a board for, let me know and I will be happy to see what I can do.

As for the schematic, I am working off of the typical application circuit on page 2 of the datasheet. The modifications are the addition of additional bypass caps, addition of a parallel film cap option for the electrolytic coupling caps, and a separation of the power supply ground from signal grounds via "RG." All other part names should be the same as the data sheet to simplify things.
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Old 24th April 2006, 04:52 PM   #7
PierreG is offline PierreG  Canada
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Quote:
Originally posted by dfdye
There are about 5 different output stages that people are using. The simplest is the version Russ White is using based on SAP-16's.
Thanks for the reply. But I won't experiment since I don't have enough electronical knowledge. But if you (or somebody else) can show me where is the Russ White design I would appreciate.
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Old 24th April 2006, 08:30 PM   #8
dfdye is offline dfdye  United States
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Quote:
Originally posted by PierreG
Thanks for the reply. But I won't experiment since I don't have enough electronical knowledge. But if you (or somebody else) can show me where is the Russ White design I would appreciate.
No problem! If you aren't comfortable with playing around, then I would definitely suggest you wait a while to let a good output stage emerge. I am sure that there will be a round of boards with output stages ordered in the future when some people get output circuits they are happy with.

PS I have your boards down, Vinnie.
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Old 25th April 2006, 12:18 AM   #9
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I am in the same situation as pierre G in that i don't have the experience to play around with outputs. Not to mention the exchange rate. I would really like to give this a go, but maybe i should wait until you deside to go with a final board...It's so good to see this project moving ahead, Ive been watching this from the begining and have finally got the 702s from national.
But if you need some more boards sold to get this underway then i would definately buy 2.

Brett
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Old 25th April 2006, 12:54 AM   #10
dfdye is offline dfdye  United States
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I'll put you down for a tentative 2.

Also, I checked Advanced Circuits online quote calculator, and their demo boards should be on par with Olimex if we can get ~20 boards (and yes, they are full spec). So far we are pretty close, so I am betting we will be able to get there and go with the nicer boards.

David

PS When the output stage is ready, I am pretty sure one of the final options will involve a point to point strategy with TO-3 transistors. I will definitely post what I end up doing, so if you want to get the boards now and implement a final output stage absent a BCB, it will be quite easy!
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