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Old 12th December 2011, 08:36 AM   #31
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Luke,

this is the current status of METAL's and my layout:

Click the image to open in full size.

http://www.abload.de/img/lookedthroughwmacr.png

I know that METAL is currently working on the backend (right side of the PCB) to improve the polygons, routing of the tracks, ...

As you can see I changed the power caps to have a diameter of max. 35mm and will use MPC74 emitter resistors.
I also inserted 4 mounting-holes and 6.3mm spades for connecting the power lines.

The frontend (left side) is a copy of ZDR's layout.
Thanks to ZDR I have now a current EAGLE-schematics of the RMI FC-100 with values given.

I will now begin and "optimize" (if possible, ZDR!) the routing of the frontend.
It won't take long anymore until METAL's and my final layout will be published.

The current size of my PCB is 165 x 72 mm.

Best regards - Rudi_Ratlos
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Old 12th December 2011, 08:42 AM   #32
Luke is offline Luke  New Zealand
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Very nice Rudi.

I assume you've decided that one cap is enough?

Other question is do we want connectors for input/output and power? I think they are worth the extra space on the board, its nice to be able to disconnect everything to get the board out and not need a soldering iron. Its also tidy.
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Old 12th December 2011, 10:22 AM   #33
zdr is offline zdr  Belgium
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Rudi, my layout was primarily made for the purpose of single-sided home-brew pcbs, I would not recommend sticking to it for double-sided designs. If you are going for double-sided design, it could be made much better than mine. Also, your output tracks are narow as in my PCB. I had to do it like that since I did not have enough space, but maybe you should use the advantage of DS PSB to make them at least as wide as in original.

Overall, great looking PCB.
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Old 12th December 2011, 10:45 AM   #34
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ZDR, since the power transistors (and others) are mounted horizontally, below the PCB, a 2-layer design with plated-through holes is needed.

Best regards - Rudi
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Old 13th December 2011, 09:08 AM   #35
roender is offline roender  Romania
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Hi guys!

Nice to know that my "little" amp has created so much passions between forum members
Can I help you in any way?

Have fun,
Mihai
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Old 13th December 2011, 09:19 AM   #36
zdr is offline zdr  Belgium
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Great to have you back Mihai!

We are playing with your pcb layout and trying not to mess up your great design in the process

Rudi has been asking me some questions for which I think you will be in much better position to answer:

1) Why four large caps and not two?
2) Why no AC/DC decoupling caps at the input?

And a question from me:

3) There seems to be lot of serious talk about matching in the main thread, and some really extreme tolerance goals, which totally put me off each time I finally try to finish the amp. I would like to know what matching you did and how for your own working build?
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Old 13th December 2011, 12:02 PM   #37
roender is offline roender  Romania
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Quote:
Originally Posted by zdr View Post
1) Why four large caps and not two?
2) Why no AC/DC decoupling caps at the input?
3) There seems to be lot of serious talk about matching in the main thread, and some really extreme tolerance goals, which totally put me off each time I finally try to finish the amp. I would like to know what matching you did and how for your own working build?

1. Low ESR.
If one do not have room or do not wanna use four general purpose capacitors, I would recommend two low ESR capacitors designated for audio applications.
2. I don't like sound colorations and, if it's possible, I would try to avoid any DC decoupling capacitors. Besides that, any modern audio source have near zero output DC. Moreover, the amplifier have DC 1 voltage amplification. So, what's the point in having an inline input capacitor?
3. Low power BJT or JFET can be effortlessly matched and I would recommend you to do it as close as you can. Anatech describe in the above replay a very good matching method.
It is not hard to match PNP and NPN 0302/0281 parts from ONsemi. I have done that without much effort using a 100mA CCS for Ic and measuring the voltage dropped over an base resistor.
RMI-FC100, a single stage audio power amplifier
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Old 13th December 2011, 12:46 PM   #38
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Hello Mihai,

I appreciate your attention to this thread very much!

My friend METAL and I - after reading a lot of articles of this forum - decided to build your RMI FC-100 amplifier and provide to everybody,
who is interested, the PCBs for it.

Our offer will also include a PCB for the frontend power-supply and "not-easy-to-get-components", such as: output NJL* - transistors,
pre-driver transistors, emitter resistors, small caps: things that will fit in a coated letter.

METAL and I have worked on the layout in the last days, and this is the current stage of our design:

Click the image to open in full size.

http://www.abload.de/img/topview79zdv.png

The major differences, compared with your design, are:

1) We will only use 2 power caps on the right side, the diameter of which can be 35mm at most
2) We have included a "big EAGLE package" for capacitor C5 that will accept a MKP 1839 (for example) on this position
3) All resistors are mounted horizontally and have the EAGLE package "0207/10"
4) We will use Futaba MPC74 emitter resistors
5) We have included 4 mounting-holes and 6.3mm spades for power- and output-connectors

The frontend is not yet finished and METAL and I still have to do several iterations on it.
We have the feeling that the frontend is too much crowded currently, and maybe we will increase the size on the left side of the PCB by 10mm.

Nevertheless: the above picture will give you an impression, how the layout will finally look like, and I would appreciate very much,
if you can give us your comment on it.

If you like to, I will send you the EAGLE files.

Best regards, many thanks for looking around: Rudi_Ratlos
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Old 13th December 2011, 01:10 PM   #39
roender is offline roender  Romania
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Hi Rudi

Your effort is laudable! It seams to be a good lucking design but is away from my main PCB design philosophy which can be resumed in few words: Avoid at any cost the parasitic and intrinsic non linear cross layers PCB capacitance, especially if you want to use FR4 substrate.
You should give it a try an see how it works, if it is stable, before offer the PCB to the others.

Best regards,
Mihai
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Old 13th December 2011, 07:55 PM   #40
Luke is offline Luke  New Zealand
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It's looking very good Rudi.
mihai, what's a good amount of capacitance to use on this amp? The reason I ask is I have 12000uF Elna cap that would work, but Im wondering if I should use more capacitance?
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