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Old 22nd October 2011, 09:00 PM   #301
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Quote:
Originally Posted by Leolo View Post
I hope to make a discrete amplifier some day soon. This design has peaked my interest. Aprox 15 CAD of silicon per channel and a forgiveness of build quality and part selection make this very interesting.

I have a few questions, some of them smarter then others:

1- Would a pair of MJE3055T work for power transistors? I ask because Heat sinks for TO-220 are easier to build. (I suspect the answer is "yes, but only for less then 20v rails")

2- Does the PSU need anything more fancy then transformer, rectifier bridge and caps?

3- (The newbie question) how does one turn the PNG that powerflux posted into a PCB. More to the point, how does one extract the bits that are copper and print that at the right scale? I gave a stab in the GIMP selecting various bits by colour, filling with white or black, but this seems ackward. What's more how do I get the scale exactly right? Powerflux hasn't posted dimensions.

I plan to do the laser-toner-flimsy-paper-iron-on transfer method for creating the PCB.
I built with MJW21196 outputs (6 mhz to3p) and b649 drivers. Also used +-40v rails. Psu was toroid + 7*2200uf per rail, crc, shared both channels. Used "stealth" (fast and soft recovery) diodes.

Before final assembly though, the test supply was lacking: 1000uf per rail and a very undersized transformer. sound was better with better supply, obviously more audible at loud volumes. I was surprised at how well it sounded with the poor supply though.

The PCB I used was made into a pdf easily printable a few pages back, by me. I used 100nf to bypass the electrolytics on the supply rails, soldered under board. The PCB does have one trivial mistake, incredibly easy to fix, that was also written about recently.
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Old 22nd October 2011, 10:06 PM   #302
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Quote:
Originally Posted by Elvee View Post
You will have to wait Powerflux is satisfied enough with his work to post the source file and/or a printable file.
I just hope he wasn't put off by my comments, that was only constructive criticism, and I appreciate any contribution, including his....
not put off at all just very busy. hopefully tomorrow. rerouting feedback combined with a proper central groundplane (most important updates) is time-consuming. i like the PCB to be 'Elvee'-approved and the schematic to be well-readable before posting eagle pcb files to prevent wild growth.

Last edited by powerflux; 22nd October 2011 at 10:08 PM.
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Old 23rd October 2011, 11:32 AM   #303
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new pcb. (v0.3)

fixed
- feedback
- central ground plane
- replaced ground connector. i'd star-ground everything at the main psu, that's why i decided to put it there.

i can't fit decoupling capacitors in the current version. The caps are either too small and other traces have to be rerouted to far away to connect them properly, or too large and thus don't fit on the board.

what i would do is simply 'free wire' the caps. that way you can place them directly
where you want to.

havent updated the schematic yet.

Click the image to open in full size.

i want to wait until Elvee approves, then i will post a pdf or the files. for the people who cannot wait: the resolution is 300dpi, good luck

possible upgrades
- space for cooling fins for drivers
- minor adjustments input stage routing

Last edited by powerflux; 23rd October 2011 at 11:50 AM.
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Old 23rd October 2011, 02:02 PM   #304
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v0.4, small adjustments. just printed it on A4 to see it in real life, see attached PDF. it is tiny

Click the image to open in full size.

comments? i'm not sure about the return currents in some places, wich is the big disadvantage of a continuous groundplane.
keeps the etching-liquid clean tough :P and more serious: there isn't much current to return through the plane where the traces are small. all the relevant ground stuff is happening on the left side, where the plane is decent.
Attached Files
File Type: pdf Circlophone v0.4.pdf (42.5 KB, 122 views)

Last edited by powerflux; 23rd October 2011 at 02:11 PM.
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Old 23rd October 2011, 06:14 PM   #305
Elvee is offline Elvee  Belgium
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The input is in the right region regarding the ground.

To avoid passing high currents at unpredictable places of the ground plane, I suggest you set the position of the supply (power) ground and output ground pads.

Placing them in proximity will avoid uncontrolled dispersion elsewhere.

Note:
By pushing the diodes towards the center of the board, there would be room enough for decouplings.
Attached Images
File Type: gif Px Corr.gif (55.0 KB, 566 views)
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Old 24th October 2011, 11:53 PM   #306
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Elvee & Kenpeter, would like to thank you both for an hour or more of very interesting reading... my small mouse infested brain is spinning in quadrature loops I am certain... fun.

The resistor comment I made months ago referred to what I have subjectively found for years and is apparently backed up by Simon's post (and off forum tests) in the John Curl Blowtorch thread.

But the best post was Elvee's on the effect of layout vs. real world performance! Nice.

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Old 25th October 2011, 08:41 AM   #307
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Quote:
Originally Posted by Elvee View Post
The input is in the right region regarding the ground.

To avoid passing high currents at unpredictable places of the ground plane, I suggest you set the position of the supply (power) ground and output ground pads.

Placing them in proximity will avoid uncontrolled dispersion elsewhere.

Note:
By pushing the diodes towards the center of the board, there would be room enough for decouplings.

why not put the output ground with the supply ground at the main capacitors (star ground)? that way the return current of the output stage won't even go through the PCB.
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Old 25th October 2011, 10:06 AM   #308
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by powerflux View Post
why not put the output ground with the supply ground at the main capacitors (star ground)? that way the return current of the output stage won't even go through the PCB.
It is an option, but then you cannot use local (free wire) decoupling caps, because they will "pollute" the local ground by injecting class B waveforms from the supply rails.
And anyway, a pad costs nothing, so why exclude that option?
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Old 25th October 2011, 09:35 PM   #309
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ok, will try fix the caps and diodes.
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Old 3rd November 2011, 08:36 AM   #310
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like this? i really dislike the way the drivers are routed. there is only space for the tiniest decoupling caps..

Click the image to open in full size.

Last edited by powerflux; 3rd November 2011 at 08:43 AM.
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