yet another Mini-A layout... (with SMD parts) - diyAudio
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Old 29th September 2003, 08:01 PM   #1
BrianGT is offline BrianGT  United States
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Default yet another Mini-A layout... (with SMD parts)

I decided to take a try at making my own Mini-A layout. I decided to use equivilant surface mount parts for all except for the output resistors and output devices. It is pretty much Grey's original schematic, with a couple of additions suggested in the thread.

Here is the schematic.

I should be getting a pair of boards made in a couple of weeks for testing.

As for the parts, the caps will be panasonic PPS film, and Panasonic FK electrolytics (lower impedence version of the FC).

I started a small stereo chassis for these things today as well

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Old 29th September 2003, 08:07 PM   #2
BrianGT is offline BrianGT  United States
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Here is a strange 3d view that the software gave me... I didn't choose what the components should look like

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Old 30th September 2003, 03:57 AM   #3
moe29 is offline moe29  United States
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Brian,

Have you worked with those SMD resistors before? Are they a
pain to solder? I've seen them in commercial amps - that picture
of that Rowland amp based on the GC chips comes to mind. I
guess they "sound" as good as normal 1/4 watt resistors? I just
haven't read much about them on the Forum.

Good luck and keep us posted - sounds like you have the makings
of a really neat little amp here

m.
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Old 30th September 2003, 04:17 AM   #4
BrianGT is offline BrianGT  United States
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Quote:
Originally posted by moe29
Brian,

Have you worked with those SMD resistors before? Are they a
pain to solder? I've seen them in commercial amps - that picture
of that Rowland amp based on the GC chips comes to mind. I
guess they "sound" as good as normal 1/4 watt resistors? I just
haven't read much about them on the Forum.

Good luck and keep us posted - sounds like you have the makings
of a really neat little amp here

m.
I actually spend a good amount of time last week, soldering various surface mount stuff. These components are some of the larger surface mount parts that you will see out there. I soldered stuff less then half the size of these.

Parts needed to solder them fairly easily:
-fine tip for the soldering iron
-fine solder (thick stuff will cause you to use too much)
-flux (i like the can of flux paste)
-patience

Basically, I like to put a lot of flux on the board first, and also cleaning the soldiering iron tip in flux.

I then put a bit of solder on one of the pads. With tweezers, I hold the part over the pad, and heat it and place the part, tacking one side down. I then pick the solder back up, and solder the other pad, and touch up the first side.

The flux should wash off really well with normal isopropyl alcohol. I would stay away from defluxer, as it requires a lot of ventilation, and will make you light headed/kill you if you breate it too much.

One consideration is for soldering the film caps: be careful not to heat them up too much. A temperature controlled iron at a lower temperature is a plus. I heated one up just to watch it die.

As for a fun exercise, grab a ruler, and zoom the picture with an image editing program until the size is exactly 2" tall (there are grid lines signifying inches), and this will be the exact size of the board.

I should have boards in a couple of weeks, and if they work out well, and people are interested, I might organize a group order, or provide the layout files to someone who would want to (not-for-profit).

As for the sound of this amplifier, you really can't know til you try it out. On one hand, it might be better with the shorter signal paths, and lower esr caps, but there is a much more limited component selection for this amp... but I figure if Nelson is using standard digikey-like components (panasonic and other run of the mill) for his commercial amps, then standard digikey components would work just fine for me for this exercise.

Also, there are some exotic SMD parts out there if you search (tantulum resistors, oscon capacitors, etc), but no black gates to my knowledge.

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Brian
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Old 30th September 2003, 11:40 AM   #5
MikeW is offline MikeW  United States
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Default Two Irons

Use two soldering irons.
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Old 30th September 2003, 02:20 PM   #6
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Something I threw together.

It only needs 1 iron, & it makes for clean flat assembly, even for ICs.

I posted it in the 'electronic parts' forum.

Easy-Cheap-DIY-SMD mounting guide.

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Old 30th September 2003, 03:52 PM   #7
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Quote:
Originally posted by BrianGT
Here is a strange 3d view that the software gave me... I didn't choose what the components should look like

--
Brian

Hi Brian,

What software are you using???


JF
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Old 30th September 2003, 03:59 PM   #8
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He is using Protel.
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Old 30th September 2003, 05:41 PM   #9
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0805 and bigger, SOT-23 and bigger are no problems to solder. I use also two soldering irons, for the 0805 parts, real easy but it's also easy with only one iron.

IC's with pin spacing 25 mil or less IS not easy to solder!

Brian, nice work! What do the audiophiles say about SMD? I think it's cool.
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Old 30th September 2003, 05:54 PM   #10
jwb is offline jwb  United States
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If you are trying to make this as small as possible, you could save a LOT of space by replacing Q1 and Q3 with 2sj109 and mounting Q2 vertically. Mounting R18-21 vertically will save space and probably reduce thermal noise by allowing the resistors to reject heat more efficiently.

Many parts are more compact in their through-hole body than in an SMD. A vertical TO-220 transistor will take up less room than a horizontally surface-mounted one, and Zetex's E-Line package uses less board space than most SMD transistor packages. Electrolytic caps are also more compact in through-hole packages.

Of course, if compactness is not your goal, you should kindly ignore me.
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