Category: Electronics

Engineer meets Bugera V22 reverb – Part 1

The Bugera V22 guitar amp is just too good to leave alone. Yes, it’s had its share of teething problems—the worst of which I believe have been sorted. Yes, it’s made in China. Yes the tube quality seems to be a crapshoot. But the build quality is better than what I’d expect at the price, and the sound is unique and just lovely. It’s a great buy.

One thing I’m not super jazzed about though is the amp’s reverb. I begin documenting my gripes below and start off in search of a solution.

It develops …

A2

Picking up from earlier, what we’re looking at here is an audio DAC reconstruction filter built around a prototype discrete opamp-like differential gain cell I’ve had in the works for quite a while. I finally chased out the last engineering details and have been listening to the final setup for about a month. I am still astonished at how good it sounds.

I designed the gain cell from the ground-up as a dedicated high-performance audio device. It uses some novel topological and other features that I’ll probably go into in a future post. For now all I want to say that the thing is wicked fast for a discrete device and has been rock-solid stable.

But why bother? Aren’t there already tons of reasonably decent, some even cheap, audio IC opamps out there? Yes, there are. But I’ve never been totally happy with any of them. Some have too much LF bloat, some are too strident—none to my ears do everything right (which is to say, do as little as possible apart from making the signal bigger and stronger).

Designing a discrete device let me optimize the gain structure specifically for audio, minimize and more effectively manage the number of parasitic interactions throughout, thermally couple and, more importantly, decouple elements as necessary, and a few other things. It started as a “Gee, let’s see…” exercise, and I have been rather shocked by the results.

Now I’m contemplating where to take things next. I’ve designed a couple small-footprint packages for the gain cell. I’m implementing a few other ideas with it too. I suspect this surprising little circuit will see some commercial application soon.

Right then. Back to listening. 😀

PDF output from KiCad in Linux from SVG

kicad-appicon-128

The ps2pdf-d script I developed earlier worked fine for getting PDF from KiCad‘s Eeschema using Postscript as an intermediate format, but it falls short with Pcbnew because there is no way in Pcbnew to make a Postscript file that merges layers. Using File > Plot, you can pretty easily get Postscript files of individual layers, but you can’t get a merge of, say, the top copper, top silkscreen, and drawing layers.

But you can do this with File > Print SVG. You’ll need to play around with the dialog to get the SVG you want, but it’s pretty simple. Thus, svg2pdf-d was born:

#!/bin/bash

# DESTRUCTIVELY convert all svg files in working directory to pdf.
# Source file extension is case sensitive!

# Requires inkscape.
# Mithat Konar 2013 <http://mithatkonar.com>

OPTIONS=""

FILES=$(ls -1 *.svg)

# There are two alternatives below for doing the conversion.

#~ ## BEGIN ALT_1:
#~ ##     This approach isn't optimal because it restarts inkscape per
#~ ##     file. However the simplicity lends itself to porting (e.g., to
#~ ##     windows BAT.
#~ for file in $FILES
#~ do
    #~ base=$(basename $file .svg)
    #~ inkscape --without-gui ${OPTIONS} ${file} --export-pdf=${base}.pdf
#~ done
#~ ## END ALT_1

## BEGIN ALT_2:
##     This approach seems to be better because it starts one inkscape
##     instance for all files, but it also involves a temp file.
# Make a temp file to store batch commands.
CMDFILE=$(mktemp) || { echo "Failed to create temp file"; exit 1; }

# build up the list of commands
for file in $FILES
do
    base=$(basename $file .svg)
    echo "${file} --export-pdf=${base}.pdf" >> $CMDFILE
done

# Process commands in a batch.
DISPLAY= inkscape ${OPTIONS} --shell < $CMDFILE rm -f $CMDFILE echo ## END ALT_2 # Delete old files. # Since inkscape exits with 0 even with errors, we need to explicitly check # for conversion before deleting originals. rv=0 for file in $FILES do     base=$(basename $file .svg)     if [[ -f ${base}.pdf ]]; then         rm $file     else         echo "$file not converted." 1>&2
        rv=1
    fi
done
exit $rv

svg2pdf-d requires Inkscape, which is not really that light. But it’s arguably something that should be in your FOSS toolkit anyway.

The Inkscape conversion used in svg2pdf-d seems to work fine with the SVG files generated by Eeschema as well. I’m seeing only minor differences between the SVG→PDF versus PS→PDF conversions, and the SVG→PDF files appear to have truer color. So the SVG approach may be the better one in general.

I’ll add I have added this to the wiki after a bit more testing making significant revisions.

Getting good PDF output from KiCad in Linux

kicad-appicon-128
Update: Turns out SVG might be a better base than PostScript for this. See PDF output from KiCad in Linux from SVG.

I’ve tried to get decent PDF output from KiCad‘s Eeschema a few different ways, but what I’ve found to work most reliably is to first export to PostScript (File > Plot > Plot PostScript) and then use the ps2pdf command from ghostscript to convert to PDF. (The Arch wiki has a good writeup on ps2pdf.)

The biggest problems with this are:

  1. It’s a lot of typing to get the conversion to happen (the minutia of which you won’t have memorized).
  2. It leaves you with both a PostScript and a PDF of the document(s), one of which is likely to get out of sync with the other, which may or may not be in sync with the actual schematic, etc.

To help with this, I use the script below. I drop a copy of it into the root of my KiCad projects and edit the OPTIONS as needed for the project. Then whenever I want PDFs of my schematics, I export PostScript from Eeschema and then click on this script in my file manager. Note that running this script will destroy any *.ps files in the directory—that’s by design.

#!/bin/bash

# DESTRUCTIVELY convert all postscript files
# in working directory to PDF.
# Requires ghostscript.

# Mithat Konar 2013 [http://mithatkonar.com]

OPTIONS="-dOptimize=true -sPAPERSIZE=11x17"

FILES=$(ls -1 *.ps)

for file in $FILES
do
  ps2pdf $OPTIONS $file && rm $file
done

I’ve not tried the script on any PostScript files other than those produced by Eeschema, but I’ve got no reason to think it won’t work on other PS files as well.