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The PWM Squeazal revisited

October
1, 2014October
1, 2014 raycharlesring
Audio Electronics, Compressors

I have enjoyed my PW modulated compressor and decided to make a feedback(the
original was feed forward) version with improved attack and shorter decay
response. The result is excellent – I love this version. I use a Zetex current
monitor IC as a full wave rectifier and this lets me really speed up the
attack. So the response is super fast, very low noise, very low distortion, and
very large dynamic range.

Schematic:

Demo: coming soon

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Updated Squezal PWM Compressor Schematic, Layout
and Demo

September
9, 2013September 13, 2013 raycharlesring
Audio Electronics, Compressors

I have completed the PWM compressor design and created a layout to fit a
1590B enclosure. The design has been simplified some and has excellent
performance both in feed forward or feedback mode. I removed the full wave
rectifier circuit. A simple compensated peak detector works fine. I also
implemented a analog switch instead of the PFET.   It provides a little
more duty cycle range and significantly more input  headroom.

The original blog post for reference:

http://circuitsalad.com/2013/08/04/coming-soon-the-pwm-squeasal

The schematic is highly annotated – the original PFET switch can be used in
place of the analog switch if desired.

Schematic Here: updated(9/12/2013)

Compressor Demos:

http://circuitsaladdotcom.files.wordpress.com/2013/09/scrapple-from-the-apple-comp-demo.mp3

Link to Layout: (Done in epresspcb single sided
thru-hole)

http://www.fileswap.com/dl/p4EePmelTS/

To scale PDF image of layout for toner transfer: (you will
still need to look at the expresspcb layout to see part designators)

http://circuitsaladdotcom.files.wordpress.com/2013/09/squeazal-single-sided.pdf

3
Comments

PWM Compressor updates

August
14, 2013 raycharlesring
Audio Electronics, Compressors

I did some experiments and found the PFET switch has a limitation of about
1.6 volts total swing it can tolerate without clipping (using a 470 ohm load)
you can get about 2 volts max with a higher  load of 4.7K or so. This is
perfectly fine for most guitar applications.For more headroom you can use a an
analog switch such as the TS12A4515. A number of manufacturers make this device.
It is a normally closed analog switch. Of course others will work also. Using
this as a switch basically makes the supply rails the headroom limit. I am going
to play with the circuit some more and come up with a board layout and will post
my final design in a few weeks.

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The PWM SQUEASAL

August
4, 2013August
5, 2013 raycharlesring
Audio Electronics, Compressors

I spent the last week working on a simple feed forward compressor using the
TL5001 pulse width modulation IC to create variable pulse with switching circuit
where signal output approximately linearly proportional to duty cycle of a
500KHz switching signal. The benefits of this include: very low noise, low
distortion and lots of attack/decay flexibilty. I had some problems with noise
early on but now the design shows great promise. It can work either in feed
forward mode or feedback mode and has tons of possibilities for modification and
refinement. Hopefully someone else can play with it and come up with some
improvements. It is super quiet because no gain is changed of any amp stage –
just the signal level itself. Other switching elements are possible, but the
PFET works very well.

Schematic:

Here is an alternate version which I may like a little better where
the compression ratio is controlled by simply bypassing the switch:

Video Demo:

PCB layout coming soon:

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a comment

Some Possible Value Mods for the Simple
Opto Compressor

March
30, 2013August
6, 2013 raycharlesring
Audio Electronics, Compressors

There is another builder/designer Jon who has experimented with a number of
my compressor circuits. He recommends a lower value for R1 of around 22k instead
of the 100k in the schematic. This will lower the max compression a little,
but will help with stray capacitance roll-off of high end.  It should work
fine.  It will load the guitar pickups a little with heavy
compression. Also the diode peak detector is biased in a more linear range by
changing R8 and R6  from 470k to 47k and C7 from 1uF to 10uF. I think these
values will work a little better.

Over my choices are:  100K for R1,  47K for R6 and 10uF for
C7

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The OPTO compressor revisited simple and works well

March
2, 2013August
6, 2013 raycharlesring
Audio Electronics, Compressors

I have been playing with all sorts compressor ideas and the circuit below
is about the simplest thing I have come up with that works well. It uses
just a handful of parts and needs no critical adjustments. It has fast attack
and slow decay – which I find the most useful  for guitar.

here is the schematic:

http://circuitsaladdotcom.files.wordpress.com/2013/03/simple-opto-comp1.gif

Additional notes here:

http://circuitsalad.com/2013/03/30/some-possible-value-mods-for-the-simple-opto-compressor/

link to ExpressPCB layout:

http://www.fileswap.com/dl/PFYBP3Gwp4/

It utilizes a number of features from my other designs and I have also
integrated some suggestions from other designers (like using a
darlington for the amp stage).

This design has the folowing features:

a  H11F1m OPTO FET variable resistor to control gain.

a darlington transistor as a shunt/shunt feedback amplifier. The biasing and
feedback (from the collector to base) is critical to the design. The reason
is that it keeps the voltage across the OPTO FET very low so as to keep it’s
behavior linear. With out this feedback – there can be distortion.

LM358 beef stew op amp as a compensated diode peak detector and as a current
mode amplifier the drive the H11F1m OPTO FET variable resistor.

The LED indicator is tied to the compression feedback loop and indicates
compression level with variable brightness.

Demo  comming soon.

2
Comments

Simple Mosfet Compressor MODs

November
27, 2012March
22, 2013 raycharlesring
Audio Electronics, Compressors

Another designer tried my mosfet compressor using a darlington pair as
the gain stage  device Q1. He described some improvements in performance –
so I tried this as well. I love it! Using a darlington such as a MPSA14 (or a
homemade one) is a drop in replacement for the MOSFET Q1. It gives a little
more gain and reduces noise in the control loop slightly (allowing more
freedom in changing and or eliminating C7, c8, C9). I definitely
can reccomend it.

New Schematic:

http://circuitsaladdotcom.files.wordpress.com/2012/11/mosfet-compressor1.gif

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