Diamond - Compressor

[This post contains information on the Diamond Compressor & Fred Briggs Diamante]

Diamond make some real high-end stuff; the Memory Lane Delay, Halo Chorus and J-Drive are all top level (expensive!) pedals. My overall choice from the Diamond pedal range is the Diamond Compressor though. It gives a nice compression effect, not the super transparent kind, you can feel the squish but it's not over powering and the "tilt" EQ is a nice addition too allowing you to gently shape your overall tone. Ok, so it's a great sounding compressor and has loads of great features, but my favourite bit; the LED that changes colour with the compression level! Ha.

Here's a description from the Diamond website;

"Recording studios often use rackmount 'vocal channels' - a mic preamp, compressor, and EQ all in one unit as a front end for vocal recording.
The Diamond Compressor is our take on a 'guitar channel' - a dynamics and tone shaping tool for live and studio use - with low-noise, ultra-linear signal buffering, smooth opto-based compression, and a versatile 'tilt' EQ that musically shifts overall frequency balance. All in a user-friendly 3-control package - just Comp, EQ and Volume.

Features:

- Vactrol opto-isolator variable resistance path as used in high-end studio compressors for smooth attack and decay characteristics while preserving initial signal transients.

- Premium audio components, including 2% polypropylene capacitors,1% metal film resistors and a pro audio grade  opamp (our signal path opamp alone costs 8 to 10 times
what the industry norm uses).
- Post-compressor 'tilt' EQ provides a very musical tailoring of frequency response - seamlessly transition from a darker jazz voicing to a brighter jangle, with flat frequency response at the center detent position.
- Double filtering stage in side chain to eliminate low frequency modulation while preserving fast compression response.
- Dual AC capacitive coupling paths for improved transient response.

- Bi-color LED provides visual indication of depth of compression.

- True bypass signal path.

- Battery or standard negative tip 9V DC adapter operation, can be powered from 9 to 24 V negative tip."

Here's the ProGuitarShop video;

Now here's a gutshot (also from the Diamond website);

And, thanks to some incredible work by WhiteKeyHole, a schematic;

So, interesting parts of the design - the Tilt EQ is taken from an early 70s stereo preamp designed by Quad Ltd, it gently tilts the eq around 900Hz simultaneously boosting treble and cutting bass and vice versa (mid position is a flat response). It's a great tool for smoothing out EQ ranges and matching various pedals up to one another without sounding too drastic and overpowering other pedal's tonal characteristics. Another addition not normally seen in stompbox design is the current source that has been added to the emitter follower buffer stages. The addition of the current source to these stages reduces the THD (Total Harmonic Distortion) from 0.01% to 0.001% - not something you're really going to hear in a guitar orientated world! Those paralleled capacitors too - not really necessary!

Here's a closer look at the Tilt control schematic;

And a graph of the EQ response curve (note the phase inversion of the signal at extreme settings of the control);

After looking at the Tilt EQ schematic you'll notice that the bypass resistors R13 & R14 have been left in the Diamond design even though they are not needed, you could in fact remove them and not notice a difference.

Parts List;

Capacitors 

NOTE - C33 on the schematic is C32 on this parts list.
Caps 2u2 and higher are electrolytic. C22/23/30/31/32 are ceramic, all other film
C1 47u
C2 47u
C3 47u
C4 5n6
C5 5n6
C6 330n
C7 100n
C8 100n
C9 100p
C10 820p
C11 100p
C12 820p
C13 1u
C14 100p
C15 330n
C16 820p
C17 820p
C18 100n
C19 10n
C20 10n
C21 2u2
C22 100n
C23 100n
C24 820p
C25 3n3
C26 15n
C27 10n
C28 4u7
C29 3n3
C30 100n
C31 100n
C32 100n

Resistors
All metal film 1% except R1 which is carbon film 5%
R1 100R
R2 10K
R3 10K
R4 100R
R5 15K
R6 3.32K
R7 22.1K
R9 15K
R10 47.5K
R11 47.5K
R12 47.5K
R13 47.5K
R15 1M
R16 475R
R17 475K
R18 475K
R19 3.32K
R20 6.41K
R22 100R
R23 475K
R24 22.1K
R25 100K
R26 1K
R27 3.32K
R28 475R
R29 221K
R30 475K
R31 100K
R32 221K
R33 100K
R34 475K
R35 221K
R36 10K
R37 1.5K
R38 10K
R39 Jumper
R40 10K


Transistors are standard NPN/PNP medium gain
LED is a Tri-colour type.

For those after a layout to build this thing check out Harald Sabro's great layout here; http://www.sabrotone.com/?attachment_id=2157

Here's the freestompboxes.org forum topic; http://freestompboxes.org/viewtopic.php?f=7&t=850

Now, I previously mentioned that the Diamond has many superfluous parts and circuit structures so I decided to simplify it right down. Here's what I came up with;

Basically it's the same circuit as the Diamond just as simple as it can be; the buffers have been removed or simplified and the EQ section has been removed completely leaving controls only for "Compression" and "Volume".

Rothwell - Love Squeeze Compressor

"Designed and Built in Britain"; the mark of quality and the Rothwell Love Squeeze doesn't disappoint - it's a great hand built compressor pedal with an interesting design.

Here's the description from the Rothwell website;

"The Love Squeeze is a compressor designed simply to sound right with guitars, without any bizarre “pumping” effects and without any noise.

This has been achieved by designing a circuit from scratch instead of adopting the more common approach of using an operational transconductance amplifier (for tech heads, it’s usually the CA3080 chip) or simply copying an existing design (like some American boutique makers have done) and gives the Love Squeeze a sound of its own. Low level signals can be raised by as much as 20dB without boosting high level signals, so when used in front of distortion - either in a pedal or an amp - leads lines can be fattened up without chords sending the distortion into mush.

When used with a clean sound the Love Squeeze can be set to just take off the ice-pick attack of single coil pickups for a tone a little easier on the ear. Like reverb (when used sensibly), this is a subtle effect which can go almost unnoticed until it is switched off - then you wonder how you could live without it."

Here's the ProGuitarShop demo of the Rothwell Love Squeeze in action;

And another (with the Rothwell and Keeley Compressor);

Now, check out some gut shots - notice the high quality PCBs, neat wiring and general high standard of construction throughout :-) An all round decent piece of work!

Here's a schematic drawn up by ever productive WhiteKeyHole;

It's an interesting concept and a nice simple design. The use of a FET as a voltage controlled resistor makes the attack nice and quick and cuts out the cost of an expensive LDR. If I were to compare the tone of this thing to anything else out there it would be the old traditional Orange Squeezer - it's subtle and transparent compression, it doesn't pump and breath a'la OTA designs or higher ratio optical compressors. Overall I'd say it's a very nice little "tone tidier" compressor.

For those who want to build this thing here's a vero layout from the fantastic Harald Sabro; http://www.sabrotone.com/wp-content/uploads/2011/09/LoveSqueeze.gif

TC Electronics - Sustain + Parametric Equalizer

This is a strange one, a super rare beast, but I had the opportunity to play with one the other day. The controls are a little tweaky and it's also sensitive to the position it's placed in the signal chain but when you get it right! Wooo, there's some great tones here; super long sustain and really punchy rhythm tones and with the parametric EQ you can really pick out certain frequencies that you want to accentuate or remove.

Personally the compression/sustain/noise gate part of this pedal is the one that I like, the parametric eq can be covered by other pedals but the sustain/noise gate section really is something unique. Flicking the distortion switch on gives you some nice clipped tones that add a nice smoothness to your tone.

There is very little info around the internet for these things and even TC Electronics struggle to provide info. I did discover that David Gilmour used a couple in his rig in the late 1980s though; http://www.gilmourish.com/?page_id=2111

Ok, so here's the description from the TC Electronics website (This description was in place for the reissue version that is also now discontinued!);

"One of the true grails of vintage effects pedals. This one really enhances your tone. Go from subtle compression to extreme sustaining effects at the tweak of a knob. This sustainer will prolong life of even your weakest tone otherwise destined for premature death.

The Classic Sustainer + Parametric EQ gives you studio quality compression in a pedal. Crank it to the extreme and it’ll give your sound that percussive “thud” brilliant for funk or country. And with its parametric EQ you’re in full control of which frequencies to target."

After even more searching I uncovered some gutshots of the pedal, check out the goofy 1980s PCB design;

After some more exhaustive searching and a trip to the WayBackMachine I discovered this;

Yes! A schematic file for the pedal. I'm going to have to study this one for a while until I really understand what is actually going on fully in the noise gate/compression section of the pedal but it's a pretty interesting design incorporating both OTAs *and* op amps in various feedback loop configurations. I'm probably going to have a play around with this design and see if I can distil the compression section into a little project for people to build up.

Pigtronix - Philosophers Tone Compressor (Germanium Gold)

I love compressors. I love them more than any other guitar effect - and there's a reason; they are the glue that sticks a great performance together. Unless you're Jimi Hendrix or Eric Clapton a compressor *will* improve your tone and help you sit in a band mix much better.

The Pigtronix Philosophers Tone has been making waves for a while now and I thought it was time to get it placed up on the blog.

Here's the description from the Pigtronix website regarding the regular version of the Philosophers Tone;

"The Pigtronix Philosopher’s Tone is a state-of-the-art analog compressor / sustainer, providing endless clean sustain. With variable Sustain, Blend and Treble controls, the Philosopher’s Tone offers a huge range of compression sounds for the discerning musician. The Philosopher’s Tone also contains a harmonic distortion for clean or dirty compression sounds and any mixture of the two. While the Philosopher’s Tone rocks on its own, it is designed to play well with other dirt pedals in order to create your ultimate distortion tone that sustains forever.

Pigtronix Philosopher’s Tone is unlike the common compressor. This pedal has more sustain and less noise. The dynamic range, touch sensitivity, overall transparency and outright sustain of the Philosopher’s Tone is un-paralleled in the crowded world of compressor pedals.

Practitioners of the mystical and ancient art of alchemy long sought an element called the Philosopher’s Stone, believing that, if found, it could turn lead into gold and bestow immortality upon the man who wielded it. For such a tiny pedal to create so much sustain, this device represents a musical equivalent to this mythical substance in the world of guitar pedals."

And to get an idea of how the Philosophers Tone sounds here's the ProGuitarShop demo video for you;

Now, onto the guts of this thing. Thanks for these photos goes to jwpartain1 of the freestompboxes.org forum;

From these gutshots and the attached information Mystic Whiskey managed to draw up a schematic and verify a build against an original Philosophers Tone Gold Germanium. Here's the scheme for you;

Let's have a look at a few of the different sections - the "Grit" control blends in either a clipped or clean version of the compressed signal. The "Blend" control blends between the unaffected signal and the compressed/clipped signal. The "Treble" control is nothing special and is set up as a simple treble cut. It's a decent design and really works for a nice overdriven yet compressed tone.

For those of you brave enough to take it on - here's a vero layout for the Philosophers Tone Gold;

For reference here's the freestompboxes.org forum topic; http://freestompboxes.org/viewtopic.php?f=7&t=11954

Bearfoot FX - Pale Green Compressor

The Bearfoot FX Pale Green compressor - twin brother of the BJFe Pale Green compressor and close cousin of the Mad Professor Forest Green Compressor (Which is one of my favourite compression pedals!). Here's the description from the Bearfoot FX website:

"The BearFoot Pale Green Compressor is an exact replica of the BJFe Pale Green Compressor - the compressor for people who hate compressors !

The PGC really shines in a live situation with a band where the heavier handed compressors, that sound good at home in a room, often sound thick and lifeless against other real instuments....

This is no squish machine or infinite artificial sustainer ... The PGC is already famous for its nearly transparent compression and dead quiet operation. You will want to leave it on all the time... You will also wonder if its on at all ~ until you turn it off to make sure and then turn it back on as quickly as possible.

The middle knob fine tunes the EQ with a stacked pot that adjusts the EQ both pre and post compression. The zero point is at 'noon' ~ to the left it adjusts the EQ to that of the classic Dyna/Ross comps and to the right it allows an increase in treble and sparkle without adding noise or hiss. And with the comp knob off it is a booster/enhancer/EQ. Especially tasty into the Honey Bee and Model H.

Voltage range 8~18v."

And here's a demo video for you;

Well here's some Pale Green guts;

Looking at the guts it becomes clear that the Pale Green Compressor is a simlification of the Mad Professor Forest Green design;

So - the long and short of it? If you want a BJF designed compressor - build yourself a Mad Professor Forest Green Compressor ;-)

Here's the Bearfoot FX Pale Green Compressor freestompboxes.org forum topic; http://freestompboxes.org/viewtopic.php?f=7&t=16698

Toadworks - Mr Squishy Compressor

I'm a fan of compressors, in my opinion they are the unsung heroes of great guitar tone - they level it all out and give you tone a consistency and sustain that would be impossible to achieve without a compressor. Toadworks have been around for a while now and offer their own compressor the "Mr Squishy". Here's a description from the Toadworks Website:

"ToadWorks Mr. Squishy is an analog compressor pedal that combines purity of tone with tight, punchy squeeze-on-demand. Mr. Squishy has been tested with a wide range of amplifiers, including tube, solid state and hybrid, and it delivers the goods every time.

ToadWorks Mr. Squishy provides great compression without oppression, remaining transparent enough that you never lose the original tonal qualities that made you love your axe in the first place. For years, guitarists have sought a natural sounding compression that did not diminish their tone, and ToadWorks has delivered.

Don't you just hate when you kick on the compressor, and your guitar sound changes? Compressors aren't supposed to do that. ToadWorks Mr. Squishy is the anti-compressor - your tone stays crystal clear and unblemished.

Mr. Squishy provides plenty of squish where you want it, and none where you don't. The Gain, Squish & Level controls allow you to compensate for all manner of differences between guitars, pickup types, etc. Mr. Squishy has a nice, tight attack, and a long, slow release, giving you the best of both worlds. Mr. Squishy won't distort unless you want it to; there is no buffer, the Op-Amp can be overdriven, but that's what the Gain control is for. And when you listen to the sound clips, notice that the Level is always around six... want to guess what happens if you turn off the Squish, crank the Gain, and set the Level at 10? A very serious clean boost that will overdrive your amp's input. Yes, that's right - Mr. Squishy can double as perfect clean boost, with power to spare."

And here's a demo of the Mr Squishy in action:

Well, thanks to phibes and aegert over at freestompboxes.org the Mr Squishy has been gutted and here's the schematic: http://www.box.com/s/194dc32665d393373c68

As you can see the circuit is a tuned variation of the original Dan Armstrong "Orange Squeezer" opamp/jfet based compressor:

This type of compressor is a good option if you are looking for a more transparent compression with a less evident "squish" on the tone (a quick attack/release time). You can get some distortion caused by overloading the input and forcing the attenuation jfet to clip but overall this compressor design works well for it's simplicity.

For further reading here's the freestompboxes.org forum topic: http://freestompboxes.org/viewtopic.php?f=7&t=16760

Demeter - Compulator

[This post also contains info on the Bajaman Optical Limiter]

The Demeter Compulator has been a popular compressor for a while now. It's got a great level of transparent compression available, is built like and tank and uses decent quality components.

Here's the description from the Demeter website:

"The sound of classic studio optical compression of the 60's and 70's at your feet! The first compressor pedal not to suck the life out of your tone.

Operation is fairly straightforward. There are two inputs on the front side of the unit: a 1/4" input jack on the right and a 1/4" output jack on the left with a battery-ground switch on the input jack.

There are two controls on the unit: compress and volume, plus a foot switch to bypass the effect, and an LED to indicate effect operation. On the side there is a trim pot to set the overall gain of the unit.

Compress affects the amount of gain reduction (compression) of the input signal. Turning this clock wise will give you up to 30dB of gain reduction (depending on input gain). Please note that the Compulators max gain is 26dB (see Trim Pot) so in some circumstances if your instrument is very hot you could achieve less than unity gain if you turn up the compress knob too much.

Volume increases and decreases the output volume of the Compulator. Use this for level matching between the effected and unaffected signal.

Trim pot sets the gain of the compressor's pre-amplifier. If distortion occurs turn this down until the signal is clean. The unit is set at the factory at 20dB of gain which is perfect for most instruments. If you have weaker pickups or want to push the envelope turn it up to its max gain 26dB."

And here's a demo video of the Compulator in action:

Works well doesn't it. Well, I've built a couple of these and I love the tone they provide. I can fully recommend the circuit for anyone who needs a quick and easy compressor. The DIY project has been available for a few years now and was provided by the great Bajaman over at freestompboxes.org, here is the schematic and PCB layout files:

PCB Layout:

PCB Transfer:

So there you go - one of the best compressor pedals out there. I will say many people have asked about the VTL5C10; you've got to use it or at least construct your own optocoupler that matches it's specs.

Bajaman liked the circuit so much he based his own design around it with the Bajaman Optical Limiter, here's the schematic - LA2A style optical limiter:

Here's what he says regarding the optocoupler: "The LEDs used are both standard yellow 5 mm types. the LDR has a resistance of about 90 ohms when exposed to the light - sorry I cannot give you the exact number for this part but i found by purchasing from a number of suppliers that there are two common types in this size (5mm circular with top and bottom sliced off). You can test with a multimeter across the terminals - expose it to sunlight and observe the reading - if it is 350 ohms or higher, then you have the wrong type for this project - it should read around 90 ohms."

And a PCB layout:

And a PCB Transfer:

Limiters and compressor, although similar, do not function in the same manner. A limiter will only limit the peak of the wave and won't increase sustain as a compressor will. This is due to the way the envelope follower is configured. Notice that with the compressor the envelope is taken from the end of the circuit (A feedback config) whereas with the limiter the signal is taken from in front of the attenuation circuit (A feed-forward config). This difference may seem trivial but you need to take into account that the feedback config is effectively reacting to it's own changes. I.e - the envelope follower detects a strong sound wave, it decreases gain in the circuit, as the wave strength falls over time the envelope follower detects this and therefore forces the gain in the circuit to rise, the envelope follower then detects this rise and forces the gain back down and so on and so forth. It is this "feedback" action that gives the illusion of increased natural sustain. In a limiter there is no reaction or feedback effect, the circuit simply sees the strong first peak of the wave and attenuates, once the signal drops below the trigger voltage for attenuation to occur the envelope follower is essentially off. Therefore with the limiter you don't get the pseudo increase in sustain.

For reference here's the freestompboxes.org forum topic: http://freestompboxes.org/viewtopic.php?f=7&t=317

Mad Professor - Forest Green Compressor

The Mad Professor Forest Green Compressor. Anyone who knows me knows I love a good compressor and the Mad Professor Forest Green Compressor is just that - a damn good compressor. It's got a great tone to it and the tone control and compressor / sustain switch adds versatility too. Here's the description from the Mad Professor website:

"FOREST GREEN COMPRESSOR (FGC) is designed to meet the highest standards of guitar and bass compression.

There is extremely low noise throughout the range and a high overload margin, which allows also a wide dynamic input range at minimum distortion and noise.

FGC is equipped with a special tone control to fine-tune the compressed sound for most transparent tone and effect.

The pedal has a switchable compressor and sustainer mode.
In Sustain mode you can get a very dynamic, touch sensitive tone with a long sustain. Here the attack is not lost, making the pedal suit-able even for blues players and works great with slide playing.

Controls

LEVEL: in Compressor mode adjusts the overal volume and the FGC can be used even as a booster. In Sustain mode the Level no longer adjusts total output but the level of the sustained part.

COMPR.: Sets the amount of compression and sustain. Lower settings give mostly peak limiting, higher settings more compression and less touch sensitive response. At maximum the output will be heavily compressed, while still retaining clarity at almost infinite sustain.
A good starting point for this control is a bit below centre (ten o’clock) with most guitars.

TONE : Tone control on FGC is designed to fine-tune the compressed sound for most transparent tone and effect: Adjust CCW for full range compression and set at noon for tighter sound with a little less bottom end and turn fully CW to slightly reduce upper treble.

COMPRESSOR/SUSTAIN SWITCH: Attack and decay times are carefully fine-tuned and internally set for swift attack and slow decay. Sustain/Compression switch set for Sustain the attack is preserved allowing dynamic touch and ease of playing as the FGC amplifies the decay and weaker parts.
For standard compression set mode switch to Compressor."

Here's the ProGuitarShop demo video:

Well, yet again the Freestompbox forumites have pulled one apart and here's what they found (thanks to anders-dc for the pictures):

Here's the schematic drawn by WhiteKeyHole (he does some great work!):

Looks like it's basic building block is the old Ibanez CP-830 (How cool does this thing look!):

There isn't currently any verified layouts (that I know of) but here's a vero from ShortScaleMike that seems correct (report back if you build it!):

Here's the freestompboxes.org forum thread for reference: http://www.freestompboxes.org/viewtopic.php?f=7&t=10725