COMPRESSOR FAQ:
Q: What is this thing?
A: A compressor pedal for guitar based on the original Dan Armstrong Orange Squeezertm compressor manufactured by Musitronics in the 1970s.
Above: A Pre-logo Musitronics Dan Armstrong Orange Squeezer
Q: What does it do?
A: The basic function of any compressor is to reduce the dynamic range of the signal: the level of loudness is limited and the level of softness is boosted. The result is the same sound but within a narrower dynamic range. By applying make-up gain after the signal has been compressed, the net effect is one of an apparent increase in volume (you can hear the quieter details as well as the loud ones). Also, because notes get quieter as they decay, the compressor acts to increase the volume of the signal as it decays, resulting in increased sustain. The Orange Squeezer was a bit unusual among the early guitar compressors in its make-up gain and output impedance conspired to make it an astonishingly good overdrive--whether or not compression was being added.
Q: Is this an exact clone of the Orange Squeezer?
A: The core circuit is the same topology, yes. However, the circuit-board design is our own, and there are some component differences worth mentioning:
The original Orange Squeezer used an RC4558T metal-can op-amp for its gain. This is the predecessor of the chip that would later become famous in the Tube Screamer. In the Hartman Compressor, we are using chips manufactured in the United Stated by Raytheon (date code 43rd work week of 1973). It is worth noting that by the time Musitronics got the OS into production, Raytheon, the original manufacturer of the RC4558T, had transferred rights to the line to JRC (Japan). Japanese 4558s are in abundance today, but when the Raytheon U.S. chips popped up, we grabbed 'em. If the compressor were only a clean thing, it would matter less which chip we select, but because this compressor overdrives, chip choice becomes critical to the character of the breakup. The Raytheons are indistinguishable in sound from the Japanese chips when the pedal is run clean, but overdrive without the latter's prickliness.
The Original OS also used a Germanium diode and a couple of FET transistors for its envelope-detection (the part of the circuit that 'tells' the compressor how loud you're playing and by how much to adjust its internal levels). In the originals we've seen, the Germanium diodes appear to have come from whatever sources were available at the time. Since we already had some, we're using mid-1960's manufacture 1N100 Germanium diodes for the sensor. The other aspect of the design we tweak a bit are the FETs. Because we've externalized the Ratio control, we pay attention to the 'gain' of the FETs we install in the circuit. The original OS had its Ratio set internally via trimpot at the factory, so FETs across the entire manufacturing spread could be accommodated. Externalizing this control means limiting the FETs installed to a narrower range of values to ensure the external control provides a meaningful range of adjustment to the pedal's compression. Otherwise, you could actually bias the thing clear out of its functioning range into silence!
Q: Is anything else different?
A: We mentioned the external controls already. Basically, the only other differences are the kind of things you could reasonably expect from a pedal in 2007: true-bypass (the original was always on), LED, external power, etc. We also use plated-thru hole boards instead of the single-side laminate of the originals. After modding and repairing so many old (and not-so-old) pedals with factory-cold solder joints, or whose copper traces have started to delaminate from their board, it is difficult to express in words how superior plated-thru construction can be. Because the solder bonds the component leads not just to the surface pads of the board, but to the interior walls of the holes through which those leads pass, the mechanical and electrical integrity of the assembly is greater. It makes a difference in soldering technique as well: the amount of time heat is applied to each component to install it is dramatically reduced, resulting in less thermal stress and drift.
Q: What's this "overdrive" thing you keep mentioning?
A: Frankly, it's the coolest thing about these. IMO what sets them apart from Ross etc. of the same era. The Hartman Compressor has close to 30dB of gain on board and a low-impedance output virtually identical to a Tube Screamer's. When pushed, the op-amp on board starts to soft-clip. It is a musical effect. Much as a good tube compressor's tube distortion compliments and extends its natural compression range/curve, the pedal's transition into overdrive is smooth and subtle. There are actually two forms of compression taking place when the pedal is overdriven: the envelope/feedback circuit's, and the compression that occurs as a byproduct of the op-amp clipping.
The other manner overdrive can occur is by virtue of the low output impedance. In this respect, the Hartman Compressor is deep in 'plays well with others' territory. Its output, even clean, can be set to tickle the input of a pedal or amp downstream into breakup. If you've ever used and overdrive or clean boost pedal in this way--same principle.
Q: Are there any options/mods available?
A: If you play bass we're happy to modify the tone capacitors to adjust the frequency range of the pedal downward at no extra-charge.
Q: I still have questions.....
A: Happy to help with them: mailto:info@hartmanelectronicstore.com or call (415) 652-8260. We get back to most inquiries within a day.
Copyright 2007 Hartman Electronics.