Official Site of Pritchard Amps

What is New About Pritchard Amps

Pritchard Amps present a super-new experience in playing by providing an awesome palette of warm, full-bodied, thick, cut-through alive tones combined with a very practical versatility. Pritchard amplifiers have a retro look that surrounds great, new artistic designs in both acoustics and electronics. The new patented and proprietary features are described briefly below in four groups: Appearance, Tone, Control, and Quality. Next are technical discussions of some of these points.

APPEARANCE

Pritchard Amps have also created a new, patented style of cabinets that give them a unique appearance and functionality. A very retro looking grill protects and hides the speakers. The amplifier is positioned down the back with the knobs on the top so that they can be seen and adjusted easily. Pritchard products stand out.

TONE, TOUCH, & FEEL

Pritchard's 15 years of amplifier research has brought the linguistically blurry concepts of amplifier behavior into focus. This process has been made much more difficult by the lack of applicable engineering theory. Tone, touch and feel are quickly dismissed by the engineering community. The following features contribute to the wonderful character of Pritchard Amps.

Pritchard's patents emphasize the output stage because the great character of vintage amplifiers comes predominately from the output stage. There are two reasons for this: First and contrary to popular sales pitches, the output stage is supplies most of the tone because it handles bigger signals, which are much more subject to amplifier characteristics. Second, the output stage is much more complicated than preamplifier stages and present players with much more diverse tonal embellishments.
Pritchard amplifiers can transition the region between clean and dirty that many amps find difficult if not impossible. With a Pritchard amp you can find that there is magic in this land. Here you can trade picking strength for harmonic character. Light picking is clean, moderate picking is crunchy, and heavy picking is dirty. This vintage feature has been ignored by many artists because most amplifiers manufactured today simply sound horrible in this region. Pritchard amplifiers can expand your artistic horizons.
Pritchard amps are quite fat both in harmonic character and in some voices. The harmonic character is created in the output stage by patented circuitry.
Pritchard amps exaggerate power supply sag to produce much higher attack powers and a "cleaner" distortion. The high attack powers gives Pritchard amps added power to cut through.
Pritchard found that some aspects of modern amplifiers are not desirable. Pritchard amps uses the vintage concept of a hardworking preamplifier stage to drive the output stage. In contrast the standard phase splitter is so hi-fi that it adds nothing to the musical experience.
The Pritchard amplifier preamp stages uniquely exceed the musical nature of the Grid-Plate Action of the very popular 12AX7. The 12AX7 was successfully engineered to engineering concepts of amplification - high gain and as linear as possible. In contrast, the Grid-Plate Action of the Pritchard preamplifiers has been designed for the artistic sensibilities of musicians. It adds expression and character to both clean and dirty sounds. Pritchard amplifiers have a high GPA.
Part of the GPA phenomena is grid conduction. This is important in over driven amplifiers because grid current via bias shifts changes the harmonic structure and that makes the amp sound differently as the note dies out.
The Pritchard amplifier preamp is mated to the guitar to optimize the guitar character.
Pritchard amps amplifies this picking character by making the amp more responsive to heavy picking than to light picking. When you really want to make a point, Pritchard amps help you.
Pritchard amps also have all of the sag characteristics, both in power and gain. When a note is picked the attack comes through at a higher gain and higher power than the middle and the end of the note.
The original Pritchard amplifiers used the vintage design philosophy exclusively, however, more recent additions, the Blood Dagger and the Gold Estoc, incorporate more modern boutique flavors of voicing. Additionally, the Gold Estoc has a post-distortion volume control to work with the Watts Knob ™ to lower the distroted volume below the clean level or to mix preamplifier and output stage distortion.

AMPLIFIER CONTROL

Pritchard amplifiers have the patented Watts Knob™ to control the output power of the amplifier. While this has the same basic function as the Master Volume Control, it maintains tone at low levels. This important for gigging in small rooms.
Pritchard amplifiers also have a patent pending speaker attenuator that optionally lets you practice or perform screaming leads at conversational levels. With this speaker attenuator, you can play with your acoustic buddies without drowning them out.
The Boost and Channel Switches also make changes to the output stage to make the amplifier sound differently. This gives the player more sounds to work with.
When the Boost and Channel Switching select nominal clean tones, the Watts Knob™ circuitry have higher clipping levels so that clean passages can be as loud as distorted passages when the Watts Knob™ is turned down.
The Gold Estoc has a post-distortion volume control to work with the Watts Knob ™ to lower the distroted volume below the clean level or to mix preamplifier and output stage distortio
Pritchard amps have Voice Knob™ that give Pritchard amps a wide variety of character from a cool clean tone A to a lead tone L:

A - Airy Art - a cool clean tone inspired by an acoustic guitar.

S - Smooth Solo - a clean-to-crunch solo voice with bass and treble emphasis..

F - Famous Flat - the standard American guitar amp tone.

M - Moderately bright - inspired by one of the British guitar amps.

V - Very bright - inspired by another British guitar amps.

L - Liquid Lead - a Pritchard combination of American and British tones.
In addition there are four other voices that replace some of the above

B - Bass boost - a bass boosted tone for mellow ballads and standard jazz.

P - Precision / Tele - a precision bass / Tele inspired tone that emphasizes upper bass and treble .

H - Heavy Dirt - a high bass notch with substantial treble emphasis

N - Nasty Notch - a low mid notch with treble emphasis

SPEAKER CABINETS

Pritchard has developed a new speaker cabinet that produces a tight bottom. This patented new speaker cabinet philosophy compliments the closed back cabinet sound. Instead of attempting to hide the speaker resonance in the reduced bass response of open back cabinets or reducing it with a port, Pritchard's Tunnel Back™ cabinets moves the resonant frequency below the lowest note. The tight bottom results from not energizing the speaker resonance.
The tunnel acts as an acoustic crossover between the front and the back. The bass from the front is reduced and redirected out of the back, similarly the treble from the back is reduced and redirected out the front. Although this presents miking problems, as noted elsewhere, it does give small boxes a very big sound - very big, tight sound..
Pritchard Amps speaker systems sound smoother for two reasons, because the speaker resonance is moved below the range of the instrument and because Pritchard amps may also use a notch filter to reduce spurious speaker resonances.

DIRECTS

Pritchard amplifiers also feature an XLR equalized direct for your sound system. This direct works with the speaker in all modes: Gig, Practice, or not connected.
Pritchard amplifiers also feature a TRS phone jack for connecting to secondary amplifiers that drive instrument speaker systems. Similarly, this jack operates in all modes.
Pritchard amplifiers also have an alternate XLR input for use with a microphone - quite useful for harp players.

QUALITY & RELIABILITY

Pritchard amplifiers are tonally reliable because the production tolerance of XGPA technology is very tight, far tighter than vacuum tubes or FET's. The device to device variation in harmonic structures varied only about 1 dB in the low order harmonics and somewhat more in the much smaller high order harmonics.
For tonal realiability, Pritchard amplifiers use 1% metal film resistors in all low power and signal applications.
For tonal reliability, Pritchard amplifiers use mostly 5% and some 10 % molded polyester capacitors as much as possible, leaving ceramics for only the smaller values and aluminum electrolytics for the larger values.
The circuit layout and lead dress is designed to minimize cross talk. This allows Pritchard Amps to produce the highest gain amplifier in a smaller package.
The output stage protects itself from excessive temperatures, currrents, and voltages - it will survive a short circuit.
The spring reverb is magnetically and acoustically shielded to eliminate hum and feedback respectively. This lets the reverb side chain have more bass and produce. All you can hear is the high frequency noise of high-gain electronics required by vintage spring reverbs.
Pritchard amplifiers use discrete dynamic noise filtering to reduce and minimize the output noise in high gain modes when the guitar is producing very little output. The noise filtering is usually only applied to the dirty channel or the high boost modes.
The main effects Send and Return are bridged with a high resistance so that the amplifier will work even though the Return jack switching does not make contact.
The Pritchard amplifier switches Boost and between channels with more reliable discrete J-FETs (junction field effect transistors) instead of relays. The J-FETs are driven by a proprietary switching circuit that lets you change channels at either the amplifier or the foot switch.
The amplifier chassis is a thick .125 inch aircraft aluminum sheet.
The cabinet is 12 millimeter (nearly 1/2 inch) thick multi-ply Baltic Birch.
The cabinet joinery uses box (finger) joints and slots.
The cabinet is covered with high quality Tolex and glued with wide temperature sprayed PUR hot melt.

TECH TALK

The following sections discuss various aspects of Pritchard amplifiers and amplifiers in general. Pritchard amplifiers are superior because their design pays detailed attention to amplifier behavior and musicians' desires.

Watts Knob™ versus MASTER VOLUME CONTROL

Pritchard amplifiers have the patented Watts Knob™ instead of a master volume control because the master volume control, when turned down, concentrates the amplifier's tone production in the stages prior to that control. Turning down the master volume control reduces if not eliminates important amplifier effects, power supply sag (a sign of life in the amplifier) and ripple fat. Reducing a tube amplifier's power by a mere 12 db changes the usual class AB operation to Class A. The power supply consequently sees a constant load and has no sag. The ripple fat is reduced by both the reduced ripple (from reduced load and reduced signal level).
The Watts Knob ™ combined with the post distortion volume control in Gold Estoc provides the unique ability to have a mixture of preamp and output stage distortion at lower volumes.
Although not generally used for cost reasons, a better tube amplifier master volume control uses a dual potentiometer between the phase splitter and the output tubes. This potentiometer lowers the gain of the output stage, raises the output impedance, and changes the interaction of the speaker with the amplifier.
On the other hand, the Watts Knob™ and related circuitry works to keep the amplifier behavior constant in spite of turned down. The Watts Knob™ is a superior solution because it does many things simultaneously as it turned down:
- Lowers the output stage clipping or distortion level to reduce the maximum power as needed in smaller venues.
- Lowers the output stage gain to keep the clipping level constant relative to the input so that the distortion levels do not change as the Watts Knob™ is adjusted..
- Increases the output stage feedback to keep the output impedance constant and consequently preserves the amplifier-speaker interactions.
- Increases the relative level of ripple and harmonic creation to preserve the same fat, feel, and tonal characteristics to maintain tone as much as possible as the Watts Knob™ is adjusted.

HARMONICS PRIOR TO CLIPPING

Pritchard amplifiers use many non-linear circuits to produce harmonics prior to clipping. These circuits are in the production of the eXaggerated Grid-Plate Action (XGPA) in both the preamplifier and output stages. The preamplifierstages use a patented non-linear circuit to exaggerate the plate characteristics of the ever popular 12AX7 and to produce the "soft-clip" commonly only attributed to vacuum tubes. The output stage uses a patented multiplying or modulator circuit to produce expansive harmonics and ripple fat as well as gain compression.

When Pritchard amplifiers are measured in the way Russell Hamm proposed in his famous paper "Tubes Versus Transistors - Is There An Audible Difference?" (Journal of the Audio Engineering Society, May 1972), they show increasing distortion over a wider range prior to clipping and then into clipping. Amplifiers that do not produce harmonics prior to clipping distort too fast.

EXPANSIVE versus COMPRESSIVE HARMONICS & CLASS A

Pritchard amplifiers incorporate expansive harmonics to counter, at least in part, the compressive, "blanketing" harmonics of clipping distortion and to help players extend their picking hand expression. Expansiveharmonics are found in Class AB and Class B output stages and far less in Class A stages. As a consequence they were not found and described by Russell Hamm in his clipping study of generally single-ended microphone preamplifiers. Russell Hamm described the third harmonic as blanketing perhaps because these microphone preamplifiers are not like power amplifiers. Quite unlike the compressive clipping harmonics the expansive harmonics are quite alive and punchy.

The exaggerated expansive harmonics help Pritchard amps cut through. By not being so blanketed they stand out.

"AMPLIFIER SPEED"

Pritchard amplifiers have circuitry that controls the player's impression of the amplifier's speed. Early amplifier prototypes were judged to be too fast. It was a blessing that a later prototype was judged to be too slow. A slight change in the patented output circuit brought this character in line. Pritchard amplifiers can be factory modified to the player's speed taste.

EXAGGERATED GRID-PLATE ACTION of PRITCHARD PREAMP STAGES

The eXaggerated Grid-Plate Action (XGPA) of Pritchard preamplifier stages is greater than found in the ubiquitous 12AX7. This is evident in the plate curves. The Pritchard plate curves have greater curvature and more unequal spacing along typical load lines. As a result the Pritchard preamplifier stages sound fuller, have more body, and have sparkling highs..

Do Pritchard Amps Sonically Die?

Pritchard amps do not sonically die in a gig. They are not covered up by bands. They cut through. Pritchard amps have tonally directed sound. Instead of splattering the amps power here, there, and everywhere, Pritchard amps direct their power to the notes being played and to their harmonics. You can hear all of the notes embellished to greater grandeur. The natural “blanketing” effect of clipping is offset by an exaggeration of the expansive life harmonics. The fantastic transient powers of Pritchard amps produce a psycho-acoustic clue. It warns your ears that something is coming. And then you hear the warm, fat, full-bodied notes. Strictly amazing.

Pritchard watts are more powerful than regular amp watts! It is true! It is true because Pritchard Amps rate their watts honestly. The 60-watts is before clipping – not after. It is also true because Pritchard Amps have a huge attack power capability – an awesome 180 estimated watts in a dirty transient. Pritchard amps have no trouble hanging with a 100-watt amp or with its Watts Knob™ turned down, with a 10-watt amp.