HegemanHAPI 2usedHegeman HAPI 2 Preamplifier -- Excellent ConditionFor sale is one HAPI 2 PreamplifierThe HAPI 2 Preamplifier is audio legend Stewart Hegeman's final pre-amplifier design, and the ultimate expression of his audio design philosophy. Hailed by audio ...475.00

Hegeman HAPI 2 Preamplifier -- Excellent Condition

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Condition
8/10
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Ships fromLake Mary, FL, 32746-3711
Ships toUnited States
Package dimensions30.0" × 19.0" × 7.0" (15.0 lbs.)
Shipping carriersUSPS, UPS or FedEx
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HAPI 2 Preamplifier




The HAPI 2 Preamplifier is audio legend Stewart Hegeman's final pre-amplifier design, and the ultimate expression of his audio design philosophy. Hailed by audio critics -- including those at The Absolute Sound -- as a miracle in its time, this preamplifier is still widely sought for its exceptional phono stage and natural, transparent sound -- a preamplifier so neutral, you can't tell it's there. "The closest thing to a straight wire with gain."   

Design Description

Written by Stewart Hegeman

"The input stage of the HAPI 2 is a fixed gain, low noise amplifier, having a flat frequency response and high input impedance. This allows the input impedance to be defined solely by the low noise 47kohm input resistor. Audio band noise caused by the RF (radio frequency) interference is avoided by the use of RF filter adjacent to the input of the first amplifier. 

Equalization is achieved by a purely passive circuit, isolated by the first flat amplifier and the flat response output amplifier. This approach assures maximum stability with optimum transient response, minimum phase shift, and eliminates the need for separate buffer amplifiers. Each pre-amplifier board is adjusted for frequency response and gain balance by the insertion of trimming components at four possible points in the equalization circuit. An emitter follower isolates the gain stage from the control section and provides a very low source impedance to the following circuits.   
The control section provides selection for photo input, plus three high level inputs, gain and balance controls, mode selection, loudness compensation and low-cut filter. A tape monitor feature is available on input position #4. 

High level inputs drive the low impedance and volume controls via an emitter follower. A flat gain stage with emitter follower output restores the insertion loss of the control circuits and provides sufficient gain to drive the power amplifier. Muting relays provide a 5 second delay on warm-up to prevent initial transient pulses passing through the power amplifier and causing speaker damage. 

The HAPI 2 is powered by a unique tracking regulator supply which ties the positive and negative supply voltages to a single Zener reference. This not only holds the supply to a stable voltage, but also assures the absolute symmetry in output and source impedance, which is essential for balanced, directionless and noise free operation. "    

-A. Stewart Hegeman 


Condition


Aesthetically, I consider this unit to be in excellent condition. I invite you to view the photos to judge for yourself. Note: there is one small area of paint damage on the back corner of the lid (see last photo). There are also some very superficial scuff/contact marks on the top of the cover -- nothing that penetrated the paint, the kind of marks you only see from certain angles. 
Note: I have the screws for the lid, I just had it unscrewed for the photos so I could take the top off. You will receive it with the lid screwed on, obviously. 
Electrically, the unit is entirely functional and in perfect working order. It produces no hum or buzz, only the background hiss typical of these units. The channels are balanced, and all inputs work properly. 
All parts are original except for:
1.) The electrolytic capacitors 2.) The relays 
I replaced the original DUNCO reed relays with modern-made equivalents. The originals were fine, but the new ones produce way less of a "thump" upon startup. 
I replaced the electrolytic capacitors because the original Sprague 30D capacitors, at nearly 40 years old, were out of spec and sounding their age. I replaced them with ELNA SILMIC II (RFS) series capacitors. 

Why not "faster" film caps? 

  1. They are huge, and even if they could fit in the preamp, the extra long leads necessary to use them would render their supposed advantages null, but more importantly:

  2. Hegeman was not an idiot. He designed this circuit taking into account the equivalent series resistance and inductance of the capacitors he used, and these ELNA caps, while being among the best audio electrolytics (if not the best) are also pretty close to the originals in terms of ESR and ESL.

Shipping


This unit will ship by FedEx or UPS anywhere in the US, and abroad by USPS Priority Mail International

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