MINT! Pro Modified Creek OBH-11 w/ Discrete Dual Mono Op Amp & New 3A Pwr Supply

This sale is for a professionally modified, Creek Audio OBH-11 (Music Hall COBH-11) Headphone Amplifier with serial # OBH-11/1011/5572. The amp is super clean and in MINT cosmetic condition! It has a brand new 100-240 VAC, 24 VDC 3 Amp Power Supply with a power cord having a 3 Prong, 120 Volt US Only mains (AC) plug. The amp comes with its original Creek factory box (good condition) and will be shipped double boxed for safety.

The unit’s circuit board is revision V2.0B and is ROHS approved. It was Creek Audio’s latest OBH-11 circuit release and has the very useful RCA "looped line level output". The Creek OBH-11 was designed specifically for 30 - 300 Ohm headphone loads (600 Ohm headphones will work perfectly). It’s the ideal amp for the audiophile who wants reliable, modern looking gear that’s not only in mint cosmetic condition but is also professionally modified for more accurate and superb musical reproduction, as well!

When this amp was stock, it was very decent sounding, and now it’s a lot better! The Creek OBH-11 was a Stereophile Recommended Component and had a suggested retail price of $275.00. It’s the ideal headphone amp for the audiophile on a budget. It was originally constructed using production grade electronic components and was then much improved with the following 19 new modification parts purchased only from bona fide US electronics distributors or well established offshore sellers:       
1 ea. Sound Hi-Fi Audience SX52B Discrete, Dual Monaural, Op Amp (original was   integrated, dual NE5532)   
1 ea. Omron Gold-plated DIP8 IC Socket (added at IC1)   
1 ea. 3300 uF 35 Volt Nichicon Audio Quality Power Supply Capacitor (C11 - original was 2200 uF 25 Volt)   
2 ea. .33 uF 250 Volt WIMA MPK 2 Polypropylene Signal Coupling Caps (C1, C101 - originals were .22 uF 63 Volt)   
2 ea. 0.10 uF 63 Volt WIMA MKP 2 Polypropylene Signal Coupling Caps (C4, C104 - under PCB & in parallel)   
1 ea. 47 uF 35 Volt Elna "Silmic II" Electrolytic Power Supply Capacitor (C11 - under PCB & in parallel)   
2 ea. 220 uF 35 Volt Nichicon "Muse BP" Audio Quality Bi-polar Coupling Capacitors (C4, C104)   
2 ea. 47 uF 25 Volt Nichicon "Muse BP" Audio Quality Bi-polar Supply Capacitors (C10, C12)   
2 ea. 47 uF 25 Volt ELNA "Silmic II" Low ESR Electrolytic Feedback Capacitors (C3, C103)   
2 ea. 1/8 Watt 1% Vishay/Dale 5.0 kOhm Precision Metal Film Resistors (IC1 - under PCB)   
1 ea. .10 uF 100 Volt WIMA MKS 4 Poly Film Capacitor (SW1 - under PCB & suppresses turn-on surge)   
1 ea. 1.0 Ohm 1 Watt Vishay BC Components Resistor (R20 - original was 10 Ohm)  
1 ea. 27 Volt 1/2 Watt Zener Diode (ZD1 - for safe overvoltage protection & prevents Zener diode interaction with 24 VDC power supplies.)      
In short, every important component in the headphone amp’s signal path and power supply section that the manufacturer couldn’t provide due to legitimate production cost concerns has been carefully selected for this modification.       
The modification helps lift a veil of haze from the music by replacing lesser quality film and electrolytic caps in the signal path and the power supply of an already decent sounding headphone amp. The op amp replacement allows for enhanced instrumental and vocal detail, and the dynamic content and clarity within the source material to flow through without ever becoming harsh and enervating. (Unless of course, the musical content is just that!) Since the Audience SX52B is a true, dual monaural op amp, cross-talk between channels in the most susceptible section of the amplifier’s circuitry is effectively reduced to zero. This op amp reveals more inner detail and musical nuance when compared to integrated op amps. Transients are very quick with no overhang. The bass is clean, deep and solid. The midrange is very smooth and full and the highs are sweet with excellent extension.       
Additionally, this modification biases this high fidelity, 8 mHz, 120 V/mS slew rate, SX52B op amp into single-ended (SE), class A operation. It is this biasing technique that helps provide a subtle, warmer and smoother, more musical presentation. This specific biasing process still remains part of Walt Jung’s audio modifications and in the late 1980’s, Nelson Pass, "The Old Man of Audio", commercially pioneered SE, class A, op amp biasing in the Threshold product, the Model Forte 2 Preamplifier. I learned this biasing while at Threshold and have implemented it extensively for nearly three decades. (For a technical explanation of the "pull down" resistor biasing used on the op amps in this headphone amp, please see the bottom of this listing.)       
Part of this modification’s superior performance over a stock OBH-11 is due to the new, fully regulated, universal, 24.0 Volt 3 Amp power supply. It is superior to almost all the other possible power supplies available for the Creek because it has a very low output impedance, high current capability AND it produces virtually no measurable noise within the audio frequency band (15 Hz to 20 kHz). It can deliver 20 times the 150 mA current needed to power the Creek HP Amp at full output. This replacement supply is FAR superior to the unregulated Creek M23 wall wart and the OBH-Uni power supplies typically provided with the Creek OBH-11 Headphone Amplifier. It even surpasses the performance of a stock (unmodified), Creek OBH-2 Linear Regulated Power Supply once available for the Creek OBH series products.       
The sonic improvements to this amp should be apparent when first powered ON and will sound better after the unit has warmed up over a period of about 30 minutes or so. It will continue to improve a bit with a few days of continual "burn in". It is quite safe for this unit to remain powered continually (24/7) and it is recommended that the buyer do so. The amp and its new power supply draw little AC current at quiescence, so let them both "idle" ON, 24/7.      
Please be sure to view all of the images and don’t hesitate to ask questions! In particular, compare the interior picture of a stock, unmodified headphone amplifier versus this fully modified unit. And if you’re an audiophile that’s considering this headphone amp, but are hesitant to buy because you’re unfamiliar with my audio modification work, just know that I’ve been doing hi-fi equipment modifications for over 35 years. I have been mil-spec soldering and materials handling certified and have modified and sold over 85 of these modified headphone amps in the last five years.     
This is a great hi-fi item for the asking price, but it is still is a relatively expensive item, so be sure you want it before you buy. Please don’t hesitate to ask questions! The headphone amp is guaranteed to work and a return is OK only for shipping damage. USPS Priority Shipping with insurance are for the US only.       
Here’s an explanation of how "pull down" biasing an op amp into single ended, class A operation is done and why it works:       
This "pull down" biasing technique is called "current sourcing" and is accomplished by directing a calculated amount of current around the PNP transistor shown as the bottom component of the "push-pull" output pair on the op amp datasheet depicting a solo channel in the circuit architecture. (This PNP transistor is the device engineers choose to bypass as it is inherently less linear in operation than its NPN counterpart because "holes", the PNP charge carriers, are less mobile in a transistor substrate and have an inferior rise time when compared to the electron charge carriers of its NPN complement.) This bypassing shunts the collector and emitter of this device, effectively turning it "off". With this PNP transistor nonoperational, the NPN device now operates fully and continually "on" within the "current envelope" specifically selected. As a result, the op amp output stage becomes converted into true SE, Class A operation and can now take full advantage of that benefit over "push-pull", Class B operation. Another equally important and often overlooked benefit of current source biasing is its creation of a safe, steady state, "thermal envelope", in which the entire op amp circuitry operates more stably due to the minimization of internal temperature fluctuation. This thermal "stasis" is particularly important when the op amp is presented with large and highly complex signal waveforms from dynamic and demanding musical passages, quite dense in differing and ever-changing harmonic overtones. While these biasing advantages will NOT alter the total harmonic distortion (THD) of the op amp, the perceived improvement in its auditory behavior is most likely the result of reduced transient intermodulation distortion (TIM), a known contributor of nonlinear, amusical artifacts in audio reproduction.