Modified Creek OBH-11 Headphone Amp (SN OBH-11/0706/0418) & New 3A Pwr Supply

For sale is for a professionally modified, Creek Audio OBH-11 Headphone Amplifier (SN 0706/0418) with its original factory box. The amp is in excellent cosmetic condition. Comes with its original factory box and has a brand new 100-240 VAC, 24 VDC 3 Amp Power Supply that has a power cord with a 3 Prong US Only plug. The Creek OBH-11 was a Stereophile Recommended Component and is 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 modification parts purchased from bona fide US electronics distributors, with the exception of the TeraDak Op Amp Adapter:

2 ea. Burr Brown OPA604AP 20 mHz FET Input Op Amps (original was NE5532)
1 ea. Omron Gold-plated DIP8 IC Socket (IC1)
1 ea. TeraDak Singles to Dual Op Amp Adapter (at IC1 and sourced from an eBay electronics distributor)
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 Polypropylene Signal Coupling Caps (C1, C101 - originals were .22 uF 63 Volt)
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 10.0 kOhm Precision Metal Film Resistors (under PCB at IC1)
1 ea. .10 uF 100 Volt WIMA MKS 4 Film Capacitor (across power switch SW1 to help suppress current surge)
1 ea. 1.0 Ohm 1 Watt Vishay BC Components Resistor (R20 - original was 10 Ohm 1/2 W)
1 ea. 27 Volt 1/2 Watt Zener Diode (at ZD1 and raises the amp’s overvoltage protection to a safe 27 VDC while eliminating Zener diode interactions with 24 VDC power supplies)

Additionally, the following components were relocated from the original circuit:

2 ea. .22 uF 63 Volt Film Signal Coupling Caps (under and parallel with C4, C104)
1 ea. 47 uF 35 Volt Rubycon YXA PET Electrolytic Power Supply Capacitor (under and parallel with C11)

Additionally, this modification biases these high fidelity, 20 mHz Burr Brown OPA604AP FET input op amps 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 Model Forte 2 Preamplifier. (NOTE: This biasing is not "pseudo-class A", whatever that’s claimed to be!) I learned this biasing while at Threshold and have implemented them 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.

Also, 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 has a low output impedance, high current capability AND it produces virtually no measurable noise within the audio frequency band. It can deliver 20 times the 150 mA current needed to power the Creek HP Amp at full output.

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 simply let them "idle" in the ON position, 24/7. 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. 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, why it works:
This resistor "pull down" biasing technique is called "current sourcing" and is accomplished by directing a small, specific amount of current from circuit ground (or -V) past the PNP output transistor which is the device shown as the bottom half in the "push-pull" transistor pair on schematics depicting an op amp channel. (While either one of these output transistors can be bypassed, it is the PNP transistor that electronic engineers choose to bypass because it is somewhat less linear in operation than its NPN counterpart. This is because PNP charge carriers, called "holes", are less mobile in a transistor substrate and have slower rise times than the electron charge carriers of an NPN complementary device.) The bypassing shunts the collector and emitter of this transistor and effectively turns it "off". With this PNP transistor nonoperational, the NPN transistor now operates fully "on" due to the current guided through it and past the PNP device now effectively removed from the circuit. Thus, the op amp output stage becomes converted to true single ended, class A operation and can now take full advantage of their sonic benefits over complementary, class B operation. (Within the class A "current envelope" created, this biasing completely removes any output stage crossover (notch) distortion and this prevents half-wave, class B artifacts (meaning nasty, third and fifth odd order harmonics), from entering the supply rails which potentially reduces noise and distortion caused from the coupling of these extraneous distortions into sensitive power supply circuit nodes.) Another important, yet often overlooked benefit of current sourcing is its creation of a steady state, "thermal envelope", in which the entire op amp circuitry operates more stably due to the minimization of internal temperature fluctuation. This thermal stability is particularly important when the op amp is handling sustained, large amplitude signal swings which are the direct result of long duration, high level musical passages.

And here's my OBH-11 modification feedback from US Audio Mart:

 It is instantly clear how much experience and knowledge went into the custom upgrades of this little beastly headphone amp. It's unassuming sitting on my desk... Then turn it on. It drives my HD-6xx's cans with such detail and ease. The full bodied sound seems to spring up from a non existent noise floor. It brings out my love for music all over again!!

Great item. Incredible detail right out of the box. I cannot wait for it to break in. The seller shipped the item immediately and I received it in 2 days. Great item...great price...easy to do business with...a GREAT experience all around. Thanks.

Item arrived quickly, and in excellent condition. The item is exactly as the ad showed. Music played through the amplifier sounds like I hoped - like a wire with gain. I would buy from you again.

Item as described. Super fast shipping. Great transaction. Highly recommended.
 
Stand up guy to work with. Knows his product very well and I am pleased with the Creek amp I received. I don't understand 80% of the tech talk, but I don't need to. Just enjoy the music. Definitely worth the price. On a budget? This is the amp  and power supply to get. Sound has improved over time, breaking in, I suppose, definitely it is better. Thx! 

Roger has impressive credentials in the audio biz, and has completely earned my trust in both his work and opinions. Fully satisfied with his mods and customer service.