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This sale is for a completely and professionally modified, Creek Audio OBH-11 Headphone Amplifier without the factory box. This vintage unit is in very good cosmetic condition overall. Its serial number is B 019561 and the circuit board is revision V2.0 from 1998. While all Creek OBH-11 units were designed in the UK, this headphone amp is one of the last production units that was still manufactured in the UK as indicated on the back panel. It has the useful RCA stereo "loop through", first integrated into the Creek OBH-11 headphone amplifiers with this "B" series production model. This is also one the their last units released with the "old school" green logo screened onto its black anodized, rectangular faceplate, making it a real favorite for Creek aficionados and collectors. The unit's circuit board is revision V2.0B that's ROHS approved and is Creek Audio's latest OBH-11 release. It is designed for 30 - 300 Ohm headphone loads and is the ideal amp for the audiophile who wants reliable, modern looking gear that's not only in factory new 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 even better! It was a Stereophile Recommended Component and an ideal headphone amp for the audiophile on a budget. It was originally constructed with production grade electronic components and was then much improved with the following modification parts purchased solely from bona fide US electronics distributors.
1 ea. Burr Brown OPA2134PA "Sound Plus" FET Input Op Amp (IC1 - original was NE5532)
1 ea. Omron Gold Plated 8 Pin DIP Socket (IC1)
1 ea. 3300 uF 25 Volt Nichicon PA "Fine Gold" Audio Quality PS Capacitor (C11 - was 2200 uF)
2 ea. .33 uF 250 Volt WIMA Polypropylene Signal Coupling Caps (C1, C101 - originals were .22 uF)
2 ea. 220 uF 35 Volt Nichicon "Muse BP" Audio Quality Bipolar Coupling Capacitors (C4, C104)
2 ea. 47 uF 25 Volt Nichicon "Muse BP" Audio Quality Bipolar Power 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 Polyester Film Capacitor (across power switch SW1)
1 ea. 1.0 Ohm Panasonic Resistor (R20 - original was 10 Ohm)
Additionally, the following components were relocated from the original circuit:
2 ea. .22 uF 63 Volt Polyfilm Signal Coupling Caps (under C4, C104)
1 ea. 47 uF 35 Volt Electrolytic Power Supply Capacitor (under C11)
A potentially interactive and noisy 24 Volt Zener diode was removed from ZD1 because it is unnecessary with the new fully regulated power supply.
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, dynamics and clarity to flow through without ever being harsh and enervating. Transients are very quick with no overhang and the bass is clean and solid and the highs are sweet and have excellent extension. Additionally, this modification biases this high fidelity, Burr Brown OPA2134PA "Sound Plus" FET input op amp into single-ended (SE), class A operation. This biasing helps provide a subtle, warmer and smoother, more "tube-like" musical presentation. And contrary to a claim by a competitor, this technique of "pull down" resistor op amp biasing is not "pseudo-class A" (whatever that is), nor is it "potentially damaging by stressing" the op amp when implemented properly, as is done in this mod. This biasing process became part of Walt Jung's "POOGE" modifications and as far back as the late 1980's, Nelson Pass, then president of The Threshold Corporation, pioneered a similar SE, class A biasing technique for the op amps used in the Forte 2 preamplifier, thus creating a high end audio industry first! I learned both biasing techniques at Threshold in the late 1980's and have implemented them extensively for nearly 30 years. Whew! (For a technical explanation of the "pull down" resistor biasing used in this amp, please see the bottom of this listing.)
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. (These components are laid out in one of the images.)
Additionally, part of this improvement is due to the new, fully regulated, 24.0 Volt 4 Amp (96 Watt) power supply with its matching green LED light. It is superior to almost all the other possible power supplies available for the Creek because it is has a very low output impedance, high current capability AND produces virtually NO measurable noise in the audio frequency band (15 Hz to 20 kHz) and out into the MHz range as well! It can produce over 25 times the 150 mA current needed to power the Creek HP Amp. (All this is a VERY good thing, but ONLY when you have a modified Creek OBH-11 that can take full advantage of this from proper alteration to its power supply circuitry.) This 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 is also superior to a stock Creek OBH-2 Linear Regulated Power Supply once available for the Creek OBH series products.
Thehone 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 60 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 and is recommended as well. The amp and its new power supply draw little current at quiescence, so just them "idle" in the ON position.
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 the interior image of a fully modified unit. (You'll easily tell which image is which!)
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 equipment modifications for well over 30 years. I have been mil-spec soldering and materials handling certified and have modified and sold over 50 of these fantastic headphone amps in the last 4 years alone. Please check the feedback from my buyers to see what they think of my modification work.
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. 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. I offer international shipping and those sales will be shipped via International First Class or USPS Priority Mail depending on its destination outside the US. This new, modified Creek Audio OBH-11 Headphone Amplifier and its new power supply come from a nonsmoking household and will be packaged properly for its safe and secure delivery to your doorstep.
Thanks for looking and Enjoy the Music!
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 resistor "pull down" biasing process 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, the device which is the conventional bottom half of the "push-pull" transistor pair in the output stage of an op amp channel. (The PNP transistor is typically the device chosen to bypass because its NPN complement is more linear in operation.) This bypassing is done using a precision resistor of a calculated, typically high Ohms value and because it shunts the collector and emitter of this transistor, it effectively turns that transistor "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. 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, 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.) Additionally, this current sourcing creates a steady state "thermal envelope", in which the entire op amp circuitry operates more stably. And while quite unlikely, should the load on the op amp require more current than was provided to bias its output stage, the op amp will simply "slide" gently and transparently back into its original design mode to fully accommodate that more demanding load requirement.
This ad was originally posted on US Audio Mart.