REDUCED! Pro Modified "Old School" Creek OBH-11 Headphone Amp (B011044) & New 3 A PS

For sale is a professionally modified, "Old School Creek Audio OBH-11 Headphone Amplifier with Serial Number B011004. The amp is in very good, vintage cosmetic condition, but has a small ding on the left, bottom corner on its faceplate. It will ship with its original, Creek factory box. (Box is only in fair condition and is without its internal factory packaging.) While all Creek OBH-11 units are designed in the UK, this headphone amp is one of the earlier production units still manufactured in the UK. It has RCA stereo "loop through", IN/OUT connectors on the back. Its tough chassis finish is a black, semi-gloss, heat-fused, electrostatic powder coat. This was one the units released with the "Old School", green logo screened onto its black anodized, rectangular faceplate which makes it a real favorite for Creek aficionados and hi-fi collectors. It was designed for 30 - 300 Ohm headphone loads (600 Ohm headphones work perfectly) and is the ideal amp for the audiophile who wants reliable, "Old School" looking gear that's not only in very good, vintage condition but is also professionally modified for superb musical reproduction, as well!

The Creek OBH-11 had a suggested retail price of $275.00 and was designed specifically for 30 - 300 Ohm headphone loads (600 Ohm headphones work perfectly). It's the ideal amp for the audiophile who wants reliable, modern looking gear, 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 much better! 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 only 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 turn-on 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 1.3 Watt Zener Diode (ZD1 - replaces 24 Volt 1/2 W ZD - raises the amp's overvoltage protection to a safe 27 VDC and eliminates interaction 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 Electrolytic Power Supply Capacitor (under PCB and parallel with C11)

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 replacements allow 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, the musical content is that way!) These op amps are the superior, single channel version of the dual Burr Brown OPA2604 op amp that's quite popular in the DIY audio community. Since each OPA604 is a monaural op amp, cross-talk between channels in the most susceptible section of the amplifier's circuitry is effectively reduced to zero. They provide wider and deeper sound staging over the single, dual Burr Brown OPA2604AP op amp. This op amp duo reveals more inner detail and musical nuance when compared to its "little brother", as well. 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 these two, high fidelity, 20 mHz Burr Brown OPA604AP FET input, 35 mA output, op amps into single-ended (SE), safe Class A operation. It is this biasing technique that helps provide a subtle, warmer and smoother, more  musical presentation. This biasing technique 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. I learned this biasing process  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, 100-240 Volt AC, 24.0 Volt, 3 Amp DC 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. 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 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", 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 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 fantastic 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, 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.