Modified Creek OBH-11 Headphone Amp

nraymond · Dec 7, 2018

No relation to this seller, but I saw this and was curious what people with more knowledge of amplifier design thought about this:

https://www.ebay.com/itm/REDUCED-Ex...ne-Amp-w-New-High-Current-Supply/223252769020

Here is the text from the detailed description, included here for posterity:

Quote:

This sale is for a professionally modified, Creek Audio OBH-11 (Music Hall COBH-11) Headphone Amplifier. The amp is in superb, cosmetic condition with NO scratches, dings or marks and comes in its original factory box with a brand new 100-240 VAC, 24 VDC 3 Amp Power Supply that has a power cord with a 3 Prong US Only Plug.
It had a suggested retail price of $275.00. The unit's circuit board is revision V2.0B, is ROHS approved and is Creek Audio's newest OBH-11 circuit release. The Creek OBH-11 was designed specifically 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 decent appearing condition but is also professionally modified for more accurate and superb musical reproduction, as well!
This headphone amplifier has the very useful RCA "looped line level output" and has the distinctive silver Creek logo that's recessed into the brushed anodized aluminum, rectangular face plate with rounded corners. 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 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. TeraDak Singles to Dual Op Amp Adapter (at IC1 and sourced from an eBay electronics distributor)
1 ea. 3300 uF 35 Volt Nichicon KW Audio Quality Power Supply Capacitor (horizontally mounted at C11 - original was 2200 uF 25 Volt)
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 Supply Capacitors (C10, C12 )
2 ea. 47 uF 50 Volt Nichicon PV 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)
1 ea. 1.0 Ohm Vishay BC Components Resistor (R20 - original was 10 Ohm)
1 ea. 27 Volt 1 Watt Zener Diode* (replaces the Zener diode at ZD1)
*This raises the amp's overvoltage protection to a safe 27 VDC which safely eliminates any potential Zener diode interaction with the new 24 VDC power supply.)
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 displayed in one of the images.)
Additionally, the following components were relocated from the original circuit:
2 ea. .22 uF 63 Volt Polyfilm Signal Coupling Caps (under and parallel with C4, C104)
1 ea. 47 uF 35 Volt Electrolytic Power Supply Capacitor (under and parallel with C11)
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 of course, the musical content is just that!) 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 genuine, 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 and the bass is clean, deep and solid and the highs are sweet and have excellent extension.
Additionally, this modification biases these high fidelity, 20 mHz Burr Brown OPA604AP FET input op amps into single-ended (SE), class A operation. This biasing technique helps provide a subtle, warmer and smoother, more musical presentation. This specific biasing process still remains part of Walt Jung's "POOGE" modifications and in the late 1980's, Nelson Pass pioneered a similar SE, class A, op amp biasing method in the Model Forte 2 Preamplifier design that he engineered while he was president and chief engineer at The Threshold Corporation. I learned those biasing techniques 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 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. (All these are very good improvements, but are effective ONLY with a modified Creek OBH-11 having proper parts alterations to its on-board 24 VDC supply section.)
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 handily surpasses the performance of the Creek OBH-2 Linear Regulated Power Supply 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 current at quiescence, so let 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 can 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 35 years. I have been mil-spec soldering and materials handling certified and have modified and sold over 75 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. 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. 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 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.

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 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.
Click to expand...

sacredgates · Dec 7, 2018

Don‘t know about the modifications, but the normal OBH-11 by today‘ standards is extremely mediocre to say it politely...
And not really a need to start a thread for your question. There is an all purpose advice thread for such questions...

nraymond · Dec 7, 2018

sacredgates said: ↑

Don‘t know about the modifications, but the normal OBH-11 is extremely mediocre to say it politely...
And not really a need to start a thread for your question. There is an all purpose advice thread for such questions...
Click to expand...

Thanks for the reply! Apologies for posting in the wrong place. Admins, please move the thread as/when appropriate.

purr1n · Dec 7, 2018

Offer $125, the going price on the 'gon. People don't get any more selling modded cars, so why should they get any more for modded audio gear?

The opamp Class A mods via the resister pull down are nothing special. People did that same exact mod on the Matrix M-Stage on HF, which BTW had an LPS instead of a cheap wall wart. Don't know why Nelson Pass was invoked. Actually offer $99 just to be a dick because of all that fluff about PNP NPN and TNT buttholes and Walt Jung's sPLOOGE.

Modified Creek OBH-11 Headphone Amp

nraymond New

sacredgates Audio-Technica's high priest

nraymond New

purr1n Desire for betterer is endless.

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Modified Creek OBH-11 Headphone Amp

nraymond New

sacredgates Audio-Technica's high priest

nraymond New

purr1n Desire for betterer is endless.

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