Musing about the HP Barney Oliver Amplifier

[unclejed613]

Agree on the tight transistor characteristics requirement.
It was common for high-performance equipment transistorized designs back then, to have commercial transistors selected for certain parameters, and then apply "house numbers" to them.
Or at least a colored dot to facilitate parameter binning.

Heck, even my Zenith Transoceanic radio has selected transistors with Zenith house numbers.

there were several companies that did that, Acoustic Controls, Phase Linear, and APT are three i can think of that had output devices that had to be below a certain beta, or the amplifier would get unstable (actually the APT amplifier was stable, but too high a beta in their output transistors would cause common conduction if signals over 50khz were applied). keep that in mind when repairing amplifiers. if you have a good channel and a blown channel, check the beta of the good output devices and make sure the new ones are about the same beta. both the Acoustic amps and Phase Linear amps had a tendency to self destruct if output devices with too high a beta were used as replacements.

back in the 60s, big consumer manufacturers like RCA and Zenith had "house numbered" transistors, requiring the parts to be ordered from the manufacturer. it was kind of odd to see RCA doing that, because RCA also manufactured and sold transistors with JEDEC 2N series numbers.

 

[unclejed613]

basically the goal is to have as high an open loop gain, with as wide as a GBW product as is possible. the real hard part of that is in getting the output stage to behave. if there is a large disparity between input stage/VAS speed and output stage speed, you get instability and oscillation. if the output stage changes it's output resistance a lot while feeding a load, it causes difficult to correct distortion (the output voltage and current must both be correctable by feedback), and the slew rate of the whole amplifier must be sufficient to drive a load to full output swing at frequencies well above 20khz to eliminate IMD and TIM. almost all of this depends on the output stage design being correct. once the output stage is taken care of, the input stage and VAS need to be optimized for as much open loop gain and GBW is possible with the output stage connected. other considerations are things like keeping the output stage from being saturated during clipping, and dealing with discharging the Miller capacitance of the output devices (i.e. keeping the amplifier from hanging up on the rails during clipping, which is very bad for tweeters, and making sure the output devices turn off at or before zero crossing with high frequency input). while there are not a lot of tape decks anymore, keeping the output devices from going into common conduction is just good design.

 

[PaulBennett]

Couple of additions as a retired hp engineer and an original BO amplifier owner.
Back in the day, Barney Oliver was a highly revered senior engineer and manager of the hp R&D Laboratory in Palo Alto next to respect to Bill Hewlett. Corp Labs did exotic research, no products.

Two happenings ... transistors started to infect everything electronic, replacing/displacing tubes. Williamson amplifiers, which led the audio world for decades, or any design with tubes became obsolete primarily because of cost. However, transistors came with with unpleasant odd harmonic distortion.

AND I don't recall the specific second event which may have been a special Barney birthday or what, perhaps Barney let it be know he needed an audio changeover or maybe bought a new house. In any case it triggered a engineering manager in the Lab to secretly initiate the project. To justify making a few extra amplifiers for local Palo Alto engineers, they sent word about the amplifier to engineers in other hp divisions and about 500 signed up including me. The initial run ran short so an additional plea came about 2 years later for the remaining few hundred units. Total was thought to be 600-700 units.

Even then $600 was a steep price. It covered parts only - assembly was done after hours by personnel at corporate Labs as a labor of love. Someone here noted 1% resistors were used where 5% would suffice but all parts came from the existing hp standard parts catalog which was always the best components available..

I recall hearing Barney's system used JBL D130 15" speakers which I already had and still do, having bought them in high school in the mid 50s. A turntable with a Shure V15 Type 3 cartridge was (and is) universal so the amplifier was designed for that Shure cartridge.

Of course now days, audiophiles have simply gone back to tubes for the lovely even harmonic sound. And many still use D130s. I even have a JBL in my tube guitar amplifier. I'm pleased that my son wants my BO amp when I leave but for now I still appreciate the great sound from disks.

I'm thankful for the opportunity to post here. I wish I had circuit info to share re: the BO but no, I ended retiring from hp in defibrillator design.

 

[audioguru]

I am also getting old (74) but I feel and act much younger. I still have my turntable with a Shure V15 Mark 2 cartridge in it but I haven't played vinyl records for ages. I have Acoustic Research speakers but one flexing wire on one woofer broke. I have a 15" high power sub-woofer speaker that has never played.

My eyes got old with cataracts and I got the cloudy original lenses replaced with much better synthetic ones for perfect vision.
I had a heart attack but my wife rushed me to the nearby hospital quickly and the doctor opened two blocked heart arteries with stents so now I am fine with no damage to my heart.
My hearing got old so now I have hearing aids that do tricks that ordinary hearing cannot do, like settings for extra sensitivity, muting, compression, noise reduction and directionality. The hearing aids tell me when the battery is low but do not tell me the weather forecast.

My Google Mini Home Assistant lets me know almost anything i ask it.