1976 Pioneer HPM 100 "West Coast to East Coast" Upgrade Project
Finished value in 2023 about $1,500
DaytonHD has refurbished several of these HPM-100 speakers, they have so many great components like the massive woofer baskets, thick baffles and solid cabinets.
A common complaint is that the cross-over design sends way more mid-range to the woofer than most designs. We have tried the popular cross-over modification and it is interesting. The HPM-100 was designed for Rock & Roll, electric guitar amps have a single large full range woofer so the cross-over design may have been intended to replicate this. Then there is the issue with the mid-range polarity, some say when Pioneer went from 100 watt to 200 watt spec, the drivers were the same but polarity was reversed on the mid-range driver. Some crossover schematics show the polarity switched at the driver and speakers have been found with polarity switched at the cross-over. Clearly Pioneer was trying to adjust the mid-range output from the speaker system.
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We found that using newer mid-range and tweeter drivers really increases the overall fidelity and sonic accuracy for a full range of music. As our professional reviewer summed them up: the new sound is a "West Coast to East Coast" upgrade*.
Dayton Audio brand “Reference Series” Fabric Dome, Ferrofluid Tweeters and Dayton Audio Reference Full Range Mid-Woofers with Paper, Kevlar and Glass Fiber components were selected. Installing the new drivers offered challenges so we had special aluminum “ring clamps” manufactured and painted to provide a secure mount with no modifications to the drivers and minimal disruption to the speaker baffle. Drilling and screwing into the baffle was required, but the result is solid and attractive.
We received the pair of HPM-100 speakers with
most all the speaker cones damaged by a child. We completely refurbished the
woofers with new new cones, coils, spiders and accordian surrounds (per original
specifications). New high-quality capacitors were installed on the cross-overs
keeping their original circuit design. The Mid and High potentiometers were
cleaned.
The massive wood cabinets were inspected and refinished. The front baffle was repainted, and the original Super tweeter and woofer frames were painted black. Chrome screws were then used to mount all the drivers onto the front baffle.
Finally the grill cloths were replaced with new black material.
Having experience with a wide range of older speakers from B&W to Focal; Magnapan to Mirage; Klisph to Cerwin Vega and JBL to Pioneer we feel comfortable judging the sound from our HPM-100 upgrade. The musicality from these new tweeter and mid-range drivers is dramatically different. Higher fidelity, less forward fatigue, greater stage and presence is achieved. The speaker system is still very efficient, requiring very little wattage to come to life. Especially nice is the high fidelity at low volumes.
* A professional reviewer compared the original speaker to our upgrade:
“There’s an interesting if apocryphal story about the development of the Pioneer HPM-100 speaker system. It’s said Pioneer wanted to make its own version of JBL’s famous L100 three-way speaker in the 1970’s so they were said to hire one of JBL’s top engineers and assign him the task. And what they developed was a fairly good imitation of the original with a Japanese translation of the “West Coast” sound: boomy bass, in-your-face midrange and sizzling highs.
The West Coast sound of the old JBL’s and the HPM-100 is many things but it’s not real high fidelity. And this is said as a long-time JBL owner. By upgrading the tweeter and mid-range drivers Mark and DaytonHD have re-engineered the HPM-100 to tame the wilder aspects of the speaker to convert it from a showy, fatiguing sound box into a true high-fidelity speaker. Mark has changed the West Coast sound for a modernized “East Coast” sound as typified by the classic Acoustic Research and KLH speakers of the ‘60’s and ‘70’s.
The bass is tight and accurate; the mids take their proper place in the audio spectrum and the highs change from sizzling to silken. These are Pioneer HPM-100’s I’d have in my own system.
Amazing stuff! I think you've done very well. The HPM-100 purists may not like the upgrade but people who have matured their listening will love the second life their speakers have been given.”
Thom Moon – 30-years a reviewer of stereo equipment for established international audio publications.
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