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Looking for an RV amplifier

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rdenney

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Okay, it’s done.

What I installed: Pioneer GM-D1004 amp. Amir tested this and thought it pretty good for the money. I’m using it bridged into two Dahlquist ALS-3 mini speakers. The speakers themselves are interesting, being tiny three-way speakers with quite a complex crossover.

I also installed a Carpuride CarPlay touchscreen. That has been a good purchase so far. I mounted it on my center table. I made use of its support for a backup camera, but I primarily use it to play music, podcasts, and audio books, in addition to showing the phone’s navigation and integrating texts and phone calls into the sound system.

The front speakers are a new pair of 3.5” Dayton Audio full-range 4-ohm speakers which I’m running off the head unit. The head unit is a Kenwood KDC-MP238 from at least 18 or 20 years ago. Turns out, it’s got good power output so I’m still using it for the front speakers. With the Dahlquist speakers, the Kenwood is strictly a preamp. I’m feeling the Pioneer amp with line-level outputs from the Kenwood.

Here’s the amp. It’s mounted on the back of the fuse panel access cover, under the glove box.

IMG_0825-dsqz.JPG


Pardon the mid-project mess, but here’s the “lounge” looking forward. The Dahlquist speakers are mounted on the walls. No, they aren’t the same height. Compromises are necessary in this use case. They are small but heavy and I wanted them to stay put, so I mounted then where I could sink screws into one of the vertical aluminum struts that serve as wall studs. But I had to avoid the overhead cabinet on the left.

IMG_0814-dsqz.JPG


And closeups of the speakers:

IMG_0815-dsqz.JPG


IMG_0816-dsqz.JPG


Here’s the cockpit. You can see why I needed something. The head unit is handy for the passenger but unreachable when traveling alone.

IMG_0818-dsqz.JPG


Here’s the Carpuride unit from the driver’s perspective.

IMG_0821-dsqz.JPG


And its connections:

IMG_0823-dsqz.JPG


The Mangos performance of the Liszt Symphonic Poems transcribed for two pianos is a standard test for me.

No, the sound is no match for my home system playing this CD through a B&K Sonata MC-101 preamp, a Buckeye NC502MP amp, and Revel tower speakers. There’s a bit of ring in the mid-bass and and congestion when driven hard. And the interior of the coach is a sea of acoustic weirdness. But despite reports that these can’t take power, all I’ll say is that they can play LOUD with the 90 watts of the bridged Pioneer amp. And these things make far more bass than anyone would guess looking ant them. The sound is really rather decent—it certainly does what I hoped it would do. In 1979 when this coach was still fairly new, those little Dahlquist speakers would have been high end in a mobile application.

For those who are interested, the backup camera is awesome. I mounted it on a stalk over the rear-mounted spare tire. Running the wire from the camera to Carpuride unit was by far the most difficult part of the project. The GMC motorhome is quite compact, which means there is no wasted space through which one can run wires. I needed 45 feet of composite video cable to make the trip from end to end of a 23-foot motorhome. The camera is powered using the backup light circuit tapped at the nearby tail light. The Carpuride senses incoming video and switches to it automatically. Video quality is good enough. Rear video is transformative in a motorhome.

IMG_0822-dsqz.JPG


Rick “big trip coming up in September” Denney
 

EJ3

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Okay, it’s done.

What I installed: Pioneer GM-D1004 amp. Amir tested this and thought it pretty good for the money. I’m using it bridged into two Dahlquist ALS-3 mini speakers. The speakers themselves are interesting, being tiny three-way speakers with quite a complex crossover.

I also installed a Carpuride CarPlay touchscreen. That has been a good purchase so far. I mounted it on my center table. I made use of its support for a backup camera, but I primarily use it to play music, podcasts, and audio books, in addition to showing the phone’s navigation and integrating texts and phone calls into the sound system.

The front speakers are a new pair of 3.5” Dayton Audio full-range 4-ohm speakers which I’m running off the head unit. The head unit is a Kenwood KDC-MP238 from at least 18 or 20 years ago. Turns out, it’s got good power output so I’m still using it for the front speakers. With the Dahlquist speakers, the Kenwood is strictly a preamp. I’m feeling the Pioneer amp with line-level outputs from the Kenwood.

Here’s the amp. It’s mounted on the back of the fuse panel access cover, under the glove box.

IMG_0825-dsqz.JPG


Pardon the mid-project mess, but here’s the “lounge” looking forward. The Dahlquist speakers are mounted on the walls. No, they aren’t the same height. Compromises are necessary in this use case. They are small but heavy and I wanted them to stay put, so I mounted then where I could sink screws into one of the vertical aluminum struts that serve as wall studs. But I had to avoid the overhead cabinet on the left.

IMG_0814-dsqz.JPG


And closeups of the speakers:

IMG_0815-dsqz.JPG


IMG_0816-dsqz.JPG


Here’s the cockpit. You can see why I needed something. The head unit is handy for the passenger but unreachable when traveling alone.

IMG_0818-dsqz.JPG


Here’s the Carpuride unit from the driver’s perspective.

IMG_0821-dsqz.JPG


And its connections:

IMG_0823-dsqz.JPG


The Mangos performance of the Liszt Symphonic Poems transcribed for two pianos is a standard test for me.

No, the sound is no match for my home system playing this CD through a B&K Sonata MC-101 preamp, a Buckeye NC502MP amp, and Revel tower speakers. There’s a bit of ring in the mid-bass and and congestion when driven hard. And the interior of the coach is a sea of acoustic weirdness. But despite reports that these can’t take power, all I’ll say is that they can play LOUD with the 90 watts of the bridged Pioneer amp. And these things make far more bass than anyone would guess looking ant them. The sound is really rather decent—it certainly does what I hoped it would do. In 1979 when this coach was still fairly new, those little Dahlquist speakers would have been high end in a mobile application.

For those who are interested, the backup camera is awesome. I mounted it on a stalk over the rear-mounted spare tire. Running the wire from the camera to Carpuride unit was by far the most difficult part of the project. The GMC motorhome is quite compact, which means there is no wasted space through which one can run wires. I needed 45 feet of composite video cable to make the trip from end to end of a 23-foot motorhome. The camera is powered using the backup light circuit tapped at the nearby tail light. The Carpuride senses incoming video and switches to it automatically. Video quality is good enough. Rear video is transformative in a motorhome.

IMG_0822-dsqz.JPG


Rick “big trip coming up in September” Denney
Good to see this progress. When you say "bridged" (& I presume that this is a 2 channel amp) does that mean that the DQ's are both getting one mono signal?
Also for the Carpuride does that have a feature that you can connect a "CD" player to it? If it has carplay this is a way to do that:
EJ3
 
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rdenney

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The Kenwood head unit has a CD player, not that I can reach it. But all my CDs that I play are on my phone anyway.

The Pioneer amp is a 4-channel amp, intended to drive front and rear stereo pairs in a car. But the four channels can be bridged into a stereo pair, rated at 90 watts into four-ohm speakers.

This Carpuride unit doesn’t appear to have a wired auxiliary input. But it does have Bluetooth. But it wasn’t a requirement for me.

Rick “probably has an old Discman somewhere” Denney
 
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rdenney

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Ha! I just blew out a fuse in the right Dahlquist by accidentally holding the volume up button in the remote a bit too long and having to wait for the software to keep up with my finger on the remote. It takes a 1.6-amp slo-blo, which I had in stock. I’m putting a couple of those in the RV.

It was loud. And it is Dream Theater. Prior to that it was Maynard Ferguson. The amp is decidedly warm.

I just figured out I can rotate the right speaker to aim it at me. That gives me almost perfect balance from the driver’s seat.

Rick “at least the speaker is protected” Denney
 

EJ3

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Ha! I just blew out a fuse in the right Dahlquist by accidentally holding the volume up button in the remote a bit too long and having to wait for the software to keep up with my finger on the remote. It takes a 1.6-amp slo-blo, which I had in stock. I’m putting a couple of those in the RV.

It was loud. And it is Dream Theater. Prior to that it was Maynard Ferguson. The amp is decidedly warm.

I just figured out I can rotate the right speaker to aim it at me. That gives me almost perfect balance from the driver’s seat.

Rick “at least the speaker is protected” Denney
I forgot (damn oldtimers disease) that that Model Pioneer is a four channel one.
My DQ M-905's & I can relate to the fuse blowing scenario. I built some 12" downward firing subs to put them on top of (naturally with a thin but somewhat spongy material between them) to help them out a bit.
EJ3
 
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rdenney

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For those keeping track, the blown fuse is not a slo-blo. It’s just the opposite—style ff—which is “super fast” blow ceramic 5x20mm fuses. I’ve ordered them from Digikey, and they are six bucks each(!) I had to search for them by part number—Digikey’s filters don’t even include the ff category.

That tells me they are there to protect the tweeter as much as the other drivers.

Rick “glad they are there” Denney
 
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rdenney

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Is the slow-blow what was in it?
No, not at all. The fuse that came out was filled with white powder, which I thought was a core around which the fuse wire was wrapped. But it was actually anti-rupture material. I sort-of assumed it was a slo-blo and discovered my error when I studied the markings on the blown fuse the next day.

I just happened to have slo-blo's in stock in the 5x20mm size. So, that's what is in it now. That means I need to be more careful until the replacements arrive :)

Rick "would not want to have to source drivers for Dahlquist ALS-3 speakers" Denney
 
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EJ3

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No, not at all. The fuse that came out was filled with white powder, which I thought was a core around which the fuse wire was wrapped. But it was actually anti-rupture material. I sort-of assumed it was a slo-blo and discovered my error when I studied the markings on the blown fuse the next day.

I just happened to have slo-blo's in stock in the 5x20mm size. So, that's what is in it now. That means I need to be more careful until the replacements arrive :)

Rick "would not want to have to source drivers for Dahlquist ALS-3 speakers" Denney
CALLING FOR PAGE 65, CALLING FOR PAGE 65, EMERGENCY, EMERGENCY!!!

If someone can find page 65 (from whatever month of this is from), a page 64 from one of the 1979 Stereo Review's has this on the

Dahlquist ALS 3:
The ALS 3 was the only three-way system
in the test group. It uses a 4 -inch bass driver, a 1.5 -inch cone
midrange, and a 1 -inch plastic -dome tweeter, all housed in a
matte -black metal enclosure with a black perforated grille. The
enclosure has removable round end caps that act as clamps for
the U-shaped automotive brackets supplied with the speaker.
The input terminals have been recessed into a cutout on the rear
panel. Next to them is a two -position "home/automotive"
switch that boosts the high -frequency output of the speaker in
the automotive position to compensate for the masking effects of

That is all I could find on these.

I did find a source for many other Dahlquist speaker's parts (which I have known about for some time, [as I am an owner of a pair DQ M-905's
that Peter @ Quirk Audio redid the crossovers on for me using the exact same spec capacitors {which I did not want changed as a test in the 70's showed a
FR of 26Hz-20KHz +-2 DB}] except having much closer tolerances & modern capacitors).

The Easy one is:
https://dahlquistspeakers.com/dahlquist__speaker_navagation_service-htm

Dahlquist Speaker service

there may be others. Your MMV.
 

EJ3

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No, not at all. The fuse that came out was filled with white powder, which I thought was a core around which the fuse wire was wrapped. But it was actually anti-rupture material. I sort-of assumed it was a slo-blo and discovered my error when I studied the markings on the blown fuse the next day.

I just happened to have slo-blo's in stock in the 5x20mm size. So, that's what is in it now. That means I need to be more careful until the replacements arrive :)

Rick "would not want to have to source drivers for Dahlquist ALS-3 speakers" Denney
It's good that you did not just go with your initial impression and just toss the fuse you pulled out but instead took a second look at it.
 
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rdenney

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From High Fidelity, May, 1979:

"Dahlquist, a leader in the current trend toward phase adjustment through driver positioning, has entered the automotive field with the three-way ALS-3 system. Priced at $250 per pair including all mounting hardware, the speakers are expected to find their way into homes as well. Dahlquist says the ALS-3 is efficient enough to be driven by the amps built into typical auto equipment without a booster, but will handle inputs up to 30 watts. The impedance is 4 ohms."

From the review of mini-monitors in HiFi Stereo Review, August, 1979:

"Dahlquist ALS 3: The ALS 3 was the only three-way system in the test group. It uses a 4 -inch bass driver, a 1.5 -inch cone midrange, and a 1 -inch plastic -dome tweeter, all housed in a matte -black metal enclosure with a black perforated grille. The enclosure has removable round end caps that act as clamps for the U-shaped automotive brackets supplied with the speaker. The input terminals have been recessed into a cutout on the rear panel. Next to them is a two -position "home/automotive" switch that boosts the high -frequency output of the speaker in the automotive position to compensate for the masking effects of road noise. Speaker-lead in-line fuse holders are also supplied with the ALS 3. Price: $125. The speaker was listened to in the horizontal position with the rear-panel switch set for home listening. The efficiency of the ALS 3 was about average for the smaller speakers of the group, though power handling was somewhat below average. Bass performance impressed the panel favorably, particularly given the small (2 -liter) enclosure volume. The speaker seemed to be somewhat lacking, in the opinion of several panelists, in a sense of "air" and openness, but its frequency balance and level of definition were both very well regarded by the panel, as was its relative lack of coloration. On balance, it was among the best liked of the smaller speakers tested. Remarks: "Unusually deep bass extension." "Nice, full sound . . sonorous." "Not bad on the whole, but seems to have a little too much in lower midrange." "Very good bass extension . . good sense of instrumental color on strings." Ratings: bass extension, B; power handling, C, general listening quality, B+."

Of course, the latter review is rather subjective and lacking in measurement, but it was also comparing these tiny automotive speakers with much larger "mini" speakers back in the day when Advent NLA's were considered average size. The power handling does not seem to be lacking in a small enough space where speakers this size would be appropriate. That includes my GMC Motor Home, which is at most 800 cubic feet.

But that's one of the issue with RV's. Modern motorhomes that (at least) resemble highway buses will be filling some multiple of the volume, but these vintage motorhomes are a lot smaller, and so are Class C motorhomes and travel trailers. In those spaces, 86 dB/watt-meter can make 100 dB SPL at the rated power of the speakers. That's more than loud enough, at RMS. Even the "ff" fuses will pass quick musical peaks unaffected. It's a different set of issues than one must address in their living rooms.

Rick "hasn't measured road noise but betting it's at least 70 dB SPL" Denney
 
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I thought I should summarize the trip that motivated the activity in this thread, as a bit of closure. I joined a caravan of local GMC owners in the NoVA/MD area and we caravanned to Michigan for a rally of about 120 similar afflictees who brought their coaches. After a week of hanging with old friends (I've owned this thing for 20 years), we drove to Pontiac to the M1 Concourse. The M1 Concourse is the former proving ground of the GMC Truck and Coach Assembly Plant in Pontiac, MI (later known as the GMC Pontiac West Assembly Plant). This was the traditional home of GMC trucks, starting when General Motors bought Rapid Motor Vehicle Company in 1913. They made pickups (up through GMC K-series and Chevrolet C-series pickups), highway buses, transit buses, and GMC Motor Homes at this facility, through its final closure in 2005. All of the buildings have been razed except for the original foundry building and the proving-ground test track and skid pan. In 2014, the facility became the M1 Concourse, self-described as a playground for auto enthusiasts, but I would describe it as a vanity race track for very rich auto enthusiasts. Those private garages in the background cost more than my house, with my (much better but much less luxurious) shop included.

About eighty of us made the trek to celebrate the 50th anniversary of the start of production.

IMG_0966.JPG

(photo by M1 Concourse--I made photos, too, but I didn't have a drone.)

The coaches were made from 1973 through 1978, and they positioned the '73's on the front row because they were the ones celebrating their 50th year. You can see that they came in two lengths, 23 feet and 26 feet. Mine is the blue 23' coach on the near end of the front row. At the event, we heard from several surviving GMC engineers and technicians who worked on the motorhome project during its development and production. The GMC Motor Home remains the only fully equipped RV ever designed, produced, and outfitted in its entirety by one of the Big Three automakers.

From there, we all parted and I drove to Jackson, Michigan to visit family, and from there to Indianapolis for a work trip. After that, I stopped in Columbus to have dinner with my niece and then drove back to NoVA. The trip was about 1600 miles total.

It was not entirely without incident. I discovered that a long-abandoned mouse nest had been constructed around the base of the fuel filler tube where it projects through the cockpit floor to the filler, which is right under the driver's window, behind the interior panel. Mouse urine is acidic and corrosive, apparently. I had a perforated rust hole that started leaking gasoline onto the ground when I filled it up. I was able to repair that at the rally. I also had a minor transmission shifting problem resulting, I surmise, from a bit of grit or something affecting the pin that the transmission's vacuum modulator actuates. A bit of manipulation freed that up and it hasn't been an issue since then. The coach now has an indoor home, so I'm anticipating that these sorts of issues will be more rare--that and the coach sat idle for too long during Covid.

The paint on my coach is about the worst of any of them you see in the picture above, but the drivetrain should be among the best as long as I drive it frequently enough. The interior is in the middle of the range--clean and highly functional but I never intended it to be like the rolling bordellos one sees at RV shows these days.

But there's absolutely no question at all that mine has the BEST sound system of any coach at the rally. During the open house, I had light classical music playing in the background and that was a surprise to everyone who went through my coach. (Being one of the few 23-footers with a General Motors interior, lots of GMC owners are curious about mine, so I usually get good traffic during the open house. But my reputation in that crowd is as a mechanic, not as a music-lover or audio enthusiast. Even so, one of my good friends in that crowd is a former top executive for a commercial audio company you have heard of.) When driving, however, the combination of road noise and being three feet from a well-tuned and header-equipped Oldsmobile big block engine makes classical music difficult, so music on the road was prog rock, played loudly.

(I did also come home with a nice PA system that included a Crate six-channel powered mixer and two Crate PA speakers with stands from back when they were made in St. Louis. The big owner's club that was hosting the rally was liquidating some old equipment in favor of newer, lighter stuff.)

This coming weekend will be more normal local camping, and my wife will be able to come this time, so no loud music.

Rick "last trip of the year" Denney
 
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Dilliw

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Got to ride in one of those back in the 70's when our friends from Missouri came for a visit. The view from the passenger's seat was amazing! Love your project.
 

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rdenny
I am curios about how you have your transmission gearing, overdrive, etc setup & what rpms you are turning at 60 and 70 MPH?
 
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rdenney

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The transmission is stock, and overdrive isn’t something that was common in the day. And power demands for a 10,000-pound vehicle aren’t conducive to overdrive gearing anyway.

Final drives are where people mess with that stuff. The stock final drive was a 3.07 differential, which is a lower gear than the 2.56 that came in the Toronado, but is still too tall. I’m using a 3.21 final drive made for the Cadillac Eldorado in its sportiest trim. It uses planetary gears and is said to be bulletproof. That puts engine RPM at about 2700 at highway speeds. This is still a little low, probably. The Olds 455 is a strong engine and mine has a forged steel crankshaft. Also, my coach is lighter than the 26’ models and I don’t tow a car, so I can get away with that.

Tires are 16” 225-75 so only about 30” in diameter.

Other solutions are available. One couples that 3.21 final drive with an alternate chain drive between the engine and transmission to provide a combined 3.55 or 3.60 gearing. And differential-style final drives are available in 3.42, 3.79, 4.10 and probably others. GMC developed the 3.42 but never implemented it before production stopped.

Production stopped because GM Corporate halted big-block engine production, except for the Chevy 454, which was too tall to fit, and there was no alternative drivetrain for the motorhome. And they figured that plant could make 100 pickups in the space and time one motorhome took. Of course, that plant was ancient even then and is now gone.

Rick “knows of one guy that installed a GM 8.1 engine in his coach” Denney
 
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