Audio Questions on 70 SF

MONC440

MONC440

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I just picked up a working 2 channel AM/FM Philips Mark 2 from a member. I want to keep the original radio, I'm not going to spend the money to have the internals updated because it isn't in the budget. I'm not looking to blow out the windows or set off car alarms, just some nice music while cruising. I have some questions about configurations for what I want to do. I would also like to hear some opinions about speaker split and best sound quality. I will say I'm a audio newbie, I have installed many complete systems that are made to work together but nothing using a 50 YO radio. I have done some searches on here and found some info but got confused because again, I'm a newbie. I know each channel on these radios need 8 ohms. I want to run 4 speakers, 2 in front and 2 in rear. I can find many 4 ohm speakers so I will run 2 in series to get the 8 ohms per channel. Below are my ideas.

First idea is split the system with one channel running the left front and rear speakers and one channel for the right front and rear speakers.
L R.png


Second idea is split the system with one channel running the front speakers and one channel for the rear speakers.
F R.png


Lastly I wanted to ask about running a 2 channel amp as shown below. Will the amp hurt the old radio? Is there a better option to boost the output to the speakers? Remember I'm a newbie. lol
AMP.png
 
HOLD THE PRESSES!!!!

If the radio only has three wires, right-left-ground, it is probably a factory stereo radio. That is how the 1970 AM/FM Multiplex Stereo radio I bought to upgrade my 1970 Monaco with. I bought it new from Chrysler Parts in about 1977.

These factory steros were UNIQUE in that they had three front speakers (rh, lh, and center) AND could have a pair of rear speakers. It used a "divider box" to run the three front speakers, with the center channel being a "composite/blend" of the two channels. The output, after the divider box, was to a dual-gang fader to the rear speakers.

The wiring of these speakers is in an inset in the wiring schematics in the 1970 Factory Service Manuals (free download at www.mymopar.com (might have to manually input that address).

Many can recite electronic "laws" about impedances and such (which I fully respect!), but many people ran 4ohm speakers in place of the factory 8 or 10 ohm speakers, in the 1970s, with no "smoke", including me.

What you CAN do, to run 4 speakers, is to use a dual-gang factory stereo fader, and run the system as if it was a GM "internal ground" system. One feed wire for each speaker. Then use the speaker terminal not used to run a wire to a mounting bolt to ground the speaker. On aftermarket speakers, you will notice any supplied wiring will have indicated polarity, a copper wire and a silver wire, which then relates to the lugs on the speaker width. To determine polarity, you can use a C-cell battery to make the speaker voice coil move one way of the other. Having them wired to all move the same way is necessary for best low frequency response.

Using the internal ground system wiring, you can probably just ground the existing ground wire to the car body, I suspect.

SO . . . enjoy the installation!
CBODY67
 
CBODY67 said:
HOLD THE PRESSES!!!!

If the radio only has three wires, right-left-ground, it is probably a factory stereo radio. That is how the 1970 AM/FM Multiplex Stereo radio I bought to upgrade my 1970 Monaco with. I bought it new from Chrysler Parts in about 1977.

These factory steros were UNIQUE in that they had three front speakers (rh, lh, and center) AND could have a pair of rear speakers. It used a "divider box" to run the three front speakers, with the center channel being a "composite/blend" of the two channels. The output, after the divider box, was to a dual-gang fader to the rear speakers.
Click to expand...
Yes that is the system my car had when I bought it. About 3 years ago I pulled out all the components (3 speakers, not working radio, wiring and divider) and sold them to a member. Mine didn't have the rear speakers or fader. I was planning on a modern stereo but have decided I want the thumbwheel radio stereo so I purchased a working on from a different member. I could track down the rest of the system as you suggested, something to think about.

Didn't the factory system have a separate thumbwheel for the fader?
 
The factory f-r fader looked the same, in the inst pnl, for both stereo and mono radios with rear speakers. Once behind the trim pnl, the fader was a t2o-gang fader. One knob and shaft running both faders (r & l) for the rear speakers.

The stereo rr fader mounts with the same mounting items, too. A bolt-in swap.

CBODY67
 
Anyone have any opinions on if an amp could damage the stereo? From what I read it would only happen if the amp ground was bad. I also read if you add an amp the stereo speaker impedance doesn’t matter and to match the speaker impedance to the amp. Any thoughts on this from people with some audio experience? Thanks
 
Back in the 1960s, when "component" home systems were coming into their own, you got a "tuner" and then put an amplifier with it to complete the system. How big the amp was did not matter, but it usually would be "plenty big enough" so that normal listening levels would barely tap the amp's capabilities. More amp power used would result in people leaving the room, by observation.

In these times, too, it was also revealed that bass notes took much higher power levels to produce those frequencies accurately and cleanly, without distortion. More power to move the speaker magnets farther and faster. As the high-frequency speakers needed a fraction of that power to do their job.

"Impedance"? I have always looked at that as "resistance", but there can be more nuances to it that that. One "electronic law" that can be "bent", it seems. Just not too far.

To me, the more power a circuit handles, the MORE important grounds can be. In "no resistance" terminals and such, as "resistance = heat". "Power generation" is similar, as many home unit amps have internal cooling fans and massive heat sinks to dissipate the heat they generate.

Also on home systems, the measure of a good or great amp was its "Total Harmonic Distortion". Lower the better, into the less than 1% range. Just like the tuners, lower percentages are the best. When I looked for similar figures for the car items in the 1980s, those measures were not there. If they were, by comparison, the car items were "horrible", if one only looked at the numbers, but sounded very good when listened to, to me. A "dead silent" home environment accentuates the need for the best reproduction accuracy, but in a car system, the outside sounds, the many surfaces which can have sympathetic resonances, and the fact the tuner "moves" as the geographical location of the vehicle moves, all can make "total reproduction accuracy" an elusive target . . . although the factories have done a great job in dealing with these things, with better components and circuitry to make that happen.

Remember the "sound competitions" of prior decades? With some systems' low-frequency capabilities that could "stop a human heart"? It wasn't the dainty 15KHz sounds that did that, it was the 20Hz frequencies, as I recall.

Y'all enjoy.

CBODY67
 
Last edited:
MONC440 said:
Anyone have any opinions on if an amp could damage the stereo? From what I read it would only happen if the amp ground was bad. I also read if you add an amp the stereo speaker impedance doesn’t matter and to match the speaker impedance to the amp. Any thoughts on this from people with some audio experience? Thanks
Click to expand...

Seems like your plan would have been as easy search on the net but most solutions are to replace the HU or the wiring inside it. Many amplifiers have inputs for high level/speaker level wiring but I'm not sure how they react to splitting your single common ground to act as grounds for both right and left speakers. Below is a combo I have NOT done myself but would do it if I wanted to keep factory HU. Other than the first common ground converter there are other options than the ones I found. Some 2 channel LOCs support common ground high level inputs.


Floating Ground Adapter
converts your common ground speaker wires (total 3) to floating ground (total of 4). I have purchased from these guys before.

https://www.amazon.com/gp/product/B09YVWCHP5/ref=ewc_pr_img_1?smid=ATVPDKIKX0DER&th=1
this LOC converts your 2 channel hi/speaker level inputs (now floating) to 4 channel low level (RCA) outputs. Plus it has a few ground isolation circuits that remove noise and will boost your signal to your amp (line driver). And allows you to set levels for front a rear so basically a fader.

https://www.amazon.com/SounDigital-...s&sprefix=4+channel+amp,electronics,90&sr=1-1
This amp is small and reviewed well. I have one. Class D so more efficient with power. There are certainly cheaper 4 channel amps with less watts. This is just an example. You dont have to get a 4-channel amp, you could use a 2 channel, but you will need one capable of 2-ohm load if you want to run 4 4ohm speakers. And you lose your fader. Yes, once you get your signal to the amp only the amp impedance specification is relevant and standard 4 ohms speakers will be fine.

https://www.amazon.com/GTO629-Coaxi...refix=jbl+car+speakers,electronics,165&sr=1-1
and then some high sensitivity speakers. I bought these once too.
 
bnz84 said:
Seems like your plan would have been as easy search on the net but most solutions are to replace the HU or the wiring inside it.
Click to expand...
Thanks for the info. Yes I found lots of examples with changing the HU but not much about keeping an original one, plus the info I found I was having a hard time following as I am a novice. In the past I would just go down to the auto audio store and buy a complete system all made to play well together and install it. I installed some killer systems but never had any experience with how they work, just install and rock. lol
 
The LOC and amp wiring is pretty straightforward. One the floating ground the description says
The “floating” ground side has 5 wires.
Channel 1 = White, White/Black stripe.
Channel 2 = Gray/ Gray/Black stripe.
Chassis ground = Black.
The “common” ground side has 3 wires
Channel 1= Gray (+)
Channel 2= Green (+)
Ground (“common” to channel 1, 2, and chassis ground) = Black

My question is are the grounds going to chassis? Then are the speakers using chassis ground or grounded thru the amp?

Thanks
 
In one respect, the "ground" can be either place, but it will eventually end up to the vehicle body.

The internal radio amp will ground to the body via a "back brace" between the radio shell and the instrument panel structure. One wire speaker or two-wire speaker wiring. OR a mix ov the two, as the 1980 Chrysler OEM stereo radios were. Front speakers were two-wire, but only one wire/speaker for the back stereo speakers.

If you are using an aftermarket radio, which might not use a back brace, then wire everything 2-wires/speaker and let the ground go through the main power lead (power and ground) connection.

Just some thoughts,
CBODY67
 
CBODY67 said:
In one respect, the "ground" can be either place, but it will eventually end up to the vehicle body.

The internal radio amp will ground to the body via a "back brace" between the radio shell and the instrument panel structure. One wire speaker or two-wire speaker wiring. OR a mix ov the two, as the 1980 Chrysler OEM stereo radios were. Front speakers were two-wire, but only one wire/speaker for the back stereo speakers.

If you are using an aftermarket radio, which might not use a back brace, then wire everything 2-wires/speaker and let the ground go through the main power lead (power and ground) connection.

Just some thoughts,
CBODY67
Click to expand...

Thanks for the info. I'm going to keep the original Radio.
 
Yes instructions are weak, but I think for the common side it is just as it says - 3 wires from head unit to 3 wires on LOC. For the floating side I would locate the ground to chassis at the same place the amp is grounded to. So thinking this thru, assuming your amp is ibn the trunk area, I'm thinking you use any Ethernet cable with really good S/FTP shielding from HU to ground adapter in trunk. Ethernet has 8 wires. twist 2 together for R+, 2 for L+ and 2 for ground. Twist the last pair together and do not use them unless you need some additional grounding between HU and amp. In this case I'm suggesting ethernet cable because its compact, great interference shielding. And cheap. The original HU produces zippy for watts so no issue with conductor size. Then on 1 piece of plywood mount adapter, LOC, and amp and ground them to the chassis at the same location. That LOC has settings to reduce noise and ground loop hum so maybe ethernet is overkill. Generally high level signal through whatever type wire you got does not pick up much noise...but strange stuff happens with old electronics.



Use good but short RCAs from LOC to amp.


btw that loc has a few clones. most of them are more expensive




 
And just to torture you, my plan for my 69 is similar but more elaborate. It starts with an aftermarket radio that has a detachable face. Then I make a new face using 3d printing that will attach to the new HU. I'm 1/2 done the design but finishing is stacked up behind other projects. The radio faceplate I'm trying to reproduce is just like yours only the AM only version. You just gotta love those thumbwheel faces


https://www.amazon.com/dp/B07Y2DQPC...5LQSMX828&ref_=list_c_wl_lv_ov_lig_dp_it&th=1
1750351889038.png
 
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