70-77 radio to modern amp (with Bluetooth)

[b_hill_86]

I’m taking a stab in the dark but has anyone successfully (or knows if it is possible to) hooked a factory 70-77 stereo radio (common ground speakers) up to a modern amp that in turn drives modern (floating ground?) speakers?

Thanks in advance. You would be a godsend if you have a solution to this.

[Grand73Am]

If you want to use the original radio with modern 4 ohm speakers, you can do it if you connect an external amplifier to the radio's speaker output wires, and then connect the 4 ohm speakers to the amp outputs. I bought the amp in the link below for that purpose, but I haven't used it yet. You'd need an amp that has the speaker-level inputs feature.  Notice that this amp says it has speaker-level inputs in the "highlights" list. So, that's the idea. There are other amps that would do the job too. You could contact an audio components dealer like Crutchfield and tell them what you're doing and get some more recommendations for amplifiers. The one I have is fairly large and would have to go in the trunk. They may have smaller ones that will fit under the dash somewhere.

https://www.crutchfield.com/S-agX2QL2kF4p/p_130GMA4704/Pioneer-GM-A4704.html?XVINQ=DST&XVVER=G04&awcp=1t1&awcr=164108351022&awdv=c&awkw=&awmt=b&awnw=g&awug=9052492&gclid=EAIaIQobChMIgMi6yvPu3wIViI3ICh2LuAtpEAAYASAAEgJotfD_BwE

[b_hill_86]

I appreciate the response. The car in your profile pic looks to be a 79 or newer? If so that means your factory radio uses a positive and negative wire for each speaker I think. Mine is a 77 and the radio uses only one wire to each speaker and each speaker is grounded through the chassis. That’s the problem I’m running into. Not sure if this even possible to hook up a radio like that to the newer amp.

I actually chatted with a crutchfield rep earlier tonight. The ultimate answer was no, it cannot be done but I’m not 100% confident the gentleman I spoke to understood my circumstances completely so I’m holding out some hope.

[Grand73Am]

Okay, sorry, I didn't know the 77 and older radios were wired like that.

[b_hill_86]

No worries. I appreciate the response anyway. I’m thinking it won’t be possible unfortunately.

[Grand73Am]

I guess you're aware of turnswitch.com that sells a variety of new 10 ohm speakers?

[76 - 455 - 4]

Turnswitch can also transform your 10 ohm radio into a modern radio with Bluetooth and modern speakers.

[Gold member]

I have a 79 stock radio hooked to a 300 amp pioneer with Pioneer 6x9 in the back that sounds incredible . This was all in the car when i bought it so that about all i can tell you . I added a thing you can plug your phone into for music and i was good for the Power tour . 

[b_hill_86]

I guess you're aware of turnswitch.com that sells a variety of new 10 ohm speakers?

Yea I think. I knew they were available. Downside is my factory radio and the 8 track would only be front and rear speaker. Plus I just recently bought new speakers for the modern head unit I installed temporarily. Guess I just can’t have the best of both worlds lol

[Aus78Formula]

Yes, it costs a lot of money to end up with a highly inferior product.

[firebirdparts]

A long time ago I had a couple of pre-amp converters on a radio, and they seemed to work.  I wonder if that would work on a radio designed for 10 ohm speakers and floating ground.  In fact I think I still have them.

https://www.crutchfield.com/S-KoGkyxF7WqA/g_721/Line-Out-Converters.html

How could floating ground really matter?  For $10 worth a try.

[b_hill_86]

Just for clarification from the research I’ve done I think the pre78 radios with one wire per speaker are common ground and the 78+ or modern radios are floating ground. I could be wrong though. Anyway, as far as the line level converter I considered that. Everything I’ve seen says that won’t work with a common ground speaker output. The impedance wouldn’t matter meaning a 78+ radio which has positive and negative wires to each speaker but still require 8-10 ohm speakers would work fine with them. The common ground output is what is killing me.

I think I found my solution, and though not ideal, it should work. What I was trying to accomplish was reinstall my factory radio and console 8 track. I planned on using a line level converter like firebirdparts mentioned which would give me a left and right line level output. I was going to split that signal with an rca Y to the 4 (LF RF LR RR) line inputs on the amp so that the radio and 8 track would work the way they’re supposed to but drive 4 modern speakers which I happen to already have installed in my car. AND that particular amp has a Bluetooth radio in it so I can connect my phone.

Instead, a local vintage audio shop that’s done some work for me is going to create line outputs on both the 8 track and radio. By bypassing the amps in each I don’t have to worry about the common ground output. I’m going to run rca cables from each source to a stereo splitter switch that has two inputs and one output. From that output I’m going to split the left and right into two lefts and two rights to plug into the 4 line inputs on the amp.

As much as I didn’t want to alter the radio nor 8 track the changes will be reversible and could be done by a novice (at best lol) like me.

[firebirdparts]

I think you're right.  I used the wrong word.

I wonder if a person suitably skilled in the art could tap the right couple of wires going into the original amp, inside the radio?

[b_hill_86]

That’s essentially what the shop is doing for me I think. I’m not sure where he’s tapping into yet but he said he’s gonna show me. I’ll post here if he does in case anyone else wonders. It can’t be that difficult I wouldn’t think.

[b_hill_86]

I haven’t had time to mess around with it much yet but here’s a sneak preview hooked up with line outputs to a home stereo amp. I have a distortion issue with the amp volume low and tape player volume high and the right channel is a bit quieter than the left but it’s progress.

https://youtu.be/Y7JgPwarBh4

[firebirdparts]

I went into a restaurant in Asheville NC last fall, and the waitress had "they tell me of an unclouded day" tattooed on her leg.  I didn't say anything, but my buddy made her tell about it.  She was a big fan of that album  (and song) you are playing in your video.  She had become a fan of Gospel music as a result of that.

We also had Willie Nelson "Troublemaker" when it came out.  I guess we had it on 8 track as well.  had been a very long time since I heard that.

[b_hill_86]

Ha that’s funny. I honestly went to our local record store (partly cause I’ve been buying some vinyl recently) and picked up two tapes I thought wouldn’t be bad to test the player out. Not much to select from. One was that album and the other was a canned heat blues album.

[b_hill_86]

Don’t mind the mess but here are some videos to show proof of concept. One is the Bluetooth portion of the amp which can be controlled, including volume, by the wired remote. It sounds really good actually!

https://youtu.be/im0yBAwyl4U

Next is the factory radio playing through added line outputs, to the amp which is driving 4 modern speakers. Also sounds better than expected!

https://youtu.be/xV9W8W4pa3E

Last is the 8 track player also outputting through added line outputs. Doesn’t sound great as there is a hum, speed is slightly off and for some reason a decent amount of distortion when the volume is high but it’s a start.

https://youtu.be/jAQvs1zCkEo

Obviously I have to mount the amp still and reinstall the console and 8 track too but overall I’m really pleased with the Bluetooth and the function of the radio.

[firebirdparts]

That turned out great!  I guess you had to have the radio and 8 track both modified to do that.  The 8 track of course has other issues that might not be easy to correct.  Willie Nelson sounds like the mayor of munchkinland.  With the bluetooth you wont' really need that anyway.

[b_hill_86]

I actually was able to adjust the speed of the 8 track player so that part is fixed.

Yea, the radio and 8 track had to be modified to add the line outputs but the guy who did it said he’d show me how. Although I have been inside the track and saw where he tapped into for the line outputs and it still looks to be above my head. He wants to see it all installed in the car though so I’m hoping he has a solution for the hum as well as the distortion at higher volume. Even though I probably won’t use the 8 track that often I would love to get rid of the home and have it sound as good as the radio which has no distortion whatsoever.

[Aus78Formula]

Nice work adding upgrades to keep an original system. I think the worlds best 8-track player still muddy compared to anything since, more a novelty feature once you are prepared for the limitations. Plenty of those on these cars!

I had big plans too, sourced uncut dash pieces to graft in, all the brackets and a suitable amp and a selection of NOS and repro stereo items to add to an original rebuilt FM radio from a '78 Firebird that I had shipped over from the states, including the I-pod port, even though I've never had an I-pod. After doing some basic tests, even dropping to an auto electrician, I couldn't get it to do anything beyond light up. So that project got shelved, too hard, and too much money wasted.

Unfortunately, most of the 'classic style' stereos for single-DIN conversions are over-priced and average quality and often look cheesy and non-convincing.

[b_hill_86]

I wish I knew how to add the line outs in order to share with everyone. I think that’s the perfect way to modernize the early stereos that are in common ground speakers. Otherwise I don’t think it’s possible to add a modern amp.

I’m really happy with it though. Especially the Bluetooth. The ONLY thing that would make it better is being able to adjust the Bluetooth volume with the radio somehow but the amps wired remote is easy enough to hide when not in use.

[b_hill_86]

I think I have a solution just about anyone could use to hook a pre 78 radio or console 8 track (or even both simultaneously) to a modern amp.  More info to follow soon

[b_hill_86]

So due to the hum I mentioned above and the distortion at roughly 70% or more volume on the 8 track player I took it back to the shop. I had previously questioned him as to whether or not something like what firebirdparts posted, the line output converter, would work with common ground speaker outputs. He didn’t think so and I was afraid I’d fry something by attempting it myself. Not something I was willing to try on a working 8 track. I scoured the net and other resources but couldn’t find any info on it. However, since his attempt at adding the line outputs by tapping into some circuit inside didn’t work he was able to find info that suggested the converter would work.

Fast forward to me picking it up and it works! All he does is attach one factory speaker output to the left positive lead on the converter, the other speaker output to the right positive lead and grounded both negative leads to the case. It seems to work perfect!

This is the exact converter he used I believe but I don’t know why any other wouldn’t work. https://m.aliexpress.com/item/1918795021.html?trace=wwwdetail2mobilesitedetail&productId=1918795021&productSubject=Car-Speaker-to-RCA-Level-Adaptor-High-to-Low-Sockets-Auto-Line-Out-Converter-Audio-transverter

Below is a video that begins with Bluetooth audio from my phone. A press of the source button (blue to red) lets the amp accept device input. The next part is only necessary because of the condition of my radio. It had a fried chip in its amp that couldn’t be sourced or fixed. Shops solution was to build a separate amp but it uses a positive and negative for each channels. Eventually we tried the line output route which works great on the radio (didn’t on 8 track) but it required me to get an RCA switch which is the button you see me press in the video. It allows me to select the radio or the 8 track since the radio signal no longer goes though the 8 track. But now that I know the output converter works if my radio worked in its original manner there is no reason I couldn’t hook it to the 8 track the way it’s supposed to be and let the converter do its job for either the radio or 8 track depending on if a tape was inserted.

Btw the shop thinks it may be able to build that chip that’s fried in the radio. Whether or not I bother yanking everything out again to do that, I haven’t decided but it’s tempting and would allow me to get rid of the rca switch. Sorry this was so long winded but I hope it helps someone get the best of all worlds. I’m thrilled it actually worked and pretty happy with it.
https://youtu.be/1_gj_jdGgqw

[firebirdparts]

interesting.  I don't know how the converters work, so I didn't know why it wouldn't work either, ha ha.  It sounds good!

[b_hill_86]

Thanks! I’m pretty happy with the setup. A bit of trial and error but it ultimately works the way I want. Almost the best of both worlds.