Stock 8 Track radio with modern speakers and AMP - Chevelle Tech
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post #1 of 14 (permalink) Old Jul 8th, 13, 12:04 AM Thread Starter
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John
 
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Stock 8 Track radio with modern speakers and AMP

I'm going to put the stock 8 track am/fm radio back in the car. Id love to run a dual radio setup where I can use the factory 8 track, xm radio (hidden) with modern speakers (non-10ohm) and amp


Anyone running the 8 track with new speakers and amp?

How are you doing it? I've heard you MUST have 10 ohm speakers. Is there an adapter or something to run inline.

I'm imagining dual wiring the speakers where there can be a 10 ohm load for the old radio and then a parallel path that the newer amp and xm can drive
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post #2 of 14 (permalink) Old Jul 8th, 13, 12:45 AM
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Derrick
 
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Re: Stock 8 Track radio with modern speakers and AMP

assuming you get an amp that doesn't have high level inputs where you just hook up the stock speaker outputs, you will need a converter box to convert your speaker outputs to rca inputs to plug into the amp- the radio will only be putting out a couple of amps at best due to the low level power draw of the amp, so the load won't matter.
then you just run modern speakers... but keep in mind that the high power sound coming out of the amp is only as good as the low power sound going in only louder, so it's going to sound like a crappy 45 year old 8 track radio that is a lot louder than stock..

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post #3 of 14 (permalink) Old Jul 8th, 13, 3:28 AM
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Levon
 
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Re: Stock 8 Track radio with modern speakers and AMP

Hi John.
You could do what I did and wire the audio from the 8 tracks pre amp out to the aux input of the newer stereo. I used a couple of capacitors as well to keep the hum out.

You have to leave the volume at almost "off" to ensure you do not blow your 8 track amp as it is open when you do not have a speaker load on it.

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post #4 of 14 (permalink) Old Jul 8th, 13, 9:45 AM
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Keith
 
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Re: Stock 8 Track radio with modern speakers and AMP

Levon,

Not too hard to get there, and several roads you can take. Basic concept: you must convert the output signal of your eight track into a line level signal and then input that converted signal into an auxiliary input of your "modern" stereo system.

3 methods To consider, with some detail...

Method 1. Take the high level low impedance output of the 8 track (AKA "speaker wires") and connect them to an T pad with about 50db attenuation. (Google "T pad calculator") Connect the output of the pad to the primary of a 600/50k matching transformer. (One of the above for each channel) voila! Instant isolated line level signal. the secondary of the transformer can feed into your modern head unit or amplifier. Treat it just like any other line level unbalanced signal. Because of the transformer isolation, you will have no issues with ground loops or hums. Because you are using the entire circuit of the eight track, any distortion present in the power amplifier of that device will naturally pass through to your main system.

Method 2: Open up the 8-track unit and tap the signal right off the output of the volume control knob. That's preamp level signal right there. (Treat that as a line level signal and put it right into your modern head unit' aux input, etc., via a 1/8 mini jack, or RCA phono plug, per your modern head unit's particular requirements. Because you're not providing isolation between the two systems, it is possible that this setup will introduce him or other noise problems which may have to be dealt with by a 1:1 isolation transformer. Careful star grounding of both systems may reduce or eliminate this issue.

Method 3. Lanzar makes a cheap and surprisingly decent performing mixer preamp called the vibe 440. It has an USB input, an SD card playback slot and a high/low-level auxiliary input on it - all front panel selectable. With this device as the control center of your modern stereo, you could take the output of your 8-track's speaker wires and connect directly to the Lanzar "high level" preamp input. You could connect your XM to the "low level input", and simply plug your iPhone or iPod into the USB port. The simple and fairly elegant solution to mix the three devices. The Lanzar 440 has volume and tone controls on it.

Whatever you use, if you have not yet selected your head unit for your "modern" system, make sure to select one that provides for at least one or preferably two auxiliary inputs (besides its own internal choices of CD/XM/etc.) back panel mounted aux inputs are of course cleaner and neater, but a front panel mini-jack intended for an iPod can be made to work. The wiring is just not as neat.

Just some thoughts...

Keith

Owner: World's Fastest 66 Chevelle - really...it's really really fast since I put on that chrome differential cover
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post #5 of 14 (permalink) Old Jul 8th, 13, 6:48 PM
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Re: Stock 8 Track radio with modern speakers and AMP

Now c'mon guys, no need to make a science experiment out of this.

Keep it simple.

Yes, you will damage the radio if it is not used with 8-10 ohm loads.

If you want to run the output of the original radio THROUGH the line level inputs of an amp or modern stereo, you will need a line level converter AND some proper loads.

The factory stereo equipment only has 2 channels, LEFT AND RIGHT for true stereo. The Left channel is composed of the LEFT FRONT SPEAKER and the RIGHT REAR SPEAKER. The Right channel is composed of the RIGHT FRONT SPEAKER and the LEFT REAR SPEAKER.

You would need to adjust the fader on the factory stereo to the full front position. Then connect these 8 ohm resistors across the left and right channels (the front outputs):

http://www.radioshack.com/product/in...ductId=2062288

This way the radio always "sees" a load. The modern line level converters and amps do no load the original radios enough and you will burn out the output circuitry.

Then you would connect your line level converter across the resistor loads. Something like this:

http://www.crutchfield.com/S-2YV2NC9...evel+converter

Too much money? do a search on ebay and spend about $10.00 for the same unit.

If you're worried someone will mess with the factory fader adjust, then attach some more of the 8 ohm resistors I linked across the rear output connections.

Incorrect loading/connecting of the factory radios is just as damaging as no speakers/incorrect speakers.

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post #6 of 14 (permalink) Old Jul 9th, 13, 9:31 AM
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Keith
 
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Re: Stock 8 Track radio with modern speakers and AMP

Good catch, Joe! Totally forgot about the OEM output. Yes, one must deal with the now "unused" output section of the 8 track.

To do that, one can certainly utilize a pair of load resistors, just as Joe noted. Or one could simply remove the B+ to the output transistors themselves...which is easy and free. No B+ = no current with which to "burn out" those output transistors. (Don't have the schematic in front of me, but if these are the typical GM single ended class A output devices, Then this is a one wire, easily reversed mod.)

This way, one doesn't have to find, purchase, wire up and make a safe place to hide those hot load resistors. :-)

More significantly, by taking the signal off the volume control, one totally avoids the additional distortion of the output section of the circuit! Yea, better tone!

Yes, this approach requires a LITTLE more effort. But, besides a little wire and solder, and perhaps a couple RCA phono plugs or a mini-jack, you've spent near zero dollars, gotten your cleanest possible line level signal and totally protected your OEM 8 track's output section - by simply "shutting it off". Don't have the schematic, but this seems like an effective and elegant solution to me, with the cleanest possible final wiring solution.

But Joe's right - it is more difficult. IMO, it is worth the effort. But I admit, I'm a recording engineer with finicky ideas about audio quality!

:-)

Of course, You will have to get a schematic, open up the 8 track player to get to the goods, though. Maybe you are not comfortable with that level of electronic hot rodding? What Joe outlined will work, and is outside the device only...

But those cheap line level converters sound pretty substandard, IME.

Keith

Owner: World's Fastest 66 Chevelle - really...it's really really fast since I put on that chrome differential cover
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post #7 of 14 (permalink) Old Jul 9th, 13, 5:42 PM
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Keith
 
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Re: Stock 8 Track radio with modern speakers and AMP

O.K. so I stopped for a minute and looked at the schematic for the typical late 60's early 70's GM 8 track.

Some details, for the curious.

http://www.gt-37.org/gallery/main.php?g2_itemId=3702

This is a schematic and service pages to the early 70's 8-track


1. First, be aware that the output section of the 8 track power amplifier is built around the standard GM DS-503 Germanium transistor equipped class A transformer coupled output section...same as any GM AM or AM/FM radio from the era. Nothing special about this.

2. Second, it looks to me like there may not actually be any need for external "load resistors", either. In fact, it appears to me that the Front/Rear fader actually provides a nominal load function. It is a 100 ohm 2 watt unit, which appears to be in the circuit at all times. Set it to the middle and forget it is a definite possibility. Appears to me that the output section will always have at least a 50 ohm load present, even without speakers connected. But if you are really paranoid, you easily can lift the .68 ohm fusible resistor (found at 14 and 23 on the schematic), disconnecting the current and completely shutting down those two DS-503 output transistors, (as I previously suggested)

3. Yes, the preamp level signal definitely appears at the output wiper of the stereo volume control. Tap it there, you're golden. Wires #12 and #21. Should be no DC present there, but check with a meter to be safe. The capacitors C30 and C34 block it downstream, and C9 and C13 block it upstream, so no DC present on the wiper of the volume control. Should be able to swing close to a volt there, which is plenty to drive any reasonable head unit aux input.


Just clarifying my previous post, for future researchers who face this same question, and might want to approach it as I suggested.

Keith

Owner: World's Fastest 66 Chevelle - really...it's really really fast since I put on that chrome differential cover
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post #8 of 14 (permalink) Old Jul 9th, 13, 11:39 PM Thread Starter
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John
 
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Re: Stock 8 Track radio with modern speakers and AMP

wow this is detailed info and a path I'm willing to take. I dont have the original unit for the car and will be buying a unit that has been completely redone. The car has of the old looking but modern guts inside.

The reason to do the 8 track is that it is just damn cool to pop in some Floyd on an 8 track go with the whole 70's feeling.

So how about disabling one set of outputs like you suggested, drive them to one set of speakers...say the foot vent speaker option. Id change that up in the interior....its hidden enough. Then run the XM to the dash and rear speakers where I can have a nice clean amp and for my audiophile friends lets see if can get a McIntosh car amp with some Focal speakers! nice and not too crazy.
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post #9 of 14 (permalink) Old Jul 9th, 13, 11:49 PM
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Keith
 
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Re: Stock 8 Track radio with modern speakers and AMP

Take that schematic link I posted to a reasonably reputable tech. He could knock out the mods in under an hour and provide you a set of pigtail lead RCA outputs without drilling a hole in your OEM 8-track deck. Connect that to the new head unit/amp/speakers of your choice,

Keith

Owner: World's Fastest 66 Chevelle - really...it's really really fast since I put on that chrome differential cover
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post #10 of 14 (permalink) Old Jul 10th, 13, 1:56 PM
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Re: Stock 8 Track radio with modern speakers and AMP

John,

So are you wanting to modify a totally stock radio/tape player or one that has been modified already with modern internals? I got confused by your most recent post.


Keith,

While I appreciate your willingness to help, you need to get your facts straight before posting. Your last post with the schematics you "assumed" are same (or close to) are different. You are correct the general layout and circuit function is typical Delco, but you shouldn't make statements in regards to things you don't know about. For example, the DS-503 is not the standard all of these audio systems were built around. Full-size standard radios and AM/FM mono units use DS-501 outputs. They also use a different emitter resistor. The Am/Fm stereo equipment and Am/Fm/combo 8's use DS-515's. Also there is no "nominal" load with factory faders. They are an interesting device and very "sensitive" if you move them one "tick" the wrong way--wrong way being towards the side of no load. Been there done that with a customer I told not to turn his stereo until all speakers were connected in his '70. Lets just say I ended replacing the output transistors and emitter resistors twice...

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post #11 of 14 (permalink) Old Jul 10th, 13, 6:44 PM
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Keith
 
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Re: Stock 8 Track radio with modern speakers and AMP

Yes, good point. I retract. Very careless of me to make that assumption.

Yes Joe, you are absolutely right - I am not familiar with schematics from every GM design from the era.

The single 8 track schematic I examined (and posted) featured the DS-503 germanium transistor transformer coupled single ended output section. It appears to be for a 1971 era 8 track. Besides the stereo aspect, the power section looks essentially identical to a 1966 Delco mid sized AM radio schematic. Because of that, I made a false leap of logic to presume it represented a general representation all GM 1960's outputs, but surely you can see how easy such a leap would be, right?

That said, the gist of the original poster's question was basically "how to acquire a reliable line level signal from an OEM 8 track", was it not?

On that topic, I remain confident that on Delco designs from the 60's and 70's, one may generally acquire the best quality line level by tapping that signal off the wiper of the device's volume control.

I've sniffed enough solder for the past 35 years to tell you that there is no way to argue against that. Joe, you and I both know that the first stage of a Delco (or ANY) class A audio preamp is inevitably cleaner than that same output after it passes through three additional stages of amplification and ends with a transformer...and THEN goes through some Chinese made "line level adaptor".

re: "all full size radio units and AM/FM mono units use DS-501"

We will have to agree to disagree on that one. I have now in my possession a full size 1966 Delco radio from an Impala which absolutely was factory equipped with a DS-503 output transistor. I know because I can spot virgin gear, and this radio was virgin as a nun when I removed it from an unmolested donor car, disassembled it and cannibalized the DS-503 into my DS-501 equipped Chevelle radio, where it now resides, perfectly functional and content.

But on the whole, you're right. Nothing like the schematic to make a liar/guesser out of me.

John, follow Joe's advice on this matter.

The moderators may remove my previous posts if they wish to eliminate any source of confusion.

Keith

Owner: World's Fastest 66 Chevelle - really...it's really really fast since I put on that chrome differential cover

Last edited by CoolBlueGlow; Jul 10th, 13 at 7:34 PM.
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post #12 of 14 (permalink) Old Jul 10th, 13, 7:33 PM
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Joe
 
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Re: Stock 8 Track radio with modern speakers and AMP

John,

PM me if you would like a schematic of the audio section for the combo am/fm/8track.


Keith,

I sent you a PM.

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post #13 of 14 (permalink) Old Jul 10th, 13, 10:48 PM Thread Starter
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Re: Stock 8 Track radio with modern speakers and AMP

My goal is to play both the 8 track and a xm sat unit.

It would be great to install nice speakers and run them a nice small hidden sub somewhere. I'm fine that the 8 track will sound like what it is but when I turn it off and turn on the sat unit I'd like modern quality. The issue as I see it is the 8 track unit and that it wants a specific load. Running the 8 track into a high line amp signal won't cut it I guess.

It would be great if I could have the stock unit with modern guts so I can drive modern components.... But I get it....supply and demand.

I think having two completely separate radios may have to be it. I'd have the person disable half the 8 track amp, getting an expert. Run the 8 track to one set of speakers, perhaps the dash.

I'd run modern speakers to the foot wells by buying those footwells with speaker provisions and the the rear deck.
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post #14 of 14 (permalink) Old Jul 11th, 13, 11:51 AM
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Joe
 
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Re: Stock 8 Track radio with modern speakers and AMP

Hmmm, well it kinda gets back to options and what you want to do.

Are you thinking of using one of those small XM receivers like my "Roady2" that needs to plug into something for high level output or leaning towards a modern head unit that receives Am/Fm/XM and powerful outputs?

There are so many configurations it can make you go dizzy... You could have someone update the output circuitry in the am/Fm/8 so it's powerful and add a line in for xm audio from the xm receiver. You could install a modern stereo and have its line in inputs connected to the 8 track as outlined. You could install a system of relays and resistors so the high output stereo could "share" speakers with the 8 track without blowing anything up....
It's all about what you have, what you want, and of course how much you want to $$.

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