2700 ETR based system, was lost, now not so much

[1987 GMC Jimmy]

I've been doing the same with mine for about a year and a half now. The distortion was really bad at first so I adjusted both EQ settings to about 80% of max. I can play it at a respectable volume that way but definitely nothing crazy or it'll distort. Personally, I have no frame of reference as to how long that can continue. Maybe it'd mess up tomorrow or maybe it'd go indefinitely working that way. By the sounds of what you're saying, it could very well go until the DM165 internal amps die. I'm pretty sure 8 ohm impedance is a peak figure for the stereo, and it's not always that much. I do know that, depending on the amplitude and frequency of the sound it's producing, there's a load on the HU that probably shouldn't be there. I'd be more comfortable with the whole thing if the impedances were matched for longevity of the 30-40 year old OEM stuff and if the output was boosted just for sound quality and loudness. I think these radios are pretty good for how old they are but laughable by what modern ones are doing. I'd rather keep the factory in every situation for the aesthetics and the feel of something old, but if I can make it sound good or even great in the process, I think that's the way to go. I'm going to attach a page talking about the DM165s with regard to 1985-93 Delco 2000 radios. I imagine this somehow translates to Delco 2700 ETRs, but I can't speak to it with any certainty.

http://www.howtoalmanac.com/Scott/HowTo/02-12-DelcoGMDM165AudioAmpRepair.htm

 

[Green79Scottsdale]

So I have been letting things roll around in the empty space between my ears for a bit.

I already emailed Crutchfield with this question, but thought I would ask it here also. I will post their response when I get it.

Say I do add an amp to the radio. Does that then negate the 8 ohm vs. 4 ohm impedance issue regarding the speakers? In my mind adding something between them kind of does away with the direct connection of ohms to watts of power that I understand is the issue. Especially if you are adding an amp that is handling the boost in watts instead of the radio itself. It would make choosing speakers a lot easier.

 

[Green79Scottsdale]

Got a response back from Crutchfield about my amp question. Here is the reply...


"Thanks for the email. I don't have a ton of info to go off on a system that old but yes if the radio is really only stable at 8 ohms, 4 ohm speakers could cause it to overheat. However very few car radios are not 4 ohm stable so I wouldn't be worried.

But if you plan on putting in an amp it makes no difference at all. The amp will take over the job of driving the speakers and all the radio is doing is feeding signal to the amp. Any modern amp will be at least 4 ohm stable and many will even be stable down to 2 ohms, but like 8 ohms, 2 ohm speakers are far less common."

My thoughts confirmed. This is probably going to push me to get an amp too. Uncharted territory for me tbh.

Thought it would be good to post for anyone who searches this type of thing in the future.

 

[Daveo91Burb]

So I have a novel solution to the 4 ohm speaker/8 ohm radio issue that I've used in my '76 vette for years, with no problems. I simply converted the original 2 speaker system to a 4 speaker system but I wired the channel pairs in series, not parallel. So the left channel has a front/rear pair wired in series and likewise with the right channel. Two 4 ohm speakers in series = 8 ohms/channel and radio doesn't know any different. I'm sure Crutchfield, Car toys, etc. will tell you that you can't do that, but it works fine, sounds decent, and hasn't ruined my original delco which for early-mid 70s Vettes often go for five or six bills in good working condition. My front vs rear speakers aren't even identical and it works fine, although I think it would be safest if they were identical.

This would obviously be a lot more complicated and possibly unworkable for you guys that are already working with 4 speaker delco systems. But I guess you could go to an 8 speaker system if you wanted to try to make it work. I mostly just threw this up here in case it would help someone do a low-buck conversion to modern speakers with the original radio.

I also went with a Scosche FM modulator that's inline with the antenna cable for iPod input. You hear a lot of static when there's no ambient noise, but going down the road with the top off and the dual magnaflows singing you don't really hear the static.

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[1987 GMC Jimmy]

So I have a novel solution to the 4 ohm speaker/8 ohm radio issue that I've used in my '76 vette for years, with no problems. I simply converted the original 2 speaker system to a 4 speaker system but I wired the channel pairs in series, not parallel. So the left channel has a front/rear pair wired in series and likewise with the right channel. Two 4 ohm speakers in series = 8 ohms/channel and radio doesn't know any different. I'm sure Crutchfield, Car toys, etc. will tell you that you can't do that, but it works fine, sounds decent, and hasn't ruined my original delco which for early-mid 70s Vettes often go for five or six bills in good working condition. My front vs rear speakers aren't even identical and it works fine, although I think it would be safest if they were identical.

This would obviously be a lot more complicated and possibly unworkable for you guys that are already working with 4 speaker delco systems. But I guess you could go to an 8 speaker system if you wanted to try to make it work. I mostly just threw this up here in case it would help someone do a low-buck conversion to modern speakers with the original radio.

I also went with a Scosche FM modulator that's inline with the antenna cable for iPod input. You hear a lot of static when there's no ambient noise, but going down the road with the top off and the dual magnaflows singing you don't really hear the static.

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Perhaps you could try the bass booster EQ on whatever you’re using to trim some of that static away. I need to do this, though.

 

[Green79Scottsdale]

So I have a novel solution to the 4 ohm speaker/8 ohm radio issue that I've used in my '76 vette for years, with no problems. I simply converted the original 2 speaker system to a 4 speaker system but I wired the channel pairs in series, not parallel. So the left channel has a front/rear pair wired in series and likewise with the right channel. Two 4 ohm speakers in series = 8 ohms/channel and radio doesn't know any different. I'm sure Crutchfield, Car toys, etc. will tell you that you can't do that, but it works fine, sounds decent, and hasn't ruined my original delco which for early-mid 70s Vettes often go for five or six bills in good working condition. My front vs rear speakers aren't even identical and it works fine, although I think it would be safest if they were identical.

This would obviously be a lot more complicated and possibly unworkable for you guys that are already working with 4 speaker delco systems. But I guess you could go to an 8 speaker system if you wanted to try to make it work. I mostly just threw this up here in case it would help someone do a low-buck conversion to modern speakers with the original radio.

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I absolutely agree with the logic. This option is still on the table for me too. I am investigating possibilities for the front speakers as I only have the middle speaker location, nothing in the corners.