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Magnavox astrosonic loudness pot issue

Ronnie baisden

Ronnie baisden

New Member
Hello everyone. I'm yet another newbie looking for some of your knowledge any appreciate any help I could get. Here's my issue:
I have a 1965 R214 chassis magnavox astrosonic. I inherited it a few years ago and remember it being louder back then. Now when I turn the loudness pot, it doesn't do anything until halfway. Then from the halfway point, it volumes up until I can't turn it any farther but ends at about half volume.
I have replaced some of the caps, not all, but the main ones, and I've cleaned the controls with deoxit focusing on the loudness pot since I knew I had a problem there. There is a sealed network of caps and resistors attached to the loudness pot. I don't know if that is my likely culprit but I don't have a tester for anything, I was just replacing everything people mentioned in other threads. I'll take it back down and replace all the rest of the old caps, but not sure if that's going to do it. Any help is appreciated. Thanks for reading.
 
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Ronnie baisden said:
Hello everyone. I'm yet another newbie looking for some of your knowledge any appreciate any help I could get. Here's my issue:
I have a 1965 R214 chassis magnavox astrosonic. I inherited it a few years ago and remember it being louder back then. Now when I turn the loudness pot, it doesn't do anything until halfway. Then from the halfway point, it volumes up until I can't turn it any farther but ends at about half volume.
I have replaced some of the caps, not all, but the main ones, and I've cleaned the controls with deoxit focusing on the loudness pot since I knew I had a problem there. There is a sealed network of caps and resistors attached to the loudness pot. I don't know if that is my likely culprit but I don't have a tester for anything, I was just replacing everything people mentioned in other threads. I'll take it back down and replace all the rest of the old caps, but not sure if that's going to do it. Any help is appreciated. Thanks for reading.
Click to expand...

You need to at least have a multimeter and some service data if you hope to make any progress.
 
I have the schematic and parts lists. There is a sealed network of resistors and capacitors attached to the pot but when I search the part number it doesn't show up online anywhere. I might be able to figure out how to replace all those pieces from the network but if it sounded like something else to anyone I was going to try that. I tried to add a photo of the sealed network.
 

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One thing to remember is that these were not really high fidelity units. They overengineered those volume and tone controls to the point where when I had one I cut cut all that **** out.

I know what you mean, it seems unnatural and it "feels" like there is something wrong, but there isn't.

If you are willing and ready to modify the unit I will be happy to assist. Most of this involves modification of the tone controls and the supposed loudness comp circuit. It is not actually, it is a network that equalizes for the installed speakers.

If you want really good sound, you cut back on the loudness comp and modify the tone controls. (are they switches on that one ? ) Generally, that is going to give you a bit too much midrange, but I found crossover mods that take care of that.

All in all, it will not go as loud as before.

If this difference you hear is not in your head, you might need some coupling caps. They would sap your bass as well. I would put a 1 KHz square wave through it and see how it comes out. But do it right at the power amp in, after all the tone n ****. If it has the rising flats you need caps.

And this all depends too, if it has those old orange plastic encased caps, don't change those, they are good forever. Other types not so much. but get the print and find out which ones are in the signal path. If it ain't hummy or noisy, leave the power supply alone. Some of those things have can lytics with the positive to ground. If you do not hear hum, cool. This is not a McIntosh or a Krell. It can sound good, but only so good.
 
JURB said:
One thing to remember is that these were not really high fidelity units. They overengineered those volume and tone controls to the point where when I had one I cut cut all that **** out.

I know what you mean, it seems unnatural and it "feels" like there is something wrong, but there isn't.

If you are willing and ready to modify the unit I will be happy to assist. Most of this involves modification of the tone controls and the supposed loudness comp circuit. It is not actually, it is a network that equalizes for the installed speakers.

If you want really good sound, you cut back on the loudness comp and modify the tone controls. (are they switches on that one ? ) Generally, that is going to give you a bit too much midrange, but I found crossover mods that take care of that.

All in all, it will not go as loud as before.

If this difference you hear is not in your head, you might need some coupling caps. They would sap your bass as well. I would put a 1 KHz square wave through it and see how it comes out. But do it right at the power amp in, after all the tone n ****. If it has the rising flats you need caps.

And this all depends too, if it has those old orange plastic encased caps, don't change those, they are good forever. Other types not so much. but get the print and find out which ones are in the signal path. If it ain't hummy or noisy, leave the power supply alone. Some of those things have can lytics with the positive to ground. If you do not hear hum, cool. This is not a McIntosh or a Krell. It can sound good, but only so good.
Click to expand...
I'm not sure all of that response was for my post, but there is definitely something wrong with the volume. Maybe an amplification issue? I'm not familiar enough with electronics to know if that's a possibility or where that happens in my unit. But I do get volume so that eliminates some possible faults. It's just that I only get half of it. There are two stages to the pot, does it seem rational to think maybe one is bad? Or is that not what the two stages are related to?
 
Some of them act extremely weird. Really. I remember them. You hardly get sound up to a certain point and it is all bassy. Then, at the loudness tap on the pot it picks up real fast and loses alot of its bass.

The reason I consider it a possibility is that it is rare for one problem to result in a gain loss equally in both channels, and if it was one channel I assumed you would have mentuoned it.

For a power supply or ground problem to affect gain equally in both channels you would have either a lack of stereo separation or it would be overseparated. Of course if your source is mono you would not be able to tell.

It probably has a TAPE or AUX input, I would try a bunch of different sources, if you have only used the FM for example, there are problems possible with that which would lower the level on both channels equally and probably not kick into stereo either.

Also, most consoles with a turntable let that be at a lower level. They could easily match the level BUT since the TT is in the same cabinet with the speakers, with the loudness comp it might get acoustic feedback. Having to turn it up higher gets rid of the bass boost and that is less likely.

Alot of this stuff is not designed exactly perfectly. You are going on an old memory of how loud it seemed to be a long time ago. So, are you sure ? Do you remember back then ever turning it up loud enough to distort ? You know, some simply do not. Not enough gain.

Hell, there was even a Pioneer preamp/amp combo out there that the preamp cannot drive the power amp to full power. I forgot the model. It was reviewed in one of the magazines to which I subscribed back then. Gaffs like that can happen to any company.

I would say, given what is considered line level and what was, a CD player should drive the amp to clipping. If it does not, unplug one side and then the other and check the stereo separation. Don't count on the balance control for that until we know how the thing is designed.

A quick Google did not come up with a free service manual. They say eservice has it but I have been run around in circles by that place so many times I am not going there. Google DID find another thread right here on it, maybe a look at that. Maybe one of the posters there has a print.

Consider that this stuff was designed when adding another stage of amplification was like pulling hen's teeth. Really, they acted like transformers were cheaper than transistors. That is why I consider the possibility that it is working fine, and that's just how it is.

Bottom line, did you ever crank it up to the point where it distorts ?
 
JURB said:
Some of them act extremely weird. Really. I remember them. You hardly get sound up to a certain point and it is all bassy. Then, at the loudness tap on the pot it picks up real fast and loses alot of its bass.

The reason I consider it a possibility is that it is rare for one problem to result in a gain loss equally in both channels, and if it was one channel I assumed you would have mentuoned it.

For a power supply or ground problem to affect gain equally in both channels you would have either a lack of stereo separation or it would be overseparated. Of course if your source is mono you would not be able to tell.

It probably has a TAPE or AUX input, I would try a bunch of different sources, if you have only used the FM for example, there are problems possible with that which would lower the level on both channels equally and probably not kick into stereo either.

Also, most consoles with a turntable let that be at a lower level. They could easily match the level BUT since the TT is in the same cabinet with the speakers, with the loudness comp it might get acoustic feedback. Having to turn it up higher gets rid of the bass boost and that is less likely.

Alot of this stuff is not designed exactly perfectly. You are going on an old memory of how loud it seemed to be a long time ago. So, are you sure ? Do you remember back then ever turning it up loud enough to distort ? You know, some simply do not. Not enough gain.

Hell, there was even a Pioneer preamp/amp combo out there that the preamp cannot drive the power amp to full power. I forgot the model. It was reviewed in one of the magazines to which I subscribed back then. Gaffs like that can happen to any company.

I would say, given what is considered line level and what was, a CD player should drive the amp to clipping. If it does not, unplug one side and then the other and check the stereo separation. Don't count on the balance control for that until we know how the thing is designed.

A quick Google did not come up with a free service manual. They say eservice has it but I have been run around in circles by that place so many times I am not going there. Google DID find another thread right here on it, maybe a look at that. Maybe one of the posters there has a print.

Consider that this stuff was designed when adding another stage of amplification was like pulling hen's teeth. Really, they acted like transformers were cheaper than transistors. That is why I consider the possibility that it is working fine, and that's just how it is.

Bottom line, did you ever crank it up to the point where it distorts ?
Click to expand...
I don't remember if it ever distorted. But I can talk over the current max volume and it is completely silent until the halfway point. I already changed out the power supply caps and no change. And both sides of speakers seem to be coming out at at the same volume. I messed with all the speaker wires shortly after finding out it worked because one side wasn't working and there were some speaker wires unplugged. I've got it as the diagram shows now. The bass and treble dials seem to make adequate adjustments to the sound so I think those are working fine. I read the other thread but it ended with someone saying they were going to try something else and then nothing more. That was a few years back. I haven't used the aux feature and I'm not really sure how. There are channel hookups in the back, I'll attach a picture.
 

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I'd first try to hook up separate speakers direct to the back of the receiver. Should see three terminals, L, R. C. for left, right channels and common ground. Eliminate a bunch of stuff after the amp that way.
 
Ronnie baisden said:
Wait, I hooked it up to the terminal in the back. Let me hook it up to the chassis
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Okay, hold up. I removed the center double yellow (see picture) and suddenly the left speakers came up to full volume. I'm going to have to look at this wiring diagram again.
 

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We need the print on this. Looks like the yellow is a common but from what you say, it should not do that. I mean like under any circumstances. I don't mean that it needs to be protected from doing that, I mean there is no way it WOULD do that, so therefore it should not.

There is s slight possibility you got HF oscillation. That causes weird symptoms like this sometimes. I'll be back after I give this more thought.
 
It's possible the loudness compensation circuit isn't working right. It could also be that PEC (Packaged Electronic Component). I have read here that someone built a separate circuit to replace the PEC and used individual parts.
 
Hmm, don't know. Never had that problem with any of my 3 Astro-Sonics. Maybe a bad ground somewhere? Just throwing things out there. :thumbsup:
 
JURB said:
We need the print on this. Looks like the yellow is a common but from what you say, it should not do that. I mean like under any circumstances. I don't mean that it needs to be protected from doing that, I mean there is no way it WOULD do that, so therefore it should not.

There is s slight possibility you got HF oscillation. That causes weird symptoms like this sometimes. I'll be back after I give this more thought.
Click to expand...
Okay, so I pulled out all the wires and reinstalled them one by one according to the diagram I am attaching. I had to make a couple wires because however it had been set up from the factory didn't match the drawing with respect to wires that had to go way too far for their length. So now it's according to the drawing and I get full volume on the right speakers, nothing out of my left. Playing with the balance just lowers the volume.
 

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