Author Topic: Newb with a few questions  (Read 1220 times)

choppinrice

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Re: Newb with a few questions
« Reply #30 on: April 10, 2018, 11:10:32 PM »
Well I will try to locate them. I did see a post on Audio Karma from 2013 that a member there had them, so I sent him a email. Keeping my fingers crossed.

In the meantime I have read some past posts of yours where you advise the changing of the power and cathode resistors. One the schematic I did supply could you tell me which of the many resistors these are? Also when you bias a amp what exactly are you doing to it?

choppinrice

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Re: Newb with a few questions
« Reply #31 on: April 16, 2018, 01:48:21 AM »
No other schematics for my unit. Was told Magnavox was famous for not covering all configurations and leaving it to the tech to figure it out in the field.
Replaced all resistors, old ones were within spec.
Installed replacement 6be6 tube and now have AM.
Pulled turntable and verified all conections.

Tested, Phono and radio lacks sound volume and clairity .
Grounded balance pot, phono rocks loud and clear. Removed ground lose sound power and clairity.
Hooked cd/dvd player to MPX input. Sound rocks loud and clear.
Replaced 6eu7 and el84 tubes, no change.
Ohms and power tests all within spec's.

So to conclude, cd/dvd player on MXP inputs thru FM stereo position. ROCKS
Phono with grounded balance pot. ROCKS
Anything else sucks A$$.
Also some how replacing resistors crapped on the radio quality which was good before.And Yes I did tripple check my work and the replacement's are quality on spec.

I'm lost for the moment at where to continue checking.

 

Motorola Minion

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Re: Newb with a few questions
« Reply #32 on: April 16, 2018, 12:02:20 PM »
When I had this issue with a balance control, I realized one of two things could have happened.

1- Check to see if the cartridge wiring is not reversed on one of the channels.
2- Check to see if the speaker wiring is not reversed to one of the speakers or groups, which could be hard out to trace on yours.

Channels out of phase voltage INTO your preamp and OUT to speakers from your amp will cancel when you listen to them simultaneously, i.e. balance in middle.
Tubes - Magical - Tubes

Dave

choppinrice

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Re: Newb with a few questions
« Reply #33 on: April 16, 2018, 01:47:34 PM »
All wiring correct. Speakers per diagram green +, black - and cartridge per instructions red-r, white-l, black ground.
Something in the tuner is reducing the output to the amp. I just can't put my finger on it.

electra225

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Re: Newb with a few questions
« Reply #34 on: April 16, 2018, 04:00:22 PM »
The best advice I can offer at this point is to ignore about 99% of what you read on AudioKarma.  Especially disregard anything you read on that site about Magnavox.  I'll see if I can come up with a schematic that makes more sense.  I have run into a situation that I needed two Photofacts folders to get what I needed.  I still believe your problem is related to the phono cartridge.  Problem is, I can't prove it.   :-[
Did you try feeding the CD player thru the phono input?  The CD player may not have enough output to drive the amp to full volume, but you should be able to tell if the audio is clear.  Try disconnecting the phono input completely from the tuner to see if the audio clears up with the cartridge unplugged.  I have a schematic for another tuner that is close to yours.  All the inputs go thru the function switch.  If the audio is good in MPX or tape input, it should be good on every input.   AM and FM mono both sound bad? 


Have you found any evidence of someone making "field modifications" to this thing in any way?  Something here is not adding up..... :-\


What happens to everything that "sucks" if you ground the balance pot?  I still haven't figured out what the balance pot has to do with anything concerning this situation.
« Last Edit: April 16, 2018, 04:32:03 PM by electra225 »
I'm great at multi-tasking.  I can listen, ignore, and forget all at the same time.

choppinrice

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Re: Newb with a few questions
« Reply #35 on: April 16, 2018, 05:32:31 PM »
If I ground the balance pot I take out 28.5k ohms per amp channel and the sound rocks. Great volume, bass and treble control.

FM stereo with a cd/dvd player plugged in to the MPX inputs Rock with or without the grounded pot. I think the cd player puts out a lot more signal power to overcome any issues at this time. It even turns the tuner itself into a speaker.

FM and am not affected by pot as it is taken out of the picture by the selector switch.

Everything was and is spot on to the schematics I posted just lacks the MPX circuit. (input and outputs)

I hooked my Dual cs522 with Otofron to the phono inputs and could barely hear anything at full volume (with pot ungrounded).
It may be that it's a different cartridge type.

The cartridge needs to put out a hell of alot power than the advertised .5v in order for this unit to sound good with the balance pot in play.
I may just bypass the balance pot as it is such a small unit with free air speakers that the pot wouldn't be used other than the center position.

As for AudioKarma I only checked there for the diagrams from the so called man of schematics. No luck from him or another schematics supplier.

How does one verify the output voltage from a cartridge?

electra225

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Re: Newb with a few questions
« Reply #36 on: April 16, 2018, 06:23:51 PM »
FM and AM operation not affected by the balance control?  Where do you see that?  You may have tried using a changer with a magnetic cartridge.  It's output will be lower than the .5 volts the system requires for full volume.  Is it possible there is an open ground on the balance pot?  The only way I know of to check the output of a cartridge would be with a scope.  Are you grounding the input to the balance pot?  I still don't follow what you're doing.   :-[


One schematic shows the value of the balance pot as 50K,with the center tap grounded. One schematic I have, closer to what you say you are working on that the one you posted, shows the value of the balance control as 750 ohms, and the center tap is not grounded.  They are wired totally differently.  A scope or a signal tracer might help shed some light on this situation.  I keep an old BSR changer with an Astatic ceramic cartridge around just for occasions like this.  That old plow has bailed me out more times than I can count on all my fingers.  I have not found the right schematic, but I have not given up. 
I'm great at multi-tasking.  I can listen, ignore, and forget all at the same time.

choppinrice

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Re: Newb with a few questions
« Reply #37 on: April 16, 2018, 06:40:53 PM »
The pot I have is controlled by the selector switch. When in a non-stereo mode the selector switch (m4) grounds both legs of the balance pot with no added resistance to the circuit.
When switched to stereo mode. The legs of the balance pot are now ungrounded from the selector switch and now grounded thru the center terminal of the balance pot instead, introducing resistance from the pot itself. The pot is a 50k so when centered it adds 25k ohms to both channels.  As resistance goes up sound goes down. As resistance goes down sound goes up.
They would have been better off not installing this pot and left the unit at a fixed balance. This may be my only option to restore quality phono/stereo sound at this time.

And I do have a scope, I just haven't learned all the settings yet. 

electra225

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Re: Newb with a few questions
« Reply #38 on: April 16, 2018, 07:29:25 PM »
I see now what you are doing.  Following this line of thought for a moment.


You said in an earlier post that the sound from your CD player in the tape input and the MPX input, stereo inputs, sounded okay.  The AM and FM mono positions did not.  This is contradictory from what you just posted.  You said that in mono, the balance control was out of the loop, in stereo it was in use.  So if a mono input sounds bad when the balance control is out of the circuit and stereo input sounds okay when the balance control is in the circuit, how does this place the fault on the balance control?  That is an odd circuit arrangement, but it should still work if everything is right.  Have you confirmed that the balance control is okay?  When you essentially short across the balance control, the audio sounds okay.  That sounds like the balance control is the problem.  This makes no sense to me, as it seems contradictory.  What am I missing?
I'm great at multi-tasking.  I can listen, ignore, and forget all at the same time.

choppinrice

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Re: Newb with a few questions
« Reply #39 on: April 16, 2018, 08:31:49 PM »
I'm sorry, I forgot to correct that statement. My antenna lead had fallen off while testing, I just confirmed that AM and FM are fine. I had too much going thru my head and confused myself.

Yes short balance to ground and Phono improves drastically. It really is a strange setup.
I tried to run the phono thru the stereo input but the selector switch keeps the phono power off unless switched to phono.
I disconnected the wires at the pot and tested with a ohm's meter and it was within spec's. on both sides,1.0-57k. It also works fine in Fm stereo with the cd/dvd player,I think the Cd/dvd player has a preamp built in and is supplying a much higher voltage so it's not the best way to test things.

Does any of the Maggies you have or had seem to sound much weaker and of less quality when in phono vs radio? It really is a big difference I'm hearing.

electra225

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Re: Newb with a few questions
« Reply #40 on: April 16, 2018, 08:52:56 PM »
Can you engineer some type of system to power the changer separate from the console?  I made up a power cord so I can do just that if I need to.  Have you gotten deeper into a possible problem with the balance control itself?


I typically find I have to use a higher volume setting on phono than I do either tape input or tuner input.  I attributed this to cartridge aging.  I would not be concerned with an approximately 10% lower output from the cartridge than from the tuner.  The sound quality from the phono is generally better.  Magnavox made their reputation playing records.  Like I said earlier, faulty performance of any kind is not normal for a Magnavox.  You should grin every time you start it up.
I'm great at multi-tasking.  I can listen, ignore, and forget all at the same time.

choppinrice

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Re: Newb with a few questions
« Reply #41 on: April 16, 2018, 09:30:55 PM »
Yes I'm sure I can make a harness up to test the phono thru the FM stereo inputs.

I have only metered and bypassed the balance pot at this time.
I'm going to do some resistance testing of the phono wiring tomorrow as I'm brain dead at the moment.
I may also solder in some resistors to replace the balance pot and see if the pot is bad under load but metering good.

I'm definitely losing a good 50-75% of amp power with terrible sound quality. Unless of course I ground the balance pot leads.
 

electra225

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Re: Newb with a few questions
« Reply #42 on: April 16, 2018, 09:42:42 PM »
Is the ground to the balance control okay? 
I'm great at multi-tasking.  I can listen, ignore, and forget all at the same time.

choppinrice

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Re: Newb with a few questions
« Reply #43 on: April 16, 2018, 09:45:27 PM »
Yep

electra225

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Re: Newb with a few questions
« Reply #44 on: April 16, 2018, 11:23:39 PM »
When you get back on this, maybe rigging up a way to run the changer on a different input will reveal something.  You deserve to make forward progress.   ;)
I'm great at multi-tasking.  I can listen, ignore, and forget all at the same time.