Old Person asking a dumb question, please.

[philbin]

Hi all,

 

I have an originally purchased 1977 Marantz 2252 receiver, driving MA-1 speakers.  It handles my Denon CD player well, but it will not perform with a portable music player, such as an iPod Classic.  The playable volume is greatly reduced and when I try to increase it I hear a relay inside the Marantz click and the volume drops to zero, until I back it off, whereupon it resumes playing.  It feels like a power insufficiency on the part of the iPod. 

 

Now I've added a Hiby R6 Pro that exhibits the same characteristics, but at a higher volume level, as if the R6 is putting out more power than the old iPod, but not enough to push the sound through the Marantz, and it is protecting itself by tripping that relay.  It may all be a construct of my imagination, seeing as how I have very little knowledge of electronics.

 

My question boils down to this:  Does the R6 Pro need a DAC to talk to the analog Marantz?  Does the R6 Pro need a pre-amp to provide enough signal for the Marantz?  Is it one or both (or neither) of these?  The R6 Pro plays fine through the car's stereo, but I assume there is a DAC in the dash, since it has a CD player.

 

AFAIK, the Marantz is still in proper working order.  Any advice you could give this fossil would be greatly appreciated. 

 

Many thanks, 

 

Philbin

[STC]

Hi Phibin,

 

I suppose you are connecting the iPod using the mini jack split to RCA.  Have you tried other inputs. You can also try AUX or Tape in. If have the manual that will be helpful. I suspect the output sensitivity from the iPod is too low or maybe the input of your receiver inputs are probably aged. A picture can be more helpful. 
 

ST

[mansr]

I can only guess what's happening here, but such behaviour could be caused by a DC offset on the source.

[philbin]

22 hours ago, STC said:

Hi Phibin,

 

I suppose you are connecting the iPod using the mini jack split to RCA.  Have you tried other inputs. You can also try AUX or Tape in. If have the manual that will be helpful. I suspect the output sensitivity from the iPod is too low or maybe the input of your receiver inputs are probably aged. A picture can be more helpful. 
 

ST

 

You are correct about the mini jack-to-RCA.  I've tried all the source inputs on the back, with the same result.  CD player and turntable (Sony bought with the receiver) work fine.  Even the flat screen TV plays through it via the mini jack-to-RCA audio-out provided.  

 

I think the iPod, or rather the R6 now, needs some kind of box to either translate for or boost the R6 signal to the receiver or both.  But I don't know what that might be.  I thought about trying a Schiit Modi for a hundred bucks just to see, but with my level of knowledge it would just be a shot in the dark.  

[STC]

56 minutes ago, philbin said:

 

You are correct about the mini jack-to-RCA.  I've tried all the source inputs on the back, with the same result.  CD player and turntable (Sony bought with the receiver) work fine.  Even the flat screen TV plays through it via the mini jack-to-RCA audio-out provided.  

 

I think the iPod, or rather the R6 now, needs some kind of box to either translate for or boost the R6 signal to the receiver or both.  But I don't know what that might be.  I thought about trying a Schiit Modi for a hundred bucks just to see, but with my level of knowledge it would just be a shot in the dark.  

I was using this for the iPod 

 

https://www.whathifi.com/onkyo/nd-s1/review

 

[mansr]

I found the schematic for this receiver. Here's the amp section, containing the only relay in the device:

 

Unless I'm mistaken, the part in the middle, between the fat black lines (ground), is a protection device that shuts off the output in case of excessive DC bias.

 

I have seen cheaply constructed (portable) devices with several volts of DC bias on the outputs. A quick internet search suggests that at least some iPod models with some firmware versions do in fact have such a problem.

 

You'll need to find a source with a properly zero-centred output, or perhaps there's some kind of DC blocker you could use.

[philbin]

Your herculean efforts on my behalf are greatly appreciated.  I can't imagine where you found that schematic.

 

Inside the Marantz as the volume is advanced (either using the iPod or R6 volume controls or the Marantz volume control), at a certain level *something happens* and there is an easily discernible 'click' inside the unit, at which point the volume drops to silence.  Backing off the volume elicits another `click' at which point the volume returns.  The cut out happens at a lower volume than is comfortable for listening, and the sound quality of that signal is very "tinny" and unpleasant.

 

If the level is left at the cut out point, the volume will intermittently cut out and back in as the level swells and recedes with the progression of the music.  There is some boundary that the input from the iPod is bumping up against.

 

I'm still trying to assess what you told me.  I thank you for your insight.

[mansr]

5 hours ago, philbin said:

Your herculean efforts on my behalf are greatly appreciated.  I can't imagine where you found that schematic.

Here: https://www.hifiengine.com/manual_library/marantz/2252.shtml

 

5 hours ago, philbin said:

Inside the Marantz as the volume is advanced (either using the iPod or R6 volume controls or the Marantz volume control), at a certain level *something happens* and there is an easily discernible 'click' inside the unit, at which point the volume drops to silence.  Backing off the volume elicits another `click' at which point the volume returns.  The cut out happens at a lower volume than is comfortable for listening, and the sound quality of that signal is very "tinny" and unpleasant.

 

If the level is left at the cut out point, the volume will intermittently cut out and back in as the level swells and recedes with the progression of the music.  There is some boundary that the input from the iPod is bumping up against.

 

I'm still trying to assess what you told me.  I thank you for your insight.

An audio signal should be a voltage varying around zero such that it spends about equal amounts of time being positive and negative. A simple sine wave should look something like this:

 

This waveform is perfectly centred around zero, so the average value over a longer period of time is also zero. In a battery powered device, generating those negative voltages requires additional components, so sometimes manufacturers cheat and output a waveform like this instead:

 

The shape of the waveform is still the same, but it has been shifted up such that it never dips below zero volts, and the long-term average is now 0.5 V. This is called DC bias or offset. If we connect a speaker, it will still sound the same since we only hear the variation. It is nevertheless undesirable since it increases power consumption and distortion, and with a power amp it can even cause damage. The Marantz detects this offset and disconnects the speakers to protect both itself and them. This is when you hear the click of the relay.

 

If you have a multimeter, you can easily check if this is indeed what is happening here. Set it to DC volts and measure the output of the iPod. It should read close to zero. Anything more than 0.1 V is a bad sign.

 

To fix the problem, you need a device that blocks the DC offset while letting the signal through. Either a capacitor or a transformer will do the job. The latter may be labeled ground loop isolators, often sold as car audio accessories. Here's an example of a cheap one that I know nothing whatsoever about: https://www.crutchfield.com/p_127SNI1/PAC-SNI-1.html?tp=61807

[PeterSt]

What mansr doesn't mention is that DC offset also causes "clipping" at the side of where the voltage shifted to. Envision the below yellow wave as DC offset to the minus side of the voltage:

 

 

The voltage "rails" does not extend to where the yellow wave wants to be (at the bottom side of it) and the voltage (= volume) stays at the level of the maximum voltage of the rails. And that thus only on one side (bottom), the other side (top) staying in-tact.

 

The louder the volume, the more will but cut off from this one side.

In the end this *is* bad for loudspeakers, because the swing of the diaphragm and magnet/coil driving it, never come at the resting midpoint (no power required there) and also can't sufficiently cool (itself). This is how the amplifier is equipped with a protection that prohibits too much DC offset. "Too much" can be anything the designer wants. But anyway when it kicks in (the relay cuts off the signal), there is no voltage (no signal) at all.

 

The louder the volume (you set), the more the clipping occurs. So envision an excursion of the yellow wave which is half of what you see (the volume is way lower) and no clipping occurs and all is fine (but speakers will still suffer, because the DC Offset did not disappear).

 

The idea of the culprit remains manrs's (he is definitely correct IMO).

 

[philbin]

4 hours ago, PeterSt said:

What mansr doesn't mention is that DC offset also causes "clipping" at the side of where the voltage shifted to. Envision the below yellow wave as DC offset to the minus side of the voltage:

 

 

The voltage "rails" does not extend to where the yellow wave wants to be (at the bottom side of it) and the voltage (= volume) stays at the level of the maximum voltage of the rails. And that thus only on one side (bottom), the other side (top) staying in-tact.

 

The louder the volume, the more will but cut off from this one side.

In the end this *is* bad for loudspeakers, because the swing of the diaphragm and magnet/coil driving it, never come at the resting midpoint (no power required there) and also can't sufficiently cool (itself). This is how the amplifier is equipped with a protection that prohibits too much DC offset. "Too much" can be anything the designer wants. But anyway when it kicks in (the relay cuts off the signal), there is no voltage (no signal) at all.

 

The louder the volume (you set), the more the clipping occurs. So envision an excursion of the yellow wave which is half of what you see (the volume is way lower) and no clipping occurs and all is fine (but speakers will still suffer, because the DC Offset did not disappear).

 

The idea of the culprit remains manrs's (he is definitely correct IMO).

 

So how would you fix it so that the R6 can be played through the receiver? 

 

Perhaps it can't be, though I find that hard to fathom.

 

 

[philbin]

On 12/5/2019 at 7:17 AM, mansr said:

To fix the problem, you need a device that blocks the DC offset while letting the signal through. Either a capacitor or a transformer will do the job. The latter may be labeled ground loop isolators, often sold as car audio accessories. Here's an example of a cheap one that I know nothing whatsoever about: https://www.crutchfield.com/p_127SNI1/PAC-SNI-1.html?tp=61807

I checked out the Crutchfield item.  Perhaps I should call them about it, though I have had wildly divergent information from them depending on the person answering the phone.

 

So I have a multi-meter.  Where do I stick the probes in the iPod to measure the output?  Into the headphone-out and then ground to any old screw on the wall?  Sorry if this is so basic.

[mansr]

4 minutes ago, philbin said:

I checked out the Crutchfield item.  Perhaps I should call them about it, though I have had wildly divergent information from them depending on the person answering the phone.

I doubt you'll get a useful answer out of a sales person. The device, or a similar one, is cheap enough that I'd just get one and see if it helps. There is also a version with a 3.5 mm headphone plug. You can find them on Amazon too, should that be more convenient.

 

4 minutes ago, philbin said:

So I have a multi-meter.  Where do I stick the probes in the iPod to measure the output?  Into the headphone-out and then ground to any old screw on the wall?  Sorry if this is so basic.

I assume you're using a headphone to RCA cable. The easiest is probably to measure at the RCA end of this. Alternatively, the Marantz has a preamp output on the rear panel where you could attach the meter, one probe in the hole and the other touching the metal rim.

[sandyk]

On ‎12‎/‎4‎/‎2019 at 9:43 PM, mansr said:

 

You'll need to find a source with a properly zero-centred output, or perhaps there's some kind of DC blocker you could use.

 

 

 Unless C701 and C702 are leaky, they should prevent this from being a problem, at least at normal volumes.

 Perhaps the Marantz protection circuit is unduly sensitive ?

 As you have said, he needs to use a DMM to check for D.C. offset from the source device.

 

 Another question would be, does the output sound distorted before it cuts out, in comparison with the audio directly from the source devices .

[mansr]

7 minutes ago, sandyk said:

Unless C701 and C702 are leaky, they should prevent this from being a problem, at least at normal volumes.

You're right. I missed those. Given the age of the device, it's quite possible they have deteriorated.

 

[One and a half]

I’ve been watching 12voltvids on you tube quite a lot Lately and the most common problem for vintage amps are 

leaky caps (electrolytic)

open resistors 

shorts on the + - rails caused by leaky caps

leakage on T01 type transistors

 

the protection relay may turn on prematurely due to a combo of the above. The signal from the source would have to be measured and compared with the rated maximum of the preamp especially and for modern devices is 2V , in those days 0.775V or 1V was common.

 

If the amp hasn’t Ben serviced for quite some time, it’s worth to recap and weed out suspect transistors. Marantz receivers now have a long history of what fails over the years, a service wouldn’t cost that much in time, and gives peace of mind for the next 10 years or more.

 

[One and a half]

1 hour ago, sandyk said:

 

 

 Unless C701 and C702 are leaky, they should prevent this from being a problem, at least at normal volumes.

 Perhaps the Marantz protection circuit is unduly sensitive ?

 As you have said, he needs to use a DMM to check for D.C. offset from the source device.

 

 Another question would be, does the output sound distorted before it cuts out, in comparison with the audio directly from the source devices .

Agreed these two are the first to look at since they are involved with a reference.

[One and a half]

Oh, just saw on a computer screen instead of a iPhone screen @philbin, see on the drawing of the amp are numbers in red latters and italics.

These are reference voltages that you can measure at these points. Black lead to a chassis ground and the red lead on the identified component. If the voltage measured is not right, the culprit is close by (sometimes).

[philbin]

On 12/7/2019 at 6:07 AM, One and a half said:

Oh, just saw on a computer screen instead of a iPhone screen @philbin, see on the drawing of the amp are numbers in red latters and italics.

These are reference voltages that you can measure at these points. Black lead to a chassis ground and the red lead on the identified component. If the voltage measured is not right, the culprit is close by (sometimes).

 

Thanks to all of you for sharing your knowledge.

 

I've seen videos on Youtube of people re-fitting Marantz receivers with new components and basically doing a restoration job to bring the units at least back to original spec, if not better.  Most are ex-engineers who do it not for the money, but for the love of the equipment.  One guy I was looking at in Charlotte, I think, has stopped doing it for now, for whatever reason.

 

 

Does anyone know of a good person in the Southeast who can do this?  The shops in my locale are mostly TV repair, and even those are getting fewer as people give up on the idea of keeping electronics past their sell-by dates.  I don't consider the Marantz disposable, as the sound is sweet, but it has been cranking out music for over 40 years now and probably needs some help, as you all have described.

 

Thanks,

 

P

 

 

[Ralf11]

I did a search on "old Marantz receivers retrofit" and saw a lot of discussion on other fora but no shop popped up.  You might try looking at those threads/fora or altering the search (e.g. add vintage to it).

 

Or you might be able to buy one that has been fixed up.  Or it might sound pretty good as is.

 

There is a lot of nostalgia and sentimental value to the old Marantz gear.  I sometimes think of buying one for my 2nd system.

[AudioDoctor]

Go check AudioKarma. They’ll have all your answers. 
 

https://audiokarma.org/forums/index.php