Marantz PM-6003 one channel midrange surpression

[Mirotvorac]

Hi,
I have a strange situation with my amp. One channel is not reproducing whole freq. range. I discovered that midrange is somehow attenuated while playing with bi-wiring - I had tweeters connected without modrange speakers, and it was clearly noticable that midrange (maybe and part of HF) is attenuated.
I double checked it with changing L and R speaker and speaker cables, and interconnects. It is in the amplifier.

Any help is appreciated.

 

[Gray]

.....while playing with bi-wiring

You need to remove any complicating factors and get back to basics before starting a meaningful elimination process.

Don't rush to condemn the amp.

Firmly fit back the links in your speakers and single-wire them to your amp.....then start the tests.

You've got all you need to diagnose - one step at a time, with logical thinking, is how you will do it.

 

[Mirotvorac]

I just did a quick test with my freq. Analiser, same speaker, same cable, L ch, than R ch. Source: phone bluetooth-DAC-PM6003.
There are differences throughout the spectrum.

Note that differences on single measured frequency varied up to 2 dB, so this is approximation (pic attached). So where result is 50, it might be from 49 to 51 dB. Still, difference is noticable on whole spectrum. Why is not more consistent, I don't know.

I tested it with another speaker, no bi-wiring (Rega RS3).

 

[nopiano]

Did you put each speaker in the same location to measure them? If not, the different room placement might account for the level differences, though I agree they vary quite significantly.

As @Gray said, eliminate the possibilities, for example by swapping /reversing channels to see if the issue stays with the speaker, or the amplifier. What speakers are they?

 

[Gray]

I just did a quick test with my freq. Analiser, same speaker, same cable, L ch, than R ch. Source: phone bluetooth-DAC-PM6003.
There are differences throughout the spectrum.

Note that differences on single measured frequency varied up to 2 dB, so this is approximation (pic attached). So where result is 50, it might be from 49 to 51 dB. Still, difference is noticable on whole spectrum. Why is not more consistent, I don't know.

I tested it with another speaker, no bi-wiring (Rega RS3).

Hopefully, to arrive at the figures in your table:

1) You used the same, single Rega speaker.

2) Position of the level meter and speaker were both constant.

3) The input signal level and volume control on Marantz amp were both constant.

If so, the first thing to do now is swap L & R between DAC and Marantz, repeat your tests and note the result.....

 

[Mirotvorac]

Did you put each speaker in the same location to measure them? If not, the different room placement might account for the level differences, though I agree they vary quite significantly.

As @Gray said, eliminate the possibilities, for example by swapping /reversing channels to see if the issue stays with the speaker, or the amplifier. What speakers are they?

I measured both channels on the same speaker to avoid what you mention. So, one speaker, one fixed position, with swapping output L & R on the amp.

 

[Mirotvorac]

Hopefully, to arrive at the figures in your table:

1) You used the same, single Rega speaker.

2) Position of the level meter and speaker were both constant.

3) The input signal level and volume control on Marantz amp were both constant.

If so, the first thing to do now is swap L & R between DAC and Marantz, repeat your tests and note the result.....

yes, yes and yes.
I tried earlier changing intercoonects between DAC and Marantz Then changing speaker cables. This results are with single speaker, single speaker cable, single interconnection cable, the inly thing I changed was the amp L & R channel output on the back of the amp.

 

[DougK1]

I take it you are using test tones, yes?

 

[Mirotvorac]

Test tones from..youtube::

https://www.youtube.com/playlist?list=PL8y869KV1Ir8ks9G0avxw9XBP1WkJjedw

 

[Gray]

I tried earlier changing intercoonects between DAC and Marantz

You need to SWAP L & R channels at the input to the Marantz - at the same time as you swap outputs to the single speaker.

Take your level meter readings before and after the swap.

....the inly thing I changed was the amp L & R channel output on the back of the amp.

Yes, the idea is to be measuring JUST any difference between the channels of the Marantz amp ✅

However, in the test you've done so far, any difference between L & R source channels will also have been part of your measurements.

Do that swap - then you will only be measuring any Marantz channel difference - because, unlike before, you will be feeding exactly the same input through each channel.

 

[twinkletoes]

Take the amp to a service centre and get them to hook it up to a load of scopes. To me it looks like the bias needs adjusting or the bias pot has gone bad, but thats just a guess but that is where id start with a channel indifference.

They will be able to measure the channels to make sure there exactly the same. If thats all you have done and there's nothing wrong at least you've sanity checked it.

this guy is very good also has a YouTube channel, Mend it mark.

perton-electronics.co.uk

 

[Mirotvorac]

You need to SWAP L & R channels at the input to the Marantz - at the same time as you swap outputs to the single speaker.

Take your level meter readings before and after the swap.

Yes, the idea is to be measuring JUST any difference between the channels of the Marantz amp ✅

However, in the test you've done so far, any difference between L & R source channels will also have been part of your measurements.

Do that swap - then you will only be measuring any Marantz channel difference - because, unlike before, you will be feeding exactly the same input through each channel.

I already did this (input swap). It happen with any source.

 

[Mirotvorac]

Take the amp to a service centre and get them to hook it up to a load of scopes. To me it looks like the bias needs adjusting or the bias pot has gone bad, but thats just a guess but that is where id start with a channel indifference.

They will be able to measure the channels to make sure there exactly the same. If thats all you have done and there's nothing wrong at least you've sanity checked it.

this guy is very good also has a YouTube channel, Mend it mark.

perton-electronics.co.uk

Thanks for the tip on servise center, I'm in Croatia.
This idea with bias makes sense.
I came to an idea to play with the volume potentiometer, but that requre some cutting on the board and soldering.
Without soldering, I can short-circuit the input to the potentiometer. If the problem persists, the path to the potentiometer is OK (which I believe it is).
Next step is to swap L & R output on the volume potentiometer. If the problem still exists, next step is a Service centre.

 

[Mirotvorac]

I have an old AKAI AM-39 which I borroved to a friend of mine. It does have some issues with reed-relays and dust and mechanical issues with one button, but the sound is cristal crisp. And it is approx. 30 years old, and I bought it after it worked for some 5 years in a smokey caffe..so comparing it to my Marantz which was never covered up..I'm a bit dissapointed.

The only possible issue I can come accross is that with Marantz I use DAC which in some conditions does create some very anoying hiss sound (when you play music from one source, but the knob input selector is set to another source).
And when a PC is connected via optical cable to the DAC, you have to be careful with volume output from the PC (anything more that some 35% of the volume creates strong sound distorsion) - many years prior to this I was concerned that some kind of bad signal from the PC might cause the damage to the amp..but it is connected thru the optical cable..so only an to excessive volume could be a potential issue. But that happened on a few occasions only.

 

[Mirotvorac]

What confuses me is the uneven difference throughout the frequency spectrum. Okay, I didn't measure it in a lab, no proffessional equipment, many interferences/reflections around, but since it was a single speaker not moved from its place, I expected same difference and the same peaks on both channels. Not 5 dB's on one freaquency on one channel, and 10 on the other with the same speaker on the same freaquency and on the same physical possition.

 

[twinkletoes]

Thanks for the tip on servise center, I'm in Croatia.
This idea with bias makes sense.
I came to an idea to play with the volume potentiometer, but that requre some cutting on the board and soldering.
Without soldering, I can short-circuit the input to the potentiometer. If the problem persists, the path to the potentiometer is OK (which I believe it is).
Next step is to swap L & R output on the volume potentiometer. If the problem still exists, next step is a Service centre.

ah that wont work then!

 

[Gray]

What confuses me is the uneven difference throughout the frequency spectrum. Okay, I didn't measure it in a lab, no proffessional equipment, many interferences/reflections around, but since it was a single speaker not moved from its place, I expected same difference and the same peaks on both channels. Not 5 dB's on one freaquency on one channel, and 10 on the other with the same speaker on the same freaquency and on the same physical possition.

Don't be confused - the sort of level meter you're using can be a very rough guide only.
(Its own frequency response will not be even).

I'm not sure you understand what I said about the input signals.
Let me just have one more go at explaining in a way that might be helpful:

If you were to take the amp somewhere for 'professional' assessment, they would feed the L & R inputs with a signal generator.

You are (effectively) doing the same.

But CRUCIALLY they would be putting an IDENTICAL signal through each of the Marantz's 2 channels.

Your test did not.
You put, first the L channel, then the R channel of your phone / DAC signal source through the Marantz.

You effectively used 2 different signal generators for your test - any discrepancy in those 2 generators will be there in your result table.
You could argue that your 2 'signal generators' should not be significantly different (and they shouldn't)....but there are variables beyond your control - not least YouTube and the creator of the tones you used.

If you want to do more meaningful future tests:
USE JUST ONE OF YOUR SOURCE CHANNELS FOR TESTS -FIRST THROUGH LEFT, THEN THROUGH RIGHT CHANNEL OF YOUR MARANTZ.

 

[Mirotvorac]

Don't be confused - the sort of level meter you're using can be a very rough guide only.
(Its own frequency response will not be even).

I'm not sure you understand what I said about the input signals.
Let me just have one more go at explaining in a way that might be helpful:

If you were to take the amp somewhere for 'professional' assessment, they would feed the L & R inputs with a signal generator.

You are (effectively) doing the same.

But CRUCIALLY they would be putting an IDENTICAL signal through each of the Marantz's 2 channels.

Your test did not.
You put, first the L channel, then the R channel of your phone / DAC signal source through the Marantz.

You effectively used 2 different signal generators for your test - any discrepancy in those 2 generators will be there in your result table.
You could argue that your 2 'signal generators' should not be significantly different (and they shouldn't)....but there are variables beyond your control - not least YouTube and the creator of the tones you used.

If you want to do more meaningful future tests:
USE JUST ONE OF YOUR SOURCE CHANNELS FOR TESTS -FIRST THROUGH LEFT, THEN THROUGH RIGHT CHANNEL OF YOUR MARANTZ.

Thanks for detailed description.
First, I need to say tha first thing I tried is to swap output channels form DAC to the input of Martz.
In both cases speaker output on Marantz on R channel output was below level of L channel output.
So my focus is on the Marantz.

What I still can't figure out, is is the problem on the preamp stage of Marantz, or on the power output stage.
All I concluded is that signal form DAC is even (same level) on both L & R channel.

Having all of that in mind, all measurements were done assuming that Output signal from DAC L &R channels is more or less the same.

I understand that my dB level meter is not professional equipment (so it might have tolerance around 10%), but tollerance is supposed to be more or less the same on both measurements, since both measurements were done with same room temperature. So, regarding the tolerance, max. expected difference shouldn't be more than a few dBs, not 5 or 10. Hmmh, 10% of 50 is 5..but still, the difference wouldn't be always on the same channel.

The difference is not arguable - it is there. The question is, is it manifesting in the preamp stage of the amplifier, or on the output stage.
Since I fed it with some questanable input audio signals from PC, I doubt the fault is on the input stage of the Marantz.
For that, I would have to measure an preamplifier output levels of the Marantz, right before Volume potentiometer, then after the volume pot (to eliminate that potentiometer is an issue).

So, I need to drive to a friend of mine, put it on a table, connect signal generator to the input of the Amplifier, and measure signal with oscilloscope probes somewhere on the preamp section. And then I'll drive to the Service center, and they will perform all of the testing again, and charge it too.
So, in conclusion, whatever I do, it is waste of time .

 

[Gray]

So, I need to drive to a friend of mine, put it on a table, connect signal generator to the input of the Amplifier, and measure signal with oscilloscope probes somewhere on the preamp section. And then I'll drive to the Service center, and they will perform all of the testing again, and charge it too.
So, in conclusion, whatever I do, it is waste of time .

That's a good idea to take it to your friend.

Yours is an unusual issue - but a real one, because you've noticed it by ear - and your measurements show it.
The R channel is significantly lower than the L.

The best thing about diagnosing a stereo amp - especially when you use the oscilloscope, is being able to identify test points and jump across from L to R channel, making comparisons.

You should be able to pinpoint precisely where the lack of R channel gain is - every bit as well as a service department could - so you won't be wasting your time.

Good luck.
I'd very much like to know the answer - if you could eventually come back and update this thread 👍

EDIT:
I just noticed this 'similar thread' from last year.
Its a newer model than yours......but if yours has relays

Question - Marantz PM 6006 amplifier - Right Channel

Hey whizz kids and detectives, I have read every other post relating to this slightly to common issue but none resemble the one I am experiencing. As the title states: Marantz PM 6006 amplifier right channel issues. I'll expand: Sometimes, the right channel on the amplifier drops out, the...

forums.whathifi.com

 

[Mirotvorac]

Wow, who knows, somw issue with Marantz? As suggested, I might try dropping the right side of amp 😃.
He mentioned that sound was OK when volume was turned to max - this gave me an idea; in that position volume potentiometer has no resitance.
So, I'll check the volume potentiometer first.