mute circuits

[east electronics]

many of our sources like CD players - tuners feature mute circuits in the analog audio outs .

I presume that the specific mute circuits are installed there to avoid digital and/or other noises to come out in the analog line out .

i wonder if those circuits beyond the benefit of muting do they have any effect in the sound quality since are directly involved in the signal path

opinions are welcome

regards sakis

 

[east electronics]

ok ...here we go

i also noticed that in a technics tuner except the muting circuit there is also a lot of filtering in the out ....

its a simple tuner that the sound comes out from a humble AN 7470 this we have to take as a fact ....not much you can do about that ... beyond that there is a astronomical 15nf capacitor that goes from signal to ground and a coil of some nh in series with the signal

removed the muting circuit totaly then removed the 15nf capacitor and replaced that with silver mica 300pf

now the radio doesnt mute any more while searching for a station ( not really importand since all your required stations are in memory ) and also while changing from memory one to memory two there some kind of not really loud pop noise .

though high become by far more crisp and clear ....then sound stage become more real and as about the low end didnt seen much eventhough i beefed up the capacitors in the output of the AN from 3.3 mfd to 10 mfd plus 100nf styroflex bypass

any comments ????

 

[east electronics]

one other thing ....i would be more pleased if in the out a small relay existed than transistors that interfere with the signal ....

this i can try first thing in the morning with a CD player ...

i ll let you know

 

[currentflow]

ok ...here we go

i also noticed that in a technics tuner except the muting circuit there is also a lot of filtering in the out ....

its a simple tuner that the sound comes out from a humble AN 7470 this we have to take as a fact ....not much you can do about that ... beyond that there is a astronomical 15nf capacitor that goes from signal to ground and a coil of some nh in series with the signal

removed the muting circuit totaly then removed the 15nf capacitor and replaced that with silver mica 300pf

now the radio doesnt mute any more while searching for a station ( not really importand since all your required stations are in memory ) and also while changing from memory one to memory two there some kind of not really loud pop noise .

though high become by far more crisp and clear ....then sound stage become more real and as about the low end didnt seen much eventhough i beefed up the capacitors in the output of the AN from 3.3 mfd to 10 mfd plus 100nf styroflex bypass

any comments ????

Hi Sakis,

Are you sure that 15nF capacitors aren't part of the FM de-emphasis circuit? The series coil in this type of tuner is usually present to reduce the residual 19KHz stereo pilot tone component. This was particularly important in the days of tape recording as the pilot tone, unless adequately filtered, would beat with the recorder's tape head bias oscillator, creating some ugly whistles.

If the above situation is the correct, your 330pF would likely result in the audio sounding too bright.

I am often surprised by manufacturers using transistors as (shunt) mute switches. Surely their non-linearity destroys audio quality?

Regards,
Steve

 

[DigitalJunkie]

Removing the muting transistors can help with sound,but you need to somehow ensure that the "clunks and pops" are still muted,or it can do ugly things-A small relay is commonly used instead. I've re-purposed the existing muting transistor(s) to trigger the relay(s),it's pretty simple.

 

[east electronics]

this is what i thought also relay would be by far better ... i mooving to this direction soon ....


as about the cap yes ....high sounds too bright but on the other hand 15nf in the signal out is too much .... will look to go higher may be up too 1000pf but not 15nf

thanks guys ..... will play arround a Sony cd player and keep you posted


( clunks and pops ....i could live with a few of these if my sound is getting a lot better !!!! )

 

[underwurlde]

Among the long list of improvements for the Marantz CD players is the removal of the muting transitors....

Andy

 

[currentflow]

as about the cap yes ....high sounds too bright but on the other hand 15nf in the signal out is too much .... will look to go higher may be up too 1000pf but not 15nf

This has got me thinking. If the tuner sounds dull, could it be that it was designed for the US market? They use 75us pre/de-emphasis, while in Europe it's 50us. A tuner designed for US use might possibly sound dull when used in Europe.

If the de-emphasis is based on a 75us CR time-constant, changing to the European standard would mean changing the filter capacitor to 10nF. Just a thought.

Regards,
Steve

 

[jan.didden]

This has got me thinking. If the tuner sounds dull, could it be that it was designed for the US market? They use 75us pre/de-emphasis, while in Europe it's 50us. A tuner designed for US use might possibly sound dull when used in Europe.

If the de-emphasis is based on a 75us CR time-constant, changing to the European standard would mean changing the filter capacitor to 10nF. Just a thought.

Regards,
Steve

You can use a muting relay two ways: in series with the signal, where it closes after the mute delay, or from signal to ground where it opens after the mute delay. The last method is best since it doesn't have the relay in the signal line. Since all sources have a series output resistors, shorting the signal to ground during the mute does no harm.

jd

 

[east electronics]

You can use a muting relay two ways: in series with the signal, where it closes after the mute delay, or from signal to ground where it opens after the mute delay. The last method is best since it doesn't have the relay in the signal line. Since all sources have a series output resistors, shorting the signal to ground during the mute does no harm.

jd

WELL....dont really think so ....i think that having a resistor to ground as termination in a line outpout signal is a diferent story than a transistor providing ground fro muting .... the idea is not to have anything messing arround with your signal

---- then again if i go for relay mode i would go fro shorting to ground than interrupt the line out signal ....

----- yeap i presumed that mods like that will be present in the marantz cd mod list ....BUT THE ALL THREAD IS WAY TOO LONG TO READ ...

thanks jan and others nice to see you arround ....will do some testing any day now and see what goes on

kind regards sakis 🙄

 

[jan.didden]

WELL....dont really think so ....i think that having a resistor to ground as termination in a line outpout signal is a diferent story than a transistor providing ground fro muting .... the idea is not to have anything messing arround with your signal [snip]

Hi Sakis,

Sorry but I don't get this part. What resistor are you talking about? I only mentioned the normal series output resistor (often 50-100 ohms) in a line out, not anything to ground. This resistor will of course protect the output stage of the line amp during the short interval that the relay shunts the ouput to ground (mute delay time).

jd

 

[AndrewT]

5k0 & 15nF give the 75us de-emphasis of FM radio.
3k33 & 15nF for 50us

 

[currentflow]

5k0 & 15nF give the 75us de-emphasis of FM radio.
3k33 & 15nF for 50us

If R is 5K0, which would confirm a 75us de-emphasis, it may be easier to change the capacitor to 10nF than find a 3k33 resistor for conversion to 50us.

Regards,
Steve

 

[east electronics]

okidoki ....

there we go Sony CDP XE320

----removed 4558 op amps replaced with 5532
---- removed the muting circuit and use similar topology to drive a small relay to shunt the outpout to ground for muting perpus
---- removed the output capacitor 500pf from signal to ground (poleyster ) and replaced it with 350pf silver mica
---- the capacitor in the output of the op amp was 47mfd /16 volt thought that this quiet ok but bypassed it with 0.47mfd styroflex .

results :

i was actually expecting the high to become more bright or even too bright ...they didnt the major change was in the low end bass become more tight more real and without more than it was before

i noticed that midle was much more clean and more separated ....meaning that in vocals with more than one singer you got a better presentation of the vocals and seemed also that sound stage was more real after that....


finally i didnt have any pops or crunks coming from the muting circuit ....

i will proceed with my yamaha tuner to see what hapens

 

[east electronics]

there we go
YAMAHA TUNER model TX530

first and most importand in the out of the LA was some filtering in a circuit including coils, caps, that finally i was too lazy too analyze .... end of story the output capacitor was a poor electrolytic 1mfd /63volt ....

----changed that with 10 mfd and bypassed it with 47mfd styroflex
----removed the muting circuit totally and didnt bother to install a shunt relay
---- replaced two capacitors of 3.3 nf that i actually found soldered on the rca out plug with silver mica 1.2 nf ( yeap ...i actually have so many of these components that i can take a swimm inside them he he he )

results ....

***low end is by far a lot better
***high is much more bright and crisp

negatives
*** now i have to live with pop/crunkle noise ( not too loud ) when i change from memory 1 to memory 2

*** sereo image is the same but with 1.2nf caps if signal is a bit weak you can hear a small hiss from behind that wasnt there before ...

very happy ... i will stop here now

thank you very much all

 

[AndrewT]

If R is 5K0, which would confirm a 75us de-emphasis, it may be easier to change the capacitor to 10nF than find a 3k33 resistor for conversion to 50us.

Regards,
Steve

all the manufacturer needs to do is add a switchable 100r and that gives both de-emphasis rates for worldwide application.

 

[currentflow]

all the manufacturer needs to do is add a switchable 100r and that gives both de-emphasis rates for worldwide application.

True in an ideal world, however if a manufacturer can save two resistors and a switch, they probably would - not to mention the cost of mains voltage selection 😉

Steve

 

[east electronics]

ok ...here is a small question / update

many of the cd players i am working with suffer the above list of mods ( basically if laser is a type that is easy to have in the feature also i proceed to further upgrades ...if not just skip it )

so working on a cd player making a number of mods such the above and someothers power supply related i had the all thing ready for relay installation ...

i had my mute transitors removed and had all the wiring ready for the relays ...meanwhile i wanted to make a "so far so good test " so made the CD player play with all the mods done except any muting circuit at all

i played for a few hours a number of various types of cd of any kind and recording no pops or clungs or any weird sound at all .... it seemed that the muting circuit was not needed at all ...Why ????

am i missing something ????

 

[Mooly]

Try playing a CD ROM or enhanced CD with extra content or a Data test track such as is on Philips test disc SBC249. Also try in all modes, fast search etc. Disconnecting mains etc.

The muting is there for a reason 🙂 whether it's implemented as well as possible is another matter.

 

[east electronics]

THANKS MOOLY

fast search was no problem at all ,
track change also no problem ,
pause no problem ,
power on and off just a small boop noise but nothing that might create any trouble ( in this player Technics SL-PG490 stand by switch no power switch ,
extra content cd or cd rom no problem...
finally hard disconnect of mains absolutely no problems at all ...

i think for this player i will also skip the relay