why mute transitors veil the sound ?

[plep]

Can someone explain why mute transistors veil the sound?
This is a classic trick, but I don’t understand how it works. My spice sims show almost no degradation as long as you pull the gates (I choose a fet version) hard enough to negative.
In advance thank you.
Philippe.

[lumanauw]

In bipolar case, maybe it's because the transistor still works (up to 7V area) when the C-E polarity is reversed?

[AndrewT]

With digital where there may be a permanent voltage bias on the muted line then reversal will not apply.
On analogue where the line to be muted is AC then the muting semiconductor is repeatedly suffering reverse polarity.

A relay avoids this problem but substitutes a bit of capacitance which must be designed for.

[Circlotron]

If the mute transistor was causing that much of a problem, wouldn't a quick sinewave check at maximum output show the distortion?

[zener_diode]

leakage current...

so, as AndrewT pointed out, use a relay.

[plep]

Dear AndrewT and zener_diode, what you describe seems to me to be a highly non linear phenomenon, why doesn't it appears in as simple linear distortion as Circlotron suggested?
Well, that shows that I don't understand what the "leakage current..." does.

I once thought that the effect of the muting transistor could be some kind of high-frequency crosstalk through the control circuit but it doesn’t seem to be the case.

Relay or nothing at all if the player doesn’t "click" is the diy audiophile solution that I use, but it’s a cure not a cause.

Best regards and thank you for your help.
Philippe.

[peranders]

Originally posted by AndrewT
With digital where there may be a permanent voltage bias on the muted line then reversal will not apply.
On analogue where the line to be muted is AC then the muting semiconductor is repeatedly suffering reverse polarity.

A relay avoids this problem but substitutes a bit of capacitance which must be designed for.

Reversed polarity is not a problem as long as the voltage is below the breakdown voltage which is 5-7 V up to 15 V depending of transistor type.

My anwser to this is that the mute transistor has a very little influence on the sound. 100 ohms plus a couple of pF isn't very harmful in a low impedance circuit.

[AndrewT]

Originally posted by peranders

Reversed polarity is not a problem as long as the voltage is below the breakdown voltage which is 5-7 V up to 15 V depending of transistor type.

My anwser to this is that the mute transistor has a very little influence on the sound. 100 ohms plus a couple of pF isn't very harmful in a low impedance circuit.

Hi Peranders,
my electronics knowledge is struggling to cope with this.
Talk me through the physics as the signal starts to reverse polarity, for the conditions with the muted and unmuted transistor in place.

[Conrad Hoffman]

The other possibility is that this is another audio myth, where one hears the effect just because the seed of the idea has been planted. A properly designed mute circuit shouldn't affect the signal to any significant degree, and it can certainly be done with transistors or FETs.

[cliffforrest]

Originally posted by Conrad Hoffman
The other possibility is that this is another audio myth, where one hears the effect just because the seed of the idea has been planted. A properly designed mute circuit shouldn't affect the signal to any significant degree, and it can certainly be done with transistors or FETs.

I agree.

I get very suspicious of claims to remember very subtle changes in audio after removing the equipment, stripping ot down, desoldering, reassembling etc etc.

One is no longer the same person, in the same position, at the same temperature or in the same mood. Expectations, however, are high ....