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diyAudio Member
Join Date: Feb 2002
Location: Perth, Australia.
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No Relay Contacts Is Sonically Better IME....
Hi Poul,
I think you will find that most owners are not concerned so much by a SMALL turn on thump, so much as the prospect of speaker damage due to amplifier fault condition.
Another reason to include an output relay is to avoid strange noises and behaviours as the supplies decay - I am using an Amcron amplifier that produces rotten sputtering sounds as the power rails decay, but the easy solution in this case is to mute the amplifier input during power down.
I (and others) have found out bitterly that rail or AC mains fuses do not always provide speaker protection, and in the case of old Phase Linear amplifiers going DC due to a failed pre-driver transistor, expensive and tear producing smoke is the result.
I entirely agree that series output relay contact reliability can be a long term liability.
In my experience however with at least 'reasonable' relay quality in production audio equipment, this is actually a very rare occurence.
I have conducted tests where I mechanically locked the relay armature in the operated condition and applied coil current or not, and indeed found a sonic change.
This I have tried with several amplifiers and always found subtle sonic changes according to coil current or not.
To my mind an amplifier with well behaved power-up and power-down characteristics with direct output connection is much preferrable.
A supervisory circuit controlling a relay connecting 240V AC to the output stage supplies would be my preferred method.
This supervisory circuit could also check for allowed load resistance before output stage power up (Accuphase E-202 did this), as well as DC fault conditions, whether caused by the amplifier itself or an externally applied audio signal with DC bias.
This supervisory circuit could also incorporate a signal presence 'wake-up' or 'go to sleep' function.
If this logic and technique was explained correctly in the sales literature it would likely be viewed as beneficial.
Eric.
Not quite the answer you were looking for I know.
Decent quality adequately rated (over rated) silver contacts should be fine in my experience, and the "A high Current 16 Amp SPST, Mains Voltage Rated Relay with Silver Alloy Contacts" ought to be entirely suitable so long as the contact geometry provides suitable 'contact wiping'.
Arcing during contact close or open is the killer, so for ultimate reliability signal muting is strongly advisable during output relay operation in either direction.
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I believe not to believe in any fixed belief system.
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