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909 switch on "thump"

NeilK

NeilK

pfm Member
I've just purchased a Quad 909 amplifier from eBay - Dada "revisions" done - and it seems to have a pretty massive switch on thump through my loudspeakers, much more so than I remember from my old 606 and certainly much louder than that from my 520.

Is this something to be concerned about or is it a "they all do that, sir..." situation?
 
I've never had a 909 but none of the many Quad amps I have had over the years have done that.
 
I’ve heard others complain of similar with the 909 and later, and it would certainly annoy me.
 
A couple of years or so ago there was a chap on forums who was waging some kind of war with iag over Quad amps and switch on thumps.
 
Arkless Electronics said:
It always amazes me that people expect SS amps not to have switch on thump....
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Easily avoided with a relay, though!

The switch-on thump on my 909 was somewhat annoying through my ESL 63s, but I suspect it would have been a lot more noticeable through 95dB/1w Tannoys (I never tried this combo, I bought the 909 specifically for my 63s).
My 909 also exhibited the somewhat odd (IMO) behaviour of delivering increasing amounts of DC offset through the outputs for a short time after it was powered off. I asked about this on here and can't remember the exact reason but was told it was harmless and likely appeared worse than it was in reality because I was measuring the DC offset without a load connected.
 
ToTo Man said:
Easily avoided with a relay, though!

The switch-on thump on my 909 was somewhat annoying through my ESL 63s, but I suspect it would have been a lot more noticeable through 95dB/1w Tannoys (I never tried this combo, I bought the 909 specifically for my 63s).
My 909 also exhibited the somewhat odd (IMO) behaviour of delivering increasing amounts of DC offset through the outputs for a short time after it was powered off. I asked about this on here and can't remember the exact reason but was told it was harmless and likely appeared worse than it was in reality because I was measuring the DC offset without a load connected.
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It is absolutely normal for SS amps to produce both a switch on thump and a switch off one plus offset when switching off. Some can even make squeals etc when switching off. I prefer a thump to having a relay in the signal path but many amps do have a relay, both as a way of avoiding the perfectly normal thump, which many lay people expect not to happen, and as a way of disconnecting the speakers in the event of the amp "going DC".
 
Arkless Electronics said:
It always amazes me that people expect SS amps not to have switch on thump....
Click to expand...

I expect high-end audio kit to be competently designed, and if that means sticking a relay in to address this then that should be done. I bet you won’t get any switch-on/off noise from an Accuphase, Luxman, Krell or whatever, just as you didn’t from the big Japanese receivers of the ‘70s. It seems to be something that came in the UK 1980s ‘black box made on the kitchen table’ era and I can accept it as a cost-cutting measure on budget stuff, but it shouldn’t apply to anything of any quality IMHO.
 
Tony L said:
I expect high-end audio kit to be competently designed, and if that means sticking a relay in to address this then that should be done. I bet you won’t get any switch-on/off noise from an Accuphase, Luxman, Krell or whatever, just as you didn’t from the big Japanese receivers of the ‘70s. It seems to be something that came in the UK 1980s ‘black box made on the kitchen table’ era and I can accept it as a cost-cutting measure on budget stuff, but it shouldn’t apply to anything of any quality IMHO.
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100% disagree. Almost all SS amps make a thump and it's only because of things like putting a relay in the signal path that that you sometimes don't hear it. It has zero to do with competent design. It makes a mockery of the idiocy which is the entire audiophool speaker cables, gold plated everything and £30 each binding posts to then have a lousy relay in the same signal path! Failure of said relay is one of the most common faults also.
 
Arkless Electronics said:
100% disagree. Almost all SS amps make a thump and it's only because of things like putting a relay in the signal path that that you sometimes don't hear it. It has zero to do with competent design. It makes a mockery of the idiocy which is the entire audiophool speaker cables, gold plated everything and £30 each binding posts to then have a lousy relay in the same signal path! Failure of said relay is one of the most common faults also.
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I also do prefer by far a thump in my speakers than a crappy/tinny relay killing the musicality and requiring replacement on a regular basis. Glad to see I’m not alone !
 
A hearty ‘thump’ after I press the go button is pleasing. Shows you have a muscular amp that reflects yourself. It’s no coincidence mine is a 260z ;)
 
Robert said:
None of mine do!
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Most of mine do. As you well know the speaker is "suspended" between + & - voltage rails in most SS amps and it takes a finite time for capacitors to charge up etc hence the thump present with most amps or hidden till after it's gone by a relay. A few are thumpless without a relay but personally I will not risk spoiling the sound quality of an amp over what it does for the first 0.3 seconds after switching on.
 
Arkless Electronics said:
Most of mine do. As you well know the speaker is "suspended" between + & - voltage rails in most SS amps and it takes a finite time for capacitors to charge up etc hence the thump present with most amps or hidden till after it's gone by a relay. A few are thumpless without a relay but personally I will not risk spoiling the sound quality of an amp over what it does for the first 0.3 seconds after switching on.
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A relay doesn't spoil sound quality though, not a decent brand with long life contacts and high current rating.
Unless the designer is determined to go for a hair shirt design for ideological reasons there is no excuse for not using a relay and rudimentary speaker protection.
 
Robert said:
A relay doesn't spoil sound quality though, not a decent brand with long life contacts and high current rating.
Unless the designer is determined to go for a hair shirt design for ideological reasons there is no excuse for not using a relay and rudimentary speaker protection.
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I wish I had a tenner for every output relay I've had to replace... As to sound quality well some may well reduce it through contacts becoming dirty or pitted before failing altogether. With many designs they are a necessary evil for protection reasons.... but some I've known use the relay only to remove the switch on and off thump! The problem is that the technically ignorant end user doesn't realise that switch on and off thumps are normal and many believe it is proof of a faulty unit etc etc.

A recent design of my own uses capacitor coupling of the speaker to get around DC protection issues without a relay.. and inevitably has a switch on thump.

Many many amps including well respected brands have no output relay and have both a switch on thump and no protection for the speakers if they do go DC... and a few have an SCR crowbar so if it goes DC the amp destroys itself to protect the speaker... the theory being that if things have gone as bad as it "going DC" then it's pretty fooked anyway and hopefully the crowbar blows the fuses.
 
Arkless Electronics said:
I wish I had a tenner for every output relay I've had to replace... As to sound quality well some may well reduce it through contacts becoming dirty or pitted before failing altogether. With many designs they are a necessary evil for protection reasons.... but some I've known use the relay only to remove the switch on and off thump! The problem is that the technically ignorant end user doesn't realise that switch on and off thumps are normal and many believe it is proof of a faulty unit etc etc.

A recent design of my own uses capacitor coupling of the speaker to get around DC protection issues without a relay.. and inevitably has a switch on thump.

Many many amps including well respected brands have no output relay and have both a switch on thump and no protection for the speakers if they do go DC... and a few have an SCR crowbar so if it goes DC the amp destroys itself to protect the speaker... the theory being that if things have gone as bad as it "going DC" then it's pretty fooked anyway and hopefully the crowbar blows the fuses.
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No! Switch on thumps are not normal in a good design. It only happens with lazy/poor/slapdash/half-hearted design. Half a century ago my home built power amps did not thump! Thats why I was very surprised at the expensive Naim kit. My NAP250 and NAP135s not only thumped but caused my table lamps on the same ring main to momentarily dim at power on!

However my Meridian 559s have no, zero, nada noise at all at switch on and also no mains xformer hum/vibration at all that I can detect from all 4 off 1.2KVA xformers nor any noise hiss or wot eva from the speakers with my lug oles pressed against them. Thats excellent design and they are getting on for 20 yo. The fault detection is also excellent. If a fast rising big transient 'click' hits the input the output stages are immediately clamped and only the smallest of clicks are heard in the speakers before the amps lock down. Excellent professional design.

Oh and I leave them powered on but in standby 24*7. In standby everything is fully powered on and ready to go except that there is no drive to the output stage. They were designed to be operated this way in the studio.

Proper professionally designed equipment designed for heavy use. They do weigh in at 42Kg each!

I await the abuse to follow,

DV
 
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