Thump

[Dirk Bruere at NeoPax]

Getting a thump when powering off an amplified speaker.
I have access to the amp, so is there any simple way of stopping this
(apart from keeping it powered on!)?

Dirk

[Serge Auckland]

Dirk Bruere at NeoPax wrote:
> Getting a thump when powering off an amplified speaker.
> I have access to the amp, so is there any simple way of stopping this
> (apart from keeping it powered on!)?
>
> Dirk

If you have access to the amp, can you put a switch in one 'speaker
lead? If so, then switch off the 'speaker before switching off the amp.
On switch-on, switch the amp on first, then the speakers.

Bit of a pain, I agree, but without a major redesign of the amp, there's
not a lot you can do about the thump.

S.

[Eeyore]

Dirk Bruere at NeoPax wrote:

> Getting a thump when powering off an amplified speaker.
> I have access to the amp, so is there any simple way of stopping this
> (apart from keeping it powered on!)?

Re-design the amp ?

Graham

[Dirk Bruere at NeoPax]

Eeyore wrote:
>
> Dirk Bruere at NeoPax wrote:
>
>> Getting a thump when powering off an amplified speaker.
>> I have access to the amp, so is there any simple way of stopping this
>> (apart from keeping it powered on!)?
>
> Re-design the amp ?

Not feasible.
The alternative would be to cut the o/p signal path on mains failure.
Mech relays used to be used.

Dirk

[Henk]

Dirk Bruere at NeoPax schreef:

> Getting a thump when powering off an amplified speaker.
> I have access to the amp, so is there any simple way of stopping this
> (apart from keeping it powered on!)?
>
> Dirk

A good amp mutes its outputs when powering on and off. If it doesn't do
that you have to take care of that manually, e.g. by turning down the
volume knob of the amp or speakers if they have any. If your speakers
have a power switch it's also easy, just turn them on AFTER turning on
your amp and BEFORE turning your amp off. Also make sure that you never
send a signal to the amp (and through its outputs) when turning on and
off. If all this doesnt work get a switch in the signal path between
the amp and the speaker (but watch out for signal loss).

Henk

[Scott Dorsey]

Dirk Bruere at NeoPax > wrote:
>Getting a thump when powering off an amplified speaker.
>I have access to the amp, so is there any simple way of stopping this
>(apart from keeping it powered on!)?

Sure, you can put a line-powered relay between the amp and speaker, so
that when the power goes off, the speaker is disconnected before the thump
begins.

Or you could just learn to ignore it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Eeyore]

Dirk Bruere at NeoPax wrote:

> Eeyore wrote:
> >
> > Dirk Bruere at NeoPax wrote:
> >
> >> Getting a thump when powering off an amplified speaker.
> >> I have access to the amp, so is there any simple way of stopping this
> >> (apart from keeping it powered on!)?
> >
> > Re-design the amp ?
>
> Not feasible.
> The alternative would be to cut the o/p signal path on mains failure.
> Mech relays used to be used.

The problem with relays is how long they take to act or I'd have suggested them.

Graham

[Scott Dorsey]

Eeyore > wrote:
>Dirk Bruere at NeoPax wrote:
>> Not feasible.
>> The alternative would be to cut the o/p signal path on mains failure.
>> Mech relays used to be used.
>
>The problem with relays is how long they take to act or I'd have suggested them.

They don't have to be THAT fast, they only need to be faster than the discharge
of the supply caps. If the relay is too slow, add more shunt capacitance to
the supply so the thump is delayed more.

The relay should be powered from the AC line, NOT from the DC rails. The
DC rails should stay powered up for a good while after the AC line drops out.
On most amps these days it may be as short as a second, though, but the old
monitor amp here keeps running for about five seconds after you pull the plug.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Arny Krueger]

"Scott Dorsey" > wrote in message

> Eeyore
> >
> wrote:
>> Dirk Bruere at NeoPax wrote:
>>> Not feasible.
>>> The alternative would be to cut the o/p signal path on
>>> mains failure. Mech relays used to be used.
>>
>> The problem with relays is how long they take to act or
>> I'd have suggested them.

> They don't have to be THAT fast, they only need to be
> faster than the discharge of the supply caps. If the
> relay is too slow, add more shunt capacitance to the
> supply so the thump is delayed more.

Agreed. Turning a power amp off creates a massive internal electrical
disturbance as the PS voltage ramps down to zero. If the PS caps are large
enough, the ramp can be very slow.

A big part of the equation is the actual cause of the thump. Usually, a good
SS power amp will have enough power supply rejection that it will not pass
the ramping down of the power supply to the output terminals, at least as
long as the power amp circuit has coherency as a power amp.

Unfortunately, as the PS voltage drops below say 12 VDC, the biasing of the
amp circuit starts to fall apart and big transients may be generated.

With adequate PS caps, a mechanical relay can disconnect the load before the
power amp circuit's operation falls apart due to insufficient rail voltage.

> The relay should be powered from the AC line, NOT from
> the DC rails.

Or, the relay can be powered from an intelligent circuit that *sees* the
power supply or amp output going way out of spec, and dumps the power to the
relay so it quickly disconnects the output before the load sees a the
transient.

> The
> DC rails should stay powered up for a good while after
> the AC line drops out.

One good reason for big PS caps.

> On most amps these days it may be
> as short as a second, though, but the old monitor amp
> here keeps running for about five seconds after you pull
> the plug.

This problem has been around since the early days of SS and common use of
direct-coupled outputs. For example, the Dyna 400 had something like 65 volt
rails, but would operate cleanly with vastly reduced power output down to
about 12 volts. There was a "Dynaguard" circuit that monitored the outputs
for DC or LF AC. A potential thump would cause the output relay to click
out.

[Michael Wozniak]

"Scott Dorsey" > wrote in message
...
> Dirk Bruere at NeoPax > wrote:
>>Getting a thump when powering off an amplified speaker.
>>I have access to the amp, so is there any simple way of stopping this
>>(apart from keeping it powered on!)?
>
> Sure, you can put a line-powered relay between the amp and speaker, so
> that when the power goes off, the speaker is disconnected before the thump
> begins.
>
> Or you could just learn to ignore it.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

Relays... capacitors.....

Uh, unplug the speaker before turning the amp off?

Mikey
Nova Music Productions

[GregS]

In article . net>, "Michael Wozniak" > wrote:
>
>"Scott Dorsey" > wrote in message
...
>> Dirk Bruere at NeoPax > wrote:
>>>Getting a thump when powering off an amplified speaker.
>>>I have access to the amp, so is there any simple way of stopping this
>>>(apart from keeping it powered on!)?
>>
>> Sure, you can put a line-powered relay between the amp and speaker, so
>> that when the power goes off, the speaker is disconnected before the thump
>> begins.
>>
>> Or you could just learn to ignore it.
>> --scott
>> --
>> "C'est un Nagra. C'est suisse, et tres, tres precis."
>
>Relays... capacitors.....
>
>Uh, unplug the speaker before turning the amp off?
>
>Mikey
>Nova Music Productions

Just leave the room and lock er up.

greg

[Romeo Rondeau]

>> Dirk Bruere at NeoPax > wrote:
>>>Getting a thump when powering off an amplified speaker.
>>>I have access to the amp, so is there any simple way of stopping this
>>>(apart from keeping it powered on!)?
>>
>> Sure, you can put a line-powered relay between the amp and speaker, so
>> that when the power goes off, the speaker is disconnected before the
>> thump
>> begins.
>>
>> Or you could just learn to ignore it.
>> --scott
>> --
>> "C'est un Nagra. C'est suisse, et tres, tres precis."
>
> Relays... capacitors.....
>
> Uh, unplug the speaker before turning the amp off?
>
> Mikey
> Nova Music Productions

Um, isn't he talking about a "powered" speaker? (he said "amplified"
though), how would you unplug the speaker?

[Dirk Bruere at NeoPax]

Dirk Bruere at NeoPax wrote:
> Eeyore wrote:
>>
>> Dirk Bruere at NeoPax wrote:
>>
>>> Getting a thump when powering off an amplified speaker.
>>> I have access to the amp, so is there any simple way of stopping this
>>> (apart from keeping it powered on!)?
>>
>> Re-design the amp ?
>
> Not feasible.
> The alternative would be to cut the o/p signal path on mains failure.
> Mech relays used to be used.

SS relays? Or too much distortion?

Dirk

[Eeyore]

Dirk Bruere at NeoPax wrote:

> Dirk Bruere at NeoPax wrote:
> > Eeyore wrote:
> >>
> >> Dirk Bruere at NeoPax wrote:
> >>
> >>> Getting a thump when powering off an amplified speaker.
> >>> I have access to the amp, so is there any simple way of stopping this
> >>> (apart from keeping it powered on!)?
> >>
> >> Re-design the amp ?
> >
> > Not feasible.
> > The alternative would be to cut the o/p signal path on mains failure.
> > Mech relays used to be used.
>
> SS relays? Or too much distortion?

What's the amp ?

Graham

[Dirk Bruere at NeoPax]

Eeyore wrote:
>
> Dirk Bruere at NeoPax wrote:
>
>> Dirk Bruere at NeoPax wrote:
>>> Eeyore wrote:
>>>> Dirk Bruere at NeoPax wrote:
>>>>
>>>>> Getting a thump when powering off an amplified speaker.
>>>>> I have access to the amp, so is there any simple way of stopping this
>>>>> (apart from keeping it powered on!)?
>>>> Re-design the amp ?
>>> Not feasible.
>>> The alternative would be to cut the o/p signal path on mains failure.
>>> Mech relays used to be used.
>> SS relays? Or too much distortion?
>
> What's the amp ?
>
> Graham
>
Powersoft DigiMod

Dirk

[Mike Rivers]

Dirk Bruere at NeoPax wrote:
> Getting a thump when powering off an amplified speaker.
> I have access to the amp, so is there any simple way of stopping this
> (apart from keeping it powered on!)?

I suppose it gets annoying after a while, but unless the thump wasn't
there when the speakers were new, it's something that the manufacturer
considers safe and you should just ignore i.

There are certainly ways of modifying the amplifier for a soft
turn-off, but it would be complex enough so that for all but the
fussiest, it wouldn't be worth the effort. You should at least mention
the brand and model. Maybe someone with the same speaker will tell you
that there's something wrong with yours.

[Arny Krueger]

"Dirk Bruere at NeoPax" > wrote in
message
> Dirk Bruere at NeoPax wrote:
>> Eeyore wrote:
>>>
>>> Dirk Bruere at NeoPax wrote:
>>>
>>>> Getting a thump when powering off an amplified speaker.
>>>> I have access to the amp, so is there any simple way
>>>> of stopping this (apart from keeping it powered on!)?
>>>
>>> Re-design the amp ?
>>
>> Not feasible.
>> The alternative would be to cut the o/p signal path on
>> mains failure. Mech relays used to be used.

Mechanical relays are still widely used, even in economy audio gear. For
example, I have a brand new ca. $90 Sherwood stereo receiver with mechanical
relays that control the speakers.

> SS relays? Or too much distortion?

SS relays for loudspeaker-level voltages and currents generally have too
much distortion for quality audio.

SS relays of a vastly different nature can work well at line levels and
impedances.