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    Shutdown of preamp - then Thump (not Trump)

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    jfine

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    Shutdown of preamp - then Thump (not Trump)

    Post by jfine on Wed Sep 27, 2017 11:41 am

    Some preamps do this, some don't.

    What is really happening here?


    If I turn off the M125 monoblocks first, which I always do, then shutdown the SP14 linestage, there is a thump sound to the speakers.

    If I wait about 30 seconds before shutting down the linestage, it does not do this.

    However, I've had other pre's in the system that don't do this at all, so it must be some kind of filter somewhere?

    Is there a mod that can be performed on the SP14 that will suppress this? Or just wait before shutting down is the best way?
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    slate1

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by slate1 on Wed Sep 27, 2017 12:26 pm

    I power up in this order: PH-16x phono stage, SP-13 preamp, then ST-120 amp.  If I move too quickly through the startup process, I will get a brief loud static type noise through the speakers.  If I give it maybe 5-10 seconds between each device power-up, it's relatively silent through the process.

    I power down in the reverse order.

    All that to say, I think it's probably normal.  I'd just power up and down everything slowly.
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    PeterCapo

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by PeterCapo on Wed Sep 27, 2017 1:34 pm

    Don't know if the SP14 has a capacitor across the power switch.  You might ask Roy about it, though I wouldn't think it is absolutely necessary.  Otherwise no problem, just wait your 30 seconds.  It's not an uncommon thing.
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    peterh

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by peterh on Wed Sep 27, 2017 2:38 pm

    If done in sequence then no bad sound is heard :
    power on :  preamp on, wait then power amp
    power off : poweramp off, wait ( until all B+ is gone ) then preamp off

    See it like this : if poweramp is turned off while the input is kept steady, it will
    die peacefully. When the B+ caps has been drained you can safely turn off
    or do anything you want with the preamp as there is no power to send to the speakers.
    The key is to wait after turning off power amp until all B+ is drained.

    I made this automatically with an arduino as controller, it also prevents repowering on power outages.
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    Peter W.

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by Peter W. on Wed Sep 27, 2017 4:37 pm

    Please note the interpolations. Others have gotten it dead-right - I will try to sum it up:

    jfine wrote:Some preamps do this, some don't.

    What is really happening here?


    If I turn off the M125 monoblocks first, which I always do, then shutdown the SP14 linestage, there is a thump sound to the speakers.

    There is residual B+ in the amp - until it dissipates, any disturbance on the input side will show up at the speakers.

    If I wait about 30 seconds before shutting down the linestage, it does not do this.

    Yes, as already noted, this would be after the residual B+ has dissipated in the amp.

    However, I've had other pre's in the system that don't do this at all, so it must be some kind of filter somewhere?

    Not necessarily. Some preamps are better designed for this issue than others. Some preamps (and integrated amps/receivers) address this by never shutting down some critical circuits - noting that these are mostly solid-state devices of a certain vintage. But consider the powering-up/down process and which components 'see' activity first - which can vary - and what has to happen before these components stabilize. For tube equipment using tube rectifiers, this will be typically be a smaller problem than with those that use solid-state rectifiers. The 'why' for this is pretty obvious. On the shut-down cycle, the advantage of a tube rectifier on start-up
    is no advantage on shut-down. And the sequence of voltage decay along the signal path is of concern.


    Is there a mod that can be performed on the SP14 that will suppress this? Or just wait before shutting down is the best way?

    Waiting is best. Sufficiently that I suggest you eschew mods for that option. It costs, perhaps 15 seconds or so. It is a funny thing with tube pre-amps. Making them dead-quiet in operation via a strong power-supply and significant capacitance to prevent sagging (yes, even pre-amps can 'sag') increases the shut-down noise, especially into an active amp. Shut down the amp first. Always, whether tube or solid-state.
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    jfine

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by jfine on Wed Sep 27, 2017 6:15 pm

    I sort of didn't want this to turn into a how to power down in sequence discussion, rather, first, what is happening physically, why is it this thump sound, what causes it?

    Second since some preamps dont do this, what is it in their circuitry that is stopping this from happening and can it be implemented in the SP14?
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    PeterCapo

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by PeterCapo on Wed Sep 27, 2017 6:28 pm

    This post/thread might help: https://www.audioasylum.com/forums/dynaco/messages/10788.html

    Hopefully this link will be of interest, or at least point you in the direction you want to go. At the same time, provided your preamp is otherwise functioning as its designer intended, I would heed the comments in this thread. It is not an unusual phenomenon and should not necessarily be taken as an indication of a problem. My suggestion would be to ask Roy, if you are still concerned.
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    slate1

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by slate1 on Thu Sep 28, 2017 8:54 am

    jfine wrote:I sort of didn't want this to turn into a how to power down in sequence discussion, rather, first, what is happening physically, why is it this thump sound, what causes it?

    Second since some preamps dont do this, what is it in their circuitry that is stopping this from happening and can it be implemented in the SP14?

    Unless I'm missing something, Peter W. answered both these questions. Agree with PeterCapo, just power it up correctly and enjoy the preamp! It's absolutely normal and nothing to be worried about.
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    jfine

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by jfine on Thu Sep 28, 2017 11:07 am

    slate1 wrote:
    Unless I'm missing something, Peter W. answered both these questions.  Agree with PeterCapo, just power it up correctly and enjoy the preamp!  It's absolutely normal and nothing to be worried about.

    I'm not at all worried, just am asking questions, anybody know what I can do to the preamp to suppress this?
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    Peter W.

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by Peter W. on Thu Sep 28, 2017 11:22 am

    jfine wrote:
    slate1 wrote:
    Unless I'm missing something, Peter W. answered both these questions.  Agree with PeterCapo, just power it up correctly and enjoy the preamp!  It's absolutely normal and nothing to be worried about.

    I'm not at all worried, just am asking questions, anybody know what I can do to the preamp to suppress this?

    Greatly compromise the power-supply would be a start. Then it would collapse at turn-off - no noise. It would be a close-run thing to have enough operational capacity to operate properly, but not so much as to have any sort of reserve. Much like the vintage PAS-series.
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    jfine

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by jfine on Thu Sep 28, 2017 11:45 am

    Maybe Roy M. will chime in, he probably knows more about his own design.
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    tubes4hifi
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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by tubes4hifi on Thu Sep 28, 2017 8:55 pm

    To answer the specific question jfine has rather than confirm the sequencing of turn on/ off which everyone seems to know, the answer is a muting relay could be added which would short the output of the preamp to ground, pretty simple
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    deepee99

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by deepee99 on Sat Sep 30, 2017 7:16 pm

    Not to contradict Roy, but shutdown sequence properly followed is the lazy man's way to go. Especially if you're using a Bendix rectifier in the SP-14, it takes as long to power-down as it does to power up. So shut down the mains, go for a beer or a walk around the block, then switch off the preamp. The M-125s don't thump when you turn them off. Those downstream thumps, while annoying, won't harm the speaks.

    Dogstar

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by Dogstar on Sun Oct 01, 2017 12:26 am

    Prior to shut down I make it a point of turning the volume control down on the preamp. I guess as an added precaution I could turn down the attenuator on the amp. I also stop my source creating a signal.

    If I accidentally leave the volume control up and my source is still playing if I shut down the amp first the sound becomes distorted.

    Therefore I power down the source first, then the preamp and finally the amp.a
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    j beede

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by j beede on Mon Oct 02, 2017 2:14 am

    Dogstar wrote:Prior to shut down I make it a point of turning the volume control down on the preamp. I guess as an added precaution I could turn down the attenuator on the amp. I also stop my source creating a signal.

    If I accidentally leave the volume control up and my source is still playing if I shut down the amp first the sound becomes distorted.

    Therefore I power down the source first, then the preamp and finally the amp.a

    What you described is precisely how not to do it. Exposing the high impedance input of your power amplifier to the unpredictable output of a powering down CD player or preamp is inviting trouble.
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    deepee99

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by deepee99 on Mon Oct 02, 2017 2:38 am

    j beede wrote:
    Dogstar wrote:Prior to shut down I make it a point of turning the volume control down on the preamp. I guess as an added precaution I could turn down the attenuator on the amp. I also stop my source creating a signal.

    If I accidentally leave the volume control up and my source is still playing if I shut down the amp first the sound becomes distorted.

    Therefore I power down the source first, then the preamp and finally the amp.a

    What you described is precisely how not to do it. Exposing the high impedance input of your power amplifier to the unpredictable output of a powering down CD player or preamp is inviting trouble.

    Amen to that. The distortion is the result of the caps' charge decaying after shut-off. I set the pre-amp selector to a unused position, turn off the main amps, then after a minute or two shut down the preamp, then the sources. It IS a good ideal to turn the volume all the way down when changing sources, esp. if you're running a Roku or Amazon video stick into your DVD and then into the preamp, as they generate some pretty loud and scary switching transients.


    Dogstar

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by Dogstar on Tue Oct 03, 2017 6:57 am

    deepee99 wrote:
    j beede wrote:
    Dogstar wrote:Prior to shut down I make it a point of turning the volume control down on the preamp. I guess as an added precaution I could turn down the attenuator on the amp. I also stop my source creating a signal.

    If I accidentally leave the volume control up and my source is still playing if I shut down the amp first the sound becomes distorted.

    Therefore I power down the source first, then the preamp and finally the amp.a

    What you described is precisely how not to do it. Exposing the high impedance input of your power amplifier to the unpredictable output of a powering down CD player or preamp is inviting trouble.

    Amen to that. The distortion is the result of the caps' charge decaying after shut-off. I set the pre-amp selector to a unused position, turn off the main amps, then after a minute or two shut down the preamp, then the sources. It IS a good ideal to turn the volume all the way down when changing sources, esp. if you're running a Roku or Amazon video stick into your DVD and then into the preamp, as they generate some pretty loud and scary switching transients.


    I have a solid state preamp....I've been powering down in that order without any issue for 3 years now.
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    j beede

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by j beede on Tue Oct 03, 2017 12:24 pm

    Dogstar wrote:
    deepee99 wrote:
    j beede wrote:
    Dogstar wrote:Prior to shut down I make it a point of turning the volume control down on the preamp. I guess as an added precaution I could turn down the attenuator on the amp. I also stop my source creating a signal.

    If I accidentally leave the volume control up and my source is still playing if I shut down the amp first the sound becomes distorted.

    Therefore I power down the source first, then the preamp and finally the amp.a

    What you described is precisely how not to do it. Exposing the high impedance input of your power amplifier to the unpredictable output of a powering down CD player or preamp is inviting trouble.

    Amen to that. The distortion is the result of the caps' charge decaying after shut-off. I set the pre-amp selector to a unused position, turn off the main amps, then after a minute or two shut down the preamp, then the sources. It IS a good ideal to turn the volume all the way down when changing sources, esp. if you're running a Roku or Amazon video stick into your DVD and then into the preamp, as they generate some pretty loud and scary switching transients.


    I have a solid state preamp....I've been powering down in that order without any issue for 3 years now.

    I think you are stating the obvious... If your sequence was creating problems I suppose it wouldn't be your sequence. That doesn't make it a recommended practice. Preamps can emit pops, thumps, and other transients when powering on or off. Many modern tube preamps are relay-protected at their outputs or have operate/mute switches for this reason. Convention is to apply a valid preamp output to, or ground the input of any high impedance amplifier whenever it is active.

    Dogstar

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by Dogstar on Tue Oct 03, 2017 10:51 pm

    When did I say I had a problem?

    I volunteered the sequence I followed for the three years I've had this setup. The only thing I said was that if I powered off the amp first while the source was still playing and the preamp was still on that the source became distorted until the amp was completed off. I didn't say it was bad or even a concern. It just is.

    The only other thing I will say is that the distorted sound during power down if I turn the amp off first is perceived by others that are listening as something bad.

    I prefer to not hear that distorted sound ...that's why I turn the volume down and power off the source and the preamp before shutting off the amp.
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    deepee99

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by deepee99 on Wed Oct 04, 2017 4:11 pm

    Dogstar wrote:When did I say I had a problem?

    I volunteered the sequence I followed for the three years I've had this setup. The only thing I said was that if I powered off the amp first while the source was still playing and the preamp was still on that the source became distorted until the amp was completed off. I didn't say it was bad or even a concern. It just is.

    The only other thing I will say is that the distorted sound during power down if I turn the amp off first is perceived by others that are listening as something bad.

    I prefer to not hear that distorted sound ...that's why I turn the volume down and power off the source and the preamp before shutting off the amp.
    Dogstar, just avoid the problem. Main amps' output will always decay unless they're shut down first. Tube or s/s/, doesn't matter. You might save your speaks from some nasty transients that way.

    Powering-up works in reverse, esp. with tube gear. Fire up all the peripherals and line pre-amp first, let them get over their warm-up belching, and after a couple of minutes, light the mains with the volume control muted or selector switch set to an un-used position.

    My speakers are the single-largest investment I have in my system and I try all I can to prevent nasty transients from getting at them, which usually originate at the source level.
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    Peter W.

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by Peter W. on Wed Oct 04, 2017 4:24 pm


    My speakers are the single-largest investment I have in my system and I try all I can to prevent nasty transients from getting at them, which usually originate at the source level.
    [/quote]

    To this end, my big power-amp (Citation 16) has the capacity to blow the voice-coils out of any speaker I own. Which means hitting it with a transient is not a very good idea. I have mated it with my tuner/pre-amp (Revox A720) that has a relay - and it also has a relay.

    But the amp still goes on last and off first.

    Start Sequence:

    Pre-amp on. Volume at 0
    Wait for relay click.
    Power-amp on. Wait for relay click.
    Apply volume.

    Stop sequence:
    Power-amp off. Wait for relay click (and cessation of sound).
    Volume to 0.
    Pre-amp off.

    The speakers are big Maggies - so you bet they are the two most valuable audio items I own.

    Corona

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by Corona on Wed Oct 04, 2017 8:21 pm

    I'll always hear a thump if I shut off my sp14 prior to my m125's. Usually I avoid the problem by just turning the amps off first and waiting 20-30 seconds.
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    tubes4hifi
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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by tubes4hifi on Fri Oct 06, 2017 11:13 am

    shouting . . . ANYBODY THAT HAS A TUBE AMP OR TUBE PREAMP . . .
    follow the sequence that Peter has shown, I've been using this sequence myself for over 25 years
    seems common knowledge isn't very common anymore . . .

    Start Sequence:

    Pre-amp on. Volume at 0
    Wait for relay click.
    Power-amp on. Wait for relay click.
    Apply volume.

    Stop sequence:

    Power-amp off. Wait for relay click (and cessation of sound).
    Volume to 0.
    Pre-amp off.
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    peterh

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by peterh on Fri Oct 06, 2017 11:39 am

    tubes4hifi wrote:shouting . . . ANYBODY THAT HAS A TUBE AMP OR TUBE PREAMP . . .
    follow the sequence that Peter has shown, I've been using this sequence myself for over 25 years
    seems common knowledge isn't very common anymore . . .

    Start Sequence:

    Pre-amp on. Volume at 0
    Wait for relay click.
    Power-amp on. Wait for relay click.
    Apply volume.

    Stop sequence:

    Power-amp off. Wait for relay click (and cessation of sound).
    Volume to 0.
    Pre-amp off.

    I have programmed an arduino to do this . code is here http://n.manet.nu/fm1/FM1.ino
    The function is as :
    When start signal(D2) comes it will power on preamp after 4s, then after
    additional 21s power amp will be turned on.

    When startsignal ( D2) goes down, poweramp is killed then after delay preamp.

    If arduino is powercycled it will aloways go through the sequence thus
    i brownout won't cycle any of the amps without any delay.

    The code is more complex as it has 2 sources for power control ( D2 and D4 )
    You can ignore D4 ( tie it to ground)
    D7 controls preamp, D8 poweramp.
    D13 controls a LED that blinks during power on/off delay, and lights when power is on.

    Arduino is supposed to be constant on in this application.
    Feel free to use/abuse in any way you want.
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    jfine

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    Re: Shutdown of preamp - then Thump (not Trump)

    Post by jfine on Mon Oct 09, 2017 9:08 pm

    tubes4hifi wrote:To answer the specific question jfine has rather than confirm the sequencing of turn on/ off which everyone seems to know, the answer is a muting relay could be added which would short the output of the preamp to ground, pretty simple

    hmmm...muting relay....mute....mute button....well yea my SP14 Khozmos has a mute button, so mute the linestage, shut off amp, then shut off linestage *without waiting* and no more thump, at least the last few times I tried it anyways, huh

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