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Turn on PRE. before POWER, but why?

Discussion in 'audio' started by Mike Reed, Jan 18, 2021.

  1. Mike Reed

    Mike Reed pfm Member

    As one of my valve mono's blew a mains fuse (and continues to do so) when I plugged in my can - amp which has a pre. out facility, I wonder if I accidentally turned the h/ph amp on secondly. Doubt it as pre first, power second is ingrained, but exploring every possibility here.

    Regardless, the pots were fully down on the mono's and I can't see a connection between interconnect and mains fuse. However, I'm not sure why the pre. first sequence is mandatory, except inasmuch as it could inadvertently come on at high volume for power amps without input pot's.
    Miss Ariel and johnacurtis like this.
  2. ABCaudio

    ABCaudio Trade: ABCaudio, representing EWA

    The convention avoids any switch-on pop from the pre being amplified downstream, possibly without proper control or attenuation.
  3. awkwardbydesign

    awkwardbydesign Officially Awesome

    And turn the power amp off first.
    nmtjb, Big John, Paul S and 4 others like this.
  4. johnacurtis

    johnacurtis pfm Member

    With my passive pre, it takes having to remember, out of the equation! :)
  5. Mike Reed

    Mike Reed pfm Member

    Is that it? I did wonder, so it must have been pure coincidence for me. I always turn the pots to zero on my EAR 509s so it shouldn't make any difference.
  6. mikeyb

    mikeyb pfm Member

    Strange I do the complete opposite, if I do it as suggested here I get pops.
  7. uncl_nigel

    uncl_nigel pfm Member

    I always put the pre and power into standby, then switch them off in any order. When switching on, they both go into standby whether I like it or not... Valve pre and hybrid power (i.e. valve input stage)

    When I had Naim amps the power amp was always last on and first off to avoid multiple nasty noises.
  8. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If you don't switch pre on first then you could potentially get a switch on thump that could damage speakers.
    nmtjb, booja30, tuga and 3 others like this.
  9. Mr Pig

    Mr Pig ^'- -'^

    You guys switch your amplifiers off ?? :0.
    deserter and Rushboy like this.
  10. Mike Reed

    Mike Reed pfm Member

    Well, that answers my question; potential speaker protection.

    Tested my 'duff' mono 509 this afternoon, as it had been blowing fuses, but this time (with the pre. on), after a minute, a medium-sized pop through the speaker, then it simply warmed up as normal and was fine for a couple of hours. Still don't know if it's defective but I'm at least relieved that only my 912 pre. has to go back (duff phono section). Luckily the other 509 is fine as I can't send both amps back together (outer box knackered).
  11. G T Audio

    G T Audio Trade: Manufacturer and Distributor

    There's a bit more to it than that!

    I have been really surprised recently that a lot of the mature generation doesn't seem to know this procedure! I find that strange as it was always mentioned in magazines like HiFi News during the 1980s when the separate preamp and power amp became popular.

    The "pre-amp is always the first on and last off". Turn off is the reverse, as in power amp first off, then the preamp.
    Note: this is extremely important you follow this procedure to prevent any possible damage to your loudspeakers.
    If you have a separate phono stage, or a DAC, or a tape deck then this can complicate things a little.
    I have produced a comprehensive procedure for the above in pdf form. If anyone wants it just PM me.
  12. Jag Audio

    Jag Audio Trade: Jag Audio

    Weirdly, I have just had one of my valve monoblock's not power up today and it is a first for me so suspect it will be the 1.6A Anti Surge 400mA fuses so will have a look tomorrow morning.
    I would love to have a PDF of yours just to be on the safe side of powering on/off sequence so PM sent.
  13. Mike Reed

    Mike Reed pfm Member

    This just seems to reiterate what's been said upthread, Graham, though when you say there's a bit more to it, I guess there is, but what? Does a valve amp need to see an incoming signal or at least, live connection? If so, how does the mute on the pre. affect things?
  14. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If a valve amp hasn't yet warmed up when you switch on the pre amp (ie you switch them on within a few seconds of each other) then it doesn't matter as any thump from the pre has long passed by the time the valves warm up.

    Some pre amps have relay delay (which could well also be used to mute depending on the pre) to avoid any thumps but it's very much best practice to just switch on pre first and off last.

    Again as best practice, switch on all sources in use even before the pre amp as if you have left the volume turned up on the pre then the same thing can happen when you then switch on a source as it's switch on thump can then pass through the pre to the power causing the same risk of speaker damage.
    Miss Ariel, naimplayer and Mike Reed like this.
  15. Dowser

    Dowser Learning to bodge again..

    I had an XTC Pre-1 and POW-1 a while back (still have the Pow-1, must get around to selling it!). The pre had a relay delay to avoid switch on issues. I tried the power amp with my Croft Micro, without switching pre on first...blew protection fuses in power amp!
    Mike Reed likes this.
  16. Mike Reed

    Mike Reed pfm Member

    Not sure about this, Jez; d'you mean 'off'? My sources are turned on only when all amplification is up and running but (a) I have the volume low and on mute (as well as off on the power amp) and (b) always select an unused input. No idea why; just do it by habit. (N.b. it's = it is and its = belonging to it) I've been a greater recipient of your knowledge of late so just giving a little back, so to grammatically speak.:)

    Now that's interesting, and I wonder if that's what happened to me. Trying my Myryad h'ph. amp for the first time as a pre. (my pre. had developed a phono stage fault), one of my mono's blew a fuse, which is why I mentioned the possibility that I hadn't followed normal guidance by switching the can amp/pre. on first. I thought I had, but maybe not.

    I'd be surprised, though, as the can amp's output is surely minimal compared to my EAR pre. I reinstated the EAR pre. immediately and tried a 1.7A fuse and it gave out a few pops into the speaker, so I turned it off. Tried again with a new regulation 2A fuse, which blew within a minute. Yesterday, I determined to try all again. Luckily, the other mono was fine; with the same 1.7 A fuse, the 'defective' mono gave a reasonably loud pop, then continued to warm up and perform as normal for two hours or so. This, I may add, with different I/Cs.

    It is possible the I/Cs I used before (T.Q. Black Diamond) had developed a fault at the RCA power amp end (yet to check) but can't see that I/Cs can have this effect, unless somehow the power amp doesn't 'see' a proper connection. No idea, but something caused the blow. Shall try again when my pre. is fixed. Boffin advice welcomed, of course !
  17. G T Audio

    G T Audio Trade: Manufacturer and Distributor

    Exactly why you should follow that procedure and preferably leave the Croft to power up for about 30 seconds before turning on the power amp. Valve amps don't just suddenly switch on like a solid state amp. They can take up to a minute to fully stabilise. Some ARC preamps used to have a timer circuit that would mute the output for 2 minutes until everything was fully stabilised.
  18. Beobloke

    Beobloke pfm Member

    When I select a source on my B&O Beomaster 8000 it switches both the receiver and the source on and applies muting until the amplifier circuits are on and stable.

    When you switch it to standby, it mutes the output, switches off the source and then switches the amplifier circuits off in the right order so that no nasty bangs or thumps, or untoward bad things happen. It’s all very clever and great use of modern technology.

    Oh, wait, it’s 40 years old... o_O
    chartz likes this.
  19. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Oh I'm well aware of "it's" and "its" but whilst this will amaze many people even I'm not perfect:rolleyes:

    The problem with your EAR gear is almost certainly a faulty power amp. Non of the things you concern yourself about are likely to have anything to do with the issue. Probably a faulty PL509 output valve.
  20. Minio

    Minio Born to be Mild

    All Naim preamps give a switch on thump AFAIK.
    This goes for their integrateds as well. There is no way of avoiding the thump with a Naim Nait.
    With the pre powers I just switch it all on together. I'm used to the thump. It's never broken any of my speakers.
    Nor should it if the amp is designed to include it as part of the operation.

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