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Turn on PRE. before POWER, but why?

Arkless Electronics said:
Oh I'm well aware of "it's" and "its" but whilst this will amaze many people even I'm not perfect:rolleyes:
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Not your expertise, Jez, but it is mine and it's a p.i.t.a. to proof-read everything and STILL get typos etc. going through; getting worse with aging sight and declining keyboard accuracy ! I get jumped on by the other unmentionable grammar queens if I make so much as a syntactic error !!!!!:D

Arkless Electronics said:
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.
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Thanks for that. I transposed the significant ECC83 as directed by EAR but no difference. However, how can a PL509 be faulty if it's been perfect up to the fuse blow and can operate perfectly AND look/sound good for more than 2 hours as per yesterday. The only malfunction, if it is one, was the pop after a minute's warm-up (but only in the suspect amp.. The biassing LEDs were spot on from warm-up for the duration. Can that really be a faulty output valve?
 
Mike Reed said:
Not your expertise, Jez, but it is mine and it's a p.i.t.a. to proof-read everything and STILL get typos etc. going through; getting worse with aging sight and declining keyboard accuracy ! I get jumped on by the other unmentionable grammar queens if I make so much as a syntactic error !!!!!:D



Thanks for that. I transposed the significant ECC83 as directed by EAR but no difference. However, how can a PL509 be faulty if it's been perfect up to the fuse blow and can operate perfectly AND look/sound good for more than 2 hours as per yesterday. The only malfunction, if it is one, was the pop after a minute's warm-up (but only in the suspect amp.. The biassing LEDs were spot on from warm-up for the duration. Can that really be a faulty output valve?
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It can be yes. Obviously there are other things that could go wrong but in a valve power amp probably 90% of all faults will be an output valve and/or further damage caused by the faulty output valve.
 
G T Audio said:
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.
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Indeed - but I’d gotten lazy as I’d used the Croft with an ML No. 29 without any such problems (I used to leave the ML on most of the time...for my sins :)).
 
Mike Reed said:
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 !
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In my case, I just think it is down to the design of the XTC power amp - as above, I never had any problems with my ML (no thumps or crackles when pre was powered after power amp). As GT says, it should just be good practice to power sources, pre & then power - I’d gotten lazy :)
 
Arkless Electronics said:
Obviously there are other things that could go wrong but in a valve power amp probably 90% of all faults will be an output valve and/or further damage caused by the faulty output valve.
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Thanks Jez. Comforting in a strange way ! ;). As I said, though, if an output valve behaves perfectly, showing negative aspects at all, for over 2 hours, surely it can't be a faulty valve. Is this logic (or at least, my logic), faulty as well? Without much experience in valves, I'd've thought a fault would be manifest in some way; crackling, pops, poor sound, whatever.
 
Beobloke said:
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
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Ha Ha! Yes, but unlike our beloved 1980 Beomasters some kit isn't really properly designed at all so you need to need to know what to do.

My 1981 Technics SU-A4-SE-A3 combo can be switched on any way you like, preamp first, amp first to the other way round, or both at the same time, ditto with switch-off. There's no noise at all. And there's no cap at all from input(s) to output.

My Quad separates only have one switch too by the way (even for the tuners and the CD players).
 
Mike Reed said:
Thanks Jez. Comforting in a strange way ! ;). As I said, though, if an output valve behaves perfectly, showing negative aspects at all, for over 2 hours, surely it can't be a faulty valve. Is this logic (or at least, my logic), faulty as well? Without much experience in valves, I'd've thought a fault would be manifest in some way; crackling, pops, poor sound, whatever.
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Yes that is unusual but I've seen it before.
 
chartz said:
Ha Ha! Yes, but unlike our beloved 1980 Beomasters some kit isn't really properly designed at all so you need to need to know what to do.

My 1981 Technics SU-A4-SE-A3 combo can be switched on any way you like, preamp first, amp first to the other way round, or both at the same time, ditto with switch-off. There's no noise at all. And there's no cap at all from input(s) to output.

My Quad separates only have one switch too by the way (even for the tuners and the CD players).
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The problem often occurs as people mix and match their equipment. Also, most don't read their manuals!
 
With ageing vintage gear i find looking at it like a stream with dams helps.. Source-pre-power.
Each have questionable power supply (smoothing) caps so filling each up in turn and allowing them to settle before sending them downstream makes a degree of sense to me.
Wherever possible the speakers are disconnected until the power amp's had a little time to settle.
I hate thumps with a passion!
 
I would have thought any decent amp of any kind would have a relay or switch of some kind to stop any output until it has stabilised
 
retrospective said:
Wherever possible the speakers are disconnected until the power amp's had a little time to settle.
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Well, yes, but how? Do you connect the speaker leads to the warmed-up amp? I think there are amps that require a speaker load to be present when turned on. Not at all sure whether that applies to my valve amps. My speakers need to be fired up long before anything else is turned on (ESLs).

Maybe some expert opinion on this aspect from our resident gurus would be helpful.
 
retrospective said:
With ageing vintage gear i find looking at it like a stream with dams helps.. Source-pre-power.
Each have questionable power supply (smoothing) caps so filling each up in turn and allowing them to settle before sending them downstream makes a degree of sense to me.
Wherever possible the speakers are disconnected until the power amp's had a little time to settle.
I hate thumps with a passion!
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NO! That is absolutely nothing to do with it! It's irrelevant and beyond the scope of this thread to discuss the many reasons switch on (and off often) thumps happen but it's not that.

There is no need to disconnect speakers and in fact unless you have an amp with a "Speaker A/B" type switch (usually Japanese amps) it is a VERY bad idea as one of the most common causes of blown up SS amplifiers is user abuse from accidentally shorting speaker cables whilst messing around with them!
 
Arkless Electronics said:
NO! That is absolutely nothing to do with it! It's irrelevant and beyond the scope of this thread to discuss the many reasons switch on (and off often) thumps happen but it's not that.

There is no need to disconnect speakers and in fact unless you have an amp with a "Speaker A/B" type switch (usually Japanese amps) it is a VERY bad idea as one of the most common causes of blown up SS amplifiers is user abuse from accidentally shorting speaker cables whilst messing around with them!
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That's what i mean't re the speaker switch (turn it off) and avoiding potential dc passing down the line due to inrush current via slow to react ps caps
 
Arkless Electronics said:
There is no need to disconnect speakers
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This may vary between amps, Jez, but does an amplifier have to have a speaker load when fired up? Changing speakers whilst an amp is on (useful in testing, e.g.) means removing the speaker end plugs; does this matter? In contrast, I don't think an input connection is required, though. Are valve and s/s amps different in either of these respects?
 
I always thought you should never have a valve amp switched on without loudspeakers connected?
 
Mike Reed said:
This may vary between amps, Jez, but does an amplifier have to have a speaker load when fired up? Changing speakers whilst an amp is on (useful in testing, e.g.) means removing the speaker end plugs; does this matter? In contrast, I don't think an input connection is required, though. Are valve and s/s amps different in either of these respects?
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No input is required ever with anything. Just don't change anything or do anything to speaker connections/amp output whilst the amp is on! Maybe a third of all the blown up SS amps I get in were destroyed by their owners in this way. A few valve amps will not like having no load. It can destroy the output transformer worse case. The vast majority will be OK but best nor risk it.
 
Arkless Electronics said:
ust don't change anything or do anything to speaker connections/amp output whilst the amp is on! Maybe a third of all the blown up SS amps I get in were destroyed by their owners in this way. A few valve amps will not like having no load. It can destroy the output
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Thanks Jez. I know that (accidentally?) shorting the 2 cores of speaker leads will likely lead to oblivion. However, especially with valve amps which shouldn't be switched on and off in a short space of time, it's handy to be able to change speakers, as I am doing at the mo', testing my mono on an old throwaway speaker rather than my ESLs.

I remember that Naim power amps had no trouble in that department as I used to frequently switch the speaker leads to power other rooms. Not sure about my 509s, though (or valve amps in general, for that matter).
 
Mike Reed said:
As one of my valve mono's blew a mains fuse (and continues to do so)
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Never realised the difference and importance between types of mains fuse. I now realise that my fast blow (F 2A) fuses were blowing but the T 1.7A ones were not. Having been told that valve amps are invariably fitted with slow-blow on account of the switch-on surge, I checked, and I think that's one problem solved and a lesson learnt.

Actually, looking at the scribbled (by the late T de P some 30+ years ago?) circuit diagram, I just spotted '3A slow-blow' in tiny writing in the margin. Presumably, EAR fitted 2A slow-blows on one of the services; not sure why. Haven't fully tested the consequences of this theory yet but am quietly confident. 55 years of thinking a fuse is a fuse for practical purposes as long as the value is correct (well, maybe not quite but my memory fades !!)

Only fly in the ointment is that 'pop' as the valves warm up (on a 1.7 slow blow); not sure about that as I've never had switch-on noises from these amps.
 
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