Re: What's your favourite voltage regs?

In article <600fuiF1o2c2cU1@xxxxxxxxxxxxxxxxxx>, David Looser
<david.looser@xxxxxxxxxxxxxx> wrote:
"Jim Lesurf" <jcgl@xxxxxxxxxxxxxxxxxx> wrote in message
news:4f66a30c8ajcgl@xxxxxxxxxxxxxxxxxxxxx


I know exactly what this thread was about before your first contribution
to it. It was about the difference between driving the DHT filament with
a voltage source, and a current source, and that's all.

Actually, that is incorrect. It started with a call from Andy to suggest
what PSU designs we favoured for applications like heating in the context
he gave. (cf below)

What you refer to was one of the various topics that subsequently arose.

The issue of how "perfectly" the PSU was floating didn't come into it.

Indeed. Nor have I ever said otherwise. Once again you are jumping to
erronious conclusions.

I am afraid that your habit of taking things out of context and snipping
away what has been responded to has confused you again if you assumed
otherwise. :-)

The comments you made in your first post did not address this issue at
all, but were, apparently, based on the misapprehension that we were
discussing the effect of the PSU not floating "perfectly". This
suggested to me that you had not read the thread properly before
contributing, I still think that to have been the case.

I am afraid that your habit of snipping what others have said and then
taking things out of their context is still confusing you. Above you state
various opinions as if they were facts. It may therefore be useful to
copy some of what was actually written to restore some relevant context.
So, according to my records the first posting I made in this thread was
actually as follows:


] Newsgroups: uk.rec.audio From: jcgl@xxxxxxxxxxxxxxxxxx Subject: Re:
] What's your favourite voltage regs? Date: Wed, 16 Jan 2008 13:35
]
] In article
] <10cf9c3d-1d47-4fdd-9159-5e5780f2faad@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, Andy
] Evans <performanceandmedia@xxxxxxxxx> wrote:
]
]
] > So - which voltage regs are your fave choices here? Good quality
] > output important, but cost also a consideration. This looks right up
] > Jim's street for starters.
]
] FWIW I tried various types of 'IC voltage regulator/stabiliser chip'
] some years ago and decided I wasn't keen on any of the common types. Too
] prone to oscillations or excess noise, etc. Newer ones may be better,
] but I lost interest in using them. :-)
]
] So I have tended to use variations on the kind of topology shown on
]
] http://www.audiomisc.co.uk/Armstrong/700/730PSU.gif
]
] As you can see, the zener sets the nominal voltage, and a capacity
] multiplier pass device smooths over the noise and gives a slow
] start/stop.
]
] That example was for about +/-20V up to about 100mA, used for the rails
] in a preamp. But the same topology has been used many times by my old
] research group for voltages in the few V region at currents up to a few
] amps, so may serve your purpose. [1] Just alter the components to suit.
] Make the pass transistor a form of darlington pair if needed. I found a
] single device was usually fine for currents of the order of an amp or
] two. But if you need high current the single-pack darlingtons made for
] cheaper SS amps might well do that well if you wanted. But these may
] need to be checked for oscillation problems.
]
] Main advantages of the topology are low noise and a gradual windup and
] rundown rather than coming on or going off with a crack. Kinder for your
] valve heaters, perhaps. You may also like the fact that it has no
] overall feedback. :-)
]
] No idea if it will suit you, but since you mentioned my name...
]
] For power amps, though, I always just used a decent transformer and
] large caps, then designed the amp to reject power line variations. So no
] need for any active smoothing/stabilisation/regulation.
]
] Slainte,
]
] Jim
]
] [1] e.g. for the PSU for 5-12V 1A Gunn diodes where noise from the PSU
] needs to be minimal as it would introduce noise sidebands to the 94GHz
] output. If you want I can see if I can dig out a diagram of the variable
] and fixed versions used for that, but they are in essence the above.


It was in other postings later one we got to various other topics...

What I wrote was to clarify what Nick had said and give a better
worded explanation for a point he made.

In view of the fact that you were addressing an entirely different issue
to the one we were discussing, it did not "clarify" anything, rather it
confused the issue.

I appreciate that it has confused you, since that was a different posting
on another issue to the above. As above, your problem here seems to be
that you have conflated and confused various issues and points that have
arisen in this thread. Since you have lost awareness of what I actually
wrote here is the first posting I made on the topic:


] Newsgroups: uk.rec.audio From: jcgl@xxxxxxxxxxxxxxxxxx Subject: Re:
] What's your favourite voltage regs? Date: Fri, 18 Jan 2008 09:35
]
] In article <478FE44C.E0C07A2B@xxxxxxxxxxx>, Eeyore
] <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote:
]
]
] > Nick Gorham wrote:
]
] > > Ian Iveson wrote:
]
] > > and the voltage reg will try and regulate that away, with a current
] > > reg, the signal is common mode, so not affected.
]
] > UH ?
]
] Can only speculate at this point as I have never tried using these
] circuits for heaters in audio amps. However...
]
] With 'direct' heating the heater psu is - I presume - connected to the
] same physical place as the cathode signal. Having a 'constant current'
] PSU means the PSU looks like a high impedance connection, so will be
] less likely to have a loading effect on signal drive to the cathode if
] the PSU common mode isolation is poor. i.e. the problem is that the
] cathode signal has to drive any loading it sees due to the PSU, so a
] high impedance might be preferred.
]
] Slainte,
]
] Jim
]


And as I pointed out, Nick and I then exchanged emails about this.

I also made responses to other points you made. Unfortunately, due to the
way you snip and then take things out of context, these then became
conflated in your mind, leading to more confusion on your part.

The question of 'floating' PSU is clearly relevant to the above point since
it may be a factor in whether or not the above has an effect on
performance. Indeed, you might note the phrase "...if the PSU common mode
isolation is poor..." :-)

But, as I have said countless times, since I have never made or tested a
DHT audio amp I can't comment on the extent to which any of the above may
matter in practice. I was just trying to clarify what others had said. So
you could even note the use of "...*if*..." in the above. ;->

Well so you said before, but I note that he has not taken the
opportunity to say that here.

I could also note that neither he, nor indeed anyone else, has supported
your own confusions. :-) TBH I assume that he and others have had better
things to do, and are content to let me waste my own time. Nick has been
reading this group for long enough to know how patient I can be. ;->
Indeed, Nick and Don have had quite an informative discussion in this
thread.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
.

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