test.

test.

I seem to have lost contact.
Patrick Turner.

Re: test.



"Patrick Turner" <info@turneraudio . com .au> wrote in message
news:482997A0.E092E497@turneraudio . com .au...
>I seem to have lost contact.
> Patrick Turner.

I wondered if your 845 amps had gone up in
smoke, and taken you with them:-)

Iain

Re: test.

On Tue, 13 May 2008 16:56:53 +0300, "Iain Churches"
<IainNG@kolumbus.fi> wrote:

>
>
>"Patrick Turner" <info@turneraudio . com .au> wrote in message
>news:482997A0.E092E497@turneraudio . com .au...
>>I seem to have lost contact.
>> Patrick Turner.
>
>I wondered if your 845 amps had gone up in
>smoke, and taken you with them:-)
>
>Iain
>

I wondered about everyone because the group seemed to be dern near
dead silent for a while.

Re: test.



"flipper" <flipper@fish . net > wrote in message
news:c2bj24hlc8fgl6msamgt38ns9fperk9sg9@4ax . com ...
> On Tue, 13 May 2008 16:56:53 +0300, "Iain Churches"
> <IainNG@kolumbus.fi> wrote:
>
>>
>>
>>"Patrick Turner" <info@turneraudio . com .au> wrote in message
>>news:482997A0.E092E497@turneraudio . com .au...
>>>I seem to have lost contact.
>>> Patrick Turner.
>>
>>I wondered if your 845 amps had gone up in
>>smoke, and taken you with them:-)
>>
> I wondered about everyone because the group seemed to be dern near
> dead silent for a while.

We are all probably fettling away on tube projects:-)
I have a tube driven VU level indicator unit just complete
and ready for calibration. Pics available if anyone is
interested.

Regards to all
Iain

Re: test.

On Tue, 13 May 2008 18:18:04 +0300, "Iain Churches"
<IainNG@kolumbus.fi> wrote:

>
>
>"flipper" <flipper@fish . net > wrote in message
>news:c2bj24hlc8fgl6msamgt38ns9fperk9sg9@4ax . com ...
>> On Tue, 13 May 2008 16:56:53 +0300, "Iain Churches"
>> <IainNG@kolumbus.fi> wrote:
>>
>>>
>>>
>>>"Patrick Turner" <info@turneraudio . com .au> wrote in message
>>>news:482997A0.E092E497@turneraudio . com .au...
>>>>I seem to have lost contact.
>>>> Patrick Turner.
>>>
>>>I wondered if your 845 amps had gone up in
>>>smoke, and taken you with them:-)
>>>
>> I wondered about everyone because the group seemed to be dern near
>> dead silent for a while.
>
>We are all probably fettling away on tube projects:-)

Well, that would explain the unusual nature of if ;)

>I have a tube driven VU level indicator unit just complete
>and ready for calibration. Pics available if anyone is
>interested.

Oh, oh, oh... me, me, me <waving hand>

>
>Regards to all
>Iain
>

Re: test.



"flipper" <flipper@fish . net > wrote in message
news:7fdj24t6n708ptju84e8bh4t7nd1mn6o7c@4ax . com ...
> On Tue, 13 May 2008 18:18:04 +0300, "Iain Churches"
> <IainNG@kolumbus.fi> wrote:
>
>>
>>
>>"flipper" <flipper@fish . net > wrote in message
>>news:c2bj24hlc8fgl6msamgt38ns9fperk9sg9@4ax . com ...
>>> On Tue, 13 May 2008 16:56:53 +0300, "Iain Churches"
>>> <IainNG@kolumbus.fi> wrote:
>>>
>>>>
>>>>
>>>>"Patrick Turner" <info@turneraudio . com .au> wrote in message
>>>>news:482997A0.E092E497@turneraudio . com .au...
>>>>>I seem to have lost contact.
>>>>> Patrick Turner.
>>>>
>>>>I wondered if your 845 amps had gone up in
>>>>smoke, and taken you with them:-)
>>>>
>>> I wondered about everyone because the group seemed to be dern near
>>> dead silent for a while.
>>
>>We are all probably fettling away on tube projects:-)
>
> Well, that would explain the unusual nature of if ;)
>
>>I have a tube driven VU level indicator unit just complete
>>and ready for calibration. Pics available if anyone is
>>interested.
>
> Oh, oh, oh... me, me, me <waving hand>


LOL:-)

In the past most of my projects although performing well,
having been pretty "agricultural" in appearance.

* w w w .kolumbus.fi/iain.churches/Pics/252Amplifier/252.02.jpg


I now share a workshop with some pretty skilled guys,
one of whom hand crafts the most beautiful acoustic guitars,
and custom made tube amps. Another is very good as machining,
CNC etc, and PCB design and so I am on a steep learning curve
(once again)

Putting a tube amp in a posh case does nothing to improve
its actual performance, but takes it out of the "home-made"
into the "hand-made" category, and greatly increases
what high-end salesmen call PQ (perceived quality:-)

It is interesting to talk with people about amplifier
cosmetic design - what they think the amplifier of their
choice should look like. Few, when confronted with
a blank sheet of paper, can come up with anything
at all:-)

Once you have made something, and demonstrate it to
them however, they invariable say: "Why have you done
it like this? If I had build it, I would have..........."

Fun innit:-)

Iain

Re: test.

On Wed, 14 May 2008 09:19:20 +0300, "Iain Churches"
<IainNG@kolumbus.fi> wrote:

>
>
>"flipper" <flipper@fish . net > wrote in message
>news:7fdj24t6n708ptju84e8bh4t7nd1mn6o7c@4ax . com ...
>> On Tue, 13 May 2008 18:18:04 +0300, "Iain Churches"
>> <IainNG@kolumbus.fi> wrote:
>>
>>>
>>>
>>>"flipper" <flipper@fish . net > wrote in message
>>>news:c2bj24hlc8fgl6msamgt38ns9fperk9sg9@4ax . com ...
>>>> On Tue, 13 May 2008 16:56:53 +0300, "Iain Churches"
>>>> <IainNG@kolumbus.fi> wrote:
>>>>
>>>>>
>>>>>
>>>>>"Patrick Turner" <info@turneraudio . com .au> wrote in message
>>>>>news:482997A0.E092E497@turneraudio . com .au...
>>>>>>I seem to have lost contact.
>>>>>> Patrick Turner.
>>>>>
>>>>>I wondered if your 845 amps had gone up in
>>>>>smoke, and taken you with them:-)
>>>>>
>>>> I wondered about everyone because the group seemed to be dern near
>>>> dead silent for a while.
>>>
>>>We are all probably fettling away on tube projects:-)
>>
>> Well, that would explain the unusual nature of if ;)
>>
>>>I have a tube driven VU level indicator unit just complete
>>>and ready for calibration. Pics available if anyone is
>>>interested.
>>
>> Oh, oh, oh... me, me, me <waving hand>
>
>
>LOL:-)
>
>In the past most of my projects although performing well,
>having been pretty "agricultural" in appearance.

Well, I don't know. By "agricultural" do you mean what we call
"utilitarian?" I.E. Little or no concern for other than function and
construction. Like things that glow do so either because it's their
nature or to indicate functions such as on/off, not to 'look cool'.
Rectangular chassis are simple to bend, round holes are simple to
drill, which makes toggle switches easy to mount, etc, etc. Or, to
illustrate, my PC Speaker amp. hehe

Or does "agricultural' have another meaning?


> * w w w .kolumbus.fi/iain.churches/Pics/252Amplifier/252.02.jpg

Looks a hell of a lot better than a tractor to me, square sides and
round hole toggle switch notwithstanding ;)


>I now share a workshop with some pretty skilled guys,
>one of whom hand crafts the most beautiful acoustic guitars,
>and custom made tube amps. Another is very good as machining,
>CNC etc, and PCB design and so I am on a steep learning curve
>(once again)

Man, I could sure use the CNC stuff. I mean, without having to pay for
it ;)


>Putting a tube amp in a posh case does nothing to improve
>its actual performance, but takes it out of the "home-made"
>into the "hand-made" category, and greatly increases
>what high-end salesmen call PQ (perceived quality:-)

You bet. Unfortunately, some times that's all there is, "perceived
quality."

People are funny, though. In 1960 a car had to have tons of chrome to
be half way decent but 50 years later it's garish crap.


>It is interesting to talk with people about amplifier
>cosmetic design - what they think the amplifier of their
>choice should look like. Few, when confronted with
>a blank sheet of paper, can come up with anything
>at all:-)
>
>Once you have made something, and demonstrate it to
>them however, they invariable say: "Why have you done
>it like this? If I had build it, I would have..........."

Hehe. Of course. What else is new? hehe

As the saying goes "everyone's a critic." But speaking of your pic,
what I would have done....

>
>Fun innit:-)
>
>Iain
>
>

Re: test.



"flipper" <flipper@fish . net > wrote in message
news:9f4l24l91n9vgmermua6l931pus71bu56f@4ax . com ...
> On Wed, 14 May 2008 09:19:20 +0300, "Iain Churches"
> <IainNG@kolumbus.fi> wrote:
>

>>In the past most of my projects although performing well,
>>having been pretty "agricultural" in appearance.
>
> Well, I don't know. By "agricultural" do you mean what we call
> "utilitarian?" I.E. Little or no concern for other than function and
> construction.

Well, I would not put it that strongly. But if you have ever
seen a 1950's British Ferguson tractor, (usually painted grey)
you would know exactly what I mean:-)

>>I now share a workshop with some pretty skilled guys,
>>one of whom hand crafts the most beautiful acoustic guitars,
>>and custom made tube amps. Another is very good as machining,
>>CNC etc, and PCB design and so I am on a steep learning curve
>>(once again)
>
> Man, I could sure use the CNC stuff. I mean, without having to pay for
> it ;)

As they say in Yorkshire, "You get owt for nowt" but being able to
pop in during the evenings or on Sunday morning suddenly becomes
an attractive proposition. CNC is a pretty process to set up, so
one-offs amy not be a sensible proposition (expecially if you have
to pay for them. Many CNC shops want to make >1000 pcs)
But once the wheels are turning you can cut, mill, ream, drill and
tap with incredible precision.

Being able to fabricate something of decent quality means that you
are not restricted to using a Hammond chassis or Eddystone diecast
boxes - excellent though these can be.
>
>
>>Putting a tube amp in a posh case does nothing to improve
>>its actual performance, but takes it out of the "home-made"
>>into the "hand-made" category, and greatly increases
>>what high-end salesmen call PQ (perceived quality:-)
>
> You bet. Unfortunately, some times that's all there is, "perceived
> quality."

Agreed. One needs to put the priorities in order. Get the audio
engineering right first, with a good schematic, and a tidy interior
layout that works. You can then think about the box.

> People are funny, though. In 1960 a car had to have tons of chrome to
> be half way decent but 50 years later it's garish crap.

That's fashion! Remember those flared jeans and platform
shoes that we used to wear in the 70's? Maybe you weren't
around then!

>>It is interesting to talk with people about amplifier
>>cosmetic design - what they think the amplifier of their
>>choice should look like. Few, when confronted with
>>a blank sheet of paper, can come up with anything
>>at all:-)
>>
>>Once you have made something, and demonstrate it to
>>them however, they invariable say: "Why have you done
>>it like this? If I had build it, I would have..........."
>
> Hehe. Of course. What else is new? hehe
>
> As the saying goes "everyone's a critic." But speaking of your pic,
> what I would have done....

For many, the prospect of acquiring a tube amp is an exciting
one because they can have a say in its cosmetic design: pick
the chassis colour (did you see Raymond's red chassis? Brilliant!)
and the wood used for the end panels. Transformer pots
black or chromed? Balanced-line inputs? Lamp or LED
indicators? Would you like anything special engraved on
the escutcheon, Sir.

It's just like buying a hand-made suit from a
bespoke tailors in Saville Row, London.

Besides having an amplifier they find more more musically
pleasing that a stock SS amp, most people are pleased to
own something that was built especially for them.

regards
Iain

Re: test.

In article <XgiWj.249$_03.86@reader1.news.saunalahti.fi>,
"Iain Churches" <IainNG@kolumbus.fi> wrote:

> "flipper" <flipper@fish . net > wrote in message
> news:c2bj24hlc8fgl6msamgt38ns9fperk9sg9@4ax . com ...
> > On Tue, 13 May 2008 16:56:53 +0300, "Iain Churches"
> > <IainNG@kolumbus.fi> wrote:
> >
> >>
> >>
> >>"Patrick Turner" <info@turneraudio . com .au> wrote in message
> >>news:482997A0.E092E497@turneraudio . com .au...
> >>>I seem to have lost contact.
> >>> Patrick Turner.
> >>
> >>I wondered if your 845 amps had gone up in
> >>smoke, and taken you with them:-)
> >>
> > I wondered about everyone because the group seemed to be dern near
> > dead silent for a while.
>
> We are all probably fettling away on tube projects:-)
> I have a tube driven VU level indicator unit just complete
> and ready for calibration. Pics available if anyone is
> interested.

"Tube driven VU level indicator unit", what is that? Why are tubes,
transistors, or any active devices needed in a VU meter unit, the ones I
have are designed to connect directly across a 600 Ohm audio line?

I would like to build a tube driven facsimile of a PPM, using a meter
movement I salvaged from a scrapped transistorized AM modulation
monitor. Any thoughts on a suitable circuit for a project like this?


Regards,

John Byrns

--
Surf my web pages at, * fmamradios . com /

Re: test.



"John Byrns" <byrnsj@sbcglobal . net > wrote in message
news:byrnsj-68097B.13303913052008@newsclstr02.news.prodigy . com ...
> In article <XgiWj.249$_03.86@reader1.news.saunalahti.fi>,
> "Iain Churches" <IainNG@kolumbus.fi> wrote:
>
>> "flipper" <flipper@fish . net > wrote in message
>> news:c2bj24hlc8fgl6msamgt38ns9fperk9sg9@4ax . com ...
>> > On Tue, 13 May 2008 16:56:53 +0300, "Iain Churches"
>> > <IainNG@kolumbus.fi> wrote:
>> >
>> >>
>> >>
>> >>"Patrick Turner" <info@turneraudio . com .au> wrote in message
>> >>news:482997A0.E092E497@turneraudio . com .au...
>> >>>I seem to have lost contact.
>> >>> Patrick Turner.
>> >>
>> >>I wondered if your 845 amps had gone up in
>> >>smoke, and taken you with them:-)
>> >>
>> > I wondered about everyone because the group seemed to be dern near
>> > dead silent for a while.
>>
>> We are all probably fettling away on tube projects:-)
>> I have a tube driven VU level indicator unit just complete
>> and ready for calibration. Pics available if anyone is
>> interested.
>
> "Tube driven VU level indicator unit", what is that? Why are tubes,
> transistors, or any active devices needed in a VU meter unit, the ones I
> have are designed to connect directly across a 600 Ohm audio line?

Hang a VU across the line and measure the increase in
distortion. You can "hear" the difference!

At least in the UK a buffer amp was commonly used.

>
> I would like to build a tube driven facsimile of a PPM, using a meter
> movement I salvaged from a scrapped transistorized AM modulation
> monitor. Any thoughts on a suitable circuit for a project like this?

Which type of PPM are you referring to John.
Does it have a scale to 12 with a red line at 8 ?

Regards

Iain

Re: test.

In article <LnvWj.578$_03.380@reader1.news.saunalahti.fi>,
"Iain Churches" <IainNG@kolumbus.fi> wrote:

> "John Byrns" <byrnsj@sbcglobal . net > wrote in message
> news:byrnsj-68097B.13303913052008@newsclstr02.news.prodigy . com ...
> > In article <XgiWj.249$_03.86@reader1.news.saunalahti.fi>,
> > "Iain Churches" <IainNG@kolumbus.fi> wrote:
> >
> >> We are all probably fettling away on tube projects:-)
> >> I have a tube driven VU level indicator unit just complete
> >> and ready for calibration. Pics available if anyone is
> >> interested.
> >
> > "Tube driven VU level indicator unit", what is that? Why are tubes,
> > transistors, or any active devices needed in a VU meter unit, the ones I
> > have are designed to connect directly across a 600 Ohm audio line?
>
> Hang a VU across the line and measure the increase in
> distortion. You can "hear" the difference!

Sure, but the distortion is mainly 2 nd harmonic and adds to the nice
warm tube sound many are seeking. IIRC when the VU meter was originally
designed the amount of distortion produced, when the standard build out
resistor is used for +4 dBm at 0 VU, was considered insignificant. The
amount of added distortion is also strongly dependent on the source
impedance of the amplifier driving the line/meter/pad(s). How audible
is the distortion when a modern high feedback low output impedance
amplifier is used? Somewhere I have an article from the late 1930s when
the VU meter was designed, which discuses various factors in the design,
including the distortion you mention. I wonder what the nature was of
the meters used in American practice before that time, and also what was
used in Europe before the advent of the PPM?

> At least in the UK a buffer amp was commonly used.

Makes sense, also a pad was often used between the amplifier output and
the VU meter further reducing the distortion contribution of the meter,
although the amplifier will probably then be producing more distortion
since it will be operating at a higher level. For example the Ampex 351
recorder/reproducer had a 4 dB pad in the meter circuit which could be
strapped out of the circuit when a +4 dBm output level was desired
rather than the standard +8 dBm output. Pads were used when driving a
transmitter which commonly required +10 dBm in the US.

> > I would like to build a tube driven facsimile of a PPM, using a meter
> > movement I salvaged from a scrapped transistorized AM modulation
> > monitor. Any thoughts on a suitable circuit for a project like this?
>
> Which type of PPM are you referring to John.
> Does it have a scale to 12 with a red line at 8 ?

As soon as I posted I realized that my post was not sufficiently
detailed, and my requirements were not well spelled out.

I do not have a PPM meter of any sort. The meter I have is salvaged
from a solid state US style AM modulation monitor, an instrument used by
AM broadcast stations in the US to insure they aren't over modulating
their transmitters. The particular meter I have has three scales sort
of like a VU meter. The main scale is linear and calibrated in percent
modulation with a full scale reading of 140%. There is also a second
percent modulation scale whose readings appear to be 10 dB lower, or
more sensitive, than the main scale, presumably 10 dB of extra gain was
switched in to read lower modulation levels more accurately. The third
scale is a secondary scale calibrated in dB running from -20 dB through
+3 dB. I measured the full scale sensitivity of this meter once, but I
am not sure where my notes on it are, but IIRC it was 1 mA full scale.

What I remembered after posting is that PPM meters use a log amplifier
in their circuitry and I certainly wouldn't want that with the linear
scale on my meter. I was thinking of an all vacuum tube circuit,
including signal "rectifiers", which would include switching to indicate
either positive or negative peaks individually, or the largest peaks of
either polarity. So far all I have decided is to use a differential
amplifier, similar to those used in US style VTVMs, to drive the meter.
I still need to settle on a buffer circuit for the audio, and the peak
detection circuits with provision for selecting the polarity of the
peaks to be measured. It is this latter part of the circuit I need some
inspiration on. An added requirement is relative simplicity. Of course
the ultimate in simplicity was seen in the old tube type AM modulation
monitors which used a more sensitive meter and were driven directly from
the transmitter, requiring a drive of somewhere between 1 and 5 Watts
depending on the maker. The entire circuit consisted of only two
rectifiers, one to demodulate the transmitter output and provide an
audio signal, and a second diode to detect the audio peak of the desired
polarity and drive the meter which was shunted by a peak hold capacitor,
can't get much simpler than that.


Regards,

John Byrns

--
Surf my web pages at, * fmamradios . com /

Re: test.



"John Byrns" <byrnsj@sbcglobal . net > wrote in message
news:byrnsj-095BA6.11550714052008@newsclstr03.news.prodigy . net ...
> In article <LnvWj.578$_03.380@reader1.news.saunalahti.fi>,
> "Iain Churches" <IainNG@kolumbus.fi> wrote:
>
>> "John Byrns" <byrnsj@sbcglobal . net > wrote in message
>> news:byrnsj-68097B.13303913052008@newsclstr02.news.prodigy . com ...
>> > In article <XgiWj.249$_03.86@reader1.news.saunalahti.fi>,
>> > "Iain Churches" <IainNG@kolumbus.fi> wrote:
>> >
>> >> We are all probably fettling away on tube projects:-)
>> >> I have a tube driven VU level indicator unit just complete
>> >> and ready for calibration. Pics available if anyone is
>> >> interested.
>> >
>> > "Tube driven VU level indicator unit", what is that? Why are tubes,
>> > transistors, or any active devices needed in a VU meter unit, the ones
>> > I
>> > have are designed to connect directly across a 600 Ohm audio line?
>>
>> Hang a VU across the line and measure the increase in
>> distortion. You can "hear" the difference!
>
> Sure, but the distortion is mainly 2 nd harmonic and adds to the nice
> warm tube sound many are seeking.

Hello John

In prof recording and broadcast, with analogue tape at 2% THD
the programme material was plenty warm enough:-) And besides I
don't think anyone would want a meter which changed the sound of their
system when it was connected. But, hey, wait a minute, this could be
the ultimate in high-end audible improvements. "Connect a VU meter
and both see and hear the improvement!" :-)

> IIRC when the VU meter was originally
> designed the amount of distortion produced, when the standard build out
> resistor is used for +4 dBm at 0 VU, was considered insignificant. The
> amount of added distortion is also strongly dependent on the source
> impedance of the amplifier driving the line/meter/pad(s). How audible
> is the distortion when a modern high feedback low output impedance
> amplifier is used?

I made a quick comparison with a Radford LDO4 low distortion
oscillator 600 Ohms at +4dB (1.22 V) I then fed this to a preamp
with attenuation and thence to a power amp. The distortion added
by hanging the meter across the line was clearly audible. I seem to
have discarded the scrap of paper on which I noted the figs.


> Somewhere I have an article from the late 1930s when
> the VU meter was designed, which discuses various factors in the design,
> including the distortion you mention.

Yes I also have some articles somewhere. The whole story
of the VU and the ANSI specification of "Volume Measurements
of Electrical Speech and Program waves" C16.5-1942 (which is
now incorporated into IEC 60268-17) is a fascinating one.


> I wonder what the nature was of
> the meters used in American practice before that time, and also what was
> used in Europe before the advent of the PPM?

I have no idea what came before the VU, but I do remember
seeing tube driven VU meters at Decca. There was a shelf full
of them in what we called the Redundancy Store. In retrospect,
Aladin's Cave might have been a better name:-) The buffer amp
was just a simple cathode follower 12AU7. I used to own an
Ampex 351-2 tape machine with VUs but I cannot recall how
the metering was done. But I do know that the meter units for
European tape machines like the Studer C37 and J37, had a
tube buffer amp just like the one I describe.
>
>> At least in the UK a buffer amp was commonly used.
>
> Makes sense, also a pad was often used between the amplifier output and
> the VU meter further reducing the distortion contribution of the meter,
> although the amplifier will probably then be producing more distortion
> since it will be operating at a higher level. For example the Ampex 351
> recorder/reproducer had a 4 dB pad in the meter circuit which could be
> strapped out of the circuit when a +4 dBm output level was desired
> rather than the standard +8 dBm output. Pads were used when driving a
> transmitter which commonly required +10 dBm in the US.
>
>> > I would like to build a tube driven facsimile of a PPM, using a meter
>> > movement I salvaged from a scrapped transistorized AM modulation
>> > monitor. Any thoughts on a suitable circuit for a project like this?
>>
>> Which type of PPM are you referring to John.
>> Does it have a scale to 12 with a red line at 8 ?
>
> As soon as I posted I realized that my post was not sufficiently
> detailed, and my requirements were not well spelled out.
>
> I do not have a PPM meter of any sort. The meter I have is salvaged
> from a solid state US style AM modulation monitor, an instrument used by
> AM broadcast stations in the US to insure they aren't over modulating
> their transmitters. The particular meter I have has three scales sort
> of like a VU meter. The main scale is linear and calibrated in percent
> modulation with a full scale reading of 140%. There is also a second
> percent modulation scale whose readings appear to be 10 dB lower, or
> more sensitive, than the main scale, presumably 10 dB of extra gain was
> switched in to read lower modulation levels more accurately. The third
> scale is a secondary scale calibrated in dB running from -20 dB through
> +3 dB. I measured the full scale sensitivity of this meter once, but I
> am not sure where my notes on it are, but IIRC it was 1 mA full scale.

That's an interesting meter. What would you use it for?

I am keeping an eye open for PPM's The best ones in Europe were
made by Ernest Turner (a company which ceased trading in the 1980s
after a takeover)
>
> What I remembered after posting is that PPM meters use a log amplifier
> in their circuitry and I certainly wouldn't want that with the linear
> scale on my meter. I was thinking of an all vacuum tube circuit,
> including signal "rectifiers", which would include switching to indicate
> either positive or negative peaks individually, or the largest peaks of
> either polarity. So far all I have decided is to use a differential
> amplifier, similar to those used in US style VTVMs, to drive the meter.
> I still need to settle on a buffer circuit for the audio, and the peak
> detection circuits with provision for selecting the polarity of the
> peaks to be measured. It is this latter part of the circuit I need some
> inspiration on. An added requirement is relative simplicity. Of course
> the ultimate in simplicity was seen in the old tube type AM modulation
> monitors which used a more sensitive meter and were driven directly from
> the transmitter, requiring a drive of somewhere between 1 and 5 Watts
> depending on the maker. The entire circuit consisted of only two
> rectifiers, one to demodulate the transmitter output and provide an
> audio signal, and a second diode to detect the audio peak of the desired
> polarity and drive the meter which was shunted by a peak hold capacitor,
> can't get much simpler than that.

John. Such a project would make a fascinating thread on RAT. I
hope that you will persevere with it.

Regards
Iain

Re: test.


"Iain Churches" <IainNG@kolumbus.fi> wrote in message
news:0cGWj.949$_03.116@reader1.news.saunalahti.fi...
>
>
> I have no idea what came before the VU, but I do remember
> seeing tube driven VU meters at Decca. There was a shelf full
> of them in what we called the Redundancy Store. In retrospect,
> Aladin's Cave might have been a better name:-) The buffer amp
> was just a simple cathode follower 12AU7. I used to own an
> Ampex 351-2 tape machine with VUs but I cannot recall how
> the metering was done. But I do know that the meter units for
> European tape machines like the Studer C37 and J37, had a
> tube buffer amp just like the one I describe.

Heres a question to you Iain as a member if the recording industry. Whenever
I see footage of recording and radio studios, it always seems like the VU
meters are slamming into the red with alarming frequency, so why do you have
the things when it seems like the engineers ignore them anyway?

In my limited experience of recording ( a friend and I used to record local
rock groups at college) we were always extremely careful to insure the the
levels never went into the red. My friend went on to become an engineer at
Abbey Road and Air records and now designs studios so maybe he changed his
attittude in later life :)

Keith

Re: test.



"keithr" <keithr@nowhere . com .au> wrote in message
news:482bc7ca$1@dnews.tpgi . com .au...
>
> "Iain Churches" <IainNG@kolumbus.fi> wrote in message
> news:0cGWj.949$_03.116@reader1.news.saunalahti.fi...
>>
>>
>> I have no idea what came before the VU, but I do remember
>> seeing tube driven VU meters at Decca. There was a shelf full
>> of them in what we called the Redundancy Store. In retrospect,
>> Aladin's Cave might have been a better name:-) The buffer amp
>> was just a simple cathode follower 12AU7. I used to own an
>> Ampex 351-2 tape machine with VUs but I cannot recall how
>> the metering was done. But I do know that the meter units for
>> European tape machines like the Studer C37 and J37, had a
>> tube buffer amp just like the one I describe.
>
> Heres a question to you Iain as a member if the recording industry.
> Whenever I see footage of recording and radio studios, it always seems
> like the VU meters are slamming into the red with alarming frequency, so
> why do you have the things when it seems like the engineers ignore them
> anyway?

Actually, one does not ignore them, but learn to
"interpret" them:-) Compared with any peak reading
analogue meter, the VU has a slow rise time of 300mS.

One of my first jobs when I started my training with
Decca in the UK was the duplication of safety masters
of Rolling Stones material, which had been recorded
at Bell Sound in New York. It was an interesting
experience..... The transfer console had PPM meters,
but the tape machines had VUs. After the white leader,
the meter whacked over to the end-stop +3 VU, and
stayed there, hardly fluctuating for the duration of the
title, and then slowly returned to the left-hand end stop
while the second leader passed, and then, whack over
to the end-stop again. This happened on every title.

My tutor, Alec Rosner, gave an excellent demonstration
of the VU characteristics. He recorded a long section of
1kHz tone at 0VU (+4dB) on analogue quarter-inch tape,
and then cut it into sections of 38cms, 19cms, 13cms,
10cms, 5cms, 2cms and 1cm etc etc all separated by 38cms
of leader.

The first segment caused the meter to rise to 0VU, likewise the
second (half-second) segment. On each subsequent segment the
durations of which were decreasing, the meter showed a lower and
lower reading as the duration oif the signal was shorter than the
rise-time of the The final segment was so short (but was still recorded
at +4dB) that it hardly caused the needle to flicker.

> In my limited experience of recording ( a friend and I used to record
> local rock groups at college) we were always extremely careful to insure
> the the levels never went into the red.

Analogue tape distortion is actually quite benign, but nevertheless
just like you, we were taught to strictly observe peak levels. At
Decca the standard was +8dB and monitored on PPMs. You
were required to write the peak level on the tape box. No one
expected it to deviate > +/-1dB. Each tape also had a frequency
alignment run, 3pips left. 4 pips right, 1kHz, 15kHz (azimuth)
12kHz (HF) etc going down in steps to 5kHz (MF) and then
down to 100Hz (LF) with 50Hz and 20Hz at the lower end.

I visited the BBC frequently when I lived in the UK, but by
that time they were using their own excellent analogue PPM.
They were meticulous about peak levels sent to the
transmitter. Heavy compression and peak limiting in
broadcasting was not common then as it is today.

There is renewed interest in the VU meter now, escpecially
in CD mastering where it makes an interesting addition to the
ubiquitous digital peak meter. The peak meter gives one no
idea at all of the amount of compression being used, but,
accurately interpreted the VU can tell you a lot. It's an
interesting meter because it gives you an indication of
"perceived loudness" to the ear.

I am currently putting the finishing touches to a tube-
driven VU meter unit. The final unit is now complete
except for top and bottom panels, and as soon as I
have these I will post a link to this project.

Regards to all

Iain

Re: test.


"Iain Churches" <IainNG@kolumbus.fi> wrote in message
news:XgiWj.249$_03.86@reader1.news.saunalahti.fi...
>
> We are all probably fettling away on tube projects:-)
> I have a tube driven VU level indicator unit just complete
> and ready for calibration. Pics available if anyone is
> interested.
>
> Regards to all
> Iain

Just out of interest Iain, what benfit is there to driving a VU meter with
tubes as against what would seem to be the much more logical alternative of
solid state components. Obviously it isn't going to affect the sound of
anything, and I don't think that you'd see any difference on the meter. So
is it "Because I can" or some deep technical reason?

Keith