sci.electronics.repair - 25 new messages in 10 topics - digest

sci.electronics.repair
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Today's topics:

==============================================================================
TOPIC: CRT: Brief contrast/brightness prob at start-up.
http://groups.google.com/group/sci.electronics.repair/t/cdf227264ff94f95?hl=en
==============================================================================

== 1 of 2 ==
Date: Fri, Jul 9 2010 11:45 pm
From: Meatman

<<
beam limiter sense resistor in ground return gone high ? >>

And where would I locate this little beast...approximately?

== 2 of 2 ==
Date: Sat, Jul 10 2010 1:49 am
From: "Arfa Daily"

"Meatman" <KevinLee33@comcast.net> wrote in message
news:3fd25b30-022b-48ff-87c6-4499945051d6@u7g2000yqm.googlegroups.com...
> <<
> beam limiter sense resistor in ground return gone high ? >>
>
> And where would I locate this little beast...approximately?

The setting of the screen control can be very critical, depending on the
circuitry design, and the condition of the CRT. Usually, there is a point to
measure a voltage on, and a critical voltage to set on that point, using the
control. A service manual will usually be helpful for that. The beam current
sense resistor, assuming that it has one in the position I indicated, is
usually physically quite close to the FBT itself.

Please note though that the observations I am making are general to CRT TV
sets from the last 20 years, and not necessarily specific to your make and
model, which I am not intimately familiar with, it being a U.S. model, and
my practical experience all being with U.K. models. However, that said, the
circuitry design from what I've seen, is generally pretty similar in all but
the front-end low level signal and colour processing circuitry.

Arfa

==============================================================================
TOPIC: Electric fence operation problem
http://groups.google.com/group/sci.electronics.repair/t/eef28366a8aa3bbf?hl=en
==============================================================================

== 1 of 4 ==
Date: Sat, Jul 10 2010 5:47 am
From: "Ian French"

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:i120g0$ofq$1@news.eternal-september.org...
>2 stage derivation of (should be) 1800V pulses.
> Fence had failure in the first stage probably due to intermittant corroded
> battery supply contact.
> Anyway the 15A 60V 8N06 powerFET blew along with an associated double
> diode
> BAV23.
> Replaced both and works to some extent. This FET has plenty of drive 5V of
> pulses of repeat 3uS for the gate and about 3V ringing swing on the output
> to the first step up transformer. I assume that is as to be expected,
> never
> having the chance to see hot-side SMPS drive scope traces.
> But rectified output only climbs to about 1V of DC before the final stage
> (unreadable marking) thyristor discharges that supply into the second step
> up transformer, but of course not even enough to get a glow on a 110V
> neon.
> Doubling the C setting the 3uS pulses, to give longer repeat rate and that
> intermediary voltage rises to about 3V but still not enough for any proper
> final output. Adding more C and DC is then much less than 3V.
> What would people expect the intermediary DC to be? obviously higher than
> 12V battery supply
> Next stage would be disconnect the thyristor if that should be working but
> leaky and draining the intermediary DC but any other ideas? Would explain
> why the printing is very indistinct I suppose.
> DC ohms of the airgap type transformers are
> intermediary 0.1R//10.6R
> HV 0.3R//29R which seem reasonable, ie not major shorted turns if any
>
>

Hi,

I found this schematic (circuit diagram) somewhere on the net, is it
anything like your one ?

http://www.electro-tech-online.com/attachments/electronic-projects-design-ideas-reviews/4007d1108193301-need-help-developing-electric-fencing-my-farm-electricfence.jpg

Ian.

== 2 of 4 ==
Date: Sat, Jul 10 2010 7:42 am
From: "N_Cook"

Ian French <ianf@dsl.pipex.com> wrote in message
news:58Sdnfy4nt1N9qXRnZ2dnUVZ8gGdnZ2d@pipex.net...
>
> "N_Cook" <diverse@tcp.co.uk> wrote in message
> news:i120g0$ofq$1@news.eternal-september.org...
> >2 stage derivation of (should be) 1800V pulses.
> > Fence had failure in the first stage probably due to intermittant
corroded
> > battery supply contact.
> > Anyway the 15A 60V 8N06 powerFET blew along with an associated double
> > diode
> > BAV23.
> > Replaced both and works to some extent. This FET has plenty of drive 5V
of
> > pulses of repeat 3uS for the gate and about 3V ringing swing on the
output
> > to the first step up transformer. I assume that is as to be expected,
> > never
> > having the chance to see hot-side SMPS drive scope traces.
> > But rectified output only climbs to about 1V of DC before the final
stage
> > (unreadable marking) thyristor discharges that supply into the second
step
> > up transformer, but of course not even enough to get a glow on a 110V
> > neon.
> > Doubling the C setting the 3uS pulses, to give longer repeat rate and
that
> > intermediary voltage rises to about 3V but still not enough for any
proper
> > final output. Adding more C and DC is then much less than 3V.
> > What would people expect the intermediary DC to be? obviously higher
than
> > 12V battery supply
> > Next stage would be disconnect the thyristor if that should be working
but
> > leaky and draining the intermediary DC but any other ideas? Would
explain
> > why the printing is very indistinct I suppose.
> > DC ohms of the airgap type transformers are
> > intermediary 0.1R//10.6R
> > HV 0.3R//29R which seem reasonable, ie not major shorted turns if any
> >
> >
>
> Hi,
>
> I found this schematic (circuit diagram) somewhere on the net, is it
> anything like your one ?
>
>
http://www.electro-tech-online.com/attachments/electronic-projects-design-id
eas-reviews/4007d1108193301-need-help-developing-electric-fencing-my-farm-el
ectricfence.jpg
>
> Ian.
>
>

The 'IV' and HV stage is very similar, this one has a lot of SM so a bit
more distributed for the higher voltages, ie tripling up of diodes and Rs

Do you have the URL of the text relating to that pic
Search on that site just enigmatically/awkwardly/insultingly returns
"The answer given for the random question was incorrect."

== 3 of 4 ==
Date: Sat, Jul 10 2010 7:45 am
From: "N_Cook"

Googled for it
http://www.electro-tech-online.com/electronic-projects-design-ideas-reviews/
13848-need-help-developing-electric-fencing-my-farm.html

== 4 of 4 ==
Date: Sat, Jul 10 2010 4:49 pm
From: Franc Zabkar

On Sat, 10 Jul 2010 15:42:04 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

>Do you have the URL of the text relating to that pic

That Dick Smith kit was based on Silicon Chip Magazine's April 1999
High Power Electric Fence Controller.

FWIW, here is the PCB and front panel label:
http://www.siliconchip.com.au/cms/attachments/show.html?year=1999&month=April

If you can't locate the technical description on SC's web site, let me
know and I'll look through my paperwork.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

==============================================================================
TOPIC: Discount Jordan 6unite1
http://groups.google.com/group/sci.electronics.repair/t/6fac27ac365eda6e?hl=en
==============================================================================

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TOPIC: Wholesale True Relig Women Jeans
http://groups.google.com/group/sci.electronics.repair/t/64818b144933cedb?hl=en
==============================================================================

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==============================================================================
TOPIC: 1394 Connectors
http://groups.google.com/group/sci.electronics.repair/t/b3645d7e1209d695?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Jul 10 2010 6:53 am
From: "William R. Walsh"

Hello all...

I recently came across an old Orange Micro combination USB 2.0 and
1394A ("Firewire 400") PCI expansion card. The outboard 1394
connectors were heavily corroded and have so far proven unfixable. An
undamaged internal 1394 connector shows the circuitry to be
functional.

I would like to replace them. The part to use seems to be Molex #
0534600629.

I have looked in a lot of places to try and find these available for
sale. I do not know what a compatible, differently branded connector
would be called (haven't researched it). But I cannot find anyone
selling these in reasonable quantities or actually having them in
stock. Short of trying to scam a few samples out of Molex (which I'd
feel bad about) I don't know what to do.

I would greatly appreciate any ideas or suggestions. Likewise, if you
have a junked Firewire card sitting around with some of these
connectors on it... (I am located in the US. Don't reply to the
indicated e-mail address. It does not work.)

William

== 2 of 2 ==
Date: Sat, Jul 10 2010 11:51 am
From: whit3rd

On Jul 10, 6:53 am, "William R. Walsh" <wm_wa...@hotmail.com> wrote:
> Hello all...
>
> I recently came across an old Orange Micro combination USB 2.0 and
> 1394A ("Firewire 400") PCI expansion card. The outboard 1394
> connectors were heavily corroded ...
> I would like to replace them. The part to use seems to be Molex #
> 0534600629.

Welcome to the wonderful world of part numbering systems. That
part number is likely to be a dead-end.

What you need is a vertical through-hole connector, IEEE-1394
DigiKey has some in stock

<http://search.digikey.com/scripts/DkSearch/dksus.dll?
Detail&name=AE9922-ND>

that might prove useful.

==============================================================================
TOPIC: HI WONDERFUL OPPORTUNITY DON'T MISS IT
http://groups.google.com/group/sci.electronics.repair/t/99c1cd30ce63b012?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Jul 10 2010 6:56 am
From: vishal

http://www.123maza.com/d-server/dna

==============================================================================
TOPIC: Crest Audio Pulse 2 1100 power amps, 1999
http://groups.google.com/group/sci.electronics.repair/t/8c6ed4787718ff07?hl=en
==============================================================================

== 1 of 4 ==
Date: Sat, Jul 10 2010 7:56 am
From: "N_Cook"

I'm wondering if it could be related to prolonged brownout if used with
generator set all the time. Anyone know the definition of brownout? mains 5
percent down? 10,20% ? Google thinks I'm trying to get Gordon Brown out

== 2 of 4 ==
Date: Sat, Jul 10 2010 8:01 am
From: Meat Plow

On Sat, 10 Jul 2010 15:56:10 +0100, N_Cook wrote:

> I'm wondering if it could be related to prolonged brownout if used with
> generator set all the time. Anyone know the definition of brownout?
> mains 5 percent down? 10,20% ? Google thinks I'm trying to get Gordon
> Brown out

I'd consider a brownout here in the US of A to be in the range of 75 to
90 volts out of 120. Certainly noticeable by amplifier and other
electronics performance by any competent music tech or even a musician.

== 3 of 4 ==
Date: Sat, Jul 10 2010 8:19 am
From: "N_Cook"

Meat Plow <mhywatt@yahoo.com> wrote in message
news:3t6nhs.377.19.1@news.alt.net...
> On Sat, 10 Jul 2010 15:56:10 +0100, N_Cook wrote:
>
> > I'm wondering if it could be related to prolonged brownout if used with
> > generator set all the time. Anyone know the definition of brownout?
> > mains 5 percent down? 10,20% ? Google thinks I'm trying to get Gordon
> > Brown out
>
> I'd consider a brownout here in the US of A to be in the range of 75 to
> 90 volts out of 120. Certainly noticeable by amplifier and other
> electronics performance by any competent music tech or even a musician.

These people think they are Douglas Adams' Disaster Area with 10KW of power
, now having to make do with 4KW, perhaps less loading on the generator will
keep the remaining 2 alive for longer , if a brownout issue.

== 4 of 4 ==
Date: Sat, Jul 10 2010 9:07 am
From: Meat Plow

On Sat, 10 Jul 2010 16:19:36 +0100, N_Cook wrote:

> Meat Plow <mhywatt@yahoo.com> wrote in message
> news:3t6nhs.377.19.1@news.alt.net...
>> On Sat, 10 Jul 2010 15:56:10 +0100, N_Cook wrote:
>>
>> > I'm wondering if it could be related to prolonged brownout if used
>> > with generator set all the time. Anyone know the definition of
>> > brownout? mains 5 percent down? 10,20% ? Google thinks I'm trying to
>> > get Gordon Brown out
>>
>> I'd consider a brownout here in the US of A to be in the range of 75 to
>> 90 volts out of 120. Certainly noticeable by amplifier and other
>> electronics performance by any competent music tech or even a musician.
>
>
> These people think they are Douglas Adams' Disaster Area with 10KW of
> power , now having to make do with 4KW, perhaps less loading on the
> generator will keep the remaining 2 alive for longer , if a brownout
> issue.

It's as easy as a voltmeter plugged into the amplifier mains and
occasionally monitored.

==============================================================================
TOPIC: Repairing an expensive speaker
http://groups.google.com/group/sci.electronics.repair/t/8fc3fa133c100ac4?hl=en
==============================================================================

== 1 of 4 ==
Date: Sat, Jul 10 2010 8:14 am
From: "N_Cook"

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:tVKZn.17551$c85.7376@newsfe15.ams2...
>
>
> "Meat Plow" <mhywatt@yahoo.com> wrote in message
> news:3t44sc.v8m.19.13@news.alt.net...
> > On Fri, 9 Jul 2010 01:45:22 +0100, "Arfa Daily"
> > <arfa.daily@ntlworld.com>wrote:
> >
> >>
> >>
> >>"Meat Plow" <mhywatt@yahoo.com> wrote in message
> >>news:3t2ats.t4n.19.4@news.alt.net...
> >>> On Thu, 08 Jul 2010 20:48:38 +0100, Ron
> >>> <ron@lunevalleyaudio.com>wrote:
> >>>
> >>>>On 08/07/2010 20:15, root wrote:
> >>>>> Meat Plow<mhywatt@yahoo.com> wrote:
> >>>>>>
> >>>>>> Seek out a professional reconing shop. You need some specialized
> >>>>>> tools
> >>>>>> of the trade and some talent to recone. My good friend did it for a
> >>>>>> living until he passed away recently. He would advise the same even
> >>>>>> if
> >>>>>> you didn't chose his service.
> >>>>>
> >>>>> You can buy kits for reconing speakers. It isn't a
> >>>>> hard job. You remove the flex outer rim from the
> >>>>> cone. Then you cut out the bulge covering the voice
> >>>>> coil and put shims (supplied with the kit) in to center
> >>>>> the cone. Then you glue new flex material around
> >>>>> the cone, and wait overnight. Then you remove the
> >>>>> shims and seal up the bulge with glue.
> >>>>>
> >>>>> Apart from the overnight wait for glue to dry, it
> >>>>> only took me about half an hour the first time.
> >>>>> With practice I might be able to get it down to
> >>>>> 10 minutes.
> >>>>
> >>>>And that takes care of the knackered voice coil does it?
> >>>>
> >>>>Ron(UK)
> >>>
> >>> The 10 minute recone part really bothers me. Sure with production line
> >>> jigs, shims, guides and people who do maybe a 100 per day that is a
> >>> tangible goal. But for an average Joe buying reconing parts and being
> >>> successful is not the average outcome. Sure there are exceptions so if
> >>> you want to try it on your own good luck.
> >>
> >>
> >>Interestingly, I was discussing exactly this issue with the owner of the
> >>music shop that I do a lot of work for, just this week. He rents a lot
of
> >>biiiiigggg PA equipment out - kilowatt amps and 4 x 15 bass cabs and
> >>such.
> >>These get damaged by inept users all the time, apparently. I suggested
> >>that
> >>it must cost him a fortune in replacement speakers, but he said "Oh no -
I
> >>just re-cone them". I asked him how long he had been doing this and he
> >>said
> >>years, but I had never seen this going on in his shop. Anyway, I asked
him
> >>how long it took, and how hard a job it was, and did he have lots of
> >>specialist shims and feeler gauges and jigs and what have you. Nope, he
> >>said. He reckons it takes him but a few minutes (literally) to do the
job.
> >>He says that the most time consuming part is making sure that all the
crud
> >>from the burnt up voice coil, is removed from the airgap. He uses a
> >>combination of compressed air, and sticky tape to do this. As to
centering
> >>the new cone's voice coil, he says that most replacement kits come with
a
> >>set of four plastic spacer shims, but that many modern designs are
> >>fundamentally self - centering anyway. He reckoned that it was basically
a
> >>piece of piss job that just needed a little care, and that much bollocks
> >>was
> >>talked on the subject. I might ask him to let me know next time he's got
> >>one
> >>to do, as I would like to watch him at work ...
> >>
> >>Arfa
> >
> > I've been around when my buddy Bart reconed some pro-audio speakers.
> > It all comes down to people doing it the way they have learned. It's
> > not as easy as you think but it isn't hard either. He chose to buy
> > specific tools and glues and treatments not relying on kits for shims
> > and glues. He knew what he was doing and reconed all my speakers.
> > Never had a re-run because of a botched repair. Hey if you can learn
> > the essentials and want to give reconing a try go for it. Maybe it's
> > for you maybe it's not.
>
> I don't reckon I've got the patience, Meat. I had always thought that it
was
> quite a tricky and skilled job, so I was just interested to have a watch
> next time Dunc does one, as he reckoned it was so straightforward !
>
> Arfa
>

Reading through this I see no ref to 3 or 4 slices of credit card to align
voice coil with the slot, maybe an omission or another reconing job I'm
remembering

This is my experience of reconing a Peavey Black Widow speaker
Not made for the UK climate, stored in a (normal for UK) damp garage for 3
years, came out making nasty "amp clipping" noise.
I don't know how general this is for different manufacturers but for
unsticking the contact adhesive of the original cone and spider skirt.
I tried hot-air gun , oven cleaner and acetone but the one that worked on
the one I did this week was petrol. Some strips of tissue paper soaked in
petrol and covered with some circular strips of plastic and leaving for half
an hour to soften the glue
Now it is totally apart, small bits of aluminium oxide in the voice coil
slot were causing the distortion along with loose skirt biased to one still
retained side. 15 inch size with aluminium basket.
The voice coil is in perfect condition and no imperfections to the cone
despite 30 years old.
Prior to me getting to look the owner had removed the 3 magnet retaining
bolts and removed some perished foam filter from inside under the mesh cover
and squirted in WD40.
The white oxide formations had burst the glued skirt off , about 80 percent
of its rim, and the same for the cone rim (after removing the periphery
bolts) and nothing much holding on the remainder, easy to prize off.
masked off the central voice coil slot area before
abraiding back the lands to take contact adhesive to replace the skirt and
cone. Then air blast and run thick plastic around the slot to clear any
crud. The magnet does not seem to be corroded, shiney, no obvious rust
spots.
The 0.08mm thick aluminium dome must have been press-formed
or by metal spinning with a cylinder
extension to the dome and the cylinder section is glued to the inside of the
VC former. So had to cut around the dome to remove and hope the
final gluing-back holds up against the air pumping process.
I just used 4 ball point pens in the rim
mount holes for rough alignment and some clothes pegs to give a bit more
clearance gap for laying down the glue. Removed them prior to dropping the
cone in case they gave some bias.

== 2 of 4 ==
Date: Sat, Jul 10 2010 9:22 am
From: TMI

FYI.....

HI Tom,
We only recone with authentic Tannoy parts returning the speaker to
exact new condition. I haven't priced this kit recently, but about one
year ago, charges for us to recone the low frequency were $440.00
each. I can check the price on Monday to make sure there haven't been
any major changes, but generally there are only a few dollar
differences or none at all. The more important question will be
availability and if you are interested, I will pursue that too.
I'm glad you saw our Over the Tannoy Post. What did you think of it?
the website?
Cathy Satin The Speaker Exchange®
1250 E. Hillsborough Avenue • Tampa, FL 33604
Phone:1-800-849-6972 • 1-813-237-4800
Fax: 1-813-238-3558 cathy@speakerex.com Mon-Fri 10-5:30 est, 1st Sat
of e month 10-3:00
AIM:cathyspex Skype: speakerex http://www.twitter.com/speakerex

Speaker Sales, Service, and all your repair needs since 1977

Please send us your impressions, comments or suggestions concerning
our new improved site www.speakerex.com
SHIPPING instructions and REPAIR FORMS: http://tinyurl.com/2c3e27k

On Jul 9, 9:31 pm, TMI <audio...@hotmail.com> wrote:
> I'll bet they don't have the machine required to degauss and
> remagnatize your speaker. Or you are talking to a salesman trying to
> manimize profit. There is no loss of flux with the correct size
> equipment. In fact, there will be more flux in a newly charged magnet
> compared to one that has been in service for a while.
>
> In the macro economics of it all, a reconer has to charge you so much
> to repair that magnet that it exceeds the value of a good basket core
> (speaker without the cone/voice coil). It will never be exactly like
> the uncracked one on the other side. No used speaker is worth more
> than a core + the recone job and that is very close to the cost of a
> new speaker.
>
> Now there are some unique drivers out there that are not available
> anymore but in most cases it makes real sense to measure the TS
> parameters of the remaining driver and make a good substitution using
> those numbers if a true replacement cannot be found.
>
> Someone who is REALLY into restorations might have a similar piece of
> ferrite or other magnetic material to replace the cracked magnet.
> There is NOTHING wrong with repairing a magnet that way, then charging
> the assembly.
>
> I have been doing this for 4 decades and that is my professional
> opinion.
>
> Tom Maguire
> TMI Engineering
>
> On Jul 9, 4:08 pm, Ron <r...@lunevalleyaudio.com> wrote:
>
>
>
> > On 09/07/2010 19:36, TMI wrote:
>
> > > This is a horse of a different color.
>
> > > You can't repair a cracked magnet and get the same flux in the gap
> > > because the crack adds extra gaps. Getting the magnet to crack in the
> > > first place usually means something horrible happened to the driver.
> > > Buy a new one.
>
> > Cracked ferrites _are_ repaired but only as a last resort in cases where
> > there's no alternative. We've been through this recently on another n/g.
> > It's not recommended, but it can be done.
>
> > According to a large professional loudspeaker repair company I contacted
> > on the subject, de-magnetising and remagnetising also is to be avoided
> > as it loses flux.
>
> > Ron(UK)
> > --
> > I am using the free version of SPAMfighter.
> > We are a community of 7 million users fighting spam.
> > SPAMfighter has removed 1445 of my spam emails to date.
> > Get the free SPAMfighter here:http://www.spamfighter.com/len
>
> > The Professional version does not have this message- Hide quoted text -
>
> - Show quoted text -

== 3 of 4 ==
Date: Sat, Jul 10 2010 12:20 pm
From: John

On Fri, 09 Jul 2010 17:15:17 -0400, John <Ya@you.com> wrote:

Some one made some reference to the use WD40 to melt the glue

I had an interesting experience with that powerful staff:
The spring load cover of an outdoor power outlet that I have, made a
screeching noise when lifted. I sprayed it with WD40 and the cover
toke off like an Arab rocket.
Einstein once defined a stupid person the one who does the same thing
and expects a different result so I did the stupid thing of
installing a new cover and spray again with WD40 and obviously the
result was the same.
Installed another cover and no more spraying. The nasty WD40 melted
the plastic holding the spring.

Ref: Material to hold the coil in position :
I used, 65 years ago, strips of plastic from photographic film
negatives.
Boston Acoustics sells a speaker with a removable voice coil and
attached to the cone by screws. There is a metal ring with threaded
holes glued to the cone.

Thank you to everybody . Fantastic help

John
>

== 4 of 4 ==
Date: Sat, Jul 10 2010 12:21 pm
From: John

On Fri, 09 Jul 2010 17:15:17 -0400, John <Ya@you.com> wrote:

Some one made some reference to the use WD40 to melt the glue

Thank you to everybody . Fantastic help

John
>

==============================================================================
TOPIC: Simple Hack To Get $2000 To Your PayPal Account
http://groups.google.com/group/sci.electronics.repair/t/dc0c3c11a0cb95a0?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Jul 10 2010 9:01 am
From: masti dunia

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==============================================================================
TOPIC: audio attenuator headphone to line
http://groups.google.com/group/sci.electronics.repair/t/b3898a02f147d683?hl=en
==============================================================================

== 1 of 5 ==
Date: Sat, Jul 10 2010 9:06 am
From: "tg"

I want to make a simple audio attenuator by soldering a couple of resistors
into a cable, similar to here:
http://www.epanorama.net/circuits/speaker_to_line.html
this page talks about attenuating speaker level down to line level with 10k
and 1k but I want to attenuate headphone level down to line level. I haven't
done this before and want to get it right so can anyone advise on the
correct resistor values to use?

== 2 of 5 ==
Date: Sat, Jul 10 2010 10:49 am
From: Fred McKenzie

In article <4c389aba$0$27995$db0fefd9@news.zen.co.uk>,
"tg" <nospam@nospameverever.net> wrote:

> I want to make a simple audio attenuator by soldering a couple of resistors
> into a cable, similar to here:
> http://www.epanorama.net/circuits/speaker_to_line.html
> this page talks about attenuating speaker level down to line level with 10k
> and 1k but I want to attenuate headphone level down to line level. I haven't
> done this before and want to get it right so can anyone advise on the
> correct resistor values to use?

My recollection is that "line level" is related to the level that would
drive a telephone earpiece, and be generated by a telephone's carbon
microphone. In other words, line level is not greatly different from
headphone level.

Just as anyone would adjust a volume control to set their personal
listening level, you would need to adjust the amplifier output for the
desired line level. The only network needed might be for impedance
matching to the line. If your headset amplifier has a very low output
impedance, a series resistor equal to the line impedance may be all that
is needed.

What kind of "line" are you working with? Some are balanced, but the
circuit you refer to is for an un-balanced line. For a balanced line
you may need an audio transformer.

Fred

== 3 of 5 ==
Date: Sat, Jul 10 2010 4:57 pm
From: "tg"

> What kind of "line" are you working with? Some are balanced, but the
> circuit you refer to is for an un-balanced line. For a balanced line
> you may need an audio transformer.

the line input is a 1/4" TRS socket on an m-audio microtrack II.
http://www.m-audio.com/images/global/manuals/MT11_flyerUK_LR.pdf
Strangely enough I haven't been able to find any proper specs on the
microtrack but I know it commonly takes microphones and such. Headphone
output is too 'heavy' for a decent recording into this input so I need to
attenuate it.
I can't use any boxes or such because the headphone device and the
microtrack will be used on the move, often in the open, on foot, running on
batteries. Thus I have to integrate any attenuation into the cable. Thanks
for any further advice.

== 4 of 5 ==
Date: Sat, Jul 10 2010 6:10 pm
From: "Arfa Daily"

"tg" <nospam@nospameverever.net> wrote in message
news:4c390954$0$12156$fa0fcedb@news.zen.co.uk...
>> What kind of "line" are you working with? Some are balanced, but the
>> circuit you refer to is for an un-balanced line. For a balanced line
>> you may need an audio transformer.
>
> the line input is a 1/4" TRS socket on an m-audio microtrack II.
> http://www.m-audio.com/images/global/manuals/MT11_flyerUK_LR.pdf
> Strangely enough I haven't been able to find any proper specs on the
> microtrack but I know it commonly takes microphones and such. Headphone
> output is too 'heavy' for a decent recording into this input so I need to
> attenuate it.
> I can't use any boxes or such because the headphone device and the
> microtrack will be used on the move, often in the open, on foot, running
> on
> batteries. Thus I have to integrate any attenuation into the cable. Thanks
> for any further advice.

The resistor values you suggested give an attenuation of 10 : 1 which is
probably rather too much. OTOH, I'm surprised that you find a headphone
output too 'heavy' to feed a standard line level input. The output from the
headphone socket of an iPod, for instance, feeds a standard line level input
on an amplifier, without issue. I do it every day with a variety of
different amplifiers, as I use my iPod as a source of test music for
amplifiers after repair. Even if the output from the headphone socket does
seem a little OTT to drive the recorder's line input, you can reduce it by
turning down the volume control on the source device.

If, however, you still want to externally attenuate the headphone signal,
prior to driving it into the recorder, then a ratio of 2 : 1 might be more
appropriate, so just use a couple of equal value resistors . You're never
going to match the impedances properly, as the output of the source device's
headphone socket, is likely to be somewhere between a few ohms, and 32 ohms.
The line input on the recorder will likely be around 47k ohms. Just use two
1k resistors. If that doesn't give enough attenuation, double up on the
'top' resistor to say 2k2.

Only thing that might make all of that wrong, is if the input that you are
trying to use on the recorder, is not a 'line level' input. I say that
because you talk about the device "commonly taking microphones". A
microphone input is probably anything up to 100 times more sensitive than a
line level input. If this is the case, then you might need an attenuator of
50 : 1 or more. In which case, try 47k for the top resistor, and 1k for the
bottom one.

Arfa

== 5 of 5 ==
Date: Sat, Jul 10 2010 7:24 pm
From: David Nebenzahl

On 7/10/2010 9:06 AM tg spake thus:

According to that propaganda sheet, the Micro Track II will accept input
from "studio monitors (and/or headphones)". So can't you just plug it
directly into the headphone output?

(Not sure what they mean by "and/or" here. I've always held that this
usage ("and/or") is needlessly confusing and should never be used, as
"or" as it's commonly understood is not an exclusive or, so it means
one, the other, or both.)

--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

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