[TechAssist] Re: 70 volt line audio amp
- From: "Jerome Silverman" <greentron@xxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Fri, 29 Apr 2005 21:27:26 -0400
A short on the secondary is transformed into a short on the primary. The
input impedance of a transformer is equal to the load impedance times the
square of the turns ratio. Ferrite is not used in audio transformers. Steel
laminations, like power transformer laminations, but thinner, are used in
audio transformers.
Jerry Silverman
Greentron Inc
4 Newland Ave Greenville SC 29609
Fax/Phone 864 232 3889
greentron@xxxxxxx
----- Original Message -----
From: "markbrock" <markbrock@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, April 29, 2005 6:39 PM
Subject: [TechAssist] Re: 70 volt line audio amp
> Jim, I disagree, a dead short on the primary may cause a problem (a
new
> one shows almost short on the primary ) but wouldn't the secondary
being
> shorted, only show no output from the speaker, it has no influence on the
> load or impedance that the amp sees, as I understand it there is only
> ferrite between the two windings inside this transformer itself, with taps
> at different intervals of the secondary coil to make up the wattage out.
> the peavey mic I'm using on the aux input works fine until you hook up
to
> the plant system, so again, I'm almost sure that Sunday I'll find an
> isolation transformer or impedance matching transformer in the ceiling
that
> is the grandfather to all of the ones down the line, I'll bet its
primary
> is open... almost sure of it....I'll know real soon and I'll let you
know
> brock
>
> Brock Electronics
> R.R.4 box 237
> 5208 cr.3385
> Independence Ks. 67301
> 620-331-0235
> fax 331-7191
>
> markbrock@xxxxxxxxxxxxx
> Zenith*Philips*Peavey*Fender*Crate
> we work on all brands,makes,models
> of anything that plugs in the wall
> ----- Original Message -----
> From: "becyn" <becyn@xxxxxxxxxx>
> To: <techassist@xxxxxxxxxxxxx>
> Sent: Friday, April 29, 2005 12:39 PM
> Subject: [TechAssist] Re: 70 volt line audio amp
>
>
> > Mark,
> > As a matter of practicallity, I personally never found some open/short
> > condidtion
> > down the line to be the problem (although a dead short on a tap seconday
> > could do it).
> >
> > Did you try the mike instead of the output from the phone sys?
> > Also, you need to use a lower gain "aux" input instead of the the high
> gain
> > mic input, otherwise the input will be overdriven.
> > There may me some mismatch at the front end causing the distortion.
> > Something about all this just doesn't ring true...sorry ;-)
> >
> > Jim McVey
> > McVey Alltronix
> > 327 Broadway
> > Newburgh N.Y. 12550
> >
> > "If it doesn't play...
> > CALL MCVEY !!!!!!"
> > Factory authorized
> > service for over 20
> > major brands.
> > 845 561 8383
> > (Last of the Mohegans)
> >
> > markbrock wrote:
> >
> > >Yes Jim, I'm hooking up to the 70 volt line port. these amps have a
> remote
> > >feature, the phone is used as a paging system, this amp is to drive
the
> > >speakers on the lot and in the shop and wash basin and paint booth and
> show
> > >room, ( car agency ), there is an auxiliary control for back ground
> music,
> > >cd, tuner, etc, the phone company controls the music on hold through a
> > >different system, this is just for PA purposes only,
> > > now back to the original question and I agree with J Silverman,
> these
> > >systems can be checked with an ohm meter, and 70 ohms is too high,
> there's
> > >and open tap somewhere, 15 foot on the ceiling I suspect to find an
> > >impedance matching transformer, ( like peavey builds ) where you can
> > >basically hook up a short or what ever but right before the amp sees it
> its
> > >isolated by a large transformer, and I strongly suspect when the
output
> > >shorted and the filter caps blew, it crammed dc directly into this
> > >transformer and opened the primary, I'm probably getting enough
leakage
> > >through it from the eddy urrents that fly around the outside of the 70
> volt
> > >signal. thats my best guess I'll see Sunday when I tear up the
ceiling
> of
> > >those nice offices and make my accent to the roof..... man I can't
wait.
> > >I'll let you all know. thanks for the help so far.
> > >brock
> > >
> > >
> > >Brock Electronics
> > >R.R.4 box 237
> > >5208 cr.3385
> > >Independence Ks. 67301
> > >620-331-0235
> > >fax 331-7191
> > >
> > >markbrock@xxxxxxxxxxxxx
> > >Zenith*Philips*Peavey*Fender*Crate
> > >we work on all brands,makes,models
> > >of anything that plugs in the wall
> > >----- Original Message -----
> > >From: "becyn" <becyn@xxxxxxxxxx>
> > >To: <techassist@xxxxxxxxxxxxx>
> > >Sent: Thursday, April 28, 2005 5:26 PM
> > >Subject: [TechAssist] Re: 70 volt line audio amp
> > >
> > >
> > >
> > >
> > >>I'm going to ask a stupid question.
> > >>Does the "new amp" have a 70v port output?
> > >>If you are hooking up an 8 ohm system to the 70v ,
> > >>you will have a MAJOR impedance mismatch.
> > >>Essentially, the 70 v is the audio version of the power grid.
> > >>Step up the voltage( reduce current) to send long distances in order
to
> > >>reduce
> > >>I^2 *R losses.
> > >>
> > >>Jim McVey
> > >>McVey Alltronix
> > >>327 Broadway
> > >>Newburgh N.Y. 12550
> > >>
> > >>"If it doesn't play...
> > >>CALL MCVEY !!!!!!"
> > >>Factory authorized
> > >>service for over 20
> > >>major brands.
> > >>845 561 8383
> > >>(Last of the Mohegans)
> > >>
> > >>J Silverman wrote:
> > >>
> > >>
> > >>
> > >>>70 ohms of resistance sounds high. Amps work into impedance, which is
a
> > >>>dynamic reflection of the load. DC ohms resistance should be much
lower
> > >>>
> > >>>
> > >than
> > >
> > >
> > >>>the impedance number. Since that is a 70 volt line output, the DC
load
> is
> > >>>just the resistance of the transformer windings.
> > >>>Jerry Silverman
> > >>>Greentron Inc
> > >>>4 Newland Ave
> > >>>Greenville SC 29609
> > >>>Fax/Phone 864 232 3889
> > >>>mail to: greentron@xxxxxxx
> > >>>----- Original Message -----
> > >>>From: "markbrock" <markbrock@xxxxxxxxxxxxx>
> > >>>To: <techassist@xxxxxxxxxxxxx>
> > >>>Sent: Thursday, April 28, 2005 2:43 PM
> > >>>Subject: [TechAssist] Re: 70 volt line audio amp
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>brand new amp, works fine with one speaker and a mic, on the bench,
> but
> > >>>>when attached to the phone system, has distortion, I tried to blame
> it
> > >>>>
> > >>>>
> > >on
> > >
> > >
> > >>>>the phone co because if I disconnected them it worked ok with one
> > >>>>
> > >>>>
> > >speaker,
> > >
> > >
> > >>>>no there pointing back at me, I need more ammo before I go further,
> > >>>>
> > >>>>
> > >wish
> > >
> > >
> > >>>>
> > >>>>
> > >>>I
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>had a spare amp to try out. old amp has blown output ic and one of
> the
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>two
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>filters popped its lid, I was just wondering if this 70 ohms of
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>resistance
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>was going to be way off base , but apparently doesn't surprise
> anybody
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>yet,
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>so I'll go a little farther.
> > >>>>Brock Electronics
> > >>>>R.R.4 box 237
> > >>>>5208 cr.3385
> > >>>>Independence Ks. 67301
> > >>>>620-331-0235
> > >>>>fax 331-7191
> > >>>>
> > >>>>markbrock@xxxxxxxxxxxxx
> > >>>>Zenith*Philips*Peavey*Fender*Crate
> > >>>>we work on all brands,makes,models
> > >>>>of anything that plugs in the wall
> > >>>>----- Original Message -----
> > >>>>From: "becyn" <becyn@xxxxxxxxxx>
> > >>>>To: <techassist@xxxxxxxxxxxxx>
> > >>>>Sent: Thursday, April 28, 2005 9:43 AM
> > >>>>Subject: [TechAssist] Re: 70 volt line audio amp
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>>Divide and conquer !
> > >>>>>
> > >>>>>Have you bench tested the amp with a 1Khz sine?
> > >>>>>It sounds more like the amp than the line.
> > >>>>>Many of those mutiple speaker setups have the taps set for a
> > >>>>>watt or less, so underpowering isn't an issue.
> > >>>>>
> > >>>>>Jim McVey
> > >>>>>McVey Alltronix
> > >>>>>327 Broadway
> > >>>>>Newburgh N.Y. 12550
> > >>>>>
> > >>>>>"If it doesn't play...
> > >>>>>CALL MCVEY !!!!!!"
> > >>>>>Factory authorized
> > >>>>>service for over 20
> > >>>>>major brands.
> > >>>>>845 561 8383
> > >>>>>(Last of the Mohegans)
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>markbrock wrote:
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>>ok, whats the limit of resistance I can have at the amp using a
70
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>volt
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>>>line, I have around 70 ohms, unit is very distorted, 40 watt
> system
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>about
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>>>15 speakers, old unit burned up, they bought a new one and its
all
> > >>>>>>distorted, then they called me, I figured someone hung a regular
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>speaker
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>>>on the line but that would be closer to 16 or less ohms, is 70
ok
> ?
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>they
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>>>may be under powered but it worked fine for 10 years previous.
> thanks
> > >>>>>>brock
> > >>>>>>
> > >>>>>>Brock Electronics
> > >>>>>>R.R.4 box 237
> > >>>>>>5208 cr.3385
> > >>>>>>Independence Ks. 67301
> > >>>>>>620-331-0235
> > >>>>>>fax 331-7191
> > >>>>>>
> > >>>>>>markbrock@xxxxxxxxxxxxx
> > >>>>>>Zenith*Philips*Peavey*Fender*Crate
> > >>>>>>we work on all brands,makes,models
> > >>>>>>of anything that plugs in the wall
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> >
>
>>>-------------------------------------------------------------------------
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