[TechAssist] Re: 70 volt line audio amp
- From: gulftech@xxxxxxxx
- To: techassist@xxxxxxxxxxxxx
- Date: Sat, 30 Apr 2005 07:17:38 -0500
Mark,
On the contrary. A short on the secondary of a transformer is reflected
as a short on the primary. No, you can't measure it with an ohmeter on
the primary. Think about it. The more you load the secondary, the more
current is drawn by the primary. That's why a fuse in the primary
protects, at least to some extent.
Kenneth Smith
Gulf Technical Services
3034 Gulf Breeze Parkway
Gulf Breeze, FL 32563
850-934-8324 (Voice) 850-932-0819 (Fax)
On Fri, 29 Apr 2005 17:39:08 -0500 "markbrock" <markbrock@xxxxxxxxxxxxx>
writes:
> 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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