[TechAssist] Re: 70 volt line audio amp

This is the way I normally run tests to isolate:

Disconnect any mikes/interfaces. Use only the amp with a tuner; or if it's a
combo reciever then just the reciever. Listen to all speakers. Clean? Sound?
Then move on
.
Add any RCA based inputs. Check for distortion. Move on.

Hook up mikes...test them. Clean? Move on...if not try a different mike.
Mikes can vary, even the jack style may be different as previous setups may
have a low z mike attached to a hi z connection or vice versa.

Last if you're dealing with distortion using a phone line or music on hold
feature, is to see if the interface box uses 110V ac to amplify, generally
hum/distortion occurs due to the 2 prong or 3 prong grounding
designs.....carry some 2 prong adaptors and isolate the amp 1st, then the
phone line interface.

Damon Brunger
Telrad Electronics
Fort Wayne IN
----- Original Message -----
From: "markbrock" <markbrock@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, April 29, 2005 5:39 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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