[TechAssist] Re: 70 volt line audio amp
- From: Al Gutz <alg@xxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Fri, 29 Apr 2005 22:25:17 -0400
An open transformer will have no affect on the system other than one
speaker will not work. All the transformers are in parallel. A shorted
secondary will only lower the output of the rest of the speakers..
70 ohms is too high, you should be reading maybe 1 or 2 ohms.
Take a transformer and connect it directly to the amp and add a speaker,
if it works you have a wireing problem, if not you have an amp problem.
Al's TV-Electronics
Pembroke Ont.
Canada
markbrock wrote:
> 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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