[TechAssist] Re: 70 volt line audio amp
- From: becyn <becyn@xxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Fri, 29 Apr 2005 13:39:51 -0400
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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