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PA System in 1A2--401A?
#636639 05/02/20 03:31 PM
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Good day to all of you! I haven't been on this thread for years after I installed my Mitel SX-50 to power my old rotary phones throughout the house, but have finally started to install my old 1A2 Key system. I will post pictures of what I have shortly, and some fun Autovon stuff I have, too!

I have a general question about the 401A, and haven't really been able to find an answer. Can it be used to connect to an external PA speaker? So when button is depressed, you can have a public address? I have an external amplifier/speaker that has a 'phone line' connection on the back of it, so was wondering if that would do the trick. I attempted it, but could not get it to work. I thought maybe I could barely hear something, but I did notice that with the 401A card installed and the jumps made (1,3,5,7,9,11,43/2,4,6,8,10,12,44) as per manual, that I was able to hear myself through the telephone handset earpiece, when a normal 400D card you wouldn't.

I am in no way an expert; quite the novice. But I love to learn, try to figure things out, and try to do as much reading as possible. Taking it all in--there's lots of experience here!! Any general info/guidance much appreciated.

-Bob Hull


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Re: PA System in 1A2--401A?
Bob-o #636641 05/02/20 05:37 PM
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Hi,

Not a expert on this but you may not have enough voltage on the line. I did try a blue tooth speaker with a aux input and I hooked it up on the Tip and Ring and it work okay on my 401 card. I do have a Melco KA-390 Direct Paging Access unit if you are interested as I can let it go dirt cheap. This unit will let you page from a dedicated button to a external amplifier/speaker. I have no use for it as I don;t have enough buttons on my sets.

Re: PA System in 1A2--401A?
morephones #636642 05/02/20 05:46 PM
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Hi there, yes I'd be interested for sure, and thanks for the info. I guess I'm having a difficult time figuring out then how the 401A card is actually intended to be wired. I have read many of the BSPs on it, and it still seems fuzzy to me. Like 'connect this to this for this outcome' kind of thing would be helpful to wrap my head around it all.

Also, the amplifier I'm using was previously used on a phone system with a phone connection on the reverse. I remember it working in the building where I work before everything switched to VOIP. It has two phone terminal screws on the back 600 ohm. I was just wondering if I was missing a step in the whole thing before I started racking my brain over it.


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Re: PA System in 1A2--401A?
Bob-o #636643 05/02/20 05:58 PM
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Hey Bob, What KSU are you using the 401c card in? Some KSUs like the WECO 551 required the 401 intercom card to be on the last card slot.

Re: PA System in 1A2--401A?
Bob-o #636645 05/02/20 06:23 PM
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The 401A is a manual intercom card that basically just feeds battery to a T/R line appearance on your phones. If one station user presses their (intercom) button and another presses their button they can converse. As I recall, the 401A provides lamp supervision to light the intercom buttons when the intercom talk path is in use, but I could be wrong. There is no signaling. Normally you would have to set up a manual buzzer system to alert another extension to pick up.

So the T/R from that card is designed to connect to the T/R on a phone. Audio with 48 VDC battery. Not meant to connect to an amp to provide paging. It would probably do something if you use an amp with a mic input, but if there is no DC isolation you could damage the amp.

What you need is an ATA like a Valcom-V2000 (T/R in, audio out) or that Melco KA-390. Actually, if you use the Valcom you can just use another 400 line card because the Valcom can be connected to a trunk as well.

-Hal


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Re: PA System in 1A2--401A?
hbiss #636646 05/02/20 07:10 PM
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That's great info, Hal. Much appreciated. So the amp I hooked up to was designed (or at least installed) in a phone/paging environment previously. It's a Precision Electronics ST100E 4-input channel mixer amplifier, with 2 mic inputs, 2 aux, 1-600 ohm Tel/Page. The Tel Page works off one of the mic inputs as I understand, and the paperwork says that the XLR mic connectors are built-in isolation transformer inputs. Is that what you meant about isolation? Could I use just a regular 400D card on this if it's just reading a 'phone' signal, and maybe not need the 401A card?

Here's what I have:

http://cdn-docs.av-iq.com/dataSheet//STE100.pdf


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Re: PA System in 1A2--401A?
Bob-o #636647 05/02/20 08:48 PM
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You need connect the 401 card to a WMT-1 (or similar) matching transformer. The 401 card is designed to connect to a 600 ohm telephone line. An auxiliary input on an amp is 15,000 ohms and a mic input is 150 ohms.

They don't play well together without a matching transformer.


Sam


"Where are we going and why are we in this hand basket?"
Re: PA System in 1A2--401A?
Bob-o #636648 05/02/20 11:26 PM
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Hi Sam. The back of the amplifier has a spot for 600 ohm phone line. It’s marked “phone line 600 ohm”. Does the 401a card have to be the last card? This is in a smaller 6-card unit


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Re: PA System in 1A2--401A?
Bob-o #636649 05/03/20 01:30 AM
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In some KSUs like the 551 A and B's yes it needs to be on the last card slot. Some 551 C's the 401 card can be in any slot. Below is from 551 BSP 518·215-407 .


Manual Intercom
3.11 This feature is provided by installing a 401A
KTU in the KSU. In early production models
of the 550/551C KSUs, only jack J4 was factory-wired
with the talk (A) battery and ground required for
operation of the 401A. Later models (indicated by
an asterisk [*] stamped after the code on the KSU)
are wired to accept a 401A KTU in any of the
four jacks.


3.12 The early models can be modified to accept
a 401A in another jack by disconnecting the
green wires from terminals 3 (A grd) and 18 (A
bat) of J4 on the back of the KSU, and transferring
them to the same terminals of the desired jack.
3.13 On the 550/551A and B KSUs (MD), the
talk battery terminals are factory-wired at
each KTU jack, but only the BR-W/W-BR pair on
J4 is wired back to the talk battery terminals on
the connecting block. The pairs from the other
jacks are dead dressed. To use a jack other than J4 for the manual intercom KTU, disconnect the
BR-W/W-BR pair from the back of the connecting
block, and connect the pair from the other jack
as shown in Table B. Insulate and store the
disconnected pair.

Last edited by morephones; 05/03/20 01:33 AM.
Re: PA System in 1A2--401A?
Bob-o #636650 05/03/20 03:42 AM
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What more phones said.

Also, you could try attaching T/R from the 401card directly to the 600 ohm input. See if it works... It might have a matching transformer built in.

Sam


"Where are we going and why are we in this hand basket?"
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