Looking for a better telephone line transformer

[UHU]

Looking for a better telephone line transformer.

Currently ETAL P5100 transformer is fitted while an older version of the same device had an ETAL P1200 which was fully enclosed and potted(?) by “vacuum impregnation” process (according to ETAL website).

There is an electrical buzzing audible via the earpiece of the “programming” telephone that connects to the device (Pyronix Vocalizer alarm system speech dialler) connection is via the UK BT telephone socket mounted directly on the PCB (top right corner – white in colour) – the “programming” telephone is just a regular UK telephone plugged in to that socket on the PCB.

An older version of the same device used the ETAL P1200 and had no buzzing but the newer version with the P5100 had a small buzz from day one – “buzz” in this context means audible only via programming telephone earpiece and very slightly audible on the telephone line but not a vibrating buzz you could hear by physically putting your ear to the device – disconnect device from phone line and line goes totally quiet and ADSL speed improves.

Having replaced all the capacitors, the buzzing is greatly reduced (less buzzing then when it was brand new) – you can no longer hear the buzzing in the alarm voice messages (telephone side-tone effect was probably transferring the buzzing to recordings).

The speech dialler in circuit buzzing is having a negative impact on ADSL/Broadband performance on the same phone line – that's why I am interested in different transformer choices, makes and models.

So, which transformer is better the P5100 or the P1200?

Other than the two transformers I mentioned - Is there an even better transformer for this application made by ETAL or a different manufacturer?

What specifications should I be looking at to compare transformers.

Here is another thread that explains the Vocaliser https://www.badcaps.net/forum/showthread.php?t=60126

[budm]

Re: Looking for a better telephone line transformer

Beside of the transformer is not the same but how about the circuit itself? May be the circuit is not the same the design or the circuit board is not laid out properly.
http://www.epanorama.net/circuits/teleinterface.html
I doubt that the transformer itself is generating the noise, more likely the active circuit itself is causing the problem, the transformer is used to interface between Balance and Unbalance circuit.

[UHU]

Re: Looking for a better telephone line transformer

Thank you for your reply - I no longer physically have access to the older (quiet) Vocaliser so cannot take a photo to compare but I have got this online manual (my paper manual is only a grainy black and white photo) which shows a clear photo showing the old ETAL P1200 transformer PCB version Vocaliser.

Besides the transformer I can see three components of the four pin chip type on the old photo on the manual they are WHITE on the newer noisier version I have they are BLACK - manufacturers generally try to reduce the cost of their parts bill during a manufacturing run so will have to identify what are those three White now Black components - and are they of higher or lower quality/performance?

Before I get a more detailed photo organized - does anyone know what those White/Black parts are?

Can anyone else spot any differences between the photos?

The manufacturer probably did not change the PCB layout - that would have cost them money! From what can be seen on the cover of the manual and my photo of the rebuilt Vocaliser the layout looks the same - but am open to suggestions of how to modify it.

I thought that perhaps the open frame P5100 transformer could create in circuit noise as it was not glued together/potted/"vacuum impregnated" (the P1200 is "vacuum impregnated" and has closed box construction) all of which I thought could negatively affect ADSL/Broadband performance but then I had a closer look at the ETAL website (using product search for "Communication" and "Through Hole") and saw that the P5100 is suggested for ADSL but the P1200 is not suggested for ADSL!

So that implies I am better off for ADSL phone lines with the P5100?

[UHU]

Re: Looking for a better telephone line transformer

ETAL Datasheets P5100 and P1200

[budm]

Re: Looking for a better telephone line transformer

Those three 4-pin devices are the Optoisolators.

[budm]

Re: Looking for a better telephone line transformer

BTW, did you use micro filter for your phone system since you have DSL?
https://kb.netgear.com/22205/How-to-...etgear_organic
http://bt.custhelp.com/app/answers/d...-do-they-go%3F

[redwire]

Re: Looking for a better telephone line transformer

Between the two models, the telephone line transformers are almost identical. Yes, one may be a few dB (isolation or balance) better but I think the real problem is elsewhere.

First, as budm mentions you need a DSL micro-filter or two. The high carrier frequency of DSL (25-138 kHz upstream, 138-1,107 kHz downstream) causes phone equipment to make strange noise.

Also, what is the power source for the Vocaliser? Hum and noise can get in from that power supply (path) too. Is the Vocaliser earth grounded? Best is a linear AC-adapter with a ground connection.
You can measure AC volts between either leg on the phone line and the DC side of the vocaliser to see if you have high level hum and noise coming in - which can overwhelm the telephone line transformer.