PCI audio mixer for hum-free line-in recording?

Better.

Welcome to the 21st century for line-level inputs. ;-)

I've seen how a LynxTWO performs in such a lotcation. Same-old, same-old.

One of the biggest problems in mixed signal design is doing quality audio on a board that also has TTL clock signals on it. Of course that describes just about every PCI audio card ever made. It also describes just about every standalone DAC, ADC, and CD player. Once that problem is solved, the rest follows.

Precisely define "tap on my home telephone line"? What exactly do you mean by this. What are you doing? What does it look like? Where did you get it? Does it have a make/model number, etc.?

In the USA, for example, it is not permitted to attach to the telephone line except by isolation & protection circuit . At the very least, this is a magnetically-coupled transformer, and also includes capacitors, voltage-limiting devices (varistors, diodes, etc.) and other components depending on what kind of functionality you are looking for.

This is an important question and all the other discussion here is dependent on this.

If you are somehow making DIRECT connection between the telephone line to your computer, THIS IS AN EXCEDINGLY BAD IDEA! You MUST use some kind of device to protect your computer from what is happening on the phone line. The ring voltage, (something approaching 100V AC) for example is particularly damaging to your computer audio card.

With a proper audio coupling device, you should not have any problems connecting to the input of most any computer audio system.

ISTR this must be a special sort of capacitor (reversible, tantulum, or something like that).

Could you or someone else please clarify this.

Correct, but 100nF isnt going to be tantalum, just plastic.

I'd suggest reading the information at

You'll want a cap rated at no less than 250 WVDC - a 400-volt cap would not be overkill. Plastic-film caps (e.g. mylar/polyester) are probably the best type to use.

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case

Hz

falling

Yes truly amazing, just a shame they couldn't be bothered providing ANY of the figures that you have.

MrT.

Or the second half of the twentieth century even :-)

MrT.

I use a USB sound adaptor for coupling my amateur radio tranceiver to my computer which is a pretty demanding application for digital modes. This gets the sensitive circuits out of the computer, much lower noise. Also, Radio Shack sells a small audio transformer that is ideal for isolation, can't find part number right now but it is pretty easy to find on the rack. That is if you are comfortable doing a little soldering to make up cables including the transformer.

This thread is a hoot.

Didn't they go through the dial-up modem craze in the UK? What's a cheap V90 modem go for now a days, $12? Don't they all have audio outputs?

Luck; Ken

Tantalums typically fail, sometimes violently if connected reversed. They are not used for this.

Use either a metal film (plastic) type or ceramic, rated for at least 250V. Metal film is preferred.

The guys above know their stuff! Something with a plastic dielectric - or even a ceramic will do. Nothing special in the way of polarisation - and certainly nothing as exotic/expensive/unreliable as a tantalum. A 250VDC rating is more than enough. Its there to pass the audio but to prevent the transformer shorting the service provider's DC supply - that's all!

John A

250V rating is actually marginal. That is barely 2x the peak ring voltage. 400V would be a safer rating. That is what I used last time I made a telephone line connection circuit.

You'd better tell BT to stop using 250VDC rated capacitors in this application, then.

Maybe you guys use lower voltages over there on your side of the Pond. Telephone lines are really pretty hazardous things, especially to solid-state equipment.

application, then.

Nope.

equipment.

Not that hazardous to plastic caps tho.

It's called a "voicemodem" it's a voice-capable modem, and the cheap ones approximate the desired price. There exists software to turn a PC into an answering machine etc.

Bye. Jasen

Not for appropriately designed equipment. Transformers are simple, easy, quick, and effective; about 20 years ago 100% silicon single chip solutions started to be available outside the telco manufacturing stream. I remember seeing all silicon SLIC (subscriber line interface circuit) about 30 years ago.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
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The transformer is no longer required, the requirement is performance based, and there are all silicon, resistor, capacitor solutions. They do take some expertise to implement. A transformer (better a store bought TIA or DAA) is quite the better solution for OP.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

I have never seen any normal PC sound card with isolation transformers built in.

Check the ground loop information and solving tips here:

Here you can find list of some audio isolation transformer products

--
Tomi Engdahl (http://www.iki.fi/then/)
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