Q about speaker simulated balanced line out.

[bakerlite]

Hey folks - attached is rough layout schem for speakersimulated (use that term loosely) and more importantly balanced line out - very handy .
A few questions though as its above me!
Why is this layout specificaly for 8ohms?
If just incorporating into an amp would i have to be careful about where I make the ground connections to avoid picking up unwanted noise
What transformer would you reccomend for this?

[soundguruman]

Well, I would not make a habit of clicking links in this forum, but the 8 ohm load is generally on the speaker, and the line out is tapped off the speaker jack.
With the speaker at 8 ohms, the line out is determined by the ratio of windings in the DI (unknown) transformer, and is not 8 ohms.
You have to select a transformer with the appropriate output impedance, like 600 ohms, or whatever you are interfacing.
Generally, consumer grade cheap transformers have poor frequency response, and sound like a telephone. Better transformers with good frequency response are very large and heavy, expensive.
It is more cost effective in many cases, (and sounds better) to mic the speaker instead of using a DI.
Also a third method, the speaker emulator, simulates the action of the speaker, and provides a more "hi fi" type of DI output. But still I don't think, as great as, mic on speaker.

[bakerlite]

Maybe not quite as great as micing for sure but close enough - infact i've used this box between my amp and speaker on a tiny 5watt amp I use and is just superb (for my taste anyway!)
Strange I thought the crimson Transformer looked pretty good quality.

The crimson 4000b a 1:1 transformer so reflects what it sees -

SO for it to work in the application i wish the curcuit preceeding the transformer has to take the 8ohms that it sees on the speaker jack and change it to/under 600ohms.

I guess my question was how does this circuit do that ?

here's the schem

and sorry did I do something wrong by posting a liunk? Sorry if I did - i hadnt seen it in the forum charter.

[J M Fahey]

Why is this layout specificaly for 8ohms?

Who says so?

If just incorporating into an amp would i have to be careful about where I make the ground connections to avoid picking up unwanted noise

Yes.

What transformer would you reccomend for this?

The best you can buy.
Check Jensen transformers and similar quality suppliers.

SO for it to work in the application i wish the curcuit preceeding the transformer has to take the 8ohms that it sees on the speaker jack and change it to/under 600ohms.

No, it does not work that way.

I guess my question was how does this circuit do that ?

It doesn't. See above.

In fact, I guess you read the parts values wrong, it's a very strange circuit and raises many doubts.
Examples:
1) the 12nF cap in series with a resistor of 6800 ohms kills all frequencies below 2KHz , at 6dB/Octave.
2) the 12nF/470nF form a capacitive divider (not exactly a popular circuit for other reasons) of 40X attenuation, within a certain band of frequencies.
3) a "682J" inductor value is 6.82uH
It has a resonant frequency , with the .47uF capacitor connected to it, of 89kHz , "slightly" above the audio band.

So this schematic raises a ton of questions, so say it kindly.

[soundguruman]

NO QUESTIONS ACTUALLY, LINE OUTS GENERALLY SUCK, as far as sound quality.
I have seen every manufacturer try to make one, and they all failed in the most miserable fashion. They all sound terrible.
The manufacturer who built the microphone (SM57) "into" the cabinet was the only one with a CLUE.
If you want a Jensen transformer, get ready to pay through the nose for it. I can't imagine why anyone would spend so much money to get "that" result.

[Steve Conner]

So this schematic raises a ton of questions, so say it kindly.

To say it unkindly, it looks like a piece of

To be fair, I would read 682 on an inductor as 6.8mH, which is more sensible. 6.8uH would be "6R8".

But the reason why you can't figure out the transformer spec is that the impedance and insertion loss of the circuit is ill-defined. The designer never thought about it.

Here's my own speaker simulator circuit. The transformer is very well specified, I even gave a part number, although it hasn't been manufactured for a good 20 years.

A simple speaker simulator

[Steve Conner]

So this schematic raises a ton of questions, so say it kindly.

To say it unkindly, it looks like a piece of

To be fair, I would read 682 on an inductor as 6.8mH, which is more sensible. 6.8uH would be "6R8".

But the reason why you can't figure out the transformer spec is that the impedance and insertion loss of the circuit is ill-defined. The designer never thought about it.

Here's my own speaker simulator circuit. The transformer is very well specified, I even gave a part number, although it hasn't been manufactured for a good 20 years.

A simple speaker simulator

[J M Fahey]

Dear Steve C.
1) thanks for sharing the schematic, I love the minimalist approach and use of "undocumented features".
2) I originally also thought in the milliHenries range, but Mr Google proved me wrong.
When you search for "682J inductor" it offers answers such as:
INDUCTOR FERRITE CORE 6.8UH SMD - 1210-682J

682J is the part value written on its body and 1210 is an SMD size code.
Live and learn !!