Which Tannoys, folks?

[Reffc]

Yep the bypass cap should be 1.5uf. I used the Russian cold war versions, it's a PLIO cap and are amazing.. better to my ears in that position than an MR.

The 47R resistor is correct or as close as can be to 50R. But with an autoformer you can take that resistor out of circuit as the autoformer on one of the settings (can't remember which) is near enough the correct impedance.

I don't think that's actually accurate Joe. The autoformer has an impedance ratio across the coils between green/orange so the driver doesn't actually see 50 Ohms at all settings, only for the one where the ratio is 1:1. I'll double check that though as you've got me thinking. It's the "green" autoformer tapping that I'm emulating for the fixed inductor/ resistor values.

[The Black Adder]

Hmm.. ok. I'll take a look in to that, Paul. But I do know that some autoformer values were published wrong. It took someone to unwind an original autoformer to find it's correct values. The original circuit diagram knocking around on the net is wrong in places but the 50R value is consistent on both the diagram and the original crossovers.

[simonms]

Lovely build Paul, they look really beautiful and really informative regarding cross overs...nice to know someone in the country is experiencing similar headaches as me at at the moment They will surely be a credit to your clear expertise and knowledge.
This stage is frustrating, you just want to listen but the final details (as we agree) make all the difference, looking forward to more.

VB Si.

[Reffc]

Hmm.. ok. I'll take a look in to that, Paul. But I do know that some autoformer values were published wrong. It took someone to unwind an original autoformer to find it's correct values. The original circuit diagram knocking around on the net is wrong in places but the 50R value is consistent on both the diagram and the original crossovers.

That's true Joe but the 50 Ohm is only 50 Ohm at one of the settings. At all other settings the value is modified by the autoformer's impedance/inductance ratio and at the highest autoformer setting, it's out of circuit as the autoformer presents sufficient electrical damping to prevent HF ringing without additional resistance.

My comments are aimed at a fixed inductor value replacing the autoformer so the resistor value depends upon the tap you want to emulate as all taps have different inductance and all but one have a voltage lift too.

The only tap which is electrically flat is the green tap and that equates to 2.8 to 2.9 MH at 0.7 Ohms inductor resistance (as measured...I don't pay any attention to what might be stated on various internet resources as I'm basing all values on those as measured with my own original Tannoy crossovers) I'll check it out and make sure that the correct value is stated here to avoid confusion!

[The Black Adder]

That's true Joe but the 50 Ohm is only 50 Ohm at one of the settings.

lol... Crossed wires quite literally, that's what I meant. heheh

[Reffc]

Lovely build Paul, they look really beautiful and really informative regarding cross overs...nice to know someone in the country is experiencing similar headaches as me at at the moment They will surely be a credit to your clear expertise and knowledge.
This stage is frustrating, you just want to listen but the final details (as we agree) make all the difference, looking forward to more.

VB Si.

Cheers Si and I better appreciate now what you went through although yours probably took way more time than mine. I'm up to 230 hours now (design and construction) although the initial design was a major headache as it was from scratch. At least I have the plans now!

First listen will be tomorrow albeit using crossovers which I believe to have a few flaws on them, so I am expecting things to sound a little bright but with better bass response than before...we'll see! The little details are what matter and ultimately what trip you up. I've spent 80% of my design time on 20% of the design if that makes sense.

[Reffc]

lol... Crossed wires quite literally, that's what I meant. heheh

LoL

[The Black Adder]

I went through 3 crossover designs/variants/components/connections, you name it. Also 6 months of listening... It's hard work but great when it's right.

I'm happy to share the wealth if needs be...

[Reffc]

Hi Joe

Right, finally got to the bottom of it and I was correct first time round. It SHOULD be 34 (or 36!) Ohms on fixed inductor settings. The reason:

Look at the circuit diagram. the green tapping may be electrically flat (ie no step up) BUT the 50 Ohm resistor is not connected to the green tap, but to a higher one where the impedance ratio between taps is 1.4. That is the same as a reflected impedance ratio across a transformer, so you have to divide the 50 Ohm resistor value by 1.4 which gets you to 35.7 ohms (soz, not 34, but 36 Ohms...good job I checked )

As far as the rest of the circuit is concerned, if a fixed inductor value of 2.9mH is chosen without the autoformer, then the only correct resistor value that can be substituted is 35.7 Ohms but a value of between 34 and 36 Ohms should be fine. I'm using two 68 Ohm resistors in parallel as that's what was available to me.

It's a difficult one to spot and it takes patience when reading the original circuit diagram with the autoformer, which is why most people I think get it wrong.

[The Black Adder]

Ah.. yes, sorry. I forgot your using a 'fixed' inductor for some reason. I'm using autoformers... Sorry fella. That is correct with a fixed inductor.

Yes I remember the diagram now, in fact I had mine incorrectly connected at first before I looked at the diagram again. Well, noticing something wasn't gelling made me look at the diagram again.. lol, live n learn.