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In Reply to: RE: Interstage transformer to 600R recommendation needed posted by Joshua_G on December 06, 2013 at 13:37:02
If you use the C windings side of the LL1692Aas Q does, the DC resistance is 690 ohms.
The data sheet says 95H for 18mA and calculations give an approximate 75-80H primary inductance for a 22mA gap.
If you look at the data sheet for the LL1620/1623/1627/9202, at the bottom of the third page there is a calculation for "small signal" (response low frequency limit) bass roll-off. I'd give you the answer here, but the text nature of the forum makes it very difficult to communicate equations.
Kevin Carter
K&K Audio
www.kandkaudio.com
Follow Ups:
Hi Kevin,
Thank you.
My math is quite rusty. I tried to fiddle with the equation from Lundahl datasheet, though I’m not sure I’ve got it correctly.
I came up with the following formula, to find out Low Frequency 1dB roll off:
f =(( L*pi)/(R/2pi))*2pi
Is it correct?
Sorry, but I don't like interpreting ASCII equations, because I usually do it wrong compared to the intent of the writer. So I will write out my reduction of the equation as I use it.
The Response Low Frequency Limit as defined in the LL1620 et al, data sheet =
the arithmetic parallel combination of Rload and Rplate divided by the multiplicative product of pi (3.14...) and the primary inductance.
Kevin Carter
K&K Audio
www.kandkaudio.com
Hi Kevin,
Thank you very much.
I got it and now I can calculate all transformers I’m interested in.
The LL1692A/18mA, in the circuit I intend to use it in, has –1dB at 5Hz, while the LL1692A/22mA has –1dB at about 6.4Hz, which isn’t bad at all, sufficient for my needs.
The LL1620/60mA, in the circuit I intend to use it in, has –1dB at about 11Hz, which is sufficient for my needs.
Edits: 12/09/13
Now it's just a matter of deciding what to do first... :)
Kevin Carter
K&K Audio
www.kandkaudio.com
Hi Kevin,
Thank you.
I got my answers.
Only there is one thing I’m not sure about, concerning the equations in the mentioned datasheet.
I believe that in Rprimary it means the reflected load of the secondary onto the primary. Is that correct?
Yes.
Kevin Carter
K&K Audio
www.kandkaudio.com
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