colt

L-pad on 1176 instead of T-pad
« on: July 06, 2016, 01:12:38 AM »
THis is my 1st post and I am a complete n00b in this field. I did some searching online and GroupDIY, but couldnt really find an answer.
I am really curious as to why we need a T-pad at the input stage of the 1176. Will an L-pad attentuator work just fine?
This question is bothering me because from what I have been reading online, in the context of (non-tube based) audio equipment, impedance mathcing is not really of intererst (because its not so importnat to have Max power transfer). In this case it doesnt seem very important to have a 600ohm matching (which I believe why we have the T-pad for).
What will happen if I just use an L-pad instead?

Thank you. 


Re: L-pad on 1176 instead of T-pad
« Reply #1 on: July 06, 2016, 02:53:50 AM »
Will an L-pad attentuator work just fine?
yes.
Quote from: colt
What will happen if I just use an L-pad instead?
slight rise in high frequency response.

colt

Re: L-pad on 1176 instead of T-pad
« Reply #2 on: July 06, 2016, 03:15:09 PM »
Thanks gridcurrent.

So is my understanding correct that 600ohm matching is not needed?
Also, in most schematics for 1176 I see online, I see that the T-pad used is UNbalanced (either bridged or straight). SHouldn't it be a balanced pad? WHy is using an unbalanced pad OK?

EDIT: I found this doc online -- http://www.prosoundtraining.com/site/wp-content/uploads/2010/02/Pads_101.pdf
It mentions something about this -- see attached excerpt -- but  I am still not clear on why it is OK to use unbalanced pad.
« Last Edit: July 06, 2016, 08:28:59 PM by colt »

Re: L-pad on 1176 instead of T-pad
« Reply #3 on: July 07, 2016, 02:50:04 AM »
So is my understanding correct that 600ohm matching is not needed?
matching not needed.  we do need to "feed" the O-12 with 600/500 ohms or less. 
a 600 ohm  L pad will provide a fixed input impedance to the source, the output Z will vary from the actual source Z to zero, which keeps the O-12 quite happy.
Quote from: colt
Also, in most schematics for 1176 I see online, I see that the T-pad used is UNbalanced (either bridged or straight). SHouldn't it be a balanced pad? WHy is using an unbalanced pad OK?
the input of 1176's from early stripes to "F" and most of the re-issues is 600 ohms terminating,
technically unbalanced, but floating.
for all intents, any driving device will "think" of the 1176 as balanced.