TEN81 2009 PROJECTS

yes. its all good. thanks. it was just a bit confusing is all.

very bloody interesting tho. i know what u mean. reverse eng these things has been fascinating. they designed sooo well. definitely worth the effort and expense.

heres another wider jpg of my earlier extrapolation.
http://ekadek.com/wp-content/uploads/2009/06/ekten818filta2.jpg
i got my thinking and self explanation a bit wrong tho. from your notes i can see  now that the bass filter has three filtering networks.  2 are progressive bass signal grounding type bass reduction networks alla sallen key hi pass filters . the other bass reduction action is (your r2) .. a feeding back reduction network to further cut bass ( which i guess is the  '2nd order'  part of your terminology " 2ND ORDER SALLEN KEY HI PASS FILTER".  

the 3 treble cut operative elements form the progressive "2nd order sallen key low pass filter" and the "ist order lo pass filter".  i think ive got that now.

the thing definitely works and sounds great anyhow. thinking about this reminds me of the issue i had with the circuit board. (tommytones b312 v3). the input to the first ba306 (pin 1) was shorted back to pin 91 by a slightly misplaced solder pad. so i had to separate that and hotwire direct onto pin1.A2  UNDER the board. commando style. heres the photo
http://ekadek.com/wp-content/uploads/2009/06/ekten829fault.jpg

In fact the whole circuit must be called a 3rd order hi and lo pass filter.

1st order filters are just passive RC´s followed by a buffer amp.
2nd order Sallen key´s introduce feedback trhu a cap or resistor.

sixtyniners query was about whether  lorlin switches that are available to him were going to be ok. and whether one can use separate gain pots in the eq circuits. its ok i reckon to use separate gain pots. it dosent alter the wiring much. as long as the gain pot is mounted close to the frequency switch on the panel i guess. it becomes impossible to fit the whole thing into 1RU then of course.. not that i'd want to do that again anyway. more space is better.

in regards the lorlin switches. well as long as they do the thing. 12 pos single pole for the midranges. that seems do able.

AND . The treble HIGH and bass LOW frequency switches are special switches!


the HIGH is  cumulatively shorting.
it starts with one cap attached at the highest freq and then ADDS  capacitors for each next freq shift downward.



the LOW is cumulatively UN-shorting
at the lowest position -  all positions are connected to the wafer.
and then it extracts a cap for each next freq shift upwards (going c/w.)


so.. i guess if you worked out all the cumulatively added and subtracted capacitor values for each position .. you could define the values to use just 1 capacitor (more likely 2 in parallel) and then u could use a NORMAL 3 pole 6 position switch. maybe the customizable  stacking wafer types available from RS and FARNELL .

crikey. i was wondering how any other builds were going.  what bass and treble switches are they using.

Very well explained bass and treble switches. The only way to use Lorlins is sacrificing the peak-shelf switch. In shelf mode only 2 poles are needed instead of 3.

must admit that the explain comes from TEKAY member. slightly different wording/english but essentially how he explained it in another ten81 thread. thanks tekay.
when i was first making the switches up i actually got it all wrong. i didnt really understand or notice the different wafer styles and mistakenly exchanged a bass and treble switch. man. that would have sounded weird.  i gotta say that the cumulative shorting and unshorting wafer styles are a great device for smooth operation. and efficient use of capacitors.  and  circuit board real estate.

Hello,
i'm looking for doc to build DIY81 eq.
nrgrecording is down !!!
thank you