NewYorkDave's Passive Equalizer

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thought i give some update on my eq plannings. i have been checking alot of different datasheets on cores, wiring diagrams, various threads about winding inductors. and i hope i make some ordering on all meterial soon.

reading some posts on the forum it seems that to high AL can cause early satuaration and that sounds a bit scary in my head. however, the db fall in the eq might keep the inductors far away from saturation with higher AL.

anyway, looking at cores, large enough to have enough turns with not to thin wire at moderate Al values, is not so easy it seems.

the largest inductors in the eq are the hard once to achieve under such demands.

cores with less AL have tighter tolerance and sounds like a good thing for a stereo unit.

also cores with a tightening screw, or at least a hole for a screw and  a nut, sounds like a neet thing for trimming the eq in he last stage. i was looking at the rm cores, the rm12/rm14 was bigger and would be good to house 1140 turns @ 630AL for the 820mH inductor but they dont have any hole so thoose plans went down the drain...

the rm10 has got threaded holes and screw but they are juuuuuust about to small for making the 67DCR requirement...

this NYD EQ is a demanding one :)

so right know the only core big enough with atleast a hole and not to high AL is a PM50 core. its a whooping 50mm in diameter, N27 material core. it will cost, with bobbin, about 18euro each. thoose are made for making power transformers. doesnt that have a nice ring to it?

i think the mid and high inductors ill use rm10 and perhaps rm7 cores. thoose are much much cheaper.

 
Two questions:

1) How hard would it be to add passive RC high-pass and low-pass filters to this? How would the effect the impedance and/or insertion loss?

2) Could this circuit be driven by a simple JFET buffer rather than a transformer? How about using a simple JFET (FETboy-esque) makeup stage immediately after without the output xfmr?
 
anybody has a number on the current rate of the tube amp?

PP 6CG7 usually pulls around around 16-18ma total but that doesn't really factor in to your choice.  Unbalanced DC  may cause problems, but it's not really a concern either because any good tube PP OT for small signal triodes will have that taken care of.  You just need to decide how much you want to spend.  I know Dave was thrifty and bristled up good at the thought of spending 100 bucks on an OT -  Much under 100 leaves you pretty much alone with Edcor's  offerings.  They do make a budget priced 15K:600 tube PP OT, but your EQ probably won't be flat to 20Hz.  So you'll have to crank the bottom up to 3 or 4 or something just to get flat response.  Sowter has at least one good 15K:600 OT with wide response.  Lundahl does too and I think Cinemag does as well.  Cinemag also makes a very nice 25K:600 which will work splendidly and may have have slightly less distortion, but you'll be slightly below unity gain too.  Hammond also makes a 20K:600 full range OT.  There may be some other modern sources for budget tube PP out there but I'm only aware of Edcor.
 
For your gain make up amp you could use my twin line amp board. This has two identical gain stages each with adjustable ttim pot gain. The output uses a £25 Carnhill VTB2291 output transformer wired 2K4:600 to drive a 600 ohm load.

Cheers

Ian
 
hi and thanks!

I'm having my eyes on lundahl ll1689PP and perhaps the amorphous version of it. costs a lot but I'm very interested in the sonic character  of those cores.

the newer carnhill 15k:600 transformers are also very interesting.

otherwise I'm pretty much in for the lundahals all they way through. they got so many variants for every need and I'm in the same country.

last night i rolled my first inductors. i have attached a picture.
 

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i have found a suitable input transformer for the eq. the lundahl ll1949. it has very low dc resistances on the windings and could work in both 4:1 and 2:1 configuration.

if id use it in 2:1, can i compensate with lower gain in the tube amp? or do you think i should stay with a 4:1 configuration?

I'm waiting for some more copper wire so i can finnish the largest inductors.  i had to make som changes since my calculations where not spot on, all the time but i was glad i made them anyway.
 
spools ready!  :)

big ones, pm50: 330mh+880mh - AL630 - 1146turns
rm10 on the sides: 33mh+150mh - AL630 - 488turns
one pair of p26: 18mh - AL100 - 425turns
and one pair p26: 3.3mh+6.6mh - AL100 - 257turns

wire resistance are well within Daves specs.
 

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oh..! thank you guys a lot!!! you really make my day!!!  :) :) :) :) :) :)

i couldn't do it with out you so its actually a proper groupDIY!!!

 
thanks lassoharp!

the pm50´s are n27 material AL630 tolerance 3% with a whole through the core

the rm10´s are n48 material AL630 tolerance 3% with a threaded hole through the core

the p26x16´s are m33 material AL100 tolerance 3% with a threaded hole through the core

i found em at mouser.

i used 32Awg 30awg and 28awg wire. the 32awg was prob not necessary.


i have no idea if the materials have different behavior sound wise. we´ll see in a couple of days how it sounds with out the tube amp!
 
the big once doesn't have any adjustment screws.

when i got one spool ready, i measured it with all the core halves in different combinations to get an idea of how to put them together in pairs to get similar results. then, with the second spool i removed or added couple  of turns on each wind to get it close to the first. when you measure the windings i think its best not to loose tension on the winding. i put on a bit of tape to hold it together, remove the spool, put it together with the core, scrape of some lamination and hook it up with alligators. then back on the winder, work it a bit more or wrap it together tight with some polyamide tape.
 
hi folks!

the greatest eq in the world is taking form slowly. still no sound though.

I'm waiting some parts so that i can make last measurements of the panel and inner layout.

meanwhile I'm trying to study tube basics. I've made a suggestion of a psu for the tube amp as well. its basically copying and pasting from stuff on the net but also what i got in my drawers plus whats cheaper and obtainable.

a simple and cheap  mos fet regulation for the B+, chip regulators for heaters and relays.  do see something that is going to blow or just not work out, please tell me!

the edcor mains transformer comes in two variants.
180vac 100ma + 6.3VAC CT 1.8A
180VAC 300ma + 6.3VAC CT 6A

i hope to use the smaller one but actually i don't know how much the amp will eat yet...
 

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i made some final check and calibration of my inductors and felt that i wanted to match the biggest once a bit better. one of them had measured around 850mH and the other 835mH so i thought id just take a couple of turns of from the one measured 850.

after taking of 5 turns, taped it together, put the cores back and measured it, i now get totally wrong figures. its down at around 90mH..! what the ...!?

its a multi tapped inductor with a 330mH tap and a total of 820mH. the 330mH winding still measures good...

everything looks like it was before except from two loose wire ends connected with alligators...

so i thought id try to remove the last winding completely and re make it. 5mins later its done but i get the same result.

even tried with other cores, no luck...  must be the first winding or something. but what could have happned? i don't get it... think ill make a new one.
 
Hej jakob!

I measure across the whole inductor just like i have done before. Checking with the big inductor of the other channel and that one shows the right values.

And if i check dcr it shows correct.

I connect the inuctors paralell with a cap and a series resistor. Feeding the circuit with a tone generator from the resistor. Checking across the inductor with oscilloscope and dmm. Then calculate the inductance with a web . I should se a peak frequency around 1.7khz but get about 5.4khz.

It measured fine yesterday before i started to rewind.
 
okey, maybe i found the problem. if i switched the ends of the last windings i get in the right  ballpark. it doesn't look right but maybe my eyes are fooling me...

but in that case i guess i just made my first transformer..! :) or justa wrongly coupled inductor... my head is not to fresh right now...
 
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