My 3 DUAL PULTECs - EQP-1a3 - Solid State

[maxwall]

Kevin,

Great info, I have not come across this info on finding the right core in most of my readings thu many posts. If and when i find the right core I will try to make these available. But now, I have to go thru the surplus cores to find the right one. wind them measure the inductance and hopefully find what I'm looking for.

I'll keep plugging away at getting the Pultec passive filter section.

I was at 125'th AES in S.F. and talked with a few vendors and there were a few reps who said they might have the passive filter section in schematic form , but I needed to email them. When I get this I'll post it for others to reference. Having this baseline establishes a level of confidence when assembling a EQ like this. I need to know I'm not building something that was reversed engineered with possible mistakes.
I always check my work when it comes to accuracy , its my way of keeping this DIY thing real and professional.

Is there a primer I can read up on for wrapping round cores so I know I'll get a accurate AL reading when I check inductance measurements you mentioned above ?

One additional note : Often when I tinker around electronics I have found the quarter sized round torrodial cores used as chokes in switching power supplies, are these cores different in composition to the inductor cores needed for a pultec inductor ?

 

[khstudio]

Hey,
Somebody - Needles - I think, sent me a PM about my faceplates.

I took the time to send the info to your EMAIL (link button) & it bounced back. :?
Just letting you know I tried.

 

[crisotop]

Awesome! Beatiful builds - congrats :thumb:

cheers
christoph

 

[khstudio]

[quote author="crisotop"]Awesome! Beatiful builds - congrats :thumb:

cheers
christoph[/quote]

Thanks for the compliments.

:green:

I'm loving these EQ's & can't believe what they do to things like Kick drum, Piano, Vocals, Snare, Bass... you name it but so far these are my favorite things.

Passive EQ's... now I know what all the fuss is about.

 

[emrr]

related:

Audio Cyclopedia regarding toroidal coils, as recommended for EQ construction:

...circular core composed of molybdenum permalloy dust mixed with a plastic binder, compressed into a doughnut under 200 tons-per-square inch. By the use of this type winding, coils with a Q of several hundred are possible. Efficiency is extremely high compared to other designs.

 

[maxwall]

Are these the toroid cores needed for a Pultec ?

http://www.cwsbytemark.com/index.php?main_page=index&cPath=206

 

[khstudio]

[quote author="maxwall"]Are these the toroid cores needed for a Pultec ?

http://www.cwsbytemark.com/index.php?main_page=index&cPath=206[/quote]

If you can figure out which ones will give you an AL Value close to 876... then I think they'd work well. Maybe you can call them?

I would NOT go any LOWER with the AL Value (because you'd need more turns & with the "876" AL, you'll need about 1300+ Turns for a 150mH Tap.

I wouldn't have a problem (myself) with a "slightly" HIGHER AL Value = Less Turns - BUT - the Resistance for each of your taps may be slightly off which will effect your BANDWIDTH Control (Compared to the Original) but I don't think this would make it sound bad, it's just not going to be EXACTLY like a Pultec. So unless you're trying to make an EXACT Clone, I would not sweat it.

Keep in mind that I wound a Ferrite Core too:
My MAX turns was 200+ :!:
& it doesn't sound bad at all & the resistance per tap is WAY off... so finding the RIGHT Core Material with a "Close" AL value will get you WAY closes than with the Ferrite Cores.

Someone else with more knowledge will have to help you figure out "Which" model to get from that site.

Also... don't be afraid to buy extra's... I'm not sure what their tolerances are, so there MAY be a few duds in an order.

 

[maxwall]

kevin,

Do you have the turn stops and dc's for the other taps. This would be
very helpful. I can't recall them listed anywhere.

150mH /DC resistance ? / turns 1300+
82mH / ? / ?
58mH / ? / ?
47mH / ? / ?
33mH / ? / ?

you wound your cores by hand, I see . I cant think of a easy way to wind a toroid other than by hand . A machine for this type of winding would be cross between a sewing machine and a lathe. Also, I noticed it does'nt require a sophisticated winding pattern to do these like other cores that use interleve patterns
(CJ where is you ? )


I think this site is a good place to start. These folks will even wind a inductor if you needed one. I'll have to call them and give them the core specs AL DC resistances , wire (awg) size and inductance taps needed. Even better 1-800 number so no time limit on talking to these folks.

The cores look dirt cheap, and a roll of wire for $10 , my kind of place.

 

[gevermil]

sorry guys , whats the proper hook up of the output transformer ?
150 : 600 or 250 : 600
thanks a bundle

 

[drpat]

...

 

[drpat]

...

 

[khstudio]

Wire Inductance DCR
Blue: 147mH 30.9
Green: 97.9mH 24
Yellow: 84.1mH 21.9
Orange: 50.9mH 16.7
Red: 32.2mH 13

Wound on a toroid core....


EDIT: fixed wire color
_________________
-Patrick

Found Here:
Pultec Inductors again...
http://www.groupdiy.com/index.php?topic=25482

 

[nielsk]

KH, you wrote that you did not servo the JLM hybrid input.... and I see no coupling caps. Have you measured for DC in the audio path?

 

[khstudio]

[quote author="nielsk"]KH, you wrote that you did not servo the JLM hybrid input.... and I see no coupling caps. Have you measured for DC in the audio path?[/quote]

No caps & less DC without the servo engaged.

All info about using the Hybrid is HERE:
From page 1 of THIS thread!

All 3 use the JLM Hybrid circuit for the input buffer - See Topic Here:
PULTEC - Input Options -Buffers- Imp - TX - JLM Hybrid opamp
http://www.groupdiy.com/index.php?topic=26790

I know I probably should have added caps (at least) to the inputs... but I know my studio & I'm aware of what gets plugged INTO them.
If I were building for others, I'd definitely add them.

 

[khstudio]

OK,
ALL this info is from Pat. Just to let everyone know, he spent a LOT of time researching, Testing & even buying, winding & trying about 30 different types of cores until he found a FEW of them that worked like his original Pultec.
His goal was to make an EXACT Clone BUT he did say that several of the other inductors sounded good too. PLEASE do not beat up Pat for info... He was kind enough to share all his hard work but will NOT hold anyone's hand thru their builds.
NOTE:
The below calculation is for an EXACT AL value of 876!!!

My inductors were NOT exactly the same AL value, so I had to do the math myself (& use an inductance meter) to wind my cores - using the calculations below... so EACH inductor will need to be calculated because of tolerances & AL.

this is the info he sent me:

As far as the Pultec inductor goes, here's the secret recipe:

The core that I used is black.
The dimensions are as follows:
Outside diameter: 23mm
Inside Diameter: 14mm
Height: 8mm

AL value of the core is 876µH. Test this by wrapping 100 turns around your core, then measure the inductance.

The wire gauge is #34AWG

Calculated turns are as follows:

32.2mH 606 turns
50.9mH add 156 extra turns
84.1mH add 218 extra turns
98mH add 78 extra turns
147.5mH add 240 extra turns

Turns formula:
N=100 x SQR(L/AL)

Where:
L= desired inductance in µH
AL= AL value in µH

So, for the 32.2mH tap...
N= 100 x SQR(32200/876)
N= 100 x SQR(36.75799)
N= 100 x 6.06284
N= 606.284 turns

NOTE that the Turns formula & calculation can be found by SEARCHING on the NET!

 

[khstudio]

re-post of what I said earlier:

Keep in mind that I also wound a Ferrite Core too (for my RED unit):
My MAX turns was 200+ :!:
& it doesn't sound bad at all & the resistance per tap is WAY off... so finding the RIGHT Core Material with a "Close" AL value will get you WAY closer than with the Ferrite Cores I used.

The moral of the story here is, that finding the ORIGINAL Inductor is not easy but using the info Pat shared with us, finding the right core material & a CLOSE AL Value will make a GREAT sounding inductor for a PULTEC or any Passive EQ. I wouldn't sweat finding the exact value BUT I also wouldn't go too much LOWER with the AL... Higher AL means LESS Turns. :wink:

Thank you Pat :!: :!: :!:

:thumb:

 

[gevermil]

Yes , thank you Pat for all the info :thumb:
kev too :sam:

 

[maxwall]

Thanks to Pat and Kevin for continuing this discussion and reducing the explanations and mathmatical material into something meaningful. This is probably one of the best inductor Q&A primer threads for the beginner as well as seasoned core winder I've seen in a while. I'm sure I have more questions , but for now its time to locate the core with the magic AL value.

I located some wire locally with a #33AWG , I was looking for #34AWG
like Kevin suggested , will 1 AWG off make a huge difference ? I'm assuming not , at least not too much in DCR hopefully.

Is there a AWG component to the formula above that tells me DCR for a given AWG size ?

Also, when creating the taps within the core with the colored insulated wire, do you just solder the insulated wire to the core wire and tape it so it wont touch any other points in the core or core wire ? then repeat the technique until all taps are made complete ?

Would the tape serve as a way to secure the tap to the core ? or was beezwax used for this purpose ?

By the way , is there a inductance meter geared for the DIY'er that is fairly accurate as well as affordable. A few have been mentioned in the past but I think those meters are out of production. any suggestions would be helpful as well as experiences. I've seen meters as low as $50 , does this mean beware ?

 

[CJ]

BK Precision makes an ok hand held meter.

To make a tap, just pull out about 6 inches of wire, the same wire you are winding with, divide it in half, twist it, put some sleeving over it and solder it to a pc board or terminal strip.
then run the pvc to the terminal.

I have solder joints on my inductors, but looking back, they could have sharp edges that can nick the next enameled wire turn.
If it is taped up, you do knot know if pressure is being applied in a bad way by the tape.
this fussy stuff is taken seriously by commercial winders, but for DIY, who cares, as long as it works and the house does not catch fire.

A side note, wire gauge is not an exact science.
Triple insulation will mic out the same as a single build, but it will have twice the dcr, since half the diameter is insulation, and not conductive copper wire.
And Phelps Dodge will be lighter for the same gauge as Essex, so when you order you have to keep that in mind.

You can get old stock wire on evilbay if you really wanna run this down, but it might be more fragile.

this is low voltage audio waves, so you only need a single build wire.

Insulation was not as good back then, so more insulation was needed to get the same voltage rating as the new fancy treatments, so do not go by voltage ratings, todays wire wqill be much higher, but the insl will be the same thickness.

kh, did you fix the clipping, or do you just watch your levels on the hybrid input?

measure an ac sine wave with 10 k, then with 620.
hold the pri V constant, see if there is a voltage drop with the 620 ohm.

only 1 ma flows at 10 k at 10 volts.

the same 10 volt audio drags 16 mils with the 620 ohm, or 16 times the current.

this can make the transformer respond differently.

interesting to note that the maximum flux density does not change with current, only voltage.

so if you have a 10 k resistor across 10 volts, and a 620 ohm resistor across the same ten volts, the transformer feels the same flux level, even though there is 16 times the current.

think about that for a while.

thats what i am going to do right now so i can fall asleep.

 

[maxwall]

Can I add CJ to the list of thankyouz

Dr Pat wrote : 150µF cap is a tant, so the “+” symbol should actually be to the right of the tant instead of the film.

Whoa , 150Uf Tant , thats a big one !!!