REDDI DI

[theokbird]

Hey all,

i moved my hum problem/questions over to the Predict build thread, where i'm now trying to diagnose and solve this hum problem. 
HOWEVER!!:
i've made some headway, which is I disconnected the gain pot and, voila, hum reduced to basically nothing-  but -now i dont have a gain control....any thoughts as to what could be the problem?  do i need to use shielded cable for the gain pot connection?

is there a quieter way to implement a gain pot in this circuit instead of strapping a rheostat across the output tx secondaries?

i'll stop posting over here and continue over on the Predict build thread, but I wanted to just ask over here, to improve the odds of someone chiming in...
thanks everybody!  and damn this DI sounds GOOOOOD!! 

-okbird

 

[ruffrecords]

In the original implementation, this pot just gradually shorts the secondary of the transformer. This alters the loading seen by the tube and changes the distortion so as you turn down the level the distortion increases. To be honest I never quite understood the benefit of doing it this way. As the tube loading increases it is possible the tube current ac increases which places a larger load on the power supply which may introduce hum.

I would recommend re-wiring the output control so it acts as a potential divider. You can keep it wired much as it is but just add a 470 ohm resistor in series with each transformer secondary wire on its way to the pot. This will make a low cost balanced output fader. The signal level is high enough that it should not be necessary to screen the cable.

Cheers

Ian

 

[GlassBass]

This is exciting! I just finished building my first proper bass, now I would like to try building this. Are Pcb's available? I am unclear on the transformers too... just signed up, digging the forum.

 

[MicDaddy]

that is indeed the 100 EI lam, sq stack,

By "square stack" does this mean that the core height is equal to the tongue width?

winding area for a 100 EI bobbin is  1 1/4" by 3/8"  = .4687 sq in.

Edcor EI100 bobbin window range from 1"x1", 1"x1.25", 1"x1.5"  not finding anything with a window 1.25"x3/8"

I've seen comments on keeping the core between square and a stack height twice as high as the tongue is wide?  Just not sure, do I shoot for a larger window bobbin on a larger stack, or run with the 1"x1".....  have since given up on the recycling of old laminates.... disassembly is 

 

[ruffrecords]

This is exciting! I just finished building my first proper bass, now I would like to try building this. Are Pcb's available? I am unclear on the transformers too... just signed up, digging the forum.

There are lots of ways of building this.Some people have done point to point, some people have used my poor man's tube gain make up PCB and others have used a complete PCB kit supplied by another member.

Cheers

ian

 

[CJ]

orig xfmr has a 1 inch stack,

 

[MicDaddy]

orig xfmr has a 1 inch stack,

Thanks CJ,

I was confusing core "window" with winding area. 

sidebar for anyone following for the transformer stuffs, this has been helpful as well as RDH4 http://www.geofex.com/article_folders/xformer_des/xformer.htm

 

[MullisMan]

Hi all,

I'm relatively new to this forum but I've been reading through this thread. Great contributions from everyone involved!

I have a question about the ground lift. I saw in one of the modified schematics a ground lift switch connected to pin 1 of the XLR output. I've read various articles from Rane (http://www.rane.com/note110.html) and others that Pin 1 of the XLR should always be connected to chassis ground. The method from this thread shows lifting that connection.

My question is, how is it being implemented in the original RED DI? I've attached one of Dirty Garry's pictures and it looks to me as if the ground lift switch is breaking the ground connection between the IEC power connector and chassis ground.  Is this safe? It looks like the toroid transformer is connected to the ground pin of the IEC connector and then the IEC connector runs to ground via the ground lift switch.

Any insight? I'm wondering how to implement this in my own build. I've read that just lifting Pin 1 of the output XLR doesn't always solve many ground loop problems.

Thanks for this awesome thread.

Jeremy

 

[dmp]

That looks like a safety violation to me. The ground prong should always be connected to the case, especially in tube gear with lethal voltages.
As to the pin1 on the XLR, people do different things without creating danger, but the Rane recommendations are good.

 

[MicDaddy]

here is the 100 EI version that goes to 60 K hz>

Why are secondary layers in parallel and not series?

Why the reverse wind on half the primary, is this to fight off EMI or act humbucking? 

Is "reverse wind" simply a change in the direction of the arbor rotation from CCW to CW or vise versa?

Why no reverse winds on the secondary?

Now a technique question... when winding a transformer that consists of sec-pri-sec-pri-sec, how does one handle the leads from the sections windings?  Some bobbins have the little solder pins, others make connections on paper and under tape near the outer most layers?

I think I'll start with little bits of trade show sticky note strips and write ,for example, "Pri ccw S" & "Pri ccw F" which would inform me that this winding is the Primary Start or Finish, and which way it was "turned"... then identifying for each section of primary secondary etc...and finally terminating properly.....  learn by doing I guess.

 

[CJ]

i noticed a tad bit more inductance with one of the primary winds reverse wound,

this means a bit more bass, which is what you want for a bass DI,

reverse winding one of the secondaries did not seem to improve either hi or lo end,

you just try different coil structures and turns til you get something good,

 

[MicDaddy]

CJ, for the DIY 100 EI drawing;

What does the added capacitance (I believe leakage capacitance?) from not using a two compartment bobbin do, lose some top end?  For a two chamber bobbin is it correct the leakage capacitance is 2^2=4 times less than a single chamber bobbin?  How or what kind of math is needed to see what this does to the frequency response? 

edit: looking back I found this "split bobbin for 1/4 C-d,"  is C-d leakage capacitance shorthand?

What is the minimum insulation requirement between windings/layers, for the DIY 100 EI?  Insulate every layer, between only each winding?  One layer of tape?  Electrostatic shielding? Taking on apprentices?  ;D

I've got all the bits to slap something together sans the dual section bobbin. 

 

[CJ]

you need insulation between the primary and secondary because there is no blocking cap in the circuit, that means you have high voltage on the primary and sometimes the secondary gets grounded, so you need to isolate those 2 windings,

magnet wire is good enough nowadays to wind the primary and secondary  layers right on top of each other,

 

[MicDaddy]

CJ,  I'm continuing my progress on the EI-100.  No split bobbin here, so I wind the full 1362t secondary-->2500t primary--> 1362t secondary--> 2500t primary(rw)--> 1362 secondary. 

Secondaries are all 3 paralleled
Primary terminated as Start to Finish--Finish to Start (with the tube plate lead (start) being buried.  I'm sure there is some strategy here to bury this plate connection, but what happens if this plate connection is on the outer part of the winding?

I'm going to attempt another with increased insulation layers between windings to try some of this..no free lunch what can I expect to lose here or otherwise what might suffer?

you set up the frequency response of the coil with insl. layers, if you have too much hi end roll off, you increase the distance between pri and sec sections, this is done by adjusting the amount of insl til you get a flat response, or whatever response roll off you are hoping for,

 

--------------------------------------------------------------------------------
Now for a split bobbin, do I have this correct?

Section 1  681t sec > 1250t pri > 681t sec > 1250t pri > 681t sec
Section 2  681t sec > 1250t pri > 681t sec > 1250t pri > 681t sec

Sections of secondaries would be terminated as follows;
Section 1 secondary (start--finish) > Section 2 secondary (start--finish) with each completed secondary then terminated in parallel.

For the Primary side on a split bobbin;
Section 1 primary (start--finish) > Section 2 primary (start--finish)
For a total of 2500turns.
Then do I terminate the finish of this back to Section 2 primary (finish--start) > Section 1 primary (finish--start)
------------------------------------------------------------------------------
Main Question for the VTB2290 & (2291)  I want to "transpose" this onto EI-100, easy way to do this or everyone gets a chuckle watching me try to figure it out  ;D

 

[CJ]

you want to fill up the bobbin equally as you wind,

so wind a 681 section in the first chamber, don't cut the wire, just pass it into the next chamber by way of a slit in the middle flange,

do the same with the pri section, 1,250 and 1,250,

this way you will save a lot of splicing,  and if using a DIY flange, the wire will not put pressure on the middle flange sides as you wind,

you can make your own two chamber bobbin, just cut up some cardboard from an old album cover (vinyl LP for young folks)    or find similar material in the recycle bin, use the bobbin to trace the inside and outside with a pen, get a small pair of scissors and trim it to fit around the bobbin, cut a slit in it so you can slip it over the bobbin, you can use this slit to also run the wire thru to the next chamber, tape the cardboard in place and don't wind all the way to the wall as this might move the cardboard,

winding this way will save you a lot of hookup pain,

a sharp eye will see that the middle sec is 1370T, instead of 1362T, this is to get the middle wind to put out the exact same voltage as the inner and outer winds, the middle sec does not link up to the core as well as the inner and outer winds, so we add turns to increase voltage a bit, since we do a parallel hookup, we do not want the sec winds to fight each other, kind of like matching output tubes,  a fussy tweak, but WTF, over?  ;D

98,750 is a ref number for the backwards running counter which is mechanical and cannot be reversed,  (we flip polarity on the DC motor instead of flipping the coil)


step 1-trace the DIY flange>

 

[CJ]

trim to the outside of the inside trace, and slightly to the inside of the outer trace,

this will keep the outside of the flange from getting in the way of the lams, as sometimes the DIY flange will shift itself a bit outward and it is dangerous to trim it after winding as you might nick the wire,

it does not have to be a perfect fit on the inside as the wire will quickly fill in the voids, otherwise you will spend all day re-cutting which will fatigue the cardboard,

 

[CJ]

tape it in two places on each side, use about an inch of tape and lay it on top of the flange, work it down the flange and across the bobbin, try not to leave slack at the bottom of the bobbin as this will take away winding space,

make sure you do not leave any tape in a place that will snag the wire as you wind,

that is all there is to it, the magnet wire will hold the DIY flange tight after you get some turns on there,

 

[MicDaddy]

8) sweet, guess what I'm doing tonight.  \m/  Split bobbin party with the kiddos.  I had my two oldest in the shop last night (6 & 8yrs ).  They say you only know as much as you can teach so we were winding coils, reading wall AC voltages and trying to get a grasp on what exactly are these things these transformers, the concept of step up step down voltages in wall warts etc.  The most fun for them was to watch the machine actually wind at 2000RPM.

On your revised drawing your primary says #32    Is that correct?  Quite a jump, not sure if my skills are going to be able to fit that on there for 5000T + the secondary windings.  Much to be learned in the technique arena. 

To find the "ideal" voltage output from your middle secondary;  is this as easy as wind up the first layers, secondary/primary and then for this middle secondary you can wind say 1370, then stack it up and send a voltage and compare the two voltages, add or unwind turns as needed until they match.... I suppose the same could be done then on the final secondary.

How much margin, if any, do you allow?  I have been winding end to end within the window allowing no margin on either end.

The tape I've been using is the stuff I use to mask parts for powder coat.  It's the green mylar/PET stuff probably far from ideal.  The paper is generic kraft paper from the hardware store.

 

[CJ]

#36 primary, #38 secondary,

no margins on a nylon bobbin,

you can leave the sec leads and stack the core, measure voltage, then solder,

 

[MicDaddy]

CJ,

Regarding back and forth winding;

Do I need to keep all windings' starting points on the same end of the bobbin?

Any problem having secondaries starting from left winding left to right back n forth, with primaries starting from right winding right to left back n forth?

This latest one I notice some rise at the high-end coupled with severe roll off immediately after... doing some reading I'm suspecting something to do with damping and capacitance..