603 Royer Mod Transformer Wiring

Hi guys,

Can anybody help me out with wiring a Vigortronix VTX-101-007 1+1:1+1 transformer for an MXL 603 SDC Royer Mod? I'm trying to wire it as a 1:2 but put it in the circuit in reverse, effectively making it a 2:1 trafo.

Here's a datasheet - http://www.farnell.com/datasheets/337936.pdf

My guess would be to link B1 and B3, B4 to + C8 (2.2uF WIMA) and B2 to ground. On the other side A2 and A3 to XLR out pin 1, A4 to XLR out pin 2, A1 to XLR out pin 3.

Is this correct?

Kris

Enchilada:

A little unclear about the "and" and "," in your description below.  But here is how I think it should work.

Assuming you are using the Secondary as the primary, and thus want the output of the tube on the B side, and the XLR on the a Side. 

Then I think this would be wired as follows:

Primary side:
B4 tied to tube output (From C8).  B2 - tied to - B3.  B1 tied to ground.

Secondary side:

A1-tied to-A2-Tied to XLR pin 3.
A3-tied to-A4-Tied to XLR pin 2.

Ground - Tied to XLR pin 1

SCR - Tied to Ground

(Ground, XLR Pin 1 and B1, chassis and Scr are all tied together)

Do not tie the transformer secondary to ground in any way.

This wiring has the effect of reversing polaritiy as well, which is intended in the original royer schematic because the cathode follower inverting phase.  So this wiring corrects that and puts it in the conventional Pin 2 hot phase.



There is one other thing, that someone far more knowledgable than me can weigh in on.

You can reverse the primary wiring and make it:

Tie B3 - Tube out
Tie B1 to B4
Tie B2 to ground

The result is the same for some winding types, and slightly better or worse for others.  It is all a little beyond my knowledge but if the windings are in layers, some layers are better choices to be tied to ground than others and result in (to my understanding) lower insertion loss.  The type of winding is not specified on the spec sheet and so I am not sure how you would choose.

You are correct, I am wiring it in reverse (the secondary as primary). Sorry, I didn't describe it very well in my original post. Perhaps this will make my first guess more clear:

Primary:
B1 tied to B3
B4 to + C8 (2.2uF WIMA)
B2 to ground.

Secondary:
A2 and A3 to XLR out pin 1
A4 to XLR out pin 2
A1 to XLR out pin 3.

Looking at your suggestion it appears I was way off. I don't know much about transformers so I'll take you direction.

Is there any way I can by looking at it the type of winding? If it helps, it's basically the same as this trafo http://au.element14.com/oep-oxford-electrical-products/a262a7e/transformer-audio-1-1-1-1/dp/1689035

Re: Winding differences.

Ignore what I said about the type of windings, (I may be talking out the wrong orifice), it is an issue I don't fully understand (My memory is that if there are layers, that you want to connect the grounded side to the inside winding for some reason), but that information is not specified, so just assume that the end on the bottom on the diagram should be grounded.  And I may have that backwards.  I will try to find where I found this information, but it really will work either way, it was just a small incremental benefit (and I forget if that benefit was in interwinding capacitance or insertion loss or leakage or what).  If it mattered, and the manufacturer knew which way it should go, they probably put it that way on the diagram.

http://www.farnell.com/datasheets/337936.pdf


Re hooking it up:


As far as your suggested wiring, B1 and B3 are ends of the same winding.  Shorting those together is not correct.  The little "hump" in the line from B3 indicates that it jumps over the line from B2, if that helps.

Here is an explanation of the diagram.

You will see that there are two secondary windings and two primaries.

One winding has ends at B1 and B3, the other has ends at B4 and B2. 

The little dots indicate which end of the windings "are in phase" that is, if you run AC into one winding, the Voltage induced in the others will be HIGH on the dot end when it is HIGH on the Dot end of the one you are running AC into.  (Of course how high will depend upon the amount of turns in each winding - more turns = higher.  In your case, everything has the same number of turns.)

You are trying to get 2:1 ratio, and all your windings have the same number of turns (this is not stated, but is implied by the specs ... 1+1:1+1 and all the 600's)

So you want to put two windings in series (longer windings ... think higher resistance, higher impedance, higher voltage  lower current).  So make your primary by connecting two windings in series into one long winding - starting at B4...ending at B1

You want lower impedance on the secondary (shorter windings, lower voltages, lower resistance, lower impedance, higher current).  So you connect the windings in parallel (keep the dotted ends together of course).    So you make your secondary by connecting one end to A1 tied to A2,  the other to A3 tied to A4.

So that's the simplified view... I hope it helps.  But if you already knew all that, I mean no offense.  There is a great document: http://www.jensen-transformers.com/an/Audio%20Transformers%20Chapter.pdf ... which is worth reading... I still don't fully understand all of it, but most of it is clear, and I am trying.

Enchilada said:

Hi guys,

Can anybody help me out with wiring a Vigortronix VTX-101-007 1+1:1+1 transformer for an MXL 603 SDC Royer Mod? I'm trying to wire it as a 1:2 but put it in the circuit in reverse, effectively making it a 2:1 trafo.

Click to expand...

It's been awhile, but from memory the Royer SDC is a cathode follower, so the 2:1 ratio sounds very low. Looking at the transformers in your list I'd use at least the VTX 101-002 stripped as 4:1, or even 101-003 as 6.45:1. Looking at those transformers Pri Z vs. their respective DCRs I see quite a bit of discrepancies. What is the price for those?

Best, M

Thanks bruce0, that was a very concise explanation. No offence taken, I've still learning and can use all the help I can get.

Marik - the VTX-101-007 is $14.86, the VTX-101-002 is $35.89, VTX-101-003 is $14.75. I've already got two of the VTX-101-007s. If the output is too hot should I switch it to a higher ratio?

Kris

Those are good prices, where do you get those, I might play around them.

Note that the original royermod2 article calls for using a Jensen MB-D mic splitter (1:1:1 - three windings) with 2 secondaries in series as primary, and the primary as the secondary.  So it runs at a 2:1 step down ratio I think.

I would not disagree with Marik, who knows more about this stuff than I do but the article says the cathode follower has a typical output impedance of less than 1000 ohms, and that the tube has no gain in this configuration (attenuates 10% approx).  So I would not worry about the levels being too hot. 

I think it will work, Impedance of your transformer is a little higher than the MB-D, and it doesn't have the faraday shields as far as I can tell, but I think it will work.

www.element14.com Just enter those part numbers.

I'll give it a go and see how out sounds.

.

PRR said:

.

Click to expand...

So you're saying I definitely shouldn't wire the transformer in reverse?

Keeping primary primary is fine too (I would defer to PRR on this) I don't know what the effect of reversing is.  But using this wiring...in the SDC Royermod remember to connect  the junction of B4 and B3 to XLR pin 3.  This uses the transformer to reverse the phase (Positive swings become negative), which is required to keep the mic in "Pin 2 hot" polarity, which is the convention (that way it will match the other mics in your collection).

PRR: Thanks for the guidance...  Do you know if there is a difference between using the primary and secondary as the primary?  The backwards wiring was suggested at the beginning of the thread, which I thought was because the DCR of the secondaries was higher, and she/he was trying to minimize the load on the tube (Does using the lower DCR winding as the primary reduce insertion loss?).  I am interested if there is a difference between which winding gets used as primary, I have looked around online and can't seem to find much guidance on that, or on the difference between the primary and secondary windings of transformers.

Also if you know about which end the two secondary windings should be connected to ground on the "headamp" (primary) side and why it might matter.  I read it somewhere but can't seem to find it, basically I think the idea was that the voltage swing the ungrounded end of the winding was much greater (swing is 0 at the grounded end and full signal at the ungrounded end) and while the currents are the same at both ends, the voltage is related to capacitive effects and so it was better to use the winding with the least capacitive coupling at the ungrounded end.  Have you ever heard about this type of thing, I read it once (I think it was in a guitar amp context) but I can't find any reference to that either.  (of course if the winding is not layered, like in a bifilar/multifilar winding, there would seem to be no difference in which end was used.)

I notice this transformer has a "screen", does that imply a faraday shield?  If so, that would seem to imply that the design of the transformer was layered and not multifilar.  This transformer stuff is still a bit of a black art to me.

Any advice or links on this would be appreciated.

This transformer is unshielded but comes with an optional can, which I did not buy, that is attached to the shield pin.

BTW, I'm a bloke. Kris is short for Kristoffer.