Royer mod w/ figure 8

[sbranco]

Hey folks,

I am pretty new to DIY. I am getting two B2 pro's with the thought of doing the Royer mod to them maybe with a couple changes suggested.

I saw that Duka did that with his B2 pro. I figure I will do this project first on perf board and then maybe try the full G7.

With a pretty good dual diaphram capsule (797), it seems a shame not to try and keep the figure 8. Is that a waste of time? and if not, has anyone done it?

Am I right that the U47 head amp used a plain switch on the mic to get cardiod and omni while the G7 uses varying voltages from the psu to get all three patterns.

I think Zebra50 suggested in an old thread to borrow that part of the circuit from the G7 to vary the voltage to obtain figure 8. I think he said you would need an extra resistor and a cap to ground.

However, that old mic building article by Debenham, Robinson and Stebbings in the Mic Meta, Fig. 6 seems to indicate that a simple three position switch with a few resistors could provide all three patterns.

A few questions:

Is the varying voltage way better because you connect more directly to the tube? ...because remote switching is desirable?

Remote switching doesn't seem that much of an advantage to me since the psu must be kept close to the mic anyway.

If I go either way, do you think I can still do it on perf board wiring point to point? One advantage of the Royer was its simplicity.

the B2 pro body is about 50 to 56 mm diameter.

Thanks for any input. I am electronically challenged but I am reading the meta's and searching the board but haven't figured this one out yet. Thought maybe I would reach out for help.

 

[sbranco]

OK I think I have answered one of my questions. It looks like the signal you are amplifying is coming from the backplate. So whether or not you bias the back electrode should not affect your ability to wire the backplate to the tube in the air. Of course, I am hoping if I do the Royer mod that everything will be in the air.

I can see how the cardiod and omni would not present too much of a problem. For cardiod I simply bias the back electrode same as the backplate. For omni, bias the back electrode same as the front electrode. Seems like that could be accomplished easy enough with a switch on the mic.

The difficult part is getting double the voltage to bias the back electrode and trying to keep it simple. Perhaps using a voltage doubler circuit?

Is any of this making sense or am I speaking from ignorance? Well OK I KNOW I am speaking from ignorance but does it make any sense at all?

Looks like some have even wired a G7 on bread board. Is it that much better that I should just abandon the Royer and go with the G7?

 

[rpd]

Mojave doesn't offer the Royer Mod kit any more, I was wonder where you can get info on this? Kit, schematic, parts, ect.

Anyone?

Thanks
Ryan

 

[sbranco]

Do a search on this board. Go to the top, click search and type in royer. Or you can click on the Meta at teh top of the page and then click on the link for the microphone meta. Eventually you can find the original article by David Royer in Tape Op magazine. That has the schematic and some directions. Other articles on this board will tell you about doing the mod without a pcb board. we are planning to do this on two B2 Pro's.

I would like to do the Royer with a switch on the mic for three patterns. I don't know why it would be hard to supply the rear diaphram with twice the voltage of the backplate to get the figure 8. But apparently there is some obvious reason that I can't see why no one is doing it or willing to talk about it.

 

[Guest]

sbranco, I haven't build the Royer circuit... but have a look at the ELA M251E schem. That will point you in the right dirrection to get cardioid, omni, and fig 8 switchable on the mic. For PSU switchable pattern look at Jacobs power supply for the G7.
I hope this is somewhat helpful. :thumb:

 

[bigugly]

sbranco,

Here is what I've done.

http://groupdiy.twin-x.com/displayimage.php?pos=-393

It is a hybrid of the G7 and the Royer. I've built it using a CEK12 from Peluso and the body of a Marshal MXL 2006. Sounds very nice.

You can use the G7 PSU but the 10k resistor between the 2 big caps on the B+ needs to be increased so the loaded output is 125v. Also, Jakobs pin #'s for the connectors are different than mine.

Hope this helps.

James

 

[sbranco]

You guys are awesome. Thank you for sharing your insights. We are getting into DIY but hopefully that doesn't mean do it from scratch. I want to build on what has already been done - especially since I am not an electrical engineer. That is really useful info from both of you guys. Now I can dig for info on the ELAM 251 and the details from big ugly are like music to my ears. ELAM 251 or Hybrid G7/Royer, one of those is certainly going to be the ticket for our first DIY MIC project - Thanks for taking the time to post and help out.