Royer Mod power supply

Zebra50 had mentioned in a previous thread in the old forum (and on his website) that you could use a G7 power supply with the Royer Mod for a regulated heater circuit and a higher B+. I'm planning on build the Royer circuit, but with the added additions described on the same site http://www.omnipressor.com/Other/G7mics/multiMic.html

I understand the need for a regulated heater circuit, to reduice noise, however I'm curious at what sort of supply voltage the Royer circuit is going to work best. A U47 from memory runs of a 105V B+ supply. I think the original Royer designed power supply is in the same ballpark, though I don't have the schematic for it in front of me. The G7 supply pumps out 160V. I think I remember reading something about voltage change and impedance of tubes etc and setting the right voltage was imperative to the design. Do you think there is anything to be gained or lost by running this circuit at 160V instead of 105V?

On another note, did anyone archive the last soundking groupbuy thread? has anyone seen Perki? I'm hoping that it can get off the ground sometime soon as I'm also working on a u87ai style circuit and I need some capsules!

tim

I just got a pair of the MXL2001's (ala the Royer mod). I was hoping to get a pair of the PCB's from him to do this project for $20 each(as he advertised in Tape Op-albet very long ago). Anyway the nice folks (they really were nice) told me that they no longer sell just the PCB's anymore, but the whole kit's for something like $200 each. Way over my budget. Is it an ethical thing to try and recreate this mod here? Royer has done alot of great things and I'd really like to support his efforts, but it is a shame they're not selling the PCB's anymore because "some people couldn't follow the schematics and were disapointed" or something along those lines...Any ideas folks?

Here is the link of the Tape Op archive:

http://www.prosoundweb.com/recording/tapeop/tube_mic_25_3.shtml

Saxtim, are you using this circuit? Are you using one of his kits?

Also here is the full link which includes U47 schematics, etc:
http://www.prosoundweb.com/recording/tapeop/tube_mic_25_1.shtml
Joel

Saxtim, are you using this circuit? Are you using one of his kits?

Click to expand...

I'm not using a kit, I'm planning on using the circuit described here:
http://www.omnipressor.com/Other/G7mics/multiMic.html
which is as stewart commented on his website more or less based on the Royer Mod with a couple of extra stabilisation caps. If you visit the site you'll see that he has kindly provided his PCB for the circuit - I'm going to etch my own copy of this.

I actually just spent the day building a body for this mic - I bought a Nady LD condensor with the intention to build a U87ai circuit inside it. I need a new capsule for this, as it requires a dual diaphragm capsule. This mean I've got the orginal single diaphragm capsule from the mic spare so I thought I'd try building this circuit with my own body. Besides it's given me a bit of practice with metal working - the body I made today isn't half bad, and I'm planning on trying some G7s soon, so it's good practice.

This is incidently why I'm keen to use the G7 supply - I'm hoping to be able to use just one power supply to power a g7 and a royer moded mic.

tim

I have done his mod on a breadboard. The circuit is too easy to waste time making a board.

Hi Tim,

That page is 'work in progress' so proceed with a little caution. I had removed the link to it whilst I was waiting for some time to do some more testing - looks like you found it anyway.

The idea of the PCB was that you could build something like the Royer mic and experiment with additional or different components. I have built this with exactly the same components as the Royer circuit, and it works fine. You can also add the stabilisation caps which brings it a little closer to the G7 design. There was a small error in the original PCB - make sure you end up with the version that V1.2 written on it. To my knowledge no-one else has tested this design so do let me know how you get on.

If you are using the 5840 tube then 105 V works fine - you can use the G7 PSU but you may need to play around with the power supply resistors until you have suitable voltages - or increase R1 in the mic until you have about 105V. In this case you may be better off using the 2M:3M voltage divider that Royer uses to set the capsule polarisation voltage.

It works fine with the 'royer' power supply.

You may wish to connect the heater cables directly to the tube and avoid using the PCB tracks. Also, the wire from the capsule membrane to the tube input should be connected in the air.

There are still some problems with the 6AU6a design which I need to go back and sort out!

I hope that helps. Good luck & post back with any more questions.

Stewart

Michael is entirely right - it is quick and easy on breadboard too.

If you are using the 5840 tube then 105 V works fine - you can use the G7 PSU but you may need to play around with the power supply resistors until you have suitable voltages - or increase R1 in the mic until you have about 105V.

Click to expand...

Stewart,
I'm planning on using a 5840 - something I didn't really think of as far as the circuit you posted on your site, the component tweaks, are they specific to the 6au6 design? You mentioned you've had it working with the 5840, did you use the same components as in the http://www.omnipressor.com/Other/Othermicpix/6AU6Amic.gif schematic but with the 5840 tube?

Any thoughts on what a different supply voltage will do to the circuit - ie will it sound any different with the +160V instead of the +105V? I looked up a datasheet and the max plate voltage of the 5840 (if i read it right) is 165V, so 160V might be pushing it a bit, but I suppose R1 and R2 on your schematic will drop some voltage before the plate. Reason I ask is the following thread
http://recforums.prosoundweb.com/index.php/m/4545/0#msg_4545
discusses this somewhat, though more with reference to heater voltages, but there is some mention of B+ supply in and its effect on tube noise and capsule distortion.

oh, and the pcb I see on your site is version 1.1 - have you got a link to the 1.2 version?

thanks

tim

I've got the PDF's for the Royer MXL 2000 PCB's if any one is interested.

I've done this project (or actually am doing it now). It is a very simple circuit so you could breadboard it. I took some time to make some boards though and they work fine. I can share my layout with you if you want.

As for the psu, Royer's design is fine and works very well. I would suggest a few mods to it (as others have already suggested). I'm using much higher value caps for the heater side...6800uF instead of 2200uF...same for the 33Uf. Right now I have 100Uf sitting there but I'm gonna try some stiffer values. Bleeder resistors are a must and are so simple to impliment. I had to fine tune the heater voltage a little...changed R2 to 100ohms for 6.2V and I'm now trying 120ohms which sits at 5.1V.

As I said above, I'm still tweaking the circuit trying to stabilize it. It is simple but a little too simple. I'm taking a few pointers from a U67 which so far have worked out well.

I just did mine point to point on perfboard, and it worked great.

ju

Thanks for the links! So whose mod sounds the best? :green:

Joel

Hi,
The 5840 circuit I used looks like this....



Which is basically the royer circuit values except that I added a couple of extra caps (the 1 gig to ground is optional). It works nicely, but to be honest I can't say there is a great deal of audible difference between this and the original. I have also tried adding extra filament heater caps inside the mic.

V1.2 should be up at the site - if you click on the PCB it should link to a hi res, reversed & updated version for printing at 300dpi. If not then...

http://www.omnipressor.com/Other/Othermicpix/u4zmicpcb.gif

I too made some tweaks to the royer PSU.... bleeders are wise and I went the route of a voltage regulator for the filament (like in the G7 PSU) rather than giant caps. This also gives you the opportuinty to set the heater voltage to taste. Incedently, I never got 160V from the gyraf supply - more like 145V. The 100K plate resistor should be dropping you down close to 60V anyway.

Tommy - we would love to hear more about your layout and tweaks.

Stewart

Thanks Stewart.

(the 1 gig to ground is optional).

Click to expand...

If that's the case, I might leave it out, seeing as they are a pain to source,(and they're quite expensive).

I'm going to start collecting parts for this soon, though I'm putting it off a bit as I'm doing an order for enough parts for several projects (including a G7) and I'm waiting for so more money to come in. In the mean time I'm hoping to have some free samples of brass woven mesh arriving so I can finish off the bodies I've done.

I'll let you know how it goes.

tim

STOP!
You may already have some 1 gig resistors. The MXL mics have two - they are marked 1kM or something similar:



Perhaps the Nady does too. Well worth salvaging. Let us know.
Stew

Perki is around...but I think he changed his name... I'm not sure the status of the sound king order, but hopefully it's still in the works. I'd still like a couple capsules...

The MXL mics have two - they are marked 1kM or something similar

Click to expand...

Thanks Zebra50!

:guinness:

STOP!
You may already have some 1 gig resistors. The MXL mics have two - they are marked 1kM or something similar:

Click to expand...

Stewart, yep the Nady has got those. I'd noticed it before but sorta forgotten about it as they are quite bulky (they look similiar to the cement film ones the RS components sell?). Originally I was thinking about salvaging them for the other project I'm working on, a u87ai clone. I forgot that idea though as I'm grappling with major space issues trying to get my two PCB designs and a transformer to fit into the Nady body. Since I've built my own body for the Royer circuit though, and it's not component intensive I should have plenty of room for one of those from cathode to ground.

Anyway, I have a couple more questions. This is only my second tube build so bare with me:

1. The data sheet I've got for the 5840 has pins 2,4 and 8 as all being the cathode/grid 3. I notice that cathode and grid 3 are connected on the schematic, but I'm now assuming that there infact connected internally in the tube? So does this mean I only have to wire one of these pins to the 750R and 100uf, or do I wire all 3 to them?

2. Grounding, I'm having some problems getting my head around this. I just finished a Fender Tube amp, so I'm trying to apply what I learned there but it's not working for me...

I'm going to use the G7 power supply, and I'll fiddle with the power supply resistors to get me down to 105 volts.

The signal ground within the mic, that should be connected to the chassis of the mic no? I'm going to hard wire in the cable instead of using a plug/socket like you did Stewart to save some cash. If I used and XLR chassis socket I'm pretty sure the signal ground connection would be connected to the chassis due to the design of the female XLR shassis connectors right? So therefore it has to be connected to the chassis?

3. (also grounding) As far as grounding the heater circuit - it's grounded in the power supply so I have one wire carrying 6.3V and another being at ground. Do I have to connect the grounded heater pin of the tube to the signal ground within the mic (assuming this means also electrically connected to the chassis)? Or should this only be grounded with in the power supply? Looking at the G7 schematic for example, it has the heater ground (pin 7) connected to the signal ground (pin 1). I'm assuming this has to happen here, but I'm a little confused as to why you need to seperate grounds in the cable if they are electrically connected to each other anyway? (I'm sure there is a good reason for this, anyone care to elaborate?)

4. Resistor wattage - I'm assuming most of the resistors in the mic can be 1/4w with the exception of the 1K, 100K and 750R? What wattage should I use for these?

thanks again
tim

Hi Tim,
Good to know the nady has free 1 gigs.
I'll help as best I can...

1. The data sheet I've got for the 5840 has pins 2,4 and 8 as all being the cathode/grid 3. I notice that cathode and grid 3 are connected on the schematic, but I'm now assuming that there infact connected internally in the tube? So does this mean I only have to wire one of these pins to the 750R and 100uf, or do I wire all 3 to them?

Click to expand...

I have always connected these externally, and Dave Royer does the same if you look at his instructions. You could try checking continuity inside the tube. I've just had another look at the data sheet and I do see your point.
We need a tube expert!

he signal ground within the mic, that should be connected to the chassis of the mic no?

Click to expand...

The signal earths are best connected inside the mic at a singal point. Look at gus's photo in this thread.
http://www.groupdiy.com/index.php?topic=234
You do need to connect the body of the mic. You can do this using one of the screws in the middle of the chassis - take a wire to that and clamp it; solder the other end to the start ground point.

Do I have to connect the grounded heater pin of the tube to the signal ground within the mic

Click to expand...

The heater circuit does share a ground at some point with the audio circuit. I prefer to take this right back to the last heater stabilization cap ground or the 'star' ground in the PSU. There is a bit of current going through the heater circuit so the idea is to take this keep away from the audio circuit in the sensitive, Hi-Z areas. This is easy to achieve if you're using the nice (expensive) Mogami or Blue 6-core microphone cables that have separate, thick wires for the heater and a twisted pair for the audio.

Having sad this, I have grounded the heater in the mic in the past so that I could get away with using (cheaper) starquad (4 core) mic cable and a 4-pin XLR.... and had no problems. If you look carefully at the Royer schematic you will see that he does ground the heater in the mic body.

. Resistor wattage - I'm assuming most of the resistors in the mic can be 1/4w with the exception of the 1K, 100K and 750R? What wattage should I use for these?

Click to expand...

1/4W should be fine throughout the mic (the PSU is another story!)

Hope that helps. Other people may have different opinions on the grounding.

Stewart, once again thanks for your help.

Ok, I'm getting a clear picture of everything, though there is still a couple of things I'm not clear about.

Firstly, the star grounding thing within the mic. I understand and have implemented star grounding with point to point wiring before, like in the tube amp I recently finished but I'm not sure how it is implemented with a PCB (I'm using your layout). Is it simply a matter of running a single wire from the ground trace on the PCB to a connector (such as a screwed down solder terminal) in the mic chassis? I think that's the obvious solution but it doesn't really look like a star in my head when I think of it that way.

As for the heater grounding, I'm going to get some of the Mogami cable. I'm still trying to visualise the grounding. I'm looking at the PCB layout for G7 power supply at the moment.(http://www.gyraf.dk/gy_pd/g7/gic_psu.pdf)
Pin 1 on the both XLR's (7 pin and 3 pin output) is signal ground. When the wire is run from the PCB to both pin 1s of the XLR chassis mounted sockets, this electrically connects the PCB signal ground to the chassis I'm guessing. So far so good. But, the heater circuit ground though, looking at the PCB is at no point connected to signal ground in the power supply PCB. When you look at the G7 PCB (the mic itself)
http://www.gyraf.dk/gy_pd/g7/gic.pdf
you can see that the trace for the heater ground is connected to the signal ground trace.

I suppose this simply means that if I dont connect the heater circuit to the mic chassis, I'll have to run a separate wire from the power supply heater circuit ground on the PCB (marked 7, Heater 0 on the layout) to the pin 1 of one the panel mounted XLR sockets. Does this sound about right?

I hope the way I explained that make sense.

thanks
tim

In the G7, the heater ground meets signal ground in - and only in - the microphone, close to the tube cathode. This is for avoiding hum.

Jakob E.