Royer Mod power supply

[zebra50]

Jakob,
Did you do any tests to find if this is noticably better than grounding the heater only at the PSU instead? I have tried both but I had figured with the 'mogami' type cable it would be better to use the two dedicated heater strands to bring the current back to the PSU. Earthing is always a tricky subject and I fear that I may have a misconception!

Tim,
My PCB is probably not as well thought out as might be and is not a true star ground. If you're cunning you can make the screw that holds the PCB in place act as the grounding.
When I used this I actually ran wires directly from the XLR to the tube for the heaters.
Have you made the PCB yet? If nt then hold on and I'll have a look this weekend and see if there is any more trouble shooting to be done.

ta!

 

[saxtim]

Jakob,
Did you do any tests to find if this is noticably better than grounding the heater only at the PSU instead? I have tried both but I had figured with the 'mogami' type cable it would be better to use the two dedicated heater strands to bring the current back to the PSU. Earthing is always a tricky subject and I fear that I may have a misconception!

I'd like an answer to this too - be interested to see the reasoning behind it.

Tim,
My PCB is probably not as well thought out as might be and is not a true star ground. If you're cunning you can make the screw that holds the PCB in place act as the grounding.
When I used this I actually ran wires directly from the XLR to the tube for the heaters.
Have you made the PCB yet? If nt then hold on and I'll have a look this weekend and see if there is any more trouble shooting to be done.

ta!

I have done up the PCB. I ended up using some scrap board I had round and drew it out with etch resistant pen rather than using the expensive photo-resist board I normally use. I might try grounding the heater both ways and see if there is any audible difference between grounding in the mic and grounding outside.

I'm still a little way off being ready to build - I've ordered most of the parts for the mic, but I still haven't ordered an output transformer (will probably go with the sowter you mentioned on your site). I still haven't ordered parts for the power supply yet - I've got the order mocked up at Farnell, just need to send it.

The other thing I'm holding off on is cable - I was thinking that I might go the Mogami from Canford, but I'm doing my best to source it locally. I found one place that will sell it to me for $10ish AU, but requires a minimum 10 metre order. When I contacted Canford via email they said they could sell it in smaller amounts (I was thinking of 3 or 4 meteres). Still it probably be a fortune to ship out here. I noted in another thread that Farnell stock a tube mic cable, but I check that out and it's $100ish AU for 5 meteres, more than twice the cost of the Mogami so I think I'll stay away from that. Maybe I'll eventually find a use for 10 metres of the Mogami cable - I am intending to try the G7 soon so I guess it'd be good to have plenty spare.

Thanks

tim

 

[zebra50]

Hi Tim,
I checked out my mic that I built on that board at the weekend and it works fine & sounds good.

For a transformer, you could try another mic input tranny reversed if you can't get the sowter easily.

For the cable, you can get away with normal 4 -core 'star quad' if you need to save money for this mic, but you'll need 6-core for the G7s.

Stewart

 

[dukasound]

[quote author="zebra50"]Hi Tim,
I checked out my mic that I built on that board at the weekend and it works fine & sounds good.

For a transformer, you could try another mic input tranny reversed if you can't get the sowter easily.

For the cable, you can get away with normal 4 -core 'star quad' if you need to save money for this mic, but you'll need 6-core for the G7s.

Stewart[/quote]
Hi Stewart
What kind (name, ratio) is in use with 5840.
Thanks
Duka

 

[dukasound]

Hi Stewart
Mistake io typing!!!!!!!
What kind transformers (name, ratio) is in use with 5840.
Thanks
Duka

 

[zebra50]

Hi Duka,

I have used Sowter 4935 with this design, which is 7:1. It is really a mic input transformer put in backwards. It works well. I have also used the lundahl that is in the G7.

Royer uses another transformer in the original Tape -op article. You can read about it at

http://www.prosoundweb.com/recording/tapeop/tube_mic_25_1.shtml
http://www.mojaveaudio.com/press.html

Cheers!
Stewart

 

[gyraf]

yes, I tried different ways of grounding the G7 signal/heater/psu references, and found that combining them close to the cathode behaved best. But this may simply have been due to the components/cables/psu's that I have used.. I don't think there's a "right" or "wrong" way to do this.

..grounding is an experimental science.. ..at best..

Jakob E.

 

[dukasound]

[quote author="zebra50"]Hi Duka,

I have used Sowter 4935 with this design, which is 7:1. It is really a mic input transformer put in backwards. It works well. I have also used the lundahl that is in the G7.

Royer uses another transformer in the original Tape -op article. You can read about it at

http://www.prosoundweb.com/recording/tapeop/tube_mic_25_1.shtml
http://www.mojaveaudio.com/press.html

Cheers!
Stewart[/quote]

Hi
I read about Davids modifications. He use Jensens. Now I have Lundahl LL1538 which is 1:2,5 and 1:5 and LL1577 1:7 and 1:14. Also I have one OEP A3E with 1:6,45 ratio. You suggest me to use 7:1 and higher or excatly 7:1?
Thans
Duka

 

[zebra50]

[quote author="gyraf"]

..grounding is an experimental science.. ..at best..

Jakob E.[/quote]

:green:

Duka,
The lundahl at 5:1 will work (I have tried this one), and I think the others will too. I doubt 14:1 will give any real advantage. I would go and try them all and see which you like best.
:thumb:

 

[saxtim]

Hey Stewart,

I just got my Sowter's in the mail today, so I'm nearly ready to wire everything up. Couple of more questions:

What did you do with the centre tap on the primary of the sowter?

The sowter has got two screws on the top - this is probably a stupid question, but I assume they're for mounting. When I got them though they're only half way screwed in - I'm nervous about screwing them all the way in incase they're not supposed to go in.

I've mentioned this before, but I've made my own body for the mic as I'm planning to use the orginal Nady body for another project. I'm taking the capsule out fo the Nady though. Do you think that capsule's mount (one of the stock chinese ones I'd assume) will provide enough shock absorbance, or is it worth making and extra silicone style one as described in the G7?

On a side note, I got a couple of great bargains - I picked up 10 6 pin female panel mount XLR's on ebay for GBP1.40 ish. I also scored two panel female mount 7 pin XLR's from canford on sale for GBP2.50 each.

Only thing I need now is the cable!

thanks
tim

 

[zebra50]

Hi Tim,

No connection to the centre tap.

The holes are for mounting but I didn't use them. If the screws look too long for the job then just cut them down to size with a hacksaw.

The stock mounting does not absorb shocks well. However, if you plane to use a proper shockmount with your mic then you won't have any problems with it. The silcone is expensive unless you plan to do quite a lot with it.

Good prices on the XLRs!

hope that helps
Stewart

 

[saxtim]

I've just had time to get round to buying the last parts I need for the power supply. I plan to build it on the weekend. Can I test the mic (voltages etc) without the capsule connected to the circuit? Because I've built my own body, the capsule would be exposed to dirt, dust etc whilst I'm checking voltages etc. It's just a capacitor, no? Could I even just put a capacitor where the capsule is in the circuit for checking voltages? If so what value?

With the capsule, is it the backplate or the diaphragm that goes to grid 2 of the 5840 - I'm not sure which is which on the schematic?

Any recommendations for under heating the tube - what's a good voltage to try the heaters at?

thanks

tim

 

[zebra50]

Hi Tim,
You can test it without the capsule - I usually fit the capsule last if I can for the reasons you describe.

Diaphragm to grid, I recall.

I have the tube at 5.8 to 6v at the moment, but I keep experimenting.

I updated some of my site: this might interest you if you haven't seen it:

http://www.omnipressor.com/Other/G7mics/MXLmod.html

Stewart

 

[saxtim]

Ok I wired up the power supply and things aren't working - I get no signal whatsoever out of the mic.

I've used the G7 power supply and I'm getting aroun 86 B+ out of it (a little on the low side, this is actually half of b+, I need to fiddle more with the ratio where the 2 100k resistors are on the pattern switch to get it a little higher.)

Heater voltage is strange, I'm not sure what I've done here. I tested it first by grounding the heater circuit in the power supply to get the trim pot set up correctly. I got a measured 6V. I then moved the heater ground into the microphone as Jacob suggested, (removing the connection the power supply chassis). Now I'm measuring -6V in respect to the chassis ground. Stranger still, when I measure the voltage coming out of the regulator it's sitting at -1.1. I don't understand this as these two voltages should be the same as they are connected, and both be positive.

Other voltage measurements from inside the mic:

B+ +86V
After 1K R +85.5V
Anode +35.5V
Juntion of 2.2M, 33M and 3.3 M +45V
Backplate +11.5V
Front diagphram -1V (this surely cant be? perhaps HighZ screwing my reading?)
Cathode +0.37V

Heater lights up when powered on, no sparks or anything flying. Any suggestions where to start looking?

Thanks
tim

 

[zebra50]

Hi Tim,
Took me a few minutes to figure this one out. It sounds like you've earthed the wrong (i.e. +ve) leg of the heater. Check your wiring and check again. Maybe you've switched them over in the cable/XLRs?

You won't get a sensible reading on the capsule with standard test gear - don't worry about it.

Get the B+ up to about 105 V and try again.
Stewart

 

[saxtim]

Stewart - yep I had screwed up the heater wiring. I've got the b+ up to aroun 103V now and it's working!

I've only tested it at home on a crappy mixer, so I'm not sure of sound/noise at the moment, I'll post back when I get a chance to try it out in my uni's studio.

I'll post some pictures of it and the power supply when I get a chance too.

thanks for all the help

tim

 

[zebra50]

Hi Tim,
Good stuff. I'm sure you'll have fun with it.

Pictures = good.

Did you go with my board? I have it in mind to do a 'version 3' which makes use of the MXL mounting posts a bit better. If I can be bothered!

Stewart

 

[saxtim]

I finally got around to testing the mic yesterday. The results were definately very pleasing. I recorded some clips of my sax playing and my voice with the original Nady mic and then with the Royer design. (sorry - they're not currently posted for listening)

Not a perfect comparison as the clips were recorded with several weeks in between. Still on my sax my general impression was that the Royer was much better, being 'darker' and 'smoother'. I found the sound across all registers of the instruments tied together well and sounded even, where the Nady sounded uneven on different registers and seemed to emphasis the mids.

The Royer mod also sounded better to my ears on my voice as well.

Did you go with my board?

I did originally but I got a bit paranoid about the High Z and my lack (at the time) of any sort of PCB cleaner to get rid of the gunk etc after soldering. So I ended up perfboarding the thing and got all the high Z stuff in the air.

Pictures = good.

I'm still planning on posting some soon.

Thanks again for all your help Stewart

tim

 

[dukasound]

Hi
Here is new PSU box for my Royer. Before I made this I used PSU from Elam (with incorporated switch to decrease voltage to 100V).
This is with stabilized filament voltage and with 4caps and three resistors (like old Neuman and AKG style PSU) with zeners on the end.