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Ribbon Microphone Preamp

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I was planning to purchase PS-1 kit from GlassWare. And a toroidal main transformer from somewhere.

Small resistors left from my experimenting with simulation. You can remove them.

Question to Ian. Why bypass caps should be that big - 220uF? What type would you recommend?
 
this has been a great and sturdy learning experience. I think I would like to finally go to the soldering station and try this out. Do you guys insist on an choked power supply? or is a plain old RC supply sufficient (audibly).

Also what is the point of having small resistors at the top of each anode on the mu-followers? 2ohms? is this just for current measuring?

You do not need a choke HT supply for a preamp. This CRCRCRC circuit will provide extremely low noise:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/power/HT350cct.png

and it also provides an elevated heater voltage.

There is no point in the small reisitor in the anodes of the mu followers - I suspect they were just an aid to simulation.

Cheers

ian
 
WE417A? I have been told a little bit about them. Recommended compared to the 12ax7? Or Hassle? Any ultimate solution for the input tube? (being that 1:10 input transformer would be a constant)

@ ruffrecords: goo transformers? What does that mean?
& Grounded Grid vs Cathode Bypass?

And I know there are debates on AC vs DC heaters, but say If I were to elevate either option, how negligible would AC heating actually be? I used AC heaters before and had pretty sweet luck so far. (I find joy in twisting solid core wire) & I have transformer convenience for 6.3v stuff.

If this were an audio power amp, I'd say "try AC heaters" but with a mic preamp there is SO MUCH GAIN and the heater current is so low that DC is best. Heck even a little LM7806 regulator can supply the heater for a preamp tube. (6V works fine. it is within the 10% spec and the tubes will last "forever")

Noise is such a issue with mic preamps, shield everything. I'd even place the input section, the transformer and phase flip switch and an=tenuators inside their own steel sub chassis. Maybe even place the power supply in a sub chassis far from the input jack.

Also I'd never use an out of production tube in a new design

I bet a "goo" is a typo "good" is what was meant.

That 1:10 transformer will make for a nice and effective "antenna" and pick up any nearby noise and hum. DC heaters will help as will distance and compartmentalization.
 
I was planning to purchase PS-1 kit from GlassWare. And a toroidal main transformer from somewhere.

Small resistors left from my experimenting with simulation. You can remove them.

Question to Ian. Why bypass caps should be that big - 220uF? What type would you recommend?

The bigger the caps the better the smoothing. That simple CRCRCRC network can reduce ripple by 130dB, better than any regulator. SOmething like this will do:

B43305B5227M000 - EPCOS - CAP, ALUM ELECT, 220UF, 450V, | Farnell United Kingdom

There's an excellent article by the great Mr. Scroggie about how several RC sections give better ripple reduction than a single stage of the same total R and total C.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/power/Scroggiefilters.pdf

Cheers

Ian
 
The bigger the caps the better the smoothing. That simple CRCRCRC network can reduce ripple by 130dB, better than any regulator. SOmething like this will do:

B43305B5227M000 - EPCOS - CAP, ALUM ELECT, 220UF, 450V, | Farnell United Kingdom

There's an excellent article by the great Mr. Scroggie about how several RC sections give better ripple reduction than a single stage of the same total R and total C.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/power/Scroggiefilters.pdf

Cheers

Ian
Also in the radiotron designer 4th ed. there are graphs that chart the article you quoted . At 130db for power supply other sources of noise will come it to play because the power supply is no longer covering them up but not to worry build this then address what pops up.
 
the final schematic
 

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One issue here, cathode of second upper tube is 210V. So its heater should be elevated up to 230V. In this case heaters of lower parts of tubes will be elevated quite high.
What to do? To use separate tubes?

The 6N23 is rated for Vhk of + or - 200V. One cathode is close to ground and the other is at 210V. The best appoack is to elevate the heaters to the half way point, say 100V. The one heater is at -100V and the other is at+110V.


Cheers

Ian
 
Haha, Dang, I was going to use the ps-1 schematic (point to point) with an antek toroid transformer. Read my mind!

As for the cathode bypass caps, I have a few nice os-con 16v organics, what is a safe voltage rating to work with down there?

Also, I wouldn't be opposed to the idea of paralelling tubes (for the sake of heater elevation).
 
Haha, Dang, I was going to use the ps-1 schematic (point to point) with an antek toroid transformer. Read my mind!

As for the cathode bypass caps, I have a few nice os-con 16v organics, what is a safe voltage rating to work with down there?

Also, I wouldn't be opposed to the idea of paralelling tubes (for the sake of heater elevation).


16V working should be fine. If the cathode ever gets near 16V the tube will be pretty much cut off.

Cheers

Ian
 
I read some negative things regarding toroid mains transformers. ( Toroidal vs EI type Power Supplies [Archive] - AudioKarma.org Home Audio Stereo Discussion Forums )
Probably I will better go with EI one and put some more iron screening around it and around input stage.

Perhaps a more important consideration is the enclosure in which you put the preamp and power supply. It is essential that this is NOT steel. If it is you will almost certainly have problems with stray flux from an EI type transformer being transmitted through the case work to the microphone input. I had exactly this problem once and the only solution was to take the power supply external. If you are going to build this all in one box put the mains transformer at one end of the box and the mic transformer at the other. Preferably use an all aluminium enclosure. I personally have never had any problems with toroidal transformers.

Cheers

Ian
 
You do need heater elevation to ensure you do not exceed the specified heater cathde voltage Vhk as I explained earlier.

Oh yes, I see.

Regarding a toroid trans, what mains power do you have? 2 or 3 phase?
I know in Russia it is 3 phases by 220V 120 degree shift (regular residential receptacles use 1 phase), in US and Canada it is 2 phases by 120V 180 dgr shift. It looks like toroids should work without problems in North America, but may be problems in Russia because of DC bias. What type of power do you have?
 
I always feel inconclusive with the EI vs Toroid debate. It looks like the emi field of a toroid is a small fraction (1/8) of a EI core. So the question is, what is the minimum acceptable distance I should keep the input transformer from? *(with either version)?

I envision putting this in an all in one multi story enclosure.
 
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