analogguru

Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #20 on: September 22, 2018, 07:51:46 PM »
And there are other variants / derivatives of the ICL7660 that work at higher frequencies. Stuff like the TC7660H - 120khz high enough for ya? :)
Feel free to use the chip of your dreams - the Klon Centaur Distortion Box uses them too.  I know why I stopped using the ICL7660 25 years ago.  And I am not convinced of the Frankentube-design, therefore it doesn't concern me which chip people use there.

Under 1eu/pc one-off from Mouser, DIP package...
You are right, my ready-made converter modules are far more expensive - they costed me EUR 1,54/pcs (including shipping & handling).

 

« Last Edit: September 22, 2018, 08:15:25 PM by analogguru »


Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #21 on: October 02, 2018, 04:01:16 PM »
Anybody knows why audio-technica dropped their patent for their AT3060 (which is very similar to the circuit used here) ?:
http://www.freepatentsonline.com/7295675.html

(At least they didn't use an opamp in the signal path of a "tube"-microphone.)

And anybody knows which grid current/(resistor) is necessary for the 6418 to ensure proper bias ?

I am not sure they DID drop the patent; you see the one YOU linked to is not the only AT3060 design!  A later one has 4 current-regulating diodes and a center-tapped primary transformer...currents to plate and Grid#2 are moving in opposing directions in the primary and a resistor network was selected to BALANCE those currents within ~5% or less, so the primary  DC fields should "cancel", thus AT could utilize a much lighter transformer in the later AT3060 = cheaper to make.   So you linked to a patent which is not the latest one.  The later one feeds 2 current regulating diode to primary CT, primary wires to plate and Grid#2, and, I think they tweak the current to grid#2 current  to approximate what should be at Plate.  If the same the opposing DC fields are the same? 

Version 1 they used oh I want to say 10K down to the 10V Zener.  The voltage divider on the grid #2 I think 43K and 100K below.
Most other part values would not matter, maybe 10pF feedback from plate to Grid#1.  [1G-Ohm to GND at main input Grid, or whatever you have in high values]   AT3060 Version 1 you need a transformer that does not saturate in the primary due to the one way DC flowing there.  Like a $75-$150 transformer not a cheapie DI box tranny.   

Zap went with QTy zero coils  on the DC-DC side.  If ya use coils etc, then you have more hash and magnetic fields...[I think].
You would not need a 52V rated buck regulator if you used a zener to pre-regulate the buck, or, a resistor-value you could maybe determine with a POT first.  Zener makes noise but so does a buck-regulator, either way you have work to do, since the cathode is the heater  too   :)  nice   not    to shove in noise THERE.   They make some pretty nice like 820uF 2.5V caps [for the heater DC]  you can find on carriers in the SMD world, those can be used through-hole after removal from carrier.  Maybe bypass that [parallel]  with 0.1uF 0805 SMD cap, and toss in a series choke or ferrite?

The UM900 is said to have an OP AMP,  people buy them.   Maybe that was your intent to say?  Could use a MOSFET follower, or bipolar follower there too, and then yah a transformer via a cap.  With a OPA you could give the mike different profiles, or just strap for unity and cap to transformer.  The tube is still first in line, sounding like a tube does.  I doubt you could hear the impact of a  GOOD unity-gain OPA after the tube.   It is certainly possible to use a OPA in Franken that happens to idle at say 1.5mA, and figure that the LM2665M6 chain is going to operate at some efficiency less that 100%.   That heater you'd want at maybe oh 9mA?  Or be a boy-scout and run at 10mA.    1.5mA at say 80% eff [chain of 2 reverse-wired LM2665M6]  would be ~9.6mA heater?  Some mike guys starve heaters a splash on purpose.  No?   

MY argument about the famous Naiant MSH4 is that the first stage IS actually a jFET [in a capsule]  not a tube off the skin of the capsule.  Vs Gefell UM900 would be LDC into tube grid#1 after a DC isolation cap since Gefell probably puts 60+ Vdc on the capsule -- unless they used the old ZapnSPark way and do not ground the non +60V side but rather shove that into grid#1 -- the capsule IS a cap.

Resistor grid #1 -to-ground? Or a series R?  Grid-to-GND,  why not use some Augat socket-pins and try: 2G-Ohms, 1G-Ohms, 100M, 10M, 1M ?   See what you see on a scope?  Listen???  None of them will hurt anything.  Any of those values will allow the tube to operate.


Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #22 on: October 02, 2018, 05:20:28 PM »
Great read!
Does anyone have schematic with original Zap's capsule polarizing? He uses LDC in the pics.

It should be quite easy to do a null test shootout of audio that passed through IC vs discrete and decide (hear) if it matters.
« Last Edit: October 02, 2018, 05:25:49 PM by kingkorg »

Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #23 on: October 02, 2018, 09:20:33 PM »
Zap's LDC bias would be at Yahoo Micbuilders under files, I also have it here in .PDF and it seems derived from an article:

https://groups.yahoo.com/neo/groups/micbuilders/files/Zapnspark/

a quote "29183Re: TSB-2555B Alternatives?
Expand Messages

    rogsarjay
    Oct 1 4:57 PM
    Yes, it looks as if ZapNSpark has uploaded the same 1983 article from the (now extinct) UK magazine Electronics Today International (ETI)  written by Rory Holmes.....
    An excellent article on how to create some simple CMOS voltage multiplier circuits, without the need to use any inductors....
    I like simple!  "

I have laid out a PCB that implements Zap's 40106 diodes/caps ladder boost in SMD, 0805 SMDs, it probably works but I have not tested it yet:

https://photos.app.goo.gl/aVQfNtTJcVMmy3fx8

the SMD 40106 is on the rear of the PCB.  The slotted wings, one breaks too easily, that's why we order prototypes. 

Another pertinent thread:

https://groupdiy.com/index.php?topic=48859.0

and this might be what you are after:

http://www.sdiy.org/oid/zapnspark/CMOSmicPolar7.pdf

at:

http://www.sdiy.org/oid/mics.html

The Boost should help LDCs:

http://www.audioimprov.com/AudioImprov/Mics/Entries/2016/7/4_Bias_Voltage_for_True_Condenser_Capsules.html

Henry shows how more capsule-bias increases signal vs noise, in his test environment ^^^^  if you use a LDC.   

You may be able to pluck some plate voltage from Zap's boost but if let' s  say you used a tap in the diode/cap ladder?  That plate circuit might need something say like 500uA, maybe more, I cannot say whether the Zap Boost can do that.  Maybe, under light load, the P48 B+ remaining might still BE 30V?  That would be handy. 

The tube plate Z vs the output Z, well, the OPA or MOSFET follower or emitter follower after the plate would help get there [provide a z-match].
Oatley Electronics in Aussie-land has many 6418 designs, some drive headphones via OPA, some feed a MOSFET gate from the plate since the MOSFET gate is "insulated" like a cap... VS say the AT3060 is tube to transformer do no pass GO.    It is rumored that UM900 is tube-->OPA-->transformer, to me that makes perfect sense.  But again, OPA can, instead,  be just a follower.  I would argue that the AT3060, a good part of how it performs is their choice of what PRR would call "Iron", and what they chose, and why they had to.  I'm guessing the UM900, if it has a OPA driving the transformer, well...things would not be so "touchie".  OPA matches Tube-plate Z to the output xformer effective z?  I am no expert but that would be the primary z and any impacts of the secondary on the primary?  I'm not a trained engineer.  Tube sees what it wants, OPA doesn't care much...and out we go. 

Then Naiant remade the MSH4 into the X-V?  To his credit he has transformer-out, again, to me though, if the first thing in the chain is honestly a jFET in a capsule, to me it's a tubed-buffered jFET-mike.    Vs Franken, you can see a 25mm TSB-2555B feeds the main grid in the 6418 with a 1GigaOhm resistor to ground right there.  Meaning that yah the tube CAN be the first stage just fine, and if I were making a tube-sounding mike I wouldn't make the tube say the last stage, no, the first!  MSH4 and X-V  it's the second.  I am not bashing Naiant; nobody else has made what he has and sold it for $50 in a kit.   THAT is one amazing DIY buy. 
When I get time I will build the X-V with a PUI HD series 80db SNR 10mm capsule, for fun.   That will be a light weight phantom powered tubed omni you could hang from a mike-cable and drive quite some distance of cable? 

Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #24 on: October 02, 2018, 09:59:42 PM »
Other obvious trivia: the AT3060 [both versions] operates the tube as a pentode, vs Frankentube operates as a triode.  I think that translates  to the pentode config having more gain but more noise? 

http://www.valvewizard.co.uk/pentode.html

Franken operates as a triode and the OPA in UNITY-gain mode, but obviously the OPA could be strapped to have {a little] gain [not a lot]  and EQ, and the OPA COULD of course drive a transformer if you wanted REAL balanced-out.  Franken is unbalanced out but would not have to be.

And food for thought:

http://vintage-technics.ru/Tube_cassette_player/Tube_cassette_player_circuit.JPG

ALL the plate current is via the primary ^^ [on one direction] and none of the Grid#2 current, so the primary is part-saturated, vs say the AT3060 version II where the currents are divided in opposing directions via a center-tapped DC-injected primary  CT and some tweaking to balance those currents even further.   VS say the UM900 where the tube doesn't "see" the "iron" "they say". 

Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #25 on: October 03, 2018, 01:27:37 AM »
Yupp, it's cardioid only. However there shouldn't be a problem with too much low end with stock oktava. I believe it's my mic that has better low end extension compared to stock, has a bit of 30-50hz rumble.

I think the Franken  330K and 1uF off the plate to GND form a high-pass filter,  you could lower the 330K to something way lower and if I am right, roll off at above your offending LF, if, say you wanted to.   Just a guess.  Or doink with the op amp.

http://sim.okawa-denshi.jp/en/CRhikeisan.htm

Here again Naiant X-V claims to roll off naturally down low, in part due to the use of a transformer that rolls off down low.  The MET-17. 

Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #26 on: December 20, 2018, 07:51:18 AM »
I know this thread hasn't had a post in months, but where do you find Oktava capsules? Oktava Shop and Oktava USA don't seem to have LDC caspules (other than the ones for the MK-012), and I'd love to get my hands on an MK220 capsule.

Re: Phantom Powered Tube Microphone (Frankentube) DONE!
« Reply #27 on: December 20, 2018, 10:29:12 AM »
I just had one left from modding mk319.

However you can contact guys in Europe, they had replacement capsules in stock.

[email protected]


 

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