Tube microphone with ef80 tube and oep transformer.
- Thread starter peterbach
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Help Support GroupDIY Audio Forum:
You probably should start somewhere else, and then work your way there...
Jakob E.
Jakob E.
Understanding you already have these elements, we'll try to make the best out of it. You probably know you'll need the power supply too. You may build it, which will give you more options, or you may buy one ready-made; That's what people do most of the time, because just the cost of the transformer and the box exceed the cost of the compelet PSU. But if you have access to a transformer winder and a metal shop, that may be different.peterbach said:
You'll also need a body for the mic. Many people choose to use a donor mic, typically a cheap Chinese mic, but again, if you have competence in metalworking, that is another possibility.
When you have answered these questions, we can focus more on the details.
Thank you ( abbey road d enfer ) for your response
And i dont have any problem in metalworks for the microphone & power supply body
The only problem is the knowledge of electronics and how to design the electronic circuit for the microphone and power supply.
And i dont have any problem in metalworks for the microphone & power supply body
The only problem is the knowledge of electronics and how to design the electronic circuit for the microphone and power supply.
Then I think you can start studying the schematic of the Neumann U47. The VF14 tube is not available anymore (only $$$ NOS) but it's a triode-connected pentode, you can do the same with the EF80. The VF14 used 4V heaters, the EF80 requires 6.3V, though. You should also study the AKG C60; it's one of the simplest designs (well, the PSU is a little complex, but it's because it's battery powered).peterbach said:
granger.frederic
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VF14 needs 60V and has 35V in a U47 (underheating)
ef80 needs 6V
http://www.tab-funkenwerk.com/id85.html
unlike the u47 design, you need to built a PSU with a high tension voltage and a separate and Heater voltage
take care to place enough RC filtering to achieve a low noise PSU
http://deeringamps.com/workbench/apex450.htm
for ef80, replace two 55v zener for HT
replace 7812 with a 7806 for heater
secondary psu transformer 200vac 10mA and 12vac 500mA min
ef80 has a higher output impedance and need a higher ratio transformer like 10:1 with a primary around 20KOhms and a secondary around 200Ohms
thus your transformer isn't suitable , ask Cinemag or AMI
take care to clean all the high value resistors and capacitors/ pcb around it
ef80 needs 6V
http://www.tab-funkenwerk.com/id85.html
unlike the u47 design, you need to built a PSU with a high tension voltage and a separate and Heater voltage
take care to place enough RC filtering to achieve a low noise PSU
http://deeringamps.com/workbench/apex450.htm
for ef80, replace two 55v zener for HT
replace 7812 with a 7806 for heater
secondary psu transformer 200vac 10mA and 12vac 500mA min
ef80 has a higher output impedance and need a higher ratio transformer like 10:1 with a primary around 20KOhms and a secondary around 200Ohms
thus your transformer isn't suitable , ask Cinemag or AMI
take care to clean all the high value resistors and capacitors/ pcb around it
That's right; where was I?granger.frederic said:
The OP already has the xfmr; assuming it's the 1+1:6.3+6.3 type, it is not too difficult to set an adequate ratio, by putting the high-Z in series and the low-Z in parallels, for a 12.6:1 ratio.
There's an issue about the quality of the xfmr. It may very well be that the inductance is too low, thus reducing the LF response. In order to overcome this potential issue, it may be a better option to use a C60-type circuit, where the tube operates as a cath-follower, with a significantly lower output Z; that's why I suggested he studies it also.
granger.frederic said:
Are you sure about the higher output impedance? As I understand it, the EF800 is a quieter and less microphonic variant, but has the same electrical properties. And moby said that the original BV08 with its 6:1 ratio is a good match for the EF800...
Did you calculate the output impedance of the ef80?
In comparison, in pentode operation, the EF80 is about twice the plate resistance/half the slope. It suggests about the same relationship in triode mode. That's why I voiced some concern about the xfmr inductance.Murdock said:
RuudNL
Well-known member
I once used the Oep a262a3e thogether with a EF86 in a plate follower configuration, but the results were not very satisfying.
But maybe it will work in your situation. Would be interested to read the results!
But maybe it will work in your situation. Would be interested to read the results!
granger.frederic
Well-known member
- Joined
- May 22, 2010
- Messages
- 488
the rode NTK is transformerless ...
try the Oep a262a3e with primary (150ohms for the mic output) in parallel, and the primary (24k input /output capacitor connected) in series
thus use it reversed...
it should work , the inductance shouldn't be an issue (10,4H)
but the result shouldn't sound like a high end adapted transformer
http://www.farnell.com/datasheets/1872254.pdf?_ga=2.11326644.1238363722.1535786152-1349142366.1535786152
be careful: don't heat too much the transformer when you solder it
try the Oep a262a3e with primary (150ohms for the mic output) in parallel, and the primary (24k input /output capacitor connected) in series
thus use it reversed...
it should work , the inductance shouldn't be an issue (10,4H)
but the result shouldn't sound like a high end adapted transformer
http://www.farnell.com/datasheets/1872254.pdf?_ga=2.11326644.1238363722.1535786152-1349142366.1535786152
be careful: don't heat too much the transformer when you solder it
Yes you can, but it's a significant task. There are much simpler options. First is connecting the tube as a cathode follower, like it's done in the C60. By far it's the easiest. Another solution is to use the same input stage and following it with a cathode-follower, but then you need two tube sections; that could be one half of the ECC83 after the capsule and the other half as a cath-follower, but the ECC83 may be a tad too noisy. That could also be the EF80 after the capsule and the ECC83 as a cath-follower (both halves can be paralleled for better drive capability and lower noise); indeed that would need to find space for two tubes in the body, and be a little complex, but not as much as recreating the Rode circuit.peterbach said:
Indeed, the 2nd half of ECC83 is used as a cath-follower. The right-hand part of the circuit makes no sense, because there is no polarity inversion; the signal at the point labelled out- is in fact in-phase with the signal at out+. There is some differential signal because the amplitudes are not strictly equal, though, so the "designer" may have concluded it works.peterbach said:
Yes.
You may have to change the value of the plate resistor in order to optimize operation, but it would work. Remember to connect the EF80 in triode mode.
For the cath-follower, you'd better take advantage of the double-triode to operate both halves in parallels. I would suggest a 47k common cathode resistor.
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RuudNL
Well-known member
The 100 K.ohm potentiometer adjusts the polarisation voltage between 84 and 115 V.
IMHO that is a pretty high value, a bit too high if you would ask me!
IMHO that is a pretty high value, a bit too high if you would ask me!
