U47 Build using EF80
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Spencerleehorton
Well-known member
Hi Opr,
Looks great, could you ask my question please?
Hi all,
Just need to know what would happen if the PSU I've made for this U47 was given 48v from a mixing desk whether it would have any effect or change the sound of the mic?
If there is any effect what could I do to protect it.
This problem would occur when using this mic into a desk which has phantom power over all channels, so you can't turn it off/on individually.
Regards
Spence.
Looks great, could you ask my question please?
Hi all,
Just need to know what would happen if the PSU I've made for this U47 was given 48v from a mixing desk whether it would have any effect or change the sound of the mic?
If there is any effect what could I do to protect it.
This problem would occur when using this mic into a desk which has phantom power over all channels, so you can't turn it off/on individually.
Regards
Spence.
Hey Spence,
I haven't seen your PSU Schematic but generally speaking the 48 V dc should not affect the mic as it will only be seen by the transformer and transformers don't pass DC.
I have heard of people hearing sonic differences on non phantom powered mics when phantom power is enabled on some preamps as often the signal is fed through some resistors which raises the Input impedance.
I haven't seen your PSU Schematic but generally speaking the 48 V dc should not affect the mic as it will only be seen by the transformer and transformers don't pass DC.
I have heard of people hearing sonic differences on non phantom powered mics when phantom power is enabled on some preamps as often the signal is fed through some resistors which raises the Input impedance.
dmp
Well-known member
Nice mics OPR and Spence.
Here's my attempt. My first mic body from scratch. Other than the head grill, it's coming out OK, looks rough but functional anyway.
The grill is a pain. Soldered it together but didn't get the mesh attached all around the base of the head basket, so it catches on the internals during assembly.
A EF800 circuit with a beyer transformer. Not going for a straight clone of anything, just a really strong mic. But it will be U47'ish, in that it has filament bias and a Thiersch capsule.
Here's my attempt. My first mic body from scratch. Other than the head grill, it's coming out OK, looks rough but functional anyway.
The grill is a pain. Soldered it together but didn't get the mesh attached all around the base of the head basket, so it catches on the internals during assembly.
A EF800 circuit with a beyer transformer. Not going for a straight clone of anything, just a really strong mic. But it will be U47'ish, in that it has filament bias and a Thiersch capsule.
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dmp
Well-known member
Spencerleehorton
Well-known member
Hi guys,
Just built a couple more for a friend and one one mic getting 14v on B+ and can't figure out why! any ideas?
Regards
Spence.
Just built a couple more for a friend and one one mic getting 14v on B+ and can't figure out why! any ideas?
Regards
Spence.
- Joined
- Jul 15, 2009
- Messages
- 2,306
Spencerleehorton said:
A-disconnect the mic first, then check for your B+ if it is too low still , problem not in the mic ,
B- check how much current you are pulling taking voltage across dropper resistor in the psu ,
C- not a big Fan of the 24V Hamelin Relay they are energyvorus, as the mic is taking about 50ma already check you current pull summary
D- make sure your pattern switch is deactivated , then recheck unloaded B+
E- Check your realy pattern setup in the psu ,
this is a starter first thing first , simple thing first , but .. saftety before all this
Hope this helps
Best,
Spencerleehorton
Well-known member
Hi,
I have built 2 of these mics and I get correct voltages on one and this 14v on b+ on other, psu works fine without mics connected and like I said works fine on other mic.
Relay seems to function but will investigate further.
Regards
Spence.
I have built 2 of these mics and I get correct voltages on one and this 14v on b+ on other, psu works fine without mics connected and like I said works fine on other mic.
Relay seems to function but will investigate further.
Regards
Spence.
jackinthebox
Member
- Joined
- Jul 2, 2011
- Messages
- 24
Slightly off topic, but does anyone know if the polarity of the DC heater connections makes a difference?
I've recently built several variations on this mic and it's interesting the subtle differences in tone due to the biasing scheme.
A separate heater ground makes a lot of difference and it makes component placement a bit tidier if i use pin 4 for the positive heater and pin 5 for the heater ground.
I also put a 220uf 16v and a 0.1uf film cap across pins 4 and 5 and another electrolytic from pin 3 to ground.
I have been suffering from the same issues with hum when using the fixed bias approach but i do prefer the sound of fixed bias and there seems to be more noise when using self bias. That may of course be due to the fact the hum masks the noise when using fixed bias.
My power supply also has increased 100hz hum when i increased the cap size which is a bit counterintuitive but i think it might possibly be to do with the transformer saturating due to increased current demand from the first reservoir capacitor.
I have also had trouble with making a variable pattern selector on the power supply (to supply 0 to 120 volts to the rear diaphragm.
Has anyone managed to do this successfully?
I've recently built several variations on this mic and it's interesting the subtle differences in tone due to the biasing scheme.
A separate heater ground makes a lot of difference and it makes component placement a bit tidier if i use pin 4 for the positive heater and pin 5 for the heater ground.
I also put a 220uf 16v and a 0.1uf film cap across pins 4 and 5 and another electrolytic from pin 3 to ground.
I have been suffering from the same issues with hum when using the fixed bias approach but i do prefer the sound of fixed bias and there seems to be more noise when using self bias. That may of course be due to the fact the hum masks the noise when using fixed bias.
My power supply also has increased 100hz hum when i increased the cap size which is a bit counterintuitive but i think it might possibly be to do with the transformer saturating due to increased current demand from the first reservoir capacitor.
I have also had trouble with making a variable pattern selector on the power supply (to supply 0 to 120 volts to the rear diaphragm.
Has anyone managed to do this successfully?
Spencerleehorton
Well-known member
Hi guys,
Both my U47 mic work fantastically now. No hum, clean as a whistle.
I'm thinking about changing the cardioid to omni selector to include more patterns so I will detail all of this for anyone who want to know.
Regards
Spence.
Both my U47 mic work fantastically now. No hum, clean as a whistle.
I'm thinking about changing the cardioid to omni selector to include more patterns so I will detail all of this for anyone who want to know.
Regards
Spence.
Spencerleehorton
Well-known member
Hi guys,
Would just like to take this opportunity to thank everyone here on group DIY for all of their valuable help with all my projects, especially dan/proctop as without his help and support I wouldn't have attempted anything else apart from his wonderful builds.
Good luck to everyone with all their project.
Regards
Spence.
Would just like to take this opportunity to thank everyone here on group DIY for all of their valuable help with all my projects, especially dan/proctop as without his help and support I wouldn't have attempted anything else apart from his wonderful builds.
Good luck to everyone with all their project.
Regards
Spence.
Hey Guys,
Just though I'd share an update on Ef80/800/802 47 builds as there is a major impedance mismatch at U47 style operating points! I made some measurements (guided by Marik/Mark Fouxman of Samar Audio design) that concluded that these tubes have around 40k plate resistance and therefore are not compatible with 6.5:1 Ratio that U47 VF14 uses. you probably have noticed a lack of bass and weird top end and lack of depth to the sound?? This is why...
THE FIX!
So there are two solutions either use two Ef80/800/802 in Parallel Which I've tested and the sound is much better!! 8) Hello low end!! Also the sound much smoother and open.
or
Marik has a solution in the way of a Bv08 specs with a compatible ratio suitable to those Tubes. I'll be running some tests on these so stay tuned...
http://groupdiy.com/index.php?topic=57644.0
Just though I'd share an update on Ef80/800/802 47 builds as there is a major impedance mismatch at U47 style operating points! I made some measurements (guided by Marik/Mark Fouxman of Samar Audio design) that concluded that these tubes have around 40k plate resistance and therefore are not compatible with 6.5:1 Ratio that U47 VF14 uses. you probably have noticed a lack of bass and weird top end and lack of depth to the sound?? This is why...
THE FIX!
So there are two solutions either use two Ef80/800/802 in Parallel Which I've tested and the sound is much better!! 8) Hello low end!! Also the sound much smoother and open.
or
Marik has a solution in the way of a Bv08 specs with a compatible ratio suitable to those Tubes.
I'll be running some tests on these so stay tuned...http://groupdiy.com/index.php?topic=57644.0
Melodeath00
Well-known member
- Joined
- Jun 7, 2012
- Messages
- 416
OPR,
I'd like to know more about those measurements that led you to conclude the 40k plate resistance. My EF802 U47 does not lack lows, nor have weird high end. I've also seen a tube data chart for the EF80 that puts the plate resistance only a tiny bit higher than the VF14 at 1.1V cathode.
I'd like to know more about those measurements that led you to conclude the 40k plate resistance. My EF802 U47 does not lack lows, nor have weird high end. I've also seen a tube data chart for the EF80 that puts the plate resistance only a tiny bit higher than the VF14 at 1.1V cathode.
(Instructions by Marik)
"Feed 1Khz signal to your tube (some 0.2-0.5V). Measure output signal with high Z (at least 1M--any DMM should work) AC voltmeter. Measure on the transformer secondary--the mic output totally unloaded (i.e. no preamp, or any other than your DMM load should be present). Write this number. After that across the secondary connect 1-2Kohm pot (connect wiper to one of the other ends) and with the DMM still applied reduce the pot resistance until you can read exactly half of the first number."
To get plate Impedance multiply the transformer ratio by it's self and the measured resistance.
ie 6.5x6.5x1008K=42588 or 42.5K
Try it your self and report back.
"Feed 1Khz signal to your tube (some 0.2-0.5V). Measure output signal with high Z (at least 1M--any DMM should work) AC voltmeter. Measure on the transformer secondary--the mic output totally unloaded (i.e. no preamp, or any other than your DMM load should be present). Write this number. After that across the secondary connect 1-2Kohm pot (connect wiper to one of the other ends) and with the DMM still applied reduce the pot resistance until you can read exactly half of the first number."
To get plate Impedance multiply the transformer ratio by it's self and the measured resistance.
ie 6.5x6.5x1008K=42588 or 42.5K
Try it your self and report back.
Spencerleehorton
Well-known member
Hi,
None of my mics suffer from lacking low end and the top end is wonderful, very balanced.
I will try this test to get some idea of what you are saying.
Regards
Spence
None of my mics suffer from lacking low end and the top end is wonderful, very balanced.
I will try this test to get some idea of what you are saying.
Regards
Spence
Spencerleehorton
Well-known member
Hi,
So would the ratio of the TXF be higher or lower?
If so that maybe why mine sounds good as I think I'm using around 4:1 ratio TXF
Regards
Spence.
So would the ratio of the TXF be higher or lower?
If so that maybe why mine sounds good as I think I'm using around 4:1 ratio TXF
Regards
Spence.
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