Microphonics in VF14 and U47

[rock soderstrom]

Hello, is this how you modified your circuit? I really want to try it out, but I only have K47

I'm not Tony Terry either but are you sure your heater arrangement will work like this? EF184 likes 6.3V on the heater according to the datasheet, your voltage will be much higher, this will be a short pleasure.

I suggest a separate heater voltage.

 

[Murdock]

Oh my gosh, I changed the picture. Thank you for pointing that out.View attachment 140891

Also, the heater arrangement does not work the way you have drawn it. The EF184 draws 300mA. If you would take it from B+ you would need a whopping 100W resistor. Don’t even know if that exist
You should use a separate heater supply.

 

[Екатерина]

I'm not Tony Terry either but are you sure your heater arrangement will work like this? EF184 likes 6.3V on the heater according to the datasheet, your voltage will be much higher, this will be a short pleasure.

I suggest a separate heater voltage.

OK. Is it connected like this？

 

[Екатерина]

R8 should be around 800K

 

[rock soderstrom]

Yep, heater is better now. But because of the high B+ voltage your polarization voltage is too high (for most capsules), I think you have to adjust the voltage divider.

Edit: yes, R8= 800K looks good

 

[Екатерина]

Yep, heater is better now. But because of the high B+ voltage your polarization voltage is too high (for most capsules), I think you have to adjust the voltage divider.

Edit: yes, R8= 800K looks good

Can you roughly estimate the output impedance of this circuit？There are still some differences between this electronic tube and the original one

 

[rock soderstrom]

Can you roughly estimate the output impedance of this circuit？There are still some differences between this electronic tube and the original one

Well, it's not all that simple, since we're talking about triode mode operation with very low anode current here and the fact that the tubes are operated outside some (data sheet) parameters plus underheating. See for yourself, my guess is that the EF184 would cope better with a 10:1 transformer, as it is not quite as current-potent as the VF14 and also has the greater internal resistance

But there are definitely people who know better...

 

[Екатерина]

Well, it's not all that simple, since we're talking about triode mode operation with very low anode current here and the fact that the tubes are operated outside some (data sheet) parameters plus underheating. See for yourself, my guess is that the EF184 would cope better with a 10:1 transformer, as it is not quite as current-potent as the VF14 and also has the greater internal resistance

But there are definitely people who know better...

View attachment 140894View attachment 140895

Good day! This is really a headache. How should I adjust if I use a 10:1 transformer?

 

[terry setter]

Hello, I'm sorry that I didn't see this thread earlier. The last diagram, posted byЕкатерина, is correct.

I use voltage divider values in the Meg Ohm range, because there's no reason to bleed off more B+ current than needed and noise is not an issue in that part of the circuit. If you're B+ is 200V (which I suggest for the EF 184) then your R7 value would be 2 Meg and R8 would be 1 Meg. That will give you 1/3rd of 200 = 66.66V to the capsule. If you want to dial it in for exactly 63V, you can use a ten-turn, one Meg linear pot for R8. If having a pot in the circuit makes you nervous, then, once you find the exact resistance that is needed for the polarizing voltage you want, you can replace the pot with a fixed resistor.

I've had great results matching the harmonic spectrum of an original U47 circuit when using a 6.5:1 output transformer (I love the NiCo 2461 from Cinemag. Not cheap, but it's THE sound).

 

[Екатерина]

Hello, I'm sorry that I didn't see this thread earlier. The last diagram, posted byЕкатерина, is correct.

I use voltage divider values in the Meg Ohm range, because there's no reason to bleed off more B+ current than needed and noise is not an issue in that part of the circuit. If you're B+ is 200V (which I suggest for the EF 184) then your R7 value would be 2 Meg and R8 would be 1 Meg. That will give you 1/3rd of 200 = 66.66V to the capsule. If you want to dial it in for exactly 63V, you can use a ten-turn, one Meg linear pot for R8. If having a pot in the circuit makes you nervous, then, once you find the exact resistance that is needed for the polarizing voltage you want, you can replace the pot with a fixed resistor.

I've had great results matching the harmonic spectrum of an original U47 circuit when using a 6.5:1 output transformer (I love the NiCo 2461 from Cinemag. Not cheap, but it's THE sound).

I'm glad to see your reply. I only have two E25-sized 6.5-ratio transformers, and I'm a little worried that the 6.5-ratio might be too low.

 

[rock soderstrom]

Hello, I'm sorry that I didn't see this thread earlier. The last diagram, posted by@Екатерина, is correct.

Hey Terry, nice of you to chime in. I still think your recipe is interesting and would like to experiment with it further soon.

I've had great results matching the harmonic spectrum of an original U47 circuit when using a 6.5:1 output transformer (I love the NiCo 2461 from Cinemag. Not cheap, but it's THE sound).

That's interesting, have you measured that, are there any results you can show? What impedance was the output loaded with?

 

[Murdock]

I measured the output impedance of my EF800 U47 and it came out to be around 250 Ohm.
According to my simulations with spice (which were always pretty accurate to my surprise), the output impedance of the EF184 is even lower. So a 6.5:1 transformer should be good.

 

[rock soderstrom]

I measured the output impedance of my EF800 U47 and it came out to be around 250 Ohm.
According to my simulations with spice (which were always pretty accurate to my surprise), the output impedance of the EF184 is even lower. So a 6.5:1 transformer should be good.

Hey Murdock, I believe you, we've already covered this topic elsewhere. I'd still like to see some measurements under known conditions, as I'm currently working on this and we can then compare the results. That would be great!

 

[Murdock]

Hey Murdock, I believe you, we've already covered this topic elsewhere. I'd still like to see some measurements under known conditions, as I'm currently working on this and we can then compare the results. That would be great!

I don’t have any EF184 here. I can provide measurements with my EF800 U47 mic.
I’m interested in your measurements and how you do it.

 

[rock soderstrom]

I measured the output impedance of my EF800 U47 and it came out to be around 250 Ohm.

How do you do this measurement, can you explain your procedure a little more? I am still at the beginning of my career as a measurement technician and I think other members would also be interested in this.

 

[rock soderstrom]

I don’t have any EF184 here. I can provide measurements with my EF800 U47 mic.
I’m interested in your measurements and how you do it.

Okay, our answers/questions came at the same time.

My setup is still under construction at the moment. I'm currently trying out the following software tools (REW, audiotester, waveforms) and seeing how I can get the best results. My test hardware is a Behringer UMC404HD.

As I said, I'm still trying out the best way to proceed, I may have to build a few more things, I'm currently reading up on the work of member @jp8 , highly recommended!

I think I have definitely measured too little and assessed too much subjectively in the past. I would like to get the human factor, i.e. myself, out of the equation a little more.

 

[Екатерина]

I measured the output impedance of my EF800 U47 and it came out to be around 250 Ohm.
According to my simulations with spice (which were always pretty accurate to my surprise), the output impedance of the EF184 is even lower. So a 6.5:1 transformer should be good.

This is really good news. So cool!