Miktek CV4 / swap capsule / Beesneez K47

[Coronargakon]

Hi there,

A couple of years ago I got a used Miktek CV4 and found as many other owners that the highs are a little bit annoying. I have swapped the stock capsule to a new Beesneez K47 (thanks to the member McIrish) and to my surprise not only the CV4 is now having a very well balanced highs but also the low mids is now more healthy/dominant too. Highly recommend the swapping to K47 from the stock capsule.


An issue that I really need your valuable technical knowledge:


I am getting from the stock PSU a very very weak hum which is obvious only when in silent passages / arming the recording process. This hum was there before swapping the capsule. Measuring the voltage on pin 2 of the 7 pin cable with mic unplugged it provides 6.76V (!). This isn’t outside the 6.3V specs that EF800 accepts for the heating voltage?



I made use of another PSU (Beesneez) that provides 6V via the pin 2 and the CV4 works ok. No hum at all! Dead silent. However after many recording tests of my voice using the Beesneez PSU and carefully comparing the results to the stock PSU I could definitively say that using the stock PSU I am getting more pronounced low mids.


My question is:

1. Is it normal for the stock PSU to provide 6.76V heating voltage to EF800? If no, is this a point that can be examined by technician for that weak hum I am getting from the stock CV4’s PSU? Using more heating voltage can affecting the low mids behavior of the mic?
2. Inside the stock PSU there are the following 6 electrolytic caps: 400v/22μF (4 caps) and 25V/10,000μF. (2 caps).Which branch/model could you recommend in order to replace those Chinese TL caps mentioned aboved? All stock are 105 degrees temp. Panasonic and Nichicon are both first class choice but which model/series exactly could do the job perfectly?…

Your reply will be highly appreciated.

Christos

 

[Khron]

Measuring the voltage on pin 2 of the 7 pin cable with mic unplugged it provides 6.76V (!).

You just answered your own question there. Have you tried measuring that voltage inside the mic, when powered up? Odds are you'll get a reading much closer to the 6.3v you were expecting.

is this a point that can be examined by technician for that weak hum I am getting from the stock CV4’s PSU?

Hum is an AC-ripple-superimposed-on-DC issue, not a DC level issue. That, or some minor ground-loop going on in the PSU and/or the mic. Or between those and the preamp / interface you're using.

Panasonic and Nichicon are both first class choice but which model/series exactly could do the job perfectly?…

Those, as well as Elna, United Chemi-Con and Rubycon. Exact series are irrelevant in this application - pick whatever physically fits, and/or fits your budget (if one exists).

You'll wanna stick with the 105C rating for longevity, and go with whatever you can find in stock with your favourite distributor, that has the longest(?) lifetime spec. Even the lousiest ones will be rated for at least 2000 hours, at the rated temperature and the rated ripple current (lifetime doubles for every 10C drop under the rated temperature: 2k @ 105C = 4k @ 95C, 8k @ 85C etc).

Probably not much point in going above the 10.000uF that's stock there - you'd only have even higher current spikes that the bridge rectifier needs to handle, which is arguably unnecessary.

 

[Coronargakon]

You just answered your own question there. Have you tried measuring that voltage inside the mic, when powered up? Odds are you'll get a reading much closer to the 6.3v you were expecting.

Measuring the voltage on the tube’s pins I got the following:

50,8v
50,8v
0,0v
0,028v
6,46v
1,05v
1,23v. (AC ?)
Not tested
1,06v

So, I guess the 6,46 refers to the heating voltage…

Hum is an AC-ripple-superimposed-on-DC issue, not a DC level issue. That, or some minor ground-loop going on in the PSU and/or the mic. Or between those and the preamp / interface you're using.

Using the Beesneez PSU with CV4 and the same interface/mic pre there is no hum. So, I could guess that something inside the stock PSU is causing this.

Those, as well as Elna, United Chemi-Con and Rubycon. Exact series are irrelevant in this application - pick whatever physically fits, and/or fits your budget (if one exists).

You'll wanna stick with the 105C rating for longevity, and go with whatever you can find in stock with your favourite distributor, that has the longest(?) lifetime spec. Even the lousiest ones will be rated for at least 2000 hours, at the rated temperature and the rated ripple current (lifetime doubles for every 10C drop under the rated temperature: 2k @ 105C = 4k @ 95C, 8k @ 85C etc).

Probably not much point in going above the 10.000uF that's stock there - you'd only have even higher current spikes that the bridge rectifier needs to handle, which is arguably unnecessary.

Hi Khron, really appreciate your extensive and informative reply. Thanks a lot!

 

[Khron]

Measuring the voltage on the tube’s pins I got the following:

50,8v
50,8v
0,0v
0,028v
6,46v
1,05v
1,23v. (AC ?)
Not tested
1,06v

You could also indicate which pin is which. And for extra clarity, you could also probe the voltages on all the points where the wires from the bottom of the mic, connect to the PCB.

 

[Accelerator]

Hi Christos @Coronargakon and greetings from Greece.

The 6,46v Heater Voltage is a little bit “high”, but it is within the +5% range that the EF800 valve/tube has as “nominal” range…

I would like to know the Heater Amperage that your valve/tube draws for heating…

It should be somewhere 275mA (Telefunken) to 295mA (AEG).

The Beesneez PSU is regulated to 6 Volts for the heaters, something that I don’t know if your stock Miktek CV4 PSU if it is regulated or not, and if it is regulated in which voltage and by what device (ICs?... Zeners?...)

The heating voltage affecting to the V.C. curves of the valve/tube, so in that way it can affecting to the biasing of the valve/tube which in that way can affecting the low mids behavior of the mic…

Have in your mind that the “Original” designing of this tube microphone schematic by Oliver Archut (RIP) of Tab – Funkenwerk, have the heating voltage down to +5.05 Volts…

 

[Coronargakon]

Hi Accelerator! Thanks for the reply...Greetings from Cyprus

Hi Christos @Coronargakon and greetings from Greece.

The 6,46v Heater Voltage is a little bit “high”, but it is within the +5% range that the EF800 valve/tube has as “nominal” range…

I would like to know the Heater Amperage that your valve/tube draws…

It should be somewhere 275mA (Telefunken) to 295mA (AEG).

Yes it should be around 275mA. Telefunken EF800 is the stock one and I keep one NOS Telefunken EF804s which I intend to test after finding out what's going wrong with that weak hum coming out of the stock PSU.

The Beesneez PSU is regulated to 6 Volts for the heaters, something that I don’t know if your stock Miktek CV4 PSU if it is it or not and if it is regulated in which voltage and by what device (ICs?... Zeners?...)

The heating voltage affecting to the V.C. curves of the valve/tube, so in that way it can affecting to the biasing of the valve/tube which in that way can affecting the low mids behavior of the mic…

The experience and the related enthusiasm that members of this group are sharing this experience is highly appreciated and especially helpful for people that create/compose music having limited technical knowledge in regards to electronics and tube circuits.
I am glad to hear that the heating voltage can affect the sonic character of the mic and in this case the low mids...

Have in your mind that the “Original” designing of this tube microphone schematic by Oliver Archut (RIP) of Tab – Funkenwerk, have the heating voltage down to +5.05 Volts…

Oliver Archut (RIP) and his schematic based on the EF800 was the reason to get this mic. I got the chance to share a few emails in the past with him...great guy and extremely generous...Swapping the stock capsule of the CV4 to a K47 type was my priority mainly due to that annoying zing of the highs.... The Beesneez K47 capsule gave to the mic a completely new character especially as a voice mic... (my 2 cents..)

 

[Accelerator]

@Coronargakon

I believe Christos that it is a good time for taking your stock Miktek CV4 PSU, your cables (microphone & XLR) and you Miktek CV4 microphone to be examined by a trustful technician if there is a ground loupe - hub in the whole microphone system that produce and amplifies this annoying hum and in general to examined the whole quality & the condition of the HT (High Tension ) & LT (Low Tension) voltages filtering by the filter capacitors…

Sometimes even a very little cold soldering join of this filter cup, or on the microphone jack connection join, or of this noised diode etc… can make you a lot of trouble…

 

[Coronargakon]

@Coronargakon

I believe Christos that it is a good time for taking your stock Miktek CV4 PSU, your cables (microphone & XLR) and you Miktek CV4 microphone to be examined by a trustful technician if there is a ground loupe - hub in the whole microphone system that produce and amplifies this annoying hum and in general to examined the whole quality & the condition of the HT (High Tension ) & LT (Low Tension) voltages filtering by the filter capacitors…

Sometimes even a very little cold soldering join of this filter cup, or on the microphone jack connection join, or of this noised diode etc… can make you a lot of trouble…

Thanks Accelerator. I’ve just examined the mic …certainly the problem is on the stock PSU. Cables (stock and Gotham GAC7/Canare/Neutrik) all working fine with CV4 and Beesneez PSU. The only noise is the forgiving one coming from the normal tube circuit…
Examining the stock PSU inside nothing strange is appearing.. but maybe you are right regarding a cold soldering joint underside the PSU’s pcb….
The problem (weak hum) would be inaudible and a good monitoring system may be needed in order to detect the problem acoustically…

Thanks again for the reply