Apex 460 Power Supply Mod: D5, D6

[bernatvm]

Yes sorry, dumb answer  I will draw it and put it back here, if you are okey to look at it and correct me if I'm wrong, I would be pleassed. Thanks!

 

[Khron]

Sounds like a plan

I don't mean to sound harsh, but i'm more of the "teach a man to fish"-kinda person ;D (rather than  "give a man a fish", if you're familiar with the saying).

 

[bernatvm]

I think this should be it. I don't know if transistors are correct for my circuit nor what do I have to take on accout for calculating the values of R5, R6, C6 and C7

 

[Matador]

I didn't see you describe the problem you are trying to fix.  Can you explain that first?  Noise can come from many places, and I didn't see that you did anything to isolate the source of the problem (or even what the problem was in the first place).

 

[Khron]

Well, those two transistors are unsuitable voltage-wise, and far over-rated current-wise.

A single 2N5551 (or similar, 160v-rated or higher NPN transistor), like in figure 2 in the link, but with a doubled-up R-C filter driving its base (like the 220R / 470u setup in figure 3). I'd go with two 10k resistors and two 1u/160v (or 250v) capacitors - you can use larger capacitor values,  but they might get physically big and/or pricey.

I think this should be it. I don't know if transistors are correct for my circuit nor what do I have to take on accout for calculating the values of R5, R6, C6 and C7

 

[bernatvm]

I didn't see you describe the problem you are trying to fix.  Can you explain that first?  Noise can come from many places, and I didn't see that you did anything to isolate the source of the problem (or even what the problem was in the first place).

My mic is noisier now that I've modded the psu than before. I like how the sound changed when i lowered B+, but noise is a problem. Apart from regular white noise, i have some strange very big peak at 5hz or so (im talking about +20db above signal). Second one is easily fixed with hpf, but anyway, makes me think something is wrong. I tryed changing electrolytic caps on mic and psu and I don't have acces to any other psu. I will just try this "addon" and see how it works.

 

[bernatvm]

Well, those two transistors are unsuitable voltage-wise, and far over-rated current-wise.

A single 2N5551 (or similar, 160v-rated or higher NPN transistor), like in figure 2 in the link, but with a doubled-up R-C filter driving its base (like the 220R / 470u setup in figure 3). I'd go with two 10k resistors and two 1u/160v (or 250v) capacitors - you can use larger capacitor values,  but they might get physically big and/or pricey.

Then only one transistor, a 2N5551. Two RC stages before the transistor (220R/470uF). Two 10k resistors for R5 and R6 and two 1u for C6 and C7

 

[Khron]

Just to be on the safe side, you'll want to add that antiparallel diode from the NPN's emitter to collector, like in Figure 2.

But to make things clear, referring to your "tweaked" schematic, by "two RC stages", i meant two sets of R5 & C6 (see Figure 3 in the capacitance multiplier link). R6 shouldn't be necessary.

I'm on the road right now, but i'll try to whip up a schematic later today.

Then only one transistor, a 2N5551. Two RC stages before the transistor (220R/470uF). Two 10k resistors for R5 and R6 and two 1u for C6 and C7

 

[Gus]

I would stop and rethink the noise issue before adding more to the circuit.

Was the noise OK when the PS was stock?

What exactly did you change in the circuit?

What did you do at the heater section?
I would not assume the noise issue is only from the B+.
What is the transformer heater voltage?

Do you know how to use a oscilloscope to  look at the voltages?

 

[bernatvm]

I would stop and rethink the noise issue before adding more to the circuit.

Was the noise OK when the PS was stock?

What exactly did you change in the circuit?

What did you do at the heater section?
I would not assume the noise issue is only from the B+.
What is the transformer heater voltage?

Do you know how to use a oscilloscope to  look at the voltages?

The noise problem with the modded psu is known isue for the mod i did.

The noise was ok with the stock mic+psu. I changed capsule, tube and transformer. Also moded the psu for multipatern, because the original one was not variable. Also changed d5 and d6 to lower the voltage of the b+.

I don't know the heater voltage, will check it.

I do have access to an oscilloscope and know how to use it.

 

[Gus]

The noise problem with the modded psu is known isue for the mod i did.

The noise was ok with the stock mic+psu. I changed capsule, tube and transformer. Also moded the psu for multipatern, because the original one was not variable. Also changed d5 and d6 to lower the voltage of the b+.

I don't know the heater voltage, will check it.

I do have access to an oscilloscope and know how to use it.

Check the filament power supply with the scope for AC noise on "top" of the DC voltage. You can inject noise into a microphone with a noisy filament supply.
It is not clear to me if you changed parts in the filament supply.

 

[bernatvm]

Check the filament power supply with the scope for AC noise on "top" of the DC voltage. You can inject noise into a microphone with a noisy filament supply.
It is not clear to me if you changed parts in the filament supply.

I didn't, all the mods took place in the b+, the control rail that changes the polar patern and the mic's components (tube, capsule and xformer). I followed instructions here: http://advancedaudio-europe.com/forum/viewtopic.php?p=4134&sid=e3d9a0e0193770fc927257a279cc0c93#.XAThsrfOE0N

 

[bernatvm]

Just to be on the safe side, you'll want to add that antiparallel diode from the NPN's emitter to collector, like in Figure 2.

But to make things clear, referring to your "tweaked" schematic, by "two RC stages", i meant two sets of R5 & C6 (see Figure 3 in the capacitance multiplier link). R6 shouldn't be necessary.

I'm on the road right now, but i'll try to whip up a schematic later today.

Do you have a moment to draw it?  :

 

[Khron]

Disregard the actual component values.

Was my description really that difficult to "get", though?  I mean, considering the referenced schematics...

 

[SubSpec]

I hate to start a new thread for this measly question, so hijacking

Adapting a Retro Tube II PSU (very similar layout to this) for a Warm WA-47. All is good out of the box except the pattern selector which is (generally) correct right off the switch but hits a resistor before going out and is thus lower than the mic needs. At least, that's what my highly noob observations are. Pictures below, but if that is the correct assumption I'm good taking the green wire right off the switch to the XLR7 right?

FWIW mic expects 0v omni, 75v card, 150v f8 and it currently outputs 27.2v and 61.1v respectively on the XLR7. The only compromise I see in this solution is the cardioid switch position would need to be right of center one notch as center is ~60v while the next is the expected 75v.

 

[Khron]

And how certain are you that your meter was NOT dragging down the voltage itself?

 

[SubSpec]

I am precisely zero percent certain

 

[RuudNL]

The series resistor from the switch is no problem, because the polarisation voltage doesn't draw any current.
(You may measure a lower voltage, because the meter is loading the output.)

 

[SubSpec]

Awesome, thanks so much for those answers! So most likely all is good, but I'm assuming I can confirm by measuring with the mic connected, is that right?

 

[Khron]

Nope. You'll still get skewed results, possibly even more so.

If you're having trouble understanding how and why, draw that piece of schematic (pattern switch resistors and whatever other is connected to that, AND where you connect your voltmeter, as a resistor with whatever the input impedance of your meter is. Then do some Ohm's law math (parallel resistors etc).