Power supply problem

  • Thread starter Thread starter PhilGood
  • Start date Start date
OK, I know this was stupid! I got itchy and fired the whole thing up!!

It worked! It really worked! Don't forget to read the previous posts to check my work, but I felt I was in close enough range to check it.

I had a few problems at first. I had a few pops that to me sounded like a bad cap. I replaced the tube on a hunch and the pops were gone. I guess overheating the filament must have damaged it. It's underheated now. Then I was hearing a radio station. I pulled the mic apart and noticed a solder lead had pulled off the number 2 pin for the tube. After resoldering the radio was gone.

How does it sound???

So far as I can tell on my initial tests it destroys the Royer mod. I'm stunned, I really am!!! This thing sounds amazing, at least on my voice. I'll have to try more instruments, but I don't own a mic that sounds this full. The bass is in control, yet enormous. The high end is extremely silky and the natural compression is about 3 times better than the Royer. I may have a little sheilding problem, cause there's a buzz when the mic is off, but it disappears when it warms up. I don't think this is wishful thinking 'cause when it first fired up it didn't sound too good. It takes alot longer than my other tube mics to warm up, but once it did - DAMN!! I'll have to see if I feel the same about it by tomorrow, but I'm just floored right now.

Again check my work to see if I'm in the ballpark or the parking lot.

BTW, the mic I used for the Sony clone is a Nady SCM900, if you can belive that.
 
Yup, it was just wishful thinking. After further evaluation, the Royer has a better bottom end. I will probably have to change the output caps to something higher. The Sony clone has better midrange and way better compression, and overall is smoother with more presence, but also isn't as hot. In fact it's quite a bit lower on the output. This may be a trait with Sony's mics. I have a couple of old C-38's and the output is low on them. I thought it was because they were old.

Further tweeking is warrented.
 
PhilGood said:
I put in a 33ohm for the filament running off the 12.6v. Now my filament is at 5v @ .66 A.

With the B+ I have the following:

141.3v B+ @ 25mA
Bias area is 70.1v
'capsule' is getting 1.1v
Click to expand...


The filament is still low.
The B+ @25ma?! :eek: It is around 1ma.
The capsule is getting 70.1V, but your voltmeter loads the voltage after 100M resistor.

Yup, it was just wishful thinking. After further evaluation, the Royer has a better bottom end. I will probably have to change the output caps to something higher. The Sony clone has better midrange and way better compression, and overall is smoother with more presence, but also isn't as hot. In fact it's quite a bit lower on the output. This may be a trait with Sony's mics. I have a couple of old C-38's and the output is low on them. I thought it was because they were old.
Click to expand...

No it is not. The low output is because a cathode follower does not have any voltage gain. It is offset however by its other advantages--1)it is impossible to oveload it, 2)its distortions are very low, 3)Input impedance is much higher, and more suited for work in a microphone, 4)Since it has lower output impedance, output x-former can be lower ratio.

What is your trafo, and what is its ratio? It may influence the low end. What is the value of your output cap? Also, try to reduce B+ to 120V and see if the low end improves.
 
Go to bed! I'll address this in the AM, and thanks again!! You have no idea how valuable you are!
 
Woo Yay! Congratulations Phil, that was a good purchase then you should be proud.

Marik said:
The capsule is getting 70.1V, but your voltmeter loads the voltage after 100M resistor.
Click to expand...

DOH! I'm a ninny :o
 
Marik said:
The filament is still low.
The B+ @25ma?! :eek: It is around 1ma.
The capsule is getting 70.1V, but your voltmeter loads the voltage after 100M resistor.
Click to expand...

Is this an OK voltage?

I have another idea for the filament trafo. I bought a 3-0-3 @ 300mA that I may try with a 1 ohm or no resistor at all. I also bought a 6-0-6 @ 500mA. If I swap my current one and use this with a 22ohm, that might put me where I need to be.


Marik said:
The low output is because a cathode follower does not have any voltage gain. It is offset however by its other advantages--1)it is impossible to oveload it, 2)its distortions are very low, 3)Input impedance is much higher, and more suited for work in a microphone, 4)Since it has lower output impedance, output x-former can be lower ratio.

What is your trafo, and what is its ratio? It may influence the low end. What is the value of your output cap? Also, try to reduce B+ to 120V and see if the low end improves.
Click to expand...

The output trafo is a Cinemag CM24110, which has a ratio of 4:1. Tom and I talked and he said that was the closest to the hand-written note of 4.08:1.

I've tried several caps for the output as well. Right now I have: 1st is .22uF, 2nd is .47uF, Third is 1.0uF. This gives the biggest tone with even balance between stages.

I can get the B+ down to 118v if I put back the 47k's in the string.
 
PhilGood said:
The output trafo is a Cinemag CM24110, which has a ratio of 4:1. Tom and I talked and he said that was the closest to the hand-written note of 4.08:1.

I've tried several caps for the output as well. Right now I have: 1st is .22uF, 2nd is .47uF, Third is 1.0uF. This gives the biggest tone with even balance between stages.
Click to expand...

The x-former should be fine.
Do all your caps workl in series, or you short first two? If you don't, then you get a value around 0.15 Mf all together, which would explain your bass cut.
 
Marik said:
The x-former should be fine.
Do all your caps workl in series, or you short first two? If you don't, then you get a value around 0.15 Mf all together, which would explain your bass cut.
Click to expand...

So capacitance is like resistance in that adding together divides it in series?

The caps work in series for the roll off. As you turn the switch to the right, it shorts each. First the .22, then the .5 until all the way to the right only the 1.0 is working. It has the best bass response there. Maybe I sould use a 1.5 there and change the .22 to something smaller?

My first issue is still to get the voltages to where you suggested.
 
I swapped the filament trafo for the 6-0-6 500mA and put in an 18ohm resister. Now the filament is a 5.95 volts. I made the whole string 47k's on the B+, and now the voltage is 125 volts.

Bass is greatly improved as well as the mics output. It sounds very smooth now. Very full. The presence is awesome!

Now I just have to figure out why the teeny buzz came back. I think it's a ground/sheild problem.
 
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