Better Circuit for the Original Capsule from the MCA SP-1?

[RuudNL]

The test circuit is the classical Schoeps circuit.
Hfe and Vbe can be measured with most digital meters.
Noise is measured with an audio analyser and a weighting filter.

 

[Paul678]

Ok, excellent.  I'll try 47nF for C14 and C15.

But first, I have to get a cheap donor mic body and basket, and a cheap PCB board....

Unfortunately, as someone else pointed out, it's often cheaper to just buy another
MXL brand new!!  crazy!

 

[Paul678]

The test circuit is the classical Schoeps circuit.
Hfe and Vbe can be measured with most digital meters.
Noise is measured with an audio analyser and a weighting filter.

BTW, I have Hfe on my meter, but not Vbe.

How close do you try to match the Hfe?  Within what %? 

What about Vbe?

 

[micaddict]

Relax, Paul. It's Sunday. 

 

[Paul678]

Relax, Paul. It's Sunday. 

    I'm relaxed, but Micaddicts never rest!      :

 

[RuudNL]

I have Hfe on my meter, but not Vbe.
How close do you try to match the Hfe?  Within what %?

On most digital multimeters there is a diode test function, that shows the forward voltage.
If your meter does not have a diode test, connect the B-E junction of the transistor under test in series with a resistor of 10K.ohm to a voltage of 10 Volts or so and measure the voltage over the junction. (ca. 600-700 mV)
Keep the voltage constant and avoid temperature changes between transistors under test, since the temperature has an influence on the B-E forward voltage.

I first select transistors in groups: good, maybe usable and bad.  (Value too far off)
Then I select the ones from the group 'good' for the best match.  The closer they match, the better!

(If you want, I can send you a close matched pair of hand-selected low-noise PNP transistors, I have some selected pairs here.)

 

[Paul678]

I have Hfe on my meter, but not Vbe.
How close do you try to match the Hfe?  Within what %?

On most digital multimeters there is a diode test function, that shows the forward voltage.
If your meter does not have a diode test, connect the B-E junction of the transistor under test in series with a resistor of 10K.ohm to a voltage of 10 Volts or so and measure the voltage over the junction. (ca. 600-700 mV)
Keep the voltage constant and avoid temperature changes between transistors under test, since the temperature has an influence on the B-E forward voltage.

I first select transistors in groups: good, maybe usable and bad.  (Value too far off)
Then I select the ones from the group 'good' for the best match.  The closer they match, the better!

(If you want, I can send you a close matched pair of hand-selected low-noise PNP transistors, I have some selected pairs here.)

Ok, thanks for the tip.

I found this method, with is similar:

      http://home.comcast.net/~ijfritz/projects/transmat001.pdf

 

[TheWoozle]

Nico Veth, the Dutch guy who made the well-known MCA SP-1 and MXL 990 mod site (site is down at the moment) uses the stock capsule, too.

Another Dutch guy, who services my vintage mics, has been doing an MCA SP-1 mod from day one. He makes a new PCB, but uses the stock the capsule.

While I'm at it, a third Dutch guy is our own Ruud. He's a rising star in mod land and, as can be seen in reply #3, he knows a thing or two.  8)
And I can tell you he's a nice guy to boot.

The fourth Dutch guy in this story would be me. And I ............ um...... love microphones.  ;D

If you meant this page, the URL changed.... here's the new link.

http://members.ziggo.nl/nvrecording/nhc/AudioTechniek/mxl990_sp1mods/mods_en.htm

There's also a similar discussion going on at a certain Site Whose Name Must Not Be Mentioned;

http://www.gearslutz.com/board/low-end-theory/717272-mca-sp-1-mod-procedure-7.html#post8877366

BTW, the SP1 is now defunct. They are shipping the new models with surface mount components, so no longer suitable for easy modding. Apparently some other MXL models are still using the old boards still, like the model 990.

 

[RuudNL]

BTW, the SP1 is now defunct. They are shipping the new models with surface mount components, so no longer suitable for easy modding.

There are unpopulated circuit boards for the SP1 available!