Become a Site Supporter and Never see Ads again!

Author Topic: MXL 990, 991 and Oktava 319 Mods  (Read 62144 times)

0 Members and 1 Guest are viewing this topic.

Offline Chuck

  • Trade Count: (42)
  • Needs to get out more...
  • *****
  • Posts: 10812
  • Gender: Male
  • time between the notes...
    • My recordings on the LMA
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #75 on: November 05, 2010, 01:00:28 PM »
So, when I measure 44v before the resistor, that is really only 90.1% of the actual voltage that the capsule gets? The reason for this is the very high resistance in the circuit negatively affects my DVM? Thank you very much for explaining that.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Chuck

  • Trade Count: (42)
  • Needs to get out more...
  • *****
  • Posts: 10812
  • Gender: Male
  • time between the notes...
    • My recordings on the LMA
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #76 on: November 05, 2010, 02:40:37 PM »
Jon, I guess that's why you design such good circuits. You've got all the formulas and math behind you.

I had no idea it was that complicated to just figure out how much voltage is getting to the mic capsules.

Since the only components I haven't swapped out of the circuit are the DC converter components, I guess that's going to be the next thing for me to look at.

My local electronics warehouse has a have a good supply of the 6.8pF and 27pF capacitors that are in that circuit. Maybe even inductors (are they RF inductors?) that are close in value. It sounds like small variations in those components may be responsible for the different DC output voltage between the mics. If I can match up those components more closely in both mics hopefully the capsules will each get the same voltage, so they will be matched more closely.

I really appreciate your input.
« Last Edit: November 05, 2010, 02:45:11 PM by Chuck »
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline chris319

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 142
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #77 on: November 07, 2010, 07:32:01 AM »
I am now set up to measure mic frequency response, which I have done with the MXL 991. Below are links to curves of an unmodified 991 and a (different) modified 991:

Unmodified:

http://groups.yahoo.com/group/micbuilders/photos/album/1663506385/pic/417612400/view?picmode=original&mode=tn&order=ordinal&start=1&dir=asc

Modified:

http://groups.yahoo.com/group/micbuilders/photos/album/1663506385/pic/953648042/view?picmode=original&mode=tn&order=ordinal&start=1&dir=asc

The output of the unmodified mic is significantly lower than the modified mic. The only components modified were capacitors. Both mics exhibit a 3 - 4 dB dip around 6 kHz.
« Last Edit: November 07, 2010, 08:46:42 AM by chris319 »

Offline Chuck

  • Trade Count: (42)
  • Needs to get out more...
  • *****
  • Posts: 10812
  • Gender: Male
  • time between the notes...
    • My recordings on the LMA
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #78 on: November 08, 2010, 09:31:40 AM »
Cool. Thanks for that Chris.

Well, I have the answers to some of the issues I had.
One of my DVM's must have a lower impedance than the other, because I still get 24 ~volts when measuring the voltage before the 1G resistor with that meter.
My other DVM measures closer to 50v. I looked up the specs on that meter and it has 10M input impedance.

I was able to regulate the voltage between the two moded mics by using different values for the 27pF capacitor in the DC converter section. I found that if I lowered the capacitor value, for the lower voltage mic it brought the voltage up enough to closely match the other mics voltage. I couldn't find the exact right ratio in the 27pf caps I had, so I paralleled two 6.8pf caps together for each mic. This brought the voltage up around 8v in each mic. Now they are both within +/- 1v of each other. The mics are much quieter now too. They seem to like the higher voltage.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Roger Gustavsson

  • Trade Count: (1)
  • Taperssection Member
  • ***
  • Posts: 423
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #79 on: November 08, 2010, 11:43:25 AM »
I am now set up to measure mic frequency response, which I have done with the MXL 991. Below are links to curves of an unmodified 991 and a (different) modified 991:

Unmodified:

http://groups.yahoo.com/group/micbuilders/photos/album/1663506385/pic/417612400/view?picmode=original&mode=tn&order=ordinal&start=1&dir=asc

Modified:

http://groups.yahoo.com/group/micbuilders/photos/album/1663506385/pic/953648042/view?picmode=original&mode=tn&order=ordinal&start=1&dir=asc

The output of the unmodified mic is significantly lower than the modified mic. The only components modified were capacitors. Both mics exhibit a 3 - 4 dB dip around 6 kHz.

How did you measure them? Cardiod microphones need to be measured at exactly the same distance, the response varies a lot with distance. I think you will have to be registrated at micbuilders to see the pictures.

Roger


Offline chris319

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 142
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #80 on: November 08, 2010, 12:59:12 PM »
How do I attach a jpg in this forum? I can't seem to find a way to.

Offline Chuck

  • Trade Count: (42)
  • Needs to get out more...
  • *****
  • Posts: 10812
  • Gender: Male
  • time between the notes...
    • My recordings on the LMA
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #81 on: November 08, 2010, 01:15:46 PM »
Use the Additional Options button when replying.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline chris319

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 142
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #82 on: November 09, 2010, 06:04:05 PM »
Quote
How did you measure them? Cardiod microphones need to be measured at exactly the same distance, the response varies a lot with distance.

I came across a paper from Neumann discussing this. The short story is that 60 cm (24") is considered a sufficient distance to overcome proximity effect.
« Last Edit: November 09, 2010, 06:33:05 PM by chris319 »

kirk97132

  • Guest
  • Trade Count: (0)
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #83 on: November 11, 2010, 01:25:19 PM »
any jfet replacement suggestions?  since we are closer to being able to bias our existing fet for ourselves, is their any room for real world improvement?

BTW, thanks to Jon for the expertise and Chuck for the motivation to mod the remaining Apex 185's I have... Thanks to Raymonda for the housing mod motivation...

Joe
Joe, Any chance of posting pix of the 185 guts?  I'm wondering how different the layout is compared to the 180's. 

Offline bugg100

  • Trade Count: (0)
  • Taperssection All-Star
  • ****
  • Posts: 1015
  • Gender: Male
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #84 on: November 11, 2010, 02:22:48 PM »
sure, i'll post this afternoon. btw, 185= 603 clone w/ rolloff and pad, 180 = 603 Clone, 190 and 195 are electret ala your c02 more than likely.

frontend audio carries the 185 stereo kit ( shocks, omni, card, body all in pairs, case ) for $110 shipped.

wonder how much busman wants for hyper caps....

kirk97132

  • Guest
  • Trade Count: (0)
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #85 on: November 11, 2010, 02:29:22 PM »
Saw hypers on ebay for $8 Dunno how good they are.  Thanks for info, I'm think bout some 180's to play with.  without changing the capsules on the CO2's there is probably a limit on the quality I can get out of them.   I thought with the switches they revert to surface mount parts to make room for things.  for me that equates to harder to work on.  I'm already wearing glasses to see this stuff and even have a "special" set that are about 5X for real small stuff. 

Offline bugg100

  • Trade Count: (0)
  • Taperssection All-Star
  • ****
  • Posts: 1015
  • Gender: Male
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #86 on: November 11, 2010, 03:53:16 PM »
   I thought with the switches they revert to surface mount parts to make room for things.

Nope still all through hole construction.... Same part to mod, same part numbers....

 Having a hard time finding previous photos after a os reinstall.... may have to shoot more for you! 

Electret capsules or externally biased? 

Offline Chuck

  • Trade Count: (42)
  • Needs to get out more...
  • *****
  • Posts: 10812
  • Gender: Male
  • time between the notes...
    • My recordings on the LMA
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #87 on: November 11, 2010, 04:08:47 PM »
Chinese SD microphones with the transformerless Schoeps style circuit
All use the same capsule(s)

797 Audio CR1-4
ADK SC-1
ADK SC-2 *
ADK SC-T
Advanced Audio CM-54 *
AMT 404
Apex 180
Apex 185 *
Audio 2000 ACM1901 *
Busman BSC-1
CAD GXL 1200
Carillon AXIS 1
Cascade M37
Cascade M39 (available in all silver & all black) *
Felio CR1-11
Feilo CR1-14 *
KAM i2 (all black) *
Marshall MXL 600
Marshall MXL 603
Marshall MXL 603S (super cardioid capsule)
Marshall MXL 604 *
Marshall MXL 991 *
Nady CM-90
Nady CM-95 *
Peluso CEMC-6 *
SE Electronics SE1
SE Electronics SE1A
SE Electronics SE2A

__________________________________________

* These microphones have the pad and high pass switches
« Last Edit: November 11, 2010, 04:20:03 PM by Chuck »
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Chuck

  • Trade Count: (42)
  • Needs to get out more...
  • *****
  • Posts: 10812
  • Gender: Male
  • time between the notes...
    • My recordings on the LMA
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #88 on: November 11, 2010, 04:13:30 PM »
This search: http://shop.ebay.com/?_from=R40&_trksid=m570&_nkw=MXL+capsules
brings up a Hong Kong vendor selling $7.49 capsules on eBay. But it's my understanding that the center pin connector does not make contact with the center pin on the 603 style mics. Also, the cardioid version and hyper-cardioid version have the venting on the capsule, if you look closely.

Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline bugg100

  • Trade Count: (0)
  • Taperssection All-Star
  • ****
  • Posts: 1015
  • Gender: Male
Re: MXL 990, 991 and Oktava 319 Mods
« Reply #89 on: November 11, 2010, 04:20:45 PM »
all the above is correct, leading back to busman being the friendly dealer of hyper caps KNOWN to work....

 

RSS | Mobile
Page created in 0.085 seconds with 38 queries.
© 2002-2024 Taperssection.com
Powered by SMF