Topic: 3 Wire Box vs. SP BB for SP AT853's

[CHURCH-AUDIO]

You are correct sorry I was thinking of something else when I was replying to that post.
I do not wire my preamp the same way I use a differnt method with a 4.7k resistor accross the ground and the output of the capsule this reduces distortion a great deal wile only reducing the output by about 4 db and just using a 10k resistor between the + and the capsule bias input. But thats how I do it everyone has there own way. This is part of why my mod works as well as it does. I also have a mod I do to my own cardioid capsules but I do not talk about that one:)


Chris Church

[poorlyconditioned]

Replace that 27k with a 4.7 k resistor and watch what happens distortion goes way down levels are not reduced as much.

Chris Church

What's the theory behind that, Chris?
These electret FET circuits are pretty much auto-biasing to a given current, regardless of the source resistor.  Reducing the source resistance should increase the distortion in a source follower circuit, not reduce it.  It would also significantly reduce the overload levels, since the 4.7k would have less than 1V across it.
I'm not saying that you're wrong - I'd just like to understand your thinking

I'm not sure about this, Graeme, but Chris might be talking about running *2 wire* with a 5K source resistor (gain degeneration?) to limit gain/reduce distortion.  I played with this a little bit using the Panasonic (WM60/61) mics.  The idea was to use standard battery box wiring (and also use cheaper headphone cables) and but still reduce the distortion.

But if you're going to use three wires, you might as well use the circuit we have.  My one change was to reduce the source resistor to 13.3k.  This allows me to use the same battery box for both AKG CK91/93 and AT853 caps.  This reduces the headroom for AT853 a bit, but not by much.

Anyway, Chris, can you please confirm the wiring of your *3-wire* box, both the plain box and the preamp version.  I think you could sell the preamp version here.  Several people asked me about mine, but I'm not building them for others...

  Richard

[CHURCH-AUDIO]

I only use mogami three wire lav cable and let me tell you I dont have theory I have tested it with my equipment and there is less distortion with this method I still use three wire cable. For the preamp I use pin 1 ground pin 2 signal pin 3 bias output is 3.5 mm stereo jack.


Chris Church

Replace that 27k with a 4.7 k resistor and watch what happens distortion goes way down levels are not reduced as much.

Chris Church

What's the theory behind that, Chris?
These electret FET circuits are pretty much auto-biasing to a given current, regardless of the source resistor.  Reducing the source resistance should increase the distortion in a source follower circuit, not reduce it.  It would also significantly reduce the overload levels, since the 4.7k would have less than 1V across it.
I'm not saying that you're wrong - I'd just like to understand your thinking

I'm not sure about this, Graeme, but Chris might be talking about running *2 wire* with a 5K source resistor (gain degeneration?) to limit gain/reduce distortion.  I played with this a little bit using the Panasonic (WM60/61) mics.  The idea was to use standard battery box wiring (and also use cheaper headphone cables) and but still reduce the distortion.

But if you're going to use three wires, you might as well use the circuit we have.  My one change was to reduce the source resistor to 13.3k.  This allows me to use the same battery box for both AKG CK91/93 and AT853 caps.  This reduces the headroom for AT853 a bit, but not by much.

Anyway, Chris, can you please confirm the wiring of your *3-wire* box, both the plain box and the preamp version.  I think you could sell the preamp version here.  Several people asked me about mine, but I'm not building them for others...

  Richard

[poorlyconditioned]

I only use mogami three wire lav cable and let me tell you I dont have theory I have tested it with my equipment and there is less distortion with this method I still use three wire cable. For the preamp I use pin 1 ground pin 2 signal pin 3 bias output is 3.5 mm stereo jack.


Chris Church

Replace that 27k with a 4.7 k resistor and watch what happens distortion goes way down levels are not reduced as much.

Chris Church

What's the theory behind that, Chris?
These electret FET circuits are pretty much auto-biasing to a given current, regardless of the source resistor.  Reducing the source resistance should increase the distortion in a source follower circuit, not reduce it.  It would also significantly reduce the overload levels, since the 4.7k would have less than 1V across it.
I'm not saying that you're wrong - I'd just like to understand your thinking

I'm not sure about this, Graeme, but Chris might be talking about running *2 wire* with a 5K source resistor (gain degeneration?) to limit gain/reduce distortion.  I played with this a little bit using the Panasonic (WM60/61) mics.  The idea was to use standard battery box wiring (and also use cheaper headphone cables) and but still reduce the distortion.

But if you're going to use three wires, you might as well use the circuit we have.  My one change was to reduce the source resistor to 13.3k.  This allows me to use the same battery box for both AKG CK91/93 and AT853 caps.  This reduces the headroom for AT853 a bit, but not by much.

Anyway, Chris, can you please confirm the wiring of your *3-wire* box, both the plain box and the preamp version.  I think you could sell the preamp version here.  Several people asked me about mine, but I'm not building them for others...

  Richard

Oh yeah, this just occured to me.  Of course 5K is correct.  The resistance depends on the current draw of the mics.  If you put a voltmeter between the audio and ground pin (ie., across the 5k or whatever resistor), you should see approx. 4 to 5 volts, ie., half the battery voltage.  The source resistor depends on the mics.  30K for AT853, 10-15K for AKG CK91/93, and perhaps 5K for your mics...

So, let me understand this:
- for your mics you use a 3.5mm plug *for each mic*, right?
- for your preamp/ battery box you use two mini XLRM panel mount jacks, right?

(Please forgive me if this is written down on your webpage or elsewhere.)

Anyway, good luck with the gear loan.  Hopefully we'll hear some smokin' tapes out of this!

  Richard

[CHURCH-AUDIO]

5K Works with AT 853 mics too I have measured the distortion. its much less with 4.7 k resistor. I tryed 10k 2k 15k and 4.7k was perfect.

I only use mogami three wire lav cable and let me tell you I dont have theory I have tested it with my equipment and there is less distortion with this method I still use three wire cable. For the preamp I use pin 1 ground pin 2 signal pin 3 bias output is 3.5 mm stereo jack.


Chris Church

Replace that 27k with a 4.7 k resistor and watch what happens distortion goes way down levels are not reduced as much.

Chris Church

What's the theory behind that, Chris?
These electret FET circuits are pretty much auto-biasing to a given current, regardless of the source resistor.  Reducing the source resistance should increase the distortion in a source follower circuit, not reduce it.  It would also significantly reduce the overload levels, since the 4.7k would have less than 1V across it.
I'm not saying that you're wrong - I'd just like to understand your thinking

I'm not sure about this, Graeme, but Chris might be talking about running *2 wire* with a 5K source resistor (gain degeneration?) to limit gain/reduce distortion.  I played with this a little bit using the Panasonic (WM60/61) mics.  The idea was to use standard battery box wiring (and also use cheaper headphone cables) and but still reduce the distortion.

But if you're going to use three wires, you might as well use the circuit we have.  My one change was to reduce the source resistor to 13.3k.  This allows me to use the same battery box for both AKG CK91/93 and AT853 caps.  This reduces the headroom for AT853 a bit, but not by much.

Anyway, Chris, can you please confirm the wiring of your *3-wire* box, both the plain box and the preamp version.  I think you could sell the preamp version here.  Several people asked me about mine, but I'm not building them for others...

  Richard

Oh yeah, this just occured to me.  Of course 5K is correct.  The resistance depends on the current draw of the mics.  If you put a voltmeter between the audio and ground pin (ie., across the 5k or whatever resistor), you should see approx. 4 to 5 volts, ie., half the battery voltage.  The source resistor depends on the mics.  30K for AT853, 10-15K for AKG CK91/93, and perhaps 5K for your mics...

So, let me understand this:
- for your mics you use a 3.5mm plug *for each mic*, right?
- for your preamp/ battery box you use two mini XLRM panel mount jacks, right?

(Please forgive me if this is written down on your webpage or elsewhere.)

Anyway, good luck with the gear loan.  Hopefully we'll hear some smokin' tapes out of this!

  Richard

[whatboutbob]

Out of curiosity, how does one measure distortion?

[Big Muff]

OK so, sorry for a thread hijack...

I've been following the "3 wire vs." thread for a little while.
I've also seen Sanjay's box for sale in the yard, (which is nice cause my cables terminate in the mini xlr's)
would love to have a box for stealthing, but have a question or two.

I have the first pair of Franken Naks Marc Kim sold. DAMN do I Love em!
These are 10v electrets that run on P48 via the AT P48>9v module.

My questions:
there's discussion about what resistors sound best in the box for the at853's..
how could i determine which are best for the Franken Naks?

And once I have that info, who would be willing to accept commission to build me a 3 wire Nak box?


Cheers!
-Mike




hope this schematic helps...

[poorlyconditioned]

OK so, sorry for a thread hijack...

I've been following the "3 wire vs." thread for a little while.
I've also seen Sanjay's box for sale in the yard, (which is nice cause my cables terminate in the mini xlr's)
would love to have a box for stealthing, but have a question or two.

I have the first pair of Franken Naks Marc Kim sold. DAMN do I Love em!
These are 10v electrets that run on P48 via the AT P48>9v module.

My questions:
there's discussion about what resistors sound best in the box for the at853's..
how could i determine which are best for the Franken Naks?

And once I have that info, who would be willing to accept commission to build me a 3 wire Nak box?


Cheers!
-Mike




hope this schematic helps...

Well, your answer is right there in the schematics!  1.2k.

Measure the voltage across that resitor.  I should be roughly 1/2 the supply voltage, ie., 4.5V.  Try different values until you get it right.  1.2k sounds a bit low, maybe 4.7k or 10k?

  Richard

[CHURCH-AUDIO]

try a 4.7 insted of the 1.2k make sure its metal film no CARBON! if you see and carbon resistors most often they are 5% gold band or 10% silver band cut it out and remove it and replace all resistors with metal film 1% I like dale resistors they are sparky. Its what I use on all of my preamps.

OK so, sorry for a thread hijack...

I've been following the "3 wire vs." thread for a little while.
I've also seen Sanjay's box for sale in the yard, (which is nice cause my cables terminate in the mini xlr's)
would love to have a box for stealthing, but have a question or two.

I have the first pair of Franken Naks Marc Kim sold. DAMN do I Love em!
These are 10v electrets that run on P48 via the AT P48>9v module.

My questions:
there's discussion about what resistors sound best in the box for the at853's..
how could i determine which are best for the Franken Naks?

And once I have that info, who would be willing to accept commission to build me a 3 wire Nak box?


Cheers!
-Mike




hope this schematic helps...

Well, your answer is right there in the schematics!  1.2k.

Measure the voltage across that resitor.  I should be roughly 1/2 the supply voltage, ie., 4.5V.  Try different values until you get it right.  1.2k sounds a bit low, maybe 4.7k or 10k?

  Richard

[Big Muff]

Thanks guys,

But now that raises more questions.. I know, I'm an electronics noob.

Why would Nakamichi or Primo put in the 1.2k in the first place?
Also, if i were to have it switched out to something higher like the 4.7k metal film what kind of results could i expect?
Assuming this were done, i expect the 3 wire box would require the same 4.7k to produce the best sound, no?

Thanks again,
cheers!
-Mike

 

try a 4.7 insted of the 1.2k make sure its metal film no CARBON! if you see and carbon resistors most often they are 5% gold band or 10% silver band cut it out and remove it and replace all resistors with metal film 1% I like dale resistors they are sparky. Its what I use on all of my preamps.

Well, your answer is right there in the schematics!  1.2k.

Measure the voltage across that resitor.  I should be roughly 1/2 the supply voltage, ie., 4.5V.  Try different values until you get it right.  1.2k sounds a bit low, maybe 4.7k or 10k?

  Richard

[/quote]

[RedRocketSr]

My current rig:
AT853 (SP) > SP BB (with Levels and Bass Rolloff) > AD20 > JB3

please forgive my ignorance, but what is the purpose of the AD20? I realize that it's a analog-digital converter, but doesn't the JB3 do that already?

thanks for all of your patience.

Brett

[CHURCH-AUDIO]

Hi I measure distortion using a earthworks m50 mic as a reference point. I use a dupont calibrator with two levels one at 96db and one at 114db at 1k. This unit puts out a sine wave that is very clean and almost distortion free it has a distortion of less then 0.003% at 114db. Its a basic decibel meter calibrator that has a coupler at the end of it to 1/2 inch, I further reduce this for my omni mics to 6mm via a rubber washer. This gives me a known source for a simple distortion measurement. I then use WINAUDIOMLS to tell me the THD and THD+NOISE. I remove the known distortion of 0.003% and add the resalt of the test. From my mics, I also use this method to match my capsules for level. I base level on 1k I find that it is very accurate. Some people would argue that point but I feel that it gets me very close. I also do a broad band freq resp measurment to tell me what the mic does in level from 20hz to 90k then I match them again. it takes a while to do this then I put the matched capsules in groups of two in a static bag until I sell them. You can do the same test at home by using a computer speaker and a decibel meter both capsules have to be placed in the same exact spot in order to make the measurment good. I use a little stand i made with a aligator clip to hold the wire to the capsule and I bolt the stand to one of our workbenches So that it does not move during our freq resp test. This is how we do it there are much better ways but they cost alot more money to do. We do try to be very scientific with our tests. Using a lab calibrated source for measurments helps. At the end of the day you still have to use your ears because in the end you dont have a computer listing to the sound you have your ears and if they are trained to know what to listen for, they are the most powerfull audio analyizer in the world.


Chris Church
 

Out of curiosity, how does one measure distortion?

[scoper]

My current rig:
AT853 (SP) > SP BB (with Levels and Bass Rolloff) > AD20 > JB3

please forgive my ignorance, but what is the purpose of the AD20? I realize that it's a analog-digital converter, but doesn't the JB3 do that already?

thanks for all of your patience.

Brett

General thought is that the ADC in many consumer level devices is a weak spot. I don't think the ADC in the jb3 is that awful, but I noticed a substantial improvement when I used the AD20 with a MiniDisc recorder.

The AD-20  is also a preamp, with a range of +17 to +45 db. At the higher reaches it is extremely noisy, though. Anything needing more than +31db gain at the show, I set it  to +31 and add the rest in post.

[RedRocketSr]

thanks scoper... one more question if you don't mind... so the a->d steps are the reading of the analog input and the conversion to a digital (1 and 0) pattern. are you saying that some devices aren't able to correctly read the analog input and therefore 'miscreate' a correct conversion?

[scoper]

thanks scoper... one more question if you don't mind... so the a->d steps are the reading of the analog input and the conversion to a digital (1 and 0) pattern. are you saying that some devices aren't able to correctly read the analog input and therefore 'miscreate' a correct conversion?

I'm sure someone here can give a better answer to this than me...

Yes, the A/D circuit is responsible for turning analog music into 1's and 0's. There are expensive boxes with very sophisticated circuitry that do this job. Now try to miniaturize that into a small circuit which can be included into a low priced consumer unit. It's the hardest part to do really well, I guess. Size and cost are the bottlenecks.

Some consumer/pro recording units are known for good ADC sections - the Edirol r-1 and r-4 (still available), the Sony PCM-M1 and TCD-D100 DAT recorders (discontinued). These are all in the $700+ range. The Sound Devices 700 series runs into the thousands. People like the Oade Brothers make a good living modifying circuits on some of these.

You can't expect a $300+/- unit to compete.

Others with more experience, please expand, correct, and clarify - I'm in over my head here.

Scott