NT2 upgrades... which is better?

[tchgtr]

It's Henry Spragens page, its phenomenal.

I made this quick mod image for a friend, that is pretty much what i did with mine. You add the red components. You can go with or without the pot, or use a switch instead of it.

The Spragens site is interesting, and I've been looking it over since I found this thread. Thinking I might try this idea in a Nady SCM 1000 to tame the 67-style capsule .
However....it seems there is a bit of confusion with the schematic.
It calls for a 500k variable resistor, but in Spragens frequency plots, he gives values for resistance of R9 from 0 to 100K Ohms, and in the text refers to it as a 100k resistor.
Seems like 100k is the proper value. 500k would cause a very small frequency dip if his plots are accurate.
Thanks for the cool link!

 

[kingkorg]

Frequency dip is achieved in full potential when pot is shorted, so when its set to zero ohms. I don't know how you came to that conclusion. You dont even have to use the pot.

 

[tchgtr]

Frequency dip is achieved in full potential when pot is shorted, so when its set to zero ohms. I don't know how you came to that conclusion. You dont even have to use the pot.

Sure, but let's have it adjustable at first to see where we like the cut.
According to his frequency plots the dip would be so small if set at 500K Ohms as to be not worthwhile, and he doesn't show a plot for 500K, only 100K.
Look at the caption under the bottom plots. He does not reference a 500K Ohm figure, only 0, 5, 10, 25, and 100K.
Plus on Pt. 4 he shows a photo of a 100K pot and refers to the adjustment pot as 100K.
http://www.audioimprov.com/AudioImprov/Mics/Entries/2014/2/8_EQ_Pt.3_-_Transformerless_Mics.html
I think the 500K figure in his schematic is a misprint.

 

[dp]

He may have chosen a larger value pot so that the taper is smoother and/or more finely adjustable?

I haven't ordered the parts yet... I got distracted by my DIYRE CP5 kit coming in the mail...  ;D

 

[kingkorg]

Tchgtr, with all due respoct i am not sure you get what the pot is doing in the circuit. It can as well be 1meg.

If pot is set to 500k there would be no attenuation, at zero ohm it would give maximum attenuation.

As you can see HS's last diagram shows that at 100k there still is some HF attenuation (gray line) and if you want flat stock response you need something like 500k. 250k would probably work too.

I have posted my measures against u87 and if that is result that's required you dont need a pot, that is maximum hf attenuation, and pot value in that case is zero ohms-short.

 

[tchgtr]

Tchgtr, with all due respoct i am not sure you get what the pot is doing in the circuit. It can as well be 1meg.

If pot is set to 500k there would be no attenuation, at zero ohm it would give maximum attenuation.

As you can see HS's last diagram shows that at 100k there still is some HF attenuation (gray line) and if you want flat stock response you need something like 500k. 250k would probably work too.

I have posted my measures against u87 and if that is result that's required you dont need a pot, that is maximum hf attenuation, and pot value in that case is zero ohms-short.

I see what you are saying. 500K would leave you with a flat (or nearly so) response.
I was just noting the discrepancy from the schemo to the photos, and observing that when he modded the mic in section 4 he used a 100K trimmer.
I may try the same in this Nady. It would  benefit from a bit trimmed off the top.
Very interesting site, and I like the way he justifies the use of this circuit. The whole site is interesting.
Thanks for your patient explanation, and linking it in the first place.

 

[dp]

I have posted my measures against u87 and if that is result that's required you dont need a pot, that is maximum hf attenuation, and pot value in that case is zero ohms-short.

Ah... I was wondering about that. I may skip the pot altogether then.

So a switch instead of the pot would be a closer to stock sound off and closer to your curve on then?

 

[kingkorg]

No, with a pot you get to tune attenuation to your taste. If you want u87 response you just set pot to zero ohms. In that case you can just use a switch, or a jumper instead of pot.

 

[dp]

No, with a pot you get to tune attenuation to your taste. If you want u87 response you just set pot to zero ohms. In that case you can just use a switch, or a jumper instead of pot.

Yes, we are saying the same thing. I think  I may have just worded it funny. That's what I MEANT to say... thanks for clarifying!

 

[dp]

So, with my Peavey VMP-2 I felt the stock  NT2 was a tad too bright. Not annoyingly so, but when my NTK was just too dark, I would swap it for the NT2 and it would add a little sparkle to it, and I would usually dial it out just a touch.

I just built a DIYRE CP5 and put the Louder Than Liftoff Royal Blue British Channel Module in it with the jumper set to a high shelf boost and holy cow... yeah the NT2 is CRAZY annoyingly WAY to bright with that.

So, the VMP-2 tames it quite a bit... the CP5 lets it shine in all of its annoying glory  ;D  SO I need to get on this mod ASAP!

The CP5 is also revealing that my NTK probably needs a cap job... getting some annoying noise with that, but that's a different story.

 

[dp]

OK so I dug around my parts stash and found all the parts i need on-hand, so I dug into this mod tonight.

Holy cow wow... thank you so much for this idea! This mic is now amazing. I have no lust for a new mic now. What a difference. It's got a nice smooth top end now, no harshness. Just clear... that's all I can say to explain it.

I gave up on the idea of a daughter PCB... and I left out the pot and/or switch, I just connected the cap straight across instead. I had two of the real tiny 1/4-watt 1% MF resistors that I installed on the bottom of the board. I stuck one lead up through the hole where the "outside" lead of the C4/C5 cap was and soldered the other end to the bottom solder point of C2/C3. The leads that were now sticking up through the PCB became like turrets that I soldered each end of my 1nF cap to, and the PCB's existing traces took care of the rest of the connections. 

wow... thanks again! this thing sounds so much better now. This helped me make up my mind for my next project. It was either going to be a micparts mic kit or another diy 500-series preamp... Hairball audio has an order coming soon! Now I just need to decide if I want to go Lola or Copper...

 

[coolman]

It's an alternative.

"Just" a capacitor in parallel with the drain resistor will have the effect of a low-pass.
A capacitor in series with a resistor, added in parallel with the drain resistor, will have a high-shelf effect (as kingkorg's suggestion).

Although some have reported an increase in the noise-floor, by adding series resistors between the JFET and the PNP bases.



[Edit: correction]

@Khron what values/models of capacitor and resistor would you recommend for best result with this mod?

 

[Khron]

@Khron what values/models of capacitor and resistor would you recommend for best result with this mod?

If you don't have any nF-range caps in your component stash, LTspice is your friend

Record something with the stock mic, play with a high-shelf attenuation (or 1st-order low-pass) until it sounds the way you like, then play with the component values until you get a similar response as the EQ curve.

I'd prefer to stick with film caps; NPO / C0G caps in the nF-range can get a bit pricey.

 

[sessizmod]

#2 did nothing for me.

I ended up adding two 10k resistors and 1n capacitor. It's part of MP mod for SP C1 mod. After that i got the mic to match HF response of u87. You can add a pot/switch as well.

http://www.audioimprov.com/AudioImprov/Mics/Entries/2014/2/8_EQ_Pt.3_-_Transformerless_Mics.html
It would be also a shame to waste that wonderful 797 audio capsule. Headbasket is better for a k67 capsule style mic. And it looks like a u87.

I have resistors but I couldn't get which capacitor to use, can you -by any chance- give me a link to see it? You can send me a pm as well.

 

[sessizmod]

#2 did nothing for me.

I ended up adding two 10k resistors and 1n capacitor. It's part of MP mod for SP C1 mod. After that i got the mic to match HF response of u87. You can add a pot/switch as well.

http://www.audioimprov.com/AudioImprov/Mics/Entries/2014/2/8_EQ_Pt.3_-_Transformerless_Mics.html
It would be also a shame to waste that wonderful 797 audio capsule. Headbasket is better for a k67 capsule style mic. And it looks like a u87.

Hey, do you think we can apply same mod to NT1-a ? Because I don't want to change the capsule. Can I get a closer frequency response to U87?

 

[kingkorg]

Hey, do you think we can apply same mod to NT1-a ? Because I don't want to change the capsule. Can I get a closer frequency response to U87?

If you feel comfortable with smd you can do this.

 

[sessizmod]

It's Henry Spragens page, its phenomenal.

I made this quick mod image for a friend, that is pretty much what i did with mine. You add the red components. You can go with or without the pot, or use a switch instead of it.

Yes i love that capsule, even without HF attenuation in some cases, Acc guitar for example. Just do a search, 797 Audio k67. It has been used in some well regarded mics, like Røde Classic I, or lately Townsend labs Sphere. Some people, way more experienced than me, consider it to be improvement over original Neumann design. The problem is, almost always they get used paired with wrong circuit.

Today I was with my electrician and were looking into the scheme and let me say, we just couldn't figure it out.. The man is mostly fixing TV's and stuff. Is there a slight chance you could upload your modded board?

 

[kingkorg]

Today I was with my electrician and were looking into the scheme and let me say, we just couldn't figure it out.. The man is mostly fixing TV's and stuff. Is there a slight chance you could upload your modded board?

You are talking about two different microphones! What microphone are you trying to mod?

 

[sessizmod]

You are talking about two different microphones! What microphone are you trying to mod?

I'm trying to mod my Nt2. Serial no: 19905
Here's the board.

 

[kingkorg]

I'm trying to mod my Nt2. Serial no: 19905
Here's the board.

Kinda weird the guy couldn't figure it out. You cut the traces after c2 and c3, add 10k resistors in series and bypass with 1nf capacitor. You don't need the pot in the drawing.