Replaced capsule in 3 pattern mic but only figure 8 is working

[pderbidge]

Here is an pic that captures the angle of the TAC1100 headbasket. You can see that It's not quite like a U87 as the mesh goes up a bit more before angling off. My Rode NT2a headbasket is probably more U87ish so I have no idea how this might affect the sound but thought someone might be interested. Still, the TAC1100 headbasket is more U87 like than the P420 (obviously) for what it's worth. I don't have a real u87 to compare to the TAC1100 so I'm basing that off of my observations of pictures of the U87 online.

 

[pderbidge]

Here's another angle for another perspective. Notice how the angle does not come all the way to the bottom of the screen/mesh. In my previous pic there is the illusion that one side is different from the other. This is NOT the case. both sides of the headbasket are exactly the same. Camera angles can play tricks on the eyes.

 

[157audio]

Thanks for posting what you posted! I agree, without mods it has a pretty good sound. I like it better with the flat k47, but stock it is lower certainly useable.

I was going to post here today that they put the mics back at their sale prices. It’s most definitely a good deal.

The tac700 was much easier to replace the capsule by the way as the board is all one piece, and the xlr connectors are part of that board as well. It also has a round headbasket. But, I do feel like the circuitry in the 1100 may be a better fit with the capsule. Maybe it’s the transformer giving it some weight or something.

I’ll post some pictures of the 700 when I get a chance. I’m fighting the flu/cold/respiratory thing that’s going around so when I’m not feeling like a truck ran over me…

 

[micolas]

Hi @157audio !
Did you buy the TAC1100 mics directly from the Adorama store in New York?
I'm very sorry that I can't buy it here in the EU.

 

[157audio]

Yes, I live close to the city and picked up the second batch of them in person.

As I browsed other mics though in the past couple of weeks, I get the feeling that this same mic is out there under other names. There’s a CAD 3000 mic that I wonder if it’s the same (I think that was the model). Externally it certainly looks the same but internally may be very different, I don’t know.

If anyone has experience with other mics that may be the same, can you post this models here in case people are in that situation of not being able to order from adorama? It sounds to me like it’s been determined that 797 Audio made these.

 

[micolas]

Yes, I live close to the city and picked up the second batch of them in person.

As I browsed other mics though in the past couple of weeks, I get the feeling that this same mic is out there under other names. There’s a CAD 3000 mic that I wonder if it’s the same (I think that was the model). Externally it certainly looks the same but internally may be very different, I don’t know.

If anyone has experience with other mics that may be the same, can you post this models here in case people are in that situation of not being able to order from adorama? It sounds to me like it’s been determined that 797 Audio made these.

Yes, they are rebranded 797 CR86

 

[pderbidge]

Yes, I live close to the city and picked up the second batch of them in person.

As I browsed other mics though in the past couple of weeks, I get the feeling that this same mic is out there under other names. There’s a CAD 3000 mic that I wonder if it’s the same (I think that was the model). Externally it certainly looks the same but internally may be very different, I don’t know.

If anyone has experience with other mics that may be the same, can you post this models here in case people are in that situation of not being able to order from adorama? It sounds to me like it’s been determined that 797 Audio made these.

The CAD 3000 is a flat circuit without negative feedback, so it's different.
http://recordinghacks.com/microphones/CAD/GXL3000

As far as I can tell, the tac1100 is the only multipattern mic with negative feedback and u87 style of headbasket in the low budget chinese brand of mics, which makes it an intriguing mod platform for sure.

 

[micolas]

There’s a CAD 3000 mic that I wonder if it’s the same (I think that was the model). Externally it certainly looks the same but internally may be very different, I don’t know.

If the TAC1100 schematic you drew is good then CAD GXL3000 is different.
His audio circuit is a 2 stage design, with the 2SK170 jFET feeding an emitter follower (a second BJT stage).
That allows the use of a cheap lo-tech output transformer (low ratio ~ 2:1)

 

[157audio]

I’ll have to take some time to digest what you all just said and try to understand it!

Does the negative feedback you speak of address the peak inherent in other capsules? I know that I like the way the flat 47 sounds in it.

 

[micolas]

I’ll have to take some time to digest what you all just said and try to understand it!

Does the negative feedback you speak of address the peak inherent in other capsules? I know that I like the way the flat 47 sounds in it.

NFB (negative feedback) is a circuit that performs a process of injecting a fraction (as level and frequency band) of the amplified signal, back to the input but with the phase reversed. Thus, certain frequencies are reduced, attenuated, at the same time distortions and noise are also reduced.
So the electronic circuit is not flat.
U87, for example, uses capsules with exaggerated highs, then through the deemphasis circuit, i.e. through NFB, it reduces those exaggerated high frequencies, avoiding the own noise of the electronic circuit, and makes the sound flatter,with less distorsions.

https://en.wikipedia.org/wiki/Negative-feedback_amplifier

 

[pderbidge]

I’ll have to take some time to digest what you all just said and try to understand it!

Does the negative feedback you speak of address the peak inherent in other capsules? I know that I like the way the flat 47 sounds in it.

Welcome to the rabbit hole!
@micolas gave you a great explanation of NFB, one that's above my pay grade, but in short, to address your first question. Yes. Assuming that the schematic you and everyone has helped come up with here is correct, then C16(part of the NFB) is the capacitor value that should help attenuate those peaky frequencies, so using a value higher than the stock 220pf "should" attenuate some of those "peaky" frequencies of the stock Capsule. If you go by the recommendations used in other circuits(V67, P420/220) with NFB, then using a value anywhere from 680pf to 1nf in place of the 220pf should do the trick. The higher the value, the more attenuation of high frequencies. You do NOT want to do this with your flat K47 since it doesn't need it and is designed for a more Flat circuit. Also, how impactful the NFB is determined by the overall circuit design. For example, in my V67G, based on my research, the NFB can be made more effective with some other mods, such as jumpering one resistor and rebiasing the jfet (another rabbit hole). I don't know if the same would be true of this tac1100 circuit. I'm not smart enough to know without others telling me. In fact, I probably sound smarter than I really am in what I've typed up here but I'm really just barely grasping these concepts myself, and that's probably an overstatement.

Here is an article( http://recordinghacks.com/2015/07/05/the-mxl-2001-v67g-capsule-swap-mod/ )discussing the NFB in the V67 type circuit. Keep in mind that the author benefits financially from the one solution he provides, but it's still a good read. The other solution is to keep the stock capsule and replace C16 with a higher value in the tac1100 (c3 in the v67g). For what it's worth, the easy solution is to do what you did and replace the K67 type capsule with something else, but rather than choose the capsules the author reccomends, I prefer the vendor you chose within that price range.