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Post by Johnkenn on Mar 2, 2017 23:36:35 GMT -6
This is interesting...$369 microphone-parts.com/products/t47-microphone-kit?variant=8663993923We started with one of the simplest and cleanest vintage mic circuits in history, Neumann's KM84. You don't need 500 components to make a great microphone; we'd agree with Neumann engineers that the simplest solution is often the best. We implemented the circuit without electrolytic or tantalum capacitors. We picked a vintage JFET, which we put through a rigorous selection and biasing procedure (see below). We removed the silly attenuator components that needlessly reduce output level. We found a wonderfully warm, US-made output capacitor. And a shockingly good transformer...
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Post by c0rtland on Mar 2, 2017 23:41:23 GMT -6
That looks like an all around good time
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Post by marten on Mar 3, 2017 6:53:51 GMT -6
Really interested too. I might order a pair soon.Worst case scenario is they'll end up on E GTR amps.
Isn't Jim Williams behind these?
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Post by Johnkenn on Mar 3, 2017 7:13:39 GMT -6
Really interested too. I might order a pair soon.Worst case scenario is they'll end up on E GTR amps. Isn't Jim Williams behind these? Welcome, marten Really? That would make me trust them even more...
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Post by mulmany on Mar 3, 2017 7:49:35 GMT -6
One of the groupdiy guys was behind this version. The m-parts owner is behind Roswell Pro Audio mics. He has collaborated with a lot of different builders/designers. Supposedly their caps come from the same high quality factory as jolly, and AA.
Well, I doubled checked and it looks like this is not the same as the Groupdiy project. Poctop did the board for that off of someone else's design (Jonathan ?).
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Post by deehope on Mar 3, 2017 10:02:43 GMT -6
After Bob Ohlsson talked about motown using km84s on vocals I started messing around with one of my km84 clones on vocals and liked it. First thought was why there wasn't a km84 voiced ldc. This looks awesome.
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Post by svart on Mar 3, 2017 10:15:24 GMT -6
Just buy some Oktava MK219/MK319. Pretty much the same circuit as the KM84, with a LDC.
BTW.. I have some 219's for sale..
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Post by deehope on Mar 3, 2017 10:23:25 GMT -6
Just buy some Oktava MK219/MK319. Pretty much the same circuit as the KM84, with a LDC. BTW.. I have some 219's for sale.. didn't know that. Everytime I hear those they sound dark to me?
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Post by svart on Mar 3, 2017 10:32:05 GMT -6
Just buy some Oktava MK219/MK319. Pretty much the same circuit as the KM84, with a LDC. BTW.. I have some 219's for sale.. didn't know that. Everytime I hear those they sound dark to me? They are indeed a little dark. The "russian" sound I've heard it called since a lot of Oktava and Lomo mics seem to be very dark. I think that's just the effect of the capsule, but some folks have "improved" them by modding some parts. I did this and it was somewhat improved.
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ericn
Temp
Balance Engineer
Posts: 15,011
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Post by ericn on Mar 4, 2017 22:11:32 GMT -6
How about a SDC kit of this with the same thread and pin as a KM 84 so I can buy it and a new KM84 Capsule from Neumann and have what we really want?
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Post by Johnkenn on Mar 4, 2017 22:37:23 GMT -6
How about a SDC kit of this with the same thread and pin as a KM 84 so I can buy it and a new KM84 Capsule from Neumann and have what we really want? Ha. No shit.
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Post by jimwilliams on Mar 5, 2017 11:26:46 GMT -6
I didn't do the design on those but they do use my "selected components" for the old KM84 design. Matt sent me one of these kits about a year ago. It came with their standard 1" rk-12 capsule. I haven't used it yet on a session as I have other stuff I favor. Compared to my rk-12 loaded MCA mics these have a thinner low end and a less open top end. In that regard it's been passed over for now as I do love the sound of the rebuilt MCA mics more.
A U-89 capsule would probably sound good in these as I put one in a rebuilt MCA mic for Ty Ford, it sounded amazing, far better than a TLM-170 to me. Then again, a KM84 capsule with that transformerless Schoeps variation circuit would also probably work for me here.
I believe the missing low end depth of the Microphone-parts KM84 circuit is caused by the output transformer. I sent it to Dave Hill at Jensen Transformers to run it on their Comtran system to quantify it. Jensen is now making replacement transformers for common Neumann mics, I'd love to get one to replace this one, I suspect it would solved the sonic issues I have.
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Post by jakeharris on Mar 5, 2017 11:35:43 GMT -6
Microphoneparts capsules are WAY too expensive.
It's standard chinaware, available on Aliexpress for 70% less
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Post by Johnkenn on Mar 5, 2017 21:21:29 GMT -6
I didn't do the design on those but they do use my "selected components" for the old KM84 design. Matt sent me one of these kits about a year ago. It came with their standard 1" rk-12 capsule. I haven't used it yet on a session as I have other stuff I favor. Compared to my rk-12 loaded MCA mics these have a thinner low end and a less open top end. In that regard it's been passed over for now as I do love the sound of the rebuilt MCA mics more. A U-89 capsule would probably sound good in these as I put one in a rebuilt MCA mic for Ty Ford, it sounded amazing, far better than a TLM-170 to me. Then again, a KM84 capsule with that transformerless Schoeps variation circuit would also probably work for me here. I believe the missing low end depth of the Microphone-parts KM84 circuit is caused by the output transformer. I sent it to Dave Hill at Jensen Transformers to run it on their Comtran system to quantify it. Jensen is now making replacement transformers for common Neumann mics, I'd love to get one to replace this one, I suspect it would solved the sonic issues I have. Hmmm...replacement transformers for U67s? sll
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ericn
Temp
Balance Engineer
Posts: 15,011
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Post by ericn on Mar 6, 2017 8:24:25 GMT -6
I didn't do the design on those but they do use my "selected components" for the old KM84 design. Matt sent me one of these kits about a year ago. It came with their standard 1" rk-12 capsule. I haven't used it yet on a session as I have other stuff I favor. Compared to my rk-12 loaded MCA mics these have a thinner low end and a less open top end. In that regard it's been passed over for now as I do love the sound of the rebuilt MCA mics more. A U-89 capsule would probably sound good in these as I put one in a rebuilt MCA mic for Ty Ford, it sounded amazing, far better than a TLM-170 to me. Then again, a KM84 capsule with that transformerless Schoeps variation circuit would also probably work for me here. I believe the missing low end depth of the Microphone-parts KM84 circuit is caused by the output transformer. I sent it to Dave Hill at Jensen Transformers to run it on their Comtran system to quantify it. Jensen is now making replacement transformers for common Neumann mics, I'd love to get one to replace this one, I suspect it would solved the sonic issues I have. Hmmm...replacement transformers for U67s? sllThe Jensen name carries plenty of weight, I'm sure between Radial house brand and Jensen they are already doing OEM for somebody! It has always amazed me if you ask a Transformer manufacturer what you just might be able to get your hands on !
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Post by sll on Mar 6, 2017 9:47:11 GMT -6
I didn't do the design on those but they do use my "selected components" for the old KM84 design. Matt sent me one of these kits about a year ago. It came with their standard 1" rk-12 capsule. I haven't used it yet on a session as I have other stuff I favor. Compared to my rk-12 loaded MCA mics these have a thinner low end and a less open top end. In that regard it's been passed over for now as I do love the sound of the rebuilt MCA mics more. A U-89 capsule would probably sound good in these as I put one in a rebuilt MCA mic for Ty Ford, it sounded amazing, far better than a TLM-170 to me. Then again, a KM84 capsule with that transformerless Schoeps variation circuit would also probably work for me here. I believe the missing low end depth of the Microphone-parts KM84 circuit is caused by the output transformer. I sent it to Dave Hill at Jensen Transformers to run it on their Comtran system to quantify it. Jensen is now making replacement transformers for common Neumann mics, I'd love to get one to replace this one, I suspect it would solved the sonic issues I have. Hmmm...replacement transformers for U67s? sll If anyone could do it right, Jensen would be on the top of the list.
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ericn
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Balance Engineer
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Post by ericn on Mar 6, 2017 15:29:13 GMT -6
Has anybody tried a KK84 on a cheap Chinese SDC body? If the threads fit, it would save a lot of work building a clone !
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Post by drbill on Mar 6, 2017 16:01:13 GMT -6
Those cheap chinese SDC preamp bodies are not worth the crushed aluminum cans it took to make em. It would ruin a KK84. Plus the threads don't match.
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ericn
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Balance Engineer
Posts: 15,011
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Post by ericn on Mar 6, 2017 18:01:02 GMT -6
Those cheap chinese SDC preamp bodies are not worth the crushed aluminum cans it took to make em. It would ruin a KK84. Plus the threads don't match. Well that last part answers the question!
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Post by dandeurloo on Mar 6, 2017 19:33:54 GMT -6
I ordered one of these the other day. I have a stash of decent capsules of a few different varieties that I want to stick into some clean mic amps circuits. Low noise, useable mics for general purpose stuff. I also, have a stash of DIY and donor bodies around here. One of them needs multiple patterns, so I grabbed one of these to try in my donor body. So, this kit seemed like a reasonable thing to try.
I question the TX as well, very few TX companies make good TX's anymore. I asked Matt about it but I didn't get much info, just that it is better then the other OEM km84 TX's that the manufacture makes. I plan on sticking a Redline M7 in this mic. I am sure I will tweak a little more and probably look for a better TX. These mics are gonna just be for extra channels and I'm not looking to spend a ton on them.
I'll let ya know how it turns out. I am sure it will be decent.
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Post by Guitar on Mar 7, 2017 9:46:34 GMT -6
I ordered one of these the other day. I have a stash of decent capsules of a few different varieties that I want to stick into some clean mic amps circuits. Low noise, useable mics for general purpose stuff. I also, have a stash of DIY and donor bodies around here. One of them needs multiple patterns, so I grabbed one of these to try in my donor body. So, this kit seemed like a reasonable thing to try. I question the TX as well, very few TX companies make good TX's anymore. I asked Matt about it but I didn't get much info, just that it is better then the other OEM km84 TX's that the manufacture makes. I plan on sticking a Redline M7 in this mic. I am sure I will tweak a little more and probably look for a better TX. These mics are gonna just be for extra channels and I'm not looking to spend a ton on them. I'll let ya know how it turns out. I am sure it will be decent. I was thinking of doing something very similar. Let us know how it turns out!
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Post by ChaseUTB on Mar 8, 2017 7:02:42 GMT -6
I use a single end class A transformer based mic with Thoersch blue line cap and fet electronics for vocals with great results.
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Post by dandeurloo on Mar 8, 2017 9:45:17 GMT -6
I use a single end class A transformer based mic with Thoersch blue line cap and fet electronics for vocals with great results. I have a stash of mics with SCHOEPS circuit and different M7's. They can be very useable nice mics.
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Post by aamicrophones on Mar 8, 2017 15:37:47 GMT -6
Hi Guys, the AA CM1084 actually uses a class "A" C451 2-stage type circuit which is a medium gain fet, coupled into a single silicon transistor configured as an emitter follower.
It is very important to check the curve of the FET in the 84/87 circuit and you can see the bias resistor in each U87 is custom selected and I am sure this would be the same for the KM84. In the KM84 they also use a negative feedback capacitor to trim the gain of the FET.
The 451 circuit is the AKG414eb circuit without the pattern change circuitry.
The CM1084 circuit drives a 2:1 output transformer not a 10:1 like the KM84 required. The low frequency distortion and response gets much better when you drive a transformer from the lower impedance of the emitter.
Now, in theory you can use anything between a 5:1 ratio and 9.5:1 ratio in a KM84/U87 whose circuits are identical except for the pattern circuitry and there is no de-emphasis in the KM84 circuit. Matt said, "he found a 6.5:1 transformer seemed to be optimum".
With the 5:1 ratio you get a 200 ohm output impedance and with the 10:1 you get a 50 ohm output impedance. The 200 ohm impedance will yield 6db more output into a 1K ohm load or greater than the 50 ohm setting.
The difference between a 5:1 transformer and a 2:1 transformer is 8db. The difference between 10:1 and 2:1 is 14db. The 10:1 have 14db greater loss. This means the class "A" emitter follower circuit has to do between 8db and 14db less work plus you have the advantage of driving the transformer from a much lower drive impedance.
The lower the transformer drive impedance the lower the LF distortion. Take a Cinemag CM2510 which you can find all the spec's for on the Cinemag site. The CM2510 has an 8:1 ratio just for example.
When you drive the Cinemag from a lower impedance (600 ohms) not only is the phase response at the high frequencies better but the distortion is lower in the low frequencies.
When the CM2510 is driven from 600 ohms there is .6% distortion at 20hz with a level of +18dbu. When you drive the CM2510 from 20K ohms the the distortion rises and +12dbu will produce .4% distortion.
So, you get almost a 6db improvement in low frequency distortion by driving the transformer from the lower impedance.
A LDC capsule also has much more output than a 22mm SDC capsule but the single FET circuit in the U87 has been successful. However, in my experience I would like to see a bit more headroom from an LDC circuit than a single fet provides.
The maximum output of a U87 is -6dbu. The maximum output from our microphone is +14dbu minimum. The KM84 circuit is very simple but adding a class "A" emitter follower circuit adds one capacitor, one transistor and one resistor for a 14db improvement.
Cheers, Dave aamicrophones.com
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Post by dandeurloo on Mar 8, 2017 22:51:23 GMT -6
Hey Dave, long its been a long time since we chatted. Question for ya, with the emitter circuit you are talking about is the capacitor in the audio path? I am assuming it must be some sort of coupling cap?
BTW, I am mixing a record next for a client that was tracked with all of your mics plus a SM7. I listened to the tracks already and they sound really good. They used one of your 87 style mics on the vocals and they sound really great.
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