New design FET consenser?

[stefan]

Has anyone done a new schematic/pcb layout KM84 style (or similar) with components that are currently available? I´m lookin for a "clean" design without any switches. :?: I think the TLM 1O3 is way overpriced and it shouldn´t be that hard to build a mic that sound as good or better than this mic.

 

[dale116dot7]

All the parts are almost available... but you might need to sub something like a 2SK170 for the FET used in there as it can be a bit hard to get. But you need to match electronics to capsule - the U67 and U87 mics have some electronic EQ that the KM84 doesn't have.

The TLM103 'sound' isn't terrible - I find it much cleaner than most Chinese mics - but you're right, it's not that nice. Most of the Chinese mics I've heard are tuned with a spitty high-end, and their transformers don't help that much. IMHO, the problem is that the second backplate without a diaphragm is rather strange, and will add phasing artifacts. If you look at the unfiltered frequency response, you'll see a lot of wiggles in the midrange, in terms of off-axis response. The second issue is the TLM103 is a follower design, so the output of the capsule is what you get. It has no place for high-end rolloff, which is there in the U87, and moreso in the U67. To accomodate this, Neumann reduced the number of blind holes in the capsule. This has the effect of lowering the HF response of the capsule - it increases damping on the diaphragm and also the blind holes act as a resonator to give the high-end lift we're used to. The reduced number of them will darken the mic slightly, so it doesn't sound quite like a U87. They probably did this in order to compensate for the lack of HF EQ and transformer in the circuit. At the same time, the 'scoop' at 4kHz isn't as pronounced because part of that is done in the U87 capsule EQ circuit.

 

[stefan]

Well I might not be the U87:s truest beliver either but I do find it very useful for some applications and it sounds more "natural" to my ears than all the cheapo largecapsule mics or even the TLM 1O3, when doing orchestral recording and such. I´ve done a lot of violin recording and that 8-10K raise (that I find in many of the chineese $200mics) is something that I try my best to avoid when choosing microphones for this purpose. I just mentioned the 103 as an example of a mic without swithches. For me it would be nice to be able to build six or maybe even eight mics just for this purpose, and not ruining my economy while doing it. I was thinking something like $250-$300/mic for the parts. Of course it would be nice to be able to switch polar patterns but I´m not sure how much this would add in building costs. I´ve been looking at AKG 414s too but I think it kind of falls into the same "OKbuttooexpensive" category as the TLM, at least when shopping for 6 or 8 of them. I will finish my G7 and them I´ll continue the search for a simple clean sounding FET schematic. Any suggestions and thoughts are welcome.

 

[Gus]

http://www.groupdiy.com/index.php?topic=217

this should give you some ideas

The 5.6K should be 56K

 

[Guest]

I've built gus's circuit and like it alot! Very transparent sounding with a lundahl xformer...

 

[gang of elk]

anybody know anything about the transformerless circuit in a gefell umt70s? i acquired one used last week and i'm very impressed w its clean detailed sound. possibly a nice circuit (and cost effective) for DIY? don't know much about it other than it's transformerless.

i started taking the mic apart to look inside but chickened out once i removed the chunky pattern selector ring and got the outer sleeve off the body. the electronics are enclosed inside a 2nd inner sleeve which looks like it would require removing the capsule to investigate further so i decided against it until i know better what i'm getting into.

 

[stefan]

Cool. Gus, is there a board layout to go with that schematic? or even better has anyone made boards that they are willing to sell?

 

[Guest]

[quote author="gang of elk"]anybody know anything about the transformerless circuit in a gefell umt70s? [/quote]
I want it toooo. plzzzzzzzzzzzz.
Every non classical designs can sound interest if used properly.
If someone have it, i will glad to read, maybe via pm.
Maybe you can write to gefell.

xvlk

 

[Gus]

Why do you want or need a PCB? It is a simple circuit and perf lets you fit it in small spaces.

 

[tk@halmi]

I have had a two FET design on a breadboard for some time. It uses a 2N3819 for gain and a 2N4393 as a source follower. My goal has been to reduce the number of FETs that have to be sorted to get enough gain. The current consumption is about 2.5 mA (500ua through the 2N3819 and 2ma through the 2N4393). I have a 1:4 JLM mic transformer in reverse for the output. It would be nice to have a few Cinemags to try there. :grin:
Has anyone tried an OEP 1+1:2+2 in reverse for mic output?

Tamas

 

[strangeandbouncy]

Gefell UM70 definately rocks. So does the pencil version with M70 nickel capsule. (Can;t remember no) i wouldn't advise taking one to bits unless you are Very Patient, and used to putting mics back together . . . ie not like me . . . !

I'd like a circuit too!

ANdy P

 

[Brent Casey]

I've been wanting to try the OEP 1+1:2+2 "backards" to see how it sounds as a mic output traf. We have a bunch around from the old JoeMeeks. I'll let you know if I get to it anytime soon (not likely).

Brent Casey

[quote author="tk@halmi"]I have had a two FET design on a breadboard for some time. It uses a 2N3819 for gain and a 2N4393 as a source follower. My goal has been to reduce the number of FETs that have to be sorted to get enough gain. The current consumption is about 2.5 mA (500ua through the 2N3819 and 2ma through the 2N4393). I have a 1:4 JLM mic transformer in reverse for the output. It would be nice to have a few Cinemags to try there. :grin:
Has anyone tried an OEP 1+1:2+2 in reverse for mic output?

Tamas[/quote]

 

[CJ]

OT:

Sorry for the OT but this is too weak to start a thread on.
Just polar patterns for the beginner:

http://homerecording.about.com/library/blpatterns2.htm

 

[stefan]

[quote author="Gus"]Why do you want or need a PCB? It is a simple circuit and perf lets you fit it in small spaces.[/quote] I know, I just don`t like the looks of perfboard. I´d rather build it 3D point to point.