Aurycle FET Mikes

[Matador]

I ordered a few Aurcyle FET mikes (their U87 copy) and wanted to start a chronicle of design changes I had planned for them.

Here's a link to the mike:

http://www.aurycle.com/aurycle-a460-large-diaphragm-fet-condenser-diy-microphone.html

Here's a few pics I took right from the box:

And a schematic I adapted from the one I was sent:

Schematic

Here's what I'm planning on doing:

1) Switching out the capsule for a 6 micron K67 type
2) Remove the JFET bootstrap and switching the front end to a regular common drain configuration per original U87/KM-84
3) Remove the PNP follower stage
4) Install a CM-2480 10:1 Cinemag output transformer
5) Ditch the tantalum caps and switch audio path to WIMA 5mm film caps, and power supply bypass to Nichicon minature aluminum electrolytic
6) Replace resistors with my favorite epoxy coated Dale 1/4W metal films
7) Restore de-emphasis circuit to original U87 values
8) Re-bias input FET for maximum signal swing

Anything else that comes recommended to look at?  Perhaps for MXL-2001 mods (same circuit)?

 

[gary o]

Im loving your plan  8).........Is this what i read people been doing to a V67 .......big thanks for schematic I have been thinking about DIYing a mic like this.....

got more questions....are you going to swap the 2sk170 for 2n2819 ? more like U87
Where will you get your K67 capsule ....who sells a good one or is there good copy in a current china mic...
Is the Cinemag OP tran similar to 87 OP tran then....
Did I read the U87 had tant capaictors in it & part of the sound, maybe be wrong...
power supply bypass caps.......will that make it quieter........
Just how bad is the Aurycle capsule........

really looking forward to this Im sure you gonna end up with great mic......

all the best.

 

[Matador]

got more questions....are you going to swap the 2sk170 for 2n2819 ? more like U87
Where will you get your K67 capsule ....who sells a good one or is there good copy in a current china mic...
Is the Cinemag OP tran similar to 87 OP tran then....
Did I read the U87 had tant capaictors in it & part of the sound, maybe be wrong...
power supply bypass caps.......will that make it quieter........
Just how bad is the Aurycle capsule........

I have 20 each of 2N3819 (I assume this is what you meant) and J305 type devices coming to try each out.  Based on the datasheet I might be able to get a bit better input swing with the 2N3819 however the noise might be worse.  I'll have to see when I'm testing things out in-circuit.

As for the capsule:  I haven't heard the stock capsule yet.  I have a Schoeps mike to try out the capsule and get an idea of the sound.  I was leaning towards the Peluso CEK-367 but haven't decided yet.

The Cinemag is a 10.5:1 ratio which I think is a bit different than the U87 original.  The Cinemag looks to have enough primary inductance to pass enough bass with the stock 4.7uF coupling capacitor.  I'm not convinced the transformer that comes with the mike does but I'm planning on testing it out nonetheless.

The stock capsule may be ok especially given the HF de-emphasis in the U87 circuit.  But I already have mikes that are biased towards the brighter end of the spectrum so I'm looking for something that has a bit more midrange emphasis for different flavors.

 

[benlindell]

I'm really interested in what/how you end up doing this. I have a pair of K67 capsules that I'd love to use, this looks like an easy way to do so.

 

[EEMO1]

  The Cinemag looks to have enough primary inductance to pass enough bass with the stock 4.7uF coupling capacitor.  I'm not convinced the transformer that comes with the mike does but I'm planning on testing it out nonetheless.

if I remember correctly, the stock transformer ratios are something like MAYBE 2:1, hence the pnp follower to drive the low ratio transformer... test it out though!

 

[Matador]

if I remember correctly, the stock transformer ratios are something like MAYBE 2:1, hence the pnp follower to drive the low ratio transformer... test it out though!

It's interesting....the documentation with the mike says it includes a 10:1 transformer, however similar mikes (mxl 2001 and v67) come with 2:1's.  I'll have to run a signal generator through it to see what it really is.

I'm on the fence about removing the follower: driving the output transformer from such a low impedance has advantages (damping factor mainly) and allows a lower ratio transformer so less gain is required in the preamp.  Using a 10:1 with the follower throws away 6db of signal.

As for caps: the pcb's have 3mm pitch layouts for the caps: no easy way to shoehorn in a film.  I think I may try a high quality bipolar electrolytic (I've had good success with Nichicon UEP series on my preamps) as they seem to fit perfectly.

 

[Sylvain D.]

I'm also interested in seeing where you will take this. The Aurycle is the same as the Golden age FC1MK2 minus the pad... I have one of these I would'nt mind tweeking

 

[EEMO1]

if I remember correctly, the stock transformer ratios are something like MAYBE 2:1, hence the pnp follower to drive the low ratio transformer... test it out though!

It's interesting....the documentation with the mike says it includes a 10:1 transformer, however similar mikes (mxl 2001 and v67) come with 2:1's.  I'll have to run a signal generator through it to see what it really is.

I guess it could be possible that it is indeed a 10:1. I guess the only way to be sure is to measure the transformer...

 

[abbey road d enfer]

Here's what I'm planning on doing:
2) Remove the JFET bootstrap and switching the front end to a regular common drain configuration per original U87/KM-84
3) Remove the PNP follower stage

You may have a problem there because of the high input and g-d capacitance of the 2SK170. The input capacitance is minimized by bootstrapping and the Miller capacitance is reduced by decreasing the gain of the input stage, which is compensated by a lower ratio of the transformer, which in turn brings the need for a emitter-follower.

4) Install a CM-2480 10:1 Cinemag output transformer 

This will further reduce the gain, but it shouldn't be a major problem, because any good preamp can generally be asked another 15dB of gain. However, the loss right at the input will bring an identical rise in equivalent noise. 

5) Ditch the tantalum caps 

  Always a good move... 

7) Restore de-emphasis circuit to original U87 values 

Why not, but the values that work for the U87 may not be correct for the different circuit. 

8) Re-bias input FET for maximum signal swing 

An obvious necessity.

 

[Matador]

You may have a problem there because of the high input and g-d capacitance of the 2SK170. The input capacitance is minimized by bootstrapping and the Miller capacitance is reduced by decreasing the gain of the input stage, which is compensated by a lower ratio of the transformer, which in turn brings the need for a emitter-follower.

This is one of the reasons I wanted to try the J305 and 2N3819 devices...if memory serves the input C was much smaller.

Why not, but the values that work for the U87 may not be correct for the different circuit.

True:  it mainly depends on the individual capsule response.  I'd like to try two different capsules:  one with a K67 response, and another with a K47 response.  The de-emphasis will have to be tailored for each one.

 

[MagnetoSound]

I'd like to try two different capsules:  one with a K67 response, and another with a K47 response.  The de-emphasis will have to be tailored for each one.

De-emphasis with a K47, though?

 

[abechap024]

I've had my eye on buying one or two of those mic kits. Interesting thread!  8)

 

[Matador]

I'd like to try two different capsules:  one with a K67 response, and another with a K47 response.  The de-emphasis will have to be tailored for each one.

De-emphasis with a K47, though?

Yes...'tailored' in the k47 case will likely mean 'deactivated'.

 

[Matador]

The capsules came in.  Here is the K47 type:

Are here is the K67 type:

Once Cinemag gets me my output transformers I'll be all set to build these.

 

[gary o]

Looking forward to this .......Matador where did those capsules come from?

all the best

 

[Matador]

Hi !
Is this DIY Mic a copy of u67 or u87?

Is the circuit the exact copy. I am wondering otherwise how that K67 capsule will sound the circuit is not following.

Manu

It's a very close copy of the U87 circuit.

 

[manulaudic]

Ok,

I guess this is the same mic too : http://www.thomann.de/fr/the_tbone_sc450.htm

Getting the Kit might be good idea but i'm in europe maybe the T-bone then swaping components.

 

[poctop]

Ho Yes This is the thread i was looking For thank God.,  quick question to start with i found a u87 traffo on ebay and ordered the aurycle kit,
and wanted to know if you guys use the board that came with it and modulate it , or you PP the whole thing is there any project Board for the U87 at the moment or will finally have to create one  from scratch never done it but i am not sure  this would any interest by anyone . i will have to come back here anyway this a gold mine. YUM YUM YUM. keep on going Man,  I dont know i much time it will take as i present my real u87 to a modern hybrid competitor. as per all the emphasis and deemphasis not surewhat you guys talk about but i see you are wel far ahead then me ,  i will surely want to find out how do you guys bias the Fet of this thing ?.
Cheers Ears.

 

[Matador]

...and wanted to know if you guys use the board that came with it and modulate it , or you PP the whole thing is there any project Board for the U87 at the moment or will finally have to create one  from scratch...

I'm planning on using the included circuit boards.  They don't appear to be of horrendous quality...

Still waiting for my CM-2480 transformers.  But here is the initial BOM I am going with:

There's a few component value substitutions as I had to use what Mouser had in stock at the time:

1) The transformer coupling cap was changed from a 4.7uF tantalum to a 22uF/50V bipolar electrolytic.  The layout is for a 4mm lead-spacing so finding something to match was a bit challenging.
2) A few of the capsule bias and FET bias bypass caps were increased in value (C12-C14 mostly):  this was purely to adapt to whatever Mouser had in stock at the time.
3) The 'Lead D' column is the lead spacing I measured on the PCB....the actual components lead spacing is listed in the comments, in case anyone wants to substitute other parts.
4) R6 has been changed to a 5K linear pot to adjust FET bias in-circuit (I already had these so they weren't on my Mouser order, but the actual ones I have are simple three terminal trimmer potentiometers).

 

[leadbreath]

hey matador nice work man!! im also keen to know where u got those nice looking capsules???

mick