DIY FET mic with De emphasis 87 esque guidance needed ......

[gary o]

Making a point to point FET circuit to use china K67 ish capsule or others basically a cross between U87 & KM83/4 maybe a dab of MXLV67......had great reults with KM83 circuit copy .... Im wanting to add de emphasis to it tho, I dont fully understand electronics as most here but wanting to learn ......I been studying the U87 circuit to identify the de empasis part also looking at V67 for help too Im intrigued about the different ways capsules are connected to the circuits as I want to only use cardiod Im looking for the best way to do this.... firstly are the de emhasis parts of U87 .....C3 10p
R8 1M C6 220p C5 0033u R9 6K8 R10 560R & C9 0.47u ?????    wondered if I could just add these parts to my KM83 circuit I can see I could come come from the drain & C4 but not sure how I would connect but to the front end ? & would I need to lose the KM83s C2 ? the different ways the capsules are connected are confusing my little brain ......failing this my plan was to basically copy the U87 circuit but copy the capsule connection of the MXL V67.... ? Is is there a better way....

Here are schematics Im looking at

 

[RuudNL]

The basic circuit is more or less the same as the U87.
You have to superimpose the signal from the drain through the 1M/220p/0033u/6K8+560R/0.47u network on the polarisation voltage.
I noticed that some 'China' K67-ish capsules require much less de-emphasis than the original K67 capsule.
So I think it might be a good idea to experiment a little with the 220 pF capacitor.
But in doubt: why not build the U87 schematic?

 

[gary o]

The basic circuit is more or less the same as the U87.
You have to superimpose the signal from the drain through the 1M/220p/0033u/6K8+560R/0.47u network on the polarisation voltage.
I noticed that some 'China' K67-ish capsules require much less de-emphasis than the original K67 capsule.
So I think it might be a good idea to experiment a little with the 220 pF capacitor.
But in doubt: why not build the U87 schematic?

Thanks RuddNL yes I dont mind building a U87 circuit Im just not sure which components to ommit as I only want cardiod thats why I was looking towards the MXL V67 circuit....I tried to attach MXL V67 & U87 schematics but look like they didnt post, I will try again.

Re china capsules I read info in the past about some K67 copies being very good but just lately with all the capsule builders & companies selling their version its getting a bit difficult to judge what is best buys outthere..... the point of this DIY is to use spare cheap capsules & to learn at same time, I like the idea of experimenting with cap values to make cheap capsule sound ok in this circuit.

Many many thanks

 

[gary o]

MXL V67 Schematic

 

[gary o]

U87 schematic

 

[Gus]

Did you see this thread?
http://groupdiy.com/index.php?topic=47569.0

 

[gary o]

Did you see this thread?
http://groupdiy.com/index.php?topic=47569.0

Thanks Gus I have seen it, interesting ... ,Im building from scratch rather than modding a V67 tho may have e re read , I sometimes struggle with understanding some electroncs

Cheers

 

[gary o]

Aha I made the U87 circuit on perf board changed capsule connection to be like MXL V67 changed cap values as per U87 using Haufe T14/1 11:1 op transformer (should that be close to U87 transformer ??) using Tim Cambell Tc12 for testing 123 seems like de emphasis is working sounds bit like a ribbon mic at the moment, very low noise too  .... I set the source trimmer to 11.5volts & I get 1.3V on the drain.....

 

[gary o]

Been reading about U87 capicitor and resistor value comninations its seems there are at least two sets of values putting the de emphasis at different frequecies.....6K8 & .033u ones set 1k2 & .15u is other..... I havent seen schematics myself I wonder does anyone have any more info....

I plan on try the different values maybe use a switch, not sure if good idea tho because of noise high imedence & whatever else....

Alsa quick question about the capsule blocking input capacitor Im using rwo in parallell to make desired value, can this be a problem ? thanks