Not entirely sure whether this is the correct forum for this so any staff member feel free to move it to the correct forum.
Anyways, I have an old Lomo MKE-100 condenser electret that has been sitting on my shelf for a good few months now so I figured I'd finally put it to good use.
It has a battery powered pre-amp built in but I've heard that their performance is mediocre at best. I'd like to convert it to a 48V phantom powered mic with a good pre and either a 6.3mm jack or XLR to plug it straight into a mixer.
I'd greatly appreciate it if you guys could recommend a good pre. One that works off of phantom power, has good performance, isn't too expensive to build and fits nicely into the mic's body.
I have an Oktava MKE-2 coming in soon that most likely need the same treatment.
Cheers!
Anyways, I have an old Lomo MKE-100 condenser electret that has been sitting on my shelf for a good few months now so I figured I'd finally put it to good use.
It has a battery powered pre-amp built in but I've heard that their performance is mediocre at best. I'd like to convert it to a 48V phantom powered mic with a good pre and either a 6.3mm jack or XLR to plug it straight into a mixer.
I'd greatly appreciate it if you guys could recommend a good pre. One that works off of phantom power, has good performance, isn't too expensive to build and fits nicely into the mic's body.
I have an Oktava MKE-2 coming in soon that most likely need the same treatment.
Cheers!
Only people from or around ex-Soviet area will have any experience at all with that Soviet era equipment, and doubt many hang around here.
You should at least find the schematic and post it here.
You should at least find the schematic and post it here.
I attached the schematic 🙂
There's the original schematic, I've done nothing but only changed the 10uF electrolytic cap with a new one.
The phantom part is an add-on. Very simple, two resistors, a cap and a zener. Would this work? It would be very easy to implement, without the batteries there's a lot of room in there.
Regards
Joel
There's the original schematic, I've done nothing but only changed the 10uF electrolytic cap with a new one.
The phantom part is an add-on. Very simple, two resistors, a cap and a zener. Would this work? It would be very easy to implement, without the batteries there's a lot of room in there.
Regards
Joel
Have you taken the internal resistance of the phantom power source into account, typically 6.8 kohm or 6.81 kohm from the 48 V source to pin 2 and 6.8 kohm or 6.81 kohm from the 48 V source to pin 3?
Simply that there are two well-matched resistors of 6.8 kohm between the actual 48 V supply and the microphone input inside your mixing console (or whatever equipment you are using to supply the phantom power). Hence, the current through your zener may be smaller than expected.
By the way, if you are using a mixing console with a transformer at the microphone input, it can also be a single 3.3 kohm resistor to the centre tap of the primary.
Scott Wurcer once wrote a good article about microphone preamplifiers for condenser microphones in Linear Audio volume 1:
Linear Audio | your tech audio resource
The follow-up is in volume 3:
Linear Audio | your tech audio resource
By the way, if you are using a mixing console with a transformer at the microphone input, it can also be a single 3.3 kohm resistor to the centre tap of the primary.
Scott Wurcer once wrote a good article about microphone preamplifiers for condenser microphones in Linear Audio volume 1:
Linear Audio | your tech audio resource
The follow-up is in volume 3:
Linear Audio | your tech audio resource
The original LOMO schematic shows a somewhat poor design, mainly because
* DC is passing through the output transformer (ugh !!!!)
* even with your conversion, it is still powered by 3Vdc (ugh!!!!)
I guess you may search around and build a much better preamp, which either fully replaces the transformer by balanced Op Amps or whatever or at least does not pass DC current through those windings.
And using a better share of those 48V available.
A preamp fed 15/18V would be immensely better.
* DC is passing through the output transformer (ugh !!!!)
* even with your conversion, it is still powered by 3Vdc (ugh!!!!)
I guess you may search around and build a much better preamp, which either fully replaces the transformer by balanced Op Amps or whatever or at least does not pass DC current through those windings.
And using a better share of those 48V available.
A preamp fed 15/18V would be immensely better.
Yea I've read somewhere before that those preamps are just borderline usable.
Got any good schematics you'd recommend?
I guess I won't waste my time on modding the original circuit. I've got a friend who can etch me PCBs. You guys give me a good schematic and I'll have it made 🙂
Just keep in mind that it's an electret, so regular condenser circuits won't work.
Maybe before I actually do anything with it, maybe I should get some batteries and test it with the original amp to see if it's still good? I've heard that these electret capsules can go sour after years of abuse and improper storage condition. I've no clue how it was handled before I got it.
Got any good schematics you'd recommend?
I guess I won't waste my time on modding the original circuit. I've got a friend who can etch me PCBs. You guys give me a good schematic and I'll have it made 🙂
Just keep in mind that it's an electret, so regular condenser circuits won't work.
Maybe before I actually do anything with it, maybe I should get some batteries and test it with the original amp to see if it's still good? I've heard that these electret capsules can go sour after years of abuse and improper storage condition. I've no clue how it was handled before I got it.
- Status
- Not open for further replies.