miktek cv4 diy mod?

[Khron]

I'm guessing those two must've been on the heater supply (also considering their can sizes). When those bulge / burst, they typically drop in capacitance (uF) and rise in ESR, so they're no longer filtering the ripple as well as they used to.

The Rubycons should be fine, they're a well-regarded Japanese brand in the industry. Jakec, not so much (chinese no-name crap)

Go right ahead and replace the two blown ones, preferably with a comparatively-specced Japanese part (Rubycon, Panasonic, Elna, Nichicon, United / Nippon Chemi-con).

 

[arnesl]

Ok, thanks,  yes the big ones they are for filament supply. I will replace all of those 10000uF.

 

[Khron]

What would be REALLY ironic, was if replacing those cures the issues with the (first?) mic...

 

[arnesl]

Yes, well would be nice, it might improve noise a bit at least I will replace caps in both supplies.
I have tried to be more pragmatic about it, it does some things good and some things not, the one i have messed around with i will keep a learn when to use it i think.

Just to be clear, if I choose to start to mod it, I have no intent of try to selling it any time soon, my thinking was that it is one  or the other,  not mod it and then sell it.

It is more like: i will see what i can get for it and if not what i want i might try to mod it.

Yes, I should probably go trough and draw up the circuit before i do anything to the mic.

Could you share what preamp (or preamps) mostly you are using with miktek?

I feel a bit bad a about been so negative to discussing  preamp in this tread, it is just a have spent more one preamps than I should already and have told my self that is it (should be good enough), but it got my thinking more about how I use the mic and progressing.  Also I would like to be able to use some smaller portable interface some day and the normally are pretty clean.

 

[McIrish]

I know I'm digging up an old thread. I was curious if the OP ever tried replacing the capsule. I have a CV4. I thought it would be quite a bit smoother and rounder than it actually is. I really should have researched more into it but bought into the hype. I do like to mod things myself and see what I can learn so, I bought another capsule to try in it. (47 type) I imagine there must be some type of LPF in the mic considering it has a 67 type capsule from the factory so I'll have to change that. The circuit doesn't seem difficult at all so I think I will scribble down some schematics at some point so I can see what circuit tweaks might be made.

I know Shannon does a great job with these mics. I'm just looking to learn something and make it into what I'm looking for. The basic components tell me it should pretty easily be modified to be more of a flat response amp with a few minor tweaks.

Anyone else try this yet?

 

[ln76d]

Try to draw schematic. If you will get some problem with it i will try to help you.
Look for thread about peluso p67, i drew schematic from the pictures only.
With any troubles, put good pics here.

 

[McIrish]

I have drawn the schematic. Maybe not so surprising is that it is very similar to one of Oliver's U47 designs. I will find a place to host the picture of the schematic if anyone else is interested. I was pleased to see that there isn't any de-emphasis circuitry so my BN K7 should not have a problem just dropping in. Now I have to wait for the capsule to arrive.

 

[ln76d]

Can't attach schematic here?
After some time some host services removed links - there's a lot of interesting old topics here but many useful informations is lost do the hosting places links.

You know, Oliver circuits are also nothing new under the sun.
There's a really few circuits to use in mikes, rest is only components values matter

 

[McIrish]

Here is the schematic for the Miktek CV4.  It's pretty straightforward and should be fairly easy to do some mods. Overall the build quality seems pretty good. A better capsule should make a difference. I'd have to do a new PCB or point to point to change out the transformer. It's got 8 leads and it took a couple minutes before I figured out how its wired. Simplified, it looks like the schematic. I've read that it is a PCB mount BV8. I'm not sure if that's accurate or not. For now, I will go with the capsule change and see how I like it. I have a Wunder CM7GTS/M7 and I'm hoping the BN K7 will get it a little more into that sound. Right now, the upper mids are too forward (harsh) and it is a bit zingy in the highs. It would be great if a capsule change could turn this into a really great mic.

The red lines show where the circuit jumps to the top PCB via J2. The wiring from the XLR to the J1 header is a simple one-to-one.

Hope this helps someone else.

 

[ln76d]

I would leave transformer in place, stay with PCB etc. You already have a microphone which isn't bad. You can try tweak it.
Capsule is good option for the start. You can always build another microphone
With any variation of M7 - if it's similar to real M7 - you can have a problem with high mids. Original M7 have a bump in this region, so if the circuit or headbasket makes another bump this will add to eachother.
Few propositions for mod:

- C4 2uF

- C5 0.5uF (best would be MP type)

- C1 (i believe) connecting both diaphragms - try 10pF (or lover) some good quality cap - ceramic NP0/C0G or polystyrene.
From my tests with similar input arrangement lower capacitance - better sensitivity, also hi mid was better. With this some folks here wouldn't agree, but worth to try It's only one cap.

-R1/R3 - you can try different value from 100M to 500M (both the same). R2 also could be lower.

- R5 - you can try to adjust cathode resistor - put potentiometer in place and make voice test changing the value. I would try 4.7k pot (linear)

- i would try to add capacitor across R5 it should be really audible change and maybe better sounding. You don't have to even solder a cap - testing microphone without pipe, you can simply put cap leads on the resistor leads. If you will change C4, i would start with cathode cap 3.3uF and possibly go higher if there would be lack of low end. If the small value would work good here, i would use film capacitor. If R5 would be higher then it's possible that lower capacitance will work good.

- R5/R6/R9 i would use good quality carbon resistors (not carbon composite) - Draloric LCA or old Beyschlag

- polarisation voltage adjustement could be also good option, but first i would try the rest of changes. You can always measure are the both polarisation voltages matched - after changing R5 can be different but overall can be

- if the new capsule wouldn't sound good in hi mid range and you will try the rest of the mods, the last thing could be removing internal mesh from headbasket.

If you will be intersted on mentioned mods i would start with the old capsule and see how it change the sound. With new capsule can be only better (if the hi mid problem will disapear).

 

[McIrish]

Thanks so much for the circuit change ideas. There's a lot of info in there. I will start with that and see where it leads. I have no idea when the BN K7 will show up. It's been a week but they are on the other side of the world.
Thank you again

 

[McIrish]

I made an error on the schematic. I just uploaded the corrected version that has C1 labeled and there is a cap across R5. It's labeled C6 and is 100uF. I should have spent a couple more minutes checking my work before I uploaded it.
I will order a few parts to do tests with.

Dan's D7 capsule seems pretty interesting as well. I might give that a shot if the K7 doesn't work out or if I get tired of waiting for it. I'm getting a little nervous that I've awakened the inner tweaker in me. I used to spend all my time modifying guitar amps and designing distortion circuits for pedals. I kind of gave it up for the last 10 years as I kick-started my music career with a new writing partner. tweak or write a song.... tweak or write a song.... hmmmm. I've opened up a can of worms!

www.hm-music.com

 

[McIrish]

I would leave transformer in place, stay with PCB etc. You already have a microphone which isn't bad. You can try tweak it.
Capsule is good option for the start. You can always build another microphone
With any variation of M7 - if it's similar to real M7 - you can have a problem with high mids. Original M7 have a bump in this region, so if the circuit or headbasket makes another bump this will add to eachother.
Few propositions for mod:

- C4 2uF

- C5 0.5uF (best would be MP type)

- C1 (i believe) connecting both diaphragms - try 10pF (or lover) some good quality cap - ceramic NP0/C0G or polystyrene.
From my tests with similar input arrangement lower capacitance - better sensitivity, also hi mid was better. With this some folks here wouldn't agree, but worth to try It's only one cap.

-R1/R3 - you can try different value from 100M to 500M (both the same). R2 also could be lower.

- R5 - you can try to adjust cathode resistor - put potentiometer in place and make voice test changing the value. I would try 4.7k pot (linear)

- i would try to add capacitor across R5 it should be really audible change and maybe better sounding. You don't have to even solder a cap - testing microphone without pipe, you can simply put cap leads on the resistor leads. If you will change C4, i would start with cathode cap 3.3uF and possibly go higher if there would be lack of low end. If the small value would work good here, i would use film capacitor. If R5 would be higher then it's possible that lower capacitance will work good.

- R5/R6/R9 i would use good quality carbon resistors (not carbon composite) - Draloric LCA or old Beyschlag

- polarisation voltage adjustement could be also good option, but first i would try the rest of changes. You can always measure are the both polarisation voltages matched - after changing R5 can be different but overall can be

- if the new capsule wouldn't sound good in hi mid range and you will try the rest of the mods, the last thing could be removing internal mesh from headbasket.

If you will be intersted on mentioned mods i would start with the old capsule and see how it change the sound. With new capsule can be only better (if the hi mid problem will disapear).

Wouldn't changing R5 to .5uF from 1uF be sort of a HPF? The microphone is a little bass light as is so I don't think I'd want to make it any thinner. I will give C1 a try once I get some parts ordered. What would changing R1, R2, R3 to 500M do to the sound? It's a pretty easy and quick job to swap out the resitors with a different type on the lower board.  Do I understand that increasing the size of C4 would tighten up the bass, by making the supply a bit stiffer?

Thanks again

 

[Gus]

I would leave transformer in place, stay with PCB etc. You already have a microphone which isn't bad. You can try tweak it.
Capsule is good option for the start. You can always build another microphone
With any variation of M7 - if it's similar to real M7 - you can have a problem with high mids. Original M7 have a bump in this region, so if the circuit or headbasket makes another bump this will add to eachother.
Few propositions for mod:

- C4 2uF

- C5 0.5uF (best would be MP type)

- C1 (i believe) connecting both diaphragms - try 10pF (or lover) some good quality cap - ceramic NP0/C0G or polystyrene.
From my tests with similar input arrangement lower capacitance - better sensitivity, also hi mid was better. With this some folks here wouldn't agree, but worth to try It's only one cap.

-R1/R3 - you can try different value from 100M to 500M (both the same). R2 also could be lower.

- R5 - you can try to adjust cathode resistor - put potentiometer in place and make voice test changing the value. I would try 4.7k pot (linear)

- i would try to add capacitor across R5 it should be really audible change and maybe better sounding. You don't have to even solder a cap - testing microphone without pipe, you can simply put cap leads on the resistor leads. If you will change C4, i would start with cathode cap 3.3uF and possibly go higher if there would be lack of low end. If the small value would work good here, i would use film capacitor. If R5 would be higher then it's possible that lower capacitance will work good.

- R5/R6/R9 i would use good quality carbon resistors (not carbon composite) - Draloric LCA or old Beyschlag

- polarisation voltage adjustement could be also good option, but first i would try the rest of changes. You can always measure are the both polarisation voltages matched - after changing R5 can be different but overall can be

- if the new capsule wouldn't sound good in hi mid range and you will try the rest of the mods, the last thing could be removing internal mesh from headbasket.

If you will be intersted on mentioned mods i would start with the old capsule and see how it change the sound. With new capsule can be only better (if the hi mid problem will disapear).

Just blindly changing the coupling cap to .5uf might not be a good idea. This needs to be selected for each variation of the triode out microphone(tube operating point, transformer used).  Also you need to think about the cable and preamp input.  MP is not always the best sometimes I like MKT, stacked and wound can sound different.  Measurement and testing by ear seem to work well together selecting the output coupling cap value and type

Adjusting the cathode bias resistor value is always a good idea.

Removing mesh often is not a good idea at all.

I would leave the circuit stock and add a lowpass filter in the preamp  to EQ out some of the highs then maybe EQ other sections of the frequency response.

I agree with trying a cap across the cathode resistor

 

[ln76d]

Wouldn't changing R5 to .5uF from 1uF be sort of a HPF? The microphone is a little bass light as is so I don't think I'd want to make it any thinner. I will give C1 a try once I get some parts ordered. What would changing R1, R2, R3 to 500M do to the sound? It's a pretty easy and quick job to swap out the resitors with a different type on the lower board.  Do I understand that increasing the size of C4 would tighten up the bass, by making the supply a bit stiffer?

Thanks again

For C5 - overall yes, but you shouldn't`notice any change with low end response, C4 also is frequency dependent part of the circuit, so raising up C4, you can freely lower C5. Total plate resistance is 137k so it's pretty high also, so guessing 120V B+ it should not give you any roll off with lower C5. Also with 2uF C4 would be better filtered.
You can always make my favourite switch test and quickly make A/B comparison. Put one 0.5uF on the board and solder another in parallel with one lead connected by the switch - then you can compare how affect 0,5uF and how 1uF.
For R1, R2, R3 - not every tube likes high impedances like 1G or more. I would have to look into datasheet later.
Mostly with FET designs higher resistance give better results, but with tube circuits sometimes lower sounds better.
If the microphone is "bass shy", definately try lower capacitance with C1. I'm courious do i am schisophrenic or is it really change sensitivity for several frequencies, but with my tests in few circuits, low end response change was really noticable.
Rest of wacky explanations in response to Gus post

 

[ln76d]

Just blindly changing the coupling cap to .5uf might not be a good idea. This needs to be selected for each variation of the triode out microphone(tube operating point, transformer used).  Also you need to think about the cable and preamp input.  MP is not always the best sometimes I like MKT, stacked and wound can sound different.  Measurement and testing by ear seem to work well together selecting the output coupling cap value and type

Adjusting the cathode bias resistor value is always a good idea.

Removing mesh often is not a good idea at all.

I would leave the circuit stock and add a lowpass filter in the preamp  to EQ out some of the highs then maybe EQ other sections of the frequency response.

I agree with trying a cap across the cathode resistor

No one said it had to be "blindly" Should i add to each sentence - in my opinion would be best and you should test it, make comparison etc. ? I think that everyone who want to work on microphone knows how to test it and will hear the results
With MP i had weak results maybe twice or three times. Just swaped capacitor for exactly the same type and then everything was excelent. Sometimes old MP are out  of spec - worth to try few if the result is weak. I also like MKT, but never had satisfiing result with polypropylene.
Ok, shoot me - i don't know how to explain that, but mostly when i tested microphones with A/B comparison ouf output caps, overall response in whole spectrum was much better with lower capacitance. I aso measured preamp response with generator and cap instead capsule and always low end corner wasn't worse than with higher capacitance. Usual drop was after 20Hz.
For some  other explanations for the value, please look in upper post.

Here we have problem with hi-midrange - which is hard to eq in the circuit - so lpf wouldn't change much. Always can be add cap from plate to ground - in some mikes i like the results, even when the highs weren't bumped.
There's also another simple mod, well known, but i will describe it after first reports when the repsonse would be still not satisfiing.
I don't see why removing mesh isn't  good at all. Look for example for C12 headbasket.
Of course after removing, there's need to be more carry when using an storing microphone
As i wrote - the last thing - there's a big chance that the mesh is bumping hi-mid, it's really often.
Without internal mesh mostly microphones sounds more "open".
Anyway usual there's an option to replace it with different mesh - more acoustic transparent.

And yes - testing is the best option! ALWAYS!
Once i calculated whole circuit, traced curves, everything was really great on the paper - after building microphone it sound so ugly, that i gave up on calculations. Usual am using switches and potentiometers to set values of components. A lot af A/B testing etc. Then the results are really great.

 

[Gus]

When I adjust the output cap I often start with a .22uf and move up in value until I get what I want or as close as I can get with the transformer in the circuit at the time.  It is funny you can get a low end bump with a smaller cap a lot depends on were the bump is and how big it is.
Most of the time it is between .33uf and 1uf.

Remember it is a RCL circuit connected to a cable and the input of a preamp.

"More" bass can be the bump and the faster rolloff.

It seems empirically adjusting the cap is faster than trying to do the math

 

[ln76d]

Agree!
0.5uF is usual safe value
Electrical measurement of the circuit usual gave me difference in roll off in not usable frequency range below 20Hz.
That's funny because in the topic related to the schoeps mod you pointed too big output caps (i didn't understand what you mean at first time), and from my tests "the bigger the better" in that circuit works better than in transformer output  tube mikes.
Why in my opinion works better? It's not about the bump or overal amount of low frequency, but i noticed that in schoeps topology with bigger caps, mike sound less coloured in overall spectrum. With tube mikes which i build or moded, usual situation is reversed

 

[McIrish]

I received the capsule from Beesneez today and installed it. I think there must be some extreme high end roll-off happening in the circuit. I expected the K7 to sound pretty similar to the other M7 variants I have heard and used. In this case, I think the circuitry is messing up something. It is very muddy with almost no high frequencies starting around 3-4K. It's not that its dark sounding. It just sounds wrong. Like a wet blanket was tossed over the top of it. The output level seems fine and exactly what I'd expect. I was thinking maybe the size of C1 is the culprit. But I'm a bit new to microphone circuitry.
I also notice the polar patterns don't act as I think they should. In cardioid, it's nearly identical level front to back. Omni sounds odd but I can't explain how. hollow or empty?
I triple checked to make sure I connected the capsule identical to how the original came out. Anyone have an idea of what to try?

 

[ln76d]

With C1 you should  get completely different result, if any - so rather not.
Try to find any additional film or ceramic capacitor in the circuit, count the amount and compare with schematic.
The only place where it should be, is from plate to ground - walues from 100pF - 1nF.
I didn't use K7 from Beesneez, but maybe it's just sound of it?
Measure polarisation voltages before R1 and R2! It's the best way to see why cardioid have similar level from both sides.
With omni usual lack of proximity effect gives that impression.