MXL 9000 (Frankenmic) assistance please....

[illacov]

I installed the 1uf and  ;D

It did exactly what I needed.

The bass response is still there but has been curbed amplitude wise so that you get proximity effect when you're actually in a close proximity to the mic instead of when you're 10 feet away.

I love it. Sounds so much better. It doesn't sound like any other mic I own. It has its own vibe and will probably fill lead vox for at least 2 to 3 songs on my current project. It just fits those songs well.

Kind of mellow. I won't compare it to any Neumann or anything else. I will say its much less sibilant and has a ton close to when the MK319 capsule was in the transformerless circuit thats in the MXL 990 which is a Schoeps circuit rip?? The transformer is there doing its thing in the MXL9000 but from top to bottom the mic has more of a controlled sound with less smooze.

Thanks a ton guys!!

I will link up some samples in a bit, but I didn't really record anything with the mic tonite, just messed around with it, but the difference was immediate!



Peace
Illumination

 

[Marik]

I went to Cinemag and they recommended a 5:1.

I still don't understand why somebody would recommend 5:1 for 12AT7 ??? Go figure...
Or is it a CF output? Where can I see the schematics?

Best, M

 

[illacov]

The schem is on the first page of this thread.

I went with a 12:1 Jensen originally Mark, however it was like speaking in the voice of Moses and getting a whisper back.

I mean seriously, you needed like 65 db of gain to get the level to a respectable amplitude.

So out the Jensen went and Cinemag and I surmised a 5:1 might do a little better.

As far as level it was wonderful.

It was the bass bloom that was a pain in the butt.

I'm a complete fool when it comes to why the 5:1 would be so bass heavy, at this point I'm guessing the output of the mic (which was hotter with the 5:1) and the tranny was soaking on the bass frequency?

Either way it appears the cap did the trick. I'm still open to swapping it to another value if people think we could do better. Then again its not like the thing is hipassed at 100hz or something its just closer to what my other mics are like when it comes to the bass response.

6 inches in and there's mellow proximity effect, however its closer to an omni now as far as proximity effect which is very very cool for vocals, but it still has that cardiod pattern.

Alot of engineers put the Sony 800G in omni when tracking vocals, which then allows them to have the vocalist dang near eat the mic at 3 inches or so for that really in the face vocal sound.

Let me know if you think of anything else.

I've kind of gotten solder happy! Any other possible improvements?? Power supply perhaps??
I can get a picture of it up! Should be the same as the V76t power supply. The MK319 reacts like the k47/67 capsules to voltage. I wonder if we could find out how much it can take, increasing the V to the capsule should alter the freq response towards brighter freqs I think.


Peace
Illumination

 

[rodabod]

I'm surprised it gave more bass. Would have expected less. Maybe the lack of damping with the 5:1 is giving a little bass resonance, but I'd be surprised with such a large output coupling cap.

Marik, it's a plate-out. There is a link in one of the posts, or try here:

http://www.groupdiy.com/index.php?action=dlattach;topic=32136.0;attach=304

 

[rodabod]

Oh, and according to the schematic, the polarisation voltage is already quite high. It's around 67V for that capsule in the Oktava valve mics.

 

[Gus]

I did give you two hints in my post.

 

[illacov]

Just recorded guitar and some freestyle vocals today. Its really smooth. Some de essing will be necessary but its very controlled top end. Im actually quite happy with it, because if it was bassier I would end up equing it out for most sources. It is definitely not as dark as it was before like a dark ribbon, now its a mids vibe sound. Not completely rich sounding but Im thinking about putting a Dynaco tube in there to give it a different character. I haven't tried it with my really good preamps yet.The better tube should sound better at least with noise and hopefully sonics.

Im hoping to get more time in with this mic. The vocal quality sounds like A tribe called quest Midnight marauders. Guitars are detailed but mid forward in a smooth way. This may change as well with a tube swap.

I noticed some people mentioned voltage to the tube was low. Would boosting voltage to the tube improve sonics?

Are there any other audible caps or resistors that might be next for swapping?

Hmmm I gotta check that schematic again and decipher Gus' hints.

Peace
Illumination

 

[illacov]

Ok a few things...

In Gus' post in the MXL exposed thread he mentioned changing the resistor to a 2.2 to 2.7k (from the original value) for the cathode R. The only thing is it was over my head as to what audible effect this would have? I know its to do with the tube.  I'm thinking this is R7 since the value is 6.2k and based on its location on the schematic.

However somebody else already knows which resistor this is and I kind of have an idea.

I was thinking a Vishay resistor 2.7k?? Any other spec I should be aware of? What about the wattage? 1/2 watt. 2 watt etc?? Recommendations?

I'm eyeing C3 + C5 and thinking about switching them with Panasonic FM capacitors, I've heard good things about them. I will try it and see.  Should I be upgrading beyond them you think as far as increasing the values? Maybe higher V?

Peace
Illumination

 

[Marik]

Ok a few things...

In Gus' post in the MXL exposed thread he mentioned changing the resistor to a 2.2 to 2.7k (from the original value) for the cathode R. The only thing is it was over my head as to what audible effect this would have? I know its to do with the tube.  I'm thinking this is R7 since the value is 6.2k and based on its location on the schematic.

However somebody else already knows which resistor this is and I kind of have an idea.

I was thinking a Vishay resistor 2.7k?? Any other spec I should be aware of? What about the wattage? 1/2 watt. 2 watt etc?? Recommendations?

Sorry, but you completely lost me here. I am sure Gus knows perfectly well what he refers to, however, which thread are you talking about? Which resistors? The R7 on which schematics and what location are you refering to? Why Vishay and where the value of 2.7K is coming from and in which location?

The schematics Roddy posted link in many parts does not make sense, esp. if you are using Oktava capsule, as you mentioned. The 5:1 does not make any sense either.

If you want to get some help could you please be specific and post the links along with the schematics, as it is impossible to follow what you are talking about.

Best, M

 

[rodabod]

In Gus' post in the MXL exposed thread he mentioned changing the resistor to a 2.2 to 2.7k (from the original value) for the cathode R. The only thing is it was over my head as to what audible effect this would have? I know its to do with the tube.  I'm thinking this is R7 since the value is 6.2k and based on its location on the schematic.

That sets the bias which does affect the sound, and also the clipping point (well, points as it is asymmetrical). You need to draw a load line for your choice of valve and from this consider what might be the best option. You also need to listen as it does affect the distortion characteristics too.

I was thinking a Vishay resistor 2.7k?? Any other spec I should be aware of? What about the wattage? 1/2 watt. 2 watt etc?? Recommendations?

You decide. I doubt anyone else is going to put the work in for you as this takes a bit of time and understanding. P=IV plus a safety margin.

I'm eyeing C3 + C5 and thinking about switching them with Panasonic FM capacitors, I've heard good things about them. I will try it and see.  Should I be upgrading beyond them you think as far as increasing the values? Maybe higher V?

You should always ask what are you trying to achieve before suggesting various swaps. C5 could be swapped for a film cap if it can fit. Your choice of size partly depends on the cathode resistor value which you are bypassing. C3 looks like NFB for high frequencies to me, possibly for stability (and in the process forming a LP filter and providing less distortion). Others, correct me if I'm wrong though. Either way, I'd probably try removing it.

I think Marik is right that the circuit just now with the Oktava capsule and 5:1 transformer is a bit of a mish-mash, although that said, if it sounds good then it is good.....

 

[illacov]

Yeah you touch on two things that Gus did mention.

He said to remove C3 for "more gain," however you mention it acting as a lo pass filter, so perhaps this may add a little hi end clarity if removed eh?

The resistor choice I believe was based on the 12AT7 being the original tube in use. That being stated I have a different 12AT7 in there than stock but I could always keep the original resistor around if the change is undesirable.

The C5 capsule is a 22uf I think. I can see what I can squeeze in there.

Marik, the schematic is correct for the STOCK version of the MXL 9000.

I have been changing different things in the mic to get it to work better with the MK319 capsule.

When I first installed the MK319 capsule and GT 12AT7, the mic did sound pretty decent but the mic was shrill in the high mids and I was pretty unhappy with it. I saw in other threads that people had been swapping out the transformers and eventually after trying a Jensen 12:1, I tried a 5:1.

The bass freqs bloomed very very early with the 5:1 in place (something to do with C6 the 33uf) and once I switched the 33 uf to 1uf it sounds alot better. A much more natural mic. If I really wanted to I might go with a little larger value cap for the C6 spot like a 3.3uf metal film, I'll do that today if possible.

What I was trying to sort out was the situation with the tube being under utilized in the design of the mic. Gus mentioned swapping a resistor I think R7 (which is 6.2k stock) to between 2.2k and 2.7k. Rod just mentioned this would change the bias point for the tube and may or not give an audible improvement.

In addition, Rod mentioned lifting C3 to see what happens. I'm quite interested if it will give a positive result with the MK319 capsule.

Hopefully that brings you up to speed.

Peace
Illumination

 

[Marik]

Those are all excellent suggestions, why would not you follow them?
Again, first, remove C3, R7 replace with 2.7K, I'd reduce the C6 to some 0.47-1uf, get rid of those R20, R21, L1, L2, C20, C21 filter components. After that try back the 12:1. Also, the tube is underheated, so you might want somewhat raise the heater voltage to 6.3V, but you can do it later.

It seems that at the moment you are doing things a bit randomly, so I'd also suggest to find Radiotron 4th edition (it circulates somewhere online) and study how the tubes work--really, it is not that difficult. Alternatively, you can find "tubes 101" on many other sites (including here).

Best, Mark

 

[rodabod]

I'd maybe also keep in mind (if you read about generic valve stages) that the plate current will be less than what you would expect at nominal voltage. You can see the plate current from the values in your schematic already, ~ 0.55mA.

 

[illacov]

Ok I've removed the R7 resistor and replaced it with a 2.2k 1/2 watt resistor 5%.

Seems to have beefed up the lo mids and mids a little.

Highs are still a slight bit "choked" if thats the word so I'm going to remove C3 and see what happens.

I'm leery about removing the resistors and caps that you guys mentioned were useless going to the secondary of the tranny. If I remove those stages would I need to use some leads to bridge anything? Ive gotten this far but I felt I should ask before embarking any further with that section.

Marik you mentioned adjusting the heater voltage? I take it thats going to make an audible difference? For what its worth the mic is getting a bit warmer now with that new 2.2k resistor at R7.

Mic sounds pretty good at this point without C3 removed but I kind of wonder if the high end could get cleared up a touch.

I will report back.

Peace
Illumination

 

[Gus]

Did you measure the plate and cathode voltages before and after?  The 2.2k will cause a higher plate current.  Measure the voltage drop across the 150k plate resistor and use ohms law for the plate current.  China, Russian, NOS tube?  You might want to go the other way in value it all depends on the tube.

 

[illacov]

Well Gus here's where I'm at with it.

Took out the 9pf and a blanket was lifted off the mic's high end.

I may have some cleaning up to do in there just to make sure everything is installed properly without problems.

At one point when the mic got pretty warm it stopped producing signal but to be fair it was in my hand and head was probably not dissipating well. That being stated once the mic cooled down some it came right back on so either theres an issue with heat or most tube mics are handheld for a good reason. Sorry for being such a bumbling idiot about all of this. I have just been swapping components til it sounds good.

But at the moment this mic sounds really really good!

I just want to thank everyone who has helped me so far.

Does anyone think that removing that stage before the transformer secondary is going to do anything audible??

So far this has turned a so so sounding mic into a really good sounding mic!

Its still a mellow warm mic, but it sounds like a condenser now instead of a dynamic with a sock over it.

Peace
Illumination

 

[illacov]

bump for further mod suggestions ;D

I would love to know what to do with the C5 cap. Gus you mentioned the size I use has to do with the Cathode R correct?

I installed a 2.2k 1/2 watt for the R7 and the mic is stable at the moment. Sounds pretty good, on the creamy side with decent high end response but not over articulate.

The C5 cap would affect what sonically?

Peace
Illumination

 

[tchgtr]

illacov, and all the heavy hitters who chimed in on this thread.
    I have one of these mics, and working on the assumption that everyone was looking at a schemo of the unmodded mic, I made some adjustments to mine. My only previous upgrade to this mic was to put in a NOS RCA 12AT7, but there was not much noticeable difference. I bought it from E-bay, used and damaged, and it has been a real education for me, largely because of this thread, and the excellent discussion about the circuit.
After each mod, I made sound files, so that I could compare later, with fresh ears.
    First, I exchanged C6 (33uf electro) for a 1uf metal film cap. Ahhhh, there's that smoothness of sound I'd come to expect from such a change. Surprisingly, volume output didn't change in any obvious way, but the tone was obviously better. Less mid-range-y.
    Then, R7 was exchanged for 2.2K. The output volume increased radically, in a good way. It seemed like the tube was more of a participant in the overall tone now. The mic was now beefy, though a bit muted.
    Lastly, I removed C3. It brought back some of the "China mic Syndrome" hi-end, but now it's a bit smoother, and the air is nice to have in the overall sound. I'm glad that I did not remove the inner mesh of the grill, as has been recommended at other threads.
  I need more time with the mic, but it's obviously much better. I may even wait for a while to play with the tranny, if at all. It seemed to run no hotter after the mods, but today I'll leave it on for a long while and see what happens.
  It's impossible for me to tell you all how much I've learned from this forum, and I thank you all very much.
Jim

 

[rodabod]

Not sure which Chinese capsule is in this, but you might want to keep the feedback cap, or try a cap from plate to ground and choose value to taste.

 

[tchgtr]

OK. Thanks for that. I'm guessing it's the 6 mil capsule, since frequency response on the mic is listed as 30hz-20Khz.
Maybe a smaller value than the 9pf that was in there would make less of a hi cut...