Topic: Pre-amp for Nak CM300s?

[dave570]

Since my Nak 300s use batteries for power and I don't wish to go "mic in" to the R09HR, what kind of pre-amp would be safe to use and still put out 24 bit into the recorder's line-in?

[Todd R]

Technically speaking, a preamp does not put out a digital signal so it would not put out a 24 bit signal.  To get a digital signal, you need an A/D converter.  There are a few units like the Lunatec V3 and Apogee Minime that combine mic preamp and A/D functions into one box which put out a digital signal.

That said, to record a 24bit digital signal, you need a recorder with a digital input, which the R09 does not have.  So you want to use a strict preamp, not a combined pre+AD, and that will put on an analog signal, not a digital 24bit signal.  To record at 24bits, set your R09 accordingly.

Thus you can use any preamp, though with the Naks you'd want one that has a selectable phantom power and you'd want to set phantom power to off.

[runonce]

The recorder is 24 bit - so you'll always be recording at 24 bits - not matter what you input. No bits about it until it hits your recorders A/D section.

Any preamp will be fine with those mics - and dont be afraid to try the mic in - naks are notorious for their low output...it might just work.

[sunjan]

with the Naks you'd want one that has a selectable phantom power and you'd want to set phantom power to off.

...or even one without P48 altogether. I believe you can run them straight into a CA-9100, with the right cables.
I don't know if there is any benefit to ask for a custom CA-9100 with mini-XLR jacks, so you can go 3-wire. Maybe it doesn't matter since the Naks are unbalanced(?), but Chris could probably elaborate...

[Roger Gustavsson]

Any preamp will be fine with those mics - and dont be afraid to try the mic in - naks are notorious for their low output...it might just work.

The low output may be raised by about 10dB, just bypass the balancing output transformer. Yes, you will loose the balanced signal feed but it will not be a problem with shorter runs of cable.

In its original state, the output is low and requires a low noise mic preamp. Of course, it depends on what you are recording. Low level acoustic music is far away from rock music...


Roger

[runonce]

Any preamp will be fine with those mics - and dont be afraid to try the mic in - naks are notorious for their low output...it might just work.

The low output may be raised by about 10dB, just bypass the balancing output transformer. Yes, you will loose the balanced signal feed but it will not be a problem with shorter runs of cable.

In its original state, the output is low and requires a low noise mic preamp. Of course, it depends on what you are recording. Low level acoustic music is far away from rock music...


Roger

Roger - does using a unbalanced (ie stock) cable bypass that transformer...or do you have to solder?

[crazifyngers]

Switching gears, has anyone used a Church 9100 pre with stock 300s? I tried it the other night, but something wasn't working. Is there a reason that won't fly, or is not advised?

The stock CM300's have transformers at the output, and basically that acts like a dead short across the "plug in power" supply for your 9100.  Chris Church advises against it.

[SmokinJoe]

I have run Nak 300's > R09 mic in, with just a Y cable.  It works, but I had to max out the gain on the R09, so hiss starts to be come apparent, and the sound is kind of "lackluster" for lack of a better term.  If you can find some of the Hosa Low-High impedance transformers that might help, but a "real" preamp is the way to go.

The original old school Nak preamp is the MX-100.  It's a 3 mic mixer, but it works fine for 2 mic preamp as well.  Set the R09 to about mid gain, line in, and adjust the gain on the MX100.  It's kind of a brick, but I've seen them for a bit more than $100, modded to run on 9V batteries.

I've had great luck with UA-5's.  They are primarily digi out, although you can use a UA-5 analog out.  This creates kind of a confusing setup because there are 3 different places you can set the gain... (a) the main knobs, (b) the headphone volume which effects the analog out the back, and (c) the gain on the R09.  Many people who try this end up putting too much gain one place, and not enough on another... and it doesn't sound as good as it should.  If you want to use a UA-5, talk to Vanark... he is one of the few people I know who run mics > UA-5 > R09 a lot, and he makes good tapes, so I would say he has a routine figured out.

I've had great luck with a V3... but you probably aren't looking to spend $900.

The Nady DMP-2 is one I don't really recommend.  Since you have to crank the gain up on the preamp it's about has hissy as running Mic-in to the R09.

Silly as this may sound... if you can find someone who has an old Sony D5 analog cassette deck, that makes a great preamp for the Naks... run Mics > D5 > R09... I haven't done it, but I've seen it done.  I think you just leave the D5 on Pause all night.

[Roger Gustavsson]

Roger - does using a unbalanced (ie stock) cable bypass that transformer...or do you have to solder?

You will have to solder. You have several alternatives how to wire them. It depends on if you want to keep the low-cut switch, keep the battery, two or three wire connection etc.


Here is a picture of the internals:


The Nakamichi MX-100 mic preamp is a brick but it is matching the CM-300 well. I have been playing with the idea of shrinking it. A new enclosure, smaller and lighter but still with room inside for a couple of rechargeable Li-Poly 11.1V/350mAh. Can also be modified to supply the microphones.   


Here a picture of my cut-down Nakamichi CM-300.  No output transformers but still with an internal battery (three CR1632):

[Todd R]

You might also want to talk with Jon at Naiant.com -- mshilarious here.  He has just started selling his littlebox preamp, which I was one of the first to try.  It is a very nice preamp, and sounds fantastic for the money.

He usually configures it for an option of 20v or 48v phantom power operation, but he might be able to build you a non-phantom version for use with the cm300's.

There's a thread in the Retail section on the littlebox preamp.

[Roger Gustavsson]

Since my Nak 300s use batteries for power and I don't wish to go "mic in" to the R09HR, what kind of pre-amp would be safe to use and still put out 24 bit into the recorder's line-in?

What level is needed for 0dBFS with the R09HR? 775mV (0dBu) or 245mV (-10dBu)? My soundcard need 2450mV (+10dBu) for 0dBFS. Acoustic music need about 40dB of gain and rock 25dB. That is with bypassed transformers.


Roger

[SmokinJoe]

Here is an MX100 for $48, listed as brand new/never used... and it looks it.  Make yourself up a battery box, and you are golden.

http://cgi.ebay.com/NAKAMICHI-MICROPHONE-MIXER-MX-100-NEVER-USED-PERFECT_W0QQitemZ170372546452QQcmdZViewItemQQptZDJ_Gear_Lighting?hash=item27aafebf94&_trksid=p3286.c0.m14

[gdplusmore]

I have great success with the MX100...you can pm me if you would like a link to some examples..of nak300 with mx100 and nak100 with mx100

[Roger Gustavsson]

I have great success with the MX100...you can pm me if you would like a link to some examples..of nak300 with mx100 and nak100 with mx100

Yes, a Nakamichi MX-100 is nice. A pity it is that large and bulky. Not the perfect partner to a Edirol R-09.

Roger

[Roger Gustavsson]

You can also fit a mic preamp inside the microphone and feed it from an internal battery. Scott Wurcers Chargeamp will fit, http://www.twin-x.com/groupdiy/albums/userpics/mike1.GIF Here is a drawing of my chopped Nakamichis, http://www.twin-x.com/groupdiy/albums/userpics/cut-down_CM-300.pdf. The output of the microphone with a 5pF feedback capacitor will be around 95-100mV/94dB. 775mV is equal to 112dB and I think that should give you 0dBFS  with the Edirol R-09. S/N will be as good as the Edirol allows. This is all DIY....

Roger

[dgale]

FWIW, in my early DAT days (and pre-Neumann days), I used to run my cm300s into my old Sony D5 for it's pre and send the analog line out to my Sony D7...I just liked the sound of the D5 better than straight to the D7, as well as giving me L/R level control I didn't have with the D7...and of course since I wasn't actually running the cassette deck, anlaog generations were a non-issue.  I realize it's not very germane here but this discussion made me think of that - I always liked the sound of the 300s and the D5.  Matter of fact I'd consider dusting off the D5 to do this again if/when I dusted off the 300s...too much gear collecting dust I guess.

[dgale]

The last time I remember running my nak300s was at a LL show in Bend OR in July 2000...makes me realize I better go check that the batteries weren't left in the mics...yikes!  Time flies.  At a minimum I'm sure the batteries are dead and I recall they were a pain to replace, although maybe less so these days with the internet being what it is.

[acidjack]

I used to run mine into the Zefiro InBox aka the Denecke AD20.  Not the cheapest option, but it's small, has dual volume control... I guess the only problem is that it can't output digitally to the R-09HR...

[dgale]

I used to run mine into the Zefiro InBox aka the Denecke AD20.  Not the cheapest option, but it's small, has dual volume control... I guess the only problem is that it can't output digitally to the R-09HR...

The R-09 doesn't have a digital input, so this is a non-issue. 

[fmaderjr]

The R-09 doesn't have a digital input, so this is a non-issue.

That's why acidjack said the only problem was that it couldn't output digitally to the R-09HR.

[JEMS]

I have been using a Naiant battery box to power my Busman modded Nak 300 capsules and it is working brilliantly. The modded caps have mini XLR and the Naiant box has two mini jacks in so the cable is mini-XLR female to mono 1/8 inch. The Edirol appears to love the feed coming into it from that. Very workable for stealth.

[Roger Gustavsson]

What about this solution for the Nakamichi CM-100/CM-300? Are there any faults in my schematic? The output is impedance balanced. There are AC-coupling capacitors at the input of my soundcard.

http://www.twin-x.com/groupdiy/albums/userpics/Nakamichi_and_SSM2019%7E0.GIF

I can be put in a small enclosure, like Hammond 1455C1201.


Roger

[Roger Gustavsson]

Thank you for your advices!

Here is a revised schematic.

http://twin-x.com/groupdiy/albums/userpics/Nakamichi_and_SSM2019%7E1.GIF

The data sheet of the SSM2019 have a simpler RF filter, just a capacitor across the input terminals of the IC. So my 15R series resistors and the parallel 220pF capacitors interfere with the shunting capacitor?

Will there be any risk of having interference on the supply to the JFET? (That was why I through in a capacitor in my original schematic)

How much do I have to worry about the DC offset? Will it not be taken care of at the input of the soundcard (DC-blocking capacitors there)?



Roger

[Roger Gustavsson]

I would probably build the amp without and measure high-gain performance through a full battery cycle, and add a compensating load if necessary.

Could that compensating load be feeding a LED from the negative supply, a power indicator? The Idss of the JFET is about 1mA.

[Roger Gustavsson]

mshilarious,

Will this solve the problem with the input offset?

http://www.twin-x.com/groupdiy/albums/userpics/CM-300_with_preamp.GIF


 
Roger

[dave570]

OK, so I have the MX-100 now and a battery box to power it for 4-5 hours of recording. I know the MX-100 has L, R and Blend for the 3rd mic. Although I do have 3 Nak 300s, my t-bar holds only 2 mics and so I can't really put the 3rd mic up. Are 3 mics required or can I get away with just 2 mics into the MX-100?

[gdplusmore]

yes...just turn the middle blend nob down all the way...