Author Topic: Nakamichi CM 300 housing question (Read 8553 times)

weedwacker · « **on:** January 09, 2011, 01:07:41 PM »

I want to build some custom mic body housings for some Nakamichi CM 300s and need to find out the following if anyone here can help out.

1. Does anyone know what thread size is used for the attenuator housing(is it a standard thread like a pipe thread or a custom thread size)?
2. What is the overall current consumption of a standard unmodded attenuator and switch/xlr connector? I want to attempt to make a shortened mic housing using different batteries than a 9v neda 1611 transistor battery and am looking at possibly using CR1612/1616/1620 3v lithium ion coin batteries and am trying to determine the overall battery life using 3 3v based on the mAh capacity of the batteries. If the original manual is correct the CM-300 should draw less than 1 mA which means using 3 50 mAh CR1616 3v batteries should give me approximately 50 hours of battery life before I need to change them.

SHINN · « **Reply #1 on:** January 09, 2011, 01:40:16 PM »

The thread is a M20 X .75 It's not a pipe thread. I'm not sure about the cap, but could measure it at work if you need to know.

Roger Gustavsson · « **Reply #2 on:** January 09, 2011, 02:10:39 PM »

Quote from: weedwacker on January 09, 2011, 01:07:41 PM

2. What is the overall current consumption of a standard unmodded attenuator and switch/xlr connector? I want to attempt to make a shortened mic housing using different batteries than a 9v neda 1611 transistor battery and am looking at possibly using CR1612/1616/1620 3v lithium ion coin batteries and am trying to determine the overall battery life using 3 3v based on the mAh capacity of the batteries. If the original manual is correct the CM-300 should draw less than 1 mA which means using 3 50 mAh CR1616 3v batteries should give me approximately 50 hours of battery life before I need to change them.

I think you can go for three CR1632 (125 mAh). I will come back with more information. In a hurry right now.

Roger

weedwacker · « **Reply #3 on:** January 09, 2011, 02:19:15 PM »

Quote from: SHINN on January 09, 2011, 01:40:16 PM

The thread is a M20 X .75 It's not a pipe thread. I'm not sure about the cap, but could measure it at work if you need to know.

Do they even make M20 X .75 taps? As far as I am aware and on a quick scan the smallest fine thread metric tap I've found is M20 X 1. And duh on my part I should know better that if it is made outside the U.S. it will be in metric.

SHINN · « **Reply #4 on:** January 09, 2011, 02:31:56 PM »

I saw one on ebay for 28.00 bucks. I was thinking of making a custom housing for my naks at work, but our machines only go to 20mm. To bad cause the thread could be made easy with a single point tool or a thread mill. The franken mod seems like the way to go for me...with a small battery in the line. The small 1.5v batteries can be stacked up to make 9v

Roger Gustavsson · « **Reply #5 on:** January 11, 2011, 08:19:58 AM »

I think the M20 x 0.75 thread has to be made on a lathe or milling machine. I would certainly like to have it done but I have no connections to any machine shop.

Here is a picture of my chopped CM-300 with an internal battery (3 stacked CR1632).

Here is a comparsion of an original and a chopped one with right-angled XLR-connector.

Roger

SmokinJoe · « **Reply #6 on:** January 11, 2011, 11:56:24 AM »

So Roger, I'm guessing you just disassembled it, cut off most of the barrel where the battery and transformer go, reusing the thread where the attenuator body screws on. The only machining was drilling a hole for that screw at the back? Cool idea.

Roger Gustavsson · « **Reply #7 on:** January 11, 2011, 01:56:28 PM »

Yes, you are right! I did the cut just leaving the Nakamichi writing intact, the barrel is 38 mm (1½ inch) long. If I could have a new thread made in the tube that is left over, it can take 3-5 CR1632 in the shorter battery compartment and still be used.

Roger

SHINN · « **Reply #8 on:** January 12, 2011, 10:19:15 AM »

Roger, I like your chopped cm 300's ! Do you have to use a 3 pin connector for this setup? Would it be possible, or advisable to use a rca connector (for a 4' cable)? What do you think about hard wiring them without a connector, would the battery go dead cause there's no switch?

I took apart my old 2 xlr into a single 1/8 mini jack cable (for my stock cm 300's). The 1 and 3 pins were joined at the mic end. Then both mic lines went into the single 1/8 stereo jack. Is this the wrong way to wire the mics?

I want to do either a chop or a Franken-nak mod but I'm not really sure of the pros and cons The only schematic I have shows the cm300 active pre mod and cm300 active post mod. But not the wiring to the battery and deck. It looks like the signal on the post mod doesn't go through the battery maybe?

Thanks for your help

It's snowing like crazy here in ct!!

Roger Gustavsson · « **Reply #9 on:** January 13, 2011, 06:02:48 AM »

Hi SHINN,

You can use a 3 pin connector. Pin 1 and 3 can be connected inside the female XLR, acting as a power switch. Without a switch, the batteries will die quickly. As there is no capacitor in series with pin 2, the mic preamp must be AC-coupled! I think most are.

I am using a 4 pin connector, in case I want to make the output impedance balanced. Just a resistor between pin 4 and ground. I have not tried it yet as my preamp does not have differential inputs.

You can also hardwire the chopped ones. Just make a suitable insert with a clamp and lock it with the small screws that normally holds the XLR insert. I am not in favour of RCA connectors, I prefer locking connectors that stay in place.

Roger

runonce · « **Reply #10 on:** January 13, 2011, 10:10:39 AM »

Here's my TEAC ME-80s that I had chopped down at my local gunsmith.

I could never make the mod work(i forget why) - and then soon decided I didnt like the original franken-nak mod - and gave up.

Now - Im favoring Rogers approach and thinking of trying that...

Problem might be - did I chop them too short!?

jbell · « **Reply #11 on:** January 13, 2011, 10:41:17 AM »

The chopped Teacs don't work??? Would you be interested in selling them?

Quote from: runonce on January 13, 2011, 10:10:39 AM

Here's my TEAC ME-80s that I had chopped down at my local gunsmith.

I could never make the mod work(i forget why) - and then soon decided I didnt like the original franken-nak mod - and gave up.

Now - Im favoring Rogers approach and thinking of trying that...

Problem might be - did I chop them too short!?

runonce · « **Reply #12 on:** January 13, 2011, 11:29:58 AM »

Quote from: jmbell on January 13, 2011, 10:41:17 AM

The chopped Teacs don't work??? Would you be interested in selling them?

Quote from: runonce on January 13, 2011, 10:10:39 AM
Here's my TEAC ME-80s that I had chopped down at my local gunsmith.

I could never make the mod work(i forget why) - and then soon decided I didnt like the original franken-nak mod - and gave up.

Now - Im favoring Rogers approach and thinking of trying that...

Problem might be - did I chop them too short!?

I think for now - I'll take another stab at getting them to work...somehow.

SHINN · « **Reply #13 on:** January 16, 2011, 12:47:49 PM »

Thanks for the help Roger,

I decided I don't want to cut the bodies right now so if wanted the mics can be brought back to stock. Plus I have those shotguns I never used.

For know I want to use your schematic for the mods, but with the battery in the line. Then down the road I'm going to buy that m20 tap on ebay and try to make some bodies from scratch with the battery in the body. I think I can thread the tube if I use a bridgeport to line up the tap. If that works and anybody wants to use the tap when I'm done they are welcome to it.

Also, does anyone know what material the bodies are? They look like stainless. I was thinking aluminum would work but would need to be a little thicker.

Thanks again,
Shinn

Roger Gustavsson · « **Reply #14 on:** January 17, 2011, 07:55:23 AM »

Shinn,

Have you found the correct M20 x 0.75 mm tap, where? Digikey have a cable clamp with M20 x 0.75 thread, HR1389-ND.
The bodies seems to be made of some alloy of brass, but I am not sure. I would be most interested in some bodies like the ones you mention! I have some extra bodies but it is a waste to cut them...

M20X0.75, Hand Tap, X150200075 http://uk.osgeurope.com/products/catalogues/OSG-UK_%20SPCL_TAP_%202007.pdf

Roger

SHINN · « **Reply #15 on:** January 17, 2011, 04:46:56 PM »

This is the one I saw on Ebay

http://cgi.ebay.com/20mm-x-0-75-Metric-HSS-Righ-Hand-Plug-Tap-M20-x-75-/110630102966?pt=LH_DefaultDomain_0&hash=item19c21167b6

I emailed the seller to find out if it is really an m20 x .75 because everyone I talked to said it was a non standard thread.

Shinn

weedwacker · « **Reply #16 on:** January 20, 2011, 07:28:17 PM »

Good stuff here and thanks for the pictures Roger. I wasn't even thinking of removing the lo cut switch but would cut down on the size also. I am not that good at reading schematics but if I am seeing it correctly you just removed the 3 wires soldered to the 3 pins for the xlr connector and hook the battery spring up directly to those points instead? I don't want to chop the original housing up since I have set of 3 all original components including caps, windscreens and stand holders along with the case and manual and if ever sell them and someone wants the set stock I can just put the original housings back on the mics then. If I remove the lo cut switches it looks like I can put them back to stock fairly easily with some soldering so that may be an option also. I can have a piece of tooling made to tap a brass or copper housing to that thread using a swiss screw machine(just cost more money then). I'll post back if I decide to make them or have a local machine shop here make the housing. Thanks for all the advice everyone has provided thus far.

Roger Gustavsson · « **Reply #17 on:** January 21, 2011, 03:52:25 AM »

Quote from: weedwacker on January 20, 2011, 07:28:17 PM

Good stuff here and thanks for the pictures Roger. I wasn't even thinking of removing the lo cut switch but would cut down on the size also. I am not that good at reading schematics but if I am seeing it correctly you just removed the 3 wires soldered to the 3 pins for the xlr connector and hook the battery spring up directly to those points instead?

Not really. Pin 1 is ground and it is connected to the body/chassis. Pin 2 is signal. Pin 3 can be used for power and/or power switching. If you use an internal battery, use a shorting link inside the female connector between Pin 1 and Pin 3 (negative pol of the battery). Pulling the connector = power off. Of course, the battery or power can be external too. +V on Pin 3 and - on Pin 1.

Quote from: weedwacker on January 20, 2011, 07:28:17 PM

I don't want to chop the original housing up since I have set of 3 all original components including caps, windscreens and stand holders along with the case and manual and if ever sell them and someone wants the set stock I can just put the original housings back on the mics then. If I remove the lo cut switches it looks like I can put them back to stock fairly easily with some soldering so that may be an option also. I can have a piece of tooling made to tap a brass or copper housing to that thread using a swiss screw machine(just cost more money then). I'll post back if I decide to make them or have a local machine shop here make the housing. Thanks for all the advice everyone has provided thus far.

I have one of these pack of three too. I will keep their bodies in original shape for now as they are in mint condition. Just wished someone could make new threads in the remains of the bodies that I cut down, now 38 mm shorter. They could still be used with three stacked CR1632 lithium cells inside. I would also be interested in having some extra bodies/housings.

Roger

SHINN · « **Reply #18 on:** January 21, 2011, 11:02:56 AM »

Hi Roger, So can I use your schematic but with the battery in the cable? I was going to use a 2 conductor plus shield cable from each mic, into a battery box, then a 2 conductor plus shield from the battery box to the mini jack. Do I need 2 separate cables going from the battery box to the mini jack? The thing that confused me is the Rane Cable diagram.

instructionshttp://www.taperssection.com/reference/pdf/DIY_CableDiagram_Rane.pdf

On page 6, example #5. It shows a 2conductor plus shield cable for each mic (even though the 1 and 3 pins are joined at the mic connector). Then the shield doesn't connect at the the recorder end. (?)

Also, I bought the M20 tap. Its supposed to come in 2 wks.

Shinn

SHINN · « **Reply #19 on:** January 21, 2011, 11:08:18 AM »

Here's the Rane cable diagram. I didn't copy the link right.

http://www.taperssection.com/reference/pdf/DIY_CableDiagram_Rane.pdf

weedwacker · « **Reply #20 on:** January 22, 2011, 12:04:17 PM »

Quote from: SHINN on January 21, 2011, 11:02:56 AM

Hi Roger, So can I use your schematic but with the battery in the cable? I was going to use a 2 conductor plus shield cable from each mic, into a battery box, then a 2 conductor plus shield from the battery box to the mini jack. Do I need 2 separate cables going from the battery box to the mini jack? The thing that confused me is the Rane Cable diagram.

instructionshttp://www.taperssection.com/reference/pdf/DIY_CableDiagram_Rane.pdf

On page 6, example #5. It shows a 2conductor plus shield cable for each mic (even though the 1 and 3 pins are joined at the mic connector). Then the shield doesn't connect at the the recorder end. (?)

Also, I bought the M20 tap. Its supposed to come in 2 wks.

Shinn

Let us know how the tap works out when you get it. If it works I will most likely order one myself or if you want rent it from you to do my project here.Thanks for the wiring diagrams looking at those I may just make a new connector outright with cabling instead. Decisions, decisions the fun part of designing things.

Roger Gustavsson · « **Reply #21 on:** January 23, 2011, 12:24:26 PM »

Quote from: SHINN on January 21, 2011, 11:02:56 AM

Hi Roger, So can I use your schematic but with the battery in the cable? I was going to use a 2 conductor plus shield cable from each mic, into a battery box, then a 2 conductor plus shield from the battery box to the mini jack. Do I need 2 separate cables going from the battery box to the mini jack?

Shinn,

I think you can do like this.

http://www.twin-x.com/groupdiy/displayimage.php?album=lastup&cat=0&pos=0

As there will be DC on the outputs, make sure there are capacitors in series with pin 2. The battery box should be close to the microphones, there is a risk of pickung up RF/HF disturbancies with long runs of cable. Maybe an electrolytic capacitor between pin 3 and 1, inside the bodies or close to them?

Roger

SHINN · « **Reply #22 on:** January 24, 2011, 06:11:19 PM »

Thanks for the wiring diagram! Thats cool...I thought I was going to need 2 batteries. I haven't completely figured out the capacitors yet, but I'm starting to understand it.

If that tap works I can loan it out no problem. I'll probably use it once and then it will just sit there for 20 years, haha. It's prob only like 2 bucks to send anyway. I think if you want to tap the original bodies though the ID needs to be opened up a little. I was getting 18.8mm on the body ID and 19.2mm on the thread ID (about .008" per side difference).

Shinn