Shure M67 Mic Mixer - Question

[rufus13]

Noise-Noise-Noise. The M67 has a bunch of self-noise at any usable setting on the several I've had.
The transformers are small. This is fine for dynamic mic's and ribbon mic's but high-output condensers will drive them to clipping and other distortions.

On teardown (lots of good metal connectors), M67 has a bunch of noise-generating carbon-comp resistors on the phenolic pcb.

Later models like M267 are better.

Cheers.

[Iggy Poop]

Originally Posted by rufus13

Noise-Noise-Noise. The M67 has a bunch of self-noise at any usable setting on the several I've had.
The transformers are small. This is fine for dynamic mic's and ribbon mic's but high-output condensers will drive them to clipping and other distortions.

On teardown (lots of good metal connectors), M67 has a bunch of noise-generating carbon-comp resistors on the phenolic pcb.

Later models like M267 are better.

Cheers.

Will the m267 work with a condenser then? They seem to go for a bit more, like $125. Is it worth it?

[Karloff70]

Get a separate phantom box and you can plug your condensers into any phantomless pre.......

The phantom needs to be between the mic and pre, and running it from your interface trying to go through the M67 won't work. If anything it might blow something in the M67, although it might have components to safeguard from this.

[MRG2U]

The october issue of Guitar, October 2009, Vol. 20, # 11, has a great article for modifying a M67 which says it will warm up vocals an incredible amount for home recording. I am going to purchase one and do the mods, which are farily simple. i will post results if I can find one and do the mods.

[chris319]

The october issue of Guitar, October 2009, Vol. 20, # 11, has a great article for modifying a M67

Wow! If I'm not mistaken the M67 dates back to the late '60s. (Then again, so does the Unidyne III which is the basis for the SM57.)

[MRG2U]

I have, since the last post, purchased one m67 and did the above mentioned mods w/ very good results, so good in fact that i purchased another along w/ an m68 stereo mixer/equalizer. The whole idea for this was to be able to incorporate these into the rack we use for live shows. All of our gear is built up in modules so we can just roll em in ad plug em in and were ready to go in 15 minutes. same for breakin down. I have used the m67 both for vocals and to mike the drums and am very pleased at the level of performance and flexibiklity I get out of these for less than $250.00. Can't beat it but you do have to be able to change out some parts.thumbsup

[retractablezing]

Originally Posted by rufus13

Noise-Noise-Noise. The M67 has a bunch of self-noise at any usable setting on the several I've had.
The transformers are small. This is fine for dynamic mic's and ribbon mic's but high-output condensers will drive them to clipping and other distortions.

On teardown (lots of good metal connectors), M67 has a bunch of noise-generating carbon-comp resistors on the phenolic pcb.

Later models like M267 are better.

Cheers.

the M267 is a different circuit, doesn't have so much gain.

while i can understand someone calling M67s noisy, i'm also sure there's a lot of ppl that can appreciate the great and interesting sound they give (me included, on my third). they're very well kept secrets and the reason they're not more expensive is cause millions were made. decent and patient gain staging between input and output will yield something very interesting indeed. the transformers are small but good and well made stuff, as with most things shure. they're basically an early silicon transistor design, with a very "vintage" sound, that i'm sure would appeal to many ppl out there looking for period correct tone, at least preamp wise. they work well with anything (condensers, ribbons, etc.), but as with most things with high gain, don't expect to be able to record loud drums with a high output condenser without a decent pad (shure makes very good ones - coincidence?).

and as for noisy, well, they were good enough to record woodstock, if that says anything.

[Bater]

Does anyone have a link to the mod mentioned? I recently purchased one of these and am interested to see what can be done with it. Thanx

[Bob Olhsson]

The M 67 has a massive amount of gain in the output stage. Running the input controls all the way up and the master way down gives you a reasonably quiet signal.

I use to run the RCA bus output on the back into a Helios mike preamp with 15 or 20 dB. of gain instead of the built in 40 and thought the thing performed remarkably well. Not as good as the Helios but not bad for when I needed more than one input.

[Bater]

No one knows where to find this mod?

I was thinking about having it recapped, pots cleaned/replaced, etc... It is like 40-50 years old after all. But I opened it up to take a look at the inside and I am amazed at how clean this thing is! Can any of you tell by these pics if it has been worked on recently? Just seems too clean to be that old.

Would you suggest a recap/refurb? Everything seems to be in working order, I just worry about a machine of this age.

[Bater]

Ok, Ive had some time to play with it and I think it may need some service work done. All the switches, knobs jacks, etc.. work correctly, but it has a very low output.

I can plug a mic into it and get a good strong signal to the VU meter, and I can get it to clip without a problem, but in order to get enough of a signal into Sonar I have to re-amp with my firebox pre's maxed out (55db) If I run it into a line level input I can only get to about -20dbs while singing. Thats clipping the m67 and running a software boost of 12db. This doesnt seem right to me. I would say that there is something getting weak in the output stage.

Does anyone know of a good place to get this unit serviced? Or better yet does anyone know of good place to get this unit modded?

Upon further inspection I have found that I can get a good signal if I run out of the "headphones" jack on the m67 into a line input on the firebox. Does this mean that there is a problem with the mic output or is it attenuated that way?

[Bob Olhsson]

Sounds like you are using the XLR mike level output. The line level output is the screw terminals. You'll need a 600 Ohm terminating resistor too.

[Bater]

OK.


What do I do with the resistor?

[Bater]

Gotta say I'm really digging the sound of this little transformer box.

So if I understand this correctly, the mic level output is just to color the sound through the m67. After that I still need to re-amp the signal to make it useable. The line level output is the 2 screw terminals next to the mic output, but in order to use them I need to do something with a 600ohm terminating resistor.

Is there a problem with just using the headphone output to get my line level signal?

If that is not the way to go then I think I will look into turning the line output into a 1/4" or XLR connection. Doesn't seem like it would be too hard, but I still dont know what the resistor is for.

[Bob Olhsson]

The output transformer is designed to be loaded by 600 Ohms which was standard for pro gear when that mixer came out. Without the termination, the meter reads wrong nd the frequency response isn't right.

The mike level output was so that you could feed the signal into a PA system in addition to recording or broadcasting it.

[Bater]

So could I run a 600 ohm resistor between the line out posts and use the 1/4 inch headphone jack for my line out? I don't feel like cutting a cable apart to connect to the posts and if this will work then I wont try to add a connector in place of the line out posts. Thanks for all the help.

Is there anything special about what kind of resistor I should get?

[Bob Olhsson]

Being anal about tech details, I always used two 1200 Ohm metal oxide resistors in parallel.

You can use the headphone jack but beware that it was designed to produce two different levels depending on how far you plugged a mono phone plug in. I used to use a banana plug and a short cable connected to a male XLR connector. I really liked the sound better taking the RCA out to a high quality mike input.

[Bater]

Ok, Im sorry for being so dense. I'm not a total noob, but this is my first foray into the field of "vintage " electronics. If I were to set this up the right way I would put a 600ohm resistor in the line between the cable and the m67? and if I wanted to be really right I would run two 1200ohm resistors side by side on the same pin going into the cable? Is this just on one of the hot outputs or both? Or do they actually run between the posts and connect them together? Thanks again

[Bob Olhsson]

The termination goes across the output, not in series. Ideally it would go at the input of the next piece of gear but that isn't very practical in today's world. To run it unbalanced, you connect the ground terminal to one side.

[Bater]

I am not much of an illustrator, but I think it should look something like this? The big box is suppose to be the M67.


I could also run the resistor(s) directly across the terminals if I decided to?

[Bob Olhsson]

exactly!

[John Suitcase]

I have an M67 that I reworked to be 4 mic preamps. I added direct outs, just ahead of the summing resistors (unbalanced.) I also rewired the high pass filter switches to be 20db pads (I think, it's been a while!)

It sounds cool with the pads off, goes into distortion easily with a loud source. With the pads engaged it has a tamer, but still vintage, sound. I wouldn't describe it as hi-fi, but it works for some things.

For the $10 I paid, it's worked out pretty well!

(My current favorite sleeper mixer is the Yamaha M406, which can be easily modded to a 6 channel preamp. You can get them for about $50, switching it up to be preamps takes some new 1/4" jacks and a couple of hours, tops.!)

[Bater]

So you have an out for each line in? Sounds like an interesting mod. Do you lose any gain by skipping the output stage? I have seen a how-to on turning the filter into a pad and I might do that to a channel.

Can I run two 300ohm resistors in series and get to 600ohms? I have a couple of those around.

When ordering new ones, do I want higher or lower tolerances and watts?

[rogerbrain]

Originally Posted by Iggy Poop

Hi,

I acquired a Shure M67. I heard they make very interesting preamps. But i wanted to know is it ok to use phantom power (48v) through them to power a condenser mic. I'm afraid to try anything since I have no knowledge of this thing. I want to plug my condenser into the m67 and then out to my Digi 002 with 48v turned on. Will this work?

NO .. you will need a separate phantom power supply to go between the mic and the Shure mixer.. then out of that to your 002

[Bater]

Well I came up with an interesting solution.

On the back there is a switch to terminate a line in on mic input 4. I dont have anything that needs a 600ohm (actuall 2x1200 like bob ohlsson recommended) termination going into the M67 so I removed the wires from the switch and ran them direct to the mic input. Then I ran 2 new wires from the line out over to the switch and viola, I have a termination switch on my output.

The cool part is that I can still use everything like it was a stock unit except that there isnt a termination on the input anymore. Also everything is internal so there arent any wires or resistors hanging outside the box or off the end of a cable. I know that the termination should be at the end of the cable, but I'm using pretty short cables anyway.

Next I plan on installing an XLR output for the line level. After that I think I will try to do the pad mod on one or two channels.

Thank for all the help.


Here is a pic in case anyone is intersted. The gray wries are what I added.

[cjac9]

Sorry to revive an old thread. I've got a quick question for Bob.

Why are two 1200 ohm resistors in parallel better than just one 600 ohm resistor?

[Bob Olhsson]

There were no 600 Ohm resistors!

[cjac9]

Haha! There are now - any reason not to use them?

[Bob Olhsson]

Not really.