Dead Coles 4038

TornadoTed · Dec 7, 2010

I have a dead Coles 4038 a friend gave me. He was micing a floor tom being played gently with hands and the coles was inside, of course somebody came along and whacked the tom with a stick and it stopped working!

Is this ribbon ok as I'm not sure how it is supposed to look? It looks a bit flattened in the centre but there are no visable rips or tears. Would it still pass some signal even if damaged?

zebra50 · Dec 7, 2010

Normally it would still pass some signal, so long as it was still conducting and moving, although it would sound weak and 'bad'.

That looks a bit weird, like it is stuck to or pressed all the way against the metal screen behind it - is that the case? That would stop it moving.

Coles still service these, or I can have a look if you want a budget option!

haima · Dec 7, 2010

nothing to add really... but, what a lovely mic! - they sound good on so many sources... love them.

definitely worth fixing - i'd contact coles and see how much it'll cost...

Biasrocks · Dec 7, 2010

Wow!!

It looks like the ribbon is flattened out and perhaps stuck to the magnet.

Coles or AEA is your best bet. They charge around $200 for a re-ribbon.

http://www.ribbonmics.com/pdf/MicRepairForm.pdf

Bet it sounded great just before it died, ain't that always the way.

Mark

zebra50 · Dec 7, 2010

Looking again at this, has the ribbon somehow slipped out from between the clamps and lost all of it's tension? If so you may be able to resurrect it yourself.

TornadoTed · Dec 8, 2010

Marik over at Gearslutz seems to think that the ribbon is fine and that Coles stretch them almost flat. He reckons it is either,

1) lost contact on the ribbon clamps--try to tighten the bolts (be very gentle)--most likely.
2) transformer leads going through the swivel holder got broken (never seen it in that mic, but possible)
3) in the barrel--transformer to connector contact.
4) transformer damage--very unlikely, but in any case we do repair those (and rewind for 200 Ohm, if yours is 30 Ohm).

I shall investigate today.

rodabod · Dec 8, 2010

Coles don't "stretch them almost flat". That might be misquoted from Marik. They use fine corrugation like you can see near the ends of the ribbon. The middle is stretched.

STC used to make piston-type ribbons for the 4040, but that was many years ago.

Check the ribbon can freely move, though it looks as though you could possibly do with a fresh one.

Marik · Dec 8, 2010

TornadoTed said:
Marik over at Gearslutz seems to think that the ribbon is fine and that Coles stretch them almost flat.

I initially said that, but half an hour later looked at the picture and edited post:

"The ribbon looks OK. It seems that it touched the mesh screen at some point, but should be fine... at least pass the signal."

Did you try to tighten the bolts, as I suggested?

Again, there is some lost contact/broken wire there.

Best, M

Marik · Dec 8, 2010

rodabod said:
Coles don't "stretch them almost flat".

Hi Roddy,

In my initial message I used "pre-stretch". On the other hand, compare to most of other ribbon microphones, the 4038 corrugation is indeed much flatter. That's the reason the ribbon in this particular mic is flattened in the middle, but still not sagging. In any case, I saw quite a few 4038 with similar (crashed in the screen) ribbons and they still sounded just fine.

STC used to make piston-type ribbons for the 4040, but that was many years ago.

Isn't the 4040 actually a new mic from Coles?

Best, M

rodabod · Dec 8, 2010

Marik said:
STC used to make piston-type ribbons for the 4040, but that was many years ago.

Click to expand...

Isn't the 4040 actually a new mic from Coles?

Oh balls! Yeah, I'm thinking of the 4033; I've had a few of these (and still own one).

(For the benefit of others), the Coles 4038 ribbon should look like it does towards the ends of the ribbon in the photo, ie. consistently corrugated across.

Ted, a quick check I sometimes do is to measure continuity between the ribbon clamps and the surrounding metal gauze to see if the ribbon is touching / there's a short somewhere.

Marik · Dec 8, 2010

rodabod said:
Marik said:

STC used to make piston-type ribbons for the 4040, but that was many years ago.

Click to expand...

Isn't the 4040 actually a new mic from Coles?

Click to expand...

Oh balls! Yeah, I'm thinking of the 4033; I've had a few of these (and still own one).

With piston corrugation

? Any chance to see it?

(For the benefit of others), the Coles 4038 ribbon should look like it does towards the ends of the ribbon in the photo, ie. consistently corrugated across.

Yes. It seems at some point there was a big wind blast (might be when it fell), which smashed the ribbon into the screen--you can see the mesh indentation.

Ted, a quick check I sometimes do is to measure continuity between the ribbon clamps and the surrounding metal gauze to see if the ribbon is touching / there's a short somewhere.

Be careful though, if you decide to measure the ribbon between clamps for continuity. The current through DMM (depending on the one you use) can through it out the gap.

Best, M

TornadoTed · Dec 8, 2010

Thanks for all the replies guys.

I did a little more investigating today and loosened and tightened the clamps. All connections to the XLR and transformer seem ok so I have given up, packaged it up and will send it to Coles tomorrow.

rodabod · Dec 8, 2010

Marik said:
With piston corrugation ? Any chance to see it?

Yeah, I'll get you a photo the next time I open one up. It's a thicker aluminium (as you may have guessed). Also, the middle section was dished rather than what Beyer do with the longitudinal indentations.

Marik · Dec 8, 2010

rodabod said:
Marik said:

With piston corrugation ? Any chance to see it?

Click to expand...

Yeah, I'll get you a photo the next time I open one up. It's a thicker aluminium (as you may have guessed). Also, the middle section was dished rather than what Beyer do with the longitudinal indentations.

I.e. it is more like B&O pistons?

zebra50 · Dec 8, 2010

I have a 4033 I could look at. I love those mics, although mine could be quieter.

Hey Roddy, how do you open it up? Are the screws behind those black wax plugs?

rodabod · Dec 9, 2010

Marik said:
rodabod said:

Marik said:

With piston corrugation ? Any chance to see it?

Click to expand...

Yeah, I'll get you a photo the next time I open one up. It's a thicker aluminium (as you may have guessed). Also, the middle section was dished rather than what Beyer do with the longitudinal indentations.

Click to expand...

I.e. it is more like B&O pistons?

From what I gather, yes. Though I'm too scared to open up any of my B&O mics since they work, and I've heard they are not much fun to work on.

zebra50 said:
I have a 4033 I could look at. I love those mics, although mine could be quieter.

Hey Roddy, how do you open it up? Are the screws behind those black wax plugs?

Yes! Fish the wax out with a small blade screwdriver and keep to one side. Screws are underneath. Then, do the reverse, and drip the wax back in, or shove it in and heat with a lighter.

rodabod · Dec 9, 2010

By the way, Marik, do you know if it is only the secondary turns number which is different on the STC 30-Ohm transformers? Just wondering if I should re-use my one and increase the turns ratio for 200-ish Ohms?

zebra50 · Dec 9, 2010

~~Whilst we're talking about the 4033, does anyone have a diagram for how the ribbon, dynamic element and transformer work together in this mic?~~

Someone give me a kick for being a lazy-ass:

Anyway, for this one I think rewinding for 200R is not so simple.

Marik · Dec 9, 2010

rodabod said:
Marik said:

rodabod said:

Marik said:

With piston corrugation ? Any chance to see it?

Click to expand...

Yeah, I'll get you a photo the next time I open one up. It's a thicker aluminium (as you may have guessed). Also, the middle section was dished rather than what Beyer do with the longitudinal indentations.

Click to expand...

I.e. it is more like B&O pistons?

Click to expand...

From what I gather, yes. Though I'm too scared to open up any of my B&O mics since they work, and I've heard they are not much fun to work on.

It depends which ones. The BM3's are fine--you take off the top cap and just slide entire motor structure out. The problem is BM6--you need a special collet to extract old and brittle plastic insert, which is a real PITA.

rodabod said:
By the way, Marik, do you know if it is only the secondary turns number which is different on the STC 30-Ohm transformers? Just wondering if I should re-use my one and increase the turns ratio for 200-ish Ohms?

Of course, you can reuse the core for the 200 Ohm--it is much better idea than to use a second step up transformer. Yep, the Pri is good, but you will need to rewind the Sec. First, pay attention to the winding direction and then unwind the Pri (save that flexible wire and cloth insulation and then reuse it if it is in good condition--it is a good wire for going through the swivel holder).

The Pri is 17 turns and for 200 Ohm you will need ~1:28 ratio. Ideally, that would be 476 turns for a Sec, but with losses and coupling I'd say, you will need at least good 500, if not more. Oh boy! Expect some 3 hours at very least, providing you will be lucky and make it from the first shot. Or... just send it my way and I'll put it on a winder. I made those by dozens.

Best, M

PRR · Dec 9, 2010

> I think rewinding for 200R is not so simple.

The schematic says the dynamic element is NOT transformered.

The "Pressure" (Omni) response is just the dynamic element, so you are stuck.

The "Ribbon" response is just the ribbon via transformer. You "could" re-wind that.

The "Cardioid" requires an exact mix of Ribbon and Dynamic. Since you can change one, but not the other, and the change would spoil the Cardioid, you are stuck.

There is also L1 and C1 which shifts frequency response in Cardioid.

Given infinite play-time, you could bring both signals out to two preamps. Relative gains give patterns from omni to sub-Card to Card to super-Card to Bi-Di. You will have to EQ one path to get consistent directivity with frequency. Along the way you could change the ribbon's line impedance. But life is too short.

What was the question? A CT-CT line transformer used 150:600 will step-up line impedance. A 4-coil transformer can give 1:9 impedance perhaps useful on 37 ohm mike.

Dead Coles 4038

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