[ACM investiupgradifications] All things MICROPHONE

[ChuckD]

Ok let me try and measure all the patterns to see what the actual voltages are. I was thinking of dropping the +B by 10 volts or so by using lower zener values.

I'll try this out tonight.

What controls the "brightness" of this circuit?

-Chuck

 

[buschfsu]

guys any word on iron for the acm3?
options are edcor and cinemag right now so anything else??

 

[Marik]

guys any word on iron for the acm3?
options are edcor and cinemag right now so anything else??

After New Year hoidays I will be offering my own amorthous torroidal core, low noise/low distortion, Premium ribbon mic tranformers.

Best, M

 

[buschfsu]

great and they fit in the acm3?  any soundclips?

 

[Marik]

great and they fit in the acm3?  any soundclips?

Yes, there are two size versions and one of them fits the ACM3. There is more info and some soundclips on page 3 of this very thread:

http://www.groupdiy.com/index.php?topic=27793.msg366758#msg366758

http://home.comcast.net/~markfuksman/Ribbon1.mp3
http://home.comcast.net/~markfuksman/Ribbon2.mp3

Best, M

 

[buschfsu]

ahhh laziness

thanks, look forward to them

 

[rodabod]

What controls the "brightness" of this circuit?

I just thought I'd add what I've already discussed a little with a few others. This circuit does sound bright to me, and that's having tried different capsules, transformers and valves.

Currently I have mine set up using the CV4003 I mentioned earlier with the Cinemag 2480 and I have measured it as being flat between 20Hz - 20KHz +/- 0.2dB. Despite the flat response though, it still sounds bright. I'm considering changing the plate coupling cap to a different value to give a little bump in the low-end, so I'll see how that works out. I've also added suitable HF filtering for when using K67-type capsules to approximate a U67 response.

Roddy

 

[okgb]

Good & bad report

Recieved two of my three parcels today ,
[ 2 73's , 2 amc - 100's , 1- amc 900
and 1 amc 200 [ subed for the 300 i ordered ]

As often the case u.s.p.s. straight to my door ,
no taxes or duties [ marking other X , helps
and they weren't overvalued , thanks ]

Worst offender is the AMC-200 , which was subbed for the
AMC-300 I Ordered is unsuable , having a amount of hiss higher than signal ,
proportionate to gain level , but always
higher , What can we do about this Chance ?
[ i know wait til all the orders are shipped ] in the meantime anyone have any idea's ?

One of the 73's seems good out of the box , the other has a slight broadband buzz
[ will do the xister mod ]

the two 100's seem to sound pretty good , not too bright
consistent to each other .

the AMC 900 , is a little hissy & dull , not unusable depending
on what's getting recorded , hard to tell if it is normal and
in spec or not .

Any comments on the mics for those who already have [ & use ] them ?

thanks & regards Greg

 

[okgb]

O.k. for reference here is my unusable ACM 200 ,
degooping required or just bypass the electronics ?

 

[rodabod]

You could try lifting the trasformer secondary and injecting AC into the active circuit and measure noise. I might have suggested tring taking the output from the trafo, but it quite possibly will not be 200 Ohms (depending on how bad the Chinese design is  :-\ )

 

[Marik]

Worst offender is the AMC-200 , which was subbed for the
AMC-300 I Ordered is unsuable , having a amount of hiss higher than signal ,
proportionate to gain level , but always
higher.

Yeah, that what to expect. All the Chinese active mics I saw had unaccepted noise level. What ratio the transformer? If it is anywhere within 1:50 then just bypass the electronics.

Best, M

 

[okgb]

Truth be told , i'm not all that interested in doing the work for him to make this right
If i get stuck with it, then i'll try to salvage the situation , for the time being i'll put it aside
and hope to return  it .

Well maybe after i stop shaking my head , i'll take some measurements for you guys if you want , I'm glad prodify is my home and not that other place

 

[mitsos]

Hi Marik,
are your ribbon mic trafos ready? Is there a price?
thanks!

 

[Marik]

Hi Marik,
are your ribbon mic trafos ready? Is there a price?
thanks!

At this point they are available only in limited quantities. The price is $129.

Best, M

 

[mitsos]

OK, I asked that before I plugged the baby in. I just opened it now, and I was surprised that it has a TAPED-ON screen (very fine) over the ribbon. Is this normal? The screen, not the tape. I'm pretty sure the tape is the chinese way.  I'm quite sure anyone else would have secured it another way.  I mean, they used something that looks like masking tape to hold this screen on, and it was lifting off of the back side of the mic. 

Anyway, didn't do much testing with it, but I liked how it sounded on my voice (did a 2 minute test only) but at high gain levels there was a buzz in the signal... This mic only has a ribbon and trafo in it, so does anyone know how I could test to see if it's coming from the ribbon/motor or trafo, or is there any other possibility?

thanks!

here is a pic of the screen, after I had re-attached it. When I opened it, it was only attached at the top half... the rest of the screen was curling upwards...

 

[rodabod]

Oliver Archut's 47-inspired mod:

http://recforums.prosoundweb.com/index.php/m/0/26173/96/13216/#msg_num_14

Doesn't look very 47-like to me, but it does look like the valve chosen is mean to couple well to a BV8-style transformer, and maybe that's been factored into the transformer design. The 6dB pad looks a bit odd to me! Has anyone else seen a pad implemented like that before?

Roddy

 

[Greg Dixon]

Oliver didn't do the circuit. Terry said it was done by Lucas.

 

[okgb]

I wouldn't call that a pad , more like a gain switch
but pad is likely more familier to mic folk

 

[andrewsamuel]

<snip>
and 1 amc 200 [ subed for the 300 i ordered ]

Worst offender is the AMC-200 , which was subbed for the
AMC-300 I Ordered is unsuable , having a amount of hiss higher than signal ,
proportionate to gain level , but always higher , What can we do about this Chance ?
[ i know wait til all the orders are shipped ] in the meantime anyone have any idea's ?

Hi all,

My 200 was also completely unusable due to hiss. I re-tensioned the ribbons, and now the hiss is merely bad....

I'd happily bypass the phantom power if someone could guide me on the wiring.... I'm an ill-equipped, newbie DIYer here, btw  :

Thanks!

Andrew 

 

[okgb]

how did you retension it ?

the electronics appear to be surface mount covered in goop [ just a few parts ,transistor i guess ]
should be able to jumper across two wires going into the glob and two wires
comin out of the glob , whether the out transformer is good for this is another ?
but maybe that's part of the problem and they just used the usual one they had
and it's not a match for the electronics ? [ with any luck ]

there's another good one , oh can't give you what you ordered but we'll sub this crap we can't
get rid of instead