[spica]

Thanks a lot for the suggestions, guys.  I will try swapping the capsule first and see how that effects the tone.  I will report back.

Cheers.

[spica]

I replaced the capsule earlier this afternoon with the original chinese capsule and everything sounded normal.  I noticed when I removed the M7 capsule that the wire to the front diaphram was very loose - to the point that it would move around on its post.  I believe this loose coupling is why I was experiencing such a lack of high end. 

I have 2 M7 capsules so I checked the other one and that seemed alright.  I just put it on the mic and it works and sounds right. 

The original 1200 capsule actually sounded pretty close to the M7 capsule - at least during my simple voice test. 

[okgb]

Anyone have the original price list ?
It's the ACM 200

i bypassed the electronics in my 48v ribbon
[ cause they were noisy ] but i don't need another
ribbon so for sale it goes

[Paul G]

Anyone have the original price list ?

i bypassed the electronics in my 48v ribbon
[ cause they were noisy ] but i don't need another
ribbon so for sale it goes

Hi Greg.  Which ribbon do you have?  Thanks.

 

[mitsos]

I have a 1200 from the group buy which I have not (yet) modded at all. I was going to just remove RF caps and upgrade the output cap, and probably change the tube and call it a day. 

First question... my output cap is a 10uF lytic instead of the 1uF on the 460 schemo (and what most people have claimed to have). Other components seem to follow the 460 schematic.  I suppose I should change this to 1uF or so?

Second, and this is the big problem... if I tap the mic on the headbasket or right below, the mic cuts out for a second, then comes back to life.  I opened it and cleaned the boards with alcohol in case that was causing the problem.  Any ideas what could be causing this?

Anyway, the mic hasn't been used much, but I did test it at first and don't remember any problems (but I may not have tapped it...)


thanks!

[mushy]

Second, and this is the big problem... if I tap the mic on the headbasket or right below, the mic cuts out for a second, then comes back to life.  I opened it and cleaned the boards with alcohol in case that was causing the problem.  Any ideas what could be causing this?

Your head basket might need a shave.  A "hair" from the inner screen might be shorting out your capsule.  Remove the head basket and look inside along the seams of the inner screen.  Does it buzz when it cuts out?  Does it ramp back up slowly or cut right back up?

[mitsos]

Opened it up and trimmed away the extra crap from the seam and .....

 

No more cutting out!!

THANK YOU!

[rodabod]

First question... my output cap is a 10uF lytic instead of the 1uF on the 460 schemo (and what most people have claimed to have). Other components seem to follow the 460 schematic.  I suppose I should change this to 1uF or so?

Try a 1uF film cap. You may as well change the capsule to grid cap for a 1nF polystyrene while you are there....

[mitsos]

Thanks Roddy,

I know I have 1nF styrenes, but I'm gonna need to find one that is high enough voltage. I'm guessing it can be lower than 630V which is what is on the Apex schemo.

Thanks!

[rodabod]

They are usually very high votage, so shouldn't be too hard to find a suitable one.

If you are happy swapping caps, then also put a better brand of electrolytic for the first stage's cathode bypass cap (it's probably 47uF or 100uF). Panasonic, Elna, Dublier, etc.

[mitsos]

cool..  Have some Pana FCs around.  Gonna get around to it in a bit...

Only found 63V styrenes, though.. guess it'll have to wait til next week....

[khstudio]

Hey guys... I know this is an old topic but I've been looking everywhere for the ACM1200 schematic & can't find it.
PLEASE.. Can someone post it or send it to me, even a link to it would be great!!!

Thanks

Email:
kevin(at)khstudio(dot)us

[clintrubber]

I should have it, will dig it up & let you know.

Funny coincidence a new message pops up in this relatively silent thread...  

... just today this came up at the yahoo-micbuilders list:

http://www.diymic.com/

The schematic given there ( ) is NOT like the '1200 though; IIRC the '1200 uses the second triode-section for a cathode-follower.

Cheers

[khstudio]

Very cool... thanks man!

Did everyone give up on these mics? I have the TNC1200 & 6802...
I was talking to GUS & he recommended leaving the capsule, TX's & just do a few changes (1 at a time=to hear & learn)
I don't think the 1200 sucks as is & don't need to make it into a race-car but was going to try:
Lowering tube to - T, Y or U
Get rid of the 10uf electro for a 1 or 2uf
change input cap to Styrene 1n
Check & drop heater voltage (remove zener-I think, in PS)

Any other simple recommendations welcome.

The ACM6802 on the other hand sounds OK but is a little thin & bright... not sure what direction to take there yet but I've been reading a lot.

[clintrubber]

Hi,

Indeed a bit silent about the ACM-mics, no idea why. Perhaps people had expected a better starting-point
(some of the ribbons) for mods - or are simply using them as they are.

From the various ACM-mics I got, I've been using a pair of unmodded ACM-583's the most by far (by far the most ?).
As 'utility'-mics for rehearsals since they have the switchable patterns and are easily taken along, no separate power-supplies etc.
They might not be the best (...), but for the price, weight, size & possibilities they're convenient to have around.

Would be interesting to hear from people how they fit their acquired ACM-mics into their total mic-usage.

And last but not least, please keep your findings/mods/experiences posted.

I'll get back to you on the '1200-schematic.

Bye,

  Peter

[mitsos]

aCM1200 = Apex 460... search for  that, there is tons of info.

If I attached it right, the schematic is below.  I think I also changed C6 for a panasonic FC or something, but can't say if it made much difference. The mic is OK as is now, but I still need to change the zeners to lower the B+.

hope that helps!

[clintrubber]

If I attached it right, the schematic is below.

Thanks for posting already, this the one I was hoping to dig up 

[okgb]

Would be interesting to hear from people how they fit their acquired ACM-mics into their total mic-usage.

And last but not least, please keep your findings/mods/experiences posted.

By getting rid of them

I had gotten 2 of the lolly pop looking goldish head model , they were o.k.
in a standard way , 1 of the phantom powered ribbon which didn't work unless
 i bypassed the active circuitry , also got one of the tube ribbons which was too noisy
to use [ i put it aside ........maybe some day  ]

doing the standard and reasonably easy mods to the apex ,
new output xfmr , better lower gain tube , film cap on output
has made that one seem decent , sometimes still sounds a little dirty
to me , depending on the ozone , amount of coffee consumed
and time of day

[zebra50]

IIRC the '1200 uses the second triode-section for a cathode-follower.

What did you guys think of that part of the circuit in the schemo that Mitsos posted?

I was sort of surprised to see the direct (i.e. no decoupling cap) connection from the first plate to the second grid, and no grid bias resistor?

I couldn't decide if it was very clever or a bit dumb!

(Some good stuff here...)
http://www.freewebs.com/valvewizard1/dccf.htm
http://www.freewebs.com/valvewizard/accf.html

[khstudio]

aCM1200 = Apex 460... search for  that, there is tons of info.

If I attached it right, the schematic is below.  I think I also changed C6 for a panasonic FC or something, but can't say if it made much difference. The mic is OK as is now, but I still need to change the zeners to lower the B+.

hope that helps!

Thanks for posting that. 

I already had the APEX460 schematic but besides the Tube & 10uf on the 1200mic... what else is different?
Is there a marked up schematic anywhere?

BTW, about the other mics (Ribbons)
I got some ACM2 & ACM70 mics just for fun & they're both pretty cool. I'm a little lucky that I'm friends with Clarence Kane of ENAC. He lives about 25 minutes from my house & the past few weeks I've been over there doing some hanging. Clarence is so cool & chill, full of knowledge. He's been teaching me how to work on my own mics, cut & corrugate the ribbons, etc...
All my mics have new RCA ribbons installed (by me  ) & new transformers. I'm actually trying the Cinemag 1:36 = 9887 right now.
The Lundahl 1:37 works well with them too. I measured the impedance to be aprox 200-300ohms for either mic with the new ribbon & TX.
The original transformers in the ACM70 & ACM2 (fat head) have a 1:52 ratio   - & impedance comes out around 600ohms for BOTH mics (even though the ACM2's specs say it's 200ohm.. WRONG!  ) The high ration makes for higher gain but also higher noise & Impedance!!!
The RCA ribbon is 1/10,000 in = 2.52 micron
Not sure what the china ribbons are but seem to be a little thicker... it's very hard to tell & they're probably not consistent.

I'd say anywhere between 1.8 - 2.5 microns with the 1:37 step-up would be a nice improvement. Actually, just re-adjusting the original ribbons & installing the new TX made a HUGH difference. YES, it lost some gain but it's MUCH smoother & Balanced.

Hope some of this info helps someone... I've been very lucky to have other experts share with me.

All things G1176 - the new "repost" thread.

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