[ACM investiupgradifications] All things MICROPHONE

okgb

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Good of him to pass on the knowledge
[ and lucky for you , but i'm sure he wouldn't do it , if
you weren't a decent person ]

how old is he ?
 

mitsos

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All the posting in this thread today got me inspired to do the zener swap in the 1200 PSU... So I made myself a cap discharger, fired up and checked the voltage between the zeners... 145 . Anyway, a lot lower than the 200 it's "supposed" to be at, so I guess I'll leave this alone.  

What's the reasoning behind this though:

rodabod said:
I should add to my original post, lowering the B+ is generally a good idea (as is removing the diode which lifts the heater voltage by 0.7V).

I guess that's D11, which sits between the 7812 and ground.. So that should give 12.7V, right? It's good to drop that to 12V?
(it's actually a 7806, so 6.75V heaters with the diode...)
FWIW, my "no-load" heater voltage is at 14V... With the mic plugged in it's at 11.6V... Would it still be recommended to remove the diode?

cheers!




 

khstudio

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I still haven't checked my voltages yet but will soon.
145v seems a little low... Rodabod's comment is probably for the ones that read closer to 200v, which I've read some do.
I think the norm is between 160 & 180v?
Your heaters seem fine as is but I'm not expert.
 

mitsos

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OK, since I already have it open... I traced out the schematic and it's more like the second PSU in the APEX mod packet (did I attach the whole thing?) so I've got 6.75V heaters. I was obviously measuring pre-regulator in the last post... oops.

So I took out the FR107 diode finally and I have a bit over 6V now... Closed up the PSU, and I think I'm done with this mic until I get a different tube.  But that's a little while off still.
 

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khstudio

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mitsos said:
OK, since I already have it open... I traced out the schematic and it's more like the second PSU in the APEX mod packet (did I attach the whole thing?) so I've got 6.75V heaters. I was obviously measuring pre-regulator in the last post... oops.

So I took out the FR107 diode finally and I have a bit over 6V now... Closed up the PSU, and I think I'm done with this mic until I get a different tube.  But that's a little while off still.

Thanks man... did you jumper pin 3 of the 7812 to ground after removing D11 FR107?

:EDIT: I mean the LM7806 on the other PSU schematic?
 

khstudio

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Oh, I forgot to ask...
I was told by "Chance" that all these mics had 797 capsules in them but they don't look like the 797 ???

What's up with that?  :mad:
 

mitsos

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yes I jumpered it to ground.  Will try to do a little sound test tomorrow maybe, but I don't know if I should expect much difference.. should I?

have no idea about the capsules.. don't really know what 797 capsules look like or sound like. I think they're in studio projects mics, I have one and think it's a bit bright, so maybe it's a good thing!

Now all the 1200 needs is a paint job to cover up it's ancestry!


speaking of chance, what's he up to lately? Took a peek at the other forum and it looks like they're going to set up some kind of repair thingy.. UPS your units to them with a return voucher and they'll fix them. Not working yet, but that's what Terry Manning posted would be the procedure.  Definitely not worth it for the preamps, I think I'd rather wait for steve hogan's fixes... hopefully he'll sell some sort of DIY list.
 

clintrubber

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Thanks all for sharing, good to see this thread back to more life.

About the heater-tweak, for 7812 the added Si-diode seems about perfect, for the 7806 it might give about the same error the other side of the target (for 6.3V: 6.7 vs 6). Could try a Ge-diode  ;)

Who knows Roddy spotted the 7806 already & then it sure makes sense to remove (short) the diode.
For the 7812 I couldn't understand, but maybe it was done by ears vs text-book ?  (Nothing wrong with that, to say the least)

Bye,

  Peter
 

mitsos

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hi Kevin,

where did you get the RCA ribbon material? Was it already corrugated, right length and everything, ready to install? What did it set you back?

I'm assuming it made a huge difference?

thanks!
 

khstudio

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mitsos said:
hi Kevin,

where did you get the RCA ribbon material? Was it already corrugated, right length and everything, ready to install? What did it set you back?

I'm assuming it made a huge difference?

thanks!

Like I said, I've been spending some time with Clarence & he's been teaching me a few things & cut & corrugated some for me.
Huge difference? it's hard to say but I do feel it's better.
The original China mics can fool you that they sound "Better" because they're louder & I'm not sure about their ribbon thickness or consistency of it... not to mention the quality of the aluminum itself. the "Spacings" have a LOT to do with the sound too.

REAL RCA BK5's, etc... have VERY tight gaps!!! But the larger ribbons like the Royers, China mics, etc... you can see the gap is larger. hen Clarence 1st re-ribboned my ACM70 (Large) we tried a tighter GAP & it didn't sound as good.

Clarence is a friend of mine & hooks me up but I'm not sure if he'd be willing to cut & corrugate ribbons to send out... although he did mention doing it for one customer but it was like $75 & you know how delicate they are & may not hold up to shipping very well.

Kevin
 

mitsos

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lucky man!  Did you test the mics with the new ribbon before swapping the trafo?  did swapping the trafo improve the mic? I'm trying to decide if it's worth it to do something like this. I remember Marik saying he was winding some trafos, but I don't want to spend the cash and just be polishing a you-know-what.  As is, I don't use it much, and I would hate to put money into it and continue to not use it....

thanks for getting back!
 

clintrubber

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FWIW, some info that _might_ be relevant to the ACM-583...

http://www.monacor.de/typo3/index.php?id=58&L=5&act=&act_sub=&artid=6924&spr=EN&typ=u

http://www.monacor.de/de/FLE/ECM170.pdf


H235520A.jpg




 

clintrubber

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alexc said:
Just while on the subject of that long ago group buy, that tnc apex460 style mic ended up being quite a good mic, after reworking the circuit, tube and capsule. I think that came out at around 450usd.

I use that mic into one acmp81 feeding a diy la2a and it remains probably my best/most comprehensive mic chain.

Again, that led to a huge amount of learning as well as lots more time in focussed listening to the mic - indeed mics in general.

So, there is definately a 'happy ending' for at least some of the tnc stuff.

Sounds good !  What made the biggest difference you think ?  Reworking the circuit, tube or capsule ? Did you replace the output-transformer ?

Bye!
 

alexc

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So it was the tnc acm-1200 which is the same as the apex 460 but with a hpf sliding switch on the mic body.

First thing I did was remove that filter - it imposes in my view some pretty major restrictions on the circuit.
Once that gone, the usual remove some other un-needed caps, change a couple of other ones, two or three of them.

After that, I rebiased the  tube circuit away from the horrible state it was in due that filter.
I kept the original amp config which I like, but changed tube type to ay7.

That alone fixed a lot of the trouble.

But then, of course, I replaced the capsule. I used a good quality chinese k67 type from BeezNeez. Still very affordable.

That made a huge difference and that was that, really.

I measured up the stock traffo and couldn't see any real problem, so I kept it.

---

End result was the mic, remained quite affordable but performs quite well.
However, I would be happy to do a transformer change too. Cinemag would be my choice.

Certainly the thing that bugs me now about the apex 460 style mods + ACMP81 mods chain, is now I can hear the *really* tiny hiss in the combo (I mean barely audible at typical recording levels).

The major issue is how well I can here the tinyest gnat farts in the room now!
What I thought was a very quiet computer fan is the biggest impacter on my noise floor.

So - all good. I think the Apex 460 is a really good platform to build a mid price great mic.

Cheers
 

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