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okgb

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1140 on: April 05, 2013, 08:25:55 AM »
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Take the tops of and they fit into 1RU but that's gotta be one of the worst production mistakes.
Ciao,
jb

Or double rip off con jobs ,  Chinese to chance and chance to us , I see they were concerned on making good
I'll NEVER look at anything from Gina with trust again .

Thanks for the first page summery and Nice pic Alex , clean rack and work  , like the wood spacers !
« Last Edit: April 05, 2013, 08:29:40 AM by okgb »
GKB Audio / Greg Boboski


clintrubber

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1141 on: April 05, 2013, 09:25:48 AM »
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 !  I've taken the liberty to copy your post to the ACM-mic 'parallel thread':

http://www.groupdiy.com/index.php?topic=27793.msg661662#msg661662

Bye!


alexc

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1142 on: April 05, 2013, 10:52:04 PM »
clean rack and work  , like the wood spacers !

Thx Greg - they are the unused slats from some common cedar venetian blinds  :)

Funny enough, the fit quite well and are easy to cut.

I just 'glue 'em on'

Am very well pleased with that solution. They do look nice.
I ping therefore I am

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1143 on: April 07, 2013, 01:44:07 AM »
I like my 460 mic too.. the only thing I kept from my lot of stuff.  Now my friend has it and wants to buy it, but I don't think I want to sell it. It turned out kinda nice after circuit mods.  Still using the stock capsule.

 
I'll NEVER look at anything from Gina with trust again .
I once knew a girl named Gina.... don't know if I'd trust anything from her either!  ;D

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1144 on: May 01, 2013, 01:06:58 AM »
Is there anyone currently who will fix these preamps, preferably near Washington DC?

JB872

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1145 on: January 09, 2017, 10:33:00 AM »
Long time lurker here.  Thanks to all who contributed to finding a fix for these units.

I've had an ACMP 81 sitting in a box for a couple years plagued with all the issues mentioned and now I'm finding myself wanting to use an EQ for tracking. 

Spent a couple days reading through this thread and have decided to go ahead with the Q4 & Q5  transistor replacement on the EQ cards (possibly Q1 as well), and the power transformer rotation.

I was able to find a source for the BC461 but no luck finding BC441.  My question is can I pair up the BC461 with one of the BC441 substititues mentioned here (2N3053A or 2N5320) or is it important that PNP/NPN combo have identical specs?  Would it be better to use the 2N5320/2N5322 combo instead for example?

Also , did anyone else find that replacing Q1 BC557 transistor with the BC560 reduced the level of hiss from the low EQ card?  I only read one mention of this and was wondering if anyone else tried this?

Thanks!

Rocinante

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1146 on: January 09, 2017, 11:35:31 AM »
From my research some options are
BC184 = BC550 or MPSA18
BC214 =BC560
BC441=2N3053A
BC461=2N2905A
If there's a harder way to do this, I haven't found it yet.

JB872

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1147 on: January 10, 2017, 07:49:50 AM »
From my research some options are
BC184 = BC550 or MPSA18
BC214 =BC560
BC441=2N3053A
BC461=2N2905A

Thanks Rocinante!  I'll look into these.

So what was the outcome of the pres that were sent to Steve Hogan?  Did they come back with significant improvements or was the hum and noise still there?



 

JB872

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1148 on: January 15, 2017, 05:08:26 PM »
So I've replaced Q4 & Q5 with 2N2905A & 2N3053 but I still have hum mainly around 80-90 Hz when the EQ is engaged.  I've attached an audio clip below.  There's some pops so please turn down your monitors

I wasn't able to find the 2N3053A which has a higher voltage rating than the 2N3053.    Is it possible that this is the problem?

clintrubber

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1149 on: January 16, 2017, 11:20:55 AM »
Nice to see this thread active again.

So I've replaced Q4 & Q5 with 2N2905A & 2N3053 but I still have hum mainly around 80-90 Hz when the EQ is engaged.  I've attached an audio clip below.  There's some pops so please turn down your monitors
Didn't see the attachment.

Quote
I wasn't able to find the 2N3053A which has a higher voltage rating than the 2N3053.    Is it possible that this is the problem?
I saw 40V & up for the '3053, that should be fine for this circuit (IIRC it does +24V, correct ?)


JB872

Re: [ACMP investiupgradifications] All things PREAMP
« Reply #1150 on: January 16, 2017, 03:34:26 PM »
Nice to see this thread active again.
Didn't see the attachment.
I saw 40V & up for the '3053, that should be fine for this circuit (IIRC it does +24V, correct ?)

Sorry, I'm new here....doesn't look like I'm able to upload mp3s or wav files so here's a Soundcloud link.  This was recorded with the gain and output almost at Max and Eq button In.   And yes, the EQ boards are +24V. 

https://soundcloud.com/user-281301181/q4-q5-replacement/s-ASAe6

I seem to be able to find a sweet spot when adjusting the EQ gain knobs and the EQ in the OFF position (specifically the lower mid eq) that reduces the hum significantly.  It's quite similar to what antichef described and recorded in this thread before replacing the Q4 and Q5 transistors.

http://homerecording.com/bbs/special-forums/diy-mods-and-homebrew/acmp-81-hum-sounds-275506/