[ACMP investiupgradifications] All things PREAMP

[okgb]

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 !

 

[clintrubber]

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]

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.

 

[mitsos]

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

 

[violindave]

Is there anyone currently who will fix these preamps, preferably near Washington DC?

 

[JB872]

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]

From my research some options are
BC184 = BC550 or MPSA18
BC214 =BC560
BC441=2N3053A
BC461=2N2905A

 

[JB872]

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]

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]

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.

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]

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/

 

[rattleyour]

One of my ACMP 73s has intermittent drops in gain. Any ideas on what to check first?

 

[rattleyour]

One of my ACMP 73s has intermittent drops in gain. Any ideas on what to check first?

Tapping the output pot seems to correct the gain drops, thinking maybe it needs a new pot.

 

[gyraf]

..or check for cracks where it's soldered to PCB..

 

[redddog]

Hey Guys,

Sorry for the bump. I am returning to recording after a looong pause (lost a child). I could not even walk into my studio until recently.

Wondering if there was ever a pictoral or video done outlining what changes could be made to get these in the ballpark. I just read all 70 pages in Gearsluts regarding the group buy. What a roller-coaster.

I have 2 - 84s and 2-73s and I am extremely stoopid with electrical engineering but I can solder and follow directions. A lot of this is over my head but again, with proper instruction, I can get it done.

Anyway, sorry again for the ridiculous bump and any direction you might have.

Red

 

[redddog]

Sorry to keep bumping this ridiculously old thread.....

I'm looking for help, specifically, with eliminating the pop out od the gain knob on a couple of 73s and a couple of 84s.

I know it's fairly simple but I've looked all over and can't seem to find any pics on how.

Anyone still around that went through the whole ACMP mess?