[ACMP investiupgradifications] All things PREAMP

[crazydoc]

Where did 1N5313 (substituted for R5) come from?


edit: " R5 resistor replaced with 1N5313 current blocking diode to further reduce ripple "

Oops, I didn't see that above. Is its regulator current still appropriate for the Darlington configurations, or would it need to be changed to a diode with a lower current rating?

 

[okgb]

from my smarter friend who causally looked at the diagram
he said to simply get a transistor with a higher beta and
that c20 could be doubled as the transistor multiples
that capacitence.

HEY PRR , can you offer any help ?

 

[PRR]

> HEY PRR , can you offer any help ?

No.

What help are you asking?

The original group-buy thread is gone. I don't know what this is.

The pictures on this thread's first page and the schematic on the second page show a lot of stuff in a very small box.

I get the impression that people bought into this project without knowing what it really was (pleas for schematics, speculation that it was a back-door version of an asian product seen at a show...).

The last page (and private messages) has something about a 48V power supply transistor. If this is JUST for the Phantom, one channel, and it isn't working(??), a Darlington or FET CCS isn't an answer.

I'm NOT going to research two and a half years of history and 53 pages of mostly useless posts, not for _my_ amusement. My time is worth something: today I saved $32 with an hour of de-rust labor.

Is the case OK? Then suck it up and DIY the guts. If that schematic is at least 90% correct (it sure isn't 100% correct), then this is all VERY ordinary stuff. If the group-buy got the wrong parts, get the right parts. If the case was CAD-ed before a prototype was built, sure it will hum/buzz.... and with that stuffed-box your only full-cure option is to put the power supply in another box several rack-spaces away.

Simplify. Plagiarize. Divide and conquer. K.I.S.S.

If you can't do it (or have other things to do with your skills and time), sell the project to some other hopeful and go shopping.

 

[tommypiper]

;D  Good advice, PRR.  Simplify.  Use known info.  Move on.  Life is short.  

I haven't touched mine yet, or powered it up!  I've been planning from the beginning to use an external PS, replace the bad transistors, and that's about it.  I may not even bother with the gain switch popping noise...  Unlikely I'll touch the inductors...  That's the beauty of DIY.  We all get to explore and try things out and do what works for us.

Thanks to everyone who has posted fixes and their experiences thus far.

 

[okgb]

Yep the question PRR
was just about the 48v circuit
does it need another transister ?
is bigger capacitence enough ?
Is it even a problem ?

NOT asking you to pass judgment or cash my cheques
but not being as smart as you don't want to lead others astray
[ trying to help them ]
Tia

 

[rodabod]

...the 48v circuit

Is it even a problem ?

Works fine for me.

Note, if you have particularly bad transformer hum, you can reduce this a little by disconnecting the rail that powers the meter and LEDs, etc.

Guys, just open up these units, print out a schematic, and fix these bloody things.

 

[wmtunate]

The 3M ultraperm I ordered last week arrived yesterday, so I cracked my pair of '81s open and started experimenting with shielding.  As others have mentioned, the noise at the inductors is influenced heavily by the lid being on or off, so some of my shielding completely eliminated the buzzing until I put the lid back on.  In the end, both units got at least two layers of ultraperm completely covering the top of each inductor.  I tried putting a layer on the chassis below those two PCBs, but that had no effect.  I also experimented with a makeshift toroid shield using the bottom of an old soup-can wrapped in ultraperm.  It helped greatly in one of my 81s, and made things worse in the other.  The biggest help in reducing the noise, however, was simply rotating the toroid.  The one without the soup-can required extending the primary leads enough to turn it almost 180 degrees from it's stock position.  In that new position, it buzzed like crazy with the lid off, but was silent with the lid on.

I know none of this info is new, but I just wanted to show that it can be fairly simple and cheap to get the buzz out of those inductors.  I used almost two sheets of ultraperm, but knowing what I know now, I could have used one and only spent $10.

 

[okgb]

Sure , i think some of Steve's " tangents " are
not deal breakers , double c20 cheap & easy , no harm
there may be ripple but you may not hear or notice it

thanks to those who have actually helped already
[ the other two can rot in it if they believe in it ]

I have compilied the thread note & steve notes
if anyone wants them [ email me ]

where was your source for the ultraperm ?

btw i believe the mark of a good peice of gear is that it can't ruin
a recording [ by itself ] Don't know that i'll ever trust these things .

Makes one appreciate [  all of you ] the redesigners
and others offering solid kits here , thank you .

 

[wmtunate]

where was your source for the ultraperm ?

http://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A

 

[Paul G]

FYI, I heard from Steve.  He's ordering more transformers and hopes to be finished with the R&D by months end.

Paul ;D

 

[redddog]

I just heard from Santa. He said they're right on track for the holidays.

 

[dustbro]

He said they're right on track for the holidays.

Right on track for another delay....  :-\

 

[Tasa]

Rudolph is slacking 

 

[Paul G]

You guys keep it up! 

But you just wait!  One of these days......say...after several more years....I'll have a totally non-functional ACMP-73 and you'll have what?



OK, so you'll have the last laugh but other than that.... what will you have.......?  sigh......  :'(

 

[mitsos]

most of the answers (at least for all the 84s and possibly the 73's) are in the thread.

If enough people are interested, I would be willing to look into a group buy for new (much better and shielded) toroids and possibly some mu-metal cans if people want to shield their inductors. We'd probably have to get at least 50-100 to get a decent price, so that's quite a few toroids.  I will look into it and post back. I will post a feeler thread in the BM to gauge interest once I have some info.

For now, though, I need some specs... My 84s have 1x24V winding, 1x 48, and 2x 12V (or is it 12-0-12..I have to open it up again to double check).

I'd say about 300-400mA on the 24V rail is good, on the 48V I'd guess 50mA would be sufficient as there is nothing else running on it.  But I'm unsure of the 12V rails consumption.  

IIRC the 81s had an extra 24V rail? Don't know what for, but if people have specs on this I can check that one too.

 

[crazydoc]

Schematics are here.

http://recordinghacks.com/tnc-audio-preamps/

Current ratings are posted on the transformer legs.

 

[mitsos]

cool, thanks. 

 

[jdbakker]

Another option is to get a good off-the-shelf 24-0-24 (or 22-0-22) transformer and use one of the many PSU designs floating around here to replace the entire power board. A possible starting point is this thread.

Plan B: same transformer, keep the original PSU board, make sure the +/-12V regs are properly heatsinked (and/or add C-R-C filtering) and add a voltage doubler/tripler a la Keith to get the +48V.

JD 'add SiC to taste' B.

 

[redddog]

FYI, I heard from Steve.  He's ordering more transformers and hopes to be finished with the R&D by months end.

Paul ;D

Aaaaaand it's month's end.

Anyone heard?

 

[Paul G]

FYI, I heard from Steve.  He's ordering more transformers and hopes to be finished with the R&D by months end.

Paul ;D

Aaaaaand it's month's end.

Anyone heard?

Ahhhhhhh....  No.