[ACMP investiupgradifications] All things PREAMP

[crazydoc]

Maybe I missed it, but can anybody tell me info about current consumption per winding for ACMP81?

Here's what's on the schematic. I've never measured them, so don't know how real the numbers are.

15v (x2 - actually 30v ct) - 100ma
26v (x2)  - 200 ma each
45v - 20ma

http://img.photobucket.com/albums/v646/red_3000/how_to/ACMP81_lout-power.gif

 

[Paul G]

Anyone heard for Steve lately?  I sent him an email several days ago and have not heard back.  Assuming he's just busy.  Thanks.

;D

 

[floxe]

i know steve and others have given lots of input in the last few months, before i start to have a look at the last 10 thread-pages: has anyone already posted kind of a summary for the easy-to-do fixes (bc441/461 change,...) for the acmp-81?

are there any known issues with the acmp-84?

best regards,
flo

 

[clintrubber]

i know steve and others have given lots of input in the last few months, before i start to have a look at the last 10 thread-pages: has anyone already posted kind of a summary for the easy-to-do fixes (bc441/461 change,...) for the acmp-81?

Hi,

Imho:
Be a man, just read them  Lot's of good info, it'll be hard to avoid learning various interesting stuff about these preamps.
Following a recipe you're asking for would not do that, you'll just be replacing which is not what DIY could be.

Bye,

  Peter

 

[floxe]

Following a recipe you're asking for would not do that, you'll just be replacing which is not what DIY could be.

hehe - when i bought the acmp's i didn't do it for DIY-purposes, i expected to get at least useable units. anyways - i don't have much time to "repair" the units but will try to get through the information given here.

thanks,
flo

 

[clintrubber]

Hi,

I understand. Despite everybody ordering these should have known that there would be at least some work to do (let's be honest, no free lunches); the amount of 'repairs' is sure more than anticipated. Hey, like always, it's time or money. So if in a hurry or not interested in DIY and/or learning (free choice, note I'm not blaming you, just go away here  8) - kidding) the obvious alternatives are sending your work to Steve or anybody else who's qualified or buy the real deal or something else that comes close. Yep, that's less time, but a lot more money...

Bye & enjoy

 

[Paul G]

In the beginning I had planed on doing some mods to these.....just not so many.  Oh well, time to get my feet wet.  LOL

;D

 

[crazydoc]

i know steve and others have given lots of input in the last few months, before i start to have a look at the last 10 thread-pages: has anyone already posted kind of a summary for the easy-to-do fixes (bc441/461 change,...) for the acmp-81?

are there any known issues with the acmp-84?

best regards,
flo

Here's a very brief overview:

73 and 84:
- New (non-resonant) eq inductors, or mumetal cans/shields for the current ones
- Rework the gain switch to remove the oscillation blast between positions 6 and 7

81:
- New eq inductors as above
- Gain switch mod as above
- Replace the Q4 and Q5 transistors on boards 2, 3, 4, and 5 which are prone to oscillate, making the entire eq section unusable.

These fixes will probably get them to the level we expected when ordering them. A better/less-noisy PSU transformer would be helpful too.

 

[rodabod]

I have modded mine fairly extensively now. Took a few days. I don't think the inductor swap is maybe necessary for the '73 and '84 unless you have a particularly radiant power transformer. Mine are quiet.

 

[okgb]

Do tell roddy , how are your's now  , what'd you do ?

i have two 73's one usable out of the box [ although i don't trust it ]
and the other with a slight broadband buzz [ haven't looked at it ]

Have to say this whole thing has soured me for any enthusiasm
to get it done ,
Still waiting on the Cinemag prototypes , they of course have allot
of business so told them it wasn't a panic

 

[rodabod]

I modded mine in several stages. Firstly damping the transformers and testing. I then followed this up with a re-cap with tantalums and poly films (some with different values), some PSU mods (these weren't 100% necessary), some resistor value changes, swapped the output transistor, changed RF filtering, and finally changed audio transformers for Carnhills and re-routed the cabling a little.

The difference is noticeable, although the stock units do some pretty fine in my opinion, maybe just slightly rougher in the top-end. From what I have seen, the sound is in the circuit, as is so often the case. It's not just a combination of distortion from tantalum caps and specific transformers.

 

[mitsos]

Hey Roddy,
did you recap the whole thing?
I've used my 84s a couple of times. They are usable, but I too noticed them being a bit "rougher in the top" but haven't had time to do anything about it. Waiting for Steve to put out that list he was talking about so I can do everything at once.

Anyway, about this top end thing.. I've noticed some people (Tommypiper maybe) saying they like to replace the tants in Neve circuits with 'lytics... Is this a possible solution, or what solved this for you? 

How much of a difference would you say there was between the original trafos and carnhills?

 

[clintrubber]

Here's a very brief overview:

Since people might read just sections, let's repeat this one as well
(it might actually be the most important one for gear of this level of (un-)reliability):

- be sure to update your fuse-ratings if you're in non-110V-mains area.

So for 230V-use switch to a lower value, start from say half the original mA rating. 

Bye,

  Peter

 

[rodabod]

Hey Roddy,
did you recap the whole thing?

I only replaced what I thought was necessary. Maybe around 30 capacitors. Some are fine as they are in my opinion.

Anyway, about this top end thing.. I've noticed some people (Tommypiper maybe) saying they like to replace the tants in Neve circuits with 'lytics... Is this a possible solution, or what solved this for you?

 

Yep, that's possible. I used tantalums though. There are ok electrolytics there already, although some values are off.

How much of a difference would you say there was between the original trafos and carnhills?

Between the Chinese transformers and the Carnhills? Not massive, but they are measurably inferior, however this can be partly rectified by using suitable damping networks. The mic model and output model do have a high end resonance as stock. I could post pictures from my phone camera of 'scope readings if people were interested.

 

[crazydoc]

Steve Hogan -

There is some discussion of the ACMP81 power supply here:
http://homerecording.com/bbs/showthread.php?t=275506&page=3

Any comments?

 

[mpinphilly]

Hello all:

I've been following this thread without joining--really appreciative of all the investigations you all are doing on these preamps--but I wanted now to ask a question...

I know that judging the usefulness or even quality of gear is tough to impossible, given that the application of a given tool is what matters, anything can be the "right" tool for a give source/song.  That said, I'm a seriously unknowledgeable person when it comes to the insides of gear and so I'm trying to get a sense of how "worth it" it is to send my two 81s and two 73s into Steve Hogan for his upgrades.  Steve has been super gracious and helpful in emails I've sent to him--explaining all the things he can do to upgrade these pres--but I still don't have an overall sense of whether or not to invest more dough in these or sell them off and put the entire cost of the the four towards one higher end pre.

I suppose my question is this simple: once Steve Hogan does his upgrades and I've invested around 500 bucks or so total in each of the pres, is that still a fairly sweet price for each of these channels?  I.e., once Steve rips out the crappy parts and adds better ones, is it likely that these pres will be nice additions to a project studio?  To give context for my pre selections, I have the Sytek 4-channel thing (with burr-brown on channels 3&4), a JoeMeek channel strip, and two channels of racked PM-1000s.  I was hoping the ACMPs would be a nice change of pace for vocals and drums, but I could get just one channel of a higher-end pre to use mainly on vocals..

Anyway--hope this is an appropriate question for this particular forum.  I know this is about investigating these pres, but I figured maybe there were other folks lurking here who, like me, always assumed we'd have someone mod these pres, but aren't clear how good they'd be post-mods.

thanks a bunch!
mp

 

[okgb]

if your's are useable as is right now ,
that's the answer try it an see

if not as some have mention
the sound is in the circuit as well as quality of parts
i don't know what compares in that price
maybe you want to pick two to start with

 

[chris carter]

Mpinphilly,

You aren't alone.  Like you, I've been following this thread for over a year    I got two 81s and am coming to the conclusion that there will not be a TNC solution. 

As far as I know, nobody knows what these will sound like when they are fully modded by Steve.  I don't think Steve even knows yet because I don't think he's done the full mod to any yet.  The CL 7602 mkii is the closest comparison as it has much in common with the TNC preamps.  One would set you back a little over $700 new with a legitimate warranty.  For me, I really want the four bands, so I think I'd rather sink the money into these 81s I have.  It has been discussed, however, to offer more than one mod price point.

Speaking of which, Steve hasn't been around here lately....since the 10th I believe.... I'm hoping he's been in the lab finalizing the mods...

 

[rodabod]

I've been following this thread without joining--really appreciative of all the investigations you all are doing on these preamps--but I wanted now to ask a question...

Have you tried rotating the transformersinside the '73 preamps? They should be fairly usable as-is.

 

[Paul G]

Mpinphilly,

You aren't alone.  Like you, I've been following this thread for over a year    I got two 81s and am coming to the conclusion that there will not be a TNC solution. 

As far as I know, nobody knows what these will sound like when they are fully modded by Steve.  I don't think Steve even knows yet because I don't think he's done the full mod to any yet.  The CL 7602 mkii is the closest comparison as it has much in common with the TNC preamps.  One would set you back a little over $700 new with a legitimate warranty.  For me, I really want the four bands, so I think I'd rather sink the money into these 81s I have.  It has been discussed, however, to offer more than one mod price point.

Speaking of which, Steve hasn't been around here lately....since the 10th I believe.... I'm hoping he's been in the lab finalizing the mods...

I got an email from Steve a few day ago.  He's been pretty busy but hoped to post this weekend.

Paul ;D