[ACMP investiupgradifications] All things PREAMP

Sorry for the dumb question, but are all the boards isolated from the case? I hadn't thought to check mine and I'm far too from home atm. thanks for keeping us posted.

Roddy
looking at your pic. see you swap the output TX for a carhnill.
i just did it for my 2 81 yesterday and it really improve the units in a significant way.
back to your trouble ,i see you swap the mic input tx too but keep the chineese one on the board. have you try unsolder it to isolate all his connections from the circuit?
your noise generator could be here..?...
keep us in touch for further infos
strange issue  ???
audioforge

mitsos said:

Sorry for the dumb question, but are all the boards isolated from the case?

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No, they are not, but it doesn't seem to be causing problems.

audioforge said:

i see you swap the mic input tx too but keep the chineese one on the board. have you try unsolder it to isolate all his connections from the circuit? your noise generator could be here..?...

Click to expand...

Yes, that's the first thing I did before fitting the new ones; lifted and grounded the old ones where necessary.

humm. to resume your troubles.
it only happen with the mic input within high gain and the cover top screwed?
not with the line input?
difficult to trace the signal with an oscillo and the cover on....

audioforge said:

it only happen with the mic input within high gain and the cover top screwed?

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Yes.

not with the line input? difficult to trace the signal with an oscillo and the cover on....

Click to expand...

Line input is fine, although there is much less gain. It is silent at max. gain.

Finally got around to looking into an 81 hiss issue (only when the EQ is engaged) 

The eq passes audio and works fine, but always with a sea of white noise.

Was able to quickly trace this to the Acmp's bass card, and swapping these cards between two 81's confirms that the fault also swaps units. A visual inspection side by side, things look pretty good.

As the fault is 100% on the card, I've re-capped all the lytics, swapped all the diodes, re-changed Q4 and Q5 (these were modded) changed both 184's Q2, Q3.

Q6 is part of the clip LED circuit and I don't have spare Q1, BC214 to hand.

If it's not the BC214, it has to be a resistor or non-polarized cap or the switch.

Any suggestions or pointers would be really welcome.

Ok, just for the record, the schematic states Q1 BC214, but it's actually a BC557 in place, I probed this and could hear hiss on the emitter.

BC560 is the nearest I have in my box! and it's pin compatible!

and did the trick!   no white noise backdrop. Yay! DIY rocks

sintech said:

Ok, just for the record, the schematic states Q1 BC214, but it's actually a BC557 in place, I probed this and could hear hiss on the emitter.

BC560 is the nearest I have in my box! and it's pin compatible!

and did the trick!   no white noise backdrop. Yay! DIY rocks

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Was known  ( http://www.groupdiy.com/index.php?topic=27791.msg409012#msg409012 ),
but it doesn't hurt repeating.

Cheers,

  Peter

I missed it , so good to see
it would also be good to make a master page
of fixes & mods

FWIW steve doesn't specificaly mention that one transister but globaly
[ still not a bad idea  ] all of them

okgb said:

it would also be good to make a master page
of fixes & mods

Click to expand...

I second that! Not that Im lazy or anything  ;D
but I do have 2 84s that are (sort of) usable atm but could use some love (read: improvement). where o where to start?

Move toroid to reduce hum to minimum level. Pay attention to hum harmionics and find a null.

Sound-wise, you can replace some caps and the transformers. Change the Zoebel networks too. I have figured out values for the original transformers; PM me with an email address if you want to see some values.

Good call Greg

A master page or sticky for just a hit list of official and proven fixes for the preamps would be real time saver
this thread is pretty large to sort thru right now. too much detail to remember over 40+ posts.

It'll sure work for a few weeks, but note there have been previous summaries & re-summaries in this thread.
(don't want to be negative, just realistic)
There might pop up 'side-threads' as well, just like for the GSSL
("don't want to read it all, please tell me exactly what I need to do in this new thread"), but
I'll make sure any of such attempts will be redirected  - I guess it's still better to have one big thread with all info in it
than various parallel ones.

Bye,

  Peter

Someone would need to be responsable for updating it
i could do that but
last time i complied something here is was above the 20,000
charactor limit and could be not be saved

but here one file and simply mark the date and the thread page that it is current to
would at least give people a start on prep .

nobody cleans there own posts where they are trying to be clever & heard
whether it is relevent or helpful so there is allot of digging reloading
comparing that burns one out somewhat having to watch people listen to
themselves talk [ just like me right now ]

cutting out all the me too , reasking the same questions from people who didn't look
in the first place ..............cut the clutter ,

I could host the master HOWTO on recordinghacks.com; it would fit well with the schematics and circuit-board photos ( e.g. http://recordinghacks.com/tnc-audio-preamps/ ).

I was sort of waiting for word from Steve Hogan on the final fixes. Every time I ping him he says he'll be back here within the week, but it hasn't happened yet.

Anyway, I'm happy to host the page and even keep it updated. I could write it too, but probably won't get to it for a while. Anyone else want to pitch in to put the first draft together?

Any word on the kit that Steve was working on?

I'd love to hear where he's at with this?

redddog said:

Any word on the kit that Steve was working on?

I'd love to hear where he's at with this?

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I haven't heard from him in quite a while.

;D

Seems like this is off the plate for him.

Paul G said:

redddog said:

Any word on the kit that Steve was working on?

I'd love to hear where he's at with this?

Click to expand...

I haven't heard from him in quite a while.

;D

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That's very disappointing and bizarre.  Wasn't he taking orders for his kits and power transformers?  He wrote that he had ordered the power transformers and other parts... I don't think he took any payments yet, but didn't he have a reserved list that guys were signing up for?  I know he put me on the transformer list...  Steve come back, man!

I sent my ACMP84 along with a sizable deposit to Steve Hogan last March.  The repairs/mods were promised to be completed by the end of April. 

Here it is nearly October.  He hasn't made the slightest effort to contact me with updates on the work.  He has replied to several of my emails with the same answer--"I'm really busy...I'll post updates next week...blah, blah , blah," then months of silence.  So much for the integrity of people you meet on  internet forums.  I don't think he is a crook but it seems this has gotten away from him.

I'm a little disgusted and dismayed.  I think these things must be cursed.  It is going on YEARS since I threw in with the Chance group buy and I still don't have a working unit.  Actually, I don't even have a non-working unit, as I shipped mine off to SH, plus I am out my deposit money and shipping costs.  Fortunately I have several othe good pres and I can't really miss what I never had. 

I am a fairly patient person but I have just about given up.  I suppose I will have to figure out how to resolve this.

Does anyone else have similar stories?  Or perhaps a little insight on what is going on with Mr. Hogan. Thanks for listening.