[ACMP investiupgradifications] All things PREAMP

[redddog]

Just out of curiosity, how much was he going to charge to fix the 84?

 

[crazydoc]

I too sent him an 81, at the end of February, for him to use as his "guinea pig," along with a deposit (and of course I paid shipping costs.)

I've had some correspondence with him since then, and it is my impression that he lost a major client due to the economic downturn, and has had to take on better paying (and probably more meaningful business-wise in the audio community) work to keep his business viable. He seems like an honest, well-meaning guy, and I still have confidence that he will come through with our fixes (if they are possible) or return our units and our money, but it seems that he too has fallen under the karmic black cloud that hovers over these group buy preamps.

I still really appreciate the meaningful information he has posted here (in what now seems the remote past), as it has been helpful in my own troubleshooting and fixes of these units.

 

[Paul G]

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.

I bought a 73 in the GB and watched the forums for mods.  When Steve Hogan came along, it sounded like a great solution!  I contacted him to get on the list and then sent him a deposit to get in on the first run of transformers.

A few months after that I put together a deal to buy two units for my two brothers.  They had them shipped directly to Steve and they also sent him deposits.  He quoted them $300 to $375, (estimate), to mod one of the 73's.  I've gotten replies to my emails, (same as doc), but that's about it.  One of my brothers was going to send out another email but I haven't heard anything yet.

Paul

 

[rodabod]

Steve's probably very busy. I get very, very busy sometimes and forget to get back to people (especially by email). It's easy. Steve, if you are reading, just tell people that you are busy with stuff; it makes things easier in the long-run.

If you have a '73 or an '84 then iI'd suggest modding yourself. The details are here. Otherwise, collate the fixes here, and get a tech. The same can be said for an '81, but it is slightly more tricky.

 

[redddog]

It's looking more and more like I will just do the fixes myself.

I'm just waiting for someone to put together a comprehensive and detailed "how to" list. I'm not real experienced with this stuff but can generally get it done with the right guidance.

I was really looking forward to Steve's Kit. He is easily one of the most thorough and complete techs I've read. I'm really disappointed that it didn't work out. It really does seem like these things are cursed.

At any rate, I'd love to see a comprehensive list of fixes for these mothers at some point. Luckily for me, I only have 84s and 73s.

 

[recordinghacks]

I just spent an entertaining 20 minutes on the phone with Steve Hogan.

He hasn't disappeared to Brazil with our preamps, and doesn't appear to have been cursed by them although he admitted (with a laugh) that sounds like an interesting theory.

He apologized for having dropped out of this community temporarily; he has been overbooked with some other projects that promised faster returns on investment. (I'm sure all other self-employed folks can sympathize.)

Anyway, at the risk of misquoting something, I'll try to give a brief status update from Steve. If anything I write below seems incorrect, confusing, upsetting, or in any way raises your blood pressure, please contact Steve directly for clarification.

The R&D on the ACMP pre's is nearly done. The remaining areas of investigation are the gain staging and the inductors.

The gain staging is tricky, in part because of the loud click between stages, but generally because the design deviates from the original and isn't very well-done.

The inductors seem to be vulnerable to EMI, and probably require shielding and/or grounding for best performance.

I think Steve will have some good news about the audio transformers, but I'll let him cover that.

Steve's plan is to upgrade the units he has on hand first, this month. He plans to ship them in October.

While modifying them, he'll document the upgrade process for the book that will be enclosed with the DIY kit.

I have to say that hearing Steve talk about these mods made me very eager to hear the new-and-improved preamps. The turnaround time on the mod process has been disappointing, but I think the ultimate result will be great.

 

[redddog]

awesome news, Matt!

I just can't wait to hear these mothers after the mods.

 

[Paul G]

Thanks for posting this, Matt.  Looks like my brothers will get their units before I get my kit.  sigh.......LOL

;D

 

[clintrubber]

It's looking more and more like I will just do the fixes myself.

I'm just waiting for someone to put together a comprehensive and detailed "how to" list. I'm not real experienced with this stuff but can generally get it done with the right guidance.
...
At any rate, I'd love to see a comprehensive list of fixes for these mothers at some point. Luckily for me, I only have 84s and 73s.

Partly in jest, partly serious: please don't increase the length of this thread by such remarks; the less of those, the easier it is to browse this thread.
Yes, it's long, but the info is all there folks, and we've had a few previous requests already for a summary.

In addition to that, the essence has already been summarized recently. Please don't come here for instant gratification, this is DIY after all.
In other words: technical questions are appreciated over here, and you'll find you get lots of help. But please don't ask for cutting corners to save time, your 24hours/day are as valuable as they are for anyone. Please note I'm not targeting you specifically. Enjoy the modding, it shouldn't be too hard.

All the best,

 Peter

 

[diyfanatic]

Hi guys,

just bought a ACMP81 and want to mod it

so after gone thru this giant thread...
here's the plan:

- shielded inductors and power tx
- Gain switch mod (resistor) for avoiding the "pop"
- Replace the Q4 and Q5 transistors on all boards
according to Steve Hogan posts, I will be using BC327-16 transistors to replace xQ4 (ACMP=BC557)
and BC337-16 for xQ5 (ACMP=BC547) as they are direct drop in (same pin out).


Now, the questions.

- worth changing 2N3055? if yes wich brand? MULTICOMP or MAGNATEC (more expensive)
- for those who have changed the output tx for carnhill, the sound change in a significant way? worth the investment?

for the transistor:

I found 2 type, bc32716 and bc327-16. are they the same? first one is available in Europe, second one only in US (but shipping 18€ )

TRANSISTOR PNP TO-92
http://fr.farnell.com/fairchild-semiconductor/bc32716/transistor-pnp-boitier-to-92/dp/1017667
Bipolar Transistor
http://fr.farnell.com/fairchild-semiconductor/bc327-16/transistor/dp/1368081

same for the bc337

TRANSISTOR NPN TO-92
http://fr.farnell.com/fairchild-semiconductor/bc33716/transistor-npn-to-92/dp/1017669
Bipolar Transistor
http://fr.farnell.com/fairchild-semiconductor/bc337-16/bipolar-transistor/dp/1368082

thanks for your help
cheers.
Jr.

 

[okgb]

With little editing , i have complied [ halfway so far ]
relevent ideas [ & speculations ] of this thread
[ simply cut & pasting leaving out me too type posts ]

recordinghacks will host it , let you know when it's done

 

[diyfanatic]

yep, after gone thru the thread again (great move Okgb, could be painless)
seems that the Carnhill tx does improve the sound, the output tx is not so good as the input...17 pound @ audiomaintenance, it could not hurt.

I'm still in the doubt for the transistors.
it look to me that the original N$ve are 2A and bc327-16/bc327-16 are 0.8A...
there also 2N5320 and 2N5322 but expensive, to-39 and I need to adapt BCE,same for BC441/461.

any idea on a straight sub to-92 package?anyone?
Jr.

 

[stereokillah]

don't remenber exactly but i had other than bc461/441 one menber give the good value on tis thread and it' is to-92

 

[diyfanatic]

Hi Mr stereo!

I recall that in the thread you said you've ordered bc327-16 and bc337-16 and that's what Steve Hogan said it should be perfect replacement.
but they are hard to find in europe!
I compared the datasheet of bc327-16 and bc32716, I can't see any big difference so I think I will go for them.

no trouble or overheating in you unit?

 

[diyfanatic]

Further investigation of the original Neve 338 plug-in amplifier as detailed in the AMS Neve '81 owners manual available as a download shows the reason for Neve using BC461-6 and BC441-6 TO-39 packaged transistors with heatsinks.
Pin 4 of the Neve BA338 Plug-In amplifier is labeled "boost (39 Ohm for 300 Ohm O/P)."  Strapping a 39 Ohm resistor betwen this pin and Ground increases the current sink Q5 collector current from 8.25 mA in the "non-boosted" position to 40 mA in the "boost" configuration.  This will increase Q4 dissipation from about 100mW to 480 mW which will be quite toasty without a heatsink and a big part.  The -6 suffix was the highest gain selection available on the BC441/BC461 transistors.  The TNC '81 clone does not use the "boost" position, so a hefty TO-92 transistor should work just fine.

ok I will go with bc32716 and bc33716,

 

[clintrubber]

I compared the datasheet of bc327-16 and bc32716, I can't see any big difference so I think I will go for them.

The same devices; as you will have suspected BC327 is the actual type-number. The '-16' addition (also '-10', '-40' are around IIRC)
indicates the hFE-range.

Regards,

 Peter

 

[diyfanatic]

great, thanks peter!!

 

[diyfanatic]

I just received my acmp81...and...hummm...yeah, gone with the wind!!  :
but not so much buzzzz.

I've got some shield from hotbaby, will try this asap...also transistor swap.

last question about output tx.
I guess wiring the same?

cheers.
Jr.

 

[redddog]

keep us posted.

(is it ok to say that, Peter?)

 

[clintrubber]

You're so funny...  8)