acmp 1081 - fully functional or not?

[cannabis]

i know, i know - wrong forum

but most of the interest

in these from the gb

is located here

just to get an idea

of the prevalence

of these problems:

has anybody here

received a fully functional 1081?

(that is, no hum or buzz

or other extraneous noise

with the output gain at max

and the eq switches fully engaged)

or are we just

a few whiners here?



i'll ignore the mic gain switch

"pop"

for now and call it a non-issue

 

[cannabis]

i guess i didn't allow

for the possibility

of multiple units

some working and some not



if you have even one

that works perfectly

answer yes



i have several

and none of them is without hum/buzz

 

[bigtom]

I don't know what a acmp 1081 is, but my acmp 81 has some issues if that helps.

 

[cannabis]

I don't know what a acmp 1081 is, but my acmp 81 has some issues if that helps.

if you don't know what it is

consider yourself lucky

and you don't have to vote

 

[Weasel9992]

I don't know that that's even at issue...I think it's pretty well established that they have issues. So do my 73's, but only if I'm using the EQ at 350Hz, which I almost *never* would. Aside from that, sure it's not the quietest pre ever, but it's great on drums.

Frank

 

[cannabis]

I don't know that that's even at issue...I think it's pretty well established that they have issues. So do my 73's, but only if I'm using the EQ at 350Hz, which I almost *never* would. Aside from that, sure it's not the quietest pre ever, but it's great on drums.

Frank

the issue is

do any of them work right?

if so, it would be nice

to find out why

so the rest of us

could fix ours



here's a quote

from another board

I really would like to add a Elma 4130 gain switch and wire it to the board to maintain all the proper gain selections ( resistors on switch, bypass resistors on the board) . Toss the cheap gain switch. This option comes second to the noise in this box. currently I have a 100% failure rate on all my boxes. The noise issue is the primary problem. Good to see that moving the transformer confirmed my findings in most of the noise.

Sure wish we were forewarned about these problems before the purchase. The boxes are unworthy for studio recording. Disclosure disclosure disclosure = integrity, right mates.

 

[drBill]

I don't see how it's possible to have a fully functional perfect unit when it's a known issue that there are 8 transistors on the boards that were spec'd wrong on the schematic and they need to be changed out before the unit will work correctly.

I think a better poll would be, does anyone have a unit with transistors swapped which is functioning as it should - ie: no noise.

I'm not even going to vote.

 

[Weasel9992]

Bill put it well. I'm quite sure that the exception would be the 81/83/73's that work well, not the other way around.

The only other thing I'll point out is that all this vitriol after the fact seems unwarranted to me. When we bought into the group buy it was with full knowledge that we really had no idea what we were getting. For my part, I think my 73's are perfectly usable. To each his own I suppose.

Frank

 

[cannabis]

Bill put it well. I'm quite sure that the exception would be the 81/83/73's that work well, not the other way around.

The only other thing I'll point out is that all this vitriol after the fact seems unwarranted to me. When we bought into the group buy it was with full knowledge that we really had no idea what we were getting. For my part, I think my 73's are perfectly usable. To each his own I suppose.

Frank

vitriol?

i think not -

i'm just trying

to find what makes

a usable unit

I don't see how it's possible to have a fully functional perfect unit when it's a known issue that there are 8 transistors on the boards that were spec'd wrong on the schematic and they need to be changed out before the unit will work correctly.

I think a better poll would be, does anyone have a unit with transistors swapped which is functioning as it should - ie: no noise.

I'm not even going to vote.

ok

i have one

with changed transistors



noise is better

but still there



i think it's the

power transformer too



but if there are

units that function perfectly

after the transistor swap

lets hear about it

 

[redddog]

It's absolutely clear that this is a universal failure in design. Expecting a functional unit is unlikely. It would amount to the Chinese accidentally manufacturing a functioning circuit. In other words, accidentally winning the lottery.

 

[cannabis]

It's absolutely clear that this is a universal failure in design. Expecting a functional unit is unlikely. It would amount to the Chinese accidentally manufacturing a functioning circuit. In other words, accidentally winning the lottery.

i've read posts

here and elsewhere

about how "awesome"

these pres are



so i guess i infer from this

that they are using

only the preamp stage

without any eq engaged



i guess that's fine

if that's all you expect



but i want the eq's

so i guess if i fix mine

(and i will)

there's no need to

post the fix here

 

[antichef]

but if there are

units that function perfectly

after the transistor swap

lets hear about it

I consider my 81s fully functional after the transistor swap and toroidal transformer re-alignment (i.e. turning it around some)

"Perfectly" is a little tough -- do they sound just like a real 1081? I doubt it (I wouldn't know), but they're eminently usable and add a lot to my little setup.

edit: *much* easier and cheaper than if I had tried the same thing with a kit, for instance, and *way* cheaper than if I had bought something comparable that was retail.

 

[redddog]

so i guess i infer from this

that they are using

only the preamp stage

without any eq engaged


but i want the eq's

so i guess if i fix mine

(and i will)

there's no need to

post the fix here

If you were looking to be an a-hole, there would be no need.

Of course we are all looking for these to be fuctional. The guys who say they work great are using them on ultra loud sources (drums, cabs etc). Almost all of the "awesome" comments disclaim that they are only usable on LOUD sources.

How you come to understand that no one would like to know a fix that brings these into the "entirely usable" camp, I can't quite put together.

 

[cannabis]

yeah, i know that

i'm an asshole


i'm just looking for a fix

and it seemed to me

in reading different boards

that many people are just accepting

of the situation

or think that tnc

is going to fix these



i seriously doubt

that that is going to happen

in light of the huge logistics

and financial considerations

that would entail



i was hoping some of these

arrived in working order

and we could find out

how they are different from the rest



i'm glad antichef feels

his are useable now

but i'd bet there is still

significant noise

with the eq engaged

on the inductor boards

 

[drBill]

yeah, i know that

i'm an asshole


i'm just looking for a fix

and it seemed to me

in reading different boards

that many people are just accepting

of the situation

or think that tnc

is going to fix these



i seriously doubt

that that is going to happen

in light of the huge logistics

and financial considerations

that would entail



i was hoping some of these

arrived in working order

and we could find out

how they are different from the rest



i'm glad antichef feels

his are useable now

but i'd bet there is still

significant noise

with the eq engaged

on the inductor boards

I commissioned 2 brand new never turned on ACMP84's yesterday at a friends studio that he is building. They were stone quiet. Hum wise. There is of course a noise floor at higher gain stages. Zero hum even at 360 fully boosted, attenuation wide open, gain full open. No hum.

His 73's were not so lucky, but manageable for his uses - (drummer). There was one QC problem on one of the 73's that will eventually need to be addressed but it will not preclude him from using it.

bp

 

[cannabis]

I commissioned 2 brand new never turned on ACMP84's yesterday at a friends studio that he is building. They were stone quiet. Hum wise. There is of course a noise floor at higher gain stages. Zero hum even at 360 fully boosted, attenuation wide open, gain full open. No hum.

that's great!

is there anyone near you

that can compare the electronics

of these to the ones with hum

to see if differences exist?



were these late arrivals

that may have been among those

that had the delayed shipping

due to quality problems?

 

[acegunn]

For reference, out of four units I have (2 x 81's and 2 x 84's), there is only one 84 that I would consider "perfect".

It has hum with EQ engaged, 360 Hz boosted, but it is barely audible compared to the noise floor, so I consider that "good enough".

The other preamps have varying degrees of hum with the worst being an 81 with hum at 180 Hz being 40 dB higher than the noise floor.

At some point if I get to it I plan to open them up to see if there are any differences in components.

 

[dgatwood]

that's great!

is there anyone near you

that can compare the electronics

of these to the ones with hum

to see if differences exist?

The difference is that the working ones are 84s. They probably don't have a major board located relative to the front right corner at the same offset as that of the transformer from the back right.... That said, I'm starting to wonder if these transformers aren't miswound or something.

 

[cannabis]

The difference is that the working ones are 84s. They probably don't have a major board located relative to the front right corner at the same offset as that of the transformer from the back right.... That said, I'm starting to wonder if these transformers aren't miswound or something.

it would be helpful

if someone could shoot a pic

of the inside of an 84

to see where things are located

and to see if it uses

the same type eq inductor

and the same toroid ps transformer

as the 81's

 

[redddog]

Should we be looking at replacing these crap transformers with good ones at this point?

That can't be THAT big a job.