clintrubber
Well-known member
*** PLEASE HAVE A LOOK AT THE INFO IN BLUE BELOW ***
Let's have a placeholder here already for the bewildering amount of threads that might arise from the TNC-groupbuy
( http://www.groupdiy.com/index.php?topic=27172 ) once the stuff has arrived.
Many months to go, but before we forget...
So let's try to combine the ACMP-preamp-related stuff here;
I guess we don't need another case of a thousand different threads about one and the same compreSSLor.... :wink:
In case a new 'wild' thread pops up we might remember this one and redirect the discussion to here.
Idea ?
And I propose likewise for the ACM-mics:
http://www.groupdiy.com/index.php?topic=27793.0
*** SUMMARY IN PROGRESS ***
This section in blue is meant to grow into a quick & dirty but convenient alternative to having to read
through all pages of this thread, nothing more.
While it'll never become as complete and make you as smart as when reading & digesting
the full thread, it'll have at least the function of getting your preamps in decent shape.
Enjoy !
Thanks go out to OKGB who collected the first batch of info.
Please all contribute/correct/comment ! Add your info at the end of this thread
& I'll try to keep the info in this first message up to date
(so check the last page of this thread as well to see new additions).
Please add your contributions in a ready-to-paste format. Thanks !
Note that not all preamp-types suffer from these and some to varying degrees,
some fixes are relative. Preamps are designated by 73/81/84, indicated where relevant.
Again, for more info you WILL have to dig through the thread,
NOT add to it with questions that have been answered already IN the thread.
Let's have a disclaimer:
All mods at your own risk, please work safely & take care when testing & modding your
preamp while live power needs to be present, etc etc...
Here we go:
Most obvious & serious problems of the chineve preamp/eqs concern the EQ-disturbances &
the loud pop on the gain-switch.
Some of these may be accumulative for some people with no one fix taking care
of everything, although the EQ transistor & shielding go a long way, maybe enough.
Do also realize that when in doubt/curious...., you can have a look at the original N-schematics.
Note that the 81 happens to be a 'lucky Frankenstein' in that it uses the class-A stage of the 73/84,
so the original N-schematics don't completely describe the 81-clone.
<< EQ-NOISE >>
#001
On the 81 units incorrect transistor pairs are on each EQ pcb,
marked as Q4 & Q5 (the output transistors of each of the four EQ-amps).
This will solve the most obvious noise problems
(possibly revealing the other problems after that)
Suitable replacements are BC xxx
I used 2N2907 & 2N2222 respectively, others transistors are possible.
Be sure to check pinout is correct for transistors you are using (some types need legs to be bent).
In case of metal-can types take care you don't make shorts with other metal stuff nearby.
#002
Lossen and twist the torriod power transformer (while listening to the audio out of unit),
until you find the point of least radiation from xfmr onto EQ pcbs. Some have flipped the xfmr
upside down , once this is as good as possible move onto next fixes ,
(may or may not help, varying reports). Again, work safely, don't get zapped.
#003
Shielding of power transformer with some kind of Mu metal, as well as shielding of inductors
on EQ boards, no common method up to you really.
#004
Replacing inductors, see Alex's posts & investigation [ insert link ] suitable replacements from
Cinemag & Carnhill. All other fixes should be performed first to possibly save you money.
#005
81: Hiss on EQ: replace BC557 transistors X [insert designation] on all four EQ-amp pcbs with lower noise type
(BC2*** or BC560C)
<< PREAMP-CLICKS >>
#101
Popping on gain control between line & mic settings, a couple fixes but quickest & easiest
is to lose one position by lifting resister X [insert designation], see full thread for other methods.
<< SAFETY >>
#201
Check the fuse-rating and adjust when needed (according to your local mains-voltage).
<< SIGNAL-TRANSFORMERS >>
#901
As reported (thanks Roddy), replacing the signal transformers by more expensive types won't improve as much as one
would hope/expect. Unless the stock ones in your unit happen to be faulty/ringing, they're decent.
[ first bunch of info from Greg, edited & added stuff, last update: 2010-06-04 ]
For now, let's compile questions & things we're wondering:
What is it:
* sound ?
* can we have a look at the three final schematics upon which these units were actually built ?
(especially for the hybrid-81: does it indeed have the cl-A output ?)
Mod-candidates ?
* quality of iron ?
* quality of caps ?
* quality of switches ?
etc...
Cheers,
Peter
Let's have a placeholder here already for the bewildering amount of threads that might arise from the TNC-groupbuy
( http://www.groupdiy.com/index.php?topic=27172 ) once the stuff has arrived.
Many months to go, but before we forget...
So let's try to combine the ACMP-preamp-related stuff here;
I guess we don't need another case of a thousand different threads about one and the same compreSSLor.... :wink:
In case a new 'wild' thread pops up we might remember this one and redirect the discussion to here.
Idea ?
And I propose likewise for the ACM-mics:
http://www.groupdiy.com/index.php?topic=27793.0
*** SUMMARY IN PROGRESS ***
This section in blue is meant to grow into a quick & dirty but convenient alternative to having to read
through all pages of this thread, nothing more.
While it'll never become as complete and make you as smart as when reading & digesting
the full thread, it'll have at least the function of getting your preamps in decent shape.
Enjoy !
Thanks go out to OKGB who collected the first batch of info.
Please all contribute/correct/comment ! Add your info at the end of this thread
& I'll try to keep the info in this first message up to date
(so check the last page of this thread as well to see new additions).
Please add your contributions in a ready-to-paste format. Thanks !
Note that not all preamp-types suffer from these and some to varying degrees,
some fixes are relative. Preamps are designated by 73/81/84, indicated where relevant.
Again, for more info you WILL have to dig through the thread,
NOT add to it with questions that have been answered already IN the thread.
Let's have a disclaimer:
All mods at your own risk, please work safely & take care when testing & modding your
preamp while live power needs to be present, etc etc...
Here we go:
Most obvious & serious problems of the chineve preamp/eqs concern the EQ-disturbances &
the loud pop on the gain-switch.
Some of these may be accumulative for some people with no one fix taking care
of everything, although the EQ transistor & shielding go a long way, maybe enough.
Do also realize that when in doubt/curious...., you can have a look at the original N-schematics.
Note that the 81 happens to be a 'lucky Frankenstein' in that it uses the class-A stage of the 73/84,
so the original N-schematics don't completely describe the 81-clone.
<< EQ-NOISE >>
#001
On the 81 units incorrect transistor pairs are on each EQ pcb,
marked as Q4 & Q5 (the output transistors of each of the four EQ-amps).
This will solve the most obvious noise problems
(possibly revealing the other problems after that)
Suitable replacements are BC xxx
I used 2N2907 & 2N2222 respectively, others transistors are possible.
Be sure to check pinout is correct for transistors you are using (some types need legs to be bent).
In case of metal-can types take care you don't make shorts with other metal stuff nearby.
#002
Lossen and twist the torriod power transformer (while listening to the audio out of unit),
until you find the point of least radiation from xfmr onto EQ pcbs. Some have flipped the xfmr
upside down , once this is as good as possible move onto next fixes ,
(may or may not help, varying reports). Again, work safely, don't get zapped.
#003
Shielding of power transformer with some kind of Mu metal, as well as shielding of inductors
on EQ boards, no common method up to you really.
#004
Replacing inductors, see Alex's posts & investigation [ insert link ] suitable replacements from
Cinemag & Carnhill. All other fixes should be performed first to possibly save you money.
#005
81: Hiss on EQ: replace BC557 transistors X [insert designation] on all four EQ-amp pcbs with lower noise type
(BC2*** or BC560C)
<< PREAMP-CLICKS >>
#101
Popping on gain control between line & mic settings, a couple fixes but quickest & easiest
is to lose one position by lifting resister X [insert designation], see full thread for other methods.
<< SAFETY >>
#201
Check the fuse-rating and adjust when needed (according to your local mains-voltage).
<< SIGNAL-TRANSFORMERS >>
#901
As reported (thanks Roddy), replacing the signal transformers by more expensive types won't improve as much as one
would hope/expect. Unless the stock ones in your unit happen to be faulty/ringing, they're decent.
[ first bunch of info from Greg, edited & added stuff, last update: 2010-06-04 ]
For now, let's compile questions & things we're wondering:
What is it:
* sound ?
* can we have a look at the three final schematics upon which these units were actually built ?
(especially for the hybrid-81: does it indeed have the cl-A output ?)
Mod-candidates ?
* quality of iron ?
* quality of caps ?
* quality of switches ?
etc...
Cheers,
Peter