[ACMP investiupgradifications] All things PREAMP

[clintrubber]

I'll try to dig up some of the info , being concise
and mail it to Clint

Appreciating that!

It takes days of reading for some of these threads now ,

I recall entering the 1176-thread... a binder full of info... too much...  :'(

Regards

 

[clintrubber]

Thanks Greg for your PM. I'm replying here (your PM-box is full):

Hi Greg,

Thanks, nice, want me to insert it already on page #1 & see it develop from there ?

Cheers,

  Peter

 

[okgb]

Hi everyone , peter is going to keep a basic mod list on page one
i sent him a rough template  [ list ] of things BUT could use your help
with specifics  [ transistor numbers & such ]
the idea is to keep it brief and concise , so that many questions can be
answered on that one page BUT if someone wants or needs to they can
dig through the thread [ can you dig it ?.............DUG ! ]
Yikes these thread almost need sub topics ,  Peter do you want people to post here
and you can edit or sent it to you ???

JUST modifying this post so i don't add to and clog up the thread , but NICE work Peter
off to a good start

 

[clintrubber]

Peter do you want people to post here
and you can edit or sent it to you ???

Hi Greg,


Let's do it in this thread: post the proposed stuff to replace/add/correct _here_ (so not by PM), in
readily pastable form (sp?), then I'll try to collect new additions once in a while & update
it on the first page.

I have to be realistic, I can't promise quick updates, lot of time went
already into this, other things to do, you'll get the picture.

But if everyone looking for info jumps to the stuff on the first page and posts
comments/additions etc here (on page 50+), we can have a nice starting point growing into
a good summary of the things to do.

I'll update the first page later today. Greg, thanks already for providing the starting point.

Cheers,

  Peter

 

[clintrubber]

I'll update the first page later today.

Done !

 

[clintrubber]

.


*** PLEASE HAVE A LOOK AT THE INFO IN BLUE IN THE FIRST MESSAGE ON THE FIRST PAGE OF THIS THREAD ***


.

 

[clintrubber]

N

Hi Greg,

N ?  8) :

Cheers,

  Peter

(Posting here, since your PM-box is full. Was probably about this thread)

 

[okgb]

Peter email me gboboski at shaw.ca so we don't clog this thread up more
i think was just saying nice work !

 

[mitsos]

Hi guys, nice work so far.  IIRC, the transistor swap only applies to the 81. I know for a fact my 84 has no PNP transistors and I looked at the 73 schemo and as far as I could see, it doesn't either. 

 

[okgb]

We'll have to be careful in only stating things THAT have worked
not all units have issues but both of my 81's did and one of my 73's
[ the other 73 was useable ] thats 3 out of 4 bad , some do work
but if they have the wrong transistors , your not hurting it by changing

there was one in the front of the eq board that helped with hiss as i recall anyone ???

 

[clintrubber]

Hi,

Thanks, partly done. Must be able to find that low-noise transistor since if I'm not mistaken I spotted it back then, I'll add that later today.

Bye all,

 Peter

edit: found, and added to first page

 

[okgb]

Steve's suggestion was to replace 12 of the transistors with bc 560's
sintech found replacing Q1 on the bass pcb with bc 560 major inprovement
start there i guess

ATTENTION ALL              

I'll post a few here with my compilation of posts , NOT 100% thorough but good start
If you are the original poster and / or know better you can repost and PLEASE be concise
so that the first post can get modified 

Somewhat random [ as the info appears in the thread ]

can we keep the " where is Steve ?" and steve has my money off of this thread
[ maybe start a new one ? ]

ATTENTION STEVE HOGAN

your idea of a fix manual seemed reasonable BUT dude , people need you to
" get it together "  I have compiled your info from the posts and won't release it
to the general public so you have a chance to make good , but C'mon  o.k. ?

Q4 & Q5 TRANSISTER INFO

Notes Opamps are for led mertering only , some feel if disconnected
it would help the sound [ not sure if pulling the i.c.'s is enough
this is speculation fwiw

Quote chuckD [ who solved the transister eq problem
But I can say ... The EQ section is a close 1081 EQ copy.
They have copied the B338 correctly it seems however they are using BC557 and BC547 for the constant current emitter follower output stage. Also they are using 1N4148 diodes instead of the correct ones BAX13 and the AA144
I don't like all that LED junk in there! 50% of the components are to support the different LEDs. You don't need that crap in there. Plus it is tapping off the output signal in each stage I think noise can get injected there easy.

Quote zmix page 6
The major difference between the 1081 and the TNC81 is that the EQ line amps in the 1081 use a complementary BC461 / BC441 pair and the TNC use a complementary BC547 / BC557 pair .
 The BC441 and BC 461 are rated at 2A Ic and the BC547  / BC 557 are rated at 200ma Ic and they run quite hot.

Page 6/7 has a significant amount of info About eq noises

Picture of eq board transistors on top of page 6 , note they are marked with the board number first  as in  4Q4 & 4Q5  
schematic & start of transistor substitute opinions
Q4/PNP BC461-6 --> BC161-16
Q5/NPN BC441-6 --> BC141-16
replace the Q4 and Q5 transistors on all 4 EQ boards to BC441 and BC461
Alternatives/ Subs below ?

BC441 = 2N3053 or 2N5320
BC461 = 2N4037 or 2N5322
those 2N5320/21 NPN and 2N5322/23 PNP parts are somewhat pricey, but this category of transistor is higher current rated , hence the price. Here is another sub 2N5681/82 NPN and 2N5679/80 PNP both 1amp rated/100-120V/hfe 40-150 (TO-39)
and another TIP110/112 NPN and TIP115/117 PNP (TO-220 case, observe BCE leg orientation) 2amp rated/60-100V/hfe 500-1000 with high power dissipation around 50W, this will last forever compared to the 10W T0-39 types and can be remotely wired with short leads from the PCB and heatsinked to the case with proper insulator. In fact it shoud'nt need a heatsink at all since it can handle much higher power.

The 2N2907A, 2N2222A ( T0-18 metal case) power dissipation capability is just marginally rated over the BC547,557 (TO-92 plastic case) parts pending replacement in the ACMP 81. This is why they still run hot. I think around 600-800mw as compared to the 10w rating of the BC441/461 and 2n5321/5322 (T0-39 metal case) variety .

quote electrochronic page 8
Also for those who intend to replace the BC557, 547 transistors with BC 461,441 , there are substitutes
which can be used like the 2N5320 or 21, 2N5322 or 23, but these are a little pricey.

If you want a cheap substitute use TIP31B or C(NPN) and TIP32B or C(PNP) both rated at B=80V C=100V, 3A. These parts will work and are overrated in their specs to carry out their jobs as subs. The BC441,461's are 75V, 2A rated.

IMPORTANT : the Legs on the TIP31B or C, and 32B or C are not pin compatible with the BC 557,547's. The legs will need to be shaped/bent to match the Collector , Base, Emitter pin arrangement exactly. The TIP transistor legs will need to be thinned to fit in the pcb pads holes as well. View available data sheets on web to familiarize yourself with both the original and replacement transistors regarding Emitter , Base and Collector pin differences before attempting installation. Also the gain on these transistors are rated lower than the 2N and BC parts

 

[okgb]

Problem with line input polarity
The Line input of the TnC 81 is in antiphase ( ø ) with the input signal... the mic input is not.
I tested all of the other modules I have... the 84 and the 73 check out fine. Both their mic and line inputs maintain polarity.
The rear connector PC board is traced and labled correctly so the inversion must be happening at the preamp board.. which is odd because that mic pre / line amp board is the same part as the 84 and 73 use.

The solution I used was to de-pin red and white wires from the wire connector that plugs into "BCZ2" on the input / output jack PCB and swap them.

Noise screen shots on page 8
Schematics again on page 11
Gain switch popping noise , there no way to avoid the short between 6/7 position in mic mode( when the b284 ampcard add the extra gain stage) easy fix is to lose 1 gain position by lifting resister X
I added an OFF switch-position to the gain knob in the #7 position where the second gain stage first kicks in. Now switching to the next position (#8) does not cause a pop.
I chose to test it out by replacing a single 680R resistor (R43) with a 1.5k, disconnecting one end of that resistor and jumpering it to the position between R42 and R43.
This pretty much replaces the #7 position sensitivity setting with OFF and keeps the original remaining 4 higher gain settings.
You could do this with a different value (replace R43 closer to 620 ohms) and replace R42, 41, and 40 with different values to make the gain steps more uniform up to the original full gain if you want. [ pix on page 13  and another on page 15 ]
Small caps [ to ground on xlr's ] should not be needed
Discussion of pwr xfmr affect on noise on page 12
Check bottom of boards for bad solder joints

 

[okgb]

First post by Alexc who does intensive investigations page 14 continues with pix of installed carnhill inductor on page 17
link to H.R. and inductor fix  http://homerecording.com/bbs/showthread.php?t=275506 posts 22 - 25


Inductor numbers
The DIY 1081 inductors :

Mid-Hi : Carnhill Part No. vtb9048 with inductance taps at 205mH, 296mH, 504mH, 767mH
Mid-Lo : Carnhill Part No. vtb9047 with inductance taps at 1.43H, 2.06H, 3.56H, 5.11H
The 1081 inductors should be :

8 pin package (5 connected), core material not specified
Shielded can

Mid-Hi : inductance taps at 767mH, 504mH, 296mH, 205mH
resistance at taps 105R, 57R, 46R, 24R

Mid-Lo : inductance taps at 5.11H, 3.56H, 2.06H, 1.43H
resistance at taps 1036R, 804R, 611R, 500R

Source : Carnhill part # VTB9048, VTB9047 measured resistance
DIY 1081 inductance specification

Physical package is :
circular outside diameter 28mm
circular pins arranged on diameter 26.2mm

Mid-Lo and Mid-Hi have same pin-out (looking at bottom of inductor)

Starting at Pin 1 and tapping to Pin 5 (max Inductance, Max Resistance)
Pins 6,7,8 are not connected.

Inductance and Resistance restated :

Mid-Hi : inductance taps at 767mH, 504mH, 296mH, 205mH
resistance at taps 105R, 57R, 46R, 24R

Pin 1 - Start of tapped inductor
2 - 205mH, 24ohms
3 - 296mH, 46ohms
4 - 504mH, 57ohms
5 - 767mH, 105ohms and end of tapped inductor


Mid-Lo : inductance taps at 5.11H, 3.56H, 2.06H, 1.43H
resistance at taps 1036R, 804R, 611R, 500R

Pin 1 - Start of tapped inductor
2 - 1.43H, 500ohms
3 - 2.06H, 611ohms
4 - 3.56H, 804ohms
5 - 5.11H, 1036ohms and end of tapped inductor

And a pin to the shield would be nice - to connect to ground.

 

[okgb]

Page 22 the first appearance of Steve Hogan & his idea's
[ to date he has not finished anything he took a deposit for ]
Hogan mod notes start on page 23

(Random member - I've got the 81s and the 73s, but not the 84s - I can confirm that the "transistor swap" with BC441[-6] and BC461[-6] doesn't apply to the 73s because transistors you want to replace aren't there to begin with -- all I've done to my 73s is shield/rotate the toroid and fix the gain switch pop)
So far after the Hogan discussions , no new problems pop up and most have solutions
Some discussions about power supply diodes
Bias current in the 3055 turns out to be 55mA. A little low but whatever - it works.

That is - input a signal and turn up gain until the onset of clipping at output.
Adjust the 3055 bias pot such that the signal clips symmetrically.

55mA is the current at that point on my unit.
Max 3055 current with wild clipping is 80mA. Current with no signal is 40mA.
To measure the current in the 2N3055 driver transistor you have to insert an ammeter in series
with the collector. I could it because I had already cut the wiring in my psu mod unit.
Lifting the wire to pin 3 (which is at _24V) on the primary of the output transformer is probably the
easiest way. I'll try that and let you know with pics.

FWIW: an easier alternative which will get you about the same number will be measuring the voltage across the 47 Ohms power resistor & using Ohms law.
The current through the resistor will be a little bit different from the current through the 2N3055 but not by much, and since this is a roughly-so-many-mA's ballpark adjustment...
Quote from: Steve Hogan on May 08, 2009, 06:45:35 pm
I am curious, when you replaced the tantalum caps with electrolytics, did you keep the same values? What differences did you hear?

Tommy piper

On the BA283 card, I swapped these tants out and replaced with electrolytics: increasing C1 and C8 from 10uf to 22uf, and C14 and C15 I kept at 22uf on one card and increased them to 33uf on another, depending what I had. Both sounded clearer, more open, particularly the top end. I used the polarized cheaper Black Gates on one card and Panasonic FCs on other. I also increased off-board caps C5 from 680 to 4700uf and C3 from 470 to 1000uf. Most of the remaining electrolytics I kept at original values or upped depending what I had. I find they sound wonderful
page 39 some discussion about swapping cap types
For anyone considering doing their own shielding, this looks like a suitable material, if used in layers, as it is thin.

http://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A

Here's something I tried yesterday that didn't work, but its a data point... One thing that bothered me about the circuit is that the output of each filter board has two grounds. Take for example the low presence board. One is 5R32 to the 24V ground. The other is 5R36 to the 12V ground. A difference in potential between these grounds will appear as signal. And I believe they arrive from separate long wires that are at opposite ends of a ribbon cable which forms a large loop right by the power transformer. So... I lifted all the clip lite stuff off the signal path. This includes 3R36, 4R32, 5R35, 6R35, and the two wire cable from board 6 to 7. Funny thing is -- the hum got worse. The 120Hz went to -39.5dBV. So I think it is correct that the clip lite circuit is adding hum, but it turned out to be mostly antiphase and cancelling the main hum.
Quote from: stereokillah on June 24, 2009, 06:48:05 pm
fine, bcause the other method are to difficult fo me.

So i don't understand how to do it he talked about link between 43 and 42 and on the pitcures 43 and 44.

Perhaps will be more explicit when i will have the board in my hand.

stereokillah (aka: mono-maker),

Take a look at the board and draw the changes on a copy of the schematic so you can follow it.

Here it is in ascii:

--------- SNIP ----------
SP SP
| |
R44 R43
| |
-------
|
SP SP
--------- SNIP ----------

I changed the value of R43 from 620 Ohms to 1k5 Ohms.
SP = Solder Pad
The lines are soldered connections.
Note that the original R43 connection to it's solder pad is NC (not-connected) on one side.

This turns that input gain position to an OFF position and prevents the momentary positive feedback path.

The reason for the pop at that position is a positive-feedback loop due to the switch being a MBB (make-before-break) type of switch. ie; when the second gainstage is switched into the chain and during the moment that both position 6&7 are active, the output of stage2 feeds input of stage1. Oops!

Check out the schematic and follow the signal flow for that state and you should see the loop.
Thank you very much for this help 0dbfs (aka:None saturation.)

and sorry but realy need to know if i weel understood

HERE THE SWITCH
--------- SNIP ----------
SP SP
| |
R44 R43
| |
------- and here the llink between 43 and 44
|
SP SP
--------- SNIP ---------

Exactly!

And the bottom (away from the switch) R43 SP connection (originally connected) is now lifted in the mod with no connection.

NOTE: I think I just bent the R43 resistor leg over, soldered it to R44, and used heat-shrink around the R43 leg to prevent connection with the original R43 solder-pad. A little tight but workable.

 

[okgb]

Pix of cinemag inductors installed on page 41 inductor info
take the old inductors out , make sure you match
the taps to the inductance of both
[ the chinese seems to start on the pin marked 2
on top of the white cup , use this as your lowest
starting tap of new inductor going clockwise looking
from the top ]

Posts from Steve Hogan get quiet around page38 / 40 ?

Audioforge quote
what i ve done change the 8 bad transistors with 2N5321 and 2N5323.
mod the pop mic input with the "0dbfs" tip.
add a 600R on a switch at the back of the output TX.
remove the input capacitor on the line TX.
eveything work good.
BUT this time i use a square wave to test the Traffos.
I ve done it for the line TX and remove the input capacitor to tame the overshoot.
but oh my god the ouput TX is AWFULL.with overshoot and crosstalk...
remove the 10n :it s worse. solder it again..
then I engage the EQ on (all others EQ switches on OFF) crosstalk nearly disappear. and small gain increase ...
Square wave is good when mesured on the 2n3055 so only the output tx is the culprit.
So I swap the output tx for a 30 Ohm/600 schlumberger traffo i have (bigger than a utc
A10 ,shielded ,pinouts within "glass pearl"..) put only a 600r across the output:
perfect square from 30 hz to 30Khz.
i will try with a carhnill output (but they re mounted on my 1084s clones)asap.
so my advice will be:
if you live in europe swap the inductors don t seems necessary.
try 2n5321 5323 instead of bc441 61 if you don t have some..
remove the input line tx capacitor. throw away the chineese output tx..

quote sterokillah
i've changed the transistor and hum lost some db
changed C11 and C16 (10uF/35V) to 100uF/35V hum lost 1or 2 dbu
put shielded sheet on the tx psu (bought on black market) and hum lost around 5db
changed the two inductor for carnill shielded with oep case and when i give mid low and mid high i have a very litlle changement aournd 50hz and mid hash
only have some noise when i give some gain on the last low band 330 to 33.
Some observations from Audioforge on page 42  output xfmrs & noises
Rodabod continues pwr xfmr investigation on page 42-43

EQ hiss fix from sintech
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
Steve hogan ;  Even when the hum is fixed, the white noise level may prove to be higher than necessary with a few well-placed better transistors and reworked, lower impedance pads. I am seriously considering adding the 12 BC560 transistors to the '81 list of mods.
re q4/5 transisters compared the datasheet of bc327-16 and bc32716,
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.

Mitos ;  solved my little buzzz issue. I posted that it mostly went away when I screwed the top on, but it would happen with a mic plugged (or dummy load) whenever I would go near the gain knob. If I touched the mic/xlr/some part of the case with my other hand, it would be silent.
Last night I had an idea.... Too much paint (fancy that!). Basically there is paint between the faceplate and the main case (where they bolt together), so the faceplate itself is isolated from the rest of the (grounded) case. Scrape that paint off (use a knife, paint is pretty thick, one thing our friends did right!) and it's gone. Be careful bolting it back on though, I stripped one of those crappy pressnut thingies. No biggie, it's sturdy enough for now, but I will find a nut to put on the back of it... eventually.

Observation from AlexC [ who came up with the inductor fix ]    My Chineve 1081s are still going strong and quiet!9months of frequent and lengthy use, in a hot climate - no blowups, brownouts or whitewashes.
Completely stock except for Carnhill inductors+OEP shields, Zmix transistor fix and gain switch pop mod (80usd in parts each)
Basically, after noting the well documented TnC 1081 EQ broadband noise and applying the Zmix transistor replacement fix, I found that there was still a lot of mains harmonic noise with EQ engaged. I isolated this to the mid-low inductor by using basic fault finding techniques.
I then replaced that inductor with a Carnhill part. That noise was then greatly reduced. Then I added an OEP mu-metal shield on that inductor. Significantly reduced noise again.
Repeated for the mid-hi inductor, even though it contributed only a minor amount of mid-freq noise.
Result was a unit with a noise floor around 23-28 dBu lower than stock. I can't hear any noise anymore.
Did the resistor mod to the gain switch to remove the 'pop' setting.
Along the way, I tested alternative mains transformers (25aud chinese toroid), alternative PSU (JLM) both internally and externally (3ft away).
I found toroid and PSU changes made no improvements at all. (Slightly worse, in fact).
I noted that toroid rotation was good for a couple of dBu, case lid on was good for a couple of dBu.
I noted that proximity to other powered on units worsened noise floor by a couple of dBu.
I also experimented with PSU cap changes, grounding changes and all of that. No improvement at all.
All of this was tested in a rack with surrounding powered up units as well as on the bench, using a DAW spectral analyser and a Motu 2408MkII set for +4dB balanced connections, line input unity gain conditions with max EQ boost settings. Mic input was similar in noise floor.
So I ended up with stock with Carnhills+OEP, Zmix transistor fix and gain switch pop fix.
Now I get easily and consistently around -80dBu at real world gain settings and boost applied on the EQs (worse when all EQs are on, full boost).
Some noise remains with mains harmonics noise at around -90dBu for worst individual components. For really high gain use, there is also some hiss, which I feel is expected for a unit of this cost. I believe that performance varies significantly from unit to unit and location to location.
And that was good enough for me, being about the same as I get with my other diy builds.
Cost was 350aud for the unit with shipping to Aust. and around 80usd in parts to fix. (4x transistors, 2x inductors, 2x shields each unit)
There are obviously a lot of other very, very, very detailed fixes which I did not feel were very well substantiated and definately not economically viable for me. I saw no reason at all why they would translate to a better sound in the real world. (I am an EE with a lot of mixed signal medical device QA experience)
And so, I use a pair all the time for DI guitars (active and passive), and tube condensor mic (no ribbons), into a diy 1176 or diy la2a then to my Yamaha digital mixer + Motu and Cubase. They are my 'go to' lounge room studio units.
Since then, I bought some HotBaby's toroid shielding strips which I will test over Xmas.
Bottom line, is that I believe trying to get these to a higher spec with even more expenditure is not worth it.
Mid late 40's pages start to Question  " where is Steve ? "  speculation , fewer fixes at this point ,  Steve returns with gain switch mods on page 48 , then disapears again

THIS INFO  current [ although maybe not 100% thorough ] as to page 51 June 6, 2010

 

[clintrubber]

Thanks again Greg for the additions. Haven't found the time yet to update pg1, but it's not forgotten.

(For the time being I added a remark to the pg1-message that people should also have a look at thie last page for additions that haven't been added yet to the pg1-summary)

Cheers & have a good weekend!

 

[Paul G]

Hi all.  Has anyone heard anything from Steve Hogan?  I sent him an email a few weeks ago and another again tonight.  Nothing.  Thanks for any info.

Paul ;D

 

[Paul G]

FYI, I just received this from Steve Hogan:

I have done some work on the TSMP’s this month and am trying to get more done on them in the next 2 weeks.

I recently worked on some NEVE 1084 modules and did extensive measurements and analysis of the inductors used in that unit.

I also modded a Golden Age PRE 73 which is made by the same Chinese company as the TNC preamps.  It uses the same input transformers and output transformers, but they got the gain switch mostly right on that box due to copying it more directly from Neve.

I was able to find a compromise RC network that really worked well, and that was encouraging that I may be able to find a similar set of values for the TSMP’s.


Steve

Another email from Steve:

My son is getting married the first week of August and I have been at a dead run all this month.

Realistically, I won’t be sending out kits till middle of next next month.

I have finalized the Darlington output pass transistor in the power supply so other than documenting the changes to the 2 different supplies, that part is now done.

Steve

 

[redddog]

Cool.

Any idea what the kit goes for?