2254C build/support thread

[bruno2000]

OK, so I've gone through all the parts values, and can't find a problem, but still about 10 dB down.  Next question, how much should the gain trimmer "trim"?  I can only get about a 3 dB "swing" using the trim pot.  Is this right?
Thanks in advance!
Best,
Bruno2000

 

[Igor]

Maybe it is I that is not working properly ;-)

No way. If you found mistake, everything is on right way to get nice sounding compressor)))))

I should expect about -25, -26 dBr at the secondary of the interstage trans, but what level should I expect to see at the junction of R27 & R64 of the B193.112 block?

Really: dunno!  ;D
Have to check myself with working unit. Too lazy to calculate. Logically:
Output stage with no makeup IIRC should have 15db of gain, THUS,  -15dbr at this junction.
Sure point to check:
Check for -26 dbr (using our dbr slang at TP_C by schemo.

Another quick check, push the unit with say 3...5V RMS input signal, and crank MAKEUP.
You should have /after trimming symmetry into 600 Ohm load with RV1, 5k/ at least 25 dbm@600 ohm of undistorted output.
This is the check for amp. stages.

OK, so I've gone through all the parts values, and can't find a problem, but still about 10 dB down.  Next question, how much should the gain trimmer "trim"?  I can only get about a 3 dB "swing" using the trim pot.  Is this right?

Yes, that's right, the range of this trimpot is about 3 db.

Possible to change R''19 at BA183.112 block to say 430R, but the unit will work wrong.

OK... BTW, did you put the reversed trafo correct way?

 

[bruno2000]

Thanks for your help! This is a great place to learn!
I usually design/steal and build mic preamps, and this is my first endeavor into this type of compressor.

I checked all of the components in the audio chain, and they seem OK

Here are some signal voltages to consider:

CV test point grounded
Gain trim pot all the way up (max gain)
Makeup gain set at "0" (1M feedback resistor)

Across input trans primary 0.775V, 0 dB
Across input trans secondary 0.355V, -6.7 dB
Across interstage trans primary 0.0195V, -32 dB
Across interstage trans secondary 0.036V, -27.4 dB
Point P of B183.112 (output of that section) 0.33V, -7.4 dB
Junction of R64 and R27 0.075V, -21.8 dB (this seems odd)
Point F of B183.110 (output meter) 0.145V, -14.6 dB
Across the Carnhill output trans secondary 0.23V, -10.5 dB

Other odd things:
The makeup gain switch will add only about 14 dB of gain from the "0" position (1M feedback) to the "20" position (100R feedback)
The output section will only put out about +19 dB (ref 0.775V) before distortion, but it doesn't 'square off" like I'm used to seeing this type of circuit do.  The trailing edge on the positive going sine wave is distorted.
I set up the output bias by measuring 4.7 VDC across R7 with no signal applied.

Both channels act the same way

Thanks in advance!

Best,
Bruno2000

 

[bruno2000]

OK, this problem SOLVED !!
The curse of the multiplier!
C2'' in the output section was 220nF.  Should have been 220pF.
Output is now +28 dBm just before clipping, and the makeup gain switch adds 2 dB per click.
Large beer tonight!
Calibration starts tomorrow!
Best,
Bruno2000

 

[Igor]

Hurray!!!! Cool than, write something about how does calibration passed etc!

 

[mylesgm]

Hi Igor,

Installing Belclere tf10016 in input position but I'm not sure where the primaries are on the tx?  which side has three terminals and which side has four?

 

[bruno2000]

Hurray!!!! Cool than, write something about how does calibration passed etc!

OK, calibration went very well, although I had to add some resistors to the meters to make them work properly.  Even though it took a long time, having the ability to plot Vin vs. Vout with both channels running was a GIANT benefit, and I was able to get the two channels to track together within about 0.2 dB throughout the compression curves.
BTW this compressor sounds WONDERFUL.
Thank you Igor!
Best,
Bruno2000

 

[Igor]

@ mylesgm :

Pinout for 10015/16, PIN SIDE VIEW:
--------
[4---8]
[3---7]
[2---6]
[1---X]
--------

X = NO PIN.

In other words, for 10016, 6 is shield, 7-8 is 10k (input for audio signal); 1,2,3,4 is output to diode bridge.

bruno2000 : happy to hear these news! Enjoy and make music!!!! When you release platinum disc?

 

[mylesgm]

and the pin configuration for tf10015?

 

[pacemaker]

hi guys !
i'm finishing my 2254C , tried to calibrate it,
but while testing it, i noticed i have some strange noises wich appears periodically,
i've verified everything and couldn't find any wrong components,
i am suspecting a bad cap or bad 2N3055,
is there a way i can investigate or test things to troubleshoot this ?
i've verified all groundings, PSU , mainboards etc...
any help would be greatly appreciated,
regards,
Francois

 

[jandoste]

Salut François,
If I remember that check twice R47 resistor and you need to fine out right Value with it too...

 

[Igor]

i noticed i have some strange noises wich appears periodically,

Me too. Aliens coming. (gah, just kidding!)
BTW, watched excellent movie, Attack The Block. IIRC same guy who did Shawn Of The Dead and Hot Fuzz.
Not attractive as Six Shooter, but good. Recommended. Well, back to our aliens.
Let's fix it.
I assume there are scope, oscillator and multimeter. Need 'em for calibration.
Description about the noise will help a lot.
In general. Check all solder joints, part's values, connections, etc.
Power supply.
Check the voltage at big cap right after rectifier; check voltage at power supply output;
hope all is up and kosher. No voltage fluctuations etc. 30...37V before LM317, 24.00V after LM317.
Than, check the control voltage point TP_CV with scope.
If nothing suspicious, next.
Measure the voltages at R42, R28, R9, R43, R44 ref to gnd.
If nothing suspicious...dunno, have to sleep on this.
Well...just some attention and you here.

 

[Igor]

and the pin configuration for tf10015?

 

[chrispbass]

Hi everyone, just designing my front panel for this and have a couple of questions about labelling based on what I believe is Perusha's case design used by a fair few. I don't have a schematic to hand so could do with this double checking please.

1. On HPF toggle switch, is 'up' HPF IN and 'down' is HPF bypass?

2. On threshold toggle switch, what does NOR stand for (normal?) and I've noticed on the modern Neve version, threshold is variable from 0 to +10 dbu, so does the switch just take us from 0, to an additional +10 setting?

3. On bypass toggle switch, 'up' is comp in (led off), 'down' is bypass (led on), or does led light up to the opposite to this?

4. Threshold rotary settings in dBu as per neve?

Any help much appreciated
cheers
Chris

 

[Igor]

http://ij-audio.com/downloads/2254c_front_meter_coreldraw.zip
You can open Corel file in AI as well. All fonts are saved as curves.

 

[Igor]

Anybody need a help here?

 

[r2d2]

Hello
i'm looking for parts at local various parts supplyers
also to know a little how the project would cost me ,
in the bom list (see attached image)
i see some "symbol" in the parts description
like :  "  , ' , r , R , etc..
please these symbols refer to particular types of components ?

peace !
r2d2

Anybody need a help here?

 

[chrispbass]

Hello
i'm looking for parts at local various parts supplyers
also to know a little how the project would cost me ,
in the bom list (see attached image)
i see some "symbol" in the parts description
like :  "  , ' , r , R , etc..
please these symbols refer to particular types of components ?

peace !
r2d2

Anybody need a help here?

'r' and 'R' is a shorthand way of specifying ohms for resistors...33r is the same as 33ohms. A standard keyboard doesn't have an omega symbol on anyway, so 'r' much more convenient. If a value has a decimal point, i.e 4.7 ohms, then it is usually written as 4r7 instead of 4.7r. This is true also when using 'K' as a multiplier, i.e 4700 ohms = 4700r = 4.7K = 4K7 and also when using 'M' (meg) for a multiplier of 1 million.

R' and R" is just Igor's convention for these particular resistors! R'17 is not the same part as R"17 so just treat them as individuals

Hope that helps a bit?

 

[earl]

just about ready to let the smoke out of this thing weighs about 50 lbs hmm feels like it oughta work...

 

[ptron]

merry christmas everyone! is not anymore but still... happy days to u all!

anyways back to it. i was wondering

1- if anyone has built one of these with cinemag trannies... would be nice to know because i like the sound of those very much!.

2-also.. if i am looking for a transformer in cinemag .. for interstage and input transformers.. do i need mic in or line in? i have also read about it here but its somehow confusing (im real sorry maybe this is all implicit but im not sure what im looking for) . i am waiting still for the pcb and kit parts ! hehe merry christmas to me too!!  *ahm.. thanks igor u rock!

http://www.cinemag.biz/line_input/line_input.html
http://www.cinemag.biz/output/output.html
http://cinemag.biz/mic_input/mic_input.html

can i use this as line out? http://www.cinemag.biz/line_input/CMOL-3x600T2.pdf

3-im not very literate on transformers as u may have already figured out yourselves .. so i have read the entire thread .. i seen a couple of mentions about 25-30VA toroid for power tx. is this only with one primary or dual primary ? like is 15-0-15 ok? or .. sorry about redundance in question (i know its been asked before) i wanna be sure before ordering!

-now for the PS.. does it have to be grounded with metalic standoffs? i read somewhere it needs to be hooked up from the middle of the pcb to make some grounding on Tx. just wanna check this also.

thank you very much in advance!
i hope u all had wonderful times with your family and have lovely new year!