2254C build/support thread

[kambo]

yes to all...
(r'19 is actually parallel to m-up connection)

 

[ultra-alex]

Hey thanks Pete I hadn't done those yet!

What a ****. Easy miss.

The square flat caps are the very same, 47uF solid tants.

-T

and the red marked side with the longer leg is + ? never seen that one before...
also i got 2 x 1000uF/25V radials left. C4?
and 2 x 330uF/25V radials. C´´17?
thanks, alex

 

[RightOnMusic]

hey alex, i had a number of random caps left over as well.  i wouldn't sweat it.

 

[kambo]

and the red marked side with the longer leg is + ? never seen that one before...
also i got 2 x 1000uF/25V radials left. C4?
and 2 x 330uF/25V radials. C´´17?
thanks, alex

for 330uf and 1000uf yes, use them as you quoted ...
for tant... i have no idea, i used normal tant but your suggestion sounds right

 

[ultra-alex]

thanks kam...

 

[substitute]

Has anyone found a bezel of any sort for the meters Igor suggested?  I am having a hell of a time cutting a decent hole for them.

 

[Igor]

ST7 VU's doe not have a bezels (AFAIK).
Can just suggest Front Pannel Designer's or Purusha case.

 

[jplum]

Hi Guys

Finally got to the point of powering up and start testing (after all this time!)

I inject 0db signal but I cant control the unity gain setting via the gain trim pot. In Bypass of course its fine but when engaged the gain trim pot is having no control at all.
I get a signal thats in phase but reduced in amplitude on scope by approx 50% (measured at XLR Out). Adjusting gain pot does nothing to the output

I'm kind of following the 33609 setup procedure and the few setup precedures that are on this thread, but before i go diving in wondered if anyone can offer any advice ?

cheers

 

[kambo]

check your wiring again.... and ur components.

 

[jplum]

check your wiring again.... and ur components.

Ok...well i'm pretty confident on my components!
Measured every measurable before soldering etc.
Wiring is a possibility, i'll double check given molex pin insertion without correct tooling can be problematic

Do you happen to have any useful measurement's i can use to try and figure out where things are going wrong ?
something like "with a 0.775mv 1Khz input signal, observe xxx at point yyy" etc ?

Many thanks
John

 

[kambo]

i certainly can do a DC chart for you later today...
give me some 4-5 hours, busy doing some work right now...

 

[kambo]

its 1.5mb jpeg... photobucket.com making it smaller file size, and my DC readings  cant be read...

sent to
[email protected] too

readings : ref to ground, at no compression

http://www.yousendit.com/download/MVNkMFhqTSsxUURIRGc9PQ

 

[jplum]

Thanks Kambo!

I'll use this as a reference point to help me debug

Regards

 

[jplum]

Ok here are my results from voltage checks

VCA
TR17
D 17.18
G 0.270
S 3.676
TR16
D 17.17
G 0.270
S 4.864
TR4
B 17.18
C 3.676
E 17.83
TR3
B 17.17
C 4.864
E 17.83

B183.112
TR"4
B 2.523
C 3.965
E 1.964

TR"5
B 3.964
C 13.21
E 3.353

TR"6
B 13.21
C 21.93
E 12.58

B183.110

TR"1
B 0.940
C 3.009
E 0.367

TR"2
B 3.004
C 23.19
E 2.444

TR"3
B 2.442
C 23.19
E 1.915

33609 COMP SIDECHAIN
TR2
B 3.654
C 0.523
E 4.320

TR15
B 0.523
C 14.68
E 0

TR5
B 23.51
C 0.749
E 23.83

TR8
B 0.748
C 24.08
E 2.053

TR9
B 2.09
C 23.54
E 1.48

TR1
B 23.54
C 1.586
E 24.08

TR14
B 0.790
C 24.08
E 1.55

Tran1 - is Carnhill VTB9046
Tran2 - is Carnhill VTB9045
Output - is Carnhill VTB9049

Any thoughts ?

thanks again

 

[kambo]

its hard to guess from your readings... go through Igors  signal structure post;

Signal structure is: 0db input-> -6db after input trafo-> -31db approx. after input pad (diode bridge can't handle line level),
then, current buffers (same level), interstage trafo-> -25dB. Signal comes balanced to bridge compressor,
and output amp is unbalanced. Audio comes out of phase, CV in common phase. Besides buffers are ac-coupled to transformer,
there's still CV swing which we have to distract from audio...transformer take care about this.
Interstage converts balanced signal to unbalanced, and matching impedances as well.

double checked for polarization on caps and diodes?

 

[jplum]

Ok I admit it....I'm an idiot 

Of course what I was doing wrong was that I failed to remember that the output is balanced and was only measuring pin-2 to ground.
When I measured across Pin2 & 3 of XLR, all was well

I got to the point of calibrating as per 33609 instructions, not sure if that is correct or Pot numbers (ie RVn) are equiv.
- I set Pot on PSU to give 3v at +CV and -CV on PSU
- Adjust gain pot to get unity gain with unit Bypass In
- I croc clipped +CV from PSU to Link on main board
- Adjust RV2 to get -8db at output XLR
- Adjust Pot on PSU for -20db at output
- Adjust RV3 for 20db on meter
- Put threshold to -2db (1st click)
- Adjust RV5 for -1db at output
- Put Threshold to -20db and measure -16db (ish - slightly less in fact on my unit)

Onto the RHS now

Thanks all

 

[jplum]

I would set the  trimmer to the middle position before switching on the unit.

yep also,
for people without a scope,
keep the V around 1.8V on RV1 trimer-to-ground...

Hi Guys
I've spent the last day or so callibrating as best as I could. I went through this thread again as I could see no mention of what RV1 callibration should be other than this from Kambo (back on page 6 or so)
I can only get about 1V (measured from RHS of R2" (which should be wiper) to ground)
Is there another post somewhere that describes setting up the B183 perhaps ?

In addition, just to be clear,  when we say 0db do we mean 0dbu (0.775) or dbv (1.00) ?


The good news is both sides are working and I callibrated using dbu...no hiss/noise etc and sounds pretty good and I love the Bass sound from this unit. I'm tempted to let my ears do the callibrating but i'd like to know i'm technically close as well 

I took the approach of getting unity at 0dbu then feeding in -20dbu and adjusting threshold pot to just react on fluke meter
thx

 

[jplum]

Ok just for reference for other folk that are new to BA183 / 283

RV1 is used to set DC Bias for headroom. You need to supply a +20dbu signal into unit and adjust RV1.
If using a scope you are supposed to be able to adjust until the distortion of both +ve and -ve amplitude of signal are the same.
I couldnt get this at all on either of my boards.

so what  I did was measure voltage across R7" (47r 1W) to be max of 7V, which should make sure that it doesnt burn out. It certainly is warm now!
Then recallibrate as per my previous post and all seems well

 

[jplum]

Hi Guys

Heres the shots of my 2254C.
Thanks to everyone on this thread whose helped along the way and especially Igor for making the effort in the first place

Ignore the TLA unit, its there in the rack

 

[ultra-alex]

nice one! well done...
cheers, alex