2254C build/support thread

[king-rb]

got the irons today. and fired up the first channel. compression is working.. but ;-) it sounds like passed through a lo-pass filter... what could be the problem ? i connectet the irons via the molex connectors. is the writing on the pcb correct? anybody got a voltage chart?

 

[Igor]

Check input/output Molex connectors on PCB 1+ 2gnd 3-
Check transformer's wiring
When going balanced to unbalanced short -output of in(out) to gnd
Etc

 

[king-rb]

hmm connections seems to be right.
today i finished the second channel soldered the irons direct on the pcb and same problem occurred here. compression, sidechainfilter aso. is working i think but ther is something like a lo-pass filter on the whole signal. Is it right to use for TR1 9046 and for TR2 9045. maybe i used wrong caps for c´´11 680p; c2´´ 220nF; c5´´ 330nF ? EDIT: are these the right values??
I also connected no meters untill now but this should be no problem right?

thanks for your help!

 

[Igor]

maybe i used wrong caps for c´´11 680p; c2´´ 220nF; c5´´ 330nF ? EDIT: are these the right values??

Right values are 680PF, 220PF, 330PF
220=220pF etc

 

[Igor]

F
Amen
/well, kidding, used same as shown at schematic with TF10015/16

 

[juniorhifikit]

Just finished up my 2254's (finally!)  And just in time for some mixing on the new Posies record.  Didn't even calibrate them yet (other than biasing) - they sound great!  I especially like the sound of the makeup gain/output section driving the transformers.  so much so that I built some 10dB pads so I wouldn't clip the converters on the way back in.  Once I get a free day I'll do the meter scale and calibrate the whole deal, but for now I'm having too much fun mixing.  I used Tat's case, and it looks pretty good.  Thanks Igor and group!

sorry about the crappy iPhone camera

 

[Igor]

HURRAY!!!!!!

 

[king-rb]

next good news: i changed the two caps with wrong value to the right value 220p and 330p and the unit now sounds great. i will install a switch on the back with a few different attack/release timing caps.

 

[juniorhifikit]

So I finally got a few days free to calibrate this thing.  Bias is good, 3V cv is good, but I can't get the gain down to unity.  I'm at the bottom of the trim pot and I'm still almost 5 dB above unity, making the other calibrations a little tricky. Should I just change R"19 (in series with the trim pot) from 820 Ohms down to something smaller?  Or is there possibly something wrong elsewhere causing the gain to be weird?

 

[haima]

so.. where are people getting their BC214s? ebay?

or has anyone tried substituting something from the current production BC5XX series?

 

[Igor]

BC212 will work as well as BC177/179.
No need for high beta, 140...500 is quite enough.
Check transistor's pinout /(datasheet!!!) to avoid headache with getting the thing working

 

[haima]

thanks igor! i think i might have some BC179s in my parts collection. i'll check the pinout for sure.

i'm getting closer to finishing my stereo 2254C, about half way stuffed - i have a big package on the way from mouser, including most of the remaining parts. fedex says it'll arrive on my birthday - happy coincidence! 

 

[king-rb]

so i also have some problems with the calibration.. i could not get the gain down so i lowered the 820 resistor to 715 but its not nearly enough. if i trimm the rv2 controllvoltage its no problem to get the gain down but then the next step is the problem.. with 3v on the link i can only get down to 0.402 what im doing wrong.. i rechecked and tryed a lot the last days ;-)

 

[Igor]

@Haima: all the best! How old you become?
@king-rb: can you please explain the problem in other words to let me a try to help?
What is your comp's gain without compression? (I.e. can you get to unity gain without
compression/makeup?)
Which 820R you mean and at which calibration stage you can't get down
the gain?

 

[haima]

igor - i turn 31 years young tomorrow 8)

i'm planning a nice day in the workshop stuffing my 2254 boards! thanks for all the great projects and support you give us. big thumbs up!

 

[king-rb]

okay sorry ;-) other words:
>i changed the R``19 to 715R
>input gain is 0.775V AC
>with the gain trim i can get to 1.150V AC minimum
>i have to trim RV2 Controller Voltage to get the gain down to 0.775V AC
>but then i dont have enough space to get the voltage down to 0.308 with the 3v on the Link
aso...
i used bc177 instead of bc214

 

[Rybow]

Editing my question as I have figured some things out. I have read this whole thread, and I am sorry if I missed what I am about to ask. For a mono unit, I need a 15VA 2 x 12V toroid. 30 VA is only needed for a dual version. So far so good?

 

[haima]

Re: availability of BC214 - i found futurlec has them for a pretty good price:

http://www.futurlec.com.au/price1.jsp?part_no=BC214

i just ordered a batch. remains to be seen what brand etc they are... i'll post my results here 

 

[king-rb]

Great! Ordered a few of this.. so maybe then i will have not such big problems with the calibration...

 

[haima]

king-rb: theoretically, i believe the BC177 should work fine - so don't rule out another source for your calibration issue...

but there's a possibility swapping them for BC214 might save you - hope so!