1290 frequency respond difference on both CH

[kambo]

couple of my  1290's  output's  have different frequency respond at same gain settings...
i set them matched at 1khz on both CH... then
if i send higher frequency ( say 7khz sine ) to both: ch_A  is higher than ch_B,
if i send lower frequency ( say 300hz sine) to both: ch_A is lower than ch_B

should i need to match output 2N transistors, or
match all transistor as close as possible....

i use choke connected to trx for balanced output...

 

[tommypiper]

Are you using the choke instead of using a gapped output transformer?

What transformers and chokes are you using, exactly?  Are they the same in each channel (have to ask)?  Are the layouts the same?  The wiring and hookups the same? 

No, you should not need to match transistors.  Are both your output 2n3055 transistors from the same source, and batch?  Some of the output transistors are known to sound and perform differently...  Same with transformers.

Have you calibrated the output transistors with a scope so they are at about the same bias, same amount of Class A?

Next would be to consider a mis-wiring, check how the transformers are connected, or a capacitor or resistor connected different in one channel, or different resistor value in your gain switches in one channel, etc...  Are you using any type of zobel or parts on the output secondaries?  Check that they are identical, etc...

Tell us more, post a photo and we'll try to help. 

 

[kambo]

original neve choke, cinemag (API) trx, output trx.
2N3055's from were from farnell, i have no idea if they were from same batch!
both calibrated the same way. PCB is ez1290, from Martin,
never had such problem, just happened tonight!


agggggggrrrr, got it...

while i was typing this, i was tapping one of my rack with my foot, 
i saw the meters are moving everytime i tap  ??? WTH... i made a relay based basic mastering patchbay last week, one of the XLR socket was loose 
back to normal again  8)

thanks anyway

 

[tommypiper]

(by same batch I meant bought from same source... glad you found the issue!)  How's it sound?

 

[kambo]

sounds really good
i have been using 1290 as my summing amp for over a year or so, thanks to Martin
recently changed the output trx configuration...
low end is cleaner, that i needed....

 

[tommypiper]

recently changed the output trx configuration...
low end is cleaner, that i needed....

Care to elaborate on the transformer change? 

Have you shown us your summing mixer?  Would like to see it. 

 

[kambo]

choke is : t1310
cinemag is : CMOQ-2S

summing mixer is not in a case.. i built on ready use xlr rack panel. and, mounted on my racks, back row...
i will place them all in one case when i have time... busy with tubes


this is relay board xlr connection on bottom, and mixer inputs on top row ...

 

[kambo]

its tight to picture back of my rack

this is mixer buss.... i used 0.1% resistors, dont waste time with hand picking them ...
10k and 220r shunt

 

[3nity]

Is that a gapped transformer out??

 

[kambo]

i suppose you are referring to 1.jpg  ;D ;D ;D
its gapped yea... i am waiting for un_gapped one 

 

[3nity]

Actually you need a CMOQ-2SG...that what i used on mine.

 

[kambo]

if "G" standing for gapped, i dont need gapped...
i have connected unbalanced output of ba283 (via choke ) to cinemag